阅读说明：本技术 一种过渡金属单原子材料及其制备方法和应用 (Transition metal monoatomic material and preparation method and application thereof ) 是由 朱起龙 韩淑果 林华 于 2020-05-14 设计创作，主要内容包括：本发明公开一种过渡金属单原子材料及其制备方法和应用。该材料含有活性组分和载体,所述活性组分为镍单原子、铁单原子和/或钴单原子,所述载体为氟掺杂碳纳米片,所述的镍单原子、铁单原子和/或钴单原子均匀地分散在所述氟掺杂碳纳米片上。所述金属镍单原子材料在电催化二氧还原制备一氧化碳的应用中,具有较高的活性和稳定性。本发明提供的制备方法在惰性气氛下可大量制备,十分适用于规模化、工业化生产。(The invention discloses a transition metal monoatomic material and a preparation method and application thereof. The material contains an active component and a carrier, wherein the active component is a nickel monoatomic atom, an iron monoatomic atom and/or a cobalt monoatomic atom, the carrier is a fluorine-doped carbon nanosheet, and the nickel monoatomic atom, the iron monoatomic atom and/or the cobalt monoatomic atom are uniformly dispersed on the fluorine-doped carbon nanosheet. The metallic nickel monatomic material has higher activity and stability in the application of preparing carbon monoxide by electrocatalytic dioxyreduction. The preparation method provided by the invention can be used for large-scale preparation in an inert atmosphere, and is very suitable for large-scale and industrial production.)

1. A transition metal monatomic material is characterized by comprising an active component and a carrier, wherein the active component is a nickel monatomic, an iron monatomic and/or a cobalt monatomic, the carrier is a fluorine-doped carbon nanosheet, and the nickel monatomic, the iron monatomic and/or the cobalt monatomic are uniformly dispersed on the fluorine-doped carbon nanosheet.

2. The material of claim 1, wherein the loading of the active component on the transition metal monatomic material is 1-10 wt%;

preferably, the fluorine-doped carbon nanosheets contain carbon, nitrogen, oxygen, hydrogen and fluorine;

preferably, the fluorine-doped carbon nanosheets are ultrathin two-dimensional nanosheets. Preferably, the thickness of the nanosheets is 0.5-5 nm.

3. A material according to claim 1 or 2, wherein the transition metal monatomic material is represented by Ni-SAs @ FNC;

wherein Ni is present in monoatomic form; SAs @ FNC represents fluorine-doped carbon nanosheets, and Ni single atoms are uniformly and highly dispersed on the fluorine-doped carbon nanosheets;

the load of Ni single atom is 1-10 wt%; the fluorine-doped carbon nanosheet is of a two-dimensional lamellar structure, and the thickness of the fluorine-doped carbon nanosheet is 0.5-5 nm.

4. A material according to claim 1 or 2, wherein the transition metal monatomic material is represented by Fe-SAs @ FNC; wherein Fe is present in a monoatomic form; SAs @ FNC represents fluorine-doped carbon nanosheets, and Fe single atoms are uniformly and highly dispersed on the fluorine-doped carbon nanosheets.

5. A material according to claim 1 or 2, wherein the transition metal monatomic material is represented by Co-SAs @ FNC; wherein Co is present in a monoatomic form; SAs @ FNC represents fluorine-doped carbon nanosheets, and Co monatomic atoms are uniformly and highly dispersed on the fluorine-doped carbon nanosheets.

6. A method for producing a transition metal monatomic material according to any one of claims 1 to 5, wherein said method comprises the steps of:

(1) mixing a carbon source, a transition metal salt and fluorine dopant dispersion liquid, and freeze-drying the obtained mixture to obtain a precursor;

(2) and cooling the precursor to room temperature after high-temperature pyrolysis to obtain the transition metal monatomic material.

