Preparation method and application of nitrogen-doped carbon nanotube coated with platinum-ruthenium alloy

Abstract

The invention relates to a preparation method and application of a nitrogen-doped carbon nanotube coated with platinum-ruthenium alloy, and is characterized in that the nitrogen-doped carbon nanotube of which the tube wall is coated with PtRu alloy nanoparticles is prepared by using a chemical vapor deposition process assisted by an anodic aluminum oxide template and subsequent ammonia gas annealing; although the contents of Pt and Ru are respectively as low as 0.8 wt% and 4.2 wt%, the combined action of Pt, Ru and N doping enables the platinum-ruthenium-nitrogen doped carbon nanotube composite material to have excellent HER electrocatalytic activity in alkaline, acidic and neutral electrolytes, and the HER activity of the composite material in the alkaline and acidic electrolytes exceeds that of a commercial Pt / C catalyst; besides, after the platinum-ruthenium-nitrogen-doped carbon nanotube composite material is used as a cathode electrocatalyst to assemble an anion exchange membrane electrolytic cell, the electrolytic cell provides low voltage of 1.78 V under the industrial grade current density of 1Acm <-2 >, and the electrolytic cell has good durability; therefore, the invention provides a new opportunity for designing and synthesizing a high-performance pH universal HER electrocatalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen evolution reaction electrocatalysts, and in particular to a preparation method and application of nitrogen-doped carbon nanotubes coated with a platinum-ruthenium alloy. Background Art

[0002] The hydrogen evolution reaction (HER) is a key process in the electrochemical splitting of water to generate hydrogen molecules. However, its slow kinetics lead to low water electrolysis efficiency, which hinders the commercial application of water electrolysis in large-scale hydrogen production. Although electrocatalysts can improve HER kinetics, the most effective HER electrocatalysts currently consist mainly of expensive and scarce precious metals (such as Pt)-based materials. Therefore, people are committed to synthesizing HER electrocatalysts that contain no or only a small amount of precious metals. In particular, nitrogen-doped carbon nanotubes coated with metal nanoparticles have attracted particular attention. This is because: (1) CNTs (carbon nanotubes) have high conductivity and large surface area, and nitrogen doping can improve their HER activity; (2) metal nanoparticles have a synergistic effect with NCNTs (nitrogen carbon nanotubes), which can induce the enhancement of HER activity; (3) the carbon layer of NCNTs can protect the metal nanoparticles from corrosion by the electrolyte. However, the HER activity of these NCNTs still needs to be further enhanced. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a preparation method and application of nitrogen-doped carbon nanotubes coated with platinum-ruthenium alloy, which can solve the problems of difficult preparation of electrocatalysts and low hydrogen evolution reaction activity in traditional electrolytic cells for hydrogen production by electrolysis of water.

[0004] To solve the above technical problems, the technical solution of the present invention is: a method for preparing nitrogen-doped carbon nanotubes coated with platinum-ruthenium alloy, the innovation of which lies in: the specific preparation method is as follows: A mixture of a ruthenium salt solution and a chloroplatinic acid solution is dropped onto a metal oxide template, and a mixture of acetylene and an inert gas is used for chemical vapor deposition to form carbon nanotubes on the metal oxide template, and platinum-ruthenium alloy nanoparticles are wrapped in the carbon nanotubes; The metal oxide template is etched away, cleaned and dried, and then annealed in ammonia to obtain a platinum ruthenium nitrogen-doped carbon nanotube structure.

[0005] Furthermore, the ruthenium salt solution is a ruthenium chloride solution.

[0006] Furthermore, the metal oxide template is an alumina template, and the alumina template is honeycomb-shaped; the alumina template is corroded by using a sodium hydroxide solution to release the platinum ruthenium carbon nanotubes from the pores of the honeycomb-shaped anodized aluminum template.

[0007] Furthermore, the inert gas is argon.

