CN114784299A - Nitrogen-sulfur doped carbon material and preparation method and application thereof - Google Patents

Abstract

The present invention provides a nitrogen-sulfur doped carbon material and a preparation method and application thereof. The preparation method comprises: a first mixed metal organic framework compound solution and a cysteine solution; after the first solid-liquid separation to obtain a precursor material calcining to obtain the nitrogen-sulfur-doped carbon material. The preparation method of the nitrogen-sulfur doped carbon material of the present invention has the advantages of environmental protection, low cost, simple and controllable synthesis process, high consistency and easy realization of mass production; the nitrogen-sulfur doped carbon material has excellent ORR catalytic performance , the ORR catalytic performance of the nitrogen-sulfur doped carbon material exceeds that of commercial noble metal platinum-carbon catalysts, and has high practical application potential.

Description

A kind of nitrogen-sulfur doped carbon material and its preparation method and application

technical field

The invention belongs to the technical field of fuel cells, and relates to a preparation method of a nitrogen-sulfur-doped carbon material, in particular to a nitrogen-sulfur-doped carbon material and a preparation method and application thereof.

Background technique

In the stack of fuel cells, the oxygen reduction reaction (ORR) on the cathode mainly employs catalysts to overcome the slow kinetic process. Cathode catalyst is the main factor affecting the activation polarization of fuel cells and is regarded as the core key material of fuel cells. At present, the most widely used catalyst in business is still the supported catalyst Pt/C, but Pt-based materials have disadvantages such as high cost (about 20% of the fuel cell cost), easy dissolution and easy agglomeration in working conditions. It is of great significance to study highly active non-precious metal catalysts to reduce the cost of fuel cells.

Carbon materials are rich in natural resources, low in price, and have the advantages of good electrical conductivity and strong corrosion resistance. However, the catalytic effect of pure carbon on oxygen reduction is far from the requirements. Through a large number of experiments, researchers have proved that transition metal (Fe, Co, etc.) and heteroatom (N, S, etc.) doped carbon materials show excellent performance. The high ORR activity of these carbon materials is attributed to the synergistic effect of transition metals and heteroatoms with the carbon matrix to generate a large number of active sites. Therefore, the synthesized carbon-based catalysts are required to possess the characteristics of high active site density, tunable pore structure, high specific surface area, good stability, high atomic doping content, and uniformly distributed active sites. In order to make non-metal doped carbon materials have the above characteristics, the most effective method is to select appropriate precursors doped with transition metals and heteroatoms. Metal-organic frameworks (MOFs) are characterized by their tunable, modifiable, and easily functionalized structures. Using them as precursors to construct carbon-based catalytic materials has unique advantages in heteroatom doping, particle confinement, and pore design. . In the current reports on the use of metal-organic framework materials as precursors, a variety of organic solvents are used in the preparation process, which is not environmentally friendly, and the preparation process is complicated and the production cost is high. It is mainly in the laboratory stage, which is not convenient for large-scale application.

CN109745950A discloses a method and application for preparing micro-mesoporous carbon positive electrode material by modifying metal organic framework with amino acid. It includes the synthesis of amino acid-modified metal-organic framework materials, the pretreatment of metal-organic framework materials, carbonization reaction and other steps. of nitrogen-doped porous carbon materials. However, the method for preparing the micro-mesoporous carbon cathode material by modifying the metal-organic framework with amino acid has high cost and poor catalytic performance for oxygen reduction reaction.

CN112591738A discloses a metal-doped graphene-like carbon material and its preparation method and application, which belong to the field of materials. The method uses clay as a template and metal-organic complex as a raw material to prepare a metal-doped graphene-like carbon material through the processes of intercalation, dispersion, adsorption, coordination, drying, carbonization and template removal. However, the metal-doped graphene-like carbon material and the preparation method thereof cannot obtain a catalyst with strong oxygen reduction reaction catalytic performance.

CN114204207A discloses a preparation method of a dual-function lithium-air battery composite diaphragm, comprising the following steps: using a variety of hydrated transition metal nitric acid salts and imidazoles containing nitrile groups as raw materials to prepare multi-metal synergistic catalytic MOFs; The surface of the synergistically catalyzed MOFs is modified by the click reaction of hydrophobic alkyl chains to realize the superhydrophobic functionalization of MOFs; the synthesized superhydrophobicized multi-metal synergistic catalyzed MOFs, binders, conductive agents and organic solvents are slurried The slurry is coated on the base film to obtain a composite separator for a bifunctional lithium-air battery. However, the preparation method of the dual-function lithium-air battery composite separator is complex, the preparation cost is high, and a large amount of organic solvent is used, which will cause pollution to the environment.

