High-entropy oxide electrocatalyst and preparation method thereof

Abstract

The invention belongs to the technical field of catalytic materials, particularly relates to an electrocatalytic anode oxygen evolution reaction catalyst based on an anion exchange membrane electrolytic cell, and particularly relates to a high-entropy oxide electrocatalyst and a preparation method thereof. The high-entropy oxide electrocatalyst is composed of five metal elements of Ni, Co, Fe, Mn and Al, is loaded on a foamed nickel substrate, has a nanosheet structure, is rich in oxygen vacancies on the surface, has excellent electrochemical catalysis performance and stability, and is suitable for electrocatalysis of an electrolytic water anode side in an alkaline environment. According to the preparation method of the high-entropy oxide electrocatalyst, foamed nickel is used as a substrate, salts of five metals of Ni, Co, Fe, Mn and Al which are equal in mole are subjected to hydrothermal synthesis to form a precursor, and then the high-entropy oxide electrocatalyst is prepared through self-etching, annealing oxidation and acid etching, and the high-entropy oxide electrocatalyst is easy and convenient to operate, good in repeatability, controllable in cost, excellent in performance and suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of catalytic materials technology, specifically to an electrocatalytic anodic oxygen evolution reaction catalyst based on an anion exchange membrane electrolyzer, and more particularly to a high-entropy oxide electrocatalyst and its preparation method. Background Technology

[0002] Renewable energy is an inexhaustible gift from nature. Solar, wind, and hydropower generation technologies have developed rapidly in recent years. By the end of April 2025, China's installed capacity of renewable energy power generation reached 2.017 billion kilowatts, a year-on-year increase of 58%, of which wind and solar power accounted for 1.53 billion kilowatts. Renewable energy power generation accounts for approximately 35% of China's total power generation and 32% globally. The continuous development of renewable energy is reshaping the global energy structure. However, the intermittency and volatility of renewable energy limit its large-scale application. Imbalances in electricity supply and demand, and the ineffective utilization and storage of electricity during peak periods, lead to waste. The emergence of hydrogen energy offers a new possibility for addressing this issue.

[0003] Hydrogen energy boasts high energy density, flexible storage and transportation, and its combustion product is only water, resulting in true zero carbon emissions. It possesses cross-sectoral application potential and is a major direction for clean energy development. However, hydrogen rarely exists in nature in its elemental form and typically requires industrial production. Hydrogen production processes are categorized into gray hydrogen, blue hydrogen, and green hydrogen. Among these, using renewable energy as an electricity source and converting it into hydrogen energy through water electrolysis for storage is the best solution for disposing of excess electricity and is also the primary source of green hydrogen. Water electrolysis is a highly efficient and carbon-free hydrogen production method, making it a promising approach. When renewable energy generation is in surplus, water electrolysis converts electricity into hydrogen energy for storage. When renewable energy is low, it is converted back into electricity through fuel cells to supplement the supply. This electricity-hydrogen-electricity conversion model effectively improves the absorption capacity of renewable energy generation and has great potential for promoting energy industry upgrading, achieving "dual carbon" goals, building a complete industrial chain, and facilitating the commercial application of hydrogen energy.

[0004] Currently, there are four main technical directions for water electrolysis: (1) Alkaline water electrolysis (ALK) technology, which is low in cost, the earliest developed, and the most mature technology, but has low efficiency, safety hazards, low current density, and is not suitable for renewable energy power; (2) Proton exchange membrane water electrolysis (PEM) technology, which has low energy consumption, compact equipment, and can be adapted to renewable energy power, but has a limited lifespan of the electrolyzer, high equipment cost, and lower energy consumption than ALK; (3) High temperature solid oxide water electrolysis (SOEC) technology, also known as high temperature water electrolysis, has high catalyst activity at high temperature, low energy consumption, and an electrolysis efficiency of up to 90%, and is corrosion resistant, but it requires a suitable heat source to operate and is not the best choice for renewable energy power; (4) Anion exchange membrane electrolyzer (AEM), which combines the advantages of low cost of ALK and simple and efficient PEM, has high hydrogen purity, good air tightness, and fast system response, which is very compatible with the characteristics of current renewable energy power generation. The range of membrane electrode catalysts is wide. One of the biggest problems facing AEM is the cost limitation of precious metal catalysts. The most advanced catalyst at present is still IrO2. Anion exchange membrane electrolyzer (AEM) water electrolysis for hydrogen production is an advanced method involving two half-reactions: the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER). However, the anodic oxygen evolution reaction (OER) involved in water electrolysis is a complex four-electron transfer process. Its slow kinetics and high overpotential limit the overall energy conversion efficiency and sustainability of water electrolysis. Therefore, developing efficient, highly stable, and low-cost electrocatalysts for the anodic oxygen evolution reaction is crucial. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a high-efficiency, high-stability, and low-cost high-entropy oxide electrocatalyst and its preparation method to promote the oxygen evolution reaction at the anode.

[0006] To achieve the objectives of this invention, the following technical solution is adopted:

[0007] A high-entropy oxide electrocatalyst, consisting of a high-entropy oxide supported on a nickel foam substrate and composed of five metallic elements: Ni, Co, Fe, Mn, and Al, possesses properties such as... Figure 2 B nanosheet structure, surface rich in oxygen vacancies, X-ray diffraction pattern as shown in... Figure 3 As shown, the X-ray photoelectron spectrum is as follows: Figure 5 As shown in Figure A, a self-supporting high-entropy oxide oxygen evolution electrocatalyst material rich in oxygen vacancies is named SE-NiCoFeMnAlO-AE@NF.

