A transition metal selenide, a preparation method and application thereof

Abstract

The present application relates to a kind of transition metal selenide and its preparation method, belong to nanometer material technical field, at least solve one of the following technical problems: (1) existing transition metal selenide grain boundary quality is poor, catalytic activity is low;(2) the grain boundary quality of transition metal selenide prepared by existing growth method is poor, it is difficult to form high catalytic activity twin grain boundary;(3) existing growth method is difficult to accurately control the grain boundary density in transition metal selenide material.The grain boundary in the transition metal selenide is all twin grain boundary with 60° rotation angle, and the twin grain boundary is composed of four-membered ring and eight-membered ring.The grain boundary quality of the transition metal selenide is high, and the catalytic activity is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanomaterials, and in particular to a transition metal selenide and a preparation method and application thereof. BACKGROUND

[0002] Two-dimensional transition metal dichalcogenides (TMDs) have attracted great interest due to their excellent physical and chemical properties. Compared with their perfect lattice, grain boundaries in polycrystalline thin films as typical one-dimensional defects can induce the intrinsic activation of two-dimensional basal planes, showing excellent sensor sensitivity, electrocatalytic activity, piezoelectric properties, etc. Notably, these performance enhancements are closely related to grain boundary engineering parameters such as atomic types, dislocation core structures, densities, and crystal orientations. For example, twin boundaries rich in octagonal rings are considered to have the most excellent electrocatalytic hydrogen evolution activity.

[0003] The existing growth method of transition metal selenide is mainly chemical vapor deposition (CVD), and the metal source will have a gasification and redeposition process. However, due to the rapid gas kinetic process and the diversity of chemical phases involved in the reaction, the grain boundary quality of the transition metal selenide prepared by the existing growth method is poor, and it is difficult to accurately control the grain boundary density in the transition metal selenide material and form high-activity twin boundaries. SUMMARY

[0004] In view of the above analysis, the embodiments of the present application aim to provide a transition metal selenide and a preparation method and application thereof, which can at least solve one of the following technical problems: (1) the existing transition metal selenide has poor grain boundary quality and low catalytic activity; (2) the grain boundary quality of the transition metal selenide prepared by the existing growth method is poor, and it is difficult to form high-catalytic-activity twin boundaries; (3) the existing growth method is difficult to accurately control the grain boundary density in the transition metal selenide material.

[0005] In one aspect, the present application provides a transition metal selenide, wherein the grain boundaries inside the transition metal selenide are all twin boundaries with a rotation angle of 60°, and the twin boundaries are composed of four-membered rings and eight-membered rings.

[0006] Preferably, the density of the twin boundaries is 10 3 -10 10 cm -2 .

[0007] Preferably, the content of the eight-membered rings in the twin boundaries is 30-60%.

[0008] In another aspect, the present application provides a preparation method of a transition metal selenide, which is used for preparing the above-mentioned transition metal selenide, and the preparation method comprises:

[0009] (1) dissolving a transition metal salt in water to obtain a precursor solution;

[0010] (2) spin-coating the precursor solution onto a substrate;

[0011] (3) placing the substrate in the middle of a tube furnace, placing selenium powder at the gas inlet end of the tube furnace, vacuumizing the tube furnace and filling it with a reducing gas and an inert gas, heating to sublimate the selenium powder and make it react with the precursor solution and anneal.

[0012] Preferably, the transition metal salt is an inorganic molybdenum salt or an inorganic tungsten salt.

[0013] Preferably, in step (1), the precursor solution further comprises a strong base.

[0014] Preferably, the mass ratio of the transition metal salt to the strong base is 1-10:2.

[0015] Preferably, the substrate is a sapphire substrate or a SiO2 / Si substrate.

[0016] Preferably, in step (3), the heating comprises: heating the middle of the tube furnace to 700-800℃ at a rate of 40-50℃ / min and keeping for 1-10 minutes, and heating the gas inlet end of the tube furnace to 300-350℃ at a rate of 40-50℃ / min and keeping for 1-10 minutes.

