阅读说明：本技术 一种金属-氟掺杂碳复合材料及其制备方法和在电催化固氮中的应用 (Metal-fluorine doped carbon composite material, preparation method thereof and application thereof in electrocatalytic nitrogen fixation ) 是由 王要兵 黄艺吟 吴茂祥 于 2019-03-11 设计创作，主要内容包括：本发明提供了一种金属-氟掺杂碳复合材料及其制备方法和在固氮还原中的应用,所述金属-氟掺杂碳复合材料包括金属、氟和碳载体,其中,所述氟和金属分布于碳载体表面；碳载体表面负载的金属(如Au、Ru、Fe或Mo)可以为复合材料催化氮还原提供有效活性位点,进行氨合成反应。另外,碳载体表面修饰有高电负性氟元素,氟元素可与氮还原中间产物作用产生氢键,稳定氮还原中间体,降低其活化能,与金属位点产生协同效应,从而提高反应活性和选择性。此外,当分散在碳载体表面的金属和氟的三维尺寸均小于10nm,使其协同效应明显加强。(The invention provides a metal-fluorine doped carbon composite material, a preparation method thereof and application thereof in nitrogen fixation reduction, wherein the metal-fluorine doped carbon composite material comprises metal, fluorine and a carbon carrier, wherein the fluorine and the metal are distributed on the surface of the carbon carrier; the metal (such as Au, Ru, Fe or Mo) loaded on the surface of the carbon carrier can provide an effective active site for the composite material to catalyze nitrogen reduction, so that ammonia synthesis reaction is carried out. In addition, the surface of the carbon carrier is modified with high electronegativity fluorine, and the fluorine can react with a nitrogen reduction intermediate product to generate hydrogen bonds, stabilize the nitrogen reduction intermediate, reduce the activation energy of the nitrogen reduction intermediate, and generate a synergistic effect with a metal site, so that the reaction activity and selectivity are improved. In addition, when the three-dimensional size of the metal and fluorine dispersed on the surface of the carbon support is less than 10nm, the synergistic effect is obviously enhanced.)

1. A metal-fluorine doped carbon composite, wherein the composite comprises a metal, fluorine and a carbon support material; the fluorine and the metal are distributed on the surface of the carbon carrier material.

2. The composite material of claim 1, wherein the fluorine is atomically distributed over the surface of the carbon support material, the fluorine being bonded to the carbon in a monoatomic form; the metal is distributed on the surface of the carbon carrier material in the form of at least one of single atoms, atom clusters or nano particles.

3. The composite material according to claim 1 or 2, wherein the metal is selected from at least one of Au, Ru, Fe, and Mo; the carbon carrier material is selected from at least one of graphene, carbon nanotubes, activated carbon, carbon nanobelts, graphdiyne and carbon nanofibers.

Preferably, at least one of the three dimensions of the metal is 50nm or less.

Preferably, the three-dimensional sizes of the metals are all less than or equal to 50 nm. Preferably, the three-dimensional size of the metal is 0.1 to 3 nm.

Preferably, the loading of the metal in the composite is from 0.1 to 50 wt.%; the loading of fluorine in the composite material is 0.1-20 wt.%.

4. The composite material according to any one of claims 1-3, wherein the carbon support material may contain oxygen, i.e. the carbon support material may be oxidized, such as graphene oxide, carbon oxide nanotubes, oxidized activated carbon, carbon oxide nanoribbons, graphite oxide alkynes and carbon oxide nanofibers; preferably, the oxygen is distributed on the surface of the carbon support.

Preferably, the oxygen is distributed atomically on the surface of the carbon support, i.e. the oxygen is bound to the carbon in monoatomic form.

Preferably, the loading of oxygen in the composite is 0-10 wt.%.

5. A method of preparing a metal-fluorine doped carbon composite material according to any one of claims 1 to 4, the method comprising the steps of:

1) carrying out fluorination treatment on the carbon carrier material to prepare a fluorine-doped carbon carrier material;

2) mixing the dispersion liquid containing the fluorine-doped carbon carrier material with a metal salt solution, and evaporating to dryness to prepare a composite material precursor;

3) and (3) placing the composite material precursor obtained in the step 2) into a tubular furnace, and carrying out reduction treatment to obtain the metal-fluorine doped carbon composite material.

