CN111592046A - Sulfur-defect-rich ferrophosphorus sulfide nanosheet and preparation method and application thereof - Google Patents

Abstract

The invention relates to the technical field of catalysts, and discloses a phosphorus sulfide iron nanosheet rich in sulfur defects and a preparation method and application thereof, wherein an electrochemical stripping method is adopted to strip massive phosphorus sulfide into phosphorus sulfide nanosheets, the phosphorus sulfide nanosheets are subjected to low-speed and high-speed centrifugal separation, washing and drying, and then calcining to obtain the phosphorus sulfide nanosheets rich in sulfur defects, the nanosheets have good electrochemical performance and stability, and when the phosphorus sulfide iron nanosheets are applied to electrochemical nitrogen fixation and ammonia synthesis, the synthesis rate of ammonia can reach 6.27 mu g h to the maximum extent^‑1mg^‑1 _catThe preparation method is simple and efficient, low in cost, high in controllability and good in reproducibility, and is suitable for industrial production.

Description

A kind of sulfur-rich ferrophosphorus sulfide nanosheets and preparation method and application thereof

technical field

The invention relates to the technical field of catalysts, in particular to a sulfur-defect-rich iron phosphorus sulfide nanosheet and a preparation method and application thereof.

Background technique

Ammonia is an important raw material for the manufacture of fertilizers, polymers, dyes and explosives. It is not only one of the most produced and widely used chemicals in the world, it is also considered a potential green energy carrier and a potential transportation fuel that can Responding to future global energy crises. At present, the Haber process is mainly used in industry for large-scale reaction of nitrogen and hydrogen to synthesize ammonia under high temperature and high pressure conditions, which requires a large amount of energy and emits a large amount of _CO2 greenhouse gas. In recent years, electrochemical ammonia synthesis technology has been regarded as an important means to solve these problems. Compared with the traditional Haber method, electrochemical nitrogen fixation ammonia synthesis technology has the characteristics of energy saving, cleanliness and convenience.

At present, noble metal catalysts are relatively efficient electrochemical nitrogen fixation catalysts for ammonia synthesis, but their high cost and scarcity of resources limit their large-scale applications. Compared with noble metal catalysts, transition metal compounds have become a research hotspot in recent years due to their unique electrochemical properties and controllable cost, especially in the field of nitrogen fixation to synthesize ammonia.

For example, publication number CN106111201A discloses a catalyst for electrochemical ammonia synthesis and a preparation method thereof. The catalyst is formed by coating carbon paper with metal organic framework, auxiliary carbon and binder. The metal ions in the metal organic framework are mainly alkaline earth metal elements, lanthanide metal elements, transition metal elements, etc. The catalyst of the present invention can synthesize ammonia at normal pressure and low temperature, and the energy consumption is greatly reduced. And it can directly use air as raw material to synthesize ammonia, which enriches the source of raw materials and reduces the cost of raw materials, thereby reducing the cost of synthetic ammonia.

Among transition metal catalysts, ferrophosphorus sulfide, as a typical ternary transition metal compound, has attracted extensive attention due to its unique two-dimensional structure, excellent physical and chemical properties, mechanical strength and flexibility. However, the use of ferric phosphorus sulfide as a cathode material for electrochemical nitrogen fixation to ammonia synthesis has not been reported yet. In addition, traditional two-dimensional nanosheet materials preparation methods, such as liquid phase exfoliation, mechanical exfoliation and redox methods, have problems such as uncontrollable product quality, difficult operation, low yield, and long time consumption.

For example, the Chinese patent document with the publication number CN108003873A discloses a chemically exfoliated ferric phosphorus sulfide quantum dot and a preparation method thereof. After ultrasonication, the large particles are removed by centrifugation, and the obtained supernatant is a solution containing ferric phosphorus sulfide quantum dots. However, this peeling method requires a heating device and has a low yield, which seriously hinders its application in industrialized large-scale production.

Therefore, it is of great significance to develop a catalytic material that is simple, efficient, low-cost, with controllable product quality, and suitable for large-scale production applications, so as to promote the widespread application of electrochemical nitrogen fixation for ammonia synthesis, thereby solving the energy crisis and other problems.

