Preparation method and application of bamboo-like carbon nanotube material with top end coated with metal

Abstract

The invention relates to a preparation method and application of a bamboo-like carbon nanotube material with the top end coated with metal, and belongs to the technical field of fuel cells. The method comprises the following steps: S1, dissolving metal salt and dicyandiamide in an absolute ethyl alcohol solution, and carrying out ultrasonic treatment and drying on the obtained mixed solution to obtain a solid mixture; and S2, fully grinding the solid mixture obtained in the step S1, and performing pyrolysis in a tubular furnace to obtain the bamboo-like carbon nanotube material with the top end coated with the metal. The method is simple in process, low in cost and suitable for batch production, shows good catalytic oxygen reduction reaction (ORR) performance under the alkaline condition, and can meet commercial large-scale production and application of the oxygen reduction catalyst for the fuel cell.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a bamboo-shaped carbon nanotube material with a metal-coated top end, and belongs to the technical field of fuel cells. Background Art

[0002] Traditional fossil fuels have made indelible contributions to the development of human society; however, fossil fuels are limited. With the rapid development of productivity, the consumption of fossil fuels has gradually increased, and the resulting pollution and greenhouse effect have become increasingly serious. Developing new, efficient, and environmentally friendly renewable energy sources is an important way to achieve sustainable development and solve environmental pollution. Using renewable energy can not only greatly reduce environmental pollution and mitigate the greenhouse effect, but also better conform to the concept of harmonious coexistence between humans and nature. After a century of exploration, renewable energy sources such as solar energy, tidal energy, and hydrogen energy have been applied in many industries.

[0003] A fuel cell is a chemical device that directly converts the chemical energy of a fuel into electrical energy, also known as an electrochemical generator. It is the fourth generation of power generation technology after hydraulic power generation, thermal power generation, and nuclear power generation. Such batteries have the advantages of high conversion efficiency, large capacity, high specific energy, no pollution, no noise, wide power range, and no need for charging. It can meet the requirements of environmental protection. The fuel cell system is expected to have broad application prospects and potential markets. As a high-tech product in the 21st century, fuel cells have been applied in industries such as the automotive industry, energy power generation, shipbuilding industry, aerospace, and household power sources.

[0004] However, the slow kinetics of the oxygen reduction reaction (ORR) at the cathode in fuel cells is a key factor limiting the battery efficiency. Traditional noble metal catalysts such as Pt-based catalysts are the most excellent ORR catalysts, but Pt has a low storage capacity on Earth, the preparation cost of noble metal catalysts is high, and their service durability is poor, which limits their large-scale commercial applications. Therefore, developing ORR catalysts with low cost, high catalytic activity, and high durability has become one of the main problems in reducing the cost of fuel cells.

[0005] So far, non-noble metal (such as Fe, Co, and Ni) supported carbon nanotube materials have attracted much attention due to their low cost, high catalytic activity, and good stability. However, the existing preparation methods have complex processes and cannot meet the large-scale production and application of ORR catalysts for commercialization. Summary of the Invention

[0006] To overcome the defects in the prior art, the present invention uses a metal salt and dicyandiamide to prepare a bamboo-shaped carbon nanotube material with a metal-coated top end through a one-step pyrolysis method and uses it to catalyze ORR, which is of great significance for the research of fuel cell ORR catalysts.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] On the one hand, the present invention provides a method for preparing a bamboo-shaped carbon nanotube material with a metal-coated top end, and the method includes the following steps:

[0009] S1. Dissolve a metal salt and dicyandiamide in an absolute ethanol solution, ultrasonically treat the obtained mixed solution, and dry it to obtain a solid mixture;

[0010] S2. After sufficiently grinding the solid mixture obtained in step S1, place it in a tubular furnace for pyrolysis to obtain the bamboo-shaped carbon nanotube material with a metal-coated top end.

[0011] In the above technical solution, further, in step S1, the ultrasonic treatment time is 10 to 15 minutes.

[0012] In the above technical solution, further, in step S1, the drying temperature is 50 to 70 °C.

[0013] In the above technical solution, further, in step S1, the mass ratio of the metal salt to dicyandiamide is 1:3 to 1:15.