The currently disclosed cathode catalysts for fuel cells and their preparation methods have certain defects, such as complex preparation methods, uncontrollable processes, high production costs, environmental pollution, and poor oxygen reduction reaction catalytic performance of the cathode catalysts. . Therefore, a novel nitrogen-sulfur-doped carbon material and its preparation method were developed and designed.

SUMMARY OF THE INVENTION

In view of the deficiencies in the prior art, the purpose of the present invention is to provide a nitrogen-sulfur doped carbon material and a preparation method and application thereof. The advantages of simple and controllable, high consistency and easy to achieve mass production; the nitrogen-sulfur-doped carbon material has excellent ORR catalytic performance, the ORR catalytic performance of the nitrogen-sulfur-doped carbon material exceeds that of commercial precious metal platinum carbon catalyst, and has High practical application potential.

In order to achieve this object of the invention, the present invention adopts the following technical solutions:

In a first aspect, the present invention provides a method for preparing a nitrogen-sulfur-doped carbon material, the preparation method comprising:

The first mixture of the metal organic framework compound solution and the cysteine solution, and the first solid-liquid separation to obtain a precursor material, followed by calcination, to obtain the nitrogen-sulfur doped carbon material.

In the present invention, the metal-organic framework compound contains nitrogen, and cysteine contains sulfur. After the precursor material is carbonized at high temperature, nitrogen and sulfur are uniformly distributed in the carbon skeleton of the nitrogen-sulfur-doped carbon material; and sulfur doping, there are a large number of _unconjugated carbon structures, namely carbon defects, in nitrogen-sulfur doped carbon materials, which in turn generate more active sites. The numerical range of _G is: 1.05～1.89.

The nitrogen-sulfur-doped carbon material of the present invention is used as a catalyst for oxygen reduction reaction, and under alkaline conditions, the half-wave potential is not lower than 0.83V, and the current density is not lower than 5.35mA/cm ² .

The preparation method of the nitrogen-sulfur doped carbon material of the present invention has the advantages of environmental protection, low cost, simple and controllable synthesis process, high consistency and easy realization of mass production; the nitrogen-sulfur doped carbon material has excellent ORR catalytic performance , the ORR catalytic performance of the nitrogen-sulfur doped carbon material exceeds that of commercial noble metal platinum-carbon catalysts, and has high practical application potential.

Preferably, the volume ratio of the metal organic framework compound solution to the cysteine solution is (2-12):1, for example, 2:1, 3:1, 4:1, 5:1, 6:1 , 7:1, 8:1, 9:1, 10:1, 11:1 or 12:1, but are not limited to the recited data, and other unrecited values within the range are also applicable.

Preferably, the mass ratio of the solute in the metal organic framework compound solution to the solute in the cysteine solution is 4:(0.1-1), for example, 4:0.1, 4:0.2, 4:0.3, 4:0.4 , 4:0.5, 4:0.6, 4:0.7, 4:0.8, 4:0.9 or 4:1, but not limited to the listed data, other unlisted values within the numerical range are also applicable; when the metal organic framework When the mass ratio of the solute in the compound solution to the solute in the cysteine solution is low, the half-wave potential will decrease and the current density will decrease. Sufficient active sites are generated; when the mass ratio of the solute in the metal-organic framework compound solution to the solute in the cysteine solution is high, it will lead to a lower half-wave potential and a decrease in the current density, which is due to the excess half-wave potential. The doping of cystine may lead to the collapse of the metal-organic framework, changing the intrinsic morphology and leading to a decrease in activity.

Preferably, the solvent of the cysteine solution includes methanol and/or water.

The solvent required in the preparation process of the nitrogen-sulfur doped carbon material of the present invention is only methanol or deionized water, the use of various organic solvents is avoided, and the preparation conditions are environmentally friendly.

Preferably, the temperature of the first mixing is 15-35° C., and the time is 1-5 h.

The present invention defines the temperature of the first mixing to be 15 to 35°C, for example, it can be 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C , 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C or 35°C, but not limited to the listed data, other unlisted values within the numerical range are the same Be applicable.

The present invention defines the first mixing time as 1-5h, for example, it can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, but it is not limited to the listed data, the numerical value The same applies to other non-recited values in the range.

Preferably, the first mixing method includes stirring and/or sonication.

Preferably, the first solid-liquid separation comprises centrifugation, washing and drying performed in sequence.

Preferably, the calcining includes sequential temperature increase and heat preservation.

Preferably, the heating rate is 2-10°C/min, and the end temperature of the heating is 800-1000°C.

The present invention defines the heating rate to be 2-10°C/min, for example, it can be 2°C/min, 3°C/min, 4°C/min, 5°C/min, 6°C/min, 7°C/min, 8°C /min, 9°C/min or 10°C/min, but are not limited to the recited data, other non-recited values within the numerical range are also applicable.

The present invention defines the end temperature of the temperature rise as 800-1000°C, for example, it can be 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C or 1000°C, but not limited to the listed data, other non-recited values within this numerical range are also applicable .

