A high-entropy layered hydroxide nano-array material, a preparation method and application thereof

Abstract

The application belongs to the field of electrocatalytic materials and energy conversion technology, and particularly relates to a high-entropy layered hydroxide nanoarray material and a preparation method and application thereof. The high-entropy layered hydroxide nanoarray material comprises a conductive substrate and a high-entropy layered hydroxide nanoarray grown on the surface of the conductive substrate. The high-entropy layered hydroxide nanoarray comprises at least uniformly distributed Ni, Fe, Co, Mn and M elements, wherein the M element is at least selected from any one of fourth period transition metals Zn, Cr, V or Cu. The method has good repeatability, mild conditions and is suitable for scale-up production, and provides a reliable technical path for low-cost and large-scale preparation of high-performance high-entropy layered hydroxide catalysts.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials and energy conversion technology, specifically relating to a high-entropy layered hydroxide nanoarray material, its preparation method, and its application. Background Technology

[0002] With global population growth and increasing environmental awareness, there is an urgent need to develop renewable energy technologies. Hydrogen energy is a clean, economical, flexible, efficient, widely available, and widely applicable energy form (such as hydrogen fuel cells and methanol production), thus it is considered one of the most promising options for achieving carbon neutrality. In this context, water electrolysis technology can directly convert electrical energy into chemical energy, making it a significant energy conversion technology widely used in the conversion and utilization of renewable energy sources such as wind and solar power. Hydrogen production through water electrolysis is a high-energy-efficiency, clean, and pollution-free hydrogen production technology. Its simple steps and high product purity make it one of the most promising hydrogen production technologies. The main principle of water electrolysis for hydrogen production is that water molecules are broken down under the influence of direct current, generating hydrogen and oxygen, which are then released from the cathode and anode of the electrolyzer, respectively.

[0003] Hydrogen production via water electrolysis consists of two half-reactions: the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode. The OER, as the core step in water electrolysis, is crucial for oxygen generation. Its four-electron process is significantly complex, involving multiple steps, surface adsorption species, energy level matching, and electron transfer. To improve OER efficiency and reduce energy consumption, a deep understanding and control of these complex factors are needed to design and develop highly efficient catalysts to drive this critical reaction. Using electrocatalysts can significantly reduce the activation energy of water splitting, thereby reducing energy consumption. Over the past few decades, Ir-based and Ru-based oxides have been considered the most effective OER electrocatalysts. However, these noble metal-based electrocatalysts are expensive and have poor stability at high potentials, making them unsuitable for large-scale production. In fact, many non-noble metal-based electrocatalysts have also shown good OER activity and stability, attracting widespread attention from researchers. However, most non-noble metal-based electrocatalysts still require a large overpotential (>350 mV) in alkaline electrolytes to reach 10 mA cm⁻¹. -2 The current density is still far from sufficient for practical applications. Therefore, developing efficient, durable, and economical OER electrocatalysts remains a significant challenge.

[0004] In recent years, high-entropy materials, including high-entropy alloys, high-entropy oxides, high-entropy nitrides, and high-entropy phosphides, have attracted considerable attention due to their unique catalytic effects and tunable electronic structures. These materials are characterized by the incorporation of five or more metal elements in equimolar or near-equimolar proportions, endowing them with tunable multi-metallic active centers. Furthermore, the random distribution of multiple metal elements induces highly disordered atomic arrangements, resulting in a structurally complex framework. This structural complexity leads to the formation of numerous surface defects and vacancies, thereby exposing additional active sites and enhancing the overall performance and activity of the electrocatalyst. Recently, the high-entropy concept has been successfully extended to layered double hydroxide (LDH) materials, greatly expanding their elemental diversity and promoting the development of high-entropy LDHs. Despite the excellent electrochemical potential of high-entropy materials, several challenges remain for OER applications. The complex multi-component nature of these materials often complicates achieving an optimal balance between stability and activity. Moreover, the increased entropy value can lead to complex interactions within the material, potentially hindering electron transport pathways and adversely affecting OER reaction kinetics. Therefore, achieving synergistic effects between metal components in high-entropy materials while optimizing their activity and stability remains a key challenge that must be addressed to advance their application in electrochemical OER.

[0005] To address the above problems, this invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing and applying high-entropy layered hydroxide nanoarray materials.

