CN114695904A - Preparation and application of self-supporting nitrogen-doped carbon nanotube-loaded platinum nano cluster - Google Patents

Abstract

The invention discloses preparation and application of a self-supporting nitrogen-doped carbon nanotube-loaded platinum nano cluster. The preparation method comprises the following steps: the carbon cloth is used as a precursor, and cobalt iron nitrate hexahydrate, ferric nitrate nonahydrate, ammonium fluoride and urea are used for preparing the cobalt iron nanowire. And then preparing the nitrogen-doped carbon nano tube by using the carbon cloth for growing the cobalt-iron nano wire and dicyandiamide. The application of the three-functional catalyst of the direct methanol fuel cell in catalyzing ORR and MOR reactions of the direct methanol fuel cell and the electrocatalysis performance in HER reactions can obviously enhance the adsorption efficiency of adsorbed gas and improve the stability and the conductivity, has lower overpotential and cost in the ORR, MOR and HER reactions, and can meet the requirements of commercial application.

Description

Preparation and application of self-supporting nitrogen-doped carbon nanotube-supported platinum nanoclusters

technical field

The invention belongs to the technical field of direct methanol fuel cell catalysts, in particular to a self-supporting nitrogen-doped carbon nanotube-supported platinum nano-cluster, a preparation method and its application in a direct methanol fuel cell.

Background technique

Nowadays, the world's energy is limited, and the unreasonable exploitation and waste of human beings have caused many problems such as energy crisis and environmental pollution. In order to meet the needs of modern society and alleviate ecological health problems, finding efficient, clean and sustainable energy technologies is an important issue in today's world. Research focus in the field of energy.

Oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) are the core reaction processes of important renewable energy technologies, and their applications involve fuel cells and metal-air batteries. Among fuel cells, proton exchange membrane fuel cells (PEMFCs) use perfluorosulfonic acid membrane as the electrolyte, the electrolyte is non-corrosive, the required operating temperature is low, the operating current is large, the power density is high, the weight is light, the start-up is fast, the environment is friendly, and the longevity Long and other advantages have become the focus of research. Direct methanol fuel cells (DMFCs) are the fuel cells with the highest energy except hydrogen fuel. As a power generation device that directly converts chemical energy into electrical energy, DMFCs have the advantages of high energy conversion efficiency, simple operation, fast start-up, and green and pollution-free. However, its performance is also affected by many factors. First, methanol can penetrate from the anode to the cathode catalyst layer through the electrolyte membrane, which severely covers the Pt surface and reduces the ORR active sites. And a "mixed potential" is generated at the cathode, which reduces the conversion efficiency of the fuel and the output power of the battery. Second, the activation polarization loss caused by the slow electrochemical reaction kinetics reduces the cell voltage. Meanwhile, methanol and its oxidized intermediates (CO) also poison commercial platinum-carbon catalysts (Pt/C), affecting the catalytic activity of Pt for ORR. Finally, the rare and limited content of platinum on earth and the high cost of commercial Pt/C catalysts are all factors that affect the commercialization of DMFCs. Therefore, finding and designing high-efficiency, inexpensive, and novel catalysts with high platinum utilization, high catalytic activity, stability, and resistance to CO poisoning is the primary task for the commercialization of DMFCs.

To find alternatives to Pt-based catalysts, 3D transition metals (TMs) have also been widely used in the field of DMFCs catalysts, such as Fe, Co, and Ni. When metal and its alloy nanoparticles are used as catalysts, they not only possess non-precious metal active sites, but also alloying enriches their individual metal functions, creating new possibilities for enhancing electrocatalytic activity. However, the agglomeration of nanoparticles reduces the active sites and reduces the activity and stability of the catalyst. Therefore, it is particularly important to confine alloy nanoparticles in a limited space and maintain their excellent electrochemical activity. For example, nitrogen-doped carbon nanotubes have the advantages of unique hollow structure, excellent electronic conductivity, high mechanical strength, high specific surface area and good chemical stability, and are considered as an ideal electrocatalyst carrier material. In previous studies, the catalyst was usually present in powder form, and the electrodes were fabricated using a polymer binder, such as Nafion. The use of binders leads to an increase in charge-transfer resistance and a decrease in the active surface area of the catalyst, which in turn affects the performance and future development of DMFCs. Therefore, growing active materials on carbon cloth can effectively prevent the agglomeration of active materials, make full use of active sites, and improve the stability of catalysts. Magnetron sputtering (PVD) is a plasma-based high-speed physical vapor deposition technique that bombards a target with ionized particles to slough off atoms on the surface of the target, which are then deposited on a substrate to form a thin film. PVD is a green, low-cost nanomaterial preparation technology. Therefore, the plasma sputtering deposition is used to uniformly load platinum on the surface of nitrogen-doped carbon nanotubes without destroying the structure of nitrogen-doped carbon nanotubes, thereby improving the electrocatalytic performance and the utilization rate of Pt. Supported platinum nanoclusters are the key to efficient ORR/MOR bifunctional catalysts for direct methanol fuel cells.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present invention realizes the uniform loading of platinum nanoclusters by supporting platinum nanoclusters on self-supporting nitrogen-doped carbon nanotubes, and has the advantages of high platinum utilization rate, strong electron conductivity and high catalytic activity. , which can be used as electrode materials for direct methanol fuel cells.

