Step-shaped nano tungsten diselenide as well as preparation method and application thereof

Abstract

The invention provides step-shaped nano tungsten diselenide as well as a preparation method and application thereof. Comprising the following steps that in a double-temperature-zone chemical vapor deposition system, selenium powder is placed on the upstream of a gas path, a metal tungsten net is placed on the downstream of the gas path, chemical vapor deposition is sequentially carried out through a heating program and a constant-temperature program, rapid cooling is carried out after the constant-temperature program is finished, and the step-shaped nano tungsten diselenide can be obtained. The highest reaction temperature is 500 DEG C in the low-temperature area of the area where the selenium powder is located; the highest reaction temperature is 700 DEG C when the area where the tungsten mesh is located is the high-temperature area. The method disclosed by the invention effectively solves the problems that the existing nano tungsten diselenide preparation process is complicated, the reaction temperature is high, the precise regulation and control of the nano scale are difficult to realize, the production cost is high and the like. Moreover, the experimental result is good in repeatability, and the step-shaped nano tungsten diselenide shows excellent catalytic activity and stability in the field of electro-catalysis and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of nano catalysts, and in particular relates to a step-shaped nano tungsten diselenide and a preparation method and application thereof. Background Art

[0002] In the context of today's increasingly serious energy crisis and environmental problems, electrocatalytic technology has received widespread attention as a green and efficient means of energy conversion. Among them, the development and application of nanomaterials are of great significance to improving electrocatalytic performance. As a two-dimensional layered material, tungsten diselenide has great application potential in the fields of electrocatalytic water decomposition, oxygen reduction reaction and nitrogen reduction reaction due to its unique electronic structure and excellent electrocatalytic activity. Therefore, the development of a fast, efficient and precisely controlled nanostructured tungsten diselenide preparation method is of great significance to promote its application in the field of electrocatalysis.

[0003] In the prior art, the traditional preparation methods of multi-edge tungsten diselenide nanomaterials include chemical vapor deposition, various stripping methods, laser cutting, ball milling, etc., but all have certain limitations. The chemical vapor deposition method has a high reaction temperature, which makes it difficult to ensure the integrity of the multi-edge structure, and it also has obvious difficulties in accurately controlling the size, shape and distribution of the edge structure. The reaction conditions of the stripping method are difficult to control, which can easily cause uneven growth of the edge structure, and the high requirements for the stripping process also further increase the preparation cost. The laser cutting method has expensive equipment and complex operation. It is easy to cause material damage during the cutting process, and it is difficult to prepare nanomaterials with ideal edge structures on a large scale. When the ball milling method relies on mechanical force to prepare multi-edge nanomaterials, it will not only introduce impurities and affect the material properties, but also it is difficult to form a regular edge structure, and the product size distribution is uneven. It can be seen that the current multi-edge tungsten diselenide materials generally have many problems such as complex preparation process, difficulty in achieving precise control at the nanoscale, and high production costs. In particular, tungsten diselenide with a multi-edge nano-step microstructure can provide a large number of edge active sites and has high catalytic activity, while the step morphology can provide better stability. It has broad application prospects, but its preparation method is obviously more challenging.

[0004] In summary, how to efficiently prepare step-shaped tungsten diselenide that has both high quality and precise control at the nanoscale, so as to apply it to fields such as energy conversion and storage, is a technical problem that needs to be urgently solved by technicians in this field. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing step-shaped nano tungsten diselenide.

[0006] Specifically, in this invention, selenium powder is used as the selenium source, tungsten mesh is used as the tungsten source, and chemical vapor deposition technology is adopted. Then, through the method of "rapid cooling", nano-step tungsten diselenide covering the metal tungsten mesh substrate is prepared. The preparation process of this method is simple, the reaction temperature is low, and there is no need for a substrate to avoid the problem of introducing impurities. The precise control of nanostructures can be achieved through efficient and rapid means. The obtained stepped nano-tungsten diselenide has high activity and high stability, and can be widely used in the field of electrocatalysis of nanomaterials, with broad industrial prospects.

[0007] To achieve the above object, the present invention provides a method for preparing stepped nano-tungsten diselenide, including the following steps: In a dual-temperature zone chemical vapor deposition system, place selenium powder upstream of the gas path and place metal tungsten mesh downstream of the gas path. Perform chemical vapor deposition successively through a heating program and a constant-temperature program. After the constant-temperature program ends, perform rapid cooling to obtain the stepped nano-tungsten diselenide.