[0017] In a third aspect, the present application also provides a use of the transition metal selenide and the transition metal selenide prepared by the above method in electrolytic water hydrogen evolution.

[0018] Compared with the prior art, the present application can achieve at least one of the following beneficial effects:

[0019] 1. The rotation angle of the grain boundary of the existing transition metal selenide is completely random, not a specific 60° grain boundary with 4 / 8-membered rings (four-membered rings and eight-membered rings), while the grain boundary inside the transition metal selenide of the present application is all uniform 60° grain boundary, that is, twin grain boundary, which is composed of 4 / 8-membered rings (four-membered rings and eight-membered rings), and the grain boundary quality is high.

[0020] 2、The preparation method of the transition metal selenide of the present application avoids the process of gasification and re-deposition of the metal source in the prior art by directly spin-coating molybdenum salt or tungsten salt on the surface of the substrate as the metal source, and then allowing selenium to react with the metal source. The method of the present application can precisely control the grain boundary density: spin-coating the precursor solution (metal source) on the surface of the substrate, and when the temperature is lower than the evaporation temperature of the metal source, the metal source on the surface of the substrate will generate a large number of nucleation points, forming a high-density grain boundary; when the annealing temperature is increased to be higher than the evaporation temperature of the metal source, the metal source will evaporate from the surface of the substrate into the air, and the nucleation point density on the surface of the substrate is reduced, thereby reducing the grain boundary density.

[0021] 3、The rotation angle of the grain boundary of the transition metal selenide prepared by the prior method is completely random, and is not a specific 60° grain boundary with a 4 / 8 ring. The grain boundary inside the transition metal selenide prepared by the method of the present application is a uniform 60° grain boundary, that is, a twin grain boundary, which is composed of a 4 / 8 ring and has excellent crystalline quality.

[0022] 4、The strong base of the present application will be adsorbed on the surface of the selenide during the growth of the selenide, and protect the selenide, so that the prepared selenide has high quality and high twin grain boundary density.

[0023] 5、The method of the present application directly spin-coats molybdenum salt or tungsten salt on the surface of the substrate as the metal source, the metal source on the surface of the substrate diffuses to form a high-density nucleation site, and the growth of selenide on different nucleation sites on the surface of the substrate will be affected by capillary force to form a high-density twin grain boundary. The capillary force makes two adjacent crystal domains rotate to share a straight edge, forming a twin grain boundary. Combined with the high-density nucleation site, a high-density (10 3 -10 10 cm -2 ) twin grain boundary is finally formed.

[0024] 6、The high-density and high-quality twin grain boundary inside the transition metal selenide prepared by the present application has excellent electrocatalytic performance and good catalytic activity in electrocatalytic hydrogen evolution, and can be used as a catalyst for electrocatalytic hydrogen evolution.

[0025] In the present application, the above-mentioned technical solutions can be combined with each other to realize more preferred combination schemes. Other features and advantages of the present application will be described in the subsequent specification, and some advantages will become apparent from the specification or will be understood by implementing the present application. The purposes and other advantages of the present application can be realized and obtained from the contents specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings are included to provide a further understanding of the application, and are incorporated herein and constitute a part of the detailed description. The drawings illustrate embodiments of the application and, together with the description, serve to explain the principles of the application. In the drawings:

[0027] Figure 1a Optical Micrograph of Molybdenum Diselenide for Example 1;

[0028] Figure 1b SHG Image of Molybdenum Diselenide for Example 1;

[0029] Figure 2 Dark Field TEM Image of Molybdenum Diselenide for Example 1;

[0030] Figure 3 Atomic Force Microscope Image of Molybdenum Diselenide for Example 1;

[0031] Figure 4a Raman Spectrogram of Molybdenum Diselenide for Example 1;

[0032] Figure 4b Raman Mapping of Molybdenum Diselenide for Example 1;

[0033] Figure 5 High Magnification STEM Image of Molybdenum Diselenide for Example 1;

[0034] Figure 6 HER Image of Molybdenum Diselenide for Example 1;