In order to realize the above-mentioned purpose of the invention, the technical scheme adopted in the present invention is:

A self-supporting nitrogen-doped carbon nanotube-loaded platinum nano-cluster, wherein the structural unit of the carbon nanotube is carbon cloth, the nitrogen-doped carbon nanotube (NCNTs) is a conductive network, and the platinum nano-cluster is The platinum nanoclusters are supported on nitrogen-doped carbon nanotubes by means of plasma sputtering deposition.

A method for preparing a self-supporting nitrogen-doped carbon nanotube-supported platinum nanocluster as described above, specifically comprising the following steps:

1. Preparation of cobalt iron nanowires: The carbon cloth was sonicated in a 10 wt.% potassium permanganate solution for 10-30 min, and continued to be sonicated in deionized water and ethanol until the solution was completely clear. After taking out the carbon cloth, dry it in a vacuum oven at 40-60°C for 6-24h. Add cobalt, iron transition metal salt, ammonium fluoride and urea into deionized water with stirring in sequence, and continue stirring at room temperature for 10-30 min to form a uniform mixed solution. Quickly transfer to a hydrothermal reactor, soak the cleaned carbon cloth in it, and react at 100-140 ℃ for 6-12 hours. Take out the carbon cloth, rinse it with deionized water and ethanol, and dry it in a vacuum oven at 40-60 °C for 6-24 hours to obtain cobalt-iron nanowires;

2. Preparation of nitrogen-doped carbon nanotubes: carbon cloth and dicyandiamide for growing cobalt-iron nanowires were placed in two different porcelain boats in a tube furnace. In a gas atmosphere, the temperature is heated to 400-600 °C at a certain heating rate and annealed for 2-4 hours, and then heated to 800-950 °C for 2-4 hours to obtain nitrogen-doped carbon nanotubes;

3. Preparation of self-supporting nitrogen-doped carbon nanotube-supported platinum nanoclusters: The carbon for growing nitrogen-doped carbon nanotubes is arranged on the substrate of a magnetron sputtering instrument, and under suitable working parameters, plasma sputtering The platinum nanoclusters are supported on the surface of the free-standing nitrogen-doped carbon nanotubes by radiation deposition to obtain the free-standing nitrogen-doped carbon nanotube-supported platinum nanoclusters.

Preferably, in step 1, the mass ratio of the cobalt transition metal salt, iron transition metal salt, ammonium fluoride and urea is 200-400:150-350:100-250:500-700, and the size of the carbon cloth is: 2 -4cm×3-5cm, the volume of deionized water: 30-50mL.

Preferably, in step 1, the cobalt transition metal salt adopts Co(NO ₃ ) ₂ .6H ₂ O, CoCl ₂ .6H ₂ O, Co(CH ₃ COO) ₂ , CoCl ₂ , CoSO ₄ .7H ₂ O, One of CoSO ₄ ·H ₂ O; the iron transition metal salt adopts Fe(NO ₃ ) ₃ ·9H ₂ O, FeCl ₃ ·6H ₂ O, Fe(OH)(CH ₃ COO) ₂ , FeSO ₄ a kind of.

Preferably, in step 2, the quality of the dicyandiamide is 1000-3000 mg.

Preferably, in step 2, the inert gas atmosphere is one of N ₂ , Ar and He.

Preferably, in step 2, the heating rate is 3-5°C/min.

Preferably, in step 3, the sputtering gas pressure, power, and duration of the plasma sputter deposition are respectively 2-8Pa, 70-150W, and 1-10min.

An application of the above-mentioned self-supporting nitrogen-doped carbon nanotube-supported platinum nanoclusters as an electrode material for direct methanol fuel cells, and the self-supporting nitrogen-doped carbon nanotube-supported platinum nanoclusters are used as direct methanol fuel The catalyst of the battery can significantly enhance the adsorption efficiency of adsorbed gas, improve the stability and conductivity, and has high catalytic activity in ORR and MOR reactions.

