A five-element high-entropy spinel / multi-walled carbon nanotube composite material and a preparation method thereof

Abstract

The application discloses a kind of five high-entropy spinel / multi-walled carbon nanotube composite materials and preparation method thereof, the preparation method includes the following steps: S1: metal salt, multi-walled carbon nanotube, ammonium fluoride, cetyltrimethylammonium bromide and urea are added to water to carry out ultrasonic mixing, and A solution is obtained;Metal salt includes chromium salt, manganese salt, nickel salt, iron salt and cobalt salt;S2: A solution is reacted at 130-150 DEG C for 6-8h, then after filtration, washing, drying, product B is obtained;S3: product B is ground into powder, then heated to 850-950 DEG C in inert gas, and heat treatment is kept for 2h, and then cooled, and it is obtained.The composite material prepared in the application can adjust electronic structure and enhance intrinsic catalytic activity due to the interaction between transition metals, the multi-walled carbon nanotube is compounded in the application, which is not only beneficial to the exposure of active site, but also enhances the conductivity and improves the OER catalytic activity.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a pentagonal high-entropy spinel / multi-walled carbon nanotube composite material and its preparation method. Background Technology

[0002] In recent years, the energy crisis has attracted global attention, and there is an urgent need to develop new green energy sources. The oxygen evolution reaction (OER) is one of the most important reactions in renewable energy conversion and storage technologies such as metal-air batteries; however, its slow kinetics hinder its industrial development, requiring suitable catalysts to improve the OER reaction rate. Currently, RuO2 and IrO2 are recognized as the most active OER catalysts, but their high cost, low reserves, and poor stability limit their large-scale application.

[0003] To address these issues, researchers have conducted extensive work on improving OER catalysts and developing novel, highly efficient, and inexpensive catalysts. Among these, high-entropy oxides with multiple (five or more) metal cations are considered to have great potential in electrocatalysis due to their high oxygen mobility resulting from high lattice distortion.

[0004] The synthesis methods of high-entropy oxides include spray pyrolysis, solid-state reaction and sputtering deposition, etc., and these methods require relatively complex reaction equipment and process conditions. Summary of the Invention

[0005] In view of the above-mentioned prior art, the present invention provides a five-element high-entropy spinel / multi-walled carbon nanotube composite material and its preparation method, so as to solve the problems of high price, low reserves, poor stability and complex preparation process of existing OER catalysts.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: to provide a method for preparing a pentagonal high-entropy spinel / multi-walled carbon nanotube composite material, comprising the following steps:

[0007] S1: Metal salts, multi-walled carbon nanotubes, ammonium fluoride, hexadecyltrimethylammonium bromide, and urea are added to water and ultrasonically mixed to obtain solution A; the metal salts include chromium salts, manganese salts, nickel salts, iron salts, and cobalt salts;

[0008] S2: React solution A at 130-150℃ for 6-8 hours, then filter, wash and dry to obtain product B;

[0009] S3: Grind product B into powder, then heat it in an inert gas to 850-950℃ and keep it at that temperature for 2 hours, then cool it to obtain the product.

[0010] Transition metals such as Cr, Mn, Ni, Fe, and Co can serve as OER catalysts due to their high reactivity, abundant abundance in the Earth's crust, and outstanding stability under alkaline conditions. The interaction of multiple transition metals can modulate the electronic structure and enhance intrinsic catalytic activity. Furthermore, combining high-entropy oxides with multi-walled carbon nanotubes not only improves the electrical conductivity of the oxides but also facilitates the exposure of active sites, accelerating OER reaction kinetics and increasing the OER reaction rate.

[0011] This invention employs a one-step hydrothermal method to prepare a pentagonal high-entropy spinel / multi-walled carbon nanotube composite material. Urea is used as a hydrolyzing agent, and hexadecyltrimethylammonium bromide as a dispersant. The composite multi-walled carbon nanotubes undergo a high-pressure, high-temperature reaction in a polytetrafluoroethylene-lined stainless steel autoclave, forming a precipitate. The precipitate is then heat-treated to obtain the composite material. The oxide particles prepared by this invention are small in size and uniformly distributed, and the use of relatively inexpensive raw materials makes it suitable for widespread application. The hydrothermal synthesis of the pentagonal high-entropy spinel / multi-walled carbon nanotube composite material simplifies the process and equipment.

