A preparation method of a transition metal / nitrogen-doped porous carbon nanocomposite

Abstract

The application relates to a preparation method of a transition metal and alloy / nitrogen-doped porous carbon nanocomposite material, belonging to the technical field of water electrolysis hydrogen evolution. A certain mass ratio of a transition metal precursor and a carbon source is used as a precursor raw material; a high-frequency induction heat plasma technology is used to prepare a transition metal / nitrogen-doped carbon composite material; under the premise that metal and alloy nanoparticles have a small size and are uniformly distributed on the nitrogen-doped carbon material, the carbon matrix has a high graphitization degree, and the material is a porous structure and has a large specific surface area. The method is simple in process, rapid in reaction process and friendly to the environment, and is of great significance for the practical application of hydrogen evolution electrocatalysts.

Description

Technical Field

[0001] The invention belongs to the technical field of electrolytic water hydrogen evolution and relates to a method for preparing a transition metal / nitrogen-doped porous carbon nanocomposite material. Background Art

[0002] As the energy crisis becomes increasingly serious, people's demand for sustainable, renewable green energy is also increasing. The development of efficient and economical energy conversion technologies has become a research hotspot in the current scientific research community. Hydrogen, as a green and renewable energy with high calorific value and a wide range of raw materials, is gradually occupying an increasingly higher proportion in the energy system. Large-scale hydrogen production can be achieved through water electrolysis technology, but the large amount of electricity consumed in this process limits its further development. Research on low-cost, efficient and stable hydrogen evolution electrocatalysts is the key to solving the above problems. Hydrogen evolution catalysts represented by precious metal Pt have the best catalytic performance, but due to their low reserves and high prices, they have not been successfully applied on an industrial scale. Therefore, in recent years, researchers have been committed to non-precious metal hydrogen evolution electrocatalysts that can be used for large-scale industrial applications.

[0003] Transition metals, such as cobalt, nickel, and iron, and their alloys are considered promising candidates to replace precious metal catalysts due to their theoretically high catalytic activity and low cost. However, single metal nanomaterials are prone to oxidation and aggregation, which can significantly degrade their catalytic activity. They are also susceptible to corrosion in acidic and alkaline electrolytes, resulting in loss of catalytic activity. Combining transition metals with highly conductive carbon matrices to create composite materials can effectively address these issues. However, this material system still has many drawbacks, such as poor stability and slow charge transfer due to the poor conductivity of the carbon material.

[0004] Since high-frequency induction thermal plasma technology has the characteristics of high reaction temperature and rapid reaction process, the metal and alloy nanoparticles in the synthesized transition metal and alloy / nitrogen-doped carbon materials have extremely small sizes (less than 10nm), and the carbon matrix material has a high degree of graphitization, which improves the conductivity of the composite material. The material has a porous structure and a large specific surface area, which is conducive to generating more catalytic active sites, accelerating the carrier transport and separation process, and thus improving the catalytic performance. Summary of the Invention

[0005] The present invention provides a method for preparing a transition metal / nitrogen-doped carbon composite material. The prepared material can be any single transition metal / nitrogen-doped carbon composite material or a multi-element transition metal alloy / nitrogen-doped carbon composite material. While ensuring that the metal and alloy nanoparticles are small and evenly distributed on the nitrogen-doped carbon material, the carbon matrix has a high degree of graphitization, and the material is porous and has a large specific surface area. This method is simple, has a rapid reaction process, and is environmentally friendly, and is of great significance for the practical application of hydrogen evolution electrocatalysts.

[0006] The method for preparing a transition metal / nitrogen-doped carbon composite material according to the present invention comprises the following steps:

[0007] (1) using a transition metal precursor and a carbon source in a certain mass ratio as precursor raw materials;

[0008] (2) Preparation of transition metal / nitrogen-doped carbon composites using high-frequency induction thermal plasma technology;

[0009] In step (1), the transition metal is selected from one or more of cobalt, nickel, iron, tungsten, molybdenum, etc., and the precursor is one or more of zero-valent metals, chlorides, nitrates, sulfates, etc.; further preferably, the precursors of transition metals such as cobalt, nickel, and iron are zero-valent metals, chlorides, nitrates, sulfates, etc., and the precursors of tungsten, molybdenum, etc. are one or more of zero-valent metals, oxides, tungstates, or molybdates; the carbon source is a nitrogen-containing or nitrogen-free solid organic precursor such as melamine, dicyandiamide, glucose, etc., or a nitrogen-containing or non-nitrogenous gas that can generate carbon, such as methane, acetylene, etc.; if the carbon source does not contain nitrogen or the amount of nitrogen contained is insufficient, additional nitrogen gas can be used as a carrier gas to supplement the nitrogen during the high-frequency induction thermal plasma reaction.