Compared with the prior art, the preparation and application of the self-supporting nitrogen-doped carbon nanotube-supported platinum nanoclusters of the present invention have the following beneficial effects:

(1) Encapsulating transition metals in carbon materials (graphene, carbon nanotubes, etc.), the outer carbon material not only effectively prevents the dissolution and agglomeration of metals in acidic media, but also maintains its initial structure and activity, resulting in The catalyst will have good electrocatalytic activity and long-term stability. Among them, carbon nanotubes (CNTs) have extremely high specific surface area and volume ratio, excellent stability, as well as regular pore structure and electrical conductivity paths. Moreover, at high temperature, carbon materials have high solubility in transition metals, fast diffusion, and strong adhesion between these metals and the prepared carbon nanotubes. Heteroatom-doped carbon-coated transition metal compound catalysts have achieved high catalytic activity and stability and have been widely used in DMFCs.

(2) Self-supporting nitrogen-doped carbon nanotubes can not only connect with each other to form an excellent electrical conductivity network, improve the weakness of insufficient electrical conductivity of metal oxides, but also help to expose more electrochemically active substances on the surface of carbon nanotubes, which can be self-contained. The supported nitrogen-doped carbon nanotube-supported platinum nanoclusters have a high specific surface area and a stable three-dimensional network structure, and their special three-dimensional structure provides a good template for the efficient deposition of platinum nanoclusters, which greatly expands such materials. Applications. The platinum nanoclusters are uniformly loaded on the surface of self-supporting nitrogen-doped carbon nanotubes, which can effectively solve the serious agglomeration problem of platinum metal structural units in the process of traditional preparation technology, thereby improving their electrochemical performance.

(3) Due to the large specific surface area, excellent flexibility, abundant active sites, and good synergy between the electrocatalyst and the conductive substrate, the orderly arrangement of CNTs on the carbon cloth can Maximize catalyst performance.

(4) Electrode materials prepared by plasma sputtering deposition technology to build nanostructures on the substrate is controllable. Compared with electrocatalysts prepared by traditional chemical methods, PVD is a green and low-cost nanomaterial preparation technology. It has the advantages of simple structure, fast preparation process, no by-products during sputtering, uniform distribution of sputtered metal and high purity density, strong adhesion between metal and substrate, precise control of metal loading, and sputtering metal activity. Unique advantages such as high ingredient loading and good corrosion resistance. The utilization of Pt is maximized while minimizing the precious metal Pt loading.

Description of drawings

1 is the microscopic morphology of the self-supporting nitrogen-doped carbon nanotube-supported platinum nanoclusters prepared in Example 1 under a scanning electron microscope (SEM);

Figure 2 is a linear scan of the oxygen reduction reaction (ORR) of the free-standing nitrogen-doped carbon nanotube-supported platinum nanoclusters prepared in Example 1, Comparative Example 1 and commercial 20 wt.% Pt/C catalysts under alkaline conditions Voltammetry chart (LSV);

Figure 3 is the linear sweep volts of the oxygen reduction reaction (ORR) of the free-standing nitrogen-doped carbon nanotube-supported platinum nanoclusters prepared in Example 1, Comparative Example 1 and commercial 20 wt.% Pt/C catalysts under acidic conditions Safety test chart (LSV);

Figure 4 shows the oxygen reduction reaction (ORR) of the self-supporting nitrogen-doped carbon nanotube-supported platinum nanoclusters prepared in Example 1, Example 2, Example 3, Example 4 and Example 5 under alkaline conditions The linear sweep voltammetry chart (LSV) of ;

5 is the oxygen reduction reaction (ORR) of the free-standing nitrogen-doped carbon nanotube-supported platinum nanoclusters prepared in Example 1, Example 2, Example 3, Example 4 and Example 5 under acidic conditions. Linear sweep voltammetry (LSV);

6 is a linear sweep voltammetry (LSV) test chart of methanol oxidation reaction (MOR) of the self-supporting nitrogen-doped carbon nanotube-supported platinum nanoclusters prepared in Example 1 and a commercial 20wt.% Pt/C catalyst;

Detailed ways

In order to make the purpose, technical solutions and beneficial technical effects of the present invention clearer, the preparation and application of the self-supporting nitrogen-doped carbon nanotube-supported platinum nanoclusters of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments described in this specification are only for explaining the present invention, not for limiting the present invention.