[0014] In the above technical solution, further, in step S1, the metal salt is one or more of chlorides, nitrates, and sulfates of Fe, Co, and Ni.

[0015] In the above technical solution, further, in step S2, the pyrolysis conditions are as follows: the protective gas is nitrogen, the temperature is raised from room temperature to 700 to 1000 °C, held for 1 to 5 hours, and then cooled to room temperature with the furnace.

[0016] In the above technical solution, further, the heating rate is 3 to 6 °C / min.

[0017] On the other hand, the present invention provides an application of the bamboo-shaped carbon nanotube material with a metal-coated top end prepared by the above preparation method in a fuel cell, and the material is used as a catalyst for fuel cell ORR.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The bamboo-shaped carbon nanotube material with a metal-coated top end obtained by the preparation method of the present invention has a carbon nanotube structure, and its hollow tube structure can shorten the mass transfer distance, achieve rapid electron transfer, and has excellent electrocatalytic ORR performance;

[0020] 2. The preparation method of the present invention has the advantages of simple process, low cost, and suitability for batch production, and can meet the large-scale production and application of fuel cell cathode catalyst materials for commercialization. Brief Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0022] Figure 1 Scanning electron microscope image of the bamboo-shaped carbon nanotube material with metal-coated tips prepared in Example 1;

[0023] Figure 2 TEM and HRTEM images of the bamboo-shaped carbon nanotube material with metal-coated tips prepared in Example 1, a is the TEM image, and b is the HRTEM image;

[0024] Figure 3 Rotating disk electrochemical test results of the bamboo-shaped carbon nanotube material with metal-coated tips prepared in Example 1;

[0025] Figure 4 Rotating disk electrochemical test results of the bamboo-shaped carbon nanotube material with metal-coated tips prepared in Example 2;

[0026] Figure 5 Rotating disk electrochemical test results of the bamboo-shaped carbon nanotube material with metal-coated tips prepared in Example 3. Detailed Description of the Embodiments

[0027] In order to clearly express the purpose and specific implementation plan of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0028] In the following embodiments, the test methods are conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0029] Example 1

[0030] (1) Add 100 mg of CoCl2·6H2O and 500 mg of dicyandiamide to 50 ml of anhydrous ethanol solution. Put the obtained mixed solution into an ultrasonic cleaner, ultrasonicate for 10 min, and then transfer it to a drying oven at 60 °C for drying for 12 h. After drying, a solid mixture is obtained;

[0031] (2) The solid mixture obtained in step (1) is thoroughly ground and then placed in a tubular furnace. During pyrolysis, nitrogen is introduced as a protective gas. It is heated from room temperature to 900 °C at a heating rate of 5 °C / min, held for 2 hours, and then cooled to room temperature with the furnace to obtain a black solid, which is the bamboo-shaped carbon nanotube material with a metal coating at the tip. The black solid is put into an agate mortar and ground into powder for standby.

[0032] It can be seen from Figure 1 the scanning electron microscope image that the prepared material is evenly distributed and the carbon nanotubes are bamboo-shaped. It can be seen from Figure 2 that a nanoparticle with a clear lattice spacing of 0.17 nm corresponds to the (200) crystal plane of metallic Co, and multilayer graphene (002) with a lattice spacing of 0.36 nm can also be observed, confirming that this material is bamboo-shaped carbon nanotubes with metallic cobalt nanoparticles coated with multilayer graphene at the tip.

[0033] Example 2

[0034] (1) 100 mg of Fe(NO3)3·9H2O and 500 mg of dicyandiamide are added to 50 ml of anhydrous ethanol solution. The resulting mixed solution is put into an ultrasonic cleaner and ultrasonicated for 10 min, and then transferred to a drying oven at 60 °C for drying for 12 h. After drying, a solid mixture is obtained;

[0035] (2) The solid mixture obtained in step (1) is thoroughly ground and then placed in a tubular furnace. During pyrolysis, nitrogen is introduced as a protective gas. It is heated from room temperature to 900 °C at a heating rate of 5 °C / min, held for 2 hours, and then cooled to room temperature with the furnace to obtain a black solid, which is the bamboo-shaped carbon nanotube material with a metal coating at the tip. The black solid is put into an agate mortar and ground into powder for standby.

