CN108569678A - A kind of Transition-metal dichalcogenide and its preparation method and application - Google Patents

Abstract

The invention provides a transition metal chalcogenide compound and its preparation method and application. The compound provided by the invention controls the ratio of transition metal to sulfur and the morphology of the crystal, so that the compound obtained in the invention can be used as a working electrode material for electrocatalysis In the electrocatalytic reaction of reducing carbon dioxide to generate synthesis gas, the volume ratio of carbon monoxide and hydrogen in the obtained synthesis gas can be approximately 1, and the synthesis of synthesis gas has high efficiency, good stability, and is environmentally friendly and sustainable. Moreover, the preparation method provided by the invention has a stable morphology of transition metal chalcogenides with a single-layer structure, and the preparation effect of binary or ternary transition metal chalcogenides is very good.

Description

A kind of transition metal chalcogenide compound and its preparation method and application

technical field

The invention relates to the field of metal chalcogenides, in particular to a transition metal chalcogenide and its preparation method and application.

Background technique

Syngas is an important industrial raw material, which can be converted into short-chain olefins (mainly ethylene, propylene and butene) or directly synthesized into liquid fuels through the Fischer-Tropsch reaction. The main components of syngas are carbon monoxide (CO) and hydrogen (H ₂ ). The traditional way of preparing syngas is mainly through the gasification of solid fuels such as coal, coke or biomass. However, the CO in syngas obtained from different raw materials (10-57%) and H ₂ (32-67%) vary greatly in volume, and since solid fuels such as coal, coke or biomass are not renewable in the short term, it is necessary to invent a sustainable and environmentally friendly It is of great significance to produce synthesis gas in a certain way.

Electrochemical reduction of carbon dioxide (CO ₂ ) and water (H ₂ O) to synthesis gas is an efficient and environmentally friendly way, which can not only reduce the dependence on fossil raw materials, but also reduce the content of CO ₂ in the atmosphere. An effective way to tackle global warming with the imminent carbon tax. So far, many electrocatalysts have been applied to convert CO ₂ to obtain synthesis gas, but highly efficient electrocatalysts are still mainly concentrated on noble metals (such as gold, silver); however, the less content and high price of noble metals limit their further development. commercialize. Therefore, the search for highly efficient non-precious metal electrocatalysts with abundant reserves and environmental friendliness has attracted extensive attention.

Transition metal dichalcogenides (TMDs) are a class of abundant, environmentally friendly materials with excellent electrocatalytic properties. In acidic medium, the equilibrium potential of electrochemically reducing water to obtain hydrogen is 0 V (relative to the reversible hydrogen electrode), and the equilibrium potential of reducing carbon dioxide to obtain carbon monoxide is -0.11 V (relative to the reversible hydrogen electrode). Due to the similar reduction potentials, TMDs are promising electrocatalytic materials for simultaneous reduction of water and carbon dioxide to synthesis gas. TMDs materials such as molybdenum disulfide and tungsten diselenide have been proven to convert CO ₂ and H ₂ O into synthesis gas; however, the preparation methods of TMDs disclosed so far are all raw materials are directly mixed and reacted, and the obtained ones are in the form of lumps TMDs, and then powdered TMDs are obtained by grinding; and the material used in the preparation of syngas has problems such as low conductivity, few active sites and weak intrinsic activity; and the obtained syngas has a large disparity between carbon monoxide and hydrogen Therefore, providing a kind of TMDs that can efficiently catalyze syngas synthesis is a problem to be solved at present.

Contents of the invention

In view of this, the technical problem to be solved by the present invention is to provide a transition metal chalcogenide and its preparation method and application, the compound provided by the present invention is used as a catalyst for the catalysis of synthesis gas, and the synthesis gas of carbon monoxide and hydrogen in the obtained The volume ratio is approximately 1, and the shape of the compound prepared by the preparation method of the compound provided by the invention is controllable.

The present invention provides a kind of transition metal chalcogenide, has the general formula shown in formula (I):

_{MoSexS (2-x)} formula (I);

Among them, 0≤x≤2;

The compound has a single-layer structure, and the thickness of the single-layer structure is 0.71-0.76 nanometers.

The present invention also provides a method for preparing the transition metal chalcogenide compound of the present invention, comprising:

1) mixing molybdenum source, sulfur powder, selenium powder and solvent to obtain a mixed solution,

Described solvent is oleylamine and water,

The molar ratio of the molybdenum source, the sulfur powder and the selenium powder is 1:(1～2.5):(1～2.5);

2) the mixed solution obtained in step 1) is heated and reacted, and separated to obtain the transition metal chalcogenide compound shown in formula (I),

_{MoSexS (2-x)} formula (I);

Among them, 0≤x≤2.