[0008] In a preferred embodiment, the selenium powder is of analytical purity 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 below 5 * 5 cm 2 ; more preferably, the metal tungsten mesh is a tungsten mesh pretreated by ultrasonic waves; the purpose of the ultrasonic cleaning is to remove impurities on the surface of the tungsten mesh, so conventional pretreatment methods mastered by those skilled in the art can be adopted, for example: clean with deionized water and absolute ethanol for 3000 s at room temperature respectively.

[0010] Traditional methods for synthesizing diselenides all use two powder raw materials, for example, selenium powder and tungsten trioxide. The drawback of this method is that a substrate is required for material synthesis, usually silicon wafers and sapphires. However, neither of these two substrates has conductivity. If a catalytic reaction is to be carried out, it needs to be transferred to a substrate with high conductivity and no catalytic effect, such as glassy carbon. And many problems will be faced during the transfer process: (1) The adhesion force between tungsten diselenide and the sapphire substrate is usually very strong, while the adhesion force between tungsten diselenide and the glassy carbon substrate is weak, resulting in difficulty in completely peeling off the tungsten diselenide layer during the transfer process, which will cause damage or residue of the material. (2) During the transfer process, the surface of tungsten diselenide is easily contaminated by dust, impurities, etc., which will affect the results of electrochemical tests. (3) The microstructure and morphology of tungsten diselenide are easily damaged during the transfer process, such as the collapse of the layer structure, which will also affect its electrochemical performance. (4) The transfer process requires precise operation techniques to ensure the integrity and original crystal structure of tungsten diselenide during the transfer process, and has high requirements for operators. Thus, it can be seen that there are many difficulties in transferring tungsten diselenide from the substrate to the glassy carbon substrate for catalytic reaction.

[0011] In the present invention, the stepped nano tungsten diselenide is directly grown on a metal tungsten mesh to construct a robust integrated (self-supporting integrated catalyst) catalyst system. During the synthesis process, the metal tungsten mesh is used as a raw material; during the catalytic stage, thanks to the support of the highly conductive metal mesh, each layer and each part of the catalyst are supplied with sufficient electrons, significantly improving the electron transport efficiency in the stepped nano tungsten diselenide catalytic layer and greatly enhancing the conductivity of the material. During the testing stage, the stepped nano tungsten diselenide catalyst directly grown on the metal tungsten mesh forms an integrated electrode without the need for other supports. This effectively avoids the problem of catalyst reloading existing in traditional catalyst testing. The structural design of the present invention simplifies the catalyst preparation process, reduces costs, 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 region; the region where the tungsten mesh is located is a high-temperature region.

[0013] In a preferred embodiment, the heating program includes: in the low-temperature region, heating from room temperature to temperature A over 30 - 50 min; in the high-temperature region, heating from room temperature to temperature B over 30 - 50 min, and temperature A is less than temperature B.

[0014] In a preferred embodiment, the constant-temperature program includes: in the low-temperature region, maintaining the temperature at temperature A for 1 - 20 min; in the high-temperature region, maintaining the temperature at temperature B for 1 - 20 min.

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

[0016] In this case, by using the metal tungsten mesh as a reaction raw material, the evaporation of the powdered tungsten source and its reaction with selenium are 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 precisely control the size and number of layers of WSe 2 and is more conducive to forming a uniform nanostructure, avoiding rapid growth and uneven deposition at high temperatures. In addition, the low-temperature synthesis avoids selenium loss or other side reactions caused by high temperatures. It not only reduces energy consumption and harmful gas emissions, is environmentally friendly, but also reduces the thermal stress on the CVD equipment at high temperatures, extends the equipment life, and improves the safety of operation, reducing the possibility of fires and equipment failures.

[0017] In a preferred embodiment, the heating rate in the low-temperature region is 10 - 15 °C / min; the heating rate in the high-temperature region is 15 - 20 °C / min; preferably, the heating rate in the low-temperature region is 12.5 °C / min; the heating rate in the high-temperature region is 17.5 °C / min.

