Preparation method of hollow nitrogen-doped carbon nano square material with co-existing cobalt monatomic and cobalt-selenium nanoparticle sites

Abstract

The invention provides a preparation method of a hollow nitrogen-doped carbon nano square block material with co-existing cobalt monatomic and cobalt selenium nano particle sites. The method comprises the following steps: (1) synthesizing a metal organic framework precursor; (2) etching the metal organic framework material; and (3) carrying out temperature programming vapor deposition. Co single atoms and cobalt selenium nanoparticle sites are jointly loaded on the nitrogen-doped carbon nano substrate, the activity of the material for catalyzing the oxygen evolution reaction is greatly improved, the preparation process is simple, the cost of the needed raw materials is low, and the method is suitable for industrial production. A new design thought and a synthesis path are provided for preparing the transition metal selenide and a nano catalytic material with coexistence of monatomic and nano particles.

Description

Technical Field

[0001] The present invention belongs to the field of electrocatalytic material preparation, and specifically relates to a method for preparing an oxygen evolution catalyst. The method uses metal sites of a metal-organic framework precursor to capture selenium during a programmed temperature rise process, and simultaneously forms cobalt single atom and cobalt selenium nanoparticle sites on a graphitized nitrogen-doped carbon support. Background Art

[0002] As the energy crisis and environmental problems become increasingly serious, more and more countries, institutions and departments are shifting their attention to the conversion and utilization of renewable energy. Using renewable energy to electrolyze water is a method of energy production with broad application prospects. It can efficiently provide hydrogen, a high calorific value, clean, and renewable alternative to fossil energy, through the input of renewable energy such as solar energy, wind energy, and hydropower. However, the slow kinetic process of the current electrolytic water anode has greatly limited the further application and development of electrolytic water. How to design and prepare efficient, durable and low-cost electrode materials to catalyze the oxygen evolution reaction at a lower overpotential is the key to breaking through the current bottleneck of electrolytic water technology. Therefore, there is an urgent need for a simple and efficient method to prepare an efficient electrocatalyst that can catalyze the oxygen evolution reaction at a lower input voltage, while controlling the raw material cost of the production process as much as possible and simplifying the production process. Summary of the invention

[0003] Based on the above-mentioned prior art, the present invention provides a method for preparing a nitrogen-doped carbon hollow nanocube material in which single cobalt atoms and cobalt-selenium nanoparticle sites coexist, and utilizes the method to effectively realize the catalytic oxygen evolution reaction at a lower overpotential.

[0004] In order to achieve the above object, the present invention adopts the following technical solution: A method for preparing a hollow nitrogen-doped carbon nanocube material in which coexistence of cobalt single atoms and cobalt-selenium nanoparticle sites is provided, comprising the following steps: (1) A certain amount of surfactant hexadecyltrimethylammonium bromide and an organic ligand 2-methylimidazole are respectively prepared into aqueous solutions of a certain concentration. Subsequently, cobalt nitrate powder and 2-methylimidazole aqueous solution are sequentially added to the hexadecyltrimethylammonium bromide aqueous solution under stirring to obtain a uniform mixed solution. After the solution is stirred or allowed to stand for a period of time at room temperature, the obtained solution is centrifuged and washed repeatedly until the upper clear liquid is almost colorless, thereby obtaining a metal organic framework as a precursor.

[0005] (2) The metal organic framework precursor obtained in step (1) is dispersed in a mixed solution of ethanol and water in a certain proportion, and then the above solution is transferred to a mixed solution of ethanol and water of tannic acid. After stirring or standing for a period of time at room temperature, the obtained solution is centrifuged and washed repeatedly until the upper clear liquid is almost colorless to obtain an intermediate product after chemical etching, which is then dried in a vacuum oven overnight.

[0006] (3) A certain mass of selenium powder and the intermediate product obtained in step (2) are placed in a porcelain boat, and the porcelain boat is placed in a tube furnace, with the selenium powder being kept upstream of the airflow and the intermediate product being kept downstream of the airflow, and a temperature program is first performed in an air atmosphere 1, and then nitrogen is introduced into the tube furnace and a temperature program is performed 2. When the tube furnace returns to room temperature, the nitrogen flow is turned off, and the product is taken out to obtain a hollow nitrogen-doped carbon nanocube material in which coexisting cobalt single atoms and cobalt-selenium nanoparticle sites are obtained.

[0007] Furthermore, in step (1), the concentrations of the aqueous solution of the surfactant and the organic ligand are 0.1-0.8 g / L and 20-100 g / L, respectively.

[0008] Furthermore, the mass of cobalt nitrate added in step (1) is 0.1-1 g.

[0009] Furthermore, the volume ratio of ethanol to water in the ethanol and water mixed solution in step (2) is 3:(1-9), and the volume of the solution is 5-40 mL.

[0010] Furthermore, in the mixed solution of tannic acid in ethanol and water described in step (2), the concentration of tannic acid is 0.1-2 g / L, the mixed volume ratio of ethanol and water is 3:1 to 1:3, and the total volume of the solution is 100-500 mL.