SUMMARY OF THE INVENTION

Aiming at the disadvantages of complicated preparation process and low yield in the prior art glass method of ferric phosphorus sulfide, the present invention provides a phosphorus sulfide rich in sulfur defects with high efficiency, controllable cost, high catalytic activity, suitable for large-scale production Preparation method of iron nanosheets.

For achieving the above object, the technical scheme adopted in the present invention is:

A preparation method of sulfur-defect-rich iron phosphorus sulfide nanosheets, comprising the steps of:

(1) Using the bulk ferrophosphorus sulfide as the working electrode and the platinum wire as the counter electrode, the bulk ferrophosphorus sulfide is electrochemically stripped in the electrolyte solution to form a nanosheet suspension;

(2) after centrifuging, washing and drying the nanosheet suspension of step (1), respectively, to obtain ferric phosphorus sulfide nanosheets;

(3) calcining the phosphorus sulfide nanosheets prepared in step (2) in a hydrogen atmosphere, and cooling to obtain the ferric phosphorus sulfide nanosheets rich in sulfur defects.

The electrolyte of the present invention includes one or more of tetramethylammonium bromide, tetraethylbutylammonium bromide, tetrapropylammonium bromide or tetrabutylammonium bromide. The molecular structure of this type of electrolyte is appropriate and can be effectively inserted between the layers of ferrophosphorus sulfide, causing the bulk ferrophosphorus sulfide to begin to expand and be exfoliated into a nano-sheet layered structure suspended in the solution.

In the prior art, the method of chemical glass is used to peel off the bulk phosphorus sulfide to obtain phosphorus sulfide quantum dots, but this method requires heating and the yield is low. In the present invention, the method of electrochemical peeling is used to peel off the bulk phosphorus sulfide. , and using tetramethylammonium bromide, tetraethylbutylammonium bromide, tetrapropylammonium bromide or tetrabutylammonium bromide as the electrolyte, before applying a negative voltage to the bulk iron phosphorus sulfide electrode, the iron phosphorus sulfide The material is still in the form of stacked sheets. When a positive voltage is applied, the tetrabutylammonium cations in the electrolyte move to the negative electrode and slowly intercalate between the iron phosphorus sulfide layers, causing the bulk iron phosphorus sulfide to expand and be exfoliated into a nanosheet-like layered structure suspended in the solution , and diffuse into the electrolyte. Compared with the prior art, the method is simple and convenient, can be operated at normal temperature, and has a considerable yield.

The concentration of the electrolyte is 1-10 mg/mL, and the concentration of the electrolyte has an important influence on the peeling speed of ferrophosphorus sulfide. The ferrophosphorus will fall off in lumps and cannot form nanosheets well.

The massive ferric phosphorus sulfide used in the present invention can be commercially available ferric phosphorus sulfide, or can be prepared by a chemical vapor transport method. The specific preparation process is as follows: mixing iron powder, phosphorus powder and sulfur powder and grinding them evenly, placing them in a sealed In the vacuum quartz tube, the heating rate is 1～10°C/min to 500～800°C, and kept for 100～140h, and after cooling, massive phosphorus sulfide is obtained.

The magnitude of the negative voltage and the pressure time during the electrochemical exfoliation process have a key impact on controlling the exfoliation speed of ferrophosphorus sulfide and the thickness of the resulting ferrophosphorus sulfide nanosheets. If the applied negative voltage is too small, the peeling speed of the ferrophosphorus sulfide material will be slow and the peeling efficiency will be low. Therefore, it is necessary to select an appropriate applied voltage to exfoliate the iron phosphorus sulfide into nanosheets at a relatively fast speed and disperse them into the electrolyte, and the thickness of the iron phosphorus sulfide nanosheets obtained after stripping is relatively uniform.

After repeated verifications, the inventor found that the negative voltage of the electrochemical stripping in step (1) was -4 to -8V; when the time of applying the negative voltage was 8 to 12 hours, the obtained ferrophosphorus sulfide nanosheets were obtained. The thickness comprehensive performance is good, and high-quality iron phosphorus sulfide nanosheets with uniform thickness can be obtained efficiently.

