CN106784900B

CN106784900B - Carbon nano tube covered by platinum-based nano particle coated tin dioxide and preparation method thereof

Info

Publication number: CN106784900B
Application number: CN201611140644.6A
Authority: CN
Inventors: 官轮辉; 黄美华
Original assignee: Fujian Institute of Research on the Structure of Matter of CAS
Current assignee: Fujian Institute of Research on the Structure of Matter of CAS
Priority date: 2016-12-12
Filing date: 2016-12-12
Publication date: 2020-05-05
Anticipated expiration: 2036-12-12
Also published as: CN106784900A

Abstract

The invention relates to a carbon nanotube covered by platinum-based nanoparticles and covered with tin dioxide and a preparation method thereof, wherein the carbon nanotube is a multi-walled carbon nanotube, and a layer of carbon dioxide is supported on the carbon nanotube. tin, and a layer of platinum-based metal is supported on the tin dioxide layer. The platinum-based metal exists in the form of nanoparticles and is connected into a network structure. The catalyst of the invention has high utilization rate of precious metals, high catalytic activity, longevity and anti-carbon monoxide poisoning performance of the catalyst, its catalytic methanol oxidation activity is more than 6.2 times that of commercial Pt/C catalyst, and its oxygen concentration at a hydrogen standard potential of 0.9V is high. The reduction mass activity is 9.6 times that of the commercial Pt/C catalyst. Its particle size is preferably between 1.0 and 10.0 nm, and preferably between 2.0 and 4.0 nm.

Description

Carbon nano tube covered by platinum-based nano particle coated tin dioxide and preparation method thereof

Technical Field

The invention relates to the field of fuel cell catalysts, in particular to a platinum-based nanoparticle coated tin dioxide covered carbon nanotube for a fuel cell and a preparation method thereof.

Background

The fuel cell is a device capable of directly and cleanly converting chemical energy of fuel into electric energy with high efficiency, and is a relatively ideal power generation technology. Due to the wide application prospect of fuel cells in vehicle power sources, various mobile power sources, military power sources and the like, research on fuel cells is highly valued by various countries.

Some problems are encountered in the current commercialization of fuel cells, most notably the high price of the catalyst, low natural reserves, low activity and short lifetime. In a fuel cell using a reformed gas as a fuel, there is also a problem that a catalyst is easily poisoned and deactivated. These problems are closely related to the performance of the catalyst, so that the development and research of a new generation of high-performance fuel cell catalyst is of great significance in promoting the research and development of fuel cells.

The preparation method of the catalyst material is mainly immersion reduction method, ion exchange method, precipitation method, gas phase reduction method, microwave method, colloid method and the like, but the methods sometimes can not control the particle size of the active component of the catalyst and the surface interface structure of the surface of the nano particles well, and the platinum-based nano catalyst with controllable surface interface component, highly dispersed active component, small particle size and very uniform dispersion is difficult to obtain.

The applicant disclosed in patent CN105655607 a platinum-based metal-loaded carbon nanotube (Pt/MWCNTs). The catalytic activity of the catalyst for oxidizing methanol is 4.4 times that of a commercial platinum-carbon (Johnson Matthey company) catalyst. Although the above catalysts have some improvement in stability and resistance to poisoning over commercial platinum carbon. However, the quality activity, stability and anti-poisoning ability are still not satisfactory, and further improvement of the performance is required.

Disclosure of Invention

The invention aims to overcome the defects and shortcomings of the prior art and provide a platinum-based nanoparticle-coated tin dioxide-covered carbon nanotube for a fuel cell and a preparation method thereof, wherein the carbon nanotube has the advantages of controllable particle size, controllable surface and interface, high dispersion and activity, strong poisoning resistance, high stability and low cost.

The purpose of the invention is realized by the following technical scheme:

the carbon nanotube with two-layer loading is characterized in that the carbon nanotube is a multi-wall carbon nanotube, a layer of tin dioxide is loaded on the carbon nanotube, and a layer of platinum-based metal is loaded on the tin dioxide layer.

According to the invention, the tin dioxide is tin dioxide nanoparticles. The particle size is preferably between 1.0 and 10.0nm, and more preferably between 2.0 and 6.0 nm.

