Step-shaped nanometer tungsten diselenide, and preparation method and application thereof

Abstract

The present invention provides a step-shaped nano-tungsten diselenide and its preparation method and application. The method comprises the following steps: in a dual-temperature zone chemical vapor deposition system, selenium powder is placed upstream of the gas path, and a metal tungsten mesh is placed downstream of the gas path; chemical vapor deposition is carried out in sequence through a temperature ramp and a constant temperature program; and rapid cooling is performed after the constant temperature program is completed to obtain the step-shaped nano-tungsten diselenide. In the low-temperature zone where the selenium powder is located, the maximum reaction temperature is 500°C; in the high-temperature zone where the tungsten mesh is located, the maximum reaction temperature is 700°C. The method of the present invention effectively solves many problems of the existing nano-tungsten diselenide preparation process, such as the complex reaction temperature, the difficulty in achieving precise control at the nanoscale, and the high production cost. Moreover, the experimental results are highly reproducible, and the step-shaped nano-tungsten diselenide exhibits excellent catalytic activity and stability in the field of electrocatalysis, and has broad application prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanocatalysts, and particularly relates to a stepped nanometer tungsten diselenide and a preparation method and application thereof. BACKGROUND

[0002] Under the background of increasingly serious energy crisis and environmental problems, electrocatalysis technology as a green and efficient energy conversion method has attracted widespread attention. The development and application of nanomaterials are of great significance to improve the electrocatalytic performance. As a two-dimensional layered material, tungsten diselenide has great application potential in the fields of electrocatalytic water splitting, oxygen reduction reaction and nitrogen reduction reaction due to its unique electronic structure and excellent electrocatalytic activity. Therefore, developing a rapid, efficient and accurate nanometer structure control method for preparing tungsten diselenide is of great significance to promote its application in the field of electrocatalysis.

[0003] In the prior art, the preparation methods of traditional multi-edge tungsten diselenide nanomaterials include chemical vapor deposition, various exfoliation methods, laser cutting method, ball milling method, etc., but all have certain limitations. The chemical vapor deposition method has a high reaction temperature, which is difficult to ensure the integrity of the multi-edge structure, and it is also difficult to accurately control the size, shape and distribution of the edge structure. The exfoliation method has a difficult reaction condition to control, which is easy to cause uneven growth of the edge structure, and the high requirement for the exfoliation process further increases the preparation cost. The laser cutting method is expensive and complicated to operate, and the material is easily damaged during the cutting process, which is difficult to mass-produce nanomaterials with ideal edge structure. When the ball milling method is used to prepare multi-edge nanomaterials by mechanical force, not only impurities are introduced to affect the material performance, but also it is difficult to form a regular edge structure, and the size distribution of the product is uneven. As can be seen, the current multi-edge tungsten diselenide material has many problems such as complex preparation process, difficulty in accurate control of nanometer scale, high production cost, etc. Especially, the micro-morphology of the multi-edge nanostep tungsten diselenide has a high catalytic activity due to the large number of edge active sites provided by the structure, and the ladder morphology can provide better stability, which has broad application prospects, but the preparation method is obviously more challenging.

[0004] In summary, how to efficiently prepare the stepped tungsten diselenide with high quality and accurate nanometer scale control, and then apply it to the field of energy conversion and storage, is a technical problem to be solved by those skilled in the art. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of stepped nanometer tungsten diselenide.

[0006] The application is specifically to use selenium powder as selenium source and tungsten mesh as tungsten source, adopt chemical vapor deposition technology, and then prepare nanometer step-shaped tungsten diselenide covering the tungsten mesh substrate by the method of "rapid cooling". The method has simple preparation process, low reaction temperature, and does not need substrate to avoid the problem of introducing impurities, and can realize accurate control of nanometer structure by high-efficiency and rapid means. The obtained step-shaped nanometer tungsten diselenide has high activity and high stability, can be widely applied in the field of nanometer material electrocatalysis, and has wide industrial prospect.

[0007] To achieve the above object, the application provides a preparation method of step-shaped nanometer tungsten diselenide, which comprises the following steps: placing selenium powder on the upstream of the gas path and placing metal tungsten mesh on the downstream of the gas path in a double-temperature-zone chemical vapor deposition system, sequentially performing chemical vapor deposition through a temperature rising program and a constant temperature program, and then performing rapid cooling after the constant temperature program is finished, so that the step-shaped nanometer tungsten diselenide is obtained.

[0008] In a preferred embodiment, the selenium powder is analytically pure, and the particle size is ≤75 μm.