[0036] Example 3

[0037] (1) 100 mg of NiSO4·6H2O and 500 mg of dicyandiamide are added to 50 ml of anhydrous ethanol solution. The resulting mixed solution is put into an ultrasonic cleaner and ultrasonicated for 10 min, and then transferred to a drying oven at 60 °C for drying for 12 h. After drying, a solid mixture is obtained;

[0038] (2) The solid mixture obtained in step (1) is thoroughly ground and then placed in a tubular furnace. During pyrolysis, nitrogen is introduced as a protective gas. It is heated from room temperature to 900 °C at a heating rate of 5 °C / min, held for 2 hours, and then cooled to room temperature with the furnace to obtain a black solid, which is the bamboo-shaped carbon nanotube material with a metal coating at the tip. The black solid is put into an agate mortar and ground into powder for standby.

[0039] Test Example 1

[0040] Weigh 5.00 mg of the samples prepared in Examples 1-3 separately and put them into glass vials. Add 20 μL of Nafion solution and 1.25 ml of isopropanol, and then disperse them by ultrasonic for 35 min to form a uniformly dispersed ink slurry. Use a micropipette to measure 5 μL of the slurry each time and drop it onto the polished glassy carbon electrode (working electrode), and drop it four times in total. After air drying at room temperature, it is reserved for use. Using a mercury / mercuric oxide electrode (Hg / HgO) as the reference electrode, a platinum mesh electrode as the counter electrode, and 0.1 mol / L KOH solution as the electrolyte, a rotating disk electrochemical test (rotation speed is 1600 revolutions per minute) is carried out at room temperature using a VMP3 (Princeton Company) electrochemical workstation.

[0041] Figure 3 Figure for the rotating disk electrochemical test results of the bamboo-shaped carbon nanotube material with metal-coated tips prepared in Example 1. The abscissa is the potential, with the unit of volt (V), and the ordinate is the current density, with the unit of: milliampere per centimeter -2 (mA cm -2 ). It can be seen from Figure 3 that the limiting diffusion current density of the prepared material under alkaline conditions reaches 4.84 mA cm -2 , the initial potential is 0.92 V, and the half-wave potential is 0.82 V, which is close to the electrocatalytic performance of commercial 20% Pt / C (purchased from Johnson Matthey Company, USA).

[0042] The above electrochemical tests prove that the prepared carbon nanotube material can be used as an oxygen reduction catalyst for fuel cells.

[0043] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of a bamboo-shaped carbon nanotube material with a metal-coated tip, characterized in that, The method includes the following steps: S1. Dissolve a metal salt and dicyandiamide in an absolute ethanol solution, ultrasonically treat the obtained mixed solution, and dry it to obtain a solid mixture; S2. Place the solid mixture obtained in step S1 in a tubular furnace after sufficient grinding for pyrolysis to obtain the bamboo-shaped carbon nanotube material with a metal-coated tip.

2. The preparation method according to claim 1, characterized in that, In step S1, the ultrasonic treatment time is 10 to 15 minutes.

3. The preparation method according to claim 1, characterized in that, In step S1, the drying temperature is 50 to 70 °C.

4. The preparation method according to claim 1, wherein In step S1, the mass ratio of the metal salt to dicyandiamide is 1:3 to 1:

15.

5. The preparation method according to claim 1, characterized in that, In step S1, the metal salt is one or more of chlorides, nitrates, and sulfates of Fe, Co, and Ni.

6. The preparation method according to claim 1, characterized in that, In step S2, the pyrolysis conditions are as follows: the protective gas is nitrogen, the temperature is raised from room temperature to 700 to 1000 °C, held for 1 to 5 hours, and then cooled to room temperature with the furnace.

7. The preparation method according to claim 6, characterized in that, The heating rate is 3 to 6 °C / min.

8. Application of the bamboo-shaped carbon nanotube material with a metal-coated top prepared by the preparation method according to any one of claims 1-7 in a fuel cell, characterized in that, The material is used as a catalyst for fuel cell ORR.

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