[0008] The present invention also provides a method for preparing the above-mentioned high-entropy oxide electrocatalyst, which uses nickel foam as a substrate and synthesizes precursors of equimolar amounts of salts of five metals, namely Ni, Co, Fe, Mn and Al, through hydrothermal synthesis, and then prepares the precursors through self-etching, annealing oxidation and acid etching.

[0009] Furthermore, the foamed nickel is pretreated foamed nickel, and the pretreatment of the foamed nickel (NF) involves ultrasonically cleaning the foamed nickel (NF) sequentially in hydrochloric acid solution, acetone and anhydrous ethanol, and then drying it.

[0010] Furthermore, the ultrasonic cleaning time is 20 to 30 minutes; 3 to 4 pieces of cleaned and dried nickel foam, each measuring 1 cm × 2 cm, are placed in each polytetrafluoroethylene liner.

[0011] Further, the hydrothermal synthesis precursor is prepared by dissolving equimolar amounts of salts of five metals (Ni, Co, Fe, Mn, and Al), ammonium fluoride, and a precipitant in deionized water and mixing them thoroughly. The resulting homogeneous solution and nickel foam are then transferred to a polytetrafluoroethylene liner, placed in a stainless steel reactor, sealed, and reacted at 100-160°C for 6-12 hours to obtain a precursor of a high-entropy oxide based on nickel foam.

[0012] The metal salts are nitrates, chlorides, or sulfates; the total molar mass ratio of the five metal salts to the precipitant and ammonium fluoride is 1:(4-8):(2-6); the precipitant is urea or hexamethylenetetramine.

[0013] In some embodiments, the metal salt is a nitrate and the precipitant is urea.

[0014] In some embodiments, the reaction temperature of the hydrothermal synthesis precursor is 120°C and the reaction time is 8 hours.

[0015] Furthermore, the self-etching process involves self-etching the precursor at room temperature for 20-36 hours, washing it until neutral, and drying it to obtain a self-etched sample. In some embodiments, the self-etching time is 24 hours.

[0016] Furthermore, the self-etching is carried out in a hydrothermal reaction mother liquor cooled to room temperature; the cleaning after self-etching is performed by alternately cleaning with deionized water and ethanol until the sample surface is neutral; and the drying after self-etching is performed by drying in a vacuum drying oven at 60°C.

[0017] Further, the annealing oxidation involves annealing the self-etched sample in an air atmosphere at a heating rate of 2-10°C / min, at a temperature of 250-450°C, and for a time of 2-4 hours, followed by cooling to obtain the annealed sample. In some embodiments, the heating rate is 5°C / min, the temperature is 350°C, and the annealing time is 3 hours.

[0018] Further, the acid etching involves immersing the annealed sample in a 0.01-0.1M acid solution for 0.25-1 hour, washing it until neutral, and drying it to obtain the high-entropy oxide electrocatalyst.

[0019] Furthermore, the acid solution is a nitric acid solution, a hydrochloric acid solution, or a sulfuric acid solution.

[0020] In some embodiments, the acid etching is performed by immersing the annealed sample in a 0.01-0.1M nitric acid solution for 0.25-1 hour.

[0021] Furthermore, the cleaning after acid etching involves alternating cleaning with deionized water and ethanol until the sample surface is neutral; the drying after acid etching involves drying in a vacuum drying oven at 60°C.

[0022] The present invention also provides an electrocatalytic anode oxygen evolution reaction, wherein the above-mentioned high-entropy oxide electrocatalyst is used to catalyze the electrolysis of water.

[0023] Furthermore, the electrolyte for the electrolysis of water is a 1M KOH solution.

[0024] As can be seen from the above technical solution, the present invention provides a high-entropy oxide electrocatalyst and its preparation method. The high-entropy oxide electrocatalyst is composed of five metal elements: Ni, Co, Fe, Mn, and Al, and is supported on a nickel foam substrate, exhibiting the following properties: Figure 2 B nanosheet structure, surface rich in oxygen vacancies, X-ray diffraction pattern as shown in... Figure 3 As shown, the X-ray photoelectron spectrum is as follows: Figure 5 As shown in Figure A, the preparation method of the high-entropy oxide electrocatalyst uses nickel foam as a substrate. Equimolar amounts of nitrates of five metals, namely Ni, Co, Fe, Mn, and Al, are synthesized as precursors via hydrothermal synthesis, followed by self-etching, annealing oxidation, and acid etching.

[0025] Compared with the prior art, the present invention has at least one of the following advantages:

[0026] 1. This invention relates to a high-entropy oxide self-supporting electrode material based on a metal system of Ni, Co, Fe, Mn and Al. The high-entropy effect enhances the structural stability of the material and synergistically enhances its activity in the alkaline anodic oxygen evolution reaction by combining multiple active components. The nanosheet structure provides a high specific surface area and abundant active sites. The abundant oxygen vacancies facilitate the regulation of intermediate adsorption and optimization of electronic structure.

[0027] 2. Through innovative stepwise etching of self-etching and acid etching, combined with annealing process, the surface and bulk structure of the material are precisely controlled. This is beneficial for optimizing the surface roughness of the catalyst, selectively dissolving specific components (such as Al oxides), and controllably introducing abundant oxygen vacancies, thereby exposing more active sites, improving reactant adsorption / desorption, optimizing electronic structure, and significantly improving its catalytic activity and stability in the anodic oxygen evolution reaction.