[0009] In a preferred embodiment, the purity of the metal tungsten mesh is ≥99.95%, and the pore size is 150-200 mesh; preferably, the area of the metal tungsten mesh is 5*5 cm 2 ; more preferably, the metal tungsten mesh is tungsten mesh after ultrasonic pretreatment; the purpose of ultrasonic cleaning is to remove impurities on the surface of the tungsten mesh, so that the conventional pretreatment method mastered by those skilled in the art can be used, for example, the tungsten mesh is cleaned with deionized water and anhydrous ethanol respectively at room temperature for 3000 s.

[0010] The traditional synthesis method of diselenide adopts two kinds of powder raw materials, for example, selenium powder and tungsten trioxide. The disadvantage of this method is that the material synthesis needs a substrate, usually silicon wafer and sapphire. However, neither of the two substrates has conductivity, and if the catalytic reaction is carried out, it needs to be transferred to a substrate with high conductivity and no catalytic effect, such as glassy carbon. However, there are many problems in the transfer process: (1) the adhesion between tungsten diselenide and sapphire substrate is usually strong, and the adhesion between tungsten diselenide and glassy carbon substrate is weak, which makes it difficult to completely peel off the tungsten diselenide layer in the transfer process, causing damage or residue of the material. (2) In the transfer process, the surface of tungsten diselenide is easily contaminated by dust, impurities and the like, which will affect the results of electrochemical test. (3) In the transfer process, the microstructure and morphology of tungsten diselenide are easily damaged, such as the collapse of layer structure, which will also affect its electrochemical performance. (4) The transfer process needs precise operation technology to ensure the integrity and original crystal structure of tungsten diselenide in the transfer process, which requires high operation skill. As can be seen, there are many difficulties in transferring tungsten diselenide from the substrate to the glassy carbon substrate for catalytic reaction.

[0011] In the present application, the step-shaped nanometer tungsten diselenide is directly grown on the metal tungsten mesh, thus constructing a solid integrated (self-supporting integrated catalyst) catalyst system. In the synthesis process, the metal tungsten mesh is used as a raw material; in the catalysis stage, thanks to the support of the high-conductivity metal mesh, each layer and each part of the catalyst is supplied with sufficient electrons, which significantly improves the electron transmission efficiency in the step-shaped nanometer tungsten diselenide catalytic layer and greatly improves the conductivity of the material. In the test stage, the step-shaped nanometer tungsten diselenide catalyst directly grown on the metal tungsten mesh constitutes an integrated electrode without other supports. The problem of catalyst reloading existing in the traditional catalyst test is effectively avoided, the structural design of the present application simplifies the preparation process of the catalyst, reduces the cost, and improves the stability and service life of the catalyst.

[0012] In a preferred embodiment, the region where the selenium powder is located is a low-temperature zone; and the region where the tungsten mesh is located is a high-temperature zone.

[0013] In a preferred embodiment, the temperature rising procedure comprises: in the low-temperature zone, rising from room temperature to temperature A within 30-50 min; and in the high-temperature zone, rising from room temperature to temperature B within 30-50 min, and temperature A is less than temperature B.

[0014] In a preferred embodiment, the constant temperature procedure comprises: in the low-temperature zone, keeping temperature A for 1-20 min; and in the high-temperature zone, keeping temperature B for 1-20 min.

[0015] In a preferred embodiment, temperature A is below 500℃; and temperature B is below 700℃.

[0016] In the present application, by using the metal tungsten mesh as a reaction raw material, the reaction of the powder tungsten source evaporation with selenium is effectively avoided, so the reaction temperature is significantly lower than the traditional process parameters. At the same time, due to the lower reaction temperature, it is helpful to accurately control the size and layer number of WSe2, which is more conducive to the formation of uniform nanostructure and avoids rapid growth and uneven deposition under high temperature. In addition, low-temperature synthesis avoids the loss of selenium or other side reactions caused by high temperature. Not only reduces energy consumption and harmful gas emission, but also is friendly to the environment, reduces the thermal stress of CVD equipment caused by high temperature, prolongs the service life of the equipment, improves the safety of operation, and reduces the possibility of fire and equipment failure.

[0017] In a preferred embodiment, the temperature rising rate of the low-temperature zone is 10-15℃ / min; and the temperature rising rate of the high-temperature zone is 15-20℃ / min; preferably, the temperature rising rate of the low-temperature zone is 12.5℃ / min; and the temperature rising rate of the high-temperature zone is 17.5℃ / min.