According to the invention, the platinum-based metal is present in the form of nanoparticles. The particle size is preferably between 1.0 and 10.0nm, and more preferably between 2.0 and 4.0 nm. The platinum-based metal nanoparticles are connected together to form a platinum-based metal nanoparticle network structure. According to the invention, the platinum-based metal is Pt or a platinum-based alloy, the platinum-based alloy is an alloy of Pt with one or more other metals, and the other metals may be one or more of Rh, Ru, Ir, Cu, Ni. The platinum-based metal can also be a core-shell structure, the inner core is platinum-based alloy, and the shell is platinum or an alloy formed by platinum and other metals which are difficult to dissolve in acid.

In yet another preferred embodiment of the present invention, the platinum-based metal may be Pt, a Pt-Rh alloy, a Pt-Ru alloy, a Pt-Cu alloy, a Pt-Ru-Rh-Ni alloy, Pt-Cu @ Pt (with the core being a Pt-Cu alloy and the shell being platinum).

The invention also provides a preparation method of the carbon nano tube with two-layer load, which comprises the following steps:

(1) dispersing the multi-walled carbon nano-tubes in concentrated nitric acid, and reacting to obtain functionalized (hydroxylated and carboxylated) multi-walled carbon nano-tubes;

(2) mixing tin dichloride, water, urea and the functionalized multi-walled carbon nano-tubes obtained in the step (1), and reacting to obtain multi-walled carbon nano-tubes covered by tin dioxide nano-particles;

(3) mixing a corresponding platinum-based metal precursor, the multi-walled carbon nano-tube covered by the tin dioxide nano-particles obtained in the step (2) and a solvent to obtain a mixture;

(4) and (a) mixing formic acid with the mixture obtained in the step (3) and reacting to obtain the carbon nano tube covered by the platinum-based metal-coated tin dioxide. Or (b) adjusting the mixture obtained in the step (3) to be alkaline by using a mixed solution of sodium hydroxide and alcohol, and heating and refluxing to obtain the platinum-based metal-coated tin dioxide-covered carbon nano tube.

According to the invention, in the step (1), the multi-walled carbon nanotubes are subjected to reflux reaction in concentrated nitric acid, wherein the reflux temperature is, for example, 120-200 ℃, preferably 140-180 ℃.

According to the present invention, in the step (2), the temperature of the reaction is preferably 60 to 100 ℃, more preferably 90 to 100 ℃, for example, 95 ℃. The reaction time is preferably 8 to 16 hours. Preferably, tin dichloride, water, urea and the functionalized multi-walled carbon nanotubes obtained in the step (1) are mixed and ultrasonically treated, and then reflux is carried out for reaction, wherein the reflux temperature is 95 ℃ for example, and the reflux time is 12 hours for example. After the reaction, cooling and filtering are carried out.

According to the invention, in the step (3), the platinum-based metal precursor is a platinum-based metal salt, such as chloride, sulfate, nitrate, etc., and in the case of Pt, the precursor may be H₂PtCl₆·6H₂O; taking Pt-Cu alloy as an example, the precursor can be H₂PtCl₆·6H₂O and CuSO₄·5H₂And O. The solvent may be ethylene glycol, water, etc.

According to the invention, in the step (3), the molar ratio of the platinum-based metal precursor is regulated according to the required proportion and loading capacity.

According to the present invention, in the step (4) (a), the reaction is performed in a solvent, which may be water, methanol, ethanol, or the like. The reaction temperature is preferably 60 to 130 ℃, preferably 90 to 120 ℃. The reaction was carried out under a nitrogen atmosphere. Preferably, the mixture obtained in the step (3) is heated to 90 ℃, a mixed solution of formic acid and ethylene glycol is dripped, and the mixture is stirred and refluxed for a period of time in a nitrogen atmosphere to obtain the carbon nanotube covered by the platinum-based metal-coated tin dioxide.

According to the present invention, in the step (4) (b), the alcohol is ethylene glycol, glycerol, or the like. The heating temperature is above 150 ℃, preferably 160-250 ℃, and the heating can be oil bath heating or microwave heating. The heating reflux was performed in a nitrogen atmosphere. For example, the mixture obtained in step (3) is made alkaline with a mixed solution of sodium hydroxide and ethylene glycol, and the mixture is refluxed at 160 ℃ or higher in a nitrogen atmosphere to obtain the platinum-based metal-coated tin dioxide-covered carbon nanotube.