Preferably, the negative voltage of the electrochemical stripping is -5--6.5V; the time for applying the negative voltage is 9-10.5h. Under this exfoliation condition, the obtained ferric phosphorus sulfide nanosheets have better comprehensive properties.

Further preferably, the negative voltage of the electrochemical stripping is -6V; the time for applying the negative voltage is 10h. Under this exfoliation condition, the obtained ferric phosphorus sulfide nanosheets have the best comprehensive performance, and the catalyst finally obtained has the best catalytic activity.

In step (2), the centrifugal separation includes low-speed centrifugation and high-speed centrifugation. The rotating speed of the low-speed centrifugation is 1000-3000 rpm, and the centrifuging time is 20-40 min; the rotating speed of the high-speed centrifuging is 9000-13000 rpm, and the centrifuging time is 20-40 min.

The low-speed centrifugation is to remove the incompletely exfoliated ferric phosphorus sulfide in the solution, and the high-speed centrifugation is to obtain the exfoliated iron phosphorus sulfide in the liquid phase. Dividing the separation process into two steps can effectively improve the purity and yield of the product.

In step (3), the calcination time is 1-3h, and the calcination temperature is 200-400°C. The iron phosphorus sulfide nanosheets will be reduced during the calcination process, resulting in the absence of sulfur atoms, and then the formation of sulfur defects on the surface of the nanosheets. The method makes full use of the large specific surface area of the two-dimensional material ferrophosphorus sulfide, and forms more active sites on the plane of the ferrophosphorus sulfide nanosheet, which improves the catalytic activity.

In step (3), the heating rate is 1-10° C./min, and the volume concentration of the hydrogen atmosphere is 3-8%.

The present invention also provides a sulfur-defect-rich ferric phosphorus sulfide nanosheet prepared according to the preparation method, wherein the average thickness of the ferric phosphorus sulfide nanosheet is not greater than 15 nm. The ferrophosphorus sulfide nanosheets prepared by the method have uniform thickness and thin thickness, which can improve the efficiency of the ferrophosphorus sulfide nanosheets in the application process, and the material has better electrochemical performance and stability.

The invention also provides the application of the sulfur-defect-rich ferric phosphorus sulfide nanosheet in electrochemical nitrogen fixation to synthesize ammonia, and the maximum generation rate of the synthesized ammonia can reach 6.27 μg h ^-1 mg ^-1 _cat .

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

(1) One-step peeling of bulk ferrophosphorus sulfide materials to prepare ferrophosphorus sulfide nanosheets by electrochemical exfoliation method, and then simple calcination of the prepared ferrophosphorus sulfide nanosheets to manufacture defects, and synthesis of sulfur-rich ferrophosphorus sulfide nanosheets The nanosheet, the preparation method of the present invention is simple and efficient, has low cost, high controllability and good reproducibility, and is suitable for industrial production.

(2) The ferric phosphorus sulfide nanosheets rich in sulfur defects are used as cathode materials for electrocatalytic nitrogen fixation to ammonia synthesis reaction, and the materials have good electrochemical performance and stability. When the electrode potential is -0.3V (relative to the standard hydrogen electrode), the maximum generation rate of ammonia for electrocatalytic nitrogen fixation synthesis can reach 6.27μg h ^-1 mg ^-1 _cat .

Description of drawings

FIG. 1 is an SEM image of the sulfur-defect-rich iron phosphorus sulfide nanosheets prepared in Example 1. FIG.

FIG. 2 is a TEM image of the sulfur-defect-rich iron phosphorus sulfide nanosheets prepared in Example 1. FIG.

FIG. 3 is an XRD image of the sulfur-defect-rich iron phosphorus sulfide nanosheets prepared in Example 1. FIG.

FIG. 4 is an ESR image of the sulfur-defect-rich iron phosphorus sulfide nanosheets prepared in Example 1. FIG.

5 is the it curve of the electrocatalytic nitrogen fixation to synthesize ammonia by the sulfur-defect-rich ferric phosphorus sulfide nanosheets prepared in the embodiment 1 of the present invention in a 0.1M Na ₂ SO ₄ solution.