[0010] The mass ratio of the transition metal precursor to the carbon source is 1:0.1-10, preferably 1:0.5-5.

[0011] The high-frequency induction thermal plasma technology used in step (2) specifically includes the following steps:

[0012] The high-frequency induction thermal plasma device is used to generate stable thermal plasma. The thermal plasma power is 1 to 100 kW, preferably 10 to 30 kW.

[0013] The precursor raw materials are delivered to the hot plasma region by carrier gas for reaction. The solid feed rate (when the carbon source is a solid organic precursor, the transition metal precursor and the carbon source are mixed and fed uniformly; when the carbon source is a gas, the transition metal precursor is fed alone) is 5-500 g min -1 , preferably 10-30g min -1When the carbon source is a gas, the carbon source is used as a carrier gas; the carrier gas can also be one or more of argon, hydrogen, and nitrogen; the flow rate of any carrier gas is 0.01 to 10 m 3 h -1 , preferably 0.1 to 5 m 3 h -1 .

[0014] The raw materials undergo gasification, reaction, condensation and precipitation in the hot plasma area.

[0015] The transition metal / nitrogen-doped composite material arrives at a collection system along with the gas flow for collection.

[0016] The present invention provides a method for preparing a transition metal and alloy / nitrogen-doped carbon composite material. The prepared material can be any single transition metal / nitrogen-doped carbon composite material or a multi-element transition metal alloy / nitrogen-doped carbon composite material, wherein the metal nanoparticles have a particle size of less than 10 nm and are uniformly distributed in the nitrogen-doped carbon matrix material, effectively suppressing the agglomeration and oxidation of the nanoparticles; the porous structure also ensures that the obtained material has a large specific surface area, which is conducive to exposing more active sites during the hydrogen evolution catalytic reaction. The composite carbon matrix material has a high degree of graphitization, which is conducive to the charge transfer process and improves the catalytic activity. The method is simple in process, has a rapid reaction process, and is environmentally friendly, and is of great significance for the practical application of hydrogen evolution electrocatalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 TEM photo (a) and HRTEM photo (b) of the cobalt / nitrogen-doped carbon material hydrogen evolution electrocatalyst prepared in Example 1 of the present invention.

[0018] Figure 2 This is the XRD pattern of the cobalt / nitrogen-doped carbon material hydrogen evolution electrocatalyst prepared in Example 1 of the present invention.

[0019] Figure 3 This is the Raman spectrum of the cobalt / nitrogen-doped carbon material hydrogen evolution electrocatalyst prepared in Example 1 of the present invention.

[0020] Figure 4 High-angle annular dark field-scanning transmission electron microscopy image (a) and C, Co, and N element distribution maps (b, c, d) of the cobalt / nitrogen-doped carbon material hydrogen evolution electrocatalyst prepared in Example 1 of the present invention.

[0021] Figure 5 (a) Nitrogen adsorption / desorption curve and (b) pore size distribution diagram of the cobalt / nitrogen-doped carbon material hydrogen evolution electrocatalyst prepared in Example 1 of the present invention.

[0022] Figure 6Polarization curve (a) of the cobalt / nitrogen-doped carbon material hydrogen evolution electrocatalyst prepared in Example 1 of the present invention in 1M KOH electrolyte and the polarization curve (b) at 10 mA cm -2 Stability under current density (b). DETAILED DESCRIPTION

[0023] To better illustrate the content of the present invention, the present invention is further described below with reference to examples, but the present invention is not limited to the following examples.

[0024] Example 1

[0025] (1) 500 g of cobalt chloride and 1500 g of melamine were weighed and mechanically mixed in a mass ratio of 1:3 to prepare a precursor.