According to the invention, in the step (4), the mixture obtained in the step (3) is heated under stirring and nitrogen protection, and then naturally cooled to room temperature.

According to the invention, in the step (4), the mixture naturally cooled to room temperature is filtered, washed and dried to obtain the catalyst. Preferably with water. Preferably, drying under vacuum, followed by cooling and grinding, gives the catalyst.

A further preferred preparation process according to the invention is as follows:

a method for preparing carbon nanotubes with two-layer loading, comprising:

(1) mixing the multi-walled carbon nano-tube with concentrated nitric acid, and refluxing to obtain a functionalized (hydroxylated and carboxylated) multi-walled carbon nano-tube;

(2) mixing tin dichloride, water, urea and the functionalized multi-walled carbon nano-tube obtained in the step (1) and performing ultrasonic treatment, then refluxing and stirring at 95 ℃ for 12 hours, cooling and filtering to obtain the multi-walled carbon nano-tube covered by tin dioxide nano-particles;

(3) mixing a corresponding platinum-based metal precursor, the multi-walled carbon nanotube covered by the tin dioxide nanoparticles obtained in the step (2) and ethylene glycol, and performing ultrasonic treatment to obtain a mixture, wherein the molar ratio and the loading capacity of the platinum-based metal precursor are regulated and controlled according to a required ratio;

(4) under the protection of nitrogen, mixing the mixture obtained in the step (3) with a mixed solution of formic acid and ethylene glycol, heating and refluxing for more than 10 hours, and controlling the temperature to be between 90 and 100 ℃; and then cooling, filtering, washing and drying to obtain the carbon nano tube covered by the platinum-based nano particle coated tin dioxide.

The invention further provides the application of the carbon nano tube with two-layer load, which is used for a fuel cell.

According to the invention, the tin dioxide layer and the platinum-based nanoparticle layer are loaded on the carbon nano tube from inside to outside, and in the platinum-based nanoparticle layer, the platinum-based metal nanoparticles are connected into a network structure, so that on one hand, the quality catalytic activity of the active component platinum and the catalytic stability of platinum are improved through the interface between the platinum-based metal nanoparticles, and on the other hand, the catalytic stability and the carbon monoxide poisoning resistance of the active component platinum are improved through the interface between the tin dioxide nanoparticles and the platinum-based nanoparticles.

Compared with the prior art, the invention at least has the following advantages and beneficial effects:

(1) the invention provides a catalyst of a platinum-based nanoparticle-coated tin dioxide-covered carbon nanotube, which can improve the catalytic activity and prolong the service life of platinum; meanwhile, the catalytic life and the anti-poisoning capability of the platinum are synergistically improved through the contact surface between the platinum-based nanoparticles and the tin dioxide nanoparticles. The peak current density of the catalyst for catalytic oxidation of methanol is 6.2 times that of a high-performance Pt/C catalyst of Johnson Matthey company. The oxygen reduction activity at 0.9V hydrogen target potential is 9.6 times that of the commercial Pt/C catalyst

(2) The high-activity catalyst with the active component granularity of 2.0-4.0 nm can be prepared by using a formic acid low-temperature reduction or heating alcohol reduction method, the granularity distribution of the active component is extremely uniform, and the utilization rate of noble metal is effectively improved.

(3) The synthesized platinum-based nanoparticles coat the carbon nanotube covered by the tin dioxide, the platinum-based nanoparticles are in a one-dimensional porous platinum-based nano network structure, and the platinum-based nanoparticles coat the surface of the tin dioxide nanoparticles, so that the catalytic life of platinum and the carbon monoxide poisoning resistance are effectively improved.

(4) The catalyst is prepared by adopting a formic acid reduction method or a heating alcohol reduction method, the process is simple, the environment is friendly, the recovery rate is high, and the catalyst cost is reduced.

