CN115341220A - A kind of preparation method of transition metal/nitrogen doped porous carbon nanocomposite material - Google Patents

Abstract

A preparation method of a transition metal and alloy/nitrogen doped porous carbon nano composite material belongs to the technical field of electrolysis water hydrogen evolution. Taking a transition metal precursor and a carbon source in a certain mass ratio as precursor raw materials; preparing a transition metal/nitrogen-doped carbon composite material by using a high-frequency induction thermal plasma technology; on the premise of ensuring that metal and alloy nano particles have small sizes and are uniformly distributed on the nitrogen-doped carbon material, the carbon matrix has higher graphitization degree, and meanwhile, the material is of a porous structure and has larger specific surface area. The method has simple process, rapid reaction process and environmental protection, and has important significance for the practical application of the hydrogen evolution electrocatalyst.

Description

A kind of preparation method of transition metal/nitrogen doped porous carbon nanocomposite material

technical field

The invention belongs to the technical field of electrolysis of water and hydrogen evolution, and relates to a preparation method of a transition metal/nitrogen-doped porous carbon nanocomposite material.

Background technique

With the increasingly serious energy crisis, people's demand for sustainable renewable green energy is also increasing. The research and development of efficient and economical energy conversion technology has become a research hotspot in the current scientific research community. Hydrogen, as a green renewable energy with high calorific value and wide sources of raw materials for preparation, is gradually occupying a higher and higher proportion in the energy system. Large-scale hydrogen production can be achieved through electrolysis of water technology, but the large amount of electrical energy consumed in this process limits its further development. The key to solving the above problems is to study the hydrogen evolution electrocatalysts with low price, high efficiency and good stability. The hydrogen evolution catalyst represented by the noble metal Pt has the best catalytic performance, but limited by its low reserves and high price, it has not been successfully realized on a large-scale industrial application. Therefore, in recent years, researchers have been working on non-noble metal hydrogen evolution electrocatalysts that can be used in large-scale industrial applications.

Transition metals and their alloys, represented by cobalt, nickel, iron, etc., are considered as promising candidate materials to replace noble metal catalysts due to their theoretically high catalytic activity and low price. However, single metal nanomaterials There is a problem of easy oxidation and agglomeration, which will drastically deteriorate its catalytic activity, and it is easily corroded in acid and alkaline electrolytes and loses its catalytic activity. Combining transition metals with carbon matrix materials with good conductivity to obtain composite materials can effectively solve the above problems. However, there are still many problems in this material system, such as poor stability and slow charge transport caused by poor conductivity of carbon materials.

Due to the 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 The degree of graphitization of the material is high, which improves the conductivity of the composite material. The material is porous and has a large specific surface area, which is conducive to generating more catalytic active sites, accelerating the carrier transmission and separation process, and improving catalytic performance.

Contents of the invention

The purpose of the present invention is to provide a preparation method of transition metal/nitrogen-doped carbon composite material, the prepared material can be any single transition metal/nitrogen-doped carbon composite material, but also can be multiple transition metal alloy/nitrogen-doped carbon composites. Under the premise of ensuring that the metal and alloy nanoparticles have a small size and are uniformly 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. The method has the advantages of simple process, rapid reaction process and environmental friendliness, which is of great significance for the practical application of hydrogen evolution electrocatalysts.

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

(1) Using a certain mass ratio of transition metal precursors and carbon sources 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, molybdenum, etc., and the precursor is zero-valent metal, chloride salt, nitrate, sulfate, etc. One or more of them; further preferably, the precursors of transition metals such as cobalt, nickel, and iron are zero-valent metals, chloride salts, nitrates, sulfates, etc., while precursors such as tungsten and molybdenum are zero-valent metals, oxidation One or more of compounds, tungstates or molybdates; the carbon source is nitrogen-containing or nitrogen-free solid organic precursors such as melamine, dicyandiamide, glucose, etc., or nitrogen-containing or non-containing gases that can produce carbon, such as methane, acetylene, etc.; if the carbon source does not contain nitrogen or the amount of nitrogen contained is not enough, an additional input of nitrogen can be used as a carrier gas in the high-frequency induction thermal plasma reaction. Add nitrogen.

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

The high-frequency induction thermal plasma technology adopted 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 1-100KW, preferably 10-30KW.

The precursor raw material is sent to the hot plasma region by the carrier gas for reaction, and 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 gas, The precursor is fed separately), 5-500g min ^-1 , preferably 10-30g min ^-1 . When the carbon source is a gas, the carbon source is used as a carrier gas; the carrier gas is also one or more of argon, hydrogen, and nitrogen; the flow rate of any carrier gas is 0.01-10m ³ h ^-1 , preferably 0.1～5m ³ h ^-1 .

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

The transition metal/nitrogen-doped composite material reaches the collection system along with the gas flow for collection.