Example 1: Preparation of a self-supporting nitrogen-doped carbon nanotube-supported platinum nanocluster, which specifically includes the following steps:

(1) Synthesis of cobalt iron nanowires:

Take a carbon cloth with a size of 3 cm × 4 cm and sonicate it in a 10 wt.% potassium permanganate solution for 10 min, continue to sonicate in deionized water and ethanol until the solution is completely clear, and then place it in a vacuum oven at 60 °C for 12 h. 388 mg of cobalt nitrate hexahydrate, 270 mg of ferric nitrate nonahydrate, 186 mg of ammonium fluoride and 600 mg of urea were added to 40 ml of deionized water while stirring, and continued stirring at room temperature for 10 min to form a uniform mixed solution. Transfer to a hydrothermal reactor, immerse the carbon cloth in it, and let it stand at 120 °C for 6 h. Then, the carbon cloth was taken out, washed with deionized water and ethanol in turn, and finally dried in a vacuum oven at 40 °C for 12 h. The resulting sample was denoted as CoFe NWs/CFC.

(2) Synthesis of nitrogen-doped carbon nanotubes:

The carbon cloth for growing cobalt-iron nanowires and 1.5 g of dicyandiamide were placed in two different porcelain boats in a tube furnace, and the dicyandiamide was located upstream of the tube furnace, and annealed at 400 °C in an Ar gas atmosphere 2h, the temperature was raised to 800°C and annealed for 2h, and the heating rate was 5°C/min. The obtained sample was denoted as CoFe@NCNT/CFC.

(3) Synthesis of nitrogen-doped carbon nanotube-supported platinum nanoclusters:

The carbon cloth on which nitrogen-doped carbon nanotubes were grown was fixed on the substrate of a magnetron sputtering apparatus, and the platinum nanoclusters were loaded on the surface by plasma sputtering deposition at 5Pa and 110W for 7min. The obtained sample was denoted as Pt-CoFe@NCNT/CFC-7min.

The morphology of the Pt-CoFe@NCNT/CFC-7min material obtained in Example 1 was analyzed by scanning electron microscopy (SEM). The results are shown in Figure 1. The surface of NCNTs is rough and opaque, and the platinum nanoclusters are uniformly loaded. on the surface of CoFe@NCNT/CFC.

ORR and MOR catalytic performance evaluation:

All electrochemical tests were performed using an electrochemical workstation model CHI 760E equipped with a PINE rotating disk electrode test system, and the electrochemical tests were performed at room temperature.

Preparation of working electrode: Before using rotating disk electrode (RDE), namely glassy carbon electrode (GCE, d = 0.4 cm), first use Al ₂ O ₃ powder to polish the electrode surface on a polishing cloth to a mirror surface, and then rinse with distilled water Several times, and ultrasonically oscillated for 10 s, and dried at room temperature for later use. A sample with a diameter of 4 mm was cut from the prepared sample with a hole punch, and 5-10 μL of Nafion solution (5 wt.%) was taken to paste the carbon cloth on the surface of the GCE, and dried naturally to obtain the working electrode used for the test. Comparative examples were prepared and tested using the same electrode preparation method. The loading amount of platinum in the catalyst on the electrode surface was about 0.7 mg cm ^-2 . As a control experiment, 14 mg of commercial 20 wt.% Pt/C, 261 μL isopropanol, 652 μL deionized water, and 87 μL Nafion (5 wt. %) were weighed and mixed. The mixture was sonicated for 1 h to obtain a homogeneous slurry. Finally, the slurry prepared above was drop-coated on the surface of a 1cm×4cm carbon cloth and dried naturally to obtain a working electrode for testing.

Electrochemical performance test: A standard three-electrode electrochemical test system was used in the test process, wherein the counter electrode was a Pt sheet, the reference electrode was a saturated calomel electrode (SCE) and the working electrode prepared above.

The ORR catalytic activity of the sample of Example 1 and the commercial 20 wt.% Pt/C catalyst in O ₂ saturated 0.1 M KOH and 0.5 MH ₂ SO ₄ electrolytes were tested using rotating disk electrode (RDE), respectively. Figures 2 and 3 are the LSV curves of the ORR catalytic performance of the sample of Example 1, respectively. As shown in Fig. 2, in 0.1 M KOH, the ORR electrocatalytic activity onset potential and half-wave potential of the sample of Example 1 were 0.97 and 0.807 V vs. RHE, respectively; as shown in Fig. 3, in 0.5 MH ₂ SO ₄ The onset potential and half-wave potential of the sample of Example 1 were 0.852 and 0.723 V vs. RHE, respectively, and its ORR electrocatalytic activity was very close to that of the commercial 20 wt.% Pt/C catalyst (in 0.1 M KOH) tested under the same conditions. , the onset potential and half-wave potential were 1.01 and 0.743 V vs. RHE, respectively; in 0.5MH ₂ SO ₄ , the onset potential and half-wave potential were 0.837 and 0.69 V vs. RHE, respectively). In alkaline electrolyte, the half-wave potential of the sample of Example 1 is more positive than Pt/C. In the acidic electrolyte, not only the half-wave potential of the sample of Example 1 is more positive than that of Pt/C, but the onset potential is also higher than that of Pt/C. This indicates that the self-supporting Pt-CoFe@NCNT/CFC-7min electrode has fast reaction kinetics and excellent activity during ORR electrocatalysis.