The end temperature of the temperature increase in the present invention is the holding temperature. When the holding temperature is too low or high, the half-wave potential will become lower and the current density will decrease. This is due to the graphitization of the catalyst when the temperature is 800-1000°C. A higher degree is more conducive to the improvement of the electrochemical activity of the catalyst.

Preferably, the incubation time is 2-4h, such as 2h, 2.2h, 2.4h, 2.6h, 2.8h, 3h, 3.2h, 3.4h, 3.6h, 3.8h or 4h, but not limited to For the recited data, other non-recited values within this numerical range also apply.

Preferably, the calcination is carried out in a protective atmosphere comprising nitrogen and/or inert gases.

Preferably, the preparation method of the metal organic framework compound solution comprises the following steps:

The nitrogen-containing ligand solution and the transition metal salt solution are mixed secondly, the metal organic framework compound is obtained after the second solid-liquid separation, and the metal organic framework compound solution is obtained after mixing the metal organic framework compound with methanol and/or water.

Preferably, the solute of the nitrogen-containing ligand solution includes any one or a combination of at least two of 2-methylimidazole, potassium ferricyanide, potassium ferrocyanide or potassium cobalt cyanide, typically but not limited to Sexual combinations include the combination of 2-methylimidazole and potassium ferricyanide, the combination of potassium ferricyanide and potassium ferrocyanide, the combination of potassium ferrocyanide and potassium cobalt cyanide, 2-methylimidazole, iron A combination of potassium cyanide and potassium ferrocyanide, or a combination of 2-methylimidazole, potassium ferricyanide, potassium ferrocyanide, and potassium cobalt cyanide.

In the preparation process of the metal-organic framework compound solution in the present invention, the nitrogen-containing ligand is used as a nitrogen source to enter the metal-organic framework compound.

Preferably, the solvent of the nitrogen-containing ligand solution includes methanol and/or water.

Preferably, the solute of the transition metal salt solution includes any one or a combination of at least two of cobalt nitrate, ferric nitrate, nickel nitrate, zinc nitrate or ferric chloride, and a typical but non-limiting combination includes cobalt nitrate and Combination of iron nitrate, combination of iron nitrate and nickel nitrate, combination of nickel nitrate and zinc nitrate, combination of zinc nitrate and iron chloride, combination of cobalt nitrate, iron nitrate and nickel nitrate, or combination of iron nitrate, nickel nitrate, zinc nitrate In combination with ferric chloride.

Preferably, the solvent of the transition metal salt solution includes methanol and/or water.

Preferably, the volume ratio of the nitrogen-containing ligand solution to the transition metal salt solution is (0.8-1.2):1, for example, 0.8:1, 0.85:1, 0.9:1, 0.95:1, 1:1, 1.05:1, 1.1:1, 1.15:1 or 1.2:1, but are not limited to the recited data, other non-recited values within the numerical range also apply.

Preferably, the mass ratio of the solute in the nitrogen-containing ligand solution to the solute in the transition metal salt solution is (1-100):1, such as 1:1, 1.5:1, 2:1, 3:1, 5:1, 7:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, or 100:1, but not Not limited to the recited data, other non-recited values within this numerical range are equally applicable.

Preferably, the temperature of the second mixing is 15-35° C., and the time is 1-5 h.

The present invention defines the temperature of the second mixing to be 15-35°C, for example, it can be 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C , 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C or 35°C, but not limited to the listed data, other unlisted values within the numerical range are the same Be applicable.

The present invention defines the second mixing time to be 1-5h, for example, it can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, but it is not limited to the listed data, the numerical value The same applies to other non-recited values in the range.

Preferably, the second mixing method includes stirring and/or sonication.

Preferably, the second solid-liquid separation includes centrifugation, washing and drying performed in sequence.

Preferably, as the preferred technical solution of the preparation method described in the first aspect, the preparation method comprises the following steps:

(1) Mix the nitrogen-containing ligand solution and the transition metal salt solution with a volume ratio of (0.8-1.2):1 under stirring and/or ultrasonic for 1-5 hours at 15-35°C, and the solute in the nitrogen-containing ligand solution is mixed with the transition metal salt solution. The mass ratio of the solute in the transition metal salt solution is (1～100):1; the metal organic framework compound is obtained after centrifugation, washing and drying in sequence, and the metal organic framework compound solution is obtained after mixing the metal organic framework compound with methanol and/or water ;

(2) The metal organic framework compound solution and the cysteine solution obtained in the step (1) obtained in the step (1) with stirring and/or ultrasonic mixing for 1 to 5 hours at a volume ratio of (2 to 12): 1 at 15 to 35° C., the metal organic framework The mass ratio of the solute in the framework compound solution to the solute in the cysteine solution is 4:(0.1～1); centrifugation, washing and drying are performed in sequence to obtain the precursor material, and then the temperature is 2～10°C/min in a protective atmosphere. The temperature is increased to 800-1000° C. at a heating rate of 2-4 hours, and the nitrogen-sulfur doped carbon material is obtained.