Drawings

FIG. 1 is a graph of MWCNTs @ SnO prepared in example 1₂An XRD spectrogram of the @ Pt catalyst, wherein MWCNTs are English abbreviation of functionalized multi-walled carbon nanotubes;

FIG. 2 is MWCNTs @ SnO prepared in example 1₂Scanning electron microscope and transmission electron microscope pictures of the synthetic process of the @ Pt catalyst. a, b are MWCNTs, c, d are MWCNTs @ SnO₂E, f is MWCNTs @ SnO₂@ Pt, inset is the respective electron diffraction pattern;

FIG. 3 is MWCNTs @ SnO prepared in example 1₂@ Pt catalyst and commercial Pt/C catalyst at 0.5mol/L H₂SO₄+0.5mol/L CH₃Cyclic voltammetry in OH solution;

FIG. 4 is MWCNTs @ SnO prepared in example 1₂@ Pt catalyst and commercial Pt/C catalyst at 0.5mol/L H₂SO₄Cyclic voltammogram of carbon monoxide in solution.

FIG. 5 is MWCNTs @ SnO prepared in example 1₂@ Pt catalyst at 0.5mol/L H₂SO₄+0.5mol/L CH₃Cyclic voltammetric stabilization profiles in OH solution

FIG. 6 shows a commercial Pt/C catalyst at 0.5mol/L H₂SO₄+0.5mol/L CH₃And (3) stabilizing the cyclic voltammetry in OH solution.

FIG. 7 is MWCNTs @ SnO prepared in example 1₂@ Pt catalyst and commercial Pt/C catalyst at 0.1mol/L HClO₄Linear scanning spectrum under the condition of oxygen saturation in the solution.

FIG. 8 is MWCNTs @ SnO prepared in example 1₂@ Pt catalyst and commercial Pt/C catalyst at 0.1mol/L HClO₄Linear scanning spectrum after 10000 times of circulation stabilization under the condition of oxygen saturation in the solution.

FIG. 9 is a commercial Pt/C catalyst at 0.1mol/L HClO₄Linear scanning atlas after 10000 times circulation stabilization under oxygen saturation condition.

Detailed Description

The present invention will be described in further detail with reference to the following examples and drawings, but the present invention is not limited thereto. Any person skilled in the art can make some changes and modifications on the basis of the technical solution of the present invention to form a new technical solution of the present invention, and still fall within the scope of the technical solution of the present invention.

Example 1: carbon nano-tube (MWCNTs @ SnO) covered by platinum-based nano-particle coated tin dioxide₂@ Pt, 86% by weight of platinum in platinum, tin dioxide and multiwall carbon nanotubes)

(1) Dispersing multi-walled carbon nanotubes (MWCNTs) in concentrated nitric acid, reacting in an oil bath at 140 ℃ for more than 10 hours, cooling, filtering, drying, and grinding to obtain functionalized multi-walled carbon nanotubes for later use;

(2) SnCl₂·2H₂And (2) stirring the functionalized multi-walled carbon nanotubes obtained in the step (1) and water at room temperature for more than 30 minutes to fully disperse the carbon nanotubes, and continuing to perform ultrasonic treatment to obtain a highly dispersed solution-like mixed solution. Followed by stirring at 90 ℃ under reflux for 10 hours in an oil bath and then cooling and filtering. And obtaining the material of the tin dioxide covered carbon nano tube.

(3) Handle H₂PtCl₆·6H₂Dispersing the multi-walled carbon nano-tubes covered by the tin dioxide obtained in the step (2) into ethylene glycol for ultrasonic treatment, introducing nitrogen to remove oxygen, introducing condensed water, and stirring for 30 minutes; h₂PtCl₆·6H₂The reduction amount of O accounts for 86% of the weight of the tin dioxide, the multi-wall carbon nano-tube and the Pt;

(4) dropwise adding the mixed solution of formic acid and ethylene glycol into the solution obtained in the step (3), stirring and refluxing for more than 10 hours at 90 ℃, and then naturally cooling to room temperature;

(5) carrying out vacuum filtration on the mixed solution obtained in the step (4), washing a filter cake with secondary distilled water, drying for 10 hours in a vacuum drying oven, cooling and grinding to obtain the carbon nano tube (MWCNTs @ SnO) covered by the platinum-based nano particles coated with the tin dioxide₂@ Pt) which is a nano-catalyst having a network porous structure.