FIG. 6 is a diagram showing the Faradaic efficiency and the rate of generating ammonia of the electrocatalytic nitrogen fixation to synthesize ammonia by electrocatalytic nitrogen fixation to ammonia in 0.1M Na ₂ SO ₄ solution prepared by sulfur-defect-rich ferric phosphorus sulfide nanosheets prepared in Embodiment 1 of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. Those skilled in the art can make modifications or equivalent replacements on the basis of understanding the technical solutions of the present invention, without departing from the spirit and scope of the technical solutions of the present invention, and all should be included within the protection scope of the present invention.

Example 1

1. Preparation of bulk ferrophosphorus sulfide

(1) Mix the iron powder, phosphorus powder and sulfur powder according to the molar ratio of 1:1:3, after fully mixing and grinding, seal the mixed powder in a vacuum quartz glass tube;

(2) The above-mentioned quartz glass tube of the sealed mixed powder is heated in a tube furnace with a temperature of 650°C, kept for 120h, and the heating rate is 5°C/min. After heating, it is naturally cooled to room temperature to obtain massive phosphorus sulfide. Iron crystals.

2. Electrochemical stripping

The bulk ferric phosphorus sulfide was fixed on the copper sheet as the working electrode, the platinum wire was used as the counter electrode, and the N-methylpyrrolidone solution containing 5 mg/mL tetrabutylammonium bromide was used as the electrolyte to make the bulk phosphorus sulfide. The iron and platinum sheets were immersed in the electrolyte; a negative voltage of -6V was continuously applied to the working electrode for 10 hours to obtain a mixed solution of exfoliated iron phosphorus sulfide nanosheets;

3. Centrifugation and Washing

(1) centrifugally separate the ferric phosphorus sulfide nanosheet mixed solution after peeling, the centrifugal rotation speed is 2000rpm, the centrifugal time is 30min, and the supernatant is taken;

(2) the supernatant is further centrifuged, the centrifugal rotating speed is 10000rpm, and the centrifugation time is 30min, and the sediment is taken;

(3) centrifuging and washing the precipitate with deionized water 3 times, the centrifugal rotation speed is 10000rpm, and the centrifugation time is 30min to obtain the precipitate, which is freeze-dried to obtain phosphorus sulfide nanosheets.

4. Introduce defects

The phosphorus sulfide nanosheets obtained in step 3 were calcined in a 5% hydrogen atmosphere, the calcination temperature was 300° C., the holding time was 1 h, and the heating rate was 5° C./min. After cooling to room temperature, sulfur-defect-rich iron phosphorus sulfide nanosheets were obtained.

The surface morphology of the prepared ferric phosphorus sulfide nanosheets rich in sulfur defects was observed with a scanning electron microscope (SEM), as shown in Fig. ) to observe its surface morphology, as shown in Figure 2, it can be seen that there are obvious defect structures on the final iron phosphorus sulfide nanosheets, which is also confirmed by electron paramagnetic resonance (ESR), as shown in Figure 4, it can be seen that sulfur-rich defects The magnetic induction intensity of ferrophosphorus sulfide nanosheets is stronger than that of defect-free ferrophosphorus sulfide nanosheets;

The prepared ferric phosphorus sulfide nanosheets rich in sulfur defects were observed with an X-ray diffractometer (XRD) to observe their crystallization, as shown in Figure 3, the crystal peaks of the ferric phosphorus sulfide nanosheets prepared in this example and the standard card can be seen. The peaks of ferric phosphorus sulfide are basically the same.

Application Example 1 Three-electrode system for electrochemical nitrogen fixation to synthesize ammonia

1. Activation treatment of catalyst

(1) Using a three-electrode system, the working electrode is the sulfur-rich ferrophosphorus sulfide nanosheet of Example 1, the counter electrode is a platinum column, the reference electrode is a saturated silver/silver chloride electrode, and the electrolyte is 0.1M sulfuric acid sodium solution;

(2) Cyclic voltammetry (CV) activation: Shanghai Chenhua CHI 660E electrochemical workstation was used, nitrogen gas was introduced into the electrolyte for 30 minutes before the test, and the CV program was used. ), the scan rate was 50 mV/s, and the CV cycle was 50 cycles, and the electrode reached a steady state.