In a second aspect, the present invention provides a nitrogen-sulfur-doped carbon material obtained by the preparation method described in the first aspect.

The nitrogen-sulfur-doped carbon material of the invention has uniform size distribution and maintains the original morphology of the precursor material, effectively solves the problem of agglomeration of transition metal atoms, and helps to further improve catalytic activity through effective compounding with heteroatoms.

Preferably, based on the mass of the nitrogen-sulfur-doped carbon material, the mass fraction of the transition metal in the nitrogen-sulfur-doped carbon material is 2.22-8.50 wt %, for example, 2.22 wt %, 2.3 wt %, 2.5 wt % , 2.7wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt% or 8.5wt%, but not only Limited to the recited data, other non-recited values within this numerical range also apply.

In a third aspect, the present invention provides an application of the nitrogen-sulfur-doped carbon material according to the second aspect, wherein the nitrogen-sulfur-doped carbon material is used as a cathode catalyst of a fuel cell.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The preparation method of the nitrogen-sulfur-doped carbon material of the present invention has the advantages of low cost, simple and controllable synthesis process, high consistency, and easy realization of mass production. The preparation process of the nitrogen-sulfur-doped carbon material requires The solvent used is only methanol or deionized water, avoiding the use of various organic solvents, and the preparation conditions are environmentally friendly;

(2) The nitrogen-sulfur-doped carbon material of the present invention has a uniform size distribution and maintains the original morphology of the precursor material, which effectively solves the problem of agglomeration of transition metal atoms, and helps to further improve the catalytic activity;

(3) In the present invention, the metal organic framework compound contains nitrogen, and cysteine contains sulfur. After the precursor material is carbonized at high temperature, nitrogen and sulfur are uniformly distributed in the carbon framework of the nitrogen-sulfur-doped carbon material. Due to the doping of nitrogen and sulfur elements, there are a large number of unconjugated carbon structures in nitrogen-sulfur doped carbon materials, that is, carbon defects, which in turn generate more active sites. The description of the degree of defects and the degree of graphitization The numerical range of the symbol ID / _IG is: _1.05 ～1.89;

(4) The nitrogen-sulfur-doped carbon material of the present invention is used as a catalyst for oxygen reduction reaction. Under alkaline conditions, the half-wave potential is not lower than 0.83V, and the current density is not lower than 5.35mA/cm ² . The ORR catalytic performance of sulfur-doped carbon materials exceeds that of commercial noble metal platinum-carbon catalysts and has high potential for practical applications.

Description of drawings

FIG. 1 is a scanning electron microscope image of the precursor material in Example 1. FIG.

FIG. 2 is a transmission electron microscope image of the nitrogen-sulfur-doped carbon material in Example 1. FIG.

FIG. 3 is a C element distribution diagram of the nitrogen-sulfur-doped carbon material in Example 1. FIG.

FIG. 4 is a diagram showing the S element distribution of the nitrogen-sulfur-doped carbon material in Example 1. FIG.

FIG. 5 is an N element distribution diagram of the nitrogen-sulfur-doped carbon material in Example 1. FIG.

FIG. 6 is a Raman spectrum diagram of the nitrogen-sulfur-doped carbon material in Example 1. FIG.

7 is the X-ray diffraction pattern of the precursor material in Example 1, Example 6, and Example 7 and Co-ZIF in Comparative Example 1.

FIG. 8 is a graph comparing the linear sweep voltammetry curves of the nitrogen-sulfur doped carbon material in Example 1 and the commercial 20% Pt/C electrode in Comparative Example 2. FIG.

FIG. 9 is a graph comparing the linear sweep voltammetry curves of the nitrogen-sulfur doped carbon material in Example 2 and the commercial 20% Pt/C electrode in Comparative Example 2. FIG.

10 is a graph comparing the linear sweep voltammetry curves of the nitrogen-sulfur doped carbon material in Example 3 and the commercial 20% Pt/C electrode in Comparative Example 2.

FIG. 11 is a graph comparing the linear sweep voltammetry curves of the nitrogen-sulfur doped carbon material in Example 4 and the commercial 20% Pt/C electrode in Comparative Example 2. FIG.

Detailed ways

The technical solutions of the present invention are further described below through specific embodiments. It should be understood by those skilled in the art that the embodiments are only for helping the understanding of the present invention, and should not be regarded as a specific limitation of the present invention.