[0035] Figure 7a SHG Image of Molybdenum Diselenide for Example 2;

[0036] Figure 7b SHG Image of Molybdenum Diselenide for Example 3;

[0037] Figure 7c SHG Image of Molybdenum Diselenide for Example 4;

[0038] Figure 8a Optical Micrograph of Tungsten Diselenide for Example 5;

[0039] Figure 8b SHG Image of Tungsten Diselenide for Example 5. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present application will be described herein below with reference to the accompanying drawings, in which:

[0041] The existing transition metal selenide growth method is mainly chemical vapor deposition method, and the metal source will have a gasification and redeposition process. However, due to the rapid gas dynamic process and the diversity of chemical phases involved in the reaction, the rotation angle of the grain boundary prepared by the existing method is completely random, and is not a specific 60° grain boundary with 4 / 8 ring (a non-60° grain boundary is composed of a 5 / 7 ring, a 60° grain boundary is composed of a 4 / 8 ring, and a 60° grain boundary containing a 4 / 8 ring has higher catalytic activity); in addition, the grain boundary density is affected by the nucleation density, and it is difficult to control the nucleation density in the CVD method.

[0042] Therefore, the present application provides a transition metal selenide, the grain boundaries inside the transition metal selenide are all twin grain boundaries with a rotation angle of 60°, and the twin grain boundaries are composed of four-membered rings and eight-membered rings.

[0043] The rotation angle of the grain boundary of the existing transition metal selenide is completely random, and is not a specific 60° grain boundary with 4 / 8 ring (four-membered ring and eight-membered ring), and the grain boundary inside the transition metal selenide of the present application is all uniform 60° grain boundary, that is, twin grain boundary, and the twin grain boundary is composed of 4 / 8 ring (four-membered ring and eight-membered ring), the grain boundary quality is high, and the catalytic activity is good.

[0044] Further, the four-membered rings and the eight-membered rings are irregularly or regularly spaced.

[0045] Further, the density of the twin grain boundary is 10 3 -10 10 cm -2 , for example, 10 3 cm -2 , 10 4 cm -2 , 10 5 cm -2 , 10 6 cm -2 , 10 7 cm -2 , 10 8 cm -2 , 10 9 cm -2 , 10 10 cm -2 ; further preferably 10 6 -10 10 cm -2 . The high-density twin grain boundary makes the transition metal selenide have better catalytic activity. The density of the twin grain boundary refers to the number of grain boundaries per unit area.

[0046] Further, the content of the eight-membered ring in the twin boundary is 30-60%. For example, 30%, 35%, 40%, 45%, 50%, 55%, 60%. The eight-membered ring has more exposed atomic sites, and thus has better catalytic activity. Therefore, the more the content of the eight-membered ring, the better the catalytic activity of the transition metal selenide. The transition metal selenide of the present application has a large content of the eight-membered ring, and thus has better catalytic performance.

[0047] Illustratively, the transition metal is molybdenum or tungsten.

[0048] Illustratively, the transition metal selenide is a regular hexagon or a regular triangle.

[0049] Further, the transition metal selenide has a single-layer thickness.

[0050] In another aspect, the present application provides a preparation method of a transition metal selenide, which comprises:

[0051] (1) dissolving a transition metal salt in water to obtain a precursor solution;

[0052] (2) spin-coating the precursor solution onto a substrate;

[0053] (3) placing the substrate in the middle of a tube furnace, placing selenium powder at the gas inlet end of the tube furnace, vacuumizing the tube furnace and filling it with a reducing gas and an inert gas, heating to sublimate the selenium powder, and making it react with the precursor solution and anneal.