[0018] In a preferred embodiment, the chemical vapor deposition specifically comprises the following steps:

[0019] In the temperature rising procedure, the low temperature zone and the high temperature zone are simultaneously raised in temperature, and before the temperature of the high temperature zone reaches temperature B, the carrier gas used is argon, and the flow rate of the argon is 80-120 sccm; preferably, the flow rate of the argon is 100 sccm.

[0020] When the temperature of the high temperature zone reaches temperature B to the end of the constant temperature procedure, the carrier gas used is hydrogen-argon mixed gas, and the flow rate of the hydrogen-argon mixed gas is 80-120 sccm; preferably, the flow rate of the hydrogen-argon mixed gas is 100 sccm.

[0021] In the present application, the carrier gas is changed from argon to hydrogen-argon mixed gas when the temperature is raised, and the purpose is to promote the formation of tungsten diselenide by using the reducing property of hydrogen, and at the same time, hydrogen can also inhibit unnecessary evaporation of selenium, maintain a high selenium pressure, and help to form a nano-step structure with rich active sites, thereby improving the electrocatalytic activity and stability of the catalyst.

[0022] The flow rate of the carrier gas has a significant influence on the formation and morphology of the nanostructure, and a higher flow rate of the carrier gas can enhance the transmission efficiency of the reactant molecules, and help to form uniform nanostructures, but at the same time, it can promote the rapid consumption of raw materials and the premature deposition of products, and a lower flow rate of the carrier gas can cause the reactants to stay in the reaction chamber for too long, resulting in local overheating and uneven growth, therefore, the suitable flow rate of the carrier gas designed in the present application is crucial for realizing the ideal nano-step structure.

[0023] In a preferred embodiment, the volume ratio of hydrogen to argon in the hydrogen-argon mixed gas is (1:9)-(2:8).

[0024] In a preferred embodiment, the rapid cooling specifically comprises the following steps:

[0025] Immediately after the end of the constant temperature procedure, the cover of the tube furnace is opened, and the pipeline is flushed with the carrier gas, and the carrier gas used is argon, and the flow rate of the argon is 400-600 sccm; preferably, the flow rate of the argon is 500 sccm.

[0026] In the present application, the strategy of rapid cooling and high flow rate carrier gas flushing is adopted, and the purpose is to rapidly terminate the reaction, prevent the high-energy nano-step edge structure formed in the reaction from being repaired during the cooling process, and thus ensure that these high-activity edge structures are retained, therefore, the defined conditions are significant for realizing the preparation of high-quality step-shaped nano tungsten diselenide.

[0027] Another purpose of the present application is to provide step-shaped nano tungsten diselenide prepared by the method of any one of the above.

[0028] In a preferred embodiment, the step width of the step-shaped nanometer tungsten diselenide is between 1-20 nm.

[0029] In the present application, by designing the nanometer step structure, the specific surface area of tungsten diselenide is significantly increased, more active sites are exposed, and more reaction sites are provided for hydrogen evolution reaction, thereby effectively improving the electrocatalytic hydrogen evolution efficiency. According to the existing theoretical calculation, the adsorption energy of hydrogen atom at the edge is significantly better than that on the basal plane, ΔG H* is closer to zero, which means that hydrogen atoms are more easily adsorbed and desorbed at the edge, and the increase of edge active sites further reduces the energy barrier of hydrogen evolution reaction, thereby improving the reaction rate. At the same time, the nanometer step structure can also promote the transmission of electrons on the surface of tungsten diselenide, thereby improving the conductivity of tungsten diselenide and further enhancing its hydrogen evolution performance.

[0030] Another object of the present application is to provide the step-shaped nanometer tungsten diselenide prepared by the method of any one of the above-mentioned applications in the field of electrocatalysis.

[0031] Compared with the prior art, the technical scheme of the present application has the following advantages:

[0032] The present application adopts the normal pressure chemical vapor deposition method, which can quickly and lowly produce nanometer step-shaped tungsten diselenide with high activity and high stability. The designed method has good repeatability and simple operation, and is especially suitable for continuous large-scale industrial production.

[0033] From the raw materials, in the present application, selenium powder is used as the selenium source, and tungsten mesh is used as the tungsten source, so that the step-shaped nanometer tungsten diselenide is directly grown on the metal tungsten mesh, thereby constructing a solid integrated (self-supporting integrated catalyst) catalyst system. In the synthesis process, the metal tungsten mesh is used as a raw material; in the catalytic stage, it serves as a high-conductivity substrate; in the test stage, the metal tungsten mesh and the catalyst form an integrated electrode without the need for other support bodies.