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

[0019] 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 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] S2 From the time when the temperature in the high-temperature zone reaches temperature B until the end of the constant-temperature program, the carrier gas used is a hydrogen-argon mixture, and the flow rate of the hydrogen-argon mixture is 80 - 120 sccm; preferably, the flow rate of the hydrogen-argon mixture is 100 sccm.

[0021] In the present invention, when the temperature rises, the carrier gas is changed from argon to a hydrogen-argon mixture. The purpose is to utilize the reducibility of hydrogen to promote the formation of tungsten diselenide. At the same time, hydrogen can also inhibit unnecessary selenium evaporation, maintain a relatively high selenium pressure, which helps 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 impact on the formation and morphology of the nanostructure. A higher flow rate of the carrier gas can enhance the transport efficiency of reactant molecules, which helps to form a uniform nanostructure. However, it may also promote the rapid consumption of raw materials and the premature deposition of products. While a lower flow rate of the carrier gas may lead to an overly long residence time of reactants in the reaction chamber, causing local overheating and non-uniform growth. Therefore, the appropriate carrier gas flow rate designed in the present invention is crucial for achieving the ideal nano-step structure.

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

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

[0025] Immediately after the end of the constant-temperature program, open the heat-insulating cover of the tubular furnace and clean the pipeline with the carrier gas. 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 invention, the strategy of rapid cooling and high-throughput carrier gas flushing is adopted. The purpose is to quickly terminate the reaction and prevent the high-energy nano-step edge structure formed during the reaction from being repaired during the cooling process, so as to ensure that these highly active edge structures are retained. Therefore, the defined conditions are meaningful for achieving the preparation of high-quality stepped nano-tungsten diselenide.

[0027] Another object of the present invention is to provide the stepped nano-tungsten diselenide prepared by the method described in any one of the above.

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

[0029] In the present invention, by designing and forming a nano-step structure, the specific surface area of tungsten diselenide is significantly increased, exposing more active sites, providing more reaction sites for the hydrogen evolution reaction, and thus effectively improving its electrocatalytic hydrogen evolution efficiency. According to existing theoretical calculations, the adsorption energy of hydrogen atoms at the edge is significantly better than that on the basal plane, and ΔG H* is closer to zero, which means that hydrogen atoms are more likely to adsorb and desorb at the edge. The increase in edge active sites further reduces the energy barrier of the hydrogen evolution reaction and improves the reaction rate. At the same time, the nano-step structure can also promote the electron transfer on the surface of tungsten diselenide, improve the conductivity of tungsten diselenide, and further enhance its hydrogen evolution performance.

[0030] Another object of the present invention is to provide the application of the stepped tungsten diselenide nanosheets prepared by the method described in any one of the above in the field of electrocatalysis.

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

[0032] The present invention adopts atmospheric pressure chemical vapor deposition method, which can rapidly and low-energy consume prepare nano-step tungsten diselenide with both 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 perspective of raw materials, in the present invention, selenium powder is used as the selenium source and tungsten mesh is used as the tungsten source, so that the stepped tungsten diselenide nanosheets grow directly on the metal tungsten mesh, constructing a solid integrated (self-supporting integrated catalyst) catalyst system. During the synthesis process, the metal tungsten mesh is used as a raw material; during the catalytic stage, it acts as a highly conductive substrate; during the testing stage, the metal tungsten mesh and the catalyst form an integrated electrode without the need for other supports.

[0034] From the perspective of the process, the present invention has found that a multi-edge nano-step structure is generated during the kinetic synthesis process of selenium powder and tungsten mesh. However, due to its high surface energy, this structure is a metastable form that is thermodynamically unstable. Therefore, the present invention designs a "rapid cooling" method to terminate the reaction by rapidly reducing the temperature, preventing the repair of the high-energy nano-step edge structure during the cooling process, and ensuring to the greatest extent that these highly active edge structures are retained, so that the morphology and properties of the nanostructure can be precisely controlled. The conventional slow cooling process will cause the system to reduce the edge positions through grain rotation and migration, tending to a lower surface energy state, thereby eliminating these high-energy edges.

[0035] In terms of the product, the nano-step tungsten diselenide prepared in the present invention uses a metal tungsten mesh as a conductive substrate to form a self-supporting integrated catalyst. The integrated catalyst can greatly improve the conductivity of the material and has high stability, eliminating the transfer and loading processes required for traditional powder or thin film catalysts during testing, reducing the testing cost and improving the material conductivity. At the same time, the nano-step structure also provides a large number of edge active sites and has excellent stability, showing better catalytic activity than the noble metal Pt / C catalyst in both three-electrode hydrogen evolution tests and proton exchange membrane (PEM) electrolyzer tests.