2. Stability test

After CV activation, switch the program to i-t program, set the applied voltage to -0.2V, -0.3V, -0.4V, -0.5V (all relative to the standard hydrogen electrode) in turn, and set the application time to 7200s. Its i-t curve is shown in Fig. 5, and the current of the catalyst remains stable, which proves that the as-prepared sulfur-defect-rich ferrophosphorus sulfide nanosheets have good stability under different voltages.

Figure 6 shows the Faradaic efficiency and ammonia production rate of the corresponding cathode material electrochemical nitrogen fixation to ammonia synthesis under different applied voltages. It can be seen from the figure that when the applied voltage is -0.3V (relative to the standard hydrogen electrode), the nitrogen reduction rate is the largest, It reaches 6.27μg h ^-1 mg ^-1 _cat ., and the corresponding Faradaic efficiency is 9.20%; with the increase of the applied voltage, the production of synthetic ammonia also increases, and when it increases to a certain value, there is a decreasing trend.

This application example shows that the obtained sulfur-rich ferrophosphorus sulfide nanosheets have excellent electrochemical performance and good stability as a catalyst for electrochemical nitrogen fixation to synthesize ammonia.

Example 2

1. Preparation of bulk ferrophosphorus sulfide

(1) Mix the iron powder, phosphorus powder and sulfur powder according to the molar ratio of 1:1:3, after fully mixing and grinding, seal the mixed powder in a vacuum quartz glass tube;

(2) The above-mentioned quartz glass tube of the sealed mixed powder is heated in a tube furnace with a temperature of 650°C, kept for 120h, and the heating rate is 5°C/min. After heating, it is naturally cooled to room temperature to obtain massive phosphorus sulfide. Iron crystals.

2. Electrochemical stripping

The bulk ferric phosphorus sulfide was fixed on the copper sheet as the working electrode, the platinum wire was used as the counter electrode, and the N-methylpyrrolidone solution containing 5 mg/mL tetrabutylammonium bromide was used as the electrolyte to make the bulk phosphorus sulfide. The iron and platinum sheets were immersed in the electrolyte; a negative voltage of -4V was continuously applied to the working electrode for 10 hours to obtain a mixed solution of exfoliated iron phosphorus sulfide nanosheets;

3. Centrifugation and Washing

(1) centrifugally separate the ferric phosphorus sulfide nanosheet mixed solution after peeling, the centrifugal rotation speed is 2000rpm, the centrifugal time is 30min, and the supernatant is taken;

(2) the supernatant is further centrifuged, the centrifugal rotating speed is 10000rpm, and the centrifugation time is 30min, and the sediment is taken;

(3) centrifuging and washing the precipitate with deionized water 3 times, the centrifugal rotation speed is 10000rpm, and the centrifugation time is 30min to obtain the precipitate, which is freeze-dried to obtain phosphorus sulfide nanosheets.

4. Introduce defects

The phosphorus sulfide nanosheets obtained in step 3 were calcined in a 5% hydrogen atmosphere, the calcination temperature was 300° C., the holding time was 1 h, and the heating rate was 5° C./min. After cooling to room temperature, sulfur-defect-rich iron phosphorus sulfide nanosheets were obtained.

Application Example 2 Three-electrode system for electrochemical nitrogen fixation to synthesize ammonia

1. Activation treatment of catalyst

(1) Using a three-electrode system, the working electrode is the sulfur-rich ferrophosphorus sulfide nanosheet of Example 2, the counter electrode is a platinum column, the reference electrode is a saturated silver/silver chloride electrode, and the electrolyte is 0.1M sulfuric acid sodium solution;

(2) Cyclic voltammetry (CV) activation: Shanghai Chenhua CHI 660E electrochemical workstation was used, nitrogen gas was introduced into the electrolyte for 30 minutes before the test, and the CV program was used. ), the scan rate was 50 mV/s, and the CV cycle was 50 cycles, and the electrode reached a steady state.