Preferably, the volume ratio of the oleylamine to the water is (15-30):(3-6).

Preferably, the volume ratio of the oleylamine to the water is (5-10):1.

Preferably, the molybdenum source is ammonium molybdate.

Preferably, the ratio of the molybdenum source to the solvent is 1 mol: (25-35) mL.

Preferably, the reaction temperature is 180-220°C.

Preferably, the reaction time is 36-50 hours.

The present invention also provides a method for preparing synthesis gas, comprising:

Synthesis gas is prepared by electrocatalytic reaction of carbon dioxide gas;

Wherein, the electrocatalytic reaction is carried out in a three-electrode system, and the working electrode in the three-electrode system is a glassy carbon electrode spin-coated with the transition metal chalcogenide described in claim 1 .

Preferably, the electrolyte in the three-electrode system is a mixed solution of EmimBF ₄ and H ₂ O.

Compared with the prior art, the transition metal chalcogenide compound with the structure of formula (I) provided by the present invention, by controlling the ratio of transition metal to sulfur and the morphology of the crystal, the compound obtained by the present invention can be used as a working electrode material in In the electrocatalytic reaction of electrocatalytic reduction of carbon dioxide to generate synthesis gas, the volume ratio of carbon monoxide and hydrogen in the obtained synthesis gas can be approximately 1, and the synthesis of synthesis gas has high efficiency, good stability, and is environmentally friendly and sustainable.

The present invention also provides a method for preparing the transition metal chalcogenide compound of the present invention, comprising: first mixing molybdenum source, sulfur powder, selenium powder and solvent to obtain a mixed solution, and then mixing the mixed solution obtained in step 1) Heating reaction, separation, obtains the general formula compound shown in formula (I), wherein, by selecting described solvent to be oleylamine and water, control the molar ratio of described molybdenum source, sulfur powder and selenium powder simultaneously to be 1: (1～ 2.5): (1-2.5); furthermore, the obtained transition metal chalcogenides have a single-layer structure, and the method provided by the present invention has good preparation effects for binary or ternary transition metal chalcogenides.

Description of drawings

The XRD diffraction patterns of the _MoS2 single-layer structure (a), MoSeS alloy single-layer structure (b) and _MoSe2 single-layer structure (c) prepared by the embodiment of Fig. 1;

Fig. 2 is the Raman spectrogram of _MoS2 single-layer structure (a), MoSeS alloy single-layer structure (b) and MoSe2 _single -layer structure (c) prepared by embodiment;

The transmission electron microscope (TEM) and high-resolution transmission electron microscope of the MoSeS alloy single-layer structure (A, D), _MoS2 single-layer structure (B, E) and MoSe2 _single -layer structure (C, F) that Fig. 3 embodiment provides graph(hrtem);

Fig. 4 provides MoSeS alloy single-layer structure (A, D), _MoS2 single-layer structure (B, E) and _MoSe2 single-layer structure (C, F) atomic force microscope figure (AFM) and corresponding height that Fig. 4 provides Fig. 1, 2 in the height map correspond to 1, 2 in the AFM map;

Fig. 5 provides MoSeS alloy monolayer structure (a), MoS ₂ monolayer structure (b) and MoSe ₂ monolayer structure (c) provided by the embodiment in EmimBF ₄ / aqueous solution in linear sweep voltammogram;

Figure 6 shows the MoSeS alloy single-layer structure, _MoS2 single-layer structure and _MoSe2 single-layer structure prepared by the example. The working electrode was prepared in _EmimBF4 /water solution and the reaction potential was -1.15V (relative to the reversible hydrogen electrode). Graph of hydrogen (open) and carbon monoxide (solid) production.

Detailed ways

The present invention provides a kind of transition metal chalcogenide, has the general formula shown in formula (I):

_{MoSexS (2-x)} formula (I);

Among them, 0≤x≤2;

The compound has a single-layer structure, and the thickness of the single-layer structure is 0.71-0.76 nanometers.

According to the present invention, said x is preferably 0.5≤x≤1.5, more preferably 1≤x≤1.2.

The transition metal chalcogenide compound with the structure of formula (I) provided by the present invention, by controlling the ratio of transition metal to sulfur and the morphology of the crystal, the compound obtained in the present invention can be used as a working electrode material for electrocatalytic reduction of carbon dioxide to generate synthesis gas In the electrocatalytic reaction, the volume ratio of carbon monoxide and hydrogen in the obtained synthesis gas can be approximately 1, and the synthesis efficiency is high, the stability is good, and the environment is friendly and sustainable.