MWCNTs @ SnO prepared in this example₂The X-ray powder diffraction patterns of the @ Pt and commercial Pt/C catalysts are shown in FIG. 1; as can be seen from the figure, the material prepared in this example has platinum in a pure phase.

MWCNTs @ SnO prepared in this example₂The scanning electron microscope and transmission electron microscope of the synthesis process of the @ Pt catalyst are shown in figure 2, wherein a) and b) are multi-walled carbon nanotubes (MWCNTs), c) and d) are multi-walled carbon nanotubes (MWCNTs @ SnO) covered by tin dioxide₂) E) and f) are carbon nano-tubes (MWCNTs @ SnO) covered by platinum-based nano-particles coated with tin dioxide₂@ Pt); as can be seen from the figure, the platinum nanoparticles in the material prepared in this example are uniformly distributed and have good crystallinity, and the platinum nanoparticles are coated on the tin dioxide to form a platinum nanoparticle network connected with each other.

Further, the MWCNTs @ SnO prepared in the example₂The catalytic performance of the @ Pt catalyst was tested and compared with that of a commercial Pt/C catalyst (20% by weight), and the catalyst in the example has better catalytic performance as can be seen by comparison, and the test results are shown in FIGS. 3-7.

FIG. 3 is MWCNTs @ SnO prepared in example 1₂@ Pt catalyst and commercial Pt/C catalyst at 0.5mol/L H₂SO₄+0.5mol/L CH₃Cyclic voltammetry in OH solution; as can be seen from the figure, the mass activity of the material prepared in this example for the catalytic oxidation of methanol is greatly improved, 6.2 times that of commercial Pt/C. While the commercial Pt/C (20%) catalytic oxidation of methanol is low because the platinum nanoparticles are present in a single isolated form, the catalyst obtained in this example has a network structure of platinum nanoparticles, and the contact surfaces between the platinum nanoparticles and the tin dioxide nanoparticles have good catalytic oxidation performance of methanol.

FIG. 4 is MWCNTs @ SnO prepared in example 1₂@ Pt catalyst and commercial Pt/C catalyst at 0.5mol/L H₂SO₄Cyclic voltammogram of carbon monoxide in solution. It can be seen from the figure that the material prepared in this example, although loaded up to 86%, had a significantly reduced peak potential for catalytic oxidation of CO, only-400 mv, compared to 0mv for the commercial platinum-carbon catalyst. This is because the platinum nanoparticles in the material synthesized in this example are uniformly distributed on the tin dioxide coated with the carbon nanotubes, the platinum nanoparticles and the tin dioxide nanoparticles form good interface contact, and the platinum nanoparticles are connected into a network structure.

FIG. 5 shows the Pt/MWCNTs catalyst prepared in example 1 at 0.5mol/L H₂SO₄+0.5mol/LCH₃And (3) stabilizing the cyclic voltammetry in OH solution. As can be seen from the figure, the stability of the material prepared in this example for the catalytic oxidation of methanol is considerably improved. After 10000 cycles, the mass activity of the catalyst for oxidizing the methanol is up to 71 percent of the initial mass activity.

Figure 6 is a graph showing that the mass activity of a commercial Pt/C catalyst after 6000 cycles to catalytically oxidize methanol was only 39% of the initial mass activity, and the rate of performance decay was much faster than the material prepared in this example.

FIG. 7 is MWCNTs @ SnO prepared in example 1₂@ Pt catalyst and commercial Pt/C catalyst at 0.1mol/L HClO₄Linear scan under oxygen saturation in solution. It can be seen from the figure that the material prepared in this example, although supported at 86% high, has a mass activity for oxygen reduction at 0.9V hydrogen target potential 9.6 times higher than that of the commercial platinum carbon catalyst.

FIG. 8 is MWCNTs @ SnO prepared in example 1₂@ Pt catalyst at 0.1mol/L HClO₄Linear scanning images after 10000 times of cyclic voltammetry under the condition of oxygen saturation in the solution. As can be seen from the figure, the half-wave potential of the material prepared in this example is not substantially changed after 10000 times of cyclic voltammetry. This is because the platinum nanoparticles in the material synthesized in this example are uniformly distributed on the tin dioxide coated with the carbon nanotubes, the platinum nanoparticles and the tin dioxide nanoparticles form good interface contact, and the platinum nanoparticles are connected into a network structure.