The 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. Composite materials, in which the particle size of metal nanoparticles is below 10nm, and they are evenly distributed in the nitrogen-doped carbon matrix material, which effectively inhibits the agglomeration and oxidation of nanoparticles; the porous structure also ensures that the obtained material has a large specific surface area, It is beneficial to expose more active sites during the hydrogen evolution catalytic reaction. The graphitization degree of the carbon matrix material of the composite material is relatively high, which is beneficial to the charge transport process and improves the catalytic activity. The method has the advantages of simple process, rapid reaction process and environmental friendliness, which is of great significance for the practical application of hydrogen evolution electrocatalysts.

Description of drawings

Fig. 1 is the TEM photo (a) and the HRTEM photo (b) of the cobalt/nitrogen doped carbon material hydrogen evolution electrocatalyst prepared in Example 1 of the present invention.

Fig. 2 is the XRD spectrum of the cobalt/nitrogen doped carbon material hydrogen evolution electrocatalyst prepared in Example 1 of the present invention.

Fig. 3 is the Raman spectrum of the cobalt/nitrogen-doped carbon material hydrogen evolution electrocatalyst prepared in Example 1 of the present invention.

Fig. 4 is the high-angle annular dark field-scanning transmission electron microscope image (a) and the element distribution diagram (b,c,d) of cobalt/nitrogen-doped carbon material hydrogen evolution electrocatalyst prepared in Example 1 of the present invention .

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

Fig. 6 is the polarization curve (a) of the cobalt/nitrogen-doped carbon material hydrogen evolution electrocatalyst prepared in Example 1 of the present invention in 1M KOH electrolyte solution (a) and the stability (b) at a current density of 10mA cm ^-2 .

Detailed ways

In order to better illustrate the contents of the present invention, the present invention will be further described below in conjunction with examples, but the present invention is not limited to the following examples.

Example 1

(1) Weigh 500g of cobalt chloride and 1500g of melamine according to the mass ratio of 1:3 and mix them mechanically as a precursor.

(2) Preparation of cobalt/nitrogen-doped carbon composite materials: 10KW plasma device is used, mainly composed of plasma generation system, stainless steel reactor, plasma lamp, feeding system, gas distribution system, product collection system, and exhaust gas emission system. Argon gas was fed into the plasma system as the central gas to form a plasma, and the precursor obtained in step (1) was added using a feeding system after the arc was stabilized 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 to obtain a cobalt/nitrogen-doped carbon composite material in the product collection system.

The structure and hydrogen evolution performance of the cobalt/nitrogen doped composite material prepared above were characterized, as shown in Figure 1-5. Figure 1 is a TEM photo of the cobalt/nitrogen doped composite material. It can be seen from the low-magnification photo that the microscopic appearance of the material presents a state where nanoparticles are uniformly distributed in the matrix. It can be seen from the high-power photo that the nanoparticle crystal plane The spacing is 0.204 nm, corresponding to the (111) crystal plane of metallic cobalt, while the matrix interplanar spacing is 0.34 nm, corresponding to the (001) crystal plane of graphitic carbon. Figure 2 is the XRD pattern of the cobalt/nitrogen-doped composite material, where the diffraction peaks at 26° correspond to graphitic carbon, and the diffraction peaks at 44.2°, 51.5° and 75.85° correspond to metallic cobalt. Figure 3 is the Raman spectrum of the cobalt/nitrogen-doped composite material. The peaks at 1350cm ^-1 and 1600cm ^-1 correspond to the D peak and the G peak, respectively, where the D peak represents the defect of the C atom lattice, and the G peak represents the C atom sp ^2. The in-plane stretching vibration of hybridization, the ratio of the intensity of D peak and G peak indicates that the carbon matrix has a higher degree of graphitization. Figure 4 is the high-angle annular dark field-scanning transmission electron microscope image of the cobalt/nitrogen doped composite material and the element distribution map of C, Co, and N. It can be seen that the elements of C, Co, and N are evenly distributed, and the element N is successfully explained. doping. Fig. 5 is the nitrogen adsorption-desorption curve and pore size distribution diagram of the cobalt/nitrogen doped composite material, the specific surface area is 76.8m ² /g, and the average pore size is 3.82nm. Figure 6 shows the hydrogen evolution performance of the cobalt/nitrogen-doped composite material. The overpotential required to achieve a current density of 10mA cm ^-2 in 1M KOH electrolyte is only 180mV, and as shown in Figure 5b, the stability after 10h After the test, there was almost no degradation in performance.

Example 2

(1) Weigh 500g nickel nitrate and 1500g dicyandiamide according to the mass ratio of 1:3 and mix them to obtain the precursor.

(2) Preparation of nickel/nitrogen-doped carbon composite materials: 10KW plasma device is used, which is mainly composed of plasma generation system, stainless steel reactor, plasma lamp, feeding system, gas distribution system, product collection system, and tail gas discharge system. Argon gas was fed into the plasma system as the central gas to form a plasma, and the precursor obtained in step (1) was added using the feeding system after the arc was stabilized at a feeding rate of 15 g min ^-1 . The carrier gas is hydrogen, and the gas flow rate is 0.1 m ³ h ^-1 . After the material is consumed, the reaction device is closed and the nickel/nitrogen-doped carbon composite material is obtained in the product collection system.