The MOR catalytic activity of the sample of Example 1 and the commercial 20 wt.% Pt/C catalyst in N ₂ saturated 0.5MH ₂ SO ₄ and 0.5M CH ₃ OH mixed electrolyte was tested using a rotating disk electrode (RDE). Figure 6 is the LSV curve of the MOR catalytic performance of the sample of Example 1. When scanning in the forward direction, the maximum current density value of the sample of Example 1 was 15.5 mA mg ^-1 _Pt , while the maximum current density value of the commercial 20 wt.% Pt/C catalyst was 4.338 mA mg ^-1 _Pt . When scanning in reverse, the maximum current density values for the sample of Example 1 and the commercial 20 wt.% Pt/C catalyst were 7.774 mA mg ^-1 _Pt and 3.768 mA mg ^-1 _Pt , respectively. Under the same test conditions, the peak current density of the sample in Example 1 is the largest, indicating that the self-supporting Pt-CoFe@NCNT/CFC-7min electrode has excellent MOR electrocatalytic activity.

Comparative Example 1: Preparation of a self-supporting nitrogen-doped carbon nanotube, which specifically includes the following steps:

(1) Synthesis of cobalt iron nanowires:

Take a carbon cloth with a size of 3 cm × 4 cm and sonicate it in a 10 wt.% potassium permanganate solution for 10 min, continue to sonicate in deionized water and ethanol until the solution is completely clear, and then place it in a vacuum oven at 60 °C for 12 h. 388 mg of cobalt nitrate hexahydrate, 270 mg of ferric nitrate nonahydrate, 186 mg of ammonium fluoride and 600 mg of urea were added to 40 ml of deionized water while stirring, and continued stirring at room temperature for 10 min to form a uniform mixed solution. Transfer to a hydrothermal reactor, immerse the carbon cloth in it, and let it stand at 120 °C for 6 h. Then, the carbon cloth was taken out, washed with deionized water and ethanol in turn, and finally dried in a vacuum oven at 40 °C for 12 h. The resulting sample was denoted as CoFe NWs/CFC.

(2) Synthesis of nitrogen-doped carbon nanotubes:

The carbon cloth for growing cobalt-iron nanowires and 1.5 g of dicyandiamide were placed in two different porcelain boats in a tube furnace, and the dicyandiamide was located upstream of the tube furnace, and annealed at 400 °C in an Ar gas atmosphere 2h, the temperature was raised to 800°C and annealed for 2h, and the heating rate was 5°C/min. The obtained sample was denoted as CoFe@NCNT/CFC.

The ORR catalytic activity of the sample of Comparative Example ₁ in _O2 -saturated 0.1 M KOH and _0.5 MH2SO4 electrolytes was tested using a rotating disk electrode (RDE). As shown in Figure 2, in 0.1M KOH, the onset potential and half-wave potential of the sample of Comparative Example 1 were 0.92 and 0.783 V vs. RHE, respectively; as shown in Figure ₃ , in _0.5MH2SO4 , the Comparative Example The onset potential and half-wave potential of the 1 sample were 0.791 and 0.682 V vs. RHE, respectively, and its ORR electrocatalytic activity was far worse than that of the Pt-CoFe@NCNT/CFC-7min sample tested under the same conditions.

Example 2: Preparation of a self-supporting nitrogen-doped carbon nanotube-supported platinum nanocluster, which specifically includes the following steps:

(1) Synthesis of cobalt iron nanowires:

Take a carbon cloth with a size of 3 cm × 4 cm and sonicate it in a 10 wt.% potassium permanganate solution for 10 min, continue to sonicate in deionized water and ethanol until the solution is completely clear, and then place it in a vacuum oven at 60 °C for 12 h. 388 mg of cobalt nitrate hexahydrate, 270 mg of ferric nitrate nonahydrate, 186 mg of ammonium fluoride and 600 mg of urea were added to 40 ml of deionized water while stirring, and continued stirring at room temperature for 10 min to form a uniform mixed solution. Transfer to a hydrothermal reactor, immerse the carbon cloth in it, and let it stand at 120 °C for 6 h. Then, the carbon cloth was taken out, washed with deionized water and ethanol in turn, and finally dried in a vacuum oven at 40 °C for 12 h. The resulting sample was denoted as CoFe NWs/CFC.