7. The method according to claim 6, wherein in the step (1), the carbon source is a carbon-containing organic substance selected from one, two or more of melamine, dicyandiamide, glucose, sucrose and urea; preferably, the carbon source is selected from one or both of melamine and glucose;

preferably, in step (1), the transition metal salt is selected from one, two or more of nickel-containing, iron-containing and/or cobalt-containing chloride salt, nitrate, acetate and sulfate; preferably nickel nitrate, nickel chloride, ferric nitrate, ferric chloride, cobalt nitrate and/or cobalt chloride;

preferably, in the step (1), the fluorine dopant may be selected from inorganic and/or organic substances containing fluorine, such as at least one of polytetrafluoroethylene, ammonium fluoride and ammonium bifluoride;

preferably, in the step (1), the mass ratio of the carbon source to the transition metal salt is (30-80): 1;

preferably, in the step (1), the mass ratio of the fluorine dopant dispersion liquid to the carbon source is (0.5-5): 1;

preferably, in the step (1), the mass ratio of the carbon source, the transition metal salt and the fluorine dopant dispersion liquid is (30-80):1 (20-200);

preferably, when the carbon source contains two substances, the mass ratio of the two substances is (30-50): 1;

preferably, in the step (1), the carbon source and the transition metal salt are dispersed in water, and then the fluorine dopant dispersion liquid is added into the water and uniformly mixed;

preferably, the mass volume ratio of the transition metal salt to the water is 1 (80-150) g/ml;

preferably, the mass content of the fluorine dopant in the fluorine dopant dispersion liquid is 50% -70%;

preferably, in step (1), the mixture is flash frozen in liquid nitrogen prior to the freeze-drying.

8. The method as claimed in claim 6 or 7, wherein in the step (2), the pyrolysis temperature is 500-1000 ℃; preferably, the pyrolysis incubation time does not exceed 5 hours;

preferably, the high temperature pyrolysis comprises two pyrolysis stages: the temperature of the first pyrolysis stage is 600-700 ℃, and the time is 0.5-2 h; the temperature of the second pyrolysis stage is 850-;

preferably, in the step (2), the temperature reduction after the high-temperature pyrolysis is carried out by naturally reducing the temperature to room temperature;

preferably, after cooling, the product does not need to be acid washed and etched.

9. Use of a transition metal monatomic material according to any one of claims 1 to 5, in carbon dioxide reduction electrocatalysis, preferably as a carbon dioxide reduction electrocatalyst.

10. A carbon dioxide reducing electrocatalyst, characterized in that the catalyst comprises a transition metal monatomic material according to any one of claims 1 to 5.

Technical Field

The invention belongs to the technical field of chemical catalysis, and particularly relates to a transition metal monoatomic material, and a preparation method and application thereof.

Background

In recent years, with the continuous development and utilization of fossil energy (coal, oil, natural gas), the emission amount of carbon dioxide has increased year by year and has a certain influence on the ecosystem balance. On the other hand, in modern society, energy becomes an indispensable part in both production and life, and the development of human society needs to enhance energy supply, but must also consider reducing carbon emission. The electrocatalytic reduction of carbon dioxide into carbon monoxide, which is an important chemical raw material and can be used for producing hydrocarbon small molecular fuel through Fischer-Tropsch synthesis, plays an important role in economic development. The process of hydrogen production by coupling water in an electrocatalysis mode can realize the in-situ reduction and conversion of carbon dioxide under a mild condition. Researchers believe that clean conversion of carbon dioxide to carbon monoxide can be achieved by using renewable energy sources such as wind or solar power to supply power in the presence of suitable electrocatalytic materials. The previous research on the carbon dioxide electrocatalytic reduction in a heterogeneous system by scientists mainly focuses on the noble metal-based catalyst, and the limitation of the noble metal in the practical application is determined by the rarity of the noble metal. In the case of nickel nanoparticles, scientists found that the (111) crystal is almost inert to electrocatalytic reduction of carbon dioxide due to its strong adsorption of CO. With the progress of the characterization technology, the monatomic catalyst is proposed and developed, and has good activity in the aspects of carbon monoxide oxidation, electrocatalytic oxygen reduction, water electrolysis hydrogen production and the like. Recent related researches show that the transition metal-based monatomic carbon composite material has high selectivity and activity for reducing carbon dioxide, realizes high-efficiency conversion of carbon dioxide into carbon monoxide, and provides a good carrier and an optimal reaction site for dispersion of monatomic active sites.

Due to its unique electronic and geometric structure, monatomic catalysts often exhibit desirable catalytic activity in a number of important chemical reactions. If the monatomic catalyst with 100% atomization can be controllably synthesized, high selectivity of carbon dioxide reduction reaction can be realized, and the generation of side reaction hydrogen evolution can be reduced. However, it is difficult to precisely control the microstructure of the synthesized monatomic catalyst at present because monatomic molecules easily diffuse to form a sub-nanostructure, resulting in a decrease in stability thereof.