Example 3

(1) Weigh 200g of nickel sulfate and 300g of ammonium molybdate, and mix them as the precursor of nickel-molybdenum alloy.

(2) Preparation of nickel-molybdenum alloy/nitrogen-doped carbon composite material: a 10KW plasma device is used, mainly composed 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 discharge system composition. Argon gas was fed into the plasma system as the central gas to form a plasma, and the precursor obtained in step (1) was added using a feeding system after the arc was stabilized at a feeding rate of 10 g min ^-1 . The carrier gas is a mixture of acetylene, nitrogen and hydrogen, and the flow rates are 1.5m ³ h ^-1 , 0.1m ³ h ^-1 and 0.05m ³ h ^-1 , respectively. After the material is consumed, the reaction device is closed and the nickel-molybdenum alloy/nitrogen-doped carbon composite material is obtained in the product collection system.

Example 4

According to the mass ratio of 1:1:3, 250g of cobalt chloride, 250g of nickel chloride, and 1500g of glucose were weighed and mixed to obtain the precursor.

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

Example 5

(1) According to the mass ratio of 1:3, 500g iron powder (74μm) and 1500g dicyandiamide were weighed and mixed mechanically as a precursor.

(2) Preparation of iron/nitrogen-doped carbon composite materials: 10KW plasma device is used, mainly composed of plasma generation system, stainless steel reactor, plasma lamp, feeding system, gas distribution system, product collection system, and tail gas discharge system. Argon gas was fed into the plasma system as the central gas to form plasma, and the precursor obtained in step (1) was added using the feeding system after the arc was stabilized 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 iron/nitrogen-doped carbon composite material is obtained in the product collection system, wherein the size of iron nanoparticles in the composite material is less than 10nm.

Claims (8)

1. a preparation method of transition metal/nitrogen-doped porous carbon nanocomposite material, is characterized in that, comprises the following steps: (1) Using a certain mass ratio of transition metal precursors and carbon sources as precursor raw materials; (2) Transition metal/nitrogen-doped carbon composites were prepared by high-frequency induction thermal plasma technology. 2. according to the preparation method of a kind of transition metal/nitrogen doped porous carbon nanocomposite material according to claim 1, it is characterized in that, in step (1), described transition metal is selected from cobalt, nickel, iron, tungsten, One or more of molybdenum, etc., the precursor is one or more of zero-valent metals, chloride salts, nitrates, sulfates, etc.; more preferably cobalt, nickel, iron and other transition metal precursors The precursors are zero-valent metals, chloride salts, nitrates, sulfates, etc., while the precursors such as tungsten and molybdenum 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, or a nitrogen-containing or non-nitrogen-containing gas that can produce carbon; if the carbon source does not contain nitrogen or contains insufficient nitrogen, it can be used at high During the frequency induction thermal plasma reaction, an additional input of nitrogen gas is used as a carrier gas to supplement the nitrogen element. 3. A method for preparing a transition metal/nitrogen-doped porous carbon nanocomposite according to claim 1, wherein the mass ratio of the transition metal precursor to the carbon source is 1:0.1 to 10, preferably 1 :0.5～5. 4. according to the preparation method of a kind of transition metal/nitrogen-doped porous carbon nanocomposite material according to claim 1, it is characterized in that, the high-frequency induction thermal plasma technique adopted in the step (2) specifically comprises the following steps: High-frequency induction thermal plasma device for generating stable thermal plasma; thermal plasma power is 1-100KW, preferably 10-30KW; The precursor raw material is sent to the thermal plasma area for reaction through the carrier gas, the solid feed rate is 5-500g min ^-1 , preferably 10-30g min ^-1 ; when the carbon source is gas, the carbon source is used as a carrier gas The carrier gas is one or more of argon, hydrogen and nitrogen; the flow rate of any one of the carrier gases is 0.01-10m ³ h ^-1 , preferably 0.1-5m ³ h ^-1 ; Raw materials undergo gasification, reaction, condensation, and precipitation processes in the hot plasma area; The transition metal/nitrogen-doped composite material reaches the collection system along with the gas flow for collection. 5. according to the preparation method of a kind of transition metal/nitrogen-doped porous carbon nanocomposite according to claim 4, it is characterized in that, solid feed: when carbon source is solid organic precursor, transition metal precursor and carbon source Mix and feed evenly; when the carbon source is gas, the transition metal precursor is fed separately. 6. A transition metal/nitrogen-doped porous carbon nanocomposite prepared by the method according to any one of claims 1-5. 7. A kind of transition metal/nitrogen-doped porous carbon nanocomposite prepared according to the method described in any one of claims 1-5, it is characterized in that metal is in the form of nanoparticles, and is uniformly distributed in the nitrogen-doped In the carbon matrix material, the particle size of metal nanoparticles is below 10nm. 8. The application of a kind of transition metal/nitrogen-doped porous carbon nanocomposite material prepared according to the method described in any one of claims 1-5, which is used for electrolysis of water and hydrogen evolution.

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