2H-phase molybdenum disulfide crystal and preparation method and application thereof

Abstract

The invention belongs to the field of material preparation, and particularly relates to a 2H-phase molybdenum disulfide crystal and a preparation method and application thereof. Comprising the following steps: mixing potassium molybdate and powdered sulfur, grinding, sintering in an Ar / H2 mixed atmosphere, and cooling to room temperature to obtain a product A; mixing the product A with sulfur powder, grinding, sintering in an Ar / H2 mixed atmosphere, and cooling to room temperature to obtain a product B; and sintering the product B in an Ar / H2 mixed atmosphere, cooling to room temperature, washing, and drying to obtain the 2H-phase MoS2 crystal. According to the preparation method disclosed by the invention, the purity and the crystal integrity of the 2H-phase MoS2 crystal are remarkably improved, and meanwhile, the interlayer spacing of the 2H-phase MoS2 crystal is optimized; in addition, the 2H-phase MoS2 crystal disclosed by the invention is used as a catalyst of a Li-CO2 battery positive electrode material, so that the electrochemical performance and the energy conversion efficiency of a Li-CO2 battery are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of material preparation, and particularly relates to a 2H-phase molybdenum disulfide crystal, a preparation method thereof, and an application thereof. Background Art

[0002] The lithium-carbon dioxide (Li-CO2) battery is a new energy storage system with the potential for both energy storage and CO2 resource utilization. Its core reaction is the reversible reduction and decomposition of CO2 during battery discharge / charging. Traditional Li-CO2 batteries face the problem that the discharge products (such as Li2CO3 and carbon) are difficult to decompose efficiently, resulting in a high charging overpotential and poor cycle stability. To improve the reaction kinetics, existing technologies mostly use noble metals or transition metal oxides as cathode catalysts, but their costs are high and their catalytic activities are still limited.

[0003] Molybdenum disulfide (MoS2) is regarded as a potential catalyst due to its unique layered structure and tunable electronic properties. Current research mostly focuses on 1T-phase (metallic phase) MoS2. Although its high conductivity is beneficial to charge transport, the 1T-phase is prone to structural degradation in an electrochemical environment and has insufficient stability. The 2H-phase (semiconductor phase) MoS2 has higher thermodynamic stability, but its intrinsic conductivity is poor and the active sites are insufficiently exposed, resulting in low catalytic activity. The existing preparation of 2H-phase MoS2 mostly relies on high-temperature sulfidation or complex liquid-phase exfoliation processes, which have problems such as low crystal phase purity and uncontrollable layer number, limiting its application in Li-CO2 batteries.

[0004] In recent years, a photo-assisted electrochemical strategy has been proposed to reduce the reaction energy barrier. However, in existing technologies, the interfacial compatibility between photosensitive materials (such as TiO2, CdS) and catalysts is poor, and the recombination rate of photo-generated carriers is high, making it difficult to synergistically improve the battery efficiency. Summary of the Invention

[0005] The purpose of the present invention is to provide a 2H-phase molybdenum disulfide material, a preparation method thereof, and an application thereof, so as to solve the problems of low synthesis purity, poor photo-electric synergy efficiency, short electrode life, and high cost of existing 2H-phase MoS2.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: In the first aspect, the present invention provides a preparation method of a 2H-phase molybdenum disulfide crystal, including the following steps: S1: Mix potassium molybdate and sulfur powder, grind them, sinter them in an Ar / H2 mixed atmosphere, and cool to room temperature to obtain product A; S2: Mix product A and sulfur powder, grind them, sinter them in an Ar / H2 mixed atmosphere, and cool to room temperature to obtain product B; S3: Sinter the product B in an Ar / H2 mixed atmosphere. After cooling to room temperature, wash and dry it to obtain the 2H-phase molybdenum disulfide crystal; Among them, the volume ratio of Ar to H2 in the Ar / H2 mixed atmosphere in S3 is less than the volume ratio of Ar to H2 in the Ar / H2 mixed atmosphere in S2; the volume ratio of Ar to H2