[0028] 3. The preparation method described in this invention is simple to operate, has good repeatability, and is cost-controllable. It can ensure that the obtained high-entropy oxide achieves uniform elemental distribution on the nickel foam substrate, suppresses component segregation, and forms a nanostructure with high specific surface area and abundant active sites, providing a technical basis for the large-scale preparation of high-performance self-supporting anodic oxygen evolution reaction electrodes. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram illustrating the synthesis of the self-supporting high-entropy oxide oxygen evolution electrocatalyst material SE-NiCoFeMnAlO-AE@NF prepared in Example 1;

[0031] Figure 2 This is a scanning electron microscope (SEM) image of the self-supporting high-entropy oxide oxygen evolution electrocatalyst material SE-NiCoFeMnAlO-AE@NF prepared in Example 1. Figure 2 A, B) and corresponding element distribution (EDS) photos ( Figure 2 C);

[0032] Figure 3 Example 1: XRD pattern of SE-NiCoFeMnAlO-AE@NF;

[0033] Figure 4 Comparison of XRD spectra of Example 1 SE-NiCoFeMnAlO-AE@NF, Comparative Example 1 NiCoFeMnAlO@NF, Comparative Example 2 SE-NiCoFeMnAlO@NF and Comparative Example 3 NiCoFeMnAlO-AE@NF;

[0034] Figure 5 The overall spectrum (A) of SE-NiCoFeMnAlO-AE@NF in Example 1, the XPS spectra (B) of O in SE-NiCoFeMnAlO-AE@NF and Comparative Example 1 NiCoFeMnAlO@NF, and the comparison diagram (C) of metal-oxygen, oxygen vacancy and adsorbed oxygen content.

[0035] Figure 6The LSV spectra (A) and overpotential spectra (B) of Example 1 SE-NiCoFeMnAlO-AE@NF, Comparative Example 1 NiCoFeMnAlO@NF, Comparative Example 2 SE-NiCoFeMnAlO@NF and Comparative Example 3 NiCoFeMnAlO-AE@NF are shown. Detailed Implementation

[0036] To make the objectives, technical solutions, and beneficial effects of this invention clearer, specific embodiments are described below. These embodiments are merely for illustrating the invention in detail and do not limit the scope of the invention in any way. Any non-essential modifications or substitutions made by those skilled in the art based on the concept of this invention and in conjunction with existing technology should be covered within the protection scope of this invention.

[0037] Unless otherwise specified, all instruments and equipment mentioned are conventional instruments and equipment;

[0038] All raw materials involved are commercially available conventional industrial raw materials or raw materials that are available to those skilled in the art;

[0039] The processing and manufacturing methods involved are all conventional methods or methods mastered by those skilled in the art;

[0040] The technical and scientific terms described are as understood by those skilled in the art.

[0041] This invention provides a high-entropy oxide electrocatalyst, which is a self-supporting high-entropy oxide oxygen evolution electrocatalyst material rich in oxygen vacancies, named SE-NiCoFeMnAlO-AE@NF, and is suitable for high-entropy oxide electrocatalysts on the anode side of water electrolysis under alkaline conditions.

[0042] High-entropy oxides (HEOs) are an important branch based on high-entropy alloys. They possess excellent configurational entropy, which can suppress elemental segregation, and exhibit four unique properties: First, the high-entropy effect significantly improves the thermal stability of the catalyst by regulating the electronic interactions of the metal-oxygen bond (MO). Second, the lattice distortion effect inhibits the dissolution of metal elements in corrosive electrolytes during the OER process, enhancing the structural stability of the catalyst. Third, the slow diffusion effect reduces the catalyst migration rate, improves the dynamic stability of the catalyst, and ensures that the active sites remain active under conditions of highly corrosive electrolytes and high potentials. Finally, the cocktail effect alters the d-band structure and electronic configuration of the active sites, synergistically enhancing catalytic performance.

[0043] This invention utilizes inexpensive, abundant, and highly catalytically active transition metals nickel, cobalt, iron, and manganese, as well as aluminum, the most abundant metal in the Earth's crust, as the active metal components of high-entropy oxides. Using excellent porous metallic material nickel foam (NF) as a substrate, the high-entropy oxide SE-NiCoFeMnAlO-AE@NF is prepared through a process of "hydrothermal-self-etching-annealing-acid etching." While leveraging the advantages of high-entropy oxides, this invention significantly improves the problems of poor oxide conductivity and catalyst shedding. Etching modification of the high-entropy oxide further enhances its activity in electrocatalysis. The preparation method of this invention employs a three-pronged strategy of component uniformity, fine structural control, and active site activation, driving material system innovation, contributing to cost reduction and efficiency improvement in electrolyzers, and achieving a balance between activity and stability in high-entropy oxide catalysts.