[0011] Furthermore, in step (3), the mass ratio of selenium powder to the intermediate product is 1:(1-10).

[0012] Furthermore, the heating rate of the programmed temperature in step (3) is 2-10°C / min, the maximum temperature is 200-1000°C, and the time maintained at the maximum temperature is 0.5-3 hours.

[0013] Furthermore, the nitrogen flow rate in step (3) is 10-100 sccm.

[0014] The hollow nitrogen-doped carbon nanocube material in which coexisting cobalt single atoms and cobalt-selenium nanoparticle sites is used as a catalyst in the catalytic oxygen evolution reaction of water electrolysis.

[0015] The advantages of the present invention are: A preparation method for nitrogen-doped carbon hollow nanocube materials with coexisting cobalt single atoms and cobalt-selenium nanoparticle sites has been developed. The modification of metal organic framework materials and the capture of free selenium are achieved by two-step programmed heating. Compared with the existing technology, this method is simple to operate, has a simple process, good reproducibility, and has the potential for large-scale preparation. In addition, the synthetic raw materials of this material are low-cost and highly abundant in nature. The catalyst material prepared by this method has better catalytic oxygen evolution reaction performance than commercial precious metal materials, and is expected to achieve the use of non-precious metals to replace precious metal catalytic materials, which is more in line with environmentally friendly production needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings of this specification are used together with the above-mentioned invention content to further illustrate the technical concept of the present invention. The present invention should not be interpreted as being limited to the contents described in the drawings.

[0017] Figure 1 This is a transmission electron micrograph of the nitrogen-doped carbon hollow nanocube material in which single cobalt atoms and cobalt-selenium nanoparticle sites coexist as prepared in Example 1, and its corresponding element distribution (red corresponds to cobalt, blue corresponds to selenium, green corresponds to carbon, orange corresponds to nitrogen, and pink corresponds to oxygen).

[0018] Figure 2 This is a spherical aberration corrected transmission electron micrograph of the nitrogen-doped carbon hollow nanocube with coexisting cobalt single atoms and cobalt-selenium nanoparticle sites prepared in Example 1 (the red circle is the nanoparticle, and the yellow circle is the single atom).

[0019] Figure 3 This is an X-ray diffraction (XRD) pattern of the nitrogen-doped carbon hollow nanocube with coexisting cobalt single atoms and cobalt-selenium nanoparticle sites prepared in Example 1.

[0020] Figure 4 The linear voltammetric curves of the electrocatalytic oxygen evolution reaction of Example 1, commercial ruthenium dioxide and Comparative Example 1. DETAILED DESCRIPTION

[0021] Hereinafter, the present invention will be described in detail with reference to embodiments to specifically describe the present invention. However, embodiments of the present invention may be modified into various other forms and the scope of the present invention should not be construed as being limited to the embodiments described below. Embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.

[0022] The experimental methods in the following examples, unless otherwise specified, are generally conventional conditions in the art or conditions recommended by the manufacturer; the raw materials and equipment used are all commercially available from conventional markets, etc., unless otherwise specified.

[0023] Example 1 Step (1): Synthesis of metal organic framework precursors Dissolve 4 mg of hexadecyltrimethylammonium bromide in 10 mL of deionized water and stir until completely dissolved. Then, add 292 mg of cobalt nitrate hexahydrate to the above solution and stir until completely dissolved. Then, add 4.54 g of 2-methylimidazole to 70 mL of deionized water and stir until completely dissolved. Then, add the 2-methylimidazole aqueous solution to the mixed solution containing cobalt nitrate hexahydrate and hexadecyltrimethylammonium bromide while stirring, and continue stirring at room temperature and pressure for 30 minutes to obtain a purple solution. Subsequently, centrifuge and wash the product with ethanol and water several times until the supernatant after centrifugation is colorless and transparent. Pour off the supernatant and the obtained purple solid product is the metal-organic framework precursor.

[0024] Step (2): Etching of metal organic framework materials The metal organic framework precursor obtained above was dispersed in 10 mL of ethanol aqueous solution (the volume ratio of ethanol to water was 1:1), uniformly dispersed by ultrasonication, and added with 300 mL of 1 mg / mL tannic acid solution (the volume ratio of ethanol to water in the solution was 1:1) during stirring. Stirring was continued for 10 minutes at room temperature and pressure. The obtained khaki solution was centrifuged and washed with ethanol and water several times until the supernatant was colorless and transparent. The supernatant was discarded, and the obtained khaki solid product was the intermediate product after chemical etching and containing a carbon source. The product was placed in a vacuum oven at 60°C to dry overnight.