[0054] Compared with the prior art, the preparation method of the transition metal selenide of the present application avoids the process of gasification and re-deposition of the metal source in the prior art by directly spin-coating molybdenum salt or tungsten salt on the surface of the substrate as the metal source, and then allowing selenium to react with the metal source. The method of the present application can accurately control the grain boundary density: spin-coating the precursor solution (metal source) on the surface of the substrate, and when the temperature is lower than the evaporation temperature of the metal source, the metal source on the surface of the substrate will generate many nucleation points, forming a high-density grain boundary; when the annealing temperature is increased to be higher than the evaporation temperature of the metal source, the metal source will evaporate from the surface of the substrate into the air, and the nucleation point density on the surface of the substrate is reduced, thereby reducing the grain boundary density. The rotation angle of the grain boundary of the transition metal selenide prepared by the prior art is completely random, and is not a specific 60° grain boundary with 4 / 8-membered ring, while the grain boundary inside the transition metal selenide prepared by the method of the present application is a uniform 60° grain boundary, that is, a twin grain boundary, which is composed of 4 / 8-membered ring and has excellent crystalline quality; has good catalytic activity in electrocatalytic hydrogen evolution, and can be used as a catalyst for electrocatalytic hydrogen evolution; in the present application, molybdenum salt or tungsten salt is directly spin-coated on the surface of the substrate as the metal source, the metal source on the surface of the substrate diffuses to form high-density nucleation sites, and the process of growing selenide on the surface of the substrate by different nucleation sites will be affected by capillary force to form high-density twin grain boundaries, the capillary force makes two adjacent crystal domains rotate to share a straight side to form a twin grain boundary, combined with high-density nucleation sites, and finally form high-density twin grain boundaries.

[0055] In the present application, the transition metal salt is used as the metal source, and exemplarily, the transition metal salt is inorganic molybdenum salt or inorganic tungsten salt, such as ammonium molybdate or ammonium tungstate. When ammonium molybdate is used, the generated transition metal selenide is molybdenum diselenide, which has a shape of regular hexagon, and when ammonium tungstate is used, the generated transition metal selenide is tungsten diselenide, which has a shape of regular triangle.

[0056] In the present application, preferably, in step (1), the precursor solution further comprises a strong base. The strong base will be adsorbed on the surface of the selenide during the growth of the selenide, and protect the selenide, so that the prepared twin grain boundary has high density and the selenide grain boundary has higher quality. Preferably, the strong base is sodium hydroxide and / or potassium hydroxide.

[0057] Specifically, the transition metal salt and the strong base are dissolved in water to obtain the precursor solution.

[0058] In the present application, the amount of the strong base is too low, which will cause the appearance of multiple layers, and the amount of the strong base is too high, which will etch the product, and preferably, the mass ratio of the transition metal salt to the strong base is 1-10:2.

[0059] In step (1), during the process of dissolving the transition metal salt and the strong base in water, the transparent and clear precursor solution is obtained by stirring.

[0060] Exemplarily, the substrate is a sapphire substrate or a SiO2 / Si substrate.

[0061] In the present application, the substrate does not need to be hydrophilic, and the hydrophilicity is moderate, because if the hydrophilicity is too good, the amount of transition metal precursor coated on the surface of the substrate will be large, resulting in multiple layers of final selenides, and if the hydrophilicity is not good, the transition metal precursor cannot be coated on the substrate because the precursor solution is aqueous.

[0062] Exemplarily, the precursor solution comprises 5-10 mmol / L ammonium molybdate and 0.5-1 mol / L NaOH or KOH.

[0063] In order to promote the growth of transition metal selenides, i.e. the smooth progress of the reaction, preferably, in step (3), the heating comprises: heating the middle part of the tube furnace to 700-800℃ at a rate of 40-50℃ / min and maintaining for 1-10 minutes. Further preferably, the middle part of the tube furnace is heated to 730-750℃ at a rate of 40-50℃ / min and maintained for 1-10 minutes, which is beneficial to the formation of high-density twin boundaries.

[0064] In order to sublimate the selenium powder, preferably, in step (3), the heating further comprises: heating the gas inlet end of the tube furnace to 300-350℃ at a rate of 40-50℃ / min and maintaining for 1-10 minutes. After the sublimation of the selenium powder, it enters the middle part of the tube furnace and reacts with the metal source on the substrate.