[0044] Specifically, this invention first grows nanosheet-like pre-NiCoFeMnAl@NF precursors in situ on self-supporting electrode nickel foam (NF) via hydrothermal reaction. The two-dimensional nanosheet structure exposes more active sites, which is beneficial for rapid electron transport and accelerates the electron transfer process. Next, a sample SE-NiCoFeMnAl@NF is obtained by self-etching (SE) under alkaline conditions. Self-etching (SE) is an advantageous method for optimizing catalyst surface roughness, improving catalyst surface hydrophilicity, exposing more active sites, and enhancing catalyst surface activity. The obtained sample SE-NiCoFeMnAl@NF is annealed in an air atmosphere to obtain a sample SE-NiCoFeMnAlO@NF with stronger toughness and conductivity. Finally, specific components (such as Al oxides) are selectively dissolved by acid etching (AE), and abundant oxygen vacancies are controllably introduced, thereby exposing more active sites and improving catalyst performance, resulting in the sample SE-NiCoFeMnAlO-AE@NF of Example 1 of this invention. It operates stably for 100 hours at voltages of 0.5A, 1A, and 2A with virtually no degradation. Through the above series of operations, the sample SE-NiCoFeMnAlO-AE@NF obtained by this invention exhibits excellent electrochemical catalytic performance and stability.

[0045] The preparation method described in this invention specifically includes the following steps:

[0046] 1. Pretreatment of nickel foam (NF):

[0047] Nickel foam (NF) (1cm × 2cm) was ultrasonically cleaned. It was ultrasonically cleaned for 20–30 minutes in 1M hydrochloric acid solution, acetone solution, and anhydrous ethanol solution, respectively, and then dried in a vacuum drying oven at 60°C.

[0048] 2. Hydrothermal synthesis precursor:

[0049] Equimolar amounts of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Mn(NO3)2·4H2O, and Al(NO3)3·9H2O were dissolved in 35 ml of deionized water, with the total molar amount of metal controlled at 1 mmol. The mixture was stirred magnetically for 5 minutes until homogeneous. 6 mmol of CO(NH2)2 and 4 mmol of NH4F were added, and the mixture was stirred continuously for 5 minutes. The resulting homogeneous solution and pretreated nickel foam (NF) were transferred to a polytetrafluoroethylene-lined container, sealed in a stainless steel reactor, and reacted at 120 °C for 8 hours to obtain a precursor sample of a high-entropy oxide based on nickel foam (NF), named pre-NiCoFeMnAl@NF.

[0050] 3. Self-Etching (SE):

[0051] The precursor sample pre-NiCoFeMnAl@NF obtained above was self-etched (SE) at room temperature for 24 h. The obtained sample was then washed alternately with deionized water and ethanol solution until the surface was neutral. It was then dried in a vacuum drying oven at 60 °C. The obtained sample was named SE-NiCoFeMnAl@NF.

[0052] 4. Annealing and oxidation:

[0053] The sample SE-NiCoFeMnAl@NF obtained above was annealed in air atmosphere. The heating rate was 5℃ / min, the annealing temperature was 350℃, and the annealing time was 3h. Then it was cooled to room temperature in the furnace. The obtained sample was named SE-NiCoFeMnAlO@NF.

[0054] 5. Acid etching (AE)

[0055] The sample SE-NiCoFeMnAlO@NF was immersed in 0.1M nitric acid solution for 1 hour, and then the sample surface was alternately cleaned with deionized water and ethanol solution until the surface was neutral. It was then dried in a vacuum drying oven at 60℃ to obtain the self-supporting high-entropy oxide oxygen evolution electrocatalyst material rich in oxygen vacancies, named SE-NiCoFeMnAlO-AE@NF.

[0056] Further, in step 3, self-etching (SE) is carried out in a hydrothermal reaction mother solution (pH≈8-9) cooled to room temperature, and the etching is allowed to stand at room temperature for 24 hours. After etching, the solution is washed alternately with deionized water and ethanol until the pH of the filtrate is ≈7, and then dried in a vacuum drying oven at 60°C.

[0057] Furthermore, in step 5, acid etching (AE) is performed using a 0.1M dilute nitric acid solution diluted with concentrated nitric acid. The sample SE-NiCoFeMnAlO@NF is placed in a 0.1M dilute nitric acid solution at room temperature and allowed to stand for 1 hour.

[0058] Furthermore, in step 5, acid etching (AE) can selectively dissolve specific components (such as Al oxides), introducing abundant oxygen vacancies, thereby exposing more active sites and improving the catalytic activity of the sample.

[0059] The preparation method of the oxygen-vacancy-rich self-supporting high-entropy oxide oxygen evolution electrocatalyst material SE-NiCoFeMnAlO-AE@NF described in this invention has the following advantages compared with the prior art:

[0060] (1) Hydrothermal synthesis is conducive to achieving uniform co-precipitation of metal ions, effectively suppressing component segregation in subsequent processing, ensuring the acquisition of uniform high-entropy oxides with high mixing entropy, giving full play to their structural stability and catalytic performance advantages, and having better catalytic performance and stability.

[0061] (2) Compared with materials with other morphologies, the self-supporting high-entropy oxide oxygen evolution electrocatalyst material SE-NiCoFeMnAlO-AE@NF of the present invention has abundant nanosheet structure, higher specific surface area, excellent mechanical properties, high carrier mobility and abundant number of active sites;

[0062] (3) Compared with unetched samples, self-etching (SE) in an alkaline environment can optimize the performance of the catalyst, enhance the hydrophilicity of the surface, and improve the surface roughness.

[0063] (4) Compared with unetched samples, acid etching (AE) can dissolve some aluminum oxides, form more available vacancies, and call other metal active sites. Moreover, the acid etching (AE) conditions are controllable and highly repeatable.