(2) Synthesis of nitrogen-doped carbon nanotubes:

The carbon cloth for growing cobalt-iron nanowires and 1.5 g of dicyandiamide were placed in two different porcelain boats in a tube furnace, and the dicyandiamide was located upstream of the tube furnace, and annealed at 400 °C in an Ar gas atmosphere 2h, the temperature was raised to 800°C and annealed for 2h, and the heating rate was 5°C/min. The obtained sample was denoted as CoFe@NCNT/CFC.

(3) Synthesis of nitrogen-doped carbon nanotube-supported platinum nanoclusters:

The carbon cloth for growing nitrogen-doped carbon nanotubes was fixed on the substrate of a magnetron sputtering apparatus, and the platinum nanoclusters were loaded on the surface by plasma sputtering deposition at 5Pa and 110W for 1 min. The obtained sample was denoted as Pt-CoFe@NCNT/CFC-1min.

The ORR catalytic activity of the sample of Example 2 in O ₂ saturated 0.1 M KOH and 0.5 MH ₂ SO ₄ electrolytes was tested using a rotating disk electrode (RDE). As shown in Figure 4, in 0.1M KOH, the onset potential and half-wave potential of the sample of Example 2 were 0.922 and 0.782V vs. RHE, respectively; as shown in Figure ₅ , in 0.5MH2SO4, Example ₂ The onset potential and half-wave potential of the 2 samples were 0.787 and 0.615 V vs. RHE, respectively. The electrocatalytic activity of its ORR is far worse than that of the Example 1 sample tested under the same conditions.

Example 3: Preparation of a self-supporting nitrogen-doped carbon nanotube-supported platinum nanocluster, which specifically includes the following steps:

(1) Synthesis of cobalt iron nanowires:

Take a carbon cloth with a size of 3 cm × 4 cm and sonicate it in a 10 wt.% potassium permanganate solution for 10 min, continue to sonicate in deionized water and ethanol until the solution is completely clear, and then place it in a vacuum oven at 60 °C for 12 h. 388 mg of cobalt nitrate hexahydrate, 270 mg of ferric nitrate nonahydrate, 186 mg of ammonium fluoride and 600 mg of urea were added to 40 ml of deionized water while stirring, and continued stirring at room temperature for 10 min to form a uniform mixed solution. Transfer to a hydrothermal reactor, immerse the carbon cloth in it, and let it stand at 120 °C for 6 h. Then, the carbon cloth was taken out, washed with deionized water and ethanol in turn, and finally dried in a vacuum oven at 40 °C for 12 h. The resulting sample was denoted as CoFe NWs/CFC.

(2) Synthesis of nitrogen-doped carbon nanotubes:

The carbon cloth for growing cobalt-iron nanowires and 1.5 g of dicyandiamide were placed in two different porcelain boats in a tube furnace, and the dicyandiamide was located upstream of the tube furnace, and annealed at 400 °C in an Ar gas atmosphere 2h, the temperature was raised to 800°C and annealed for 2h, and the heating rate was 5°C/min. The obtained sample was denoted as CoFe@NCNT/CFC.

(3) Synthesis of nitrogen-doped carbon nanotube-supported platinum nanoclusters:

The carbon cloth on which nitrogen-doped carbon nanotubes were grown was fixed on the substrate of a magnetron sputtering apparatus, and the platinum nanoclusters were loaded on the surface by plasma sputtering deposition at 5Pa and 110W for 3min. The obtained sample was denoted as Pt-CoFe@NCNT/CFC-3min.

The ORR catalytic activity of the sample of Example 3 in O ₂ saturated 0.1 M KOH and 0.5 MH ₂ SO ₄ electrolytes was tested using a rotating disk electrode (RDE). As shown in Figure 4, in 0.1M KOH, the onset potential and half-wave potential of the sample of Example 3 were 0.913 and 0.773V vs. RHE, respectively; as shown in Figure ₅ , in 0.5MH2SO4, Example ₃ The onset potential and half-wave potential of the 3 samples were 0.79 and 0.636 V vs. RHE, respectively, and the electrocatalytic activity of its ORR was far worse than that of the sample of Example 1 tested under the same conditions.

Example 4: Preparation of a self-supporting nitrogen-doped carbon nanotube-supported platinum nanocluster, which specifically includes the following steps:

(1) Synthesis of cobalt iron nanowires:

Take a carbon cloth with a size of 3 cm × 4 cm and sonicate it in a 10 wt.% potassium permanganate solution for 10 min, continue to sonicate in deionized water and ethanol until the solution is completely clear, and then place it in a vacuum oven at 60 °C for 12 h. 388 mg of cobalt nitrate hexahydrate, 270 mg of ferric nitrate nonahydrate, 186 mg of ammonium fluoride and 600 mg of urea were added to 40 ml of deionized water while stirring, and continued stirring at room temperature for 10 min to form a uniform mixed solution. Transfer to a hydrothermal reactor, immerse the carbon cloth in it, and let it stand at 120 °C for 6 h. Then, the carbon cloth was taken out, washed with deionized water and ethanol successively, and finally dried in a vacuum oven at 40 °C for 12 h. The obtained sample was denoted as CoFe NWs/CFC.