[0007] The first aspect of the present invention provides a high-entropy layered hydroxide nanoarray material, the high-entropy layered hydroxide nanoarray material comprising a conductive substrate and a high-entropy layered hydroxide nanoarray grown on the surface of the conductive substrate.

[0008] Preferably, the high-entropy layered hydroxide nanoarray contains at least Ni, Fe, Co, Mn and M elements, wherein the M element is selected from at least one of the fourth-period transition metals Zn, Cr, V or Cu.

[0009] Preferably, the molar ratio of Ni, Fe, Co, Mn and M in the high-entropy layered hydroxide nanoarray is 1:1:1:1:(1-3).

[0010] Preferably, the high-entropy layered hydroxide nanoarray is formed by tightly packed spherical structures, each of which is a nanosphere structure formed by nanosheets with different orientations.

[0011] A second aspect of this invention provides a method for preparing the high-entropy layered hydroxide nanoarray material described in the first aspect, wherein the synthesis method of the high-entropy layered hydroxide nanoarray material is a hydrothermal reaction method. Specifically:

[0012] The hydrothermal reaction method includes the following steps: adding the metal salt corresponding to the metal ion, urea and ammonium fluoride to water and dissolving them, transferring the solution to a hydrothermal reactor, adding a conductive substrate, and carrying out a hydrothermal reaction at 110-130°C for 10-13 hours.

[0013] The metal salts are prepared in a molar ratio of nickel salt, iron salt, cobalt salt, manganese salt and salt of element M of 1:1:1:1:(1-3), where element M is selected from any one of the fourth-period transition metals Zn, Cr, V or Cu.

[0014] Preferably, the molar ratio of the metal ions to urea is 1:2 to 1:5, and the molar ratio of the metal ions to ammonium fluoride is 1:2 to 1:3.

[0015] Preferably, the conductive substrate is one or more of a metal or carbon material.

[0016] The third aspect of this invention provides the use of the high-entropy layered hydroxide nanoarray material described in the first aspect as an electrocatalyst for use as an anode in water electrolysis for oxygen evolution.

[0017] Preferably, the electrolyte for the electrolysis of water is an alkaline electrolyte.

[0018] Preferably, the alkaline electrolyte contains an alkaline substance selected from one or more of sodium hydroxide, potassium hydroxide, or other alkaline substances, with a total concentration of 0.5 to 2 mol per liter.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. In terms of preparation process, this invention employs a hydrothermal reaction method to synthesize high-entropy layered hydroxide nanoarray materials. The process is simple, requiring no complex equipment or post-processing. By controlling parameters such as the metal salt ratio, the concentrations of urea and ammonium fluoride, and the reaction temperature and time, the chemical composition, crystallinity, and three-dimensional nanomorphology of the product can be effectively controlled. This method exhibits good reproducibility and mild conditions, making it suitable for scale-up production. It provides a reliable technical route for the low-cost, large-scale preparation of high-performance, high-entropy layered hydroxide catalysts.

[0021] 2. The high-entropy layered hydroxide nanoarray material of the present invention is formed by the close stacking of microspheres. Each microsphere is a nanosphere structure formed by nanosheets with different orientations. This three-dimensional structure is conducive to the diffusion of electrolytes during catalytic reactions and exposes a large number of accessible active sites.

[0022] Furthermore, the five metal elements are uniformly distributed in the high-entropy layered hydroxide nanoarray material. Through the synergistic effect of high-entropy effect and multi-metal synergistic effect, the electronic structure of the material is significantly optimized, and the electron conduction rate and ion diffusion rate are improved, thus exhibiting excellent catalytic activity for water electrolysis.

[0023] 3. In particular, not any combination of elements can form a high-entropy layered hydroxide nanoarray material, and thus the nanosphere structure of this application, while exhibiting excellent catalytic activity for oxygen evolution in water electrolysis. For example, the performance of NiFeCoMn-LDH is not as good as that of NiFeCoMnZn-LDH in Example 1 and NiFeCoMnCr-LDH in Example 2.

[0024] 4. In particular, this application also unexpectedly discovered that the NiFeCoMnZn-LDH material of Example 1 has better catalytic activity than the NiFeCoMnCr-LDH material of Example 2. This may be because of the amphoteric nature of Zn. In an alkaline environment, the dissolution of Zn will expose more active sites, which will regulate the electronic structure of the material and enhance the catalytic activity. Attached Figure Description

[0025] Figure 1 The image shows the XRD pattern of the nickel-iron-cobalt-manganese-zinc layered hydroxide nanoarray material prepared in Example 1.