The present invention also provides a method for preparing the transition metal chalcogenide compound of the present invention, comprising:

1) mixing molybdenum source, sulfur powder, selenium powder and solvent to obtain a mixed solution,

Described solvent is oleylamine and water,

The molar ratio of the molybdenum source, sulfur powder and selenium powder is 1: (1～2.5): (1～2.5);

2) the mixed solution obtained in step 1) is heated and reacted, and separated to obtain a general formula transition metal chalcogenide compound shown in formula (I),

_{MoSexS (2-x)} formula (I);

According to the present invention, the present invention mixes molybdenum source, sulfur powder, selenium powder and solvent, obtains mixed solution; Wherein, described molybdenum source is preferably ammonium molybdate; The volume ratio of the oleylamine in the described solvent and water is preferably ( 15～30): (3～6), more preferably (5～10): 1, most preferably (6～8): 1; The molar ratio of described molybdenum source and sulfur powder is 1: (1.1～2.3 ), more preferably 1: (1.3-2.1); the molar ratio of the molybdenum source to the selenium powder is 1: (1.1-2.3), more preferably 1: (1.3-2.1); the molybdenum source and the The consumption ratio of solvent is 1mol: (25～35) mL, more preferably 1mol: (27～33) mL, most preferably 1mol: (28～31) mL; Any conventional known mixing method may be used.

According to the present invention, the mixed solution obtained in step 1) is heated for reaction and separated to obtain the general formula transition metal chalcogen compound shown in formula (I); wherein, the temperature of the reaction is preferably 180-220° C., more preferably 200° C. ~210°C; the reaction time is preferably 36 to 50 hours, more preferably 40 to 48 hours; after the reaction is completed, the present invention preferably also cools the reaction solution heated and reacted to room temperature naturally, and then separates to obtain formula (I) The transition metal chalcogenide of shown general formula; The present invention has no special limitation to the mode of separation, preferably obtains general formula transition metal chalcogenide shown in formula (I) by centrifugation; In order to make product purity higher, the present invention preferably The isolated product is also washed and dried; wherein, the washing solvents are ethanol and cyclohexane; the drying temperature is generally 60-80°C.

The present invention also provides the preparation method of the transition metal chalcogenide compound of the present invention, comprising: first mixing molybdenum source, sulfur powder, selenium powder and solvent to obtain a mixed solution, and then heating and reacting the mixed solution obtained in step 1) , separate to obtain the general formula compound shown in formula (I), wherein, by selecting the solvent to be oleylamine and water, the molar ratio of simultaneously controlling the molybdenum source, sulfur powder and selenium powder is 1: (1～2.5) : (1～2.5); and then make the obtained transition metal chalcogenide compound have a single-layer structure.

The present invention also provides a method for preparing synthesis gas, comprising:

Synthesis gas is prepared by electrocatalytic reaction of carbon dioxide gas;

Wherein, the electrocatalytic reaction is carried out in a three-electrode system, and the working electrode in the three-electrode system is a glassy carbon electrode spin-coated with the transition metal chalcogenide compound of the present invention.

In the present invention, in the three-electrode system, the reference electrode is preferably Ag/AgCl, the counter electrode is preferably a platinum electrode; the electrolyte is preferably a mixed solution of EmimBF ₄ and H ₂ O; the electrode In the catalytic reaction, the reaction potential of the working electrode is preferably -0.5 to -1.15V, more preferably -0.8 to -1.1V, and most preferably -0.9 to -1V.

The preparation method of the synthesis gas provided by the present invention, by selecting the compound described in the present invention as the working electrode material, and selecting a suitable electrolyte and reaction potential at the same time, the preparation method of the synthesis gas provided by the present invention has high synthesis efficiency and can A synthesis gas with a volume ratio of carbon monoxide to hydrogen of 1 is obtained.

The following will clearly and completely describe the technical solutions of the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Example 1

Dissolve 159mg ammonium molybdate, 30mg sulfur powder and 74mg selenium powder in a mixed solution of 28.5mL oleylamine and 1.5mL water, stir vigorously for 10min, then transfer the resulting mixture into a 50mL autoclave, seal it, and react at 220°C 48h. After the reaction was completed, it was naturally cooled to room temperature, and the obtained product was centrifuged, washed several times with ethanol and cyclohexane to remove residual organic matter. Finally, dry at 60° C. in a vacuum drying oven to obtain a black powder, which is a single-layer MoSeS alloy structure, and store it in a desiccator for future use.