[0036] Especially in the PEM electrolyzer test, using the nano-step tungsten diselenide as the cathode electrocatalyst and commercial IrO 2 as the anode electrocatalyst, at a current density of 1.0 A / cm 2 and 2.0 A / cm 2 , the cell voltage required for the electrolyzer is only 1.85 V and 2.32 V, which is better than the case of using commercial noble metal Pt / C as the 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 tungsten diselenide is only $0.5, much lower than $2 for Pt / C (calculated based on a Pt loading of 0.4 mg / cm 2 ). Moreover, the PEM electrolyzer with the nano-step tungsten diselenide as the cathode can operate stably for 200 h, with the voltage remaining at about 1.86 V without significant increase. These excellent electrolysis voltages and stabilities further demonstrate the practical potential of the nano-step tungsten diselenide electrocatalyst of the present invention in the field of water electrolysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] From the following detailed description of the embodiments of the present invention in conjunction with the drawings, these and / or other aspects and advantages of the present invention will become clearer and easier to understand, where:

[0038] Figure 1 is a schematic diagram of the experimental device for preparing nano-step tungsten diselenide by chemical vapor deposition according to the present invention;

[0039] Figure 2 is a transmission electron microscope photograph of the nano-step tungsten diselenide grown on a metal tungsten mesh substrate prepared by three repeated experiments in Example 2 of the present invention;

[0040] Figure 3 is a transmission electron microscope photograph of the nano-step tungsten diselenide grown on a metal tungsten mesh substrate prepared in Example 1 (left figure) and Example 3 (right figure) of the present invention;

[0041] Figure 4Transmission electron microscope photograph of tungsten diselenide nanosheets grown on the metallic tungsten mesh substrate prepared in Comparative Example 1;

[0042] Figure 5 Raman spectrum of stepped tungsten diselenide nanosheets grown on the metallic tungsten mesh substrate prepared in Example 2 of the present invention;

[0043] Figure 6 Current density - electrode potential curve in the electrochemical hydrogen evolution reaction in 0.5 M H 2 SO 4 electrolyte with stepped nanoscale tungsten diselenide prepared in Examples 1 - 3 of the present invention as the cathode catalyst;

[0044] Figure 7 Current density - electrode potential curve in the electrochemical hydrogen evolution reaction in 0.5 M H 2 SO 4 electrolyte with stepped tungsten diselenide nanosheets prepared in Example 2 of the present invention and tungsten diselenide nanosheets prepared in Comparative Example 1 as the cathode catalysts;

[0045] Figure 8 Current density - electrode potential curve in the electrochemical hydrogen evolution reaction in a PEM electrolyzer test with pure water as the electrolyte using stepped tungsten diselenide nanosheets prepared in Example 2 of the present invention and tungsten diselenide nanosheets prepared in Comparative Example 1;

[0046] Figure 9 Stability test graph obtained by the constant current method in a PEM electrolyzer test with pure water as the electrolyte using stepped tungsten diselenide nanosheets prepared in Example 2 of the present invention;

[0047] Figure 10 Raman spectrum of stepped tungsten diselenide nanosheets prepared in Example 2 of the present invention after 200 h stability test; Detailed Description of the Invention

[0048] In order to enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0049] By providing a stepped nanoscale tungsten diselenide and its preparation method and application, the embodiments of the present invention solve many problems in the prior art, such as the complex preparation process of traditional tungsten diselenide nanomaterials, the difficulty in achieving precise control at the nanoscale, and the high production cost.

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

[0051] Unless otherwise specified, the technical means used in the present invention are conventional means well-known to those skilled in the art. All kinds of raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods. The reagents used in the present invention are of analytical purity unless otherwise specified.

[0052] Example 1

[0053] A preparation method of stepped nano tungsten diselenide includes the following steps:

[0054] Preparation of metal tungsten mesh: At room temperature, clean it with deionized water and absolute ethanol for 3000 s respectively to obtain the tungsten source.