[0064] (5) Compared with unetched or single-etched high-entropy oxides, the self-supported high-entropy oxide oxygen evolution electrocatalyst material SE-NiCoFeMnAlO-AE@NF, which has undergone self-etching (SE) and acid etching (AE) in an alkaline environment, can achieve more controllable surface reconstruction: self-etching (SE) mainly optimizes the overall morphology and hydrophilicity, while acid etching (AE) selectively dissolves specific components (such as Al oxides) and precisely introduces oxygen vacancies, avoiding the excessive corrosion or insufficient effect that may be caused by single etching.

[0065] (6) Compared with unetched high-entropy oxides, the self-supported high-entropy oxide oxygen evolution electrocatalyst material SE-NiCoFeMnAlO-AE@NF, which has undergone self-etching (SE) and acid etching (AE), has more oxygen vacancies. Oxygen vacancies can regulate intermediate adsorption, promote electron transfer, optimize electronic structure, improve the catalytic activity of the sample and enhance the stability of the sample.

[0066] In summary, the preparation method provided by this invention is simple to operate, highly reproducible, inexpensive, has controllable structure and composition, and superior performance, making it suitable for large-scale production.

[0067] The oxygen-vacancy-rich, self-supporting high-entropy oxide oxygen evolution electrocatalyst material SE-NiCoFeMnAlO-AE@NF described in this invention enables highly efficient water electrolysis in an anion exchange membrane electrolyzer, suitable for electrocatalysis on the anode side of water electrolysis under alkaline conditions. Therefore, this invention also provides an electrocatalytic anode oxygen evolution reaction using the aforementioned high-entropy oxide electrocatalyst for water electrolysis.

[0068] Furthermore, the electrolyte for the electrolysis of water is a 1M KOH solution.

[0069] Specifically, this invention provides a self-supporting high-entropy oxide oxygen evolution electrocatalyst material SE-NiCoFeMnAlO-AE@NF rich in oxygen vacancies.

[0070] Example 1: Preparation of SE-NiCoFeMnAlO@NF

[0071] A method for preparing a self-supporting high-entropy oxide oxygen evolution electrocatalyst material SE-NiCoFeMnAlO-AE@NF rich in oxygen vacancies.

[0072] The specific method is as follows:

[0073] (1) Nickel foam (NF) pretreatment:

[0074] Use ultrasonic cleaning to clean nickel foam (NF) (1cm×2cm). Sonicate in 1M hydrochloric acid solution, acetone solution and anhydrous ethanol solution for 20-30 minutes in sequence, then rinse with ethanol solution and dry in a vacuum drying oven at 60℃.

[0075] (2) Hydrothermal synthesis precursor:

[0076] Equimolar amounts of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Mn(NO3)2·4H2O, and Al(NO3)3·9H2O were dissolved in 35 mL of deionized water, with the total molar amount of metal controlled at 1 mmol. The mixture was stirred magnetically for 5 minutes until homogeneous. 6 mmol of CO(NH2)2 and 4 mmol of NH4F were added, and stirring continued for 5 minutes. The resulting homogeneous solution and pretreated nickel foam (NF) were transferred to a polytetrafluoroethylene-lined container, sealed in a stainless steel reactor, and reacted at 120 °C for 8 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The precursor sample loaded on the nickel foam was removed, thoroughly washed with deionized water and ethanol, and vacuum dried at 60 °C to obtain a high-entropy oxide precursor sample based on nickel foam (NF), named pre-NiCoFeMnAl@NF.

[0077] (3) Self-etching (SE):

[0078] The precursor sample pre-NiCoFeMnAl@NF obtained in step (2) was placed in a hydrothermal reaction mother liquor (pH≈8-9) cooled to room temperature and self-etched (SE) for 24 h at room temperature. After etching, the sample was washed alternately with deionized water and ethanol solution until the filtrate pH≈7 and dried in a vacuum drying oven at 60℃. The obtained sample was named SE-NiCoFeMnAl@NF.

[0079] (4) Annealing oxidation:

[0080] The sample SE-NiCoFeMnAl@NF obtained above was placed in a muffle furnace in an air atmosphere. The heating rate was 5℃ / min, the annealing temperature was 350℃, and the annealing time was 3h. Then, it was cooled to room temperature with the furnace. The obtained sample was named SE-NiCoFeMnAlO@NF.

[0081] (5) Acid etching (AE):

[0082] The sample SE-NiCoFeMnAlO@NF was placed in 0.1M nitric acid solution (obtained by dilution with concentrated nitric acid) and allowed to stand and soak for 1 hour at room temperature. After etching, it was washed alternately with deionized water and ethanol until the pH of the filtrate was ≈7. It was then dried in a vacuum drying oven at 60℃ to obtain the self-supporting high-entropy oxide oxygen evolution electrocatalyst material rich in oxygen vacancies, named SE-NiCoFeMnAlO-AE@NF.

[0083] Comparative Example 1: NiCoFeMnAlO@NF (without etching treatment)

[0084] This comparative example provides a method for preparing a self-supporting high-entropy oxide oxygen evolution electrocatalyst material NiCoFeMnAlO@NF without any etching treatment, for comparison.

[0085] The specific method is as follows:

[0086] (1) Nickel foam pretreatment:

[0087] Use ultrasonic cleaning to clean nickel foam (NF) (1cm×2cm). Sonicate in 1M hydrochloric acid solution, acetone solution and anhydrous ethanol solution for 20-30 minutes in sequence, then rinse with ethanol solution and dry in a vacuum drying oven at 60℃.