FIG. 9 is a commercial Pt/C catalyst at 0.1mol/L HClO₄Linear scanning images after 10000 times of cyclic voltammetry under the condition of oxygen saturation in the solution. The half-wave potential of the Pt/C catalyst is shifted negative by 20 mV.

Example 2: carbon nano tube (MWCNTs @ SnO) covered by platinum-copper core-shell structure nano particles and coated with tin dioxide₂Preparation of @ Pt-Cu @ Pt)

(1) H is to be₂PtCl₆·6H₂O、CuSO₄·5H₂And stirring the multi-walled carbon nano-tube covered by O and stannic oxide and ethylene glycol at room temperature for 30 minutes to fully disperse the multi-walled carbon nano-tube. The molar ratio of Pt to Cu in the mixed solution is 1: 3;

(2) alternately stirring and ultrasonically treating the mixed solution obtained in the step (1), and then adjusting the pH value of the mixed solution to 10 by using a sodium hydroxide glycol solution;

(3) continuing to alternately use ultrasound and stirring the mixed solution obtained in the step (2) until a solution-like dispersion liquid is formed;

(4) putting the mixed solution obtained in the step (3) into a microwave reactor, introducing nitrogen to remove oxygen, introducing condensed water, and stirring for 30 minutes;

(5) heating the solution obtained in the step (4) by microwave for more than 3 minutes (more than 160 ℃), and then naturally cooling to room temperature;

(6) carrying out vacuum filtration on the mixed solution obtained in the step (5), washing a filter cake with secondary distilled water, drying the filter cake in a vacuum drying oven at 90 ℃ for 10 hours, cooling and grinding to obtain a sample MWCNTs @ SnO₂@Pt-Cu；

(7) Placing the sample obtained in the step (6) in 0.3M nitric acid, stirring for 30 minutes, preserving for more than 2 days, and then carrying out ultrasonic treatment for more than 30 minutes;

(8) carrying out vacuum filtration on the acidic dispersion liquid obtained in the step (7), washing a filter cake with secondary distilled water, drying for 10 hours in a vacuum drying oven, cooling and grinding to obtain the carbon nano tube (MWCNTs @ SnO) covered by the platinum-copper core-shell structure nano particles coated with tin dioxide₂@Pt-Cu@Pt)。

As described above, the present invention can be preferably realized.

Claims

1. a carbon nanotube with two-layer load, it is characterized in that, described carbon nanotube is multi-wall carbon nanotube, and a deck of tin dioxide is loaded on described carbon nanotube, and in the described tin dioxide layer A layer of platinum-based metal is supported thereon, the tin dioxide is tin dioxide nanoparticles, the platinum-based metal exists in the form of nanoparticles, and the platinum-based metal nanoparticles are connected to form a network structure;

The carbon nanotubes with two-layer loading are prepared by the following method, and the method includes:

(1) Disperse multi-walled carbon nanotubes in concentrated nitric acid, and react to obtain functionalized multi-walled carbon nanotubes;

(2) mixing tin dichloride, water, urea and the functionalized multi-walled carbon nanotubes obtained in step (1), and reacting to obtain multi-walled carbon nanotubes covered by tin dioxide nanoparticles;

(3) mixing the corresponding platinum-based metal precursor, the multi-walled carbon nanotubes covered by the tin dioxide nanoparticles obtained in step (2), and a solvent to obtain a mixture;

(4) (a) mixing formic acid with the mixture obtained in step (3) and reacting to obtain platinum-based metal-coated tin dioxide-covered carbon nanotubes; or (b) mixing the mixture obtained in step (3) with sodium hydroxide The mixed solution with alcohol is adjusted to alkaline, and then heated to reflux to obtain carbon nanotubes covered with platinum-based metal and covered with tin dioxide.

2. The carbon nanotube with two layers of support according to claim 1, wherein the particle size of the tin dioxide nanoparticles is between 1.0 and 10.0 nm.