[0034] From the process, the present application finds that a multi-edge nanometer step-shaped structure is generated in the kinetic synthesis process of selenium powder and tungsten mesh, but this structure is a metastable state due to its high surface energy, which is unstable in thermodynamics. Therefore, the present application designs a "rapid cooling" method to terminate the reaction by rapidly reducing the temperature, thereby preventing the repair of the high-energy nanometer step edge structure during the cooling process, and ensuring that these high-activity edge structures are retained to the greatest extent, so that the morphology and properties of the nanostructure can be accurately controlled. The conventional slow cooling process will cause the system to reduce the edge position through grain rotation and migration, thereby tending to a lower surface energy state, and thus eliminating these high-energy edges.

[0035] From the product, the nano step-shaped tungsten diselenide prepared by the present application uses the metal tungsten net as the conductive substrate to form a self-supporting integrated catalyst. The integrated catalyst can greatly improve the conductivity of the material and has high stability, eliminates the transfer and loading process required by the traditional powder or thin film catalyst during testing, reduces the testing cost and improves the material conductivity. At the same time, the nano step-shaped structure also provides a large number of edge active sites and has excellent stability, and has better catalytic activity than the noble metal Pt / C catalyst in the three-electrode hydrogen evolution test and proton exchange membrane (PEM) electrolytic cell test.

[0036] Particularly in the PEM electrolytic cell test, the nano step-shaped tungsten diselenide is used as a cathode electrocatalyst, and a commercial IrO2 is used as an anode electrocatalyst. When the current density is 1.0 A / cm 2 and 2.0 A / cm 2 , the required cell voltage of the electrolytic cell is only 1.85 V and 2.32 V, which is better than the case of using a commercial noble metal Pt / C as a cathode catalyst (1.857 V and 2.51 V, respectively). At the same time, in the effective active area of 4*4 cm 2 , the cost of the nano step-shaped tungsten diselenide is only 0.5 dollars, which is much lower than the 2 dollars of Pt / C (calculated according to the loading amount of Pt of 0.4 mg / cm 2 ). And the PEM electrolytic cell with nano step-shaped tungsten diselenide as the cathode can be stably operated for 200 h, and the voltage is maintained at about 1.86 V without significant increase. These excellent electrolysis voltage and stability further prove the practical potential of the nano step-shaped tungsten diselenide electrocatalyst of the present application in the field of water electrolysis. BRIEF DESCRIPTION OF DRAWINGS

[0037] These and / or other aspects and advantages of the present application will become more apparent and more readily appreciated from the following detailed description of the embodiments of the present application, taken in conjunction with the accompanying drawings in which:

[0038] Figure 1 The experimental device schematic diagram for preparing the nano step-shaped tungsten diselenide of the present application by chemical vapor deposition method;

[0039] Figure 2 The transmission electron microscope photo of the nano step-shaped tungsten diselenide grown on the metal tungsten net substrate prepared by the three repeated experiments of Example 2 of the present application;

[0040] Figure 3 The transmission electron microscope photo of the nano step-shaped tungsten diselenide grown on the metal tungsten net substrate prepared by Example 1 (left photo) and Example 3 (right photo) of the present application;

[0041] Figure 4A transmission electron microscope photo of nanometer tungsten diselenide grown on a metal tungsten mesh substrate prepared for Comparative Example 1;

[0042] Figure 5 A Raman spectrum of nanometer step-shaped tungsten diselenide grown on a metal tungsten mesh substrate prepared for Example 2 of the present application;

[0043] Figure 6 A current density-potential curve diagram in an electrochemical hydrogen evolution reaction of step-shaped nanometer tungsten diselenide prepared for Examples 1-3 of the present application as a cathode catalyst in a 0.5M H2SO4 electrolyte;

[0044] Figure 7 A current density-potential curve diagram in an electrochemical hydrogen evolution reaction of step-shaped nanometer tungsten diselenide prepared for Example 2 of the present application and nanometer tungsten diselenide prepared for Comparative Example 1 as a cathode catalyst in a 0.5M H2SO4 electrolyte;

[0045] Figure 8 A current density-potential curve diagram in an electrochemical hydrogen evolution reaction of step-shaped nanometer tungsten diselenide prepared for Example 2 of the present application and nanometer tungsten diselenide prepared for Comparative Example 1 in a PEM electrolysis cell test with pure water as an electrolyte;

[0046] Figure 9 A stability test diagram of step-shaped nanometer tungsten diselenide prepared for Example 2 of the present application in a PEM electrolysis cell test with pure water as an electrolyte obtained by a constant current method.