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

[0056] Before heating, first evacuate to remove the air in the tube furnace, and then introduce argon with a flow rate of 100 sccm as the carrier gas.

[0057] Specific heating program and constant temperature program:

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

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

[0060] After the constant temperature ends, quickly cool down. Immediately open the heat preservation cover of the tube furnace and clean the pipeline with the carrier gas. The carrier gas used is argon, and the flow rate of the carrier is 500 sccm.

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

[0062] Example 2

[0063] A preparation method of stepped nano tungsten diselenide includes the following steps:

[0064] Preparation of tungsten metal mesh: At room temperature, clean it with deionized water and absolute ethanol for 3000 s respectively to obtain the tungsten source.

[0065] In a dual-temperature chemical vapor deposition system, weigh 0.05 g of selenium powder and place it in a quartz boat in the left temperature zone of the tube furnace. The 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, first evacuate to remove the air in the tube furnace, and then introduce argon with a flow rate of 100 sccm as the carrier gas.

[0067] Specific heating program and constant-temperature program:

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

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

[0070] After the constant temperature, quickly cool down. Immediately open the insulation cover of the tube furnace and clean the pipeline with the carrier gas. The carrier gas used is argon, and the flow rate of the carrier is 500 sccm.

[0071] After cooling to room temperature, stepped nano tungsten diselenide is obtained.

[0072] Example 3

[0073] A preparation method of stepped nano tungsten diselenide, comprising the following steps:

[0074] Preparation of tungsten metal mesh: At room temperature, clean it with deionized water and absolute ethanol for 3000 s respectively to obtain the tungsten source.

[0075] In a dual-temperature chemical vapor deposition system, weigh 0.05 g of selenium powder and place it in a quartz boat in the left temperature zone of the tube furnace. The 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, first evacuate to remove the air in the tube furnace, and then introduce argon with a flow rate of 100 sccm as the carrier gas.

[0077] Specific heating program and constant-temperature program:

[0078] In the heating program, the low-temperature zone is heated from room temperature to 500 °C at a rate of 12.5 °C / min for 40 min; at the same time, the high-temperature zone is heated from room temperature to 700 °C at a rate of 17.5 °C / min for 40 min; in this program, the carrier gas is argon with a flow rate of 100 sccm;

[0079] In the constant-temperature program, the low-temperature zone is kept at 500 °C for 20 min, and the high-temperature zone is kept at 700 °C for 20 min; 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 100 sccm;

[0080] After the constant-temperature ends, it is rapidly cooled. Immediately open the thermal insulation cover of the tube furnace and clean the pipeline with the carrier gas. The carrier gas used is argon, and the flow rate of the carrier is 500 sccm.

[0081] After cooling to room temperature, stepped nano tungsten diselenide is obtained.

[0082] Comparative Example 1

[0083] A preparation method of nano tungsten diselenide includes the following steps:

[0084] Preparation of metal tungsten mesh: Wash with deionized water and absolute ethanol for 3000 s at room temperature respectively to obtain the tungsten source.

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

[0086] Before heating, first evacuate to remove the air in the tube furnace, and then introduce argon with a flow rate of 100 sccm as the carrier gas.

[0087] Specific heating program and constant-temperature program:

[0088] In the heating program, the low-temperature zone is heated from room temperature to 500 °C at a rate of 12.5 °C / min for 40 min; at the same time, the high-temperature zone is heated from room temperature to 700 °C for 40 min; in this program, the carrier gas is argon, and the flow rate is 100 sccm;

[0089] In the constant-temperature program, the low-temperature zone is kept at 500 °C for 10 min, and the high-temperature zone is kept at 700 °C for 10 min; 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 100 sccm;

[0090] After the constant-temperature ends, it is cooled to room temperature to obtain nano tungsten diselenide.

[0091] Application Example 1

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

[0093] Among them, Figure 2 are the results of three repeated experiments in Example 2. It can be seen from the figure that the nano step-shaped tungsten diselenide prepared by the method of the present invention has an obvious multi-layer nano step-shaped structure under a transmission electron microscope (TEM), and the nano step-shaped structure is widely distributed. Most of the step widths are between 1 nm and 20 nm. The step-shaped structure provides rich edge active sites for the catalytic reaction. The crystal plane spacing of 0.29 nm corresponds to the (010) crystal plane of WSe 2 , proving that the material is WSe 2 .