[0026] Figure 2 SEM image of the nickel-iron-cobalt-manganese-zinc layered hydroxide nanoarray material prepared in Example 1;

[0027] Figure 3 The image shows the EDS-Mapping diagram of the nickel-iron-cobalt-manganese-zinc layered hydroxide nanoarray material prepared in Example 1.

[0028] Figure 4 SEM image of the nickel-iron-cobalt-manganese-chromium layered hydroxide array material prepared in Example 2;

[0029] Figure 5 The polarization curves of the nanoarray materials in Examples 1 and 2 in a 1 mole per liter potassium hydroxide solution are shown.

[0030] Figure 6 The current-suspension curve of the nickel-iron-cobalt-manganese-zinc layered hydroxide nanoarray material prepared in Example 1 is shown.

[0031] Figure 7 Here is a SEM image of the nickel-iron layered double hydroxide prepared in Comparative Example 1;

[0032] Figure 8 EDS-Mapping diagram of the nickel-iron layered double hydroxide prepared in Comparative Example 1;

[0033] Figure 9 This is a polarization curve of Comparative Example 2 in a 1 mol / L potassium hydroxide solution. Detailed Implementation

[0034] The present invention will be further described below through embodiments, but is not limited to these embodiments. Experimental methods not specifically described in the embodiments generally use conventional conditions and conditions described in the manual, or conditions recommended by the manufacturer. The general equipment, materials, reagents, etc., used are all commercially available unless otherwise specified. The raw materials used in the following embodiments and comparative examples are all commercially available.

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are some embodiments of this application, but not all embodiments.

[0036] Example 1

[0037] This embodiment provides a method for preparing a high-entropy layered hydroxide nanoarray material, the specific steps of which are as follows:

[0038] Step (1) Pretreatment of nickel foam: The nickel foam is completely immersed in acetone solution and ultrasonically cleaned to remove any organic contaminants that may remain on the surface. After rinsing with deionized water, it is soaked in hydrochloric acid solution with a concentration of 3 mol / L for 10 minutes under ultrasonic action. Then it is rinsed three times alternately with deionized water and anhydrous ethanol. Finally, it is vacuum dried at 60°C for 5 hours.

[0039] Step (2) A solution was prepared by mixing 0.116 g (0.4 mmol) of nickel nitrate, 0.162 g (0.4 mmol) of ferric nitrate, 0.116 g (0.4 mmol) of cobalt nitrate, 0.1 g (0.4 mmol) of manganese nitrate, 0.119 g (0.4 mmol) of zinc nitrate, 0.3 g (5 mmol) of urea, 0.148 g (4 mmol) of ammonium fluoride, and deionized water. The solution was poured into a 50 mL high-pressure hydrothermal reactor, and the pretreated nickel foam was added. The reactor was then sealed and placed in an oven at 120 °C for hydrothermal reaction for 12 hours. After the reaction, the resulting solid was washed three times with deionized water and anhydrous ethanol, and then dried in a vacuum drying oven at 60 °C for 10 hours to obtain the nickel-iron-cobalt-manganese-zinc layered hydroxide array material (NiFeCoMnZn-LDH array material).

[0040] X-ray diffraction (XRD) tests were performed on the above NiFeCoMnZn-LDH array material. The diffraction pattern is shown in the figure. Figure 1 . Figure 1 As can be seen, the NiFeCoMnZn-LDH is consistent with the standard NiFe-LDH card, and the diffraction peaks match well, indicating that no phase separation occurs in the prepared material. The morphology of the material was then characterized by scanning electron microscopy (SEM), as shown below. Figure 2 As shown. Figure 2 The NiFeCoMnZn-LDH array material shows that the NiFeCoMnZn-LDH nanoarray is formed by a tight stacking of spherical structures, and each microsphere structure is composed of a large number of nanosheets with different orientations.

[0041] X-ray energy dispersive spectroscopy (EDS-Mapping) was performed on the above-mentioned NiFeCoMnZn-LDH array material, and the results are as follows: Figure 3 As shown. Figure 3 The results show that the elements in the NiFeCoMnZn-LDH array material are uniformly distributed, confirming the successful synthesis of the material.

