Nitrogen-doped carbon nanotubes coated with ruthenium nanoparticles, preparation method and use thereof

Abstract

The present invention belongs to the technical fields of fuel cells and hydrogen production by water electrolysis, and particularly relates to a nitrogen-doped carbon nanotube coated with ruthenium nanoparticles, a preparation method thereof, and uses thereof. In the present invention, porous alumina is used as a template, and nitrogen-doped carbon nanotubes with ruthenium nanoparticles coated on the tube walls are prepared by combining chemical vapor deposition and subsequent ammonia treatment, and then ruthenium@nitrogen-doped carbon nanotubes are used as highly active oxygen / hydrogen / chlorine evolution reaction trifunctional electrocatalysts. Since the ruthenium nanoparticles are coated inside the tube walls of the nitrogen-doped carbon nanotubes, direct contact with the electrolyte during the electrochemical reaction is avoided. The electrocatalytic activity of ruthenium@nitrogen-doped carbon nanotubes for the oxygen evolution reaction exceeds that of commercial iridium oxide catalysts, the electrocatalytic activity for the hydrogen evolution reaction is close to that of commercial platinum / carbon catalysts, and the electrocatalytic activity for the chlorine evolution reaction exceeds that of commercial dimensionally stable anodes, making it an excellent trifunctional electrocatalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanotube composite films, and particularly relates to a nitrogen-doped carbon nanotube coated with ruthenium nanoparticles, a preparation method thereof and uses thereof. Background Art

[0002] A composite structure composed of ruthenium and carbon nanomaterials can have high electrocatalytic activity for both oxygen evolution reaction and hydrogen evolution reaction, and thus has been widely studied for use in fields such as fuel cells and hydrogen production by water decomposition. However, the ruthenium nanoparticles obtained by existing preparation methods are often modified on the surface of carbon nanomaterials. Since the ruthenium nanoparticles are directly in contact with the electrolyte in an electrochemical reaction, they are easily corroded by the electrolyte, thereby reducing the electrocatalytic activity and stability of the composite structure composed of ruthenium and carbon nanomaterials. Summary of the Invention

[0003] One of the objectives of the present invention is to provide a preparation method of a nitrogen-doped carbon nanotube coated with ruthenium nanoparticles, wherein the ruthenium nanoparticles are coated inside the tube wall of the nitrogen-doped carbon nanotube, so as to avoid direct contact with the electrolyte in an electrochemical reaction. The results of electrochemical tests show that the obtained ruthenium@nitrogen-doped carbon nanotubes have high electrocatalytic activity for oxygen / hydrogen / chlorine evolution reactions and are excellent trifunctional electrocatalysts.

[0004] To achieve the above objective, the present invention adopts the following technical solutions: A preparation method of a nitrogen-doped carbon nanotube coated with ruthenium nanoparticles, comprising the following steps:

[0005] S1. Immerse a porous alumina template in an aqueous ruthenium salt solution with a concentration of 0.01 - 0.1 mol / L for a period of time, then take it out, dry it, and place it in a quartz tube of a tube furnace. When the temperature rises to 600 - 700 °C, introduce a mixed gas of acetylene and argon / nitrogen into the quartz tube and react for 1 - 2 h, so as to prepare carbon nanotubes inside the pore walls of the porous alumina template, and ruthenium nanoparticles are coated in the tube walls of the carbon nanotubes; wherein the mixed gas of acetylene and argon / nitrogen is a mixed gas of acetylene and argon, or a mixed gas of acetylene and nitrogen;

[0006] S2. Remove the porous alumina template, place the carbon nanotubes in a quartz tube of a tube furnace. When the temperature rises to 900 - 1100 °C, introduce a mixed gas of ammonia and argon / nitrogen into the quartz tube and react for 0.3 - 1 h, so as to prepare a nitrogen-doped carbon nanotube coated with ruthenium nanoparticles; wherein the mixed gas of ammonia and argon / nitrogen is a mixed gas of ammonia and argon, or a mixed gas of ammonia and nitrogen.