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

[0095] Figure 4 is the morphology diagram of tungsten diselenide synthesized by slow cooling in Comparative Example 1. It can be seen from the figure that tungsten diselenide has a regular edge structure under TEM and no obvious nano step-shaped morphology. Therefore, it can be proved again that the generation of the nano step-shaped structure is due to rapid cooling. Among them, the crystal plane spacing of 0.29 nm corresponds to the (010) crystal plane of WSe 2 , proving that the material is WSe 2 .

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

[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 methods include:

[0099] (1) Linear sweep voltammetry (LSV) test was carried out on an electrochemical workstation (CHI660E). The nano step-shaped WSe2 catalyst supported by a W mesh was used as the working electrode, and Ag / AgCl and Pt electrodes were used as the reference electrode and the counter electrode respectively. All the mentioned potentials are related to the reversible hydrogen electrode (RHE): E RHE = E (Ag / AgCl)+0.059*pH+0.197V. Electrochemical measurement at 0.5MH 2 SO 4 The results were carried out in . High purity Ar gas was bubbled into the electrolyte for 30 minutes before the measurement. Linear sweep voltammetry (LSV) measurements were performed between 0 and -0.6 V relative to 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) water electrolysis test, commercial Nafion 115 was heated to 5 wt% H at 60 °C. 2 O 2 、1MH 2 SO 4 and deionized water for 2 h, and the treated membrane was stored in deionized water for later use. 2 and commercially available Pt / C(M Pt =0.4mg / cm 2 ) were used as cathode catalysts, IrO 2 (M Ir =2.0mg / cm 2 ) as anode catalyst. Pt / C and IrO 2 The catalyst-coated membrane was prepared using a commercial membrane electrode assembly and coated on a 80 μm thick Nafion 115 membrane roll by roll. The PEM electrolyzer test fixed model was WMM-PEM-A25, platinum-coated titanium felt was used as the anode diffusion layer, and nano-stepped WSe 2 Used as cathode diffusion layer. Polarization curve and stability test were carried out at 80℃, circulating water flow rate was 0.6L / min, all data were not corrected by iR.

[0101] Results and Discussion:

[0102] Figure 6 The catalytic performance of tungsten diselenide prepared by the rapid cooling method in Example 1-3 at different holding times is shown in the figure, i.e., the catalytic performance of the material when the holding time is 1 min, 10 min, and 20 min. 2 The overpotentials at the current density were 43mV and 97mV, respectively, which were much smaller than the holding time of 1min (10mA / cm 2 85mV, 100mA / cm 2 175mV) and 20min(10mA / cm 2 200mV, 100mA / cm 2The catalytic performance of the material at 281 mV (when [conditions not specified]). It is proven that when using the rapid cooling method, the optimal holding time for the constant temperature program is 10 minutes.

[0103] Figure 7 Compared the catalytic performance of the nano-step tungsten diselenide - RC - WSe prepared by the rapid cooling method with a 10 - minute holding time 2 (Example 2), tungsten diselenide - WSe prepared by slow cooling 2 (Comparative Example 1), commercial noble metal Pt / C catalyst, and a metal W mesh for the catalytic performance of the four materials. At 10 and 100 mA / cm 2 The overpotential at the current density was used to evaluate the HER catalytic activity. Selenization greatly improved the catalytic performance of the W mesh. The RC - WSe 2 (Example 2) catalyst had an overpotential of only 43 mV at 10 mA / cm 2 and only 97 mV at 100 mA / cm 2 These two values are much lower than those of the original W mesh (518 mV at 10 mA / cm 2 ) and WSe prepared by slow cooling in Comparative Example 1 2 (225 mV at 10 mA / cm 2 and 325 mV at 100 mA / cm 2 ). Importantly, as the current density increases, the advantage of RC - WSe 2 becomes more obvious. These test results show the excellent catalytic performance of the nano - step WSe prepared by rapid cooling 2 at low and high current densities.