(2) Synthesis of nitrogen-doped carbon nanotubes:

The carbon cloth for growing cobalt-iron nanowires and 1.5 g of dicyandiamide were placed in two different porcelain boats in a tube furnace, and the dicyandiamide was located upstream of the tube furnace, and annealed at 400 °C in an Ar gas atmosphere 2h, the temperature was raised to 800°C and annealed for 2h, and the heating rate was 5°C/min. The obtained sample was denoted as CoFe@NCNT/CFC.

(3) Synthesis of nitrogen-doped carbon nanotube-supported platinum nanoclusters:

The carbon cloth for growing nitrogen-doped carbon nanotubes was fixed on the substrate of the magnetron sputtering apparatus, and the platinum nanoclusters were loaded on the surface by plasma sputtering deposition at 5Pa and 110W for 5min. The obtained sample was denoted as Pt-CoFe@NCNT/CFC-5min.

The ORR catalytic activity of the sample of Example 4 in O ₂ saturated 0.1 M KOH and 0.5 MH ₂ SO ₄ electrolytes was tested using a rotating disk electrode (RDE). As shown in Figure 4, in 0.1M KOH, the onset potential and half-wave potential of Example 4 samples were 0.932 and 0.771V vs. RHE, respectively; as shown in Figure ₅ , in 0.5MH2SO4, Example ₄ The onset potential and half-wave potential of sample 4 were 0.816 and 0.634 V vs. RHE, respectively, and the electrocatalytic activity of its ORR was far worse than that of the sample of Example 1 tested under the same conditions.

Example 5: Preparation of a self-supporting nitrogen-doped carbon nanotube-supported platinum nanocluster, which specifically includes the following steps:

(1) Synthesis of cobalt iron nanowires:

Take a carbon cloth with a size of 3 cm × 4 cm and sonicate it in a 10 wt.% potassium permanganate solution for 10 min, continue to sonicate in deionized water and ethanol until the solution is completely clear, and then place it in a vacuum oven at 60 °C for 12 h. 388 mg of cobalt nitrate hexahydrate, 270 mg of ferric nitrate nonahydrate, 186 mg of ammonium fluoride and 600 mg of urea were added to 40 ml of deionized water while stirring, and continued stirring at room temperature for 10 min to form a uniform mixed solution. Transfer to a hydrothermal reactor, immerse the carbon cloth in it, and let it stand at 120 °C for 6 h. Then, the carbon cloth was taken out, washed with deionized water and ethanol in turn, and finally dried in a vacuum oven at 40 °C for 12 h. The resulting sample was denoted as CoFe NWs/CFC.

(2) Synthesis of nitrogen-doped carbon nanotubes:

The carbon cloth for growing cobalt-iron nanowires and 1.5 g of dicyandiamide were placed in two different porcelain boats in a tube furnace, and the dicyandiamide was located upstream of the tube furnace, and annealed at 400 °C in an Ar gas atmosphere 2h, the temperature was raised to 800°C and annealed for 2h, and the heating rate was 5°C/min. The obtained sample was denoted as CoFe@NCNT/CFC.

(3) Synthesis of nitrogen-doped carbon nanotube-supported platinum nanoclusters:

The carbon cloth for growing nitrogen-doped carbon nanotubes was fixed on the substrate of the magnetron sputtering apparatus, and the platinum nanoclusters were loaded on the surface by plasma sputtering deposition at 5Pa and 110W for 10min. The obtained sample was denoted as Pt-CoFe@NCNT/CFC-10min.

The ORR catalytic activity of the sample of Example ₅ in _O2 -saturated 0.1 M KOH and _0.5 MH2SO4 electrolytes was tested using a rotating disk electrode (RDE). As shown in Figure 4, in 0.1M KOH, the onset potential and half-wave potential of the sample of Example 5 were 0.975 and 0.843 V vs. RHE, respectively; as shown in Figure ₅ , in 0.5MH2SO4, Example ₅ The onset potential and half-wave potential of the 5 sample are 0.827 and 0.742 V vs. RHE, respectively, and the electrocatalytic activity of its ORR is far worse than that of the Example 1 sample tested under the same conditions.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, but not 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: It is still possible to modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for 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 technical solutions of the embodiments of the present invention. range.