[0007] As a further improvement of the preparation method of the nitrogen-doped carbon nanotube coated with ruthenium nanoparticles:

[0008] Preferably, the pore diameter of the porous alumina template is 30 - 100 nm, and the pore wall thickness is 10 - 50 μm.

[0009] Preferably, the ruthenium salt is one of ruthenium chloride, ruthenium acetate or ruthenium sulfate.

[0010] Preferably, in step S2, the porous alumina template is removed by soaking the product of step S1 in a 2 - 4 mol / L NaOH solution.

[0011] Preferably, in the mixed gas of acetylene and argon / nitrogen in step S1, the flow rate of acetylene is 10 - 30 mL / min, and the flow rate of argon / nitrogen is 100 - 200 mL / min.

[0012] Preferably, in the mixed gas of ammonia and argon / nitrogen in step S2, the flow rate of ammonia is 20 - 40 mL / min, and the flow rate of argon / nitrogen is 10 - 30 mL / min.

[0013] The second object of the present invention is to provide a nitrogen - doped carbon nanotube coated with ruthenium nanoparticles prepared by the above - mentioned preparation method.

[0014] The third object of the present invention is to provide a use of the above - mentioned nitrogen - doped carbon nanotube coated with ruthenium nanoparticles in hydrogen evolution, oxygen evolution or chlorine evolution.

[0015] The beneficial effects of the present invention compared with the prior art are as follows:

[0016] The present invention relates to a method for preparing nitrogen - doped carbon nanotubes (Ru@nitrogen - doped carbon nanotubes) with ruthenium nanoparticles coated on the tube walls by using porous alumina as a template, combining chemical vapor deposition and subsequent ammonia treatment, and then using Ru@nitrogen - doped carbon nanotubes as highly active trifunctional electrocatalysts for oxygen / hydrogen / chlorine evolution reactions. Among them, the electrocatalytic activity of Ru@nitrogen - doped carbon nanotubes for oxygen evolution reaction exceeds that of commercial iridium oxide catalysts, the electrocatalytic activity for hydrogen evolution reaction is close to that of commercial platinum / carbon catalysts, and the electrocatalytic activity for chlorine evolution reaction exceeds that of commercial dimensionally stable anodes (DSA). BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram for preparing Ru@nitrogen - doped carbon nanotubes.

[0018] Figure 2 (a) is a scanning electron microscope photograph of Ru@nitrogen - doped carbon nanotubes; (b) is a transmission electron microscope photograph of Ru@nitrogen - doped carbon nanotubes, and (c) is a high - resolution transmission photograph of ruthenium nanoparticles.

[0019] Figure 3(a) X-ray photoelectron spectroscopy pattern of ruthenium@nitrogen-doped carbon nanotubes, (b) high-resolution X-ray photoelectron spectroscopy pattern of N1s, and (c) high-resolution X-ray photoelectron spectroscopy pattern of Ru 3p.

[0020] Figure 4 X-ray diffraction pattern of ruthenium@nitrogen-doped carbon nanotubes.

[0021] Figure 5 Test results of electrocatalytic activity of ruthenium@nitrogen-doped carbon nanotubes for oxygen evolution reaction; (a) linear sweep voltammetry curve, (b) Tafel polarization curve, and (c) electrochemical impedance spectroscopy.

[0022] Figure 6 Test results of electrocatalytic activity of ruthenium@nitrogen-doped carbon nanotubes for hydrogen evolution reaction; (a) linear sweep voltammetry curve, (b) Tafel polarization curve, and (c) electrochemical impedance spectroscopy.