Structural identification of the compounds prepared in the examples, the results are shown in Figures 1 to 4, the _MoS2 single-layer structure (a), the MoSeS alloy single-layer structure (b) and the _MoSe2 single-layer structure (c) prepared in the embodiment of Figure 1 ) XRD diffraction pattern; Fig. 2 is the Raman spectrogram of _MoS2 monolayer structure (a), MoSeS alloy monolayer structure (b) and _MoSe2 monolayer structure (c) prepared by embodiment; Fig. 3 embodiment provides Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) of MoSeS alloy single-layer structure (A, D), MoS ₂ single-layer structure (B, E) and MoSe ₂ single-layer structure (C, F); 4 MoSeS alloy single-layer structure (A, D), _MoS2 single-layer structure (B, E) and _MoSe2 single-layer structure (C, F) atomic force microscope (AFM) and corresponding height map provided by the example , where 1, 2 in the height map correspond to 1, 2 in the AFM map.

Example 2

Dissolve 159mg ammonium molybdate and 60mg sulfur powder in a mixed solution of 28.5mL oleylamine and 1.5mL water, stir vigorously for 10min, then transfer the resulting mixture into a 50mL autoclave, seal it, and react at 220°C for 48h. After the reaction was completed, it was naturally cooled to room temperature, and the obtained product was centrifuged, washed several times with ethanol and cyclohexane to remove residual organic matter. Finally, dry at 60° C. in a vacuum drying oven to obtain a product that is MoS ₂ with a single-layer structure, which is stored in a desiccator for future use.

Structural identification of the compounds prepared in the examples, the results are shown in Figures 1 to 4, the _MoS2 single-layer structure (a), the MoSeS alloy single-layer structure (b) and the _MoSe2 single-layer structure (c) prepared in the embodiment of Figure 1 ) XRD diffraction pattern; Fig. 2 is the Raman spectrogram of _MoS2 monolayer structure (a), MoSeS alloy monolayer structure (b) and _MoSe2 monolayer structure (c) prepared by embodiment; Fig. 3 embodiment provides Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images of MoSeS alloy single-layer structure (A, D), _MoS2 single-layer structure (B, E) and _MoSe2 single-layer structure (C, F): Fig. 4 MoSeS alloy single-layer structure (A, D), _MoS2 single-layer structure (B, E) and _MoSe2 single-layer structure (C, F) atomic force microscope (AFM) and corresponding height map provided by the example , where 1, 2 in the height map correspond to 1, 2 in the AFM map.

Example 3

Dissolve 159mg ammonium molybdate and 148mg selenium powder in a mixed solution of 28.5mL oleylamine and 1.5mL water, stir vigorously for 10min, then transfer the resulting mixture into a 50mL autoclave, seal it, and react at 220°C for 48h. After the reaction was completed, it was naturally cooled to room temperature, and the obtained product was centrifuged, washed several times with ethanol and cyclohexane to remove residual organic matter. Finally, dry at 60° C. in a vacuum drying oven to obtain a product that is MoS ₂ with a single-layer structure, which is stored in a desiccator for future use.

Structural identification of the compounds prepared in the examples, the results are shown in Figures 1 to 4, the _MoS2 single-layer structure (a), the MoSeS alloy single-layer structure (b) and the _MoSe2 single-layer structure (c) prepared in the embodiment of Figure 1 ) XRD diffraction pattern; Fig. 2 is the Raman spectrogram of _MoS2 monolayer structure (a), MoSeS alloy monolayer structure (b) and _MoSe2 monolayer structure (c) prepared by embodiment; Fig. 3 embodiment provides Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) of MoSeS alloy single-layer structure (A, D), MoS ₂ single-layer structure (B, E) and MoSe ₂ single-layer structure (C, F); 4 MoSeS alloy single-layer structure (A, D), _MoS2 single-layer structure (B, E) and _MoSe2 single-layer structure (C, F) atomic force microscope (AFM) and corresponding height map provided by the example , where 1, 2 in the height map correspond to 1, 2 in the AFM map.

Comparative example 1

Dissolve 220mg molybdenum nitrate pentahydrate, 35mg sulfur powder and 80mg selenium powder in a mixed solution of 22mL oleylamine and 3mL water, stir vigorously for 10min, then transfer the resulting mixture into a 50mL autoclave, seal it, and react at 220°C for 48h . After the reaction was completed, it was naturally cooled to room temperature, and the obtained product was centrifuged, washed several times with ethanol and cyclohexane to remove residual organic matter. Finally, it was dried in a vacuum oven at 60°C, and the obtained product was not a single-layer structure of MoSeS alloy after detailed characterization.