2. Stability test

After CV activation, switch the program to i-t program, set the applied voltage to -0.2V, -0.3V, -0.4V, -0.5V (all relative to the standard hydrogen electrode) in turn, and set the application time to 7200s. The current of the catalyst remains relatively stable, which proves that the as-prepared sulfur-rich ferrophosphorus sulfide nanosheets have good stability under different voltages.

When the applied voltage is -0.3V (relative to the standard hydrogen electrode), the nitrogen reduction rate is the largest, reaching 5.11μgh ^-1 mg ^-1 _cat . The corresponding Faradaic efficiency is 6.23%; with the increase of the applied voltage, the synthesis of ammonia The output also increased, and after reaching a certain value, there was a decreasing trend.

This application example illustrates that the sulfur-defect-rich ferric phosphorus sulfide nanosheets obtained in Example 2 are used as catalysts for electrochemical nitrogen fixation to synthesize ammonia, and the electrochemical performance is also superior and the stability is good.

Example 3

1. Preparation of bulk ferrophosphorus sulfide

(1) Mix the iron powder, phosphorus powder and sulfur powder according to the molar ratio of 1:1:3, after fully mixing and grinding, seal the mixed powder in a vacuum quartz glass tube;

(2) The above-mentioned quartz glass tube of the sealed mixed powder is heated in a tube furnace with a temperature of 650°C, kept for 120h, and the heating rate is 5°C/min. After heating, it is naturally cooled to room temperature to obtain massive phosphorus sulfide. Iron crystals.

2. Electrochemical stripping

The bulk ferric phosphorus sulfide was fixed on the copper sheet as the working electrode, the platinum wire was used as the counter electrode, and the N-methylpyrrolidone solution containing 5 mg/mL tetrabutylammonium bromide was used as the electrolyte to make the bulk phosphorus sulfide. The iron and platinum sheets were immersed in the electrolyte; a negative voltage of -8V was continuously applied to the working electrode for 10 h to obtain a mixed solution of exfoliated iron phosphorus sulfide nanosheets;

3. Centrifugation and Washing

(1) centrifugally separate the ferric phosphorus sulfide nanosheet mixed solution after peeling, the centrifugal rotation speed is 2000rpm, the centrifugal time is 30min, and the supernatant is taken;

(2) the supernatant is further centrifuged, the centrifugal rotating speed is 10000rpm, and the centrifugation time is 30min, and the sediment is taken;

(3) centrifuging and washing the precipitate with deionized water 3 times, the centrifugal rotation speed is 10000rpm, and the centrifugation time is 30min to obtain the precipitate, which is freeze-dried to obtain phosphorus sulfide nanosheets.

4. Introduce defects

The phosphorus sulfide nanosheets obtained in step 3 were calcined in a 5% hydrogen atmosphere, the calcination temperature was 300° C., the holding time was 1 h, and the heating rate was 5° C./min. After cooling to room temperature, sulfur-defect-rich iron phosphorus sulfide nanosheets were obtained.

Application Example 3 Three-electrode system for electrochemical nitrogen fixation to synthesize ammonia

1. Activation treatment of catalyst

(1) Using a three-electrode system, the working electrode is the sulfur-rich ferrophosphorus sulfide nanosheet of Example 3, the counter electrode is a platinum column, the reference electrode is a saturated silver/silver chloride electrode, and the electrolyte is 0.1M sulfuric acid sodium solution;

(2) Cyclic voltammetry (CV) activation: Shanghai Chenhua CHI 660E electrochemical workstation was used, nitrogen gas was introduced into the electrolyte for 30 minutes before the test, and the CV program was used. ), the scan rate was 50 mV/s, and the CV cycle was 50 cycles, and the electrode reached a steady state.

2. Stability test

After CV activation, switch the program to i-t program, set the applied voltage to -0.2V, -0.3V, -0.4V, -0.5V (all relative to the standard hydrogen electrode) in turn, and set the application time to 7200s. The current retention of the catalyst is also relatively stable, proving that the as-prepared sulfur defect-rich ferrophosphorus sulfide nanosheets have good stability under different voltages.

When the applied voltage is -0.3V (relative to the standard hydrogen electrode), the nitrogen reduction rate is the largest, reaching 5.24μgh ^-1 mg ^-1 _cat . The corresponding Faradaic efficiency is 7.11%; with the increase of the applied voltage, the synthesis of ammonia The output also increased, and after reaching a certain value, there was a decreasing trend.