[0023] Figure 7 Test results of electrocatalytic activity of ruthenium@nitrogen-doped carbon nanotubes for chlorine evolution reaction; (a) linear sweep voltammetry curve, (b) Tafel polarization curve, and (c) electrochemical impedance spectroscopy. Detailed implementation manners

[0024] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further elaborates on the present invention in conjunction with embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0025] Embodiment 1

[0026] This embodiment provides a preparation method for nitrogen-doped carbon nanotubes coated with ruthenium nanoparticles, which specifically includes the following steps:

[0027] S1. Immerse porous alumina (pore diameter: 30 - 100 nm, thickness: 10 - 50 μm) in an aqueous solution of ruthenium chloride with a concentration of 0.05 mol / L, take it out and dry it, and then place it in a quartz tube of a horizontal tube furnace. When the temperature of the tube furnace is 650 °C, introduce a mixed gas of acetylene and argon into the quartz tube for 1.5 hours. Among them, the flow rate of acetylene is 20 mL / min, and the flow rate of argon is 150 mL / min. After the reaction, carbon nanotubes with ruthenium nanoparticles coated on the tube walls are obtained inside the pores of the porous alumina.

[0028] S2. Etch the porous alumina with 3 mol / L NaOH to release the carbon nanotubes from the pores of the porous alumina. Finally, place the carbon nanotubes in the quartz tube of a horizontal tube furnace. When the temperature of the tube furnace is 1000 °C, introduce a mixed gas of ammonia and argon into the quartz tube for 0.5 hours. Among them, the flow rate of ammonia is 30 mL / min, and the flow rate of argon is 20 mL / min. After the reaction, the carbon nanotubes are transformed into nitrogen-doped carbon nanotubes, thus obtaining Ru@nitrogen-doped carbon nanotubes.

[0029] Figure 1 is a schematic diagram of the preparation of Ru@nitrogen-doped carbon nanotubes in the present invention. It can be seen from Figure 1 that by immersing the porous alumina in ruthenium chloride solution and then taking it out for drying, ruthenium chloride particles are deposited on the pore walls of the porous alumina. Then, place the porous alumina in a mixed gas of acetylene and argon for chemical vapor deposition. During the chemical vapor deposition process, the ruthenium chloride particles on the pore walls of the porous alumina are first pyrolyzed into ruthenium nanoparticles, and then the ruthenium nanoparticles are coated with carbon deposited on the pore walls of the porous alumina, thus forming carbon nanotubes coated with ruthenium nanoparticles. Then, remove the porous alumina template by etching to release the carbon nanotubes. Finally, perform high-temperature annealing on the carbon nanotubes in a mixed gas of ammonia and argon to perform nitrogen doping on the carbon nanotubes, that is, ruthenium nanoparticles-coated nitrogen-doped carbon nanotubes are prepared.

[0030] Figure 2 (a) is a scanning electron microscope photograph of Ru@nitrogen-doped carbon nanotubes, Figure 2 (b) is a transmission electron microscope photograph of Ru@nitrogen-doped carbon nanotubes, Figure 2 (c) is a high-resolution transmission photograph of ruthenium nanoparticles. It can be seen from the electron microscope images that the ruthenium nanoparticles are coated inside the tube walls of the carbon nanotubes. The interplanar spacing of the lattice fringes in figure (c) can prove that this ruthenium nanoparticle is metallic ruthenium.

[0031] Figure 3 (a) is an X-ray photoelectron spectroscopy diagram of Ru@nitrogen-doped carbon nanotubes, proving that the carbon nanotubes contain three elements: carbon, nitrogen, and ruthenium; (b) is a high-resolution X-ray photoelectron spectroscopy diagram of N1s, proving that the doped nitrogen elements include pyridine nitrogen and pyrrole nitrogen; (c) is a high-resolution X-ray photoelectron spectroscopy diagram of Ru 3p. The peak positions of Ru 3p 3 / 2 and Ru 3p 1 / 2 are 461.9 eV and 484.4 eV respectively, proving that the nanoparticles coated inside the tube walls of the carbon nanotubes are metallic ruthenium.