[0047] Figure 10 A Raman spectrum of step-shaped nanometer tungsten diselenide prepared for Example 2 of the present application after a 200h stability test. DETAILED DESCRIPTION

[0048] In order to make the skilled in the art better understand the present application, the present application is further described in detail below in combination with the drawings and specific embodiments, but it should be understood that the protection scope of the present application is not limited by the specific embodiments.

[0049] The present application provides a step-shaped nanometer tungsten diselenide, a preparation method and application thereof, and solves the problems of complex preparation process, difficulty in accurate control of nanometer scale, high production cost and other problems of conventional tungsten diselenide nanometer material in the prior art.

[0050] The technical solutions of the present application are described in detail below through specific embodiments, Figure 1 A synthesis process diagram of the present application, the synthesis process adopts a chemical vapor deposition double-temperature zone synthesis method, and selenium powder and a metal tungsten mesh are used as reaction raw materials.

[0051] Unless otherwise specified, the technical means used in the present application are the conventional means familiar to those skilled in the art, and various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or prepared by existing methods. The reagents used in the present application are analytical pure unless otherwise specified.

[0052] Example 1

[0053] A preparation method of a stepped nanometer tungsten diselenide, comprising the following steps:

[0054] The metal tungsten mesh is prepared, and deionized water and anhydrous ethanol are used to clean the tungsten mesh at room temperature for 3000s to obtain a tungsten source.

[0055] In a double-temperature-zone chemical vapor deposition system, 0.05g of selenium powder is weighed and placed in a quartz boat in the left temperature zone of the tube furnace, and the tungsten mesh (with an area of 1*1cm 2 ) is placed in a quartz boat in the right temperature zone of the tube furnace.

[0056] Before heating, vacuum is first performed to exhaust the air in the tube furnace, and then argon gas with a flow rate of 100sccm is introduced as a carrier gas.

[0057] The specific temperature rising program and constant temperature program are as follows:

[0058] In the temperature rising program, the low-temperature zone is heated from room temperature to 500℃ at a rate of 12.5℃ / min for 40min; at the same time, the high-temperature zone is heated from room temperature to 700℃ at a rate of 17.5℃ / min for 40min; in this program, the carrier gas is argon, and the flow rate is 100sccm;

[0059] In the constant temperature program, the low-temperature zone is kept at 500℃ for 1min, and the high-temperature zone is kept at 700℃ for 1min; in this program, the carrier gas is a mixed gas of hydrogen and argon with a volume ratio of 1:9, and the flow rate is 100sccm;

[0060] After the constant temperature ends, rapid cooling is performed, the tube furnace insulation cover is immediately opened, and the pipeline is cleaned with a carrier gas, wherein the carrier gas is argon, and the flow rate of the carrier gas is 500sccm.

[0061] After cooling to room temperature, a stepped nanometer tungsten diselenide is obtained.

[0062] Example 2

[0063] A preparation method of a stepped nanometer tungsten diselenide, comprising the following steps:

[0064] The metal tungsten mesh is prepared, and deionized water and anhydrous ethanol are used to clean the tungsten mesh at room temperature for 3000s to obtain a tungsten source.

[0065] In the double-temperature-zone chemical vapor deposition system, 0.05 g of selenium powder is placed in a quartz boat in the left temperature zone of the tube furnace, and a tungsten mesh (with an area of 1*1 cm 2 ) is placed in a quartz boat in the right temperature zone of the tube furnace.

[0066] Before heating, vacuum is first performed to discharge the air in the tube furnace, and then argon gas with a flow rate of 100 sccm is introduced as the carrier gas.

[0067] The specific temperature rising program and the constant temperature program are as follows:

[0068] In the temperature rising program, the low-temperature zone is heated from room temperature to 500℃ at a rate of 12.5℃ / min for 40 min; at the same time, the high-temperature zone is heated from room temperature to 700℃ at a rate of 17.5℃ / min for 40 min; in this program, the carrier gas is argon, and the flow rate is 100 sccm;

[0069] In the constant temperature program, the low-temperature zone is kept at 500℃ for 10 min, and the high-temperature zone is kept at 700℃ for 10 min; in this program, the carrier gas is a mixture of hydrogen and argon with a volume ratio of 1:9, and the flow rate is 100 sccm;

[0070] After the constant temperature program ends, rapid cooling is performed, the tube furnace insulation cover is immediately opened, and the pipeline is cleaned with the carrier gas, which is argon, and the flow rate of the carrier gas is 500 sccm.