[0042] Example 2

[0043] This embodiment provides a method for preparing a high-entropy layered hydroxide nanoarray material, the specific steps of which are as follows:

[0044] Step (1) Pretreatment of nickel foam: The nickel foam is completely immersed in acetone solution and ultrasonically cleaned to remove any organic contaminants that may remain on the surface. After rinsing with deionized water, it is soaked in hydrochloric acid solution with a concentration of 3 mol / L for 10 minutes under ultrasonic action. Then it is rinsed three times alternately with deionized water and anhydrous ethanol. Finally, it is vacuum dried at 60°C for 5 hours.

[0045] Step (2) A solution was prepared by mixing 0.116 g (0.4 mmol) of nickel nitrate, 0.162 g (0.4 mmol) of ferric nitrate, 0.116 g (0.4 mmol) of cobalt nitrate, 0.1 g (0.4 mmol) of manganese nitrate, 0.16 g (0.4 mmol) of chromium nitrate, 0.3 g (5 mmol) of urea, 0.148 g (4 mmol) of ammonium fluoride, and deionized water. The solution was poured into a 50 mL high-pressure hydrothermal reactor, and the cleaned nickel foam was added. The reactor was then sealed and placed in an oven at 120 °C for hydrothermal reaction for 12 hours. After the reaction, the obtained solid was washed three times with deionized water and anhydrous ethanol, and then dried in a vacuum drying oven at 60 °C for 10 hours to obtain the NiFeCoMnCr-LDH array material.

[0046] Figure 4The SEM image of the prepared NiFeCoMnCr-LDH array material shows that the material is formed by the close packing of spherical structures, and each spherical structure is composed of a large number of nanosheets with different orientations.

[0047] Application examples

[0048] The test was conducted using a three-electrode system: the reference electrode was a mercury / mercury oxide electrode, the counter electrode was a platinum sheet electrode, the working electrode was a high-entropy layered hydroxide nanoarray material with an effective area of ​​1*1 square centimeters obtained in Examples 1 and 2, and the electrolyte was a potassium hydroxide solution with a concentration of 1 mole per liter.

[0049] Figure 5 The figures show the polarization curves of the high-entropy layered hydroxide array materials obtained in Examples 1 and 2 in a three-electrode system, measured in a 1 mol / L potassium hydroxide solution. As shown, the NiFeCoMnZn-LDH provided in Example 1 is the most preferred embodiment, with an overpotential of only 232 mV at a current density of 100 mA / cm², while the overpotential of NiFeCoMnCr-LDH in Example 2 is 254 mV. This indicates that the materials of Examples 1 and 2 exhibit excellent oxygen evolution activity in alkaline electrolytes.

[0050] The stability of the NiFeCoMnZn-LDH nanoarray material obtained in Example 1 was tested using a two-electrode system: the cathode was a platinum sheet, the anode was a NiFeCoMnZn-LDH electrode with an effective area of ​​1*1 square centimeters, and the electrolyte was a 1 mol / L potassium hydroxide aqueous solution. A constant current test of 1 ampere per square centimeter was performed, and the obtained constant current curve is shown below. Figure 6 As shown. Figure 6 It can be seen that the NiFeCoMnZn-LDH electrode has excellent durability and can maintain anodic stability for a long time, up to about 2000 hours.

[0051] Comparative Example 1

[0052] This comparative example provides a method for preparing NiFeCoMn-LDH nanoarray materials:

[0053] Step (1) Pretreatment of nickel foam: The nickel foam is completely immersed in acetone solution and ultrasonically cleaned to remove any organic contaminants that may remain on the surface. After rinsing with deionized water, it is soaked in hydrochloric acid solution with a concentration of 3 mol / L for 10 minutes under ultrasonic action. Then it is rinsed three times alternately with deionized water and anhydrous ethanol. Finally, it is vacuum dried at 60°C for 5 hours.

[0054] Step (2): Prepare a solution by mixing 0.116 g of nickel nitrate, 0.162 g of ferric nitrate, 0.116 g of cobalt nitrate, 0.1 g of manganese nitrate, 0.3 g of urea, 0.148 g of ammonium fluoride, and deionized water. Pour the solution into a 50 mL high-pressure hydrothermal reactor and add the pretreated nickel foam. Seal the reactor and place it in an oven at 120 °C for hydrothermal reaction for 12 hours. After the reaction, wash the obtained solid three times with deionized water and anhydrous ethanol, and dry it in a vacuum drying oven at 60 °C for 10 hours to obtain NiFeCoMn-LDH nanoarray material.