Comparative Example 1

Compared with Example 1, the only difference is that the unexfoliated bulk iron phosphorus sulfide powder is directly used for electrochemical nitrogen fixation to synthesize ammonia, and other conditions are the same.

As shown in Application Example 1, the three-electrode system is used for electrochemical nitrogen fixation to synthesize ammonia. The working electrode is bulk ferric phosphorus sulfide supported on carbon paper. When the applied voltage is -0.3V (relative to the standard hydrogen electrode), the electrocatalytic nitrogen fixation to synthesize ammonia The Faradaic efficiency was 4.71%, and the rate of synthesis of ammonia was 3.96 μg h ^-1 mg ^-1 _cat. .

Comparative Example 2

Compared with Example 1, the only difference lies in the electrochemical synthesis of ammonia by directly using ferrophosphorus sulfide nanosheets, and other conditions are the same.

The three-electrode system shown in Application Example 1 was used for electrochemical synthesis of ammonia, and the working electrode was ferrophosphorus sulfide nanosheets supported on carbon paper. Under the voltage of -0.3V (relative to the standard hydrogen electrode), the Faradaic efficiency of electrocatalytic ammonia synthesis was 6.13%, and the ammonia formation rate was 4.85μg h ^-1 mg ^-1 _cat. .

Claims (9)

1. A preparation method of a sulfur defect-rich ferro-phosphorus sulfide nanosheet is characterized by comprising the following steps:

(1) the method comprises the following steps of (1) electrochemically stripping blocky ferric phosphate sulfide in an electrolyte solution by using the blocky ferric phosphate sulfide as a working electrode and a platinum wire as a counter electrode to form a nanosheet suspension;

(2) respectively carrying out centrifugal separation, washing and drying on the nanosheet suspension liquid obtained in the step (1) to obtain a ferric phosphorus sulfide nanosheet;

(3) and (3) calcining the phosphorus sulfide nanosheet prepared in the step (2) in a hydrogen atmosphere, and cooling to obtain the sulfur defect-rich phosphorus sulfide iron nanosheet.

2. The method of preparing sulfur-deficient iron phosphorous sulfide nanoplates as in claim 1, wherein the electrolyte comprises one or more of tetramethylammonium bromide, tetrabutylammonium bromide, tetrapropylammonium bromide, or tetrabutylammonium bromide.

3. The method for preparing sulfur-defect-rich iron phosphorous sulfide nanosheets according to claim 1, wherein the concentration of electrolyte in the electrolyte solution is 1-10 mg/mL.

4. The method for preparing sulfur-defect-rich iron phosphorous sulfide nanosheets according to claim 1, wherein in step (1), the negative voltage for electrochemical stripping is from-4 to-8V; the time for applying the negative voltage is 8-12 h.

5. The method for preparing sulfur-defect-rich iron phosphorous sulfide nanosheets according to claim 1, wherein in step (1), the negative voltage for electrochemical stripping is from-5 to-6.5V; the time for applying the negative voltage is 9-10.5 h.

6. The preparation method of sulfur-defect-rich iron phosphorous sulfide nanosheets according to claim 1, wherein in the step (2), the centrifugal separation comprises low-speed centrifugation and high-speed centrifugation, wherein the rotation speed of the low-speed centrifugation is 1000-3000 rpm, and the centrifugation time is 20-40 min; the rotating speed of the high-speed centrifugation is 9000-13000 rpm, and the centrifugation time is 20-40 min.

7. The preparation method of sulfur-defect-rich iron phosphorus sulfide nanosheets according to claim 1, wherein in step (3), the roasting temperature is 200-400 ℃ and the roasting time is 1-3 h.

8. A sulfur defect-rich iron phosphorus sulfide nanosheet prepared according to the preparation method of any one of claims 1-7, the iron phosphorus sulfide nanosheet having an average thickness of no greater than 15 nm.

9. The use of sulfur-defect-rich iron phosphorous sulfide nanoplates as defined in claim 8 in the electrochemical nitrogen fixation synthesis of ammonia.

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