[0104] Figure 8 For the PEM water electrolysis test, the PEM water electrolysis test was used to evaluate the actual water electrolysis ability of the material. RC - WSe of Example 2 2 or Pt / C was used as the cathode electrocatalyst, and commercial IrO 2 was used as the anode electrocatalyst. The test was carried out in pure water at 80 °C using Nafion 115. For the RC - WSe 2 ||IrO 2 electrolyzer, the electrolysis voltages required at 1.0 A / cm 2 and 2.0 A / cm 2 current densities were 1.85 V and 2.32 V respectively, which were better than those of Pt / C||IrO 2 (1.857 V, 2.51 V) and the WSe of Comparative Example 1 2 ||IrO 2 voltages (2.691 V, 3.577 V), indicating that RC - WSe 2 ||IrO 2The electrolytic cell has higher activity. In addition, within the effective area of 4*4 cm 2 , the cost of RC-WSe 2 is $0.5, which is significantly lower than the cost of $2 for Pt / C (MPt = 0.4 mg / cm 2 ). According to our statistics, the voltage required for RC-WSe 2 to achieve a current density of 1 A / cm 2 is better than that of most PEM cathode catalysts, including a large number of noble metal catalysts.

[0105] As Figure 9 shown, the PEM electrolytic cell using RC-WSe 2 ||IrO 2 operates continuously at 1 A / cm 2 for 200 hours, and the voltage stabilizes at about 1.86 V without any significant increase. Figure 9 The inset shows the actual test device diagram. The excellent electrolysis voltage and stability confirm the great potential of RC-WSe 2 electrocatalyst in the practical application of PEM water electrolysis.

[0106] Figure 10 The Raman test diagram of the material after 200 h stability test shows that the material can still maintain its original structure unchanged, indicating its excellent stability.

[0107] From the above experiments, it can be seen that the present invention successfully prepares stepped nano tungsten diselenide, which has a large number of edge active sites, significantly improves the catalytic activity, and at the same time the stepped shape has excellent stability. It effectively solves many problems such as the complex preparation process, high reaction temperature, difficulty in achieving precise control at the nanoscale, and high production cost of the existing nano tungsten diselenide. Moreover, the experimental results have good repeatability, and the stepped nano tungsten diselenide has broad application prospects in the field of electrocatalysis.

[0108] The foregoing description of the specific exemplary embodiments of the present invention is for purposes of illustration and exemplification. These descriptions are not intended to limit the present invention to the precise forms disclosed, and obviously, many changes and variations are possible in light of the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical applications, so that those skilled in the art can implement and utilize the various different exemplary embodiments of the present invention as well as various different selections and changes. The scope of the present invention is intended to 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.

2. The method for preparing step-shaped nano-tungsten diselenide according to claim 1, characterized in that: 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.

3. The method for preparing step-shaped nano-tungsten diselenide according to claim 2, characterized in that: The temperature rising procedure includes: in the low temperature zone, heating from room temperature to temperature A within 30-50 minutes; in the high temperature zone, heating from room temperature to temperature B within 30-50 minutes, and temperature A is lower than temperature B.

4. The method for preparing step-shaped nano-tungsten diselenide according to claim 3, characterized in that: 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.

5. The method for preparing step-shaped nano-tungsten diselenide according to claim 4, characterized in that: The temperature A is below 500°C; the temperature B is below 700°C.

6. The method for preparing step-shaped nano-tungsten diselenide according to claim 5, characterized in that: The chemical vapor deposition specifically comprises the following steps: S1: In the temperature raising procedure, the low temperature zone and the high temperature zone are heated simultaneously. Before the temperature of the high temperature zone reaches temperature B, the carrier used is argon gas, and the flow rate of the argon gas is 80-120 sccm; S2 is from 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 mixed gas, and the flow rate of the hydrogen-argon mixed gas is 80-120sccm.

7. The method for preparing step-shaped nano-tungsten diselenide according to claim 6, characterized in that: The volume ratio of hydrogen to argon in the hydrogen-argon mixed gas is (1:9)-(2:8).

8. The method for preparing step-shaped nano-tungsten diselenide according to claim 1, characterized in that: The rapid cooling specifically comprises the following steps: After the constant temperature program is finished, the insulation cover of the tubular furnace is immediately opened, and the pipeline is cleaned with carrier gas; the carrier gas used is argon gas, and the flow rate of the argon gas is 400-600 sccm.

9. Step-shaped nano-tungsten diselenide prepared by the method according to any one of claims 1 to 8.

10. Application of the step-shaped nano-tungsten diselenide prepared by the method according to any one of claims 1 to 8 in the field of electrocatalysis.

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