[0012] Based on the above technical solution, the present invention can be further improved as follows.

[0013] Furthermore, the molar amounts of chromium salts, manganese salts, nickel salts, iron salts, and cobalt salts in the metal salts are the same.

[0014] Furthermore, the molar concentrations of the metal salt, ammonium fluoride, and urea are 0.02–0.03 mol / L, 0.075–0.085 mol / L, and 0.18–0.22 mol / L, respectively, while the mass concentrations of multi-walled carbon nanotubes and hexadecyltrimethylammonium bromide are 2.5–3.5 g / L and 8–10 g / L, respectively.

[0015] Furthermore, the metal salt is a metal chloride or a metal nitrate.

[0016] Furthermore, the ultrasonic mixing time should be no less than 30 minutes.

[0017] Furthermore, the washing process involves rinsing with deionized water and ethanol at least three times, alternating between the two.

[0018] Further drying is carried out at 80–90°C for 11–13 hours.

[0019] Furthermore, the inert gas is nitrogen or argon.

[0020] Furthermore, the heating rate of the heat treatment in S3 is 5℃ / min.

[0021] The present invention also provides a pentagonal high-entropy spinel / multi-walled carbon nanotube composite material prepared by the above preparation method.

[0022] The beneficial effects of this invention are:

[0023] (1) The preparation process of this invention is simple;

[0024] (2) This invention can prepare high-entropy spinel composite multi-walled carbon nanotubes with five or more elements by controlling the types of metal salts.

[0025] (3) The five-element high-entropy spinel / multi-walled carbon nanotube composite material prepared by the present invention can regulate the electronic structure and enhance the intrinsic catalytic activity due to the interaction between transition metals.

[0026] (4) The present invention uses composite multi-walled carbon nanotubes, which not only facilitates the exposure of active sites, but also enhances electrical conductivity and improves OER catalytic activity. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope image of the five-element high-entropy spinel / multi-walled carbon nanotube composite material of the present invention;

[0028] Figure 2 The X-ray diffraction pattern of the five-element high-entropy spinel / multi-walled carbon nanotube composite material of the present invention is shown below.

[0029] Figure 3 This is a cyclic voltammetry curve of the five-element high-entropy spinel / multi-walled carbon nanotube composite material of the present invention;

[0030] Figure 4 This is a chronopotential curve of the pentagonal high-entropy spinel / multi-walled carbon nanotube composite material of the present invention. Detailed Implementation

[0031] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0032] Example 1

[0033] A method for preparing a pentagonal high-entropy spinel / multi-walled carbon nanotube composite material includes the following steps:

[0034] S1: Dissolve 1.2 mmol each of chromium chloride hexahydrate, manganese chloride tetrahydrate, nickel chloride hexahydrate, ferrous chloride tetrahydrate, and cobalt chloride hexahydrate, 0.15 g of multi-walled carbon nanotubes, 0.5 g of hexadecyltrimethylammonium bromide, 4 mmol of ammonium fluoride, and 10 mmol of urea in 50 ml of deionized water, and sonicate for 30 min to obtain solution A.

[0035] S2: Add solution A into the polytetrafluoroethylene inner liner of a stainless steel autoclave, heat it at 140℃ for 7 hours in a forced-air drying oven, cool it naturally to room temperature, filter and separate the product, wash it three times alternately with deionized water and ethanol, and dry it at 85℃ for 12 hours to obtain product B.

[0036] S3: Grind product B into powder using an agate mortar and pestle, spread it evenly in a covered alumina crucible, place it in a tube furnace, introduce nitrogen gas, heat at 900℃ for 2 hours at a heating rate of 5℃ / min, and then allow it to cool naturally to obtain the product.