[0088] (2) Hydrothermal synthesis precursor:

[0089] Equimolar amounts of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Mn(NO3)2·4H2O, and Al(NO3)3·9H2O were dissolved in 35 mL of deionized water, with the total molar amount of metal controlled at 1 mmol. The mixture was stirred magnetically for 5 minutes until homogeneous. 6 mmol of CO(NH2)2 and 4 mmol of NH4F were added, and stirring continued for 5 minutes. The resulting homogeneous solution and pretreated nickel foam (NF) were transferred to a polytetrafluoroethylene-lined container, sealed in a stainless steel reactor, and reacted at 120 °C for 8 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The precursor sample loaded on the nickel foam was removed, thoroughly washed with deionized water and ethanol, and vacuum dried at 60 °C to obtain a high-entropy oxide precursor sample based on nickel foam (NF), named pre-NiCoFeMnAl@NF.

[0090] (3) Direct annealing oxidation:

[0091] The sample pre-NiCoFeMnAl@NF obtained in step (2) was placed in a muffle furnace with an air atmosphere. The heating rate was 5℃ / min, the annealing temperature was 350℃, and the annealing time was 3h. Then, it was cooled to room temperature with the furnace. The resulting sample was named NiCoFeMnAlO@NF.

[0092] Comparative Example 2: SE-NiCoFeMnAlO@NF (self-etching treatment only)

[0093] This comparative example provides a method for preparing a self-supporting high-entropy oxide oxygen evolution electrocatalyst material SE-NiCoFeMnAlO@NF through self-etching treatment only, for comparison.

[0094] The specific method is as follows:

[0095] (1) Nickel foam pretreatment:

[0096] Use ultrasonic cleaning to clean nickel foam (NF) (1cm×2cm). Sonicate in 1M hydrochloric acid solution, acetone solution and anhydrous ethanol solution for 20-30 minutes in sequence, then rinse with ethanol solution and dry in a vacuum drying oven at 60℃.

[0097] (2) Hydrothermal synthesis precursor:

[0098] Equimolar amounts of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Mn(NO3)2·4H2O, and Al(NO3)3·9H2O were dissolved in 35 mL of deionized water, with the total molar amount of metal controlled at 1 mmol. The mixture was stirred magnetically for 5 minutes until homogeneous. 6 mmol of CO(NH2)2 and 4 mmol of NH4F were added, and stirring continued for 5 minutes. The resulting homogeneous solution and pretreated nickel foam (NF) were transferred to a polytetrafluoroethylene-lined container, sealed in a stainless steel reactor, and reacted at 120 °C for 8 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The precursor sample loaded on the nickel foam was removed, thoroughly washed with deionized water and ethanol, and vacuum dried at 60 °C to obtain a high-entropy oxide precursor sample based on nickel foam (NF), named pre-NiCoFeMnAl@NF.

[0099] (3) Self-etching (SE):

[0100] The precursor sample pre-NiCoFeMnAl@NF obtained in step (2) was placed in a hydrothermal reaction mother liquor (pH≈8-9) cooled to room temperature and self-etched (SE) for 24 h at room temperature. After etching, the sample was washed alternately with deionized water and ethanol solution until the filtrate pH≈7 and dried in a vacuum drying oven at 60℃. The obtained sample was named SE-NiCoFeMnAl@NF.

[0101] (4) Annealing oxidation:

[0102] The sample SE-NiCoFeMnAl@NF obtained above was placed in a muffle furnace in an air atmosphere. The heating rate was 5℃ / min, the annealing temperature was 350℃, and the annealing time was 3h. Then, it was cooled to room temperature with the furnace. The obtained sample was named SE-NiCoFeMnAlO@NF.

[0103] Comparative Example 3: NiCoFeMnAlO-AE@NF (acid etching only)

[0104] This comparative example provides a method for preparing a self-supporting high-entropy oxide oxygen evolution electrocatalyst material NiCoFeMnAlO-AE@NF for comparison.

[0105] The specific method is as follows:

[0106] (1) Nickel foam pretreatment:

[0107] Use ultrasonic cleaning to clean nickel foam (NF) (1cm×2cm). Sonicate in 1M hydrochloric acid solution, acetone solution and anhydrous ethanol solution for 20-30 minutes in sequence, then rinse with ethanol solution and dry in a vacuum drying oven at 60℃.

[0108] (2) Hydrothermal synthesis precursor:

[0109] Equimolar amounts of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Mn(NO3)2·4H2O, and Al(NO3)3·9H2O were dissolved in 35 mL of deionized water, with the total molar amount of metal controlled at 1 mmol. The mixture was stirred magnetically for 5 minutes until homogeneous. 6 mmol of CO(NH2)2 and 4 mmol of NH4F were added, and stirring continued for 5 minutes. The resulting homogeneous solution and pretreated nickel foam (NF) were transferred to a polytetrafluoroethylene-lined container, sealed in a stainless steel reactor, and reacted at 120 °C for 8 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The precursor sample loaded on the nickel foam was removed, thoroughly washed with deionized water and ethanol, and vacuum dried at 60 °C to obtain a high-entropy oxide precursor sample based on nickel foam (NF), named pre-NiCoFeMnAl@NF.