3. The carbon nanotube with two layers of support according to claim 1, wherein the particle size of the tin dioxide nanoparticles is between 2.0 and 6.0 nm.

4. The carbon nanotube with two layers of support according to claim 1, wherein the particle size of the platinum-based metal nanoparticles is between 1.0 and 10.0 nm.

5. The carbon nanotube with two layers of support according to claim 1, wherein the particle size of the platinum-based metal nanoparticles is between 2.0 and 4.0 nm.

6. The carbon nanotube with two-layer loading of claim 1, wherein the platinum-based metal is Pt or a platinum-based alloy, and the platinum-based alloy is an alloy of Pt and one or more other metals .

7 . The carbon nanotube with two layers of support according to claim 6 , wherein the other metal is one or more of Rh, Ru, Ir, Cu, and Ni. 8 .

8. The carbon nanotube with two-layer loading according to claim 1, wherein the platinum-based metal is a core-shell structure, the inner core is a platinum-based alloy, and the outer shell is platinum or platinum and other insoluble in acid Metal.

9. The carbon nanotube with two-layer loading according to claim 1, wherein the platinum-based metal is Pt, Pt-Rh alloy, Pt-Ru alloy, Pt-Cu alloy, Pt-Ru-Cu alloy, Pt-Ru-Rh-Ni alloy, Pt-Cu@Pt.

10. The preparation method of carbon nanotubes with two-layer loading according to any one of claims 1-9, comprising:

11. The preparation method according to claim 10, wherein, in the step (1), the multi-walled carbon nanotubes are subjected to reflux reaction in concentrated nitric acid, and the reflux temperature is 120-200°C.

12. The preparation method according to claim 11, wherein, in the step (1), the reflux temperature is 140-180°C.

13. The preparation method according to claim 10, wherein, in the step (2), the temperature of the reaction is 60-100°C.

14. The preparation method according to claim 13, wherein, in the step (2), the temperature of the reaction is 90-100°C.

15. The preparation method according to claim 10, wherein, in the step (4) (a), the reaction is carried out in a solvent, and the solvent is water, methanol, or ethanol.

16. The preparation method according to claim 10, wherein, in the step (4) (a), the reaction temperature is 60-130°C.

17. The preparation method according to claim 10, wherein, in the step (4)(a), the reaction is carried out under a nitrogen atmosphere.

The preparation method according to claim 10, wherein, in the step (4) (b), the alcohol is ethylene glycol and glycerol.

19. The preparation method according to claim 10, wherein, in the step (4) (b), the heating temperature is above 150°C.

20. The preparation method according to claim 10, wherein, in the step (4) (b), the heating temperature is 160-250°C.

21. The preparation method according to claim 10, wherein, in the step (4)(b), the heating and refluxing is performed in a nitrogen atmosphere.

22 . The preparation method according to claim 10 , wherein, in the step (3), the platinum-based metal precursor is a platinum-based metal salt. 23 .

23 . The preparation method according to claim 22 , wherein, in the step (3), the platinum-based metal salt is a chloride salt, a sulfate salt, or a nitrate salt. 24 .

24. The preparation method of claim 10, wherein the preparation method comprises:

(1) Mixing multi-walled carbon nanotubes with concentrated nitric acid and refluxing to obtain functionalized multi-walled carbon nanotubes;

(2) The tin dichloride, water, urea and the functionalized multi-walled carbon nanotubes obtained in step (1) were mixed and sonicated, and then cooled and filtered at 95 ° C under reflux for 12 hours to obtain tin dioxide nanoparticles covered multi-walled carbon nanotubes;

(3) mixing the corresponding platinum-based metal precursor, the multi-walled carbon nanotubes covered by the tin dioxide nanoparticles obtained in step (2), and ethylene glycol, and ultrasonicating to obtain a mixture;

(4) Under nitrogen protection, the mixture obtained in step (3) is mixed with the mixture of formic acid and ethylene glycol, heated to reflux for more than 10 hours, and the temperature is controlled between 90 and 100 degrees Celsius; then cooling, suction filtration, washing, and drying to obtain the platinum-based nanoparticle-coated tin dioxide-coated carbon nanotubes.

25. Use of carbon nanotubes with two layers of support as claimed in any one of claims 1 to 9 in a fuel cell.