[0037] Example 2

[0038] A method for preparing a pentagonal high-entropy spinel / multi-walled carbon nanotube composite material includes the following steps:

[0039] S1: Dissolve 1 mmol each of chromium chloride hexahydrate, manganese chloride tetrahydrate, nickel chloride hexahydrate, anhydrous ferrous chloride, and cobalt chloride hexahydrate, 0.125 g of multi-walled carbon nanotubes, 0.4 g of hexadecyltrimethylammonium bromide, 3.75 mmol of ammonium fluoride, and 11 mmol of urea in 50 ml of deionized water, and sonicate for 40 min to obtain solution A.

[0040] S2: Add solution A into the polytetrafluoroethylene liner of a stainless steel autoclave, heat it at 130°C for 8 hours in a vacuum drying oven, cool it naturally to room temperature, filter and separate the product, wash it 4 times alternately with deionized water and ethanol, and dry it at 80°C for 13 hours to obtain product B.

[0041] S3: Grind product B into powder using an agate mortar and pestle, spread it evenly in a covered alumina crucible, place it in a tube furnace, introduce nitrogen gas, heat at 850℃ for 2 hours at a heating rate of 5℃ / min, and then allow it to cool naturally to obtain the product.

[0042] Example 3

[0043] A method for preparing a pentagonal high-entropy spinel / multi-walled carbon nanotube composite material includes the following steps:

[0044] S1: Dissolve 1.5 mmol each of chromium nitrate nonahydrate, manganese nitrate, nickel nitrate hexahydrate, ferric nitrate nonahydrate, and cobalt nitrate hexahydrate, 0.175 g of multi-walled carbon nanotubes, 0.4 g of hexadecyltrimethylammonium bromide, 4.25 mmol of ammonium fluoride, and 9 mmol of urea in 50 ml of deionized water, and sonicate for 35 min to obtain solution A.

[0045] S2: Add solution A into the polytetrafluoroethylene liner of a stainless steel autoclave, heat it at 150°C for 6 hours in a vacuum drying oven, cool it naturally to room temperature, filter and separate the product, wash it 4 times alternately with deionized water and ethanol, and dry it at 90°C for 11 hours to obtain product B.

[0046] S3: Grind product B into powder using an agate mortar and pestle, spread it evenly in a covered alumina crucible, place it in a tube furnace, introduce nitrogen gas, heat at 950℃ for 2 hours at a heating rate of 5℃ / min, and then allow it to cool naturally to obtain the product.

[0047] Experimental Example

[0048] Weigh 7.5 mg of the pentagonal high-entropy spinel / multi-walled carbon nanotube composite material prepared in Example 1, add 2.5 mg of EC-600JD, 350 μl of isopropanol, and 95 μl of Nafion solution (5 wt%), and mix for 40 min using a cell disruptor to form a homogeneous slurry. Drop 7 μl of the slurry onto the surface of a glassy carbon electrode (0.19625 cm⁻¹). 2 After natural drying, the mercury oxide electrode was used as the working electrode, the mercury oxide electrode as the reference electrode, and the carbon rod as the counter electrode. Cyclic voltammetry was performed using a Chenhua CHI660 electrochemical workstation with a rotating disk speed of 1600 rpm and an oxygen-saturated 1M KOH solution as the electrolyte solution. The current density was 10 mA / cm². 2 At that time, the overpotential of OER was 305mV.

[0049] Weigh 7.5 mg of the pentagonal high-entropy spinel / multi-walled carbon nanotube composite material prepared in Example 2, add 2.5 mg of EC-600JD, 350 μl of isopropanol, and 95 μl of Nafion solution (5 wt%), and mix for 40 min using a cell disruptor to form a homogeneous slurry. Drop 100 μl of the slurry onto carbon paper (1 cm). 2 The surface of the Toray Industries (Japan) had a loading of 2.25 mg / cm³. 2 After natural drying, the mercury oxide electrode was used as the working electrode, the mercury oxide electrode as the reference electrode, and the carbon rod as the counter electrode. Chronopotential stability testing was performed using a Chenhua CHI660 electrochemical workstation. The electrolyte solution was an oxygen-saturated 1M KOH solution. The current density was 10 mA / cm². 2 At that time, the overpotential of OER remained at 280mV within 48h, demonstrating excellent stability.