Disclosure of Invention

The invention provides a transition metal monoatomic material which contains an active component and a carrier, wherein the active component is a nickel monoatomic atom, an iron monoatomic atom and/or a cobalt monoatomic atom, the carrier is a fluorine-doped carbon nanosheet, and the nickel monoatomic atom, the iron monoatomic atom and/or the cobalt monoatomic atom are uniformly dispersed on the fluorine-doped carbon nanosheet.

According to an embodiment of the invention, the loading of the active component on the transition metal monatomic material is 1 to 10 wt%, such as 2 to 8 wt%, illustratively 3 wt%, 4 wt%, 5 wt%, 5.92%, 5.95%, 6 wt%, 6.12%, 7 wt%, 8 wt%.

According to an embodiment of the present invention, the fluorine-doped carbon nanosheets contain elemental carbon, elemental nitrogen, elemental oxygen, elemental hydrogen, and elemental fluorine.

According to an embodiment of the present invention, the fluorine-doped carbon nanosheets are ultrathin two-dimensional nanosheets. For example, the nanoplatelets have a thickness of 0.5-5nm, such as 0.8-4 nm; illustratively, the thickness may be 0.8nm, 1.0nm, 1.25nm, 1.3nm, 2nm, 3.2 nm. The fluorine-doped carbon nanosheet has a high specific surface area and high conductivity, can sufficiently expose an active component, and is doped in a carbon nanosheet structure, and fluorine has high electronegativity, so that a metal monoatomic atom can be stabilized and the loading amount of the metal monoatomic atom can be increased.

According to an exemplary aspect of the present invention, the transition metal monoatomic material is represented by Ni-SAs @ FNC;

wherein Ni is present in monoatomic form; SAs @ FNC represents fluorine-doped carbon nanosheets, and Ni single atoms are uniformly and highly dispersed on the fluorine-doped carbon nanosheets;

the loading of Ni monatomic is 1 to 10 wt%, for example, 5.92 wt%; the fluorine-doped carbon nanosheet is a two-dimensional lamellar structure having a thickness of 0.5-5nm, such as 1.25 nm.

According to an exemplary aspect of the invention, the transition metal monoatomic material is represented by Fe-SAs @ FNC; wherein Fe is present in a monoatomic form; SAs @ FNC represents fluorine-doped carbon nanosheets, and Fe single atoms are uniformly and highly dispersed on the fluorine-doped carbon nanosheets.

According to an exemplary aspect of the invention, the transition metal monoatomic material is represented by Co-SAs @ FNC; wherein Co is present in a monoatomic form; SAs @ FNC represents fluorine-doped carbon nanosheets, and Co monatomic atoms are uniformly and highly dispersed on the fluorine-doped carbon nanosheets.

The invention also provides a preparation method of the transition metal monoatomic material, which comprises the following steps:

(1) mixing a carbon source, a transition metal salt and fluorine dopant dispersion liquid, and freeze-drying the obtained mixture to obtain a precursor;

(2) and cooling the precursor to room temperature after high-temperature pyrolysis to obtain the transition metal monatomic material.

According to the embodiment of the present invention, in the step (1), the carbon source is a carbon-containing organic substance, and may be one, two or more selected from melamine, dicyandiamide, glucose, sucrose and urea; preferably, the carbon source is selected from one or both of melamine and glucose.

According to an embodiment of the present invention, in step (1), the transition metal salt is selected from one, two or more of nickel-containing, iron-and/or cobalt-containing chloride salt, nitrate, acetate and sulfate; preferably nickel nitrate, nickel chloride, ferric nitrate, ferric chloride, cobalt nitrate and/or cobalt chloride.

According to an embodiment of the present invention, in the step (1), the fluorine dopant may be selected from inorganic substances containing fluorine and/or organic substances containing fluorine, such as at least one of polytetrafluoroethylene, ammonium fluoride, ammonium bifluoride, and the like, and is exemplified by polytetrafluoroethylene.

According to an embodiment of the invention, in step (1), the mass ratio of the carbon source to the transition metal salt may be (30-80):1, for example (40-80):1, exemplified by 40:1, 41:1, 50:1, 60:1, 70:1, 80: 1.