6. The production method according to claim 5, wherein the step 1) includes the steps of:

1-1) dispersing a carbon carrier material in an acid solution, carrying out ultrasonic treatment, and heating to prepare an oxidized carbon carrier material;

1-2) dispersing the oxidized carbon carrier material in a hydrofluoric acid solution, performing ultrasonic treatment and hydrothermal reaction to prepare the fluorine-doped carbon carrier material.

Preferably, step 1) comprises the following steps:

1-3) uniformly mixing the carbon carrier material and the fluorine-containing compound, then placing the mixture in a tube furnace, and heating the mixture in the inert atmosphere for fluorination treatment to prepare the fluorine-doped carbon carrier material.

7. The preparation method according to claim 6, wherein the heating temperature in step 1-1) is 100-150 ℃; the heating time is 2 hours to 24 hours.

Preferably, in the step 1-2), the concentration of the hydrofluoric acid solution is 35-40%; the mass ratio of the carbon carrier material to the hydrofluoric acid is 1: 0.01-0.1.

Preferably, in the step 1-2), the temperature of the hydrothermal reaction is 100-250 ℃; the hydrothermal reaction time is 10 hours to 100 hours.

Preferably, in step 1-3), the fluorine-containing compound is selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride and the like, and the mass ratio of the fluorine-containing compound to the carbon support material is 0.1: 10-10: 0.1.

preferably, in the step 1-3), the temperature of the fluorination treatment is 500-1000 ℃, and the time of the fluorination treatment is 1-6h, such as 2 h; the temperature increase rate of the fluorination treatment is 5 to 15 ℃/min, for example, 10 ℃/min.

8. The production method according to any one of claims 5 to 7, wherein the step 2) comprises the steps of:

2-1) dispersing the fluorine-doped carbon carrier material into a solvent to obtain a dispersion liquid containing the fluorine-doped carbon carrier material, adding a metal salt solution into the dispersion liquid, mixing, heating and evaporating to dryness to prepare the composite material precursor.

Preferably, in step 2-1), the solvent is one or more of water, ethanol or acetone, and the mass-to-volume ratio of the fluorine-doped carbon support material to the solvent is 100 mg: 1-50 ml.

Preferably, in the step 2-1), the metal salt is chloride salt, nitrate salt, sulfate salt, molybdate salt, etc. of Au, Ru, Fe and Mo. Chloride salts are preferred.

Preferably, in step 2-1), the mass ratio of the fluorine-doped carbon support material to the metal salt is 100: 0.1-20.

9. The production method according to any one of claims 5 to 8, wherein the step 3) comprises the steps of:

3-1) placing the composite material precursor in a tube furnace, heating in a reducing atmosphere for reduction treatment, and preparing the metal-fluorine doped carbon composite material.

Preferably, in the step 3-1), after washing with a reducing atmosphere for five times, heating in a reducing atmosphere for reduction treatment; the reduction treatment is carried out under the condition of introducing argon-hydrogen mixed gas; the composition of the argon-hydrogen mixture is 80-95 vol.% argon and 5-20 vol.% hydrogen.

Preferably, in the step 3-1), the temperature of the reduction treatment is 200-700 ℃, and the time of the reduction treatment is 1-6 h; the heating rate of the reduction treatment is 1-10 ℃/min.

10. Use of a metal-fluorine doped carbon composite material according to any one of claims 1 to 4 in the field of nitrogen fixation, preferably in the field of electrolytic nitrogen reduction for the preparation of ammonia.

Technical Field

The invention relates to a metal-fluorine doped carbon composite material, a preparation method thereof and application thereof in electrocatalysis nitrogen fixation, belonging to the technical field of electrochemistry, catalysis and material synthesis.