[0065] In the present application, the reducing gas is used to reduce the transition metal and promote the formation of transition metal selenides, and the inert gas acts as a carrier gas to transport the reducing gas. The reducing gas and the inert gas are input from the gas inlet of the tube furnace and carry the sublimated selenium into the middle part of the tube furnace, so that the selenium reacts with the metal source on the substrate to form transition metal selenides.

[0066] Exemplarily, in step (3), the reducing gas is hydrogen, and the inert gas is argon.

[0067] In order to promote the growth of high-quality twin boundaries, preferably, the volume ratio of the reducing gas to the inert gas is 5:95-10:90.

[0068] After the reaction and annealing are completed, natural cooling can be performed.

[0069] In a third aspect, the present application also provides the use of the transition metal selenide and the transition metal selenide obtained by the above preparation method in electrolytic water hydrogen evolution.

[0070] The transition metal selenide has good catalytic activity in electrocatalytic hydrogen evolution and can be used as a catalyst for electrocatalytic hydrogen evolution. The hydrogen evolution overpotential of the transition metal selenide is 195-480 mV, and the Tafel slope is 70-160 mV dec 2 at a current density of 10 mA / cm -1 .

[0071] Hereinafter, the transition metal selenide and the preparation method thereof of the present application are further illustrated by specific examples.

[0072] Example 1

[0073] (1) 0.05 g of ammonium molybdate tetrahydrate and 0.05 g of potassium hydroxide were respectively dissolved in 5 mL of ultrapure water, and each was ultrasonically stirred for 5 minutes to make the solution transparent and clear, to obtain a molybdenum precursor solution;

[0074] (2) A 1 cm x 1 cm Si / SiO2 substrate was blown with nitrogen to clean the surface of the substrate; the cleaned Si / SiO2 substrate was placed on a spin coater, the rotation speed was set to 8000 rpm / s, and the spin coating time was 30 seconds; after the substrate reached the maximum rotation speed, the precursor solution was dropped onto the surface of the Si / SiO2 substrate to make the solution spread evenly;

[0075] (3) After spin coating, the Si / SiO2 substrate coated with the precursor solution was placed in a clean porcelain boat, and then the porcelain boat was placed in the center of a tube furnace; 0.1 g of selenium powder was placed at one end of the gas inlet of the tube furnace (i.e. the gas inlet end), and after vacuumizing, argon was filled (5% volume concentration of H2 / Ar gas was maintained during the heating and cooling processes); the heating program of the tube furnace was set as follows: the heating rate of the central position of the tube furnace was 50℃ per minute, and after the temperature reached 740℃, it was kept for 3 minutes (i.e. the reaction and annealing process); the heating rate of the position where the selenium powder was placed was 40℃ per minute, and after the temperature reached 300℃, it was kept for 3 minutes; after the end, it was naturally cooled. High-quality molybdenum diselenide containing high-density twin boundaries was obtained on the surface of the Si / SiO2 substrate, and the molybdenum diselenide showed a hexagonal morphology, as shown in Figure 1a .

[0076] As shown in the polarized SHG picture of FIG. 1(b), a large number of 60° boundaries exist inside the molybdenum diselenide prepared in Example 1;

[0077] As shown in the dark field TEM picture of FIG. 2(a), the boundaries inside the molybdenum diselenide prepared in Example 1 are uniform 60° boundaries, that is, twin boundaries; Figure 2

[0078] As shown in the dark field TEM picture of FIG. 2(a), the boundaries inside the molybdenum diselenide prepared in Example 1 are uniform 60° boundaries, that is, twin boundaries; Figure 3 ​The AFM image shown proves that the molybdenum diselenide prepared in Example 1 is single-layer thickness, the single-layer thickness is the thinnest thickness of a layered material, the single-layer material has a special direct band gap, and space of a device can be saved;

[0079] As Figure 4a shown in the Raman spectrum, the material grown in Example 1 is molybdenum diselenide;

[0080] As Figure 4b shown in the Raman Mapping image, the molybdenum diselenide prepared in Example 1 has excellent optical uniformity;

[0081] As Figure 5 shown in the high-magnification scanning transmission electron microscope image, the twin boundaries in the molybdenum diselenide prepared in Example 1 are composed of 4 / 8 rings (marked in the figure), and have excellent crystallization quality;

[0082] The density of the twin boundaries is 10 8 cm -2 , and the content of the eight-membered rings is 44%.