According to an embodiment of the invention, in step (1), the mass ratio of the fluorine dopant dispersion to the carbon source may be (0.5-5):1, for example (1-4):1, exemplified by 1:1, 2:1, 2.9:1, 3:1, 4:1, 5: 1.

According to an embodiment of the present invention, in the step (1), the mass ratio of the carbon source, the transition metal salt and the fluorine dopant dispersion may be (30-80):1 (20-200), for example (40-80):1 (30-150), (40-70):1 (40-120), illustratively 40:1:40, 40:1:80, 40:1:120, 41:1:40, 41:1:80, 41:1:120, 50:1:100, 60:1:120, 70:1:100, 80:1: 80.

According to an embodiment of the present invention, when the carbon source contains two substances, such as melamine and glucose, the mass ratio of the two substances is not particularly limited, and may be, for example, (30-50):1, such as (35-45):1, and is illustratively 40: 1.

According to an exemplary embodiment of the present invention, the carbon source comprises melamine and glucose in a mass ratio of 40: 1.

According to an exemplary embodiment of the present invention, the carbon source is melamine, and the mass ratio of the transition metal salt to the melamine is 1: 40.

According to an exemplary embodiment of the present invention, the carbon source is melamine, and the mass ratio of the fluorine dopant dispersion to the melamine is 1:1, 2:1, and 3: 1.

According to an embodiment of the present invention, in the step (1), the carbon source and the transition metal salt may be dispersed in water, and then the fluorine dopant dispersion may be added thereto and mixed uniformly.

Preferably, the mass to volume ratio of the transition metal salt to water is 1 (80-150) g/ml, such as 1 (100) 130) g/ml, illustratively 1:100g/ml, 1:110g/ml, 1:120g/ml, 1:130 g/ml.

Preferably, the fluorine dopant dispersion needs to be slowly added dropwise.

Preferably, the fluorine dopant is present in the fluorine dopant dispersion in an amount of 50 wt% to 70 wt%, such as 53 wt% to 68 wt%, illustratively 50 wt%, 55 wt%, 60 wt%, 62 wt%, 65 wt%, 70 wt%. Further, the dispersing agent in the fluorine dopant dispersion liquid is deionized water.

Wherein, the dispersing and mixing can be selected from the known methods in the field, such as stirring, ultrasonic and the like. So as to promote the dissolution and dispersion of the materials and obtain uniform dispersion liquid.

According to an embodiment of the present invention, in step (1), the mixture may be flash-frozen in liquid nitrogen before the freeze-drying. Wherein the freeze-drying time may be 12-36h, such as 15-30h, exemplary 20h, 24 h.

According to the technical scheme of the invention, in the step (2), the high-temperature pyrolysis temperature is 500-. Further, the pyrolysis is maintained for a period of time not exceeding 5 hours, for example, 0.5 to 4 hours.

Preferably, the high temperature pyrolysis comprises two pyrolysis stages: the temperature of the first pyrolysis stage is 600-700 ℃, and the time is 0.5-2 h; the temperature of the second pyrolysis stage is 850-. Preferably, the temperature of the first pyrolysis stage is 630-680 ℃ and the time is 1-1.5 h. Preferably, the temperature of the second pyrolysis stage is 880-930 ℃ and the time is 1-1.5 h. Illustratively, the temperature of the first pyrolysis stage is 650 ℃ for 1 h; the temperature of the second pyrolysis stage was 900 ℃ for 1 h.

According to the embodiment of the present invention, in the step (2), the temperature reduction after the high-temperature pyrolysis may be performed by naturally reducing the temperature to room temperature. Further pickling and etching of the product is not required.

According to an embodiment of the present invention, the method for preparing the transition metal monatomic material includes the steps of:

(1) mixing melamine, glucose, transition metal salt and polytetrafluoroethylene dispersion liquid to form a uniform mixture, and freeze-drying the mixture to obtain a precursor;

(2) and cooling the precursor to room temperature after high-temperature pyrolysis to obtain the transition metal monatomic material.