Example 1

This embodiment provides a method for preparing a nitrogen-sulfur doped carbon material, and the preparation method includes the following steps:

(1) The mass of 2-methylimidazole methanol solution and cobalt nitrate methanol solution, the solute in 2-methylimidazole methanol solution and the solute in cobalt nitrate methanol solution with a volume ratio of 1:1 under stirring for 4 hours at 25°C The ratio is 50:1; the metal organic framework compounds (Co-ZIFs) are obtained after centrifugation, washing and drying in sequence, and the Co-ZIFs methanol solution is obtained after mixing Co-ZIFs and methanol;

(2) The Co-ZIFs methanol solution and the cysteine aqueous solution obtained in the step (1) were stirred for 3 h at 25°C and the volume ratio was 5:1, and the solute in the Co-ZIFs methanol solution was mixed with the cysteine aqueous solution. The mass ratio of the solute is 4:0.5; centrifugation, washing and drying are performed in sequence to obtain the precursor material, and then the temperature is raised to 950°C at a heating rate of 6°C/min in nitrogen and kept for 2.5h to obtain the nitrogen-sulfur doped carbon. materials, based on the mass of the nitrogen-sulfur-doped carbon material, the mass fraction of transition metals in the nitrogen-sulfur-doped carbon material is 5.4 wt %.

The SEM image of the precursor material obtained by scanning the precursor material with a scanning electron microscope is shown in Figure 1;

The scanning electron microscope image of nitrogen-sulfur-doped carbon material obtained by scanning the nitrogen-sulfur-doped carbon material by transmission electron microscope is shown in Figure 2, the C element distribution is shown in Figure 3, the S element distribution is shown in Figure 4, and the N element is shown in Figure 4. The distribution diagram is shown in Figure 5;

Figure 6 shows the Raman spectrum of the nitrogen-sulfur-doped carbon material obtained by the Raman spectrometer.

Example 2

This embodiment provides a method for preparing a nitrogen-sulfur doped carbon material, and the preparation method includes the following steps:

(1) The mass ratio of 2-methylimidazole methanol solution and ferric nitrate methanol solution, the solute in 2-methylimidazole methanol solution and the ferric nitrate methanol solution with a volume ratio of 1.1:1 was mixed by ultrasonic for 3 hours at 20°C. The ratio is 30:1; centrifugation, washing and drying are performed in sequence to obtain metal organic framework compounds (Fe-ZIFs), and Fe-ZIFs methanol solution is obtained after mixing Fe-ZIFs and methanol;

(2) The Fe-ZIFs methanol solution and the cysteine aqueous solution obtained in the step (1) were mixed by ultrasonic for 2 h at 30°C with a volume ratio of 7:1, the solute in the Fe-ZIFs methanol solution and the cysteine aqueous solution The mass ratio of the solute is 4:0.3; centrifugation, washing and drying are performed in sequence to obtain the precursor material, and then the temperature is raised to 900°C at a heating rate of 8°C/min in nitrogen and kept for 3h to obtain the nitrogen-sulfur doped carbon material. , based on the mass of the nitrogen-sulfur-doped carbon material, the mass fraction of transition metals in the nitrogen-sulfur-doped carbon material is 3.8 wt %.

Example 3

This embodiment provides a method for preparing a nitrogen-sulfur doped carbon material, and the preparation method includes the following steps:

(1) at 30° C. with 2h of ultrasonic mixing volume ratio of 0.8:1 potassium ferrocyanide aqueous solution and nickel nitrate aqueous solution, the mass ratio of the solute in the potassium ferrocyanide aqueous solution to the solute in the nickel nitrate aqueous solution is 80: 1; the metal organic framework compound (FeNi-PBA) is obtained after centrifugation, washing and drying in sequence, and FeNi-PBA aqueous solution is obtained after mixing FeNi-PBA and water;

(2) The FeNi-PBA aqueous solution and the cysteine methanol solution obtained in the step (1) in which the volume ratio was 10:1 under stirring for 4 h at 20° C., the solute in the FeNi-PBA aqueous solution and the cysteine methanol solution The mass ratio of the solute is 4:0.8; centrifugation, washing and drying are performed in sequence to obtain the precursor material, and then the temperature is raised to 850°C at a heating rate of 4°C/min in argon and kept for 3.5h to obtain the nitrogen-sulfur doped material. The carbon material is based on the mass of the nitrogen-sulfur-doped carbon material, and the mass fraction of the transition metal in the nitrogen-sulfur-doped carbon material is 6.50 wt %.