[0083] The molybdenum diselenide is used in a four-electrode system micro-electrolytic water hydrogen evolution battery as an electrocatalytic hydrogen evolution catalyst, and it can be seen from Figure 6 that the molybdenum diselenide prepared in Example 1 has excellent electrocatalytic performance, and the potential of the molybdenum diselenide is only 190 mV when the current density is 10 mA / cm 2 , and the molybdenum diselenide has good electrocatalytic hydrogen evolution performance.

[0084] Example 2

[0085] The molybdenum diselenide is prepared according to the method of Example 1, except that the central temperature of the tube furnace is kept at 770 DEG C for 3 minutes. As shown in FIG. 7(a), the grain boundary density inside the molybdenum diselenide grown in Example 2 is reduced compared with Example 1. The density of the twin boundaries is 10 5 cm -2 , and the content of the eight-membered rings is 35%.

[0086] Example 3

[0087] The molybdenum diselenide is prepared according to the method of Example 1, except that the central temperature of the tube furnace is kept at 800 DEG C for 3 minutes. As shown in FIG. 7(b), the grain boundary density inside the molybdenum diselenide grown in Example 3 is further reduced compared with Example 2. The density of the twin boundaries is 10 4 cm -2 , and the content of the eight-membered rings is 33%.

[0088] It can be seen from the comparison of Examples 1-3 that the preparation method of the application can accurately control the density of the grain boundaries by controlling the reaction temperature. It can be seen from the comparison of Examples 1-3 that the preparation method of the application can accurately control the density of the grain boundaries by controlling the reaction temperature. It can be seen from the comparison of Examples 1-3 that the preparation method of the application can accurately control the density of the grain boundaries by controlling the reaction temperature. It can be seen from the comparison of Examples 1-3 that the preparation method of the application can accurately control the density of the grain boundaries by controlling the reaction temperature.

[0089] Example 4

[0090] Molybdenum diselenide was prepared according to the method of Example 1, except that potassium hydroxide was not added to the precursor solution in step (1). As shown in Figure 7(c), a single hexagonal molybdenum diselenide has only six grain boundaries inside. The density of twin boundaries is 10. 3 cm -2 The content of eight-membered rings is 30%. This indicates that the addition of a strong base can increase the density of twin boundaries.

[0091] Example 5

[0092] Molybdenum diselenide was prepared according to the method of Example 1, except that 0.05 g of ammonium tungstate was used instead of 0.05 g of ammonium molybdate tetrahydrate. Figure 8a and Figure 8b As shown, the tungsten diselenide grown in Example 5 contains a high density of twin boundaries. The density of the twin boundaries is 10-1. 8 cm -2 The content of octet rings is 40%.

[0093] Comparative Example 1

[0094] Molybdenum diselenide was prepared using an existing vapor-phase precipitation method. The steps included: using 0.03 g of molybdenum trioxide as the molybdenum source and 0.05 g of selenium powder as the selenium source. A clean silica substrate was placed on top of the molybdenum oxide. After the molybdenum trioxide was vaporized at 800°C, it was deposited onto the substrate surface and reacted with selenium vapor to grow MoSe2. The twin boundary density was 10. 2 cm -2 The content of octetral rings is 25%.