The inventor finds that in the preparation process of the traditional supported monatomic material, metal atoms are easy to agglomerate in the carbonization process of the carrier, so that the metal loading capacity cannot be improved, and the fluorine-doped carrier can inhibit the migration and agglomeration of the metal monatomic through a charge effect due to the strong electronegativity of fluorine. In the preparation method provided by the invention, the obtained carrier has an ultrathin two-dimensional nanosheet structure, has a high specific surface area and high conductivity, can expose active sites in a reaction environment to the maximum extent, is favorable for a catalytic process, and further increases the loading capacity of metal monoatomic atoms on the carrier.

The invention also provides the transition metal monatomic material prepared by the method.

The invention also provides the use of the transition metal monatomic material in carbon dioxide reduction electrocatalysis (reduction of carbon dioxide to carbon monoxide), for example as a carbon dioxide reduction electrocatalyst.

The invention provides a carbon dioxide reduction electrocatalyst which contains the transition metal monoatomic material.

The invention has the beneficial effects that:

(1) the transition metal monatomic material provided by the invention takes a nickel, iron or cobalt metal monatomic as an active component, takes a fluorine-doped ultrathin carbon nanosheet as a carrier, and has a load capacity of 1-10 wt% of the nickel, iron or cobalt metal monatomic in the transition metal monatomic material; meanwhile, the micro-morphology of the material is regulated and controlled by introducing the heteroatom, so that the morphology of the material is uniform.

(2) The invention provides a preparation method of a high-load metal monatomic material synthesized under the assistance of nonmetallic element fluorine with strong electronegativity. Fluorine-containing compounds are used as a doping agent of a carrier to induce and form fluorine-doped ultrathin carbon nanosheets, the morphology of the fluorine-doped ultrathin carbon nanosheets can expose active sites in a reaction environment to the maximum extent, and fluorine is doped in a carbon layer to effectively inhibit migration and aggregation of metal atoms, so that the metal single atom loading capacity of the catalyst is further improved.

In addition, the preparation method has low cost and simple process, and lays a foundation for industrial mass production in practical application.

(3) The transition metal monatomic material provided by the invention can be used as a catalyst and applied to preparation of carbon monoxide by electrocatalysis of carbon dioxide reduction. It has high activity, stability, selectivity and Faraday efficiency, and has outstanding advantages in long-term circulation stability and quality activity.

The selectivity of carbon monoxide can be kept above 90% in the range of-0.67 to-0.97V vs RHE voltage, the best performance is achieved at-0.77V, the selectivity of carbon monoxide is high, and the activity is not attenuated in a constant voltage stability test for 10 hours.

Drawings

FIG. 1 is a powder diffraction (XRD) pattern of the Ni-SAs @ FNC catalyst prepared in example 1.

FIG. 2 is a Scanning Electron Microscope (SEM) image of the Ni-SAs @ FNC catalyst prepared in example 1.

FIG. 3 is an Atomic Force Microscope (AFM) image of the Ni-SAs @ FNC catalyst prepared in example 1.

FIG. 4 is a Transmission Electron Microscope (TEM) image of the Ni-SAs @ FNC catalyst prepared in example 1.

FIG. 5 is a transmission electron microscopy (AC-HAADF-STEM) image of spherical aberration corrected Ni-SAs @ FNC catalyst prepared in example 1.

FIG. 6 is a graph of the electrocatalytic carbon dioxide reduction performance of the Ni-SAs @ FNC catalyst prepared in example 1.

FIG. 7 is a graph of the 10 hour stability of the electrocatalytic carbon dioxide reduction of the Ni-SAs @ FNC catalyst prepared in example 1.

Fig. 8 is an XRD pattern of the Ni monatomic material synthesized in example 2 and example 3.

FIG. 9 is a powder diffraction (XRD) pattern of the Ni-NPs @ NC catalyst prepared in example 4.

FIG. 10 is a Transmission Electron Microscope (TEM) image of the Ni-NPs @ NC catalyst prepared in example 4.

Fig. 11 is a powder diffraction (XRD) pattern of the different carbonization temperature catalysts prepared in examples 5 and 6.

Fig. 12 is a powder diffraction (XRD) pattern of different transition metal catalysts prepared in example 7.

Detailed Description

The technical solution of the present invention will be further described in detail with reference to specific embodiments. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

Unless otherwise indicated, the raw materials and reagents used in the following examples are all commercially available products or can be prepared by known methods.