Example 4

This embodiment provides a method for preparing a nitrogen-sulfur doped carbon material, and the preparation method includes the following steps:

(1) at 15° C., the volume ratio of the cobalt potassium cyanide aqueous solution and the nickel nitrate aqueous solution is 0.8:1 with stirring for 5 hours, and the mass ratio of the solute in the cobalt potassium cyanide aqueous solution and the solute in the nickel nitrate aqueous solution is 1:1; The metal organic framework compound (CoNi-PBA) is obtained after centrifugation, washing and drying in sequence, and the CoNi-PBA aqueous solution is obtained after mixing CoNi-PBA and water;

(2) The CoNi-PBA aqueous solution and the cysteine aqueous solution obtained in the step (1) in which the volume ratio of ultrasonic mixing for 1 h at 35°C is 2:1, and the ratio of the solute in the CoNi-PBA aqueous solution to the solute in the cysteine aqueous solution The mass ratio is 4:0.1; centrifugation, washing and drying are performed in sequence to obtain the precursor material, and then the precursor material is heated to 800°C at a heating rate of 10°C/min in helium gas and kept for 4 hours to obtain the nitrogen-sulfur doped carbon material, Based on the mass of the nitrogen-sulfur-doped carbon material, the mass fraction of transition metals in the nitrogen-sulfur-doped carbon material is 2.22 wt %.

Example 5

This embodiment provides a method for preparing a nitrogen-sulfur-doped carbon material, and the preparation method includes the following steps:

(1) Mix 2-methylimidazole methanol solution and ferric chloride methanol solution, the solute in 2-methylimidazole methanol solution and the solute in ferric chloride methanol solution with a volume ratio of 1.2:1 under stirring for 1 h at 35°C The mass ratio of Fe-ZIFs is 100:1; the metal organic framework compounds (Fe-ZIFs) are obtained after centrifugation, washing and drying in sequence, and Fe-ZIFs methanol solution is obtained after mixing Fe-ZIFs and methanol;

(2) The Fe-ZIFs methanol solution and the cysteine methanol solution obtained in step (1) were mixed at a volume ratio of 12:1 under stirring for 5 h at 15 °C, and the solute in the Fe-ZIFs methanol solution was mixed with cysteine methanol The mass ratio of the solute in the solution is 4:1; centrifugation, washing and drying are carried out in sequence to obtain the precursor material, and then the temperature is raised to 1000°C at a heating rate of 2°C/min in nitrogen and kept for 2h to obtain the nitrogen-sulfur doped material. The carbon material is based on the mass of the nitrogen-sulfur-doped carbon material, and the mass fraction of the transition metal in the nitrogen-sulfur-doped carbon material is 8.50 wt %.

Example 6

This example provides a method for preparing a nitrogen-sulfur doped carbon material, which is the same as Example 1 except that the mass ratio of the solute in the Co-ZIFs methanol solution to the solute in the cysteine aqueous solution is 4:0.05.

Example 7

This example provides a method for preparing a nitrogen-sulfur doped carbon material, which is the same as Example 1 except that the mass ratio of the solute in the Co-ZIFs methanol solution to the solute in the cysteine aqueous solution is 4:1.5.

Example 8

This embodiment provides a method for preparing a nitrogen-sulfur doped carbon material, which is the same as in Example 1, except that the precursor material is heated to 700°C at a heating rate of 6°C/min in nitrogen and kept for 2.5h.

Example 9

This embodiment provides a method for preparing a nitrogen-sulfur doped carbon material, which is the same as Example 1 except that the precursor material is heated to 1100°C at a heating rate of 6°C/min in nitrogen and kept for 2.5h.

Comparative Example 1

This comparative example provides Co-ZIFs, which are the same as the Co-ZIFs in Example 1.

Comparative Example 2

This comparative example provides a commercial 20% Pt/C electrode.

The X-ray diffraction patterns obtained by X-ray diffraction of the precursor materials in Example 1, Example 6, and Example 7 and Co-ZIF in Comparative Example 1 are shown in Figure 7;

The nitrogen-sulfur doped carbon materials in Examples 1 to 9, the Co-ZIFs in Comparative Example 1, and the commercial 20% Pt/C electrodes in Comparative Example 2 were used for electrochemical tests to obtain linear sweep voltammetry curves. The electrochemical test method was as follows: : Take 0.1MKOH solution as the electrolyte, pass oxygen for 30min before the test to replace the dissolved gas, and keep the oxygen saturation in the electrolyte throughout the test process, the test potential range is 0.2~1.1V (vs.RHE), and the scan rate is 10mV/ s, the rotational speed of the rotating disk electrode was 1600 rpm.

The comparison of the linear sweep voltammetry curves of the nitrogen-sulfur doped carbon material in Example 1 and the commercial 20% Pt/C electrode in Comparative Example 2 is shown in Figure 8;

The comparison of the linear sweep voltammetry curves of the nitrogen-sulfur-doped carbon material in Example 2 and the commercial 20% Pt/C electrode in Comparative Example 2 is shown in Figure 9;

The comparison diagram of the linear sweep voltammetry curves of the nitrogen-sulfur-doped carbon material in Example 3 and the commercial 20% Pt/C electrode in Comparative Example 2 is shown in Figure 10;

The comparison chart of the linear sweep voltammetry curves of the nitrogen-sulfur-doped carbon material in Example 4 and the commercial 20% Pt/C electrode in Comparative Example 2 is shown in Figure 11;

The half-wave potential and current density obtained from the test are shown in Table 1.