[0071] After cooling to room temperature, a step-shaped nano tungsten diselenide is obtained.

[0072] Example 3

[0073] A preparation method of a step-shaped nano tungsten diselenide includes the following steps:

[0074] The tungsten mesh is prepared by cleaning with deionized water and anhydrous ethanol for 3000 s at room temperature to obtain a tungsten source.

[0075] In the double-temperature-zone chemical vapor deposition system, 0.05 g of selenium powder is placed in a quartz boat in the left temperature zone of the tube furnace, and a tungsten mesh (with an area of 1*1 cm 2 ) is placed in a quartz boat in the right temperature zone of the tube furnace.

[0076] Before heating, vacuum is first performed to discharge the air in the tube furnace, and then argon gas with a flow rate of 100 sccm is introduced as the carrier gas.

[0077] The specific temperature rising program and the constant temperature program are as follows:

[0078] In the temperature rising procedure, the low temperature zone is raised from room temperature to 500℃ at a rate of 12.5℃ / min for 40min; meanwhile, the high temperature zone is raised from room temperature to 700℃ at a rate of 17.5℃ / min for 40min; the carrier gas is argon with a flow rate of 100sccm;

[0079] In the constant temperature procedure, the low temperature zone is kept at 500℃ for 20min, and the high temperature zone is kept at 700℃ for 20min; the carrier gas is a mixture of hydrogen and argon with a volume ratio of 1:9, and the flow rate is 100sccm;

[0080] After the constant temperature procedure, the furnace is rapidly cooled, the cover of the tube furnace is opened, and the pipeline is cleaned with the carrier gas, which is argon with a flow rate of 500sccm.

[0081] After cooling to room temperature, the step-shaped nano tungsten diselenide is obtained.

[0082] Comparative Example 1

[0083] A method for preparing nano tungsten diselenide, comprising the following steps:

[0084] The tungsten mesh is prepared by cleaning with deionized water and anhydrous ethanol for 3000s at room temperature to obtain a tungsten source.

[0085] In a double-temperature-zone chemical vapor deposition system, 0.05g of selenium powder is placed in a quartz boat in the left temperature zone of the tube furnace, and the tungsten mesh (with an area of 1*1cm 2 ) is placed in a quartz boat in the right temperature zone of the tube furnace.

[0086] Before heating, the tube furnace is evacuated to remove air, and then argon gas with a flow rate of 100sccm is introduced as the carrier gas.

[0087] The specific temperature rising procedure and constant temperature procedure are as follows:

[0088] In the temperature rising procedure, the low temperature zone is raised from room temperature to 500℃ at a rate of 12.5℃ / min for 40min; meanwhile, the high temperature zone is raised from room temperature to 700℃ at a rate of 17.5℃ / min for 40min; the carrier gas is argon with a flow rate of 100sccm;

[0089] In the constant temperature procedure, the low temperature zone is kept at 500℃ for 10min, and the high temperature zone is kept at 700℃ for 10min; the carrier gas is a mixture of hydrogen and argon with a volume ratio of 1:9, and the flow rate is 100sccm;

[0090] After the constant temperature procedure, the furnace is rapidly cooled, the cover of the tube furnace is opened, and the pipeline is cleaned with the carrier gas, which is argon with a flow rate of 500sccm.

[0091] Application Example 1

[0092] The step-shaped nano tungsten diselenide prepared in Examples 1-3 was characterized, and the results are shown in Figures 2-5

[0093] Among them, Figure 2 The three repeated experimental results of Example 2 are shown in the figure. As can be seen from the figure, the nano step-shaped tungsten diselenide prepared by the method of the present application has a clear multi-layer nano step-shaped structure under a transmission electron microscope (TEM), and the nano step-shaped structure is widely distributed. Most of the steps are between 1 nm and 20 nm wide, and the step-shaped structure provides a rich edge active site for catalytic reaction. The interplanar spacing of 0.29 nm is for the (010) crystal plane of WSe2, which proves that the material is WSe2.

[0094] Figure 3 The left figure is the morphology of tungsten diselenide under TEM when the tungsten diselenide of Example 1 is kept for 1 min. The material has a certain multi-layer nano step-shaped structure; Figure 3 The right figure is the morphology of tungsten diselenide under TEM when the tungsten diselenide is kept for 10 min. Part of the step-shaped structure of the material is repaired.