[0032] Figure 4 is the X-ray diffraction pattern of the prepared Ru@nitrogen-doped carbon nanotubes. Only the peak positions of metallic ruthenium can be seen from the spectrum, which once again proves that the nanoparticles coated inside the tube walls of the carbon nanotubes are metallic ruthenium. Perform electrochemical tests on the prepared Ru@nitrogen-doped carbon nanotubes:

[0033] The electrochemical tests were carried out using a three-electrode system and a Chenhua electrochemical workstation (CHI 760E). For the electrocatalytic activity test of the oxygen evolution reaction, a platinum sheet was used as the counter electrode, a mercury / mercuric oxide electrode was used as the reference electrode, and the electrolyte was 1 mol / L KOH aqueous solution; for the electrocatalytic activity test of the hydrogen evolution reaction, a graphite rod was used as the counter electrode, a mercury / mercuric oxide electrode was used as the reference electrode, and the electrolyte was 1 mol / L KOH aqueous solution; for the electrocatalytic activity test of the chlorine evolution reaction, a graphite rod was used as the counter electrode, a silver / silver chloride electrode was used as the reference electrode, and the electrolyte was 4 mol / L NaCl aqueous solution.

[0034] The working electrode was prepared as follows: 10 mg of ruthenium@nitrogen-doped carbon nanotubes were dispersed in 1 mL of absolute ethanol, and then 10 μL of 5 wt% Nafion solution was added thereto. After ultrasonic treatment, an ink with uniform dispersion of the sample was obtained. Next, 100 μL of the ink was pipetted and dropped on the surface of a 1 square centimeter carbon cloth and naturally dried at room temperature.

[0035] Figure 5 Fig. shows the test results of the electrocatalytic activity of ruthenium@nitrogen-doped carbon nanotubes for the oxygen evolution reaction. Among them, (a) is the linear sweep voltammetry curve. It can be seen that the overpotential corresponding to a current density of 100 mA / cm² for ruthenium@nitrogen-doped carbon nanotubes is 428 mV, which is significantly lower than that of commercial iridium oxide (451 mV). This indicates that ruthenium@nitrogen-doped carbon nanotubes have higher electrocatalytic activity for the oxygen evolution reaction than iridium oxide. (b) is the Tafel polarization curve, and the Tafel slope of ruthenium@nitrogen-doped carbon nanotubes is 105 mV dec -1 , indicating that ruthenium@nitrogen-doped carbon nanotubes have good electrocatalytic kinetics for the oxygen evolution reaction. (c) is the electrochemical impedance spectroscopy. The interfacial charge transfer resistance of ruthenium@nitrogen-doped carbon nanotubes (3.3 Ω) is smaller than that of iridium oxide (6.3 Ω), indicating that ruthenium@nitrogen-doped carbon nanotubes have faster electron transport performance than iridium oxide.

[0036] Figure 6 Fig. shows the test results of the electrocatalytic activity of ruthenium@nitrogen-doped carbon nanotubes for the hydrogen evolution reaction. Among them, (a) is the linear sweep voltammetry curve. It can be seen that the overpotential corresponding to a current density of 10 mA / cm² for ruthenium@nitrogen-doped carbon nanotubes is 45 mV, which is very close to that of commercial platinum / carbon (41 mV). This indicates that ruthenium@nitrogen-doped carbon nanotubes have comparable electrocatalytic activity for the hydrogen evolution reaction to commercial platinum / carbon. (b) is the Tafel polarization curve. The Tafel slope of ruthenium@nitrogen-doped carbon nanotubes is 47 mV dec -1 , which is very close to that of platinum / carbon (40 mV dec -1). (c) is the electrochemical impedance spectrum. The interfacial charge transfer resistance of ruthenium@nitrogen-doped carbon nanotubes is 2.9 Ω, slightly larger than that of platinum / carbon (2.6 Ω), indicating that ruthenium@nitrogen-doped carbon nanotubes have similar electron transport properties to platinum / carbon.