Background

Nitrogen-containing compounds are one of the most important components of living organisms such as animals and plants. Artificially utilizing energy, reducing the nitrogen in the atmosphere into ammonia, and further preparing various inorganic/organic matters containing nitrogen, which is an effective way for simulating natural nitrogen fixation. At present, the mature artificial nitrogen fixation mode is the Haber-Bosch nitrogen fixation process invented in the middle century. According to statistics, the amount of fixed nitrogen generated in the process accounts for about 50% of the current nitrogen source of human bodies. However, this nitrogen fixation process requires high temperature and pressure conditions, requires the use of large amounts of fossil energy (1-2% of global energy utilization), and produces large amounts of CO₂And (4) discharge, which brings about serious environmental problems. Therefore, the development of new environmentally friendly nitrogen fixation approaches is imminent. Among various nitrogen fixation approaches, the electrochemical nitrogen fixation process has high controllability and strong adaptability, can utilize clean secondary energy sources, such as electricity generated by solar energy, wind energy, water energy and the like, and is one of the ideal approaches for replacing the Haber-Bosch nitrogen fixation process at present. At present, the bottleneck of the electrochemical nitrogen fixation approach is the electrode catalyst with low catalytic activity and selectivity, and therefore, the development of a novel effective electrocatalyst is the key to realizing the electrochemical nitrogen fixation process.

Electrocatalytic nitrogen fixation, i.e. electrochemical nitrogen reduction process, undergoes a number of proton coupled electron transfer steps. Among them, the adsorption process of nitrogen, the stabilization and hydrogenation of intermediates, and the desorption of ammonia are several more critical steps. The electrochemical nitrogen reduction catalyst studied at home and abroad mainly comprises metal such as Au, Ru, Fe and Mo based catalyst; and the non-metal catalyst is mainly nitrogen and boron doped carbon material catalyst. At present, the electrocatalytic activity of the two major catalysts is not high, the catalytic selectivity is poor, the integral activity of nitrogen reduction is poor, and the requirement of large-scale nitrogen fixation cannot be met.

Disclosure of Invention

The invention aims to overcome the problems of low activity and selectivity of a nitrogen reduction electrocatalyst, and provides a metal-fluorine doped carbon composite material, a preparation method thereof and application thereof in electrocatalysis nitrogen fixation.

The purpose of the invention is realized by the following technical scheme:

a metal-fluorine doped carbon composite, the composite comprising a metal, fluorine and a carbon support material; the fluorine and the metal are distributed on the surface of the carbon carrier material.

According to the invention, the fluorine is distributed on the surface of the carbon carrier material in an atomic form, and the fluorine is combined with carbon in a single atomic form; the metal is distributed on the surface of the carbon carrier material in the form of at least one of single atoms, atom clusters or nano particles.

According to the invention, the metal is selected from at least one of Au, Ru, Fe and Mo; the carbon carrier material is selected from at least one of graphene, carbon nanotubes, activated carbon, carbon nanobelts, graphdiyne and carbon nanofibers.

According to the invention, the metal has at least one of its three dimensions of less than or equal to 50nm, for example 50nm, 25nm, 10nm, 5nm, 2nm, 1nm or 0.05 nm.

Preferably, the three dimensional dimensions of the metal are each less than or equal to 50nm, such as 50nm, 25nm, 10nm, 5nm, 2nm, 1nm or 0.05 nm. Preferably, the three-dimensional size of the metal is 0.1 to 3 nm.

According to the invention, the loading of the metal in the composite material is 0.1-50 wt.%, e.g. 0.1 wt.%, 1 wt.%, 5 wt.%, 10 wt.%, 20 wt.%, 30 wt.%, 50 wt.%.

According to the invention, the loading of fluorine in the composite material is 0.1-20 wt.%, e.g. 0.1 wt.%, 1 wt.%, 5 wt.%, 10 wt.%, 20 wt.%.

According to the invention, the carbon support material may contain oxygen, i.e. the carbon support material may be oxidized, such as graphene oxide, carbon nanotubes, oxidized activated carbon, carbon nanoribbons, graphite alkynes and carbon nanofibers; preferably, the oxygen is distributed on the surface of the carbon support.

According to the invention, the oxygen is distributed atomically on the surface of the carbon support, i.e. the oxygen is bound to the carbon in monoatomic form.

According to the present invention, the loading of the oxygen in the composite material is 0-10 wt.%, e.g., 0.001 wt.%, 0.01 wt.%, 0.1 wt.%, 1 wt.%, 5 wt.%, 10 wt.%.