Table 1

It can be obtained from Table 1 and Figures 1 to 11:

(1) It can be found from Figure 1 that the precursor material retains the rhombic dodecahedron morphology. From Figure 7, it can be found that the precursor materials in Example 1, Example 6, and Example 7 are the same as the Co-ZIF in Comparative Example 1. The diffraction peaks of Co-ZIF are consistent, indicating that the addition of cysteine does not destroy the crystal structure of Co-ZIF; it can be found from Figures 2-5 that nitrogen and sulfur are uniformly distributed in the framework of the carbon material, and the precursor's The original morphology has not changed; it can be found from Figure 6 that two typical characteristic peaks of _D -band and _G -band appear near 1330cm ^-1 and 1580cm ^-1 , and the value of ID /IG reaches 1.89;

(2) When the nitrogen-sulfur-doped carbon material obtained in Examples 1 to 5 is used as a catalyst for the oxygen reduction reaction, the half-wave potential is not lower than 0.83V, and the current density is not lower than 5.35mA/cm ² ;

(3) It can be seen from the comparison between Example 1 and Examples 6 and 7 that the mass ratio of the solute in the metal-organic framework compound solution of the present invention to the solute in the cysteine solution will affect the catalytic performance of the nitrogen-sulfur-doped carbon material ; When the mass ratio of the solute in the metal-organic framework compound solution to the solute in the cysteine solution is low, it will lead to a lower half-wave potential and a reduction of the current density, which is due to the less doping amount of sulfur. Carbonization of the precursor cannot generate enough active sites; when the mass ratio of the solute in the metal-organic framework compound solution to the solute in the cysteine solution is too high, it will lead to a lower half-wave potential and a decrease in the current density. It is because the doping of excessive cysteine may cause the collapse of the metal-organic framework, changing the intrinsic morphology and leading to a decrease in activity;

(4) It can be seen from the comparison between Example 1 and Examples 8 and 9 that the holding temperature of the present invention will affect the catalytic performance of the nitrogen-sulfur doped carbon material; when the holding temperature is low or high, it will lead to a half-wave potential The decrease of the current density is due to the higher degree of graphitization of the catalyst when the temperature is 800-1000 °C, which is more conducive to the improvement of the electrochemical activity of the catalyst;

(5) It can be seen from the comparison between Example 1 and Comparative Example 1 that the incorporation of cysteine according to the present invention helps to improve the catalytic performance of the metal-organic framework compound; the metal-organic framework compound of the present invention contains nitrogen element , Cysteine contains sulfur element, and nitrogen and sulfur elements are uniformly distributed in the carbon framework of nitrogen-sulfur-doped carbon materials after the precursor material is carbonized at high temperature; due to the doping of nitrogen and sulfur elements, nitrogen-sulfur doping There are a large number of unconjugated carbon structures in carbon materials, that is, carbon defects, which in turn generate more active sites. The _numerical range of ID/ _IG , the descriptor of the degree of defects and the degree of graphitization, is: 1.05 to 1.89;

(6) It can be seen from the comparison between Example 1 and Comparative Example 2 that the catalytic performance of the nitrogen-sulfur doped carbon material of the present invention exceeds that of the commercial 20% Pt/C electrode catalyst, and has high practical application potential.

To sum up, the preparation method of the nitrogen-sulfur doped carbon material of the present invention has the advantages of low cost, simple and controllable synthesis process, high consistency and easy realization of mass production. The preparation process of the nitrogen-sulfur doped carbon material The required solvent is only methanol or deionized water, avoiding the use of various organic solvents, and the preparation conditions are environmentally friendly;

The nitrogen-sulfur-doped carbon material of the invention has uniform size distribution and maintains the original morphology of the precursor material, effectively solves the problem of agglomeration of transition metal atoms, and helps to further improve catalytic activity through effective compounding with heteroatoms;

In the present invention, the metal-organic framework compound contains nitrogen and cysteine contains sulfur. After the precursor material is carbonized at high temperature, nitrogen and sulfur are uniformly distributed in the carbon framework of the nitrogen-sulfur-doped carbon material; Doping of nitrogen and sulfur elements, there are a large number of unconjugated carbon structures, namely carbon defects, in nitrogen-sulfur doped carbon materials, which in turn generate more active sites, the degree of defect and the degree of _{graphitization} Descriptor ID The value range of / _IG is: 1.05～1.89;

The nitrogen-sulfur doped carbon material of the present invention is used as a catalyst for oxygen reduction reaction. Under alkaline conditions, the half-wave potential is not lower than 0.83V and the current density is not lower than 5.35mA/cm ² . The ORR catalytic performance of carbon materials exceeds that of commercial noble metal platinum-carbon catalysts and has high potential for practical applications.