Comparative example 2

Dissolve 159mg ammonium molybdate, 30mg sulfur powder and 80mg selenium powder in a mixed solution of 18mL oleylamine and 6mL water, stir vigorously for 10min, then transfer the resulting mixture into a 50mL autoclave, seal it, and react at 160°C for 48h. After the reaction was completed, it was naturally cooled to room temperature, and the obtained product was centrifuged, washed several times with ethanol and cyclohexane to remove residual organic matter. Finally, it was dried in a vacuum oven at 60°C, and the obtained product was not a single-layer structure of MoSeS alloy after detailed characterization.

Example 4

Examples of electrocatalytic reduction of _CO2 to synthesis gas by single-layer MoSeS:

The electrocatalytic reaction was carried out in a three-electrode system. Disperse 4 mg of MoSeS alloy monolayer in a mixture of 0.3 mL of isopropanol and 0.7 mL of water, then add 30 μL of Nafion (5 wt%) solution, and ultrasonically disperse the mixture for 10 min to obtain a uniform electrode solution. Spin-coat 4 μL of electrode solution on a glassy carbon electrode, and dry naturally to obtain a working electrode; Ag/AgCl is used as a reference electrode, and a platinum electrode is used as a counter electrode; the electrolyte is a mixture of EmimBF ₄ /H ₂ O. Before the reaction, feed high-purity CO ₂ into the electrolyte for 30 minutes, control the reaction potential of the working electrode at -1.15V, and react for a certain period of time to obtain synthesis gas composed of CO and H ₂ (the ratio is close to 1:1).

The working electrode was prepared by replacing MoSeS with MoSe ₂ and MoS ₂ respectively according to the above method, and other reaction conditions remained unchanged, and carbon dioxide was used as raw material to prepare synthesis gas.

Among them, the results of preparing synthesis gas are shown in Figures 5 to 6, wherein Figure 5 shows the MoSeS alloy single-layer structure (a), MoS ₂ single-layer structure (b) and MoSe ₂ single-layer structure (c) provided in the example. The linear sweep voltammogram in EmimBF ₄ /water solution; Figure 6 is the working electrode prepared by the MoSeS alloy single-layer structure, MoS ₂ single-layer structure and MoSe ₂ single-layer structure provided by the embodiment in EmimBF ₄ /water solution, and the reaction potential is - Graph of hydrogen gas (open) and carbon monoxide (solid) production produced at 1.15 V (vs. reversible hydrogen electrode).

The descriptions of the above embodiments are only used to help understand the method and core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, some improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims (10)

1. A transition metal chalcogenide, having general formula shown in formula (I): _{MoSexS (2-x)} formula (I); Among them, 0≤x≤2; The compound has a single-layer structure, and the thickness of the single-layer structure is 0.71-0.76 nanometers. 2. a preparation method of transition metal chalcogenides as claimed in claim 1, comprising: 1) mixing molybdenum source, sulfur powder, selenium powder and solvent to obtain a mixed solution, Described solvent is oleylamine and water, The molar ratio of the molybdenum source, the sulfur powder and the selenium powder is 1:(1～2.5):(1～2.5); 2) the mixed solution obtained in step 1) is heated and reacted, and separated to obtain the transition metal chalcogenide compound shown in formula (I), _{MoSexS (2-x)} formula (I); Among them, 0≤x≤2. 3. The preparation method according to claim 2, characterized in that the volume ratio of the oleylamine to the water is (15-30): (3-6). 4. The preparation method according to claim 2, characterized in that the volume ratio of the oleylamine to the water is (5-10):1. 5. preparation method according to claim 2 is characterized in that, described molybdenum source is ammonium molybdate. 6. The preparation method according to claim 2, characterized in that the ratio of the molybdenum source to the solvent is 1 mol: (25-35) mL. 7. The preparation method according to claim 2, characterized in that the reaction temperature is 180-220°C. 8. The preparation method according to claim 2, characterized in that, the reaction time is 36-50 hours. 9. A method for preparing synthesis gas, comprising: Synthesis gas is prepared by electrocatalytic reaction of carbon dioxide gas; Wherein, the electrocatalytic reaction is carried out in a three-electrode system, and the working electrode in the three-electrode system is a glassy carbon electrode spin-coated with the transition metal chalcogenide described in claim 1 . 10 . The preparation method according to claim 9 , wherein the electrolyte in the three-electrode system is a mixed solution of EmimBF ₄ and H ₂ O. 11 .