[0026] (2) Preparation of cobalt / nitrogen-doped carbon composite materials: A 10KW plasma device was used, which mainly consisted of a plasma generation system, a stainless steel reactor, a plasma lamp, a feeding system, a gas distribution system, a product collection system, and an exhaust gas emission system. Argon gas was introduced into the plasma system as the central gas to form a plasma. After the arc was stable, the precursor obtained in step (1) was added using the feeding system at a feeding rate of 10 g min -1 The carrier gas is argon, and the gas flow rate is 0.5m 3 h -1 After the material is consumed, the reaction device is closed in the product collection system to obtain the cobalt / nitrogen-doped carbon composite material.

[0027] The structure and hydrogen evolution performance of the cobalt / nitrogen doped composite material prepared above were characterized, such as Figure 1-5 shown. Figure 1 This is a TEM photo of the cobalt / nitrogen doped composite material. From the low-magnification photo, it can be seen that the microscopic morphology of the material shows that the nanoparticles are uniformly distributed in the matrix. From the high-magnification photo, it can be seen that the interplanar spacing of the nanoparticles is 0.204nm, corresponding to the (111) crystal plane of metallic cobalt, while the interplanar spacing of the matrix is ​​0.34nm, corresponding to the (001) crystal plane of graphitic carbon. Figure 2 : This is the XRD pattern of the cobalt / nitrogen-doped composite material, wherein the diffraction peak at 26° corresponds to graphite carbon, and the diffraction peaks at 44.2°, 51.5°, and 75.85° correspond to metallic cobalt. Figure 3 Raman spectrum of cobalt / nitrogen doped composite material, 1350cm -1 and 1600cm -1 The peaks at the 200 nm and 200 nm correspond to the D peak and the G peak, respectively, where the D peak represents the defects of the C atomic lattice and the G peak represents the sp 2 The ratio of the hybrid in-plane stretching vibration and the intensity of the D peak and G peak indicates that the carbon matrix has a high degree of graphitization. Figure 4This is a high-angle annular dark field-scanning transmission electron microscopy image of the cobalt / nitrogen doped composite material and the element distribution diagram of C, Co, and N. It can be seen that the C, Co, and N elements are evenly distributed, and the doping of element N is successfully demonstrated. Figure 5 The nitrogen adsorption-desorption curve and pore size distribution of the cobalt / nitrogen doped composite material have a specific surface area of ​​76.8m 2 / g, and the average pore diameter is 3.82nm. Figure 6 The hydrogen evolution performance of the cobalt / nitrogen doped composite material reached 10 mA cm in 1 M KOH electrolyte. -2 The overpotential required for the current density is only 180 mV, and as Figure 5 As shown in b, after 10 hours of stability testing, the performance has hardly decayed.

[0028] Example 2

[0029] (1) 500 g of nickel nitrate and 1500 g of dicyandiamide were weighed and mixed in a mass ratio of 1:3 to obtain a precursor.

[0030] (2) Preparation of nickel / nitrogen-doped carbon composite materials: A 10KW plasma device was used, which mainly consisted of a plasma generation system, a stainless steel reactor, a plasma lamp, a feeding system, a gas distribution system, a product collection system, and an exhaust gas emission system. Argon gas was introduced into the plasma system as the central gas to form a plasma. After the arc was stable, the precursor obtained in step (1) was added using the feeding system at a feeding rate of 15 g min -1 The carrier gas is hydrogen, and the gas flow rate is 0.1m 3 h -1 After the material is consumed, the reaction device is closed and the product collection system is used to obtain the nickel / nitrogen-doped carbon composite material.

[0031] Example 3

[0032] (1) Weigh 200 g of nickel sulfate and 300 g of ammonium molybdate and mix them as a precursor of nickel-molybdenum alloy.

[0033] (2) Preparation of nickel-molybdenum alloy / nitrogen-doped carbon composite material: A 10KW plasma device was used, which mainly consisted of a plasma generation system, a stainless steel reactor, a plasma lamp, a feeding system, a gas distribution system, a product collection system, and an exhaust gas emission system. Argon gas was introduced into the plasma system as the central gas to form a plasma. After the arc was stable, the precursor obtained in step (1) was added using the feeding system at a feeding rate of 10 g min -1 The carrier gas is a mixture of acetylene, nitrogen and hydrogen, with a flow rate of 1.5m 3 h -1 , 0.1m 3 h -1 and 0.05m3 h -1 After the material is consumed, the reaction device is closed in the product collection system to obtain the nickel-molybdenum alloy / nitrogen-doped carbon composite material.