[0050] In summary, this invention employs a simple one-step hydrothermal method to synthesize a pentagonal high-entropy spinel / multi-walled carbon nanotube composite material with a spinel structure as a catalyst for the oxygen evolution reaction (OER). Five transition metal elements with similar radii modulate the electronic structure, enhancing the intrinsic catalytic activity. The multi-walled carbon nanotubes not only facilitate the exposure of active sites but also improve the catalyst's conductivity, enabling the pentagonal high-entropy spinel / multi-walled carbon nanotube composite material to exhibit excellent OER catalytic activity and stability. At a current density of 10 mA / cm², [the synthesis was successful]. 2 At that time, the overpotential of OER was 305mV, and the overpotential stabilization time was 48h.

[0051] Figure 1 This is a scanning electron microscope (SEM) image of the pentagonal high-entropy spinel / multi-walled carbon nanotube composite material prepared in Example 1 of this invention. Figure 1 As can be seen, in the prepared pentagonal high-entropy spinel / multi-walled carbon nanotube composite material, (CrMnNiFeCo)3O4 and multi-walled carbon nanotubes are tightly wrapped together, which is beneficial to improving the conductivity of the composite material.

[0052] Figure 2 This is the X-ray diffraction pattern of the pentagonal high-entropy spinel / multi-walled carbon nanotube composite material prepared in Example 1 of this invention. Figure 2 As can be seen, the prepared composite material contains spinel phase and other metal oxide phases. In addition, it also shows characteristic peaks of multi-walled carbon nanotubes, further demonstrating the successful synthesis of the composite material.

[0053] Figure 3 This is a cyclic voltammetry curve of the pentagonal high-entropy spinel / multi-walled carbon nanotube composite material prepared in Example 1 of this invention. Figure 3 As can be seen, the prepared composite material exhibits excellent OER catalytic activity at a current density of 10 mA / cm². 2 At that time, the overpotential of OER was 305mV.

[0054] Figure 4 This is a chronopotential curve of carbon paper supported on a pentagonal high-entropy spinel / multi-walled carbon nanotube composite material prepared in Example 2 of this invention. Figure 4 As can be seen, the composite material has good OER stability, and the overpotential did not change significantly within 48 hours.

[0055] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A method for preparing a quinary high-entropy spinel / multi-walled carbon nanotube composite material, characterized in that, The preparation method comprises the following steps: S1: adding metal salt, multi-walled carbon nanotubes, ammonium fluoride, cetyltrimethylammonium bromide and urea into water for ultrasonic mixing to obtain solution A; the metal salt comprises chromium salt, manganese salt, nickel salt, iron salt and cobalt salt; the molar amount of the chromium salt, the manganese salt, the nickel salt, the iron salt and the cobalt salt in the metal salt is the same; in the solution A, the molar concentration of the metal salt, the ammonium fluoride and the urea is 0.02-0.03 mol / L, 0.075-0.085 mol / L and 0.18-0.22 mol / L respectively, and the mass concentration of the multi-walled carbon nanotubes and the cetyltrimethylammonium bromide is 2.5-3.5 g / L and 8-10 g / L respectively; the ultrasonic mixing time is not less than 30 min; S2: reacting the solution A at 130-150 ℃ for 6-8 h, and then filtering, washing and drying to obtain product B; S3: grinding the product B into powder, heating to 850-950 ℃ in an inert gas and heat treating for 2 h, and then cooling to obtain the product.

2. The method of claim 1, wherein: The metal salt is a metal chloride or a metal nitrate.

3. The method of claim 1, wherein: The washing is washing with deionized water and ethanol alternately for at least three times.

4. The method of claim 1, wherein: The drying is drying at 80-90 ℃ for 11-13 h.

5. The method of claim 1, wherein: The inert gas is nitrogen or argon.

6. The method of claim 1, wherein: The heating rate in S3 is 5 ℃ / min.

7. A five-element high-entropy spinel / multi-walled carbon nanotube composite material prepared by the preparation method in any one of claims 1-6.

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