The invention also provides a preparation method of the metal-fluorine doped carbon composite material, which comprises the following steps:

1) carrying out fluorination treatment on the carbon carrier material to prepare a fluorine-doped carbon carrier material;

2) mixing the dispersion liquid containing the fluorine-doped carbon carrier material with a metal salt solution, and evaporating to dryness to prepare a composite material precursor;

3) and (3) placing the composite material precursor obtained in the step 2) into a tubular furnace, and carrying out reduction treatment to obtain the metal-fluorine doped carbon composite material.

According to the present invention, the carbon support material may be subjected to the oxidation treatment and then the fluorination treatment, or the carbon support material may be directly subjected to the fluorination treatment.

According to the invention, step 1) comprises the following steps:

1-1) dispersing a carbon carrier material in an acid solution, carrying out ultrasonic treatment, and heating to prepare an oxidized carbon carrier material;

1-2) dispersing the oxidized carbon carrier material in a hydrofluoric acid solution, performing ultrasonic treatment and hydrothermal reaction to prepare the fluorine-doped carbon carrier material.

According to the invention, step 1) comprises the following steps:

1-3) uniformly mixing the carbon carrier material and the fluorine-containing compound, then placing the mixture in a tube furnace, and heating the mixture in the inert atmosphere for fluorination treatment to prepare the fluorine-doped carbon carrier material.

According to the invention, in the step 1-1), the acid solution can be sulfuric acid, nitric acid or a sulfuric acid/nitric acid mixed acid solution; the molar concentration of the acid solution is more than or equal to 5 mol/L.

According to the present invention, in step 1-1), the ultrasonic treatment is preferably performed using an ultrasonic machine having a power of 800W or more, and the ultrasonic treatment time may be 0.5 or 1 hour.

According to the invention, in step 1-1), the heating temperature is 100-150 ℃, such as 120 ℃; the heating time is 2 hours to 24 hours, such as 6 hours.

According to the invention, in step 1-1), after heating, the product is preferably subjected to cooling, neutralization, filtration, washing and drying; the cooling is preferably to room temperature, the neutralization is preferably carried out by adding a proper amount of alkali (such as sodium hydroxide or potassium hydroxide) or alkali solution (such as aqueous solution of sodium hydroxide or aqueous solution of potassium hydroxide) for acid-base neutralization, the washing is preferably carried out by washing the filtered solid product with deionized water until the filtrate is neutral, and the drying is preferably carried out in an air drying box at 80 ℃.

According to the invention, in step 1-2), the concentration of the hydrofluoric acid solution is 35-40%; the mass ratio of the carbon carrier material to the hydrofluoric acid is 1: 0.01-0.1.

According to the invention, in the step 1-2), the temperature of the hydrothermal reaction is 100-250 ℃, such as 180 ℃; the hydrothermal reaction is carried out for a period of time ranging from 10 hours to 100 hours, such as 30 hours.

According to the invention, in step 1-2), after the reaction, the product is preferably cooled, filtered, washed and dried; the cooling is preferably to room temperature, the washing is preferably with deionized water to wash the filtered solid product, and the drying is preferably carried out in an air drying cabinet at 80 ℃.

According to the invention, in the step 1-3), the fluorine-containing compound is at least one selected from polytetrafluoroethylene, polyvinylidene fluoride and the like.

According to the invention, in step 1-3), the mass ratio of the fluorine-containing compound to the carbon support material is 0.1: 10-10: 0.1.

according to the invention, in the step 1-3), the temperature of the fluorination treatment is 500-1000 ℃, and the time of the fluorination treatment is 1-6h, such as 2 h; the temperature increase rate of the fluorination treatment is 5 to 15 ℃/min, for example, 10 ℃/min.

According to the invention, said step 2) comprises the following steps:

2-1) dispersing the fluorine-doped carbon carrier material into a solvent to obtain a dispersion liquid containing the fluorine-doped carbon carrier material, adding a metal salt solution into the dispersion liquid, mixing, heating and evaporating to dryness to prepare the composite material precursor.

According to the present invention, in step 2-1), the solvent may be one or more of water, ethanol, or acetone, and the mass-to-volume ratio of the fluorine-doped carbon support material to the solvent is 100 mg: 1-50ml, such as 100 mg: 20 ml.