[0095] Figure 4 The figure is the morphology of tungsten diselenide synthesized by slow cooling of Comparative Example 1. As can be seen from the figure, the tungsten diselenide has a regular edge structure under TEM, and has no obvious nano step-shaped morphology. Therefore, it can be proved again that the generation of the nano step-shaped structure is due to the rapid cooling. Among them, the interplanar spacing of 0.29 nm is for the (010) crystal plane of WSe2, which proves that the material is WSe2.

[0096] Figure 5 The figure is the Raman spectrum of the nano step-shaped WSe2 of Example 2. The figure shows the A 1g vibration signal of WSe2, verifying the successful synthesis of WSe2.

[0097] Application Example 2

[0098] The electrochemical performance of the step-shaped nano tungsten diselenide prepared in Examples 1-3 was tested. The specific experimental method includes:

[0099] (1) Linear sweep voltammetry (LSV) test was carried out on an electrochemical workstation (CHI660E). The nano step-shaped WSe2 catalyst supported by W mesh was used as the working electrode, and Ag / AgCl and Pt electrode were used as the reference electrode and the counter electrode, respectively. All the potentials mentioned are related to the reversible hydrogen electrode (RHE): E RHE = E (Ag / AgCl) ​+ 0.059*pH + 0.197V. Electrochemical measurements were performed in 0.5 M H2SO4. High purity Ar gas was bubbled into the electrolyte for 30 minutes before the measurements. Linear sweep voltammetry (LSV) measurements were performed between 0 and -0.6 V vs. Ag / AgCl at a scan rate of 5 mV / s. All results were corrected by 95% ohmic potential drop (iR) correction.

[0100] (2) In the proton exchange membrane (PEM) electrolysis water test, commercial Nafion 115 was pretreated with 5 wt% H2O2, 1 M H2SO4 and deionized water for 2 hours at 60°C, and the treated membrane was stored in deionized water for later use. Nano-step WSe2 supported by W mesh and commercial Pt / C (M Pt = 0.4 mg / cm 2 ) were used as cathode catalysts, and IrO2 (M Ir = 2.0 mg / cm 2 ) was used as anode catalyst. Pt / C and IrO2 were prepared by using a commercial membrane electrode assembly to prepare a catalyst-coated membrane, which was coated on an 80 μm thick Nafion 115 membrane. The fixed model of the PEM electrolysis cell test was WMM-PEM-A25, and a platinum-coated titanium felt was used as an anode diffusion layer, and nano-step WSe2 was used as a cathode diffusion layer. Polarization curves and stability tests were performed at 80°C, with a circulating water flow rate of 0.6 L / min, and all data were not iR corrected.

[0101] Results and discussion:

[0102] Figure 6 For Examples 1-3, the rapid cooling method was used, and the catalytic performance of the tungsten diselenide prepared at different holding times, i.e., the catalytic performance of the material when held for 1 min, 10 min, and 20 min, respectively. As shown in the figure, when the holding time is 10 min, the overpotential of the material at 10 and 100 mA / cm 2 is 43 mV and 97 mV, respectively, which is much smaller than the catalytic performance of the material when the holding time is 1 min (85 mV at 10 mA / cm 2 , 175 mV at 100 mA / cm 2 , 200 mV at 10 mA / cm 2 , and 281 mV at 100 mA / cm 2 ), proving that when the rapid cooling method is used, the optimal holding time of the constant temperature program is 10 min.

[0103] Figure 7The catalytic performance of four materials, nano-stepped tungsten diselenide-RC-WSe2 prepared by rapid cooling and holding for 10 minutes (Example 2), tungsten diselenide-WSe2 prepared by slow cooling (Comparative Example 1), commercial precious metal Pt / C catalyst, and metal W mesh, were compared. 2 The overpotential at the current density was used to evaluate the HER catalytic activity. Selenization greatly improved the catalytic performance of the W network. The RC-WSe2 (Example 2) catalyst was 2 The overpotential is only 43mV at 100mA / cm 2 The overvoltage is only 97mV under the condition of 10mA / cm2. Both values ​​are much lower than the original W mesh (10mA / cm2). 2 518mV) and the slowly cooled WSe2 of Comparative Example 1 (10mA / cm 2 225mV, 100mA / cm 2 Importantly, the advantage of RC-WSe2 becomes more pronounced as the current density increases. These test results demonstrate the excellent catalytic performance of the nano-stepped WSe2 prepared by rapid cooling at both low and high current densities.