[0055] The morphology of the above NiFeCoMn-LDH nanoarray material was characterized by scanning electron microscopy (SEM). Figure 7 As can be seen, the NiFeCoMn-LDH nanoarray material is a three-dimensional structure formed by numerous random nanosheets with different orientations. X-ray energy dispersive spectroscopy-elemental mapping (EDS-Mapping) was performed on the above NiFeCoMn-LDH nanoarray material, as shown... Figure 8 As shown. Figure 8 As can be seen, the elements in the NiFeCoMn-LDH nanoarray material are evenly distributed, confirming the successful synthesis of the material.

[0056] Comparative application examples

[0057] The test was conducted using a three-electrode system: the reference electrode was a mercury / mercury oxide electrode, the counter electrode was a platinum sheet electrode, the working electrode was a NiFeCoMn-LDH array material with an effective area of ​​1*1 square centimeters obtained in Comparative Example 1, and the electrolyte was a 1 mole per liter potassium hydroxide solution.

[0058] Figure 9 The polarization curve of the high-entropy layered hydroxide array material obtained in Comparative Example 1, measured in a three-electrode system in a 1 mol / L potassium hydroxide solution, is shown below. Figure 9 As shown, the NiFeCoMn-LDH material prepared in Comparative Example 1 has an overpotential of 286 mV at a current density of 100 mA / cm², which is higher than that in Examples 1 and 2. Therefore, the oxygen evolution activity of the high-entropy layered hydroxide nanoarray materials in Examples 1 and 2 is far superior to that of NiFeCoMn-LDH in Comparative Example 1. This indicates that the five metal elements are uniformly distributed in the high-entropy layered hydroxide nanoarray material of this application. Through the synergistic effect of high-entropy effect and multi-metal synergistic effect, the specific surface area is increased, exposing a large number of accessible active sites, which significantly improves the catalytic activity.

Claims

1. A high-entropy layered hydroxide nanoarray material, characterized in that, The high-entropy layered hydroxide nanoarray material comprises a conductive substrate and a high-entropy layered hydroxide nanoarray grown on the surface of the conductive substrate. The high-entropy layered hydroxide nanoarray contains at least uniformly distributed Ni, Fe, Co, Mn and M elements, wherein the M element is selected from at least one of the fourth-period transition metals Zn, Cr, V or Cu.

2. The high-entropy layered hydroxide nanoarray material according to claim 1, characterized in that, In the high-entropy layered hydroxide nanoarray, the molar ratio of Ni, Fe, Co, Mn and M is 1:1:1:1:(1-3).

3. The high-entropy layered hydroxide nanoarray material according to claim 1, characterized in that, The high-entropy layered hydroxide nanoarray is formed by the close stacking of spherical structures, each of which is a nanosphere structure formed by nanosheets with different orientations.

4. The method for preparing high-entropy layered hydroxide nanoarray material according to any one of claims 1-3, characterized in that, The preparation method includes the following steps: Metal salt, urea and ammonium fluoride are added to water and dissolved. The solution is then transferred to a hydrothermal reactor. After adding a conductive substrate, the hydrothermal reaction is carried out at 110–130°C for 10–13 hours. The metal salts include: nickel salts, iron salts, cobalt salts, manganese salts and salts of element M, with the molar ratio of the five elements being 1:1:1:1:(1 to 3), and element M being selected from any one of the fourth-period transition metals Zn, Cr, V or Cu.

5. The preparation method according to claim 4, characterized in that, The molar ratio of the metal ions to urea is 1:2 to 1:5, and the molar ratio of the metal ions to ammonium fluoride is 1:2 to 1:

3. The metal ions are those found in all metal salts.

6. The preparation method according to claim 4, characterized in that, The conductive substrate is one or more of foamed metal or carbon materials.

7. The use of the high-entropy layered hydroxide nanoarray material according to any one of claims 1-3 as an anode for oxygen evolution in water electrolysis.

8. In the use according to claim 7, the electrolyte for electrolyzing water is an alkaline electrolyte.

9. According to claim 8, the alkaline electrolyte contains an alkaline substance, which is one or more of sodium hydroxide and potassium hydroxide, and the concentration of the alkaline substance is 0.5 to 2 mol per liter.

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