[0008] Furthermore, a ruthenium chloride solution and a chloroplatinic acid solution were dripped onto a honeycomb anodic aluminum oxide template, which was then placed in a tube furnace and subjected to chemical vapor deposition using a mixture of acetylene and argon. Carbon nanotubes were grown within the honeycomb pores of the anodic aluminum oxide template, and platinum-ruthenium alloy nanoparticles were encapsulated within the carbon nanotubes. The honeycomb anodic aluminum oxide template is corroded by using NaOH solution. After the platinum ruthenium carbon nanotubes are washed and dried, the platinum ruthenium carbon nanotubes are annealed in ammonia gas to obtain a platinum ruthenium nitrogen-doped carbon nanotube structure.

[0009] Furthermore, a 0.05 M ruthenium chloride solution and a 0.01 M chloroplatinic acid solution are dropped onto the treated honeycomb anodized aluminum template. After it is naturally dried, it is placed in a tube furnace and chemical vapor deposition is carried out for 1-2 hours at 650°C, an acetylene flow rate of 20 sccm and an argon flow rate of 100 sccm to grow carbon nanotubes in the pores of the honeycomb anodized aluminum template and wrap platinum-ruthenium alloy nanoparticles in the carbon nanotubes; subsequently, the honeycomb anodized aluminum template is corroded by a NaOH solution to release the platinum-ruthenium carbon nanotubes from the pores of the honeycomb anodized aluminum template; after washing with pure water and drying, the platinum-ruthenium carbon nanotubes are annealed for 20-30 minutes at an ammonia flow rate of 30 sccm and a temperature of 950°C to achieve nitrogen doping of the platinum-ruthenium carbon nanotubes, and finally platinum-ruthenium nitrogen-doped carbon nanotubes are obtained.

[0010] The innovation of the nitrogen-doped carbon nanotubes coated with platinum-ruthenium alloy lies in that the nitrogen-doped carbon nanotubes coated with platinum-ruthenium alloy comprise carbon nanotubes, and the carbon nanotubes are loaded with platinum-ruthenium alloy nanoparticles and nitrogen doping.

[0011] Application of nitrogen-doped carbon nanotubes coated with platinum-ruthenium alloy as cathode electrocatalyst in hydrogen evolution reaction.

[0012] The advantages of the present invention are: 1) In the present invention, nitrogen-doped carbon nanotubes with PtRu alloy nanoparticles coated on the tube wall were prepared by chemical vapor deposition process assisted by anodized aluminum oxide template and subsequent ammonia annealing. Although the contents of Pt and Ru were as low as 0.8 wt% and 4.2 wt%, respectively, the combined effect of Pt, Ru and N doping made the PtRuN-doped carbon nanotube composite material have excellent HER electrocatalytic activity in alkaline, acidic and neutral electrolytes. The HER activity of the composite material in alkaline and acidic electrolytes exceeded that of commercial Pt / C catalyst. In addition, after assembling an anion exchange membrane electrolyzer using the PtRuN-doped carbon nanotube composite material as the cathode electrocatalyst, the electrolyzer exhibited excellent HER electrocatalytic activity at 1 Acm -2A low voltage of 1.78 V was provided at industrial-grade current density, and the electrolyzer had good durability; therefore, this invention provides new opportunities for the design and synthesis of high-performance pH-universal HER electrocatalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0014] Figure 1 The figure is a schematic diagram of the preparation process of nitrogen-doped carbon nanotubes coated with platinum-ruthenium alloy according to the present invention.

[0015] Figure 2 These are the XRD patterns of platinum ruthenium nitrogen doped carbon nanomaterials and ruthenium nitrogen doped carbon nanomaterials.

[0016] Figure 3 This is the SEM image of platinum ruthenium nitrogen doped carbon nanomaterial.

[0017] Figure 4 TEM image of platinum-ruthenium-nitrogen doped carbon nanomaterials.

[0018] Figure 5 High-resolution TEM image of platinum-ruthenium alloy nanoparticles.