[0110] (3) Annealing oxidation:

[0111] The sample pre-NiCoFeMnAl@NF obtained in step (2) was placed in a muffle furnace with an air atmosphere. The heating rate was 5℃ / min, the annealing temperature was 350℃, and the annealing time was 3h. Then, it was cooled to room temperature with the furnace. The obtained sample was named NiCoFeMnAlO@NF.

[0112] (4) Acid etching (AE):

[0113] The sample NiCoFeMnAlO@NF was placed in a 0.1M nitric acid solution (diluted with concentrated nitric acid) and allowed to stand for 1 hour at room temperature. After etching, it was washed alternately with deionized water and ethanol until the pH of the filtrate was approximately 7. The filtrate was then dried in a vacuum drying oven at 60°C to obtain the oxygen-vacancy-rich self-supporting high-entropy oxide oxygen evolution electrocatalyst material, named NiCoFeMnAlO-AE@NF.

[0114] Experimental Example: Characterization and Performance Testing

[0115] 1. Scanning electron microscopy (SEM) analysis

[0116] The morphological structure of the samples was analyzed using a Zeiss Sigma 500 scanning electron microscope (SEM). The elemental composition and distribution of the catalyst were characterized using an Oxford X-Max energy dispersive spectroscopy (EDS) instrument, with an analytical range of Be-Cf 98.

[0117] Figure 2 This is a SEM image of the self-supporting high-entropy oxide SE-NiCoFeMnAlO-AE@NF prepared in Example 1 of this invention. Figure 2 A, B) and EDS Figure 2 C), as can be seen from the EDS images, the Ni, Co, Fe, Mn, and Al are uniformly distributed on the surface of the prepared self-supported high-entropy oxide SE-NiCoFeMnAlO-AE@NF catalyst. From the SEM images (…), Figure 2 B) It can be seen that the sample maintains a nanosheet structure. The nanosheet structure gives the sample a large specific surface area, which can expose more active sites. The two-dimensional nanosheet structure is conducive to rapid electron transport and accelerates the electron transfer process.

[0118] 2. X-ray diffraction (XRD) characterization

[0119] The crystal structure of the catalyst was analyzed using a Haoyuan DX-2700BH X-ray diffractometer (XRD). A Cu target (Cu Kα radiation) was used, with an operating current and voltage of 40 kV and 30 mA, a scanning range (2θ Range) from 10° to 80°, and a scanning speed of 5° / min.

[0120] Figure 3 The XRD pattern of SE-NiCoFeMnAlO-AE@NF in Example 1 shows the diffraction peaks observed at angles of 30.31°, 35.70°, 37.44°, 43.38°, 52.04°, and 63.02° in the XRD pattern. After comparison with the standard diffraction database (PDF#54-0964), these peaks can be attributed to the (220), (311), (222), (400), (422), and (440) crystal planes in the spinel NiFe2O4 crystal structure. This is common for synthesizing Ni, Co, and Fe as catalysts for active metal elements.

[0121] Figure 4 This is a comparison of the XRD spectra of Example 1 SE-NiCoFeMnAlO-AE@NF, Comparative Example 1 NiCoFeMnAlO@NF, Comparative Example 2 SE-NiCoFeMnAlO@NF, and Comparative Example 3 NiCoFeMnAlO-AE@NF.

[0122] 3. X-ray photoelectron spectroscopy (XPS) characterization

[0123] The elemental composition and valence states of the sample surface were analyzed using a Thermo Fisher Scientific ESCALAB 250Xi X-ray photoelectron spectroscopy (XPS) system. The excitation source was an Al target, the test area was 500 μm, the step size was 0.05 eV, and the test pressure was below 10⁻⁷ Pa.

[0124] Figure 5 The AXPS total spectrum shows the presence of Ni, Co, Fe, Mn and Al.

[0125] Figure 5 In the XPS spectra of oxygen in Examples 1SE-NiCoFeMnAlO-AE@NF and Comparative Example 1NiCoFeMnAlO@NF (B and 4C), the oxygen content near ~529.7 eV is attributed to metal-oxygen bonds, near ~531.5 eV to oxygen vacancies, and near ~533 eV to adsorbed oxygen. The comparison revealed that after two-step etching, the oxygen vacancy content of Example 1SE-NiCoFeMnAlO-AE@NF increased from 39.19% to 45.67%, indicating an increase in oxygen vacancy abundance. Oxygen vacancies can regulate the electronic structure of the catalyst surface, optimize adsorption energy, provide more active sites to stabilize intermediates, and optimize reaction pathways, thus playing an important role in improving OER performance. The preparation method provided by this invention is highly advantageous for constructing catalysts rich in oxygen vacancies.

[0126] 4. Electrochemical testing

[0127] The oxygen evolution performance of water electrolysis in the examples and comparative examples was tested using an electrochemical workstation, Gamry Reference 3000 (USA). A three-electrode system was employed, with the Hg / HgO electrode as the reference electrode, a platinum sheet electrode as the counter electrode, and the corresponding examples and comparative examples as the working electrode. The electrolyte concentration was 1M KOH aqueous solution. The potential conversion formula between the Hg / HgO electrode and the reversible hydrogen electrode is as follows:

[0128] E RHE =E SCE +0.059ph +0.243.