[0104] Figure 8 The PEM water electrolysis test was used to evaluate the material's actual water electrolysis capability. The RC-WSe2 or Pt / C of Example 2 was used as the cathode electrocatalyst, and commercial IrO2 was used as the anode electrocatalyst. The test was conducted using Nafion 115 in pure water at 80°C. For the RC-WSe2||IrO2 electrolyzer, the electrolytic capacity was 1.0A / cm 2 and 2.0A / cm 2 The electrolysis voltages required for the current density are 1.85V and 2.32V, respectively, which are better than Pt / C||IrO2 (1.857V, 2.51V) and the WSe2||IrO2 voltage of Comparative Example 1 (2.691V, 3.577V), indicating that the RC-WSe2||IrO2 electrolytic cell has higher activity. 2 The cost of RC-WSe2 is $0.5 per effective area, significantly lower than the $2 per Pt / C (MPt = 0.4 mg / cm 2 ) cost. According to our statistics, RC-WSe2 achieves 1A / cm 2 The voltage required for the current density is superior to that of most PEM cathode catalysts, including a large number of precious metal catalysts.

[0105] like Figure 9 As shown, the PEM electrolyzer using RC-WSe2||IrO2 is at 1A / cm 2After 200 hours of continuous operation, the voltage stabilized at about 1.86V without any significant increase, Figure 9 The inserted figure is the actual test device diagram. The excellent electrolysis voltage and stability prove that the RC-WSe2 electrocatalyst has great potential in the practical application of PEM water electrolysis.

[0106] Figure 10 The inserted figure is the Raman test diagram of the material after 200h stability test. The material can still maintain the original structure, indicating that it has excellent stability.

[0107] From the above experiments, it can be seen that the step-shaped nano tungsten diselenide is successfully prepared, which has a large number of edge active sites, significantly improves the catalytic activity, and the step-shaped structure also has excellent stability. Effectively solve the problems of complex preparation process, high reaction temperature, difficult to realize the precise control of nanometer scale, high production cost and other problems of existing nano tungsten diselenide. Moreover, the experimental results have good repeatability, and the step-shaped nano tungsten diselenide has broad application prospects in the field of electrocatalysis.

[0108] The foregoing description of specific exemplary embodiments of the application is intended to be illustrative only and is not intended to limit the application to the precise forms described. Many modifications and variations are possible in light of the above teachings without departing from the spirit or essential characteristics of the present application. The exemplary embodiments are chosen and described in order to explain the principles of the application and its practical application to thereby enable others skilled in the art to best utilize the application and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the application be defined by the claims and their equivalents.

Claims

1. A method for preparing step-shaped nano-tungsten diselenide, characterized in that: The following steps are involved: In a dual-temperature zone chemical vapor deposition system, selenium powder is placed upstream of the gas path, and a metal tungsten mesh is placed downstream of the gas path. Chemical vapor deposition is performed in sequence through a heating program and a constant temperature program. After the constant temperature program is completed, rapid cooling is performed to obtain the step-shaped nano-tungsten diselenide. The area where the selenium powder is located is a low-temperature area; the area where the tungsten mesh is located is a high-temperature area; The heating program includes: in the low temperature zone, heating from room temperature to temperature A over 30-50 minutes; in the high temperature zone, heating from room temperature to temperature B over 30-50 minutes, and temperature A is lower than temperature B; The constant temperature program includes: keeping the temperature at temperature A for 1-20 minutes in the low temperature zone; keeping the temperature at temperature B for 1-20 minutes in the high temperature zone; The temperature A is 500° C.; the temperature B is 700° C.; The chemical vapor deposition specifically comprises the following steps: S1 in the heating program, the low temperature zone and the high temperature zone are heated simultaneously, before the temperature in the high temperature zone reaches temperature B, the carrier used is argon, the argon flow rate is 80-120sccm; S2 is performed from the time when the temperature in the high temperature zone reaches temperature B to the end of the constant temperature program. The carrier used is a hydrogen-argon mixture gas with a flow rate of 80-120 sccm. The volume ratio of hydrogen to argon in the hydrogen-argon mixture gas is (1:9)-(2:8).

2. The method for preparing stepped nano-tungsten diselenide according to claim 1, wherein: The rapid cooling specifically comprises the following steps: After the constant temperature program is completed, the insulation cover of the tubular furnace is immediately opened, and the pipeline is purged with carrier gas; the carrier gas used is argon, and the flow rate of the argon gas is 400-600 sccm.

3. The step-shaped nano-tungsten diselenide prepared by the method according to any one of claims 1 to 2.

4. Application of the stepped nano-tungsten diselenide prepared by the method according to any one of claims 1 to 2 in the field of electrocatalysis.

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