According to the present invention, in the step 2-1), the metal salt is a chloride salt, a nitrate salt, a sulfate salt, a molybdate salt, or the like of Au, Ru, Fe, and Mo. Chloride salts are preferred.

According to the invention, in step 2-1), the mass ratio of the fluorine-doped carbon support material to the metal salt is 100: 0.1-20.

According to the invention, in step 2-1), the temperature at which the evaporation to dryness is carried out is 60 to 100 ℃, for example 80 ℃.

According to the invention, said step 3) comprises the following steps:

3-1) placing the composite material precursor in a tube furnace, heating in a reducing atmosphere for reduction treatment, and preparing the metal-fluorine doped carbon composite material.

According to the present invention, in step 3-1), it is preferable to perform reduction treatment by washing five times with a reducing atmosphere and then raising the temperature in a reducing atmosphere protection; the reduction treatment is preferably carried out under the condition of introducing argon-hydrogen mixed gas. The composition of the argon-hydrogen mixture is 80-95 vol.% argon and 5-20 vol.% hydrogen, for example 95 vol.% argon and 5 vol.% hydrogen.

According to the invention, in the step 3-1), the temperature of the reduction treatment is 200-700 ℃, and the time of the reduction treatment is 1-6h, such as 5 h; the temperature rise rate of the reduction treatment is 1 to 10 ℃/min, for example, 2 ℃/min.

The invention also provides application of the metal-fluorine doped carbon composite material, which is used in the field of nitrogen fixation, preferably in the field of preparing ammonia by electrolytic nitrogen reduction.

The invention has the beneficial effects that:

1. the invention provides a metal-fluorine doped carbon composite material, a preparation method thereof and application thereof in nitrogen fixation reduction, wherein the metal-fluorine doped carbon composite material comprises metal, fluorine and a carbon carrier material, wherein the fluorine and the metal are distributed on the surface of the carbon carrier material; the metal (such as Au, Ru, Fe or Mo) loaded on the surface of the carbon carrier material can provide an effective active site for the composite material to catalyze nitrogen reduction so as to carry out ammonia synthesis reaction. In addition, the surface of the carbon carrier material is modified with high electronegativity fluorine, and the fluorine can react with a nitrogen reduction intermediate product to generate hydrogen bonds, stabilize the nitrogen reduction intermediate, reduce the activation energy of the nitrogen reduction intermediate, and generate a synergistic effect with a metal site, so that the reaction activity and selectivity are improved. In addition, when the three-dimensional sizes of the metal and fluorine dispersed on the surface of the carbon support material are both less than 10nm, the synergistic effect is obviously enhanced.

2. Compared with the high-performance nitrogen reduction catalyst reported at present, the metal-fluorine doped carbon composite material prepared by the invention has the following structural characteristics and performance advantages:

(1) the metal-fluorine doped carbon composite material has the advantages that the metal can be noble metal or non-noble metal, the using amount of the metal can be controlled, the lowest using amount can reach 0.1 wt.%, most of the material components are cheap carbon carrier materials, and the cost of the composite material is greatly reduced;

(2) in the process of carbon-nitrogen reduction, metal and fluorine generate synergistic effect on the surface of a carbon carrier, so that the catalytic activity of the metal-fluorine-doped carbon composite material is higher and can be 100 times of that of a pure carbon carrier material without metal and fluorine, and meanwhile, the dispersion and loading effects of the carbon carrier material can enable the composite material to have higher stability.

(3) At present, the synthesis process of other nitrogen reduction catalytic materials is relatively complicated and has poor controllability. Compared with the prior art, the metal-fluorine doped carbon composite material is simple to synthesize and can be realized only by using a conventional heating and stirring device and a low-temperature atmosphere furnace device; the preparation can be realized through two-step reaction, the whole process is simple in process, short in period and high in efficiency, and the method is suitable for large-scale production.

Drawings

FIG. 1 is an XRD pattern of the Au-F/G composite material prepared in example 1.

FIG. 2 is a TEM image of the Au-F/G composite prepared in example 1.

FIG. 3 is a graph comparing the nitrogen reduction activity of the Au-F/G composite prepared in example 1 with that of other materials.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are only for illustrating the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that various changes or modifications can be made by those skilled in the art after reading the disclosure of the present invention, and such equivalents also fall within the scope of the invention.

The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.