[0129] Linear sweep voltammetry (LSV) curves and corresponding overpotential histograms were performed on Example 1 SE-NiCoFeMnAlO-AE@NF, Comparative Example 1 NiCoFeMnAlO@NF, Comparative Example 2 SE-NiCoFeMnAlO@NF, and Comparative Example 3 NiCoFeMnAlO-AE@NF. Figure 6 A and B show that when the current density is 100 mA·cm⁻¹ -2At a current density of 1000 mA·cm⁻², the overpotentials of Examples 1, 3, 2, and 1 were 254 mV, 271 mV, 277 mV, and 300 mV, respectively; and at a current density of 320 mV, 346 mV, 349 mV, and 380 mV, respectively. Example 1 exhibited the lowest overpotential and the lowest Tafel slope, indicating that it possessed the best catalytic performance.

[0130] In Example 1, the stability of SE-NiCoFeMnAlO-AE@NF was tested by chronopotentiometric method at 0.5A, 1A and 2A respectively. After 100 hours, the corresponding voltage basically did not increase and the stability did not decrease.

[0131] Example 1 demonstrated superior stability during testing.

[0132] In summary, this invention prepares a self-supporting high-entropy oxide SE-NiCoFeMnAlO-AE@NF rich in oxygen vacancies using a "hydrothermal-self-etching (SE)-annealing-acid etching (AE)" technique. First, nanosheet-like pre-NiCoFeMnAl@NF precursors are grown in situ on a self-supporting nickel foam (NF) electrode via a hydrothermal reaction. The two-dimensional nanosheet structure exposes more active sites, facilitating rapid electron transport and accelerating the electron transfer process. Next, the SE-NiCoFeMnAl@NF sample is obtained through self-etching (SE) under alkaline conditions. Etching (SE) is an advantageous method for optimizing catalyst surface roughness, improving catalyst surface hydrophilicity, exposing more active sites, and enhancing catalyst surface activity. The obtained sample SE-NiCoFeMnAl@NF was annealed in air to obtain a sample SE-NiCoFeMnAlO@NF with stronger toughness and conductivity. Finally, acid etching (AE) was used to selectively dissolve specific components (such as Al oxides) and controllably introduce abundant oxygen vacancies, thereby exposing more active sites and improving catalyst performance, resulting in the sample SE-NiCoFeMnAlO-AE@NF of Example 1 of this invention. It operated stably for 100 hours at voltages of 0.5A, 1A, and 2A with virtually no degradation. Through the above series of operations, the sample SE-NiCoFeMnAlO-AE@NF obtained in this invention exhibits excellent electrochemical catalytic performance and stability.

[0133] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. High-entropy oxide electrocatalyst SE-NiCoFeMnAlO-AE@NF, characterized in that, The high-entropy oxide composed of Ni, Co, Fe, Mn, and Al and loaded on a nickel foam substrate has a nanosheet structure as shown in FIG. 2B, a surface rich in oxygen vacancies, an X-ray diffraction pattern as shown in FIG. 3, and an X-ray photoelectron spectrum as shown in FIG. 5A.

2. The method of producing a high-entropy oxide electrocatalyst of claim 1, characterized in that, The high-entropy oxide is prepared by hydrothermal synthesis of a precursor on a nickel foam substrate, self-etching, annealing and oxidation, and acid etching of the precursor.

3. The production method according to claim 2, characterized by, The nickel foam is pretreated by ultrasonic cleaning in a hydrochloric acid solution, acetone, and anhydrous ethanol, and drying.

4. The production method according to claim 2 or 3, characterized by, The method for hydrothermal synthesis of the precursor comprises dissolving equal molar amounts of salts of Ni, Co, Fe, Mn, and Al, ammonium fluoride, and a precipitant in deionized water, mixing the solution uniformly, transferring the uniform solution and the nickel foam into a polytetrafluoroethylene liner, sealing the liner in a stainless steel reactor, and reacting at 100-160°C for 6-12h to obtain the precursor of the high-entropy oxide on the nickel foam substrate. The salts of the metals are nitrate, chloride, or sulfate, and the total molar mass of the salts of the five metals, the molar mass of the precipitant, and the molar mass of ammonium fluoride are in a ratio of 1:(4-8):(2-6). The precipitant is urea or hexamethylenetetramine.

5. The method of any one of claims 2-4, wherein, The self-etching is performed at room temperature for 20-36h, the sample is washed with deionized water and ethanol alternately until the surface of the sample is neutral, and the sample is dried.

6. The production method according to claim 5, wherein The self-etching is performed in a hydrothermal reaction mother liquor cooled to room temperature, the sample is washed with deionized water and ethanol alternately until the surface of the sample is neutral, and the sample is dried in a vacuum drying oven at 60°C.

7. The method of any one of claims 2-6, wherein, The annealing and oxidation is performed by annealing the self-etched sample in an air atmosphere, the annealing is performed at a heating rate of 2-10°C / min, the annealing temperature is 250-450°C, the annealing time is 2-4h, and the sample is cooled to obtain an annealed sample.

8. The method of any one of claims 2-7, wherein, The acid etching is performed by immersing the annealed sample in an acid solution with a concentration of 0.01-0.1M for 0.25-1h, the sample is washed with deionized water and ethanol alternately until the surface of the sample is neutral, and the sample is dried.

9. The production method according to claim 8, characterized by, The acid etching is performed in an acid solution, and the acid solution is a nitric acid solution, a hydrochloric acid solution, or a sulfuric acid solution.

10. An electrocatalytic anodic oxygen evolution reaction, characterized in that, The high-entropy oxide electrocatalyst is used to catalyze electrolysis of water.

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