[0019] Figure 6 This is the XPS spectrum of platinum ruthenium nitrogen doped carbon nanomaterials.

[0020] Figures 7 to 10 High-resolution XPS spectra of C1s, N1s, Ru3p and Pt4f respectively.

[0021] Figure 11 Performance diagram of electrocatalytic HER in 1 M KOH; LSV curves of CNTs, NCNTs, Ru-NCNTs, PtRu-NCNT composites and Pt / C.

[0022] Figure 12 Performance diagram of electrocatalytic HER in 1 M KOH; Tafel slopes of Ru-NCNTs, PtRu-NCNT composites and Pt / C.

[0023] Figure 13 Performance diagram of electrocatalytic HER in 1 M KOH; Nyquist plots of CNTs, NCNTs, Ru-NCNTs and PtRu-NCNT composites.

[0024] Figure 14 Performance diagram of electrocatalytic HER in 1 M KOH; chronoamperometric curve of PtRu-NCNT composite material.

[0025] Figure 15LSV curves of PtRu-NCNT composite materials before and after 2000 CV cycles.

[0026] Figure 16 This is the current density-voltage curve of the assembled AEM electrolyzer.

[0027] Figure 17 The current density of the AEM electrolyzer is 1 A cm -2 Chronopotentiometry test curve.

[0028] Figure 18 Performance diagram of electrocatalytic HER in 0.5 M H2SO4; LSV curves of CNTs, NCNTs, Ru-NCNTs, PtRu-NCNT composites and Pt / C.

[0029] Figure 19 Performance diagram of electrocatalytic HER in 0.5 M H2SO4; Tafel slopes of Ru-NCNTs, PtRu-NCNT composites and Pt / C.

[0030] Figure 20 Performance diagram of electrocatalytic HER in 0.5 M H2SO4; Nyquist plots of CNTs, NCNTs, Ru-NCNTs and PtRu-NCNT composites.

[0031] Figure 21 Performance diagram of electrocatalytic HER in 0.5 M H2SO4; chronoamperometric curve of PtRu-NCNT composite material.

[0032] Figure 22 HER performance diagram in 1 M phosphate buffered saline (PBS); LSV curves of CNTs, NCNTs, Ru-NCNTs, PtRu-NCNT composites and Pt / C.

[0033] Figure 23 Figure 2 shows the HER performance in 1 M phosphate buffered saline (PBS); Tafel slopes of Ru-NCNTs, PtRu-NCNT composites, and Pt / C.

[0034] Figure 24 HER performance diagram in 1 M phosphate buffered saline (PBS); Nyquist plots of CNTs, NCNTs, Ru-NCNTs and PtRu-NCNT composites.

[0035] Figure 25 HER performance diagram in 1 M phosphate buffered saline (PBS); chronoamperometric curve of PtRu-NCNT composite material. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0037] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0038] like Figures 1 to 10 The preparation method of nitrogen-doped carbon nanotubes coated with platinum-ruthenium alloy is shown as follows: Example 1: First, 600 μL of a 0.05 M ruthenium chloride solution and 600 μL of a 0.01 M chloroplatinic acid solution were dropped onto a treated honeycomb anodic aluminum oxide template. After it was naturally dried, it was placed in a tube furnace and subjected to chemical vapor deposition for 1-2 h at 650° C., an acetylene flow rate of 20 sccm, and an argon flow rate of 100 sccm, so that carbon nanotubes grew in the pores of the honeycomb anodic aluminum oxide template and platinum-ruthenium alloy nanoparticles were wrapped in the carbon nanotubes. Subsequently, the honeycomb anodic aluminum oxide template was corroded by a NaOH solution to release the platinum-ruthenium carbon nanotubes from the pores of the honeycomb anodic aluminum oxide template. After washing with pure water and drying, the platinum-ruthenium carbon nanotubes were annealed at an ammonia flow rate of 30 sccm and a temperature of 950° C. for 20-30 min to achieve nitrogen doping of the platinum-ruthenium carbon nanotubes, thereby finally obtaining platinum-ruthenium nitrogen-doped carbon nanotubes.