Claims (9)

1. a method for preparing a self-supporting nitrogen-doped carbon nanotube-loaded platinum nanocluster, characterized in that the structural unit of the carbon nanotube is carbon cloth, and the nitrogen-doped carbon nanotube (NCNTs) is In the conductive network, the platinum nanoclusters are loaded objects, and the platinum nanoclusters are supported on nitrogen-doped carbon nanotubes by means of plasma sputtering deposition. 2. The preparation method of a self-supporting nitrogen-doped carbon nanotube-supported platinum nanocluster according to claim 1, wherein the preparation method specifically comprises the following steps: 1. Preparation of cobalt iron nanowires: The carbon cloth was sonicated in a 10 wt.% potassium permanganate solution for 10-30 min, and continued to be sonicated in deionized water and ethanol until the solution was completely clear. After taking out the carbon cloth, dry it in a vacuum oven at 40-60°C for 6-24h. Add cobalt, iron transition metal salt, ammonium fluoride and urea into deionized water with stirring in sequence, and continue stirring at room temperature for 10-30 min to form a uniform mixed solution. Quickly transfer to a hydrothermal reactor, soak the cleaned carbon cloth in it, and react at 100-140 ℃ for 6-12 hours. Take out the carbon cloth, rinse it with deionized water and ethanol, and dry it in a vacuum oven at 40-60 °C for 6-24 hours to obtain cobalt-iron nanowires; 2. Preparation of nitrogen-doped carbon nanotubes: carbon cloth and dicyandiamide for growing cobalt-iron nanowires were placed in two different porcelain boats in a tube furnace. In a gas atmosphere, the temperature is raised to 400-600 °C for 2-4 hours at a certain heating rate, and then heated to 800-950 °C for 2-4 hours to obtain nitrogen-doped carbon nanotubes; 3. Preparation of self-supporting nitrogen-doped carbon nanotube-supported platinum nanoclusters: The carbon for growing nitrogen-doped carbon nanotubes is arranged on the substrate of a magnetron sputtering instrument, and under suitable working parameters, plasma sputtering The free-standing nitrogen-doped carbon nanotube-supported platinum nanoclusters are prepared by supporting platinum metal on the surface of the self-supporting nitrogen-doped carbon nanotubes by radiation deposition. 3. The method for preparing a self-supporting nitrogen-doped carbon nanotube-supported platinum nano-cluster according to claim 2, wherein the cobalt transition metal salt, iron transition metal salt, fluorinated transition metal salt described in step 1 The mass ratio of ammonium and urea is 200-400:150-350:100-250:500-700, the size of carbon cloth is: 2-4cm×3-5cm, and the volume of deionized water is: 30-50ml. 4. The preparation method of a self-supporting nitrogen-doped carbon nanotube-supported platinum nanocluster according to claim 2, wherein the cobalt transition metal salt in the step 1 adopts Co(NO ₃ ) ₂ . One of 6H ₂ O, CoCl ₂ ·6H ₂ O, Co(CH ₃ COO) ₂ , CoCl ₂ , CoSO ₄ ·7H ₂ O, CoSO ₄ ·H ₂ O; the iron transition metal salt adopts Fe(NO ₃ ) One of ₃ ·9H ₂ O, FeCl ₃ ·6H ₂ O, Fe(OH)(CH ₃ COO) ₂ , and FeSO ₄ . 5 . The method for preparing a self-supporting nitrogen-doped carbon nanotube-supported platinum nanocluster according to claim 2 , wherein the mass of the dicyandiamide in step 2 is 1000-3000 mg. 6 . 6 . The method for preparing a self-supporting nitrogen-doped carbon nanotube-supported platinum nanocluster according to claim 2 , wherein the inert gas atmosphere described in step 2 is in N ₂ , Ar, and He. 7 . a kind of. 7 . The method for preparing a self-supporting nitrogen-doped carbon nanotube-supported platinum nanocluster according to claim 2 , wherein the heating rate in step 2 is 3-5° C./min. 8 . 8 . The method for preparing a self-supporting nitrogen-doped carbon nanotube-supported platinum nanocluster according to claim 2 , wherein the gas pressure, power, and duration of the plasma sputtering deposition described in step 3 Respectively: 2-8Pa, 70-150W, 1-10min. 9. An application of the self-supporting nitrogen-doped carbon nanotube-loaded platinum nanoclusters as described above as an electrode material for direct methanol fuel cells, wherein the self-supporting nitrogen-doped carbon nanotube-loaded platinum nanoclusters As a catalyst for direct methanol fuel cells, the catalyzer can significantly enhance the adsorption efficiency of adsorbed gas, improve the stability and electrical conductivity, and has high catalytic activity in ORR and MOR reactions.

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