[0095] Catalytic performance testing: The molybdenum diselenide prepared in Examples 1-5 and Comparative Example 1, as well as the single-crystal MoSe2 without grain boundaries purchased from Zhongke Leiming (Beijing) Technology Co., Ltd., were used to prepare microcells for the electrocatalytic hydrogen evolution performance (HER). The testing methods are as follows:

[0096] (1) First, the device was fabricated by transferring a monolayer of molybdenum diselenide onto a clean Si / SiO2 (300 nm thick SiO2) substrate using a PMMA film. Then, two gold electrodes were deposited on a molybdenum diselenide nanosheet using an electron beam. Subsequently, the entire device was covered with a 500 nm PMMA film. Then, the PMMA above the region of interest in the molybdenum diselenide nanosheet was removed by EBL. The exposed molybdenum diselenide was used as a catalyst for HER testing.

[0097] (2) The HER performance of molybdenum diselenide was tested using a four-electrode system with 0.5 M H2SO4 as the electrolyte and the scan rate set to 5 mV per step.

[0098] (3) In the test, the current density and voltage of the test sample were tested, and it was proved that the sample of Example 1 with the highest grain boundary density had the best electrocatalytic activity, as shown in Figure 6 and Table 1, the overpotential of Example 1 was 195 mV at 10 mA / cm 2 , which was higher than that of Examples 2-5 with lower grain boundary density, because the octagonal ring in the twin grain boundary had excellent electrocatalytic activity, as shown in Figure 5 Therefore, the high-density twin grain boundary greatly promoted the catalytic effect of the molybdenum diselenide basal plane on the electrocatalytic hydrogen evolution.

[0099] Table 1

[0100]

[0101]

[0102] The above description is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A transition metal selenide, characterized in that, The grain boundaries inside the transition metal selenide are all twin boundaries with a rotation angle of 60°, and the twin boundaries are composed of four-membered rings and eight-membered rings; The four-membered rings and eight-membered rings are arranged at irregular or regular intervals; The method for preparing the transition metal selenide includes: (1) Dissolve the transition metal salt in water to obtain a precursor solution; (2) Spin-coating the precursor solution onto the substrate; (3) Place the substrate in the middle of the tubular furnace, place the selenium powder at the gas inlet end of the tubular furnace, evacuate the tubular furnace and fill it with reducing gas and inert gas, heat it to sublimate the selenium powder, and then react and anneal it with the precursor solution. In step (3), the heating includes: the middle part of the tubular furnace is heated to 700-800℃ at a rate of 40-50℃ / min and then held for 1-10 minutes; the gas inlet end of the tubular furnace is heated to 300-350℃ at a rate of 40-50℃ / min and then held for 1-10 minutes.

2. The transition metal selenide according to claim 1, characterized in that, The density of the twin boundaries is 10. 3 -10 10 cm -2 .

3. The transition metal selenide according to claim 1, characterized in that, The content of eight-membered rings in the twin boundaries is 30-60%.

4. A method for preparing transition metal selenides, used to prepare the transition metal selenides according to claims 1-3, characterized in that, The preparation method includes: (1) Dissolve the transition metal salt in water to obtain a precursor solution; (2) Spin-coating the precursor solution onto the substrate; (3) Place the substrate in the middle of the tubular furnace, place the selenium powder at the gas inlet end of the tubular furnace, evacuate the tubular furnace and fill it with reducing gas and inert gas, heat it to sublimate the selenium powder, and then react and anneal it with the precursor solution. In step (3), the heating includes: the middle part of the tubular furnace is heated to 700-800℃ at a rate of 40-50℃ / min and then held for 1-10 minutes; the gas inlet end of the tubular furnace is heated to 300-350℃ at a rate of 40-50℃ / min and then held for 1-10 minutes.

5. The preparation method according to claim 4, characterized in that, The transition metal salt is an inorganic molybdenum salt or an inorganic tungsten salt.

6. The preparation method according to claim 4, characterized in that, In step (1), the precursor solution also includes a strong base.

7. The preparation method according to claim 6, characterized in that, The mass ratio of the transition metal salt to the strong base is 1-10:

2.

8. The preparation method according to claim 4, characterized in that, The substrate is a sapphire substrate or a SiO2 / Si substrate.

9. The application of the transition metal selenides according to claims 1-3 and the transition metal selenides obtained by the preparation methods according to claims 4-8 in hydrogen evolution by water electrolysis.

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