[0039] The nitrogen-doped carbon nanotube coated with platinum-ruthenium alloy comprises carbon nanotubes, wherein platinum-ruthenium alloy nanoparticles and nitrogen doping are loaded in the carbon nanotubes.

[0040] Nitrogen-doped carbon nanotubes coated with platinum-ruthenium alloy are used to prepare cathode electrocatalysts in hydrogen evolution reaction.

[0041] To evaluate the HER electrocatalytic performance of the material, a standard three-electrode system of an electrochemical workstation was used to test its electrochemical activity. In 1 M KOH solution, a Hg / HgO electrode and a graphite rod were used as the reference electrode and the counter electrode, respectively. The LSV curve is scanned at a scan rate of 100 nm. During data processing, the measured potential is converted to the potential relative to the standard RHE according to the Nernst equation: ERHE = E Hg / HgO + 0.059 × pH + 0.098; Under acidic conditions, for 0.5 M H2SO4, a Hg / H2SO4 electrode and a graphite rod were used as the reference electrode and the counter electrode, respectively; at scan rate, the LSV curve was recorded, and the measured potential was converted to the standard RHE according to the Nernst equation: E RHE = E Hg / H2SO4 + 0.059×pH + 0.652; Under neutral conditions, for 1 M PBS (pH = 7), an Ag / AgCl electrode and a Pt sheet were used as the reference electrode and the counter electrode, respectively; at scan rate, the LSV curve was recorded, and the measured potential was converted to the standard RHE according to the Nernst equation: E RHE =E Ag / AgCl + 0.059 × pH + 0.197.

[0042] The EIS test conditions under alkaline conditions were as follows: within the frequency range of 0.1 - 100000 Hz, the amplitude was set to 5 mV, and the EIS at 0.213 V (vs RHE) was recorded. Under acidic conditions, at -0.29 V (vs RHE), within the frequency range of 0.1 - 100000 Hz, the EIS with an amplitude of 5 mV was recorded. Under neutral conditions, at -0.09 V (vs RHE), within the frequency range of 0.1 - 100000 Hz, the EIS with an amplitude of 5 mV was recorded.

[0043] As Figure 11 shown: The overpotential of the PtRu-NCNT composite material at a current density of 10 mA cm -2 ( 10) was 23 mV, lower than that of the commercial Pt / C (20 wt%) catalyst (28 mV). Therefore, the PtRu-NCNT composite material has excellent HER activity. In addition, the HER activity of the PtRu-NCNT composite material is also better than that of CNTs (> 400 mV), NCNTs (219 mV), and Ru-NCNTs (53 mV). The HER activities of these four samples are in the order of: CNT < NCNT < Ru-NCNT < PtRu-NCNT composite material.

[0044] As Figure 12 shown: The Tafel slope of the PtRu-NCNT composite material is 30 mV dec -1 , less than that of the Pt / C catalyst (36 mV dec -1) and Ru-NCNTs (60 mV dec -1 ). Therefore, the PtRu-NCNT composite material has good catalytic kinetics.

[0045] like Figure 13 As shown in the figure, the charge transfer resistance (Rct, 0.9 Ω) of the PtRu-NCNT composite is smaller than that of Ru-NCNTs (2.6 Ω), NCNTs (55 Ω), and CNTs (>200 Ω). Therefore, the PtRu-NCNT composite has the fastest HER electron transfer rate.

[0046] like Figure 14 Shown: Chronoamperometric curve of PtRu-NCNT composite material (at overpotential of 23 mV); after 24 h of continuous testing, the current density of PtRu-NCNT composite material only decreased slightly.

[0047] like Figure 15 As shown: After 2000 cyclic voltammetry scans (CV), the η10 of the PtRu-NCNT composite material underwent a slight negative shift.