[0037] Figure 7 This is the test result of the electrocatalytic activity of ruthenium@nitrogen-doped carbon nanotubes for the chlorine evolution reaction. Among them, (a) is the linear sweep voltammetry curve. It can be seen that the overpotential corresponding to a current density of 100 mA / cm² for ruthenium@nitrogen-doped carbon nanotubes is 175 mV, significantly lower than that of commercial DSA (259 mV), indicating that ruthenium@nitrogen-doped carbon nanotubes have higher electrocatalytic activity for the chlorine evolution reaction than DSA. (b) is the Tafel polarization curve. The Tafel slope of ruthenium@nitrogen-doped carbon nanotubes is 63 mV dec -1 , very close to that of DSA (59 mV dec -1 ). This indicates that ruthenium@nitrogen-doped carbon nanotubes have comparable electrocatalytic kinetics for the chlorine evolution reaction to DSA. (c) is the electrochemical impedance spectrum. The interfacial charge transfer resistance of ruthenium@nitrogen-doped carbon nanotubes (2.6 Ω) is less than that of DSA (3.1 Ω), indicating that ruthenium@nitrogen-doped carbon nanotubes have faster electron transport properties than DSA.

[0038] Example 2

[0039] This example provides a preparation method for nitrogen-doped carbon nanotubes coated with ruthenium nanoparticles. The specific steps are referred to Example 1, except that the parameters of the obtained ruthenium@nitrogen-doped carbon nanotubes are different. Specifically as follows:

[0040] S1. Immerse porous alumina (pore diameter: 30 - 100 nm, pore wall thickness: 10 - 50 μm) in an aqueous solution of ruthenium chloride with a concentration of 0.01 mol / L, take it out and dry it, and then place it in the quartz tube of a horizontal tube furnace. When the temperature of the tube furnace is 600 °C, a mixed gas of acetylene and argon is introduced into the quartz tube for 1.0 hour. Among them, the flow rate of acetylene is 10 mL / min, and the flow rate of argon is 100 mL / min. After the reaction, carbon nanotubes with ruthenium nanoparticles coated on the tube walls are obtained inside the pores of the porous alumina.

[0041] S2. Corrode the porous alumina with 2 mol / L NaOH to release the carbon nanotubes from the pores of the porous alumina. Finally, place the carbon nanotubes in the quartz tube of a horizontal tube furnace. When the temperature of the tube furnace is 900 °C, a mixed gas of ammonia and argon is introduced into the quartz tube for 0.3 hour. Among them, the flow rate of ammonia is 20 mL / min, and the flow rate of argon is 10 mL / min. After the reaction, the carbon nanotubes are transformed into nitrogen-doped carbon nanotubes, thus obtaining ruthenium@nitrogen-doped carbon nanotubes.

[0042] Electrochemical tests were carried out on the prepared ruthenium@nitrogen-doped carbon nanotubes, and the test results are as follows:

[0043] For the electrocatalytic activity of the oxygen evolution reaction, the overpotential corresponding to a current density of 100 mA / cm² for ruthenium@nitrogen-doped carbon nanotubes is 438 mV, and the Tafel slope is 110 mV dec -1 , and the interfacial charge transfer resistance is 3.6 Ω. For the electrocatalytic activity of the hydrogen evolution reaction, the overpotential corresponding to a current density of 10 mA / cm² for ruthenium@nitrogen-doped carbon nanotubes is 48 mV, and the Tafel slope is 51 mV dec -1 , and the interfacial charge transfer resistance is 3.3 Ω. For the electrocatalytic activity of the chlorine evolution reaction, the overpotential corresponding to a current density of 100 mA / cm² for ruthenium@nitrogen-doped carbon nanotubes is 180 mV, and the Tafel slope is 67 mV dec -1 , and the interfacial charge transfer resistance is 3.0 Ω.

[0044] Example 3

[0045] This example provides a preparation method for nitrogen-doped carbon nanotubes coated with ruthenium nanoparticles. The specific steps refer to Example 1, except that the parameters of the prepared ruthenium@nitrogen-doped carbon nanotubes are different. Specifically as follows:

[0046] S1. Immerse porous alumina (pore diameter: 30 - 100 nm, pore wall thickness: 10 - 50 μm) in an aqueous solution of ruthenium chloride with a concentration of 0.1 mol / L, take it out and dry it, and then place it in the quartz tube of a horizontal tube furnace. When the temperature of the tube furnace is 700 °C, a mixed gas of acetylene and argon is introduced into the quartz tube for 2 hours. Among them, the flow rate of acetylene is 30 mL / min, and the flow rate of argon is 200 mL / min. After the reaction, carbon nanotubes with ruthenium nanoparticles coated on the tube walls are obtained inside the pores of the porous alumina.