[0025] Step (3): Programmed temperature vapor deposition 10 mg of selenium powder and 30 mg of the intermediate product dried in step (2) were placed in a porcelain boat, and the porcelain boat was placed in a tube furnace, with the selenium powder kept upstream of the airflow and the intermediate product kept downstream of the airflow. The temperature was first programmed to rise 1 in an air atmosphere: the heating rate was 10°C / min, the maximum temperature was 200°C, and the time at the maximum temperature was kept for 0.5 hours. Then nitrogen was introduced into the tube furnace, the nitrogen flow rate was maintained at 20 sccm, and the temperature was programmed to rise 2: the heating rate was 2°C / min, the maximum temperature was 500°C, and the time at the maximum temperature was kept for 2 hours. When the tube furnace returned to room temperature, the nitrogen flow was turned off, and the product was taken out to obtain a hollow nitrogen-doped carbon nanocube material with coexisting cobalt single atoms and cobalt-selenium nanoparticle sites.

[0026] Figure 1 This is a transmission electron microscope image of the hollow nanocube material prepared in Example 1 and its corresponding element distribution. It can be seen that the material has a hollow nanocube morphology, which minimizes the dead volume inside that is difficult to contact with the reaction intermediates and increases the mass specific activity. Cobalt, selenium, carbon, nitrogen, and oxygen elements are evenly distributed on the surface of the material, and the active sites are evenly and regularly distributed. Figure 2This is a spherical aberration corrected transmission electron micrograph of the material prepared in Example 1. It can be seen that at the microscopic scale, single cobalt atoms and cobalt selenium nanoparticle sites coexist, and the electronic interaction between the cobalt selenium particles and adjacent single atoms optimizes the adsorption energy of the cobalt selenium particles for oxygen evolution intermediates, thereby improving the intrinsic activity of a single active site. Figure 3 This is the XRD spectrum of the material prepared in Example 1. It can be seen that the cobalt-selenium nanoparticles in the material are in the form of Co 0.85 Se.

[0027] Comparative Example 1 Repeat steps (1) to (3) of Example 1 to obtain the product, except that no selenium powder is added in step (3). The remaining operations are the same as those of Example 1.

[0028] Figure 4 The linear voltammetric curves of the electrocatalytic oxygen evolution reaction of Example 1, commercial ruthenium dioxide and Comparative Example 1 are shown. The nitrogen-doped carbon hollow nanocube material with coexisting cobalt single atoms and cobalt-selenium nanoparticle sites prepared in Example 1 has a lower oxygen evolution overpotential than the commercial precious metal material ruthenium dioxide. Example 1, commercial ruthenium dioxide and Comparative Example require 298 mV, 377 mV and 477 mV, respectively, to reach an oxygen evolution current density of 10 mA / cm 2 , proving that Example 1 has great application potential as a non-precious metal catalyst.

[0029] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a hollow nitrogen-doped carbon nanocube material in which coexistence of cobalt single atoms and cobalt-selenium nanoparticle sites is achieved, characterized in that: The following steps are involved: (1) mixing a surfactant, an organic ligand and a metal inorganic salt of cobalt nitrate in deionized water in a certain proportion, stirring for a period of time, and washing the obtained mixed solution by centrifugation to obtain a metal organic framework precursor; (2) chemically etching the metal organic framework precursor obtained in step (1) in a mixed solution of tannic acid, ethanol and water, and obtaining an intermediate product by centrifugation and washing the mixed solution and drying it in a vacuum oven; (3) A certain mass of selenium powder and the intermediate product obtained in step (2) are placed in a porcelain boat, and are located respectively in the upstream and downstream of the gas path of the tubular furnace, and programmed to rise in temperature twice in air and nitrogen to obtain a hollow nitrogen-doped carbon nanocube material in which coexisting cobalt single atoms and cobalt-selenium nanoparticle sites.

2. The preparation method according to claim 1, characterized in that: The surfactant is hexadecyltrimethylammonium bromide.

3. The preparation method according to claim 1, characterized in that: The organic ligand is 2-methylimidazole.

4. The preparation method according to claim 1, characterized in that In the mixed solution of tannic acid in ethanol and water described in step (2), the concentration of tannic acid is 0.1-2 g / L, and the mixed volume ratio of ethanol and water is 3:1 to 1:

3.

5. The preparation method according to claim 1, characterized in that: In step (3), the mass ratio of selenium powder to the intermediate product is 1:(1-10).

6. The preparation method according to claim 1, characterized in that: The heating rate of the programmed temperature in step (3) is 2-10°C / min, the maximum temperature is 200-1000°C, and the time maintained at the maximum temperature is 0.5-3 hours.

7. The preparation method according to claim 1, characterized in that The nitrogen flow rate in step (3) is 10-100 sccm.

8. A hollow nitrogen-doped carbon nanocube material in which coexisting cobalt single atoms and cobalt-selenium nanoparticle sites are obtained according to the preparation method according to any one of claims 1 to 7.

9. Use of the hollow nitrogen-doped carbon nanocube material in which coexisting cobalt single atoms and cobalt-selenium nanoparticle sites according to claim 8 as a catalyst in the catalytic oxygen evolution reaction of water electrolysis.

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