[0048] like Figure 16 As shown: With carbon paper loaded with PtRu-NCNT composite material as cathode and nickel foam loaded with NiFe layered double hydroxide (LDH) as anode, the AEM electrolytic cell was tested under 1 M KOH and 80 °C. KOH solution was circulated on the anode side. When the industrial-grade high current density was 1 A cm -2 The cell voltage at this time is 1.78 V. Compared with the AEM electrolyzer of the prior art, the AEM electrolyzer assembled in the present invention has a lower or similar voltage.

[0049] like Figure 17 Shown: At 1 A cm -2 After 150 hours of testing, the AEM electrolyzer was -2 The voltage under the condition of high current density increased to about 1.92 V, and the results showed that the AEM electrolyzer had good durability for long-term hydrogen production at industrial-grade high current density.

[0050] like Figure 18 As shown: It can be observed that the η10 of the PtRu-NCNT composite in 0.5 M H2SO4 is 21 mV, which is lower than the η10 of the commercial Pt / C catalyst (26 mV). In addition, for CNTs, NCNTs, Ru-NCNTs, Pt-NCNTs and PtRu-NCNT composites in 0.5 M H2SO4, their HER activities in 0.5 M H2SO4 are also ranked as CNT (>300 mV). <NCNT(270 mV)<Pt-NCNT( 10 = 88 mV) < Ru-NCNT (48 mV) < PtRu-NCNT composite. Therefore, the HER activity of the PtRu-NCNT composite in 0.5 M H2SO4 also stems from the combined contributions of N, Pt, and Ru, and there is also a synergistic effect between Pt and Ru.

[0051] As Figure 19 shown: The Tafel slope of the PtRu-NCNT composite is 16 mV dec -1 , greater than that of the Pt / C catalyst (23 mV dec -1 ) and Ru-NCNTs (52 mV dec -1 ). Therefore, the PtRu-NCNT composite also exhibits excellent catalytic kinetics in 0.5 M H2SO4.

[0052] As Figure 20 shown: The Rct (0.5 Ω) of the PtRu-NCNT composite is less than that of Ru-NCNTs (2.0 Ω), NCNTs (40 Ω), and CNTs (170 Ω), indicating that they have the fastest electron transfer rate in 0.5 M H2SO4.

[0053] As Figure 21 shown: The chronoamperometry curve of the PtRu-NCNT composite (at an overpotential of 21 mV). The i-t stability was measured by chronoamperometry at an overpotential of 21 mV. The chronoamperometry curve shows that after continuous testing for 24 h, the current density of the PtRu-NCNT composite slightly decays, confirming that the PtRu-NCNT composite has good HER durability in 0.5 M H2SO4.

[0054] As Figure 22 shown: The curve shows that the η10 of the PtRu-NCNT composite is 40 mV, slightly higher than that of the Pt / C catalyst (35 mV), but significantly less than that of Ru-NCNTs (65 mV), NCNTs (320 mV), and CNTs (>400 mV). Therefore, the PtRu-NCNT composite has good HER activity in 1 M PBS, indicating its versatility as a highly active HER electrocatalyst in alkaline, acidic, and neutral electrolytes. In addition, the combined contributions of N, Ru, and Pt should contribute to the superior HER activity of the PtRu-NCNT composite in 1 M PBS. <​​​​​​-1 ) is close to, but smaller than, the Tafel slope of Ru-NCNTs (80 mV dec -1 ).

[0056] like Figure 24 As shown in Figure 3, the PtRu-NCNT composite has a smaller Rct (1.47Ω) than Ru-NCNTs, NCNTs, and CNTs, which means that they have a faster electron transfer rate in 1 M PBS.

[0057] like Figure 25 Shown: Chronoamperometric curve of PtRu-NCNT composite material (at overpotential of 40 mV); after 24 hours of testing, the current density can still reach 93% of the initial current density, proving that PtRu-NCNT composite material has good HER durability in 1 M PBS.

[0058] Those skilled in the art should understand that the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may be subject to various changes and improvements, and these changes and improvements shall fall within the scope of the present invention to be protected.