[0047] S2. Corrode the porous alumina with 4 mol / L NaOH to release the carbon nanotubes from the pores of the porous alumina. Finally, place the carbon nanotubes in the quartz tube of a horizontal tube furnace. When the temperature of the tube furnace is 1100 °C, a mixed gas of ammonia and argon is introduced into the quartz tube for 1.0 hour. Among them, the flow rate of ammonia is 40 mL / min, and the flow rate of argon is 30 mL / min. After the reaction, the carbon nanotubes are transformed into nitrogen-doped carbon nanotubes, thus obtaining ruthenium@nitrogen-doped carbon nanotubes.

[0048] Electrochemical tests were carried out on the prepared ruthenium@nitrogen-doped carbon nanotubes, and the test results are as follows:

[0049] For the electrocatalytic activity of the oxygen evolution reaction, the overpotential corresponding to a current density of 100 mA / cm² for ruthenium@nitrogen-doped carbon nanotubes is 450 mV, and the Tafel slope is 130 mV dec -1 , and the interfacial charge transfer resistance is 4.0 Ω. For the electrocatalytic activity of the hydrogen evolution reaction, the overpotential corresponding to a current density of 10 mA / cm² for ruthenium@nitrogen-doped carbon nanotubes is 55 mV, and the Tafel slope is 60 mV dec -1 , and the interfacial charge transfer resistance is 3.9 Ω. For the electrocatalytic activity of the chlorine evolution reaction, the overpotential corresponding to a current density of 100 mA / cm² for ruthenium@nitrogen-doped carbon nanotubes is 200 mV, and the Tafel slope is 78 mV dec -1 , and the interfacial charge transfer resistance is 4.3 Ω.

[0050] Those skilled in the art should understand that the above are only several specific embodiments of the present invention, rather than all embodiments. It should be noted that many modifications and improvements can be made by those of ordinary skill in the art, and all modifications or improvements that do not exceed the scope of the claims should be regarded as the protection scope of the present invention.

Claims

1. A nitrogen-doped carbon nanotube coated with ruthenium nanoparticles, characterized in that: The preparation method comprises the following steps: S1. Immerse the porous alumina template in a ruthenium salt aqueous solution with a concentration of 0.01-0.1 mol / L for a period of time, then remove and dry it, and then place it in a quartz tube of a tube furnace. When the temperature rises to 600-700°C, introduce acetylene and a mixed gas of argon / nitrogen into the quartz tube and react for 1-2 hours to produce carbon nanotubes in the pore walls of the porous alumina template. The carbon nanotubes are coated with ruthenium nanoparticles in the tube walls. The pore diameter of the porous alumina template is 30-100 nm and the thickness is 10-50 μm. In the mixed gas of acetylene and argon / nitrogen, the flow rate of acetylene is 10-30 ml / min, and the flow rate of argon / nitrogen is 100-200 ml / min. S2. Remove the porous alumina template and place the carbon nanotubes in a quartz tube of a tube furnace. When the temperature rises to 900-1100°C, introduce a mixed gas of ammonia and argon / nitrogen into the quartz tube and react for 0.3-1h; thus, nitrogen-doped carbon nanotubes coated with ruthenium nanoparticles are obtained, which are used to catalyze hydrogen evolution, oxygen evolution, or chlorine evolution reactions; in the mixed gas of ammonia and argon / nitrogen, the flow rate of ammonia is 20-40 ml / min, and the flow rate of argon / nitrogen is 10-30 ml / min.

2. The nitrogen-doped carbon nanotubes coated with ruthenium nanoparticles according to claim 1, characterized in that: The ruthenium salt is one of ruthenium chloride, ruthenium acetate or ruthenium sulfate.

3. The nitrogen-doped carbon nanotubes coated with ruthenium nanoparticles according to claim 1, characterized in that: In step S2, the product of step S1 is placed in a 2-4 mol / L NaOH solution to immerse and remove the porous alumina template.

Images