The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any person skilled in the art is within the technical scope disclosed by the present invention, Changes or substitutions that can be easily conceived fall within the scope of protection and disclosure of the present invention.

Claims (10)

1. A preparation method of a nitrogen-sulfur doped carbon material is characterized by comprising the following steps:

and carrying out first solid-liquid separation on the first mixed metal organic framework compound solution and a cysteine solution to obtain a precursor material, and then calcining to obtain the nitrogen-sulfur doped carbon material.

2. The preparation method according to claim 1, wherein the volume ratio of the metal-organic framework compound solution to the cysteine solution is (2-12): 1;

preferably, the mass ratio of the solute in the metal organic framework compound solution to the solute in the cysteine solution is 4 (0.1-1);

preferably, the solvent of the cysteine solution comprises methanol and/or water.

3. The method according to claim 1 or 2, wherein the temperature of the first mixing is 15 to 35 ℃ and the time is 1 to 5 hours;

preferably, the method of first mixing comprises stirring and/or sonication;

preferably, the first solid-liquid separation comprises centrifugation, washing and drying which are sequentially carried out.

4. The production method according to any one of claims 1 to 3, wherein the calcination includes sequentially performing temperature rise and temperature preservation;

preferably, the heating rate is 2-10 ℃/min, and the temperature of the heating end point is 800-1000 ℃;

preferably, the heat preservation time is 2-4 h;

preferably, the calcination is carried out in a protective atmosphere comprising nitrogen and/or an inert gas.

5. The method according to any one of claims 1 to 4, wherein the method for preparing the metal-organic framework compound solution comprises the steps of:

and (3) carrying out second solid-liquid separation on the second mixed nitrogenous ligand solution and the transition metal salt solution to obtain a metal organic framework compound, and mixing the metal organic framework compound with methanol and/or water to obtain a metal organic framework compound solution.

6. The method according to claim 5, wherein the solute of the nitrogen-containing ligand solution comprises any one of 2-methylimidazole, potassium ferricyanide, potassium ferrocyanide or potassium cobaltcyanide or a combination of at least two of them;

preferably, the solvent of the nitrogen-containing ligand solution comprises methanol and/or water;

preferably, the solute of the transition metal salt solution comprises any one of cobalt nitrate, iron nitrate, nickel nitrate, zinc nitrate or ferric chloride or a combination of at least two of the above;

preferably, the solvent of the transition metal salt solution comprises methanol and/or water;

preferably, the volume ratio of the nitrogen-containing ligand solution to the transition metal salt solution is (0.8-1.2): 1;

preferably, the mass ratio of the solute in the nitrogen-containing ligand solution to the solute in the transition metal salt solution is (1-100): 1;

preferably, the temperature of the second mixing is 15-35 ℃ and the time is 1-5 h;

preferably, the method of second mixing comprises stirring and/or sonication;

preferably, the second solid-liquid separation comprises centrifugation, washing and drying which are carried out in sequence.

7. The method according to any one of claims 1 to 6, wherein the method comprises the steps of:

(1) stirring and/or ultrasonically mixing a nitrogen-containing ligand solution and a transition metal salt solution at 15-35 ℃ for 1-5 h in a volume ratio of (0.8-1.2): 1, wherein the mass ratio of solute in the nitrogen-containing ligand solution to solute in the transition metal salt solution is (1-100): 1; sequentially carrying out centrifugation, washing and drying to obtain a metal organic framework compound, and mixing the metal organic framework compound with methanol and/or water to obtain a metal organic framework compound solution;

(2) stirring and/or ultrasonically mixing the metal organic framework compound solution and the cysteine solution at the temperature of 15-35 ℃ for 1-5 h in a volume ratio of (2-12): 1, wherein the mass ratio of the solute in the metal organic framework compound solution to the solute in the cysteine solution is 4 (0.1-1); and sequentially centrifuging, washing and drying to obtain a precursor material, heating to 800-1000 ℃ at a heating rate of 2-10 ℃/min in a protective atmosphere, and keeping the temperature for 2-4 h to obtain the nitrogen-sulfur doped carbon material.

8. A nitrogen-sulfur-doped carbon material obtained by the production method according to any one of claims 1 to 7.

9. The nitrogen-sulfur-doped carbon material according to claim 8, wherein the mass fraction of the transition metal in the nitrogen-sulfur-doped carbon material is 2.22 to 8.50 wt% based on the mass of the nitrogen-sulfur-doped carbon material.

10. Use of the nitrogen-sulfur-doped carbon material according to claim 8 or 9 as a cathode catalyst for a fuel cell.

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