Claims

1. A method for preparing nitrogen-doped carbon nanotubes coated with a platinum-ruthenium alloy, characterized in that: The specific preparation method is as follows: A mixture of a ruthenium salt solution and a chloroplatinic acid solution is dropped onto a metal oxide template, and a mixture of acetylene and an inert gas is used for chemical vapor deposition to form carbon nanotubes on the metal oxide template, and platinum-ruthenium alloy nanoparticles are wrapped in the carbon nanotubes; The metal oxide template is etched away, cleaned and dried, and then annealed in ammonia to obtain a platinum ruthenium nitrogen-doped carbon nanotube structure.

2. The method for preparing nitrogen-doped carbon nanotubes coated with a platinum-ruthenium alloy according to claim 1, wherein: The ruthenium salt solution is a ruthenium chloride solution.

3. The method for preparing nitrogen-doped carbon nanotubes coated with platinum-ruthenium alloy according to claim 1, characterized in that: The metal oxide template is an aluminum oxide template, and the aluminum oxide template is honeycomb-shaped; the aluminum oxide template is corroded by using a sodium hydroxide solution to release the platinum ruthenium carbon nanotubes from the pores of the honeycomb-shaped anodized aluminum oxide template.

4. The method for preparing nitrogen-doped carbon nanotubes coated with a platinum-ruthenium alloy according to claim 1, wherein: The inert gas is argon.

5. The method for preparing nitrogen-doped carbon nanotubes coated with platinum-ruthenium alloy according to claim 1, wherein: A ruthenium chloride solution and a chloroplatinic acid solution are dropped onto a honeycomb anodic aluminum oxide template, which is then placed in a tube furnace and subjected to chemical vapor deposition using a mixture of acetylene and argon. Carbon nanotubes are grown within the honeycomb pores of the anodic aluminum oxide template, and platinum-ruthenium alloy nanoparticles are encapsulated within the carbon nanotubes. The honeycomb anodic aluminum oxide template is corroded by using NaOH solution. After the platinum ruthenium carbon nanotubes are washed and dried, the platinum ruthenium carbon nanotubes are annealed in ammonia gas to obtain a platinum ruthenium nitrogen-doped carbon nanotube structure.

6. The method for preparing nitrogen-doped carbon nanotubes coated with platinum-ruthenium alloy according to claim 5, characterized in that: A 0.05 M ruthenium chloride solution and a 0.01 M chloroplatinic acid solution were dropped onto the treated honeycomb anodic aluminum oxide template. After it was naturally dried, it was placed in a tube furnace and chemical vapor deposition was carried out for 1-2 hours at 650°C, an acetylene flow rate of 20 sccm, and an argon flow rate of 100 sccm. Carbon nanotubes were grown in the pores of the honeycomb anodic aluminum oxide template and platinum-ruthenium alloy nanoparticles were wrapped in the carbon nanotubes. Subsequently, the honeycomb anodic aluminum oxide template was corroded with a NaOH solution to release the platinum-ruthenium carbon nanotubes from the pores of the honeycomb anodic aluminum oxide template. After washing with pure water and drying, the platinum-ruthenium carbon nanotubes were annealed for 20-30 min at an ammonia flow rate of 30 sccm and a temperature of 950°C to achieve nitrogen doping of the platinum-ruthenium carbon nanotubes, and finally platinum-ruthenium nitrogen-doped carbon nanotubes were obtained.

7. Nitrogen-doped carbon nanotubes coated with platinum-ruthenium alloy prepared by the method of claims 1-6, characterized in that: The nitrogen-doped carbon nanotube coated with platinum-ruthenium alloy comprises carbon nanotubes, and the carbon nanotubes are loaded with platinum-ruthenium alloy nanoparticles and nitrogen doping.

8. Use of the nitrogen-doped carbon nanotubes coated with platinum-ruthenium alloy according to claim 7 as a cathode electrocatalyst in hydrogen evolution reaction.

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