[0034] Example 4

[0035] 250 g of cobalt chloride, 250 g of nickel chloride, and 1500 g of glucose were weighed and mixed in a mass ratio of 1:1:3 to obtain a precursor.

[0036] Preparation of nickel-cobalt alloy / nitrogen-doped carbon composite material: A 10KW plasma device was used, which mainly consisted of a plasma generation system, a stainless steel reactor, a plasma lamp, a feeding system, a gas distribution system, a product collection system, and an exhaust gas emission system. Argon gas was introduced into the plasma system as the central gas to form a plasma. After the arc was stable, the precursor obtained in step (1) was added using the feeding system at a feeding rate of 20 g min -1 The carrier gas is nitrogen, and the gas flow rate is 0.1m 3 h -1 After the material is consumed, the reaction device is closed in the product collection system to obtain the nickel-cobalt alloy / nitrogen-doped carbon composite material.

[0037] Example 5

[0038] (1) 500 g of iron powder (74 μm) and 1500 g of dicyandiamide were weighed and mechanically mixed in a mass ratio of 1:3 to prepare a precursor.

[0039] (2) Preparation of iron / nitrogen doped carbon composite materials: A 10KW plasma device was used, which mainly consisted of a plasma generation system, a stainless steel reactor, a plasma lamp, a feeding system, a gas distribution system, a product collection system, and an exhaust gas emission system. Argon gas was introduced into the plasma system as the central gas to form a plasma. After the arc was stable, the precursor obtained in step (1) was added using the feeding system at a feeding rate of 20 g min -1 The carrier gas is argon, and the gas flow rate is 0.5m 3 h -1 After the material is consumed, the reaction device is closed and the product collection system is used to obtain an iron / nitrogen-doped carbon composite material, wherein the size of the iron nanoparticles in the composite material is less than 10 nm.

Claims

1. A method for preparing a transition metal / nitrogen-doped porous carbon nanocomposite material, characterized in that: The following steps are involved: (1) using a transition metal precursor and a carbon source in a certain mass ratio as precursor raw materials; (2) Preparation of transition metal / nitrogen-doped carbon composites using high-frequency induction thermal plasma technology; In step (1), the transition metal is selected from one or more of cobalt, nickel, iron, tungsten, and molybdenum, wherein the precursors of cobalt, nickel, and iron are one or more of zero-valent metals, chloride salts, nitrates, and sulfates, and the precursors of tungsten and molybdenum are one or more of zero-valent metals, oxides, tungstates, or molybdates; the carbon source is a solid organic precursor containing or not containing nitrogen, or the carbon source is a nitrogen-containing or nitrogen-free gas that can provide carbon. When the carbon source does not contain nitrogen, additional nitrogen gas is input as a carrier gas to supplement the nitrogen during the high-frequency induction thermal plasma reaction; The mass ratio of the transition metal precursor to the carbon source is 1:0.5-5; The high-frequency induction thermal plasma technology used in step (2) specifically includes the following steps: a high-frequency induction thermal plasma device is used to generate stable thermal plasma; the thermal plasma power is 10KW; The precursor raw materials are delivered to the thermal plasma area by carrier gas for reaction, and the solid feeding rate is 10-30g min -1 When the carbon source is a gas, the carbon source is used as a carrier gas; the carrier gas can also be one or more of argon, hydrogen, and nitrogen; the carrier gas flow rate is 0.1 to 5 m 3 h -1 ; The raw materials undergo gasification, reaction, condensation and precipitation in the hot plasma area; The transition metal / nitrogen-doped composite material arrives at a collection system along with the gas flow for collection.

2. The method for preparing a transition metal / nitrogen-doped porous carbon nanocomposite material according to claim 1, wherein: Solid feed: When the carbon source is a solid organic precursor, the transition metal precursor and the carbon source are mixed evenly and fed; when the carbon source is a gas, the transition metal precursor is fed alone.

3. A transition metal / nitrogen-doped porous carbon nanocomposite material prepared according to the method of any one of claims 1-2, wherein the metal is in the form of nanoparticles and is uniformly distributed in the nitrogen-doped carbon matrix material, and the particle size of the metal nanoparticles is less than 10 nm.

4. The use of the transition metal / nitrogen-doped porous carbon nanocomposite material according to claim 3, characterized in that: Used for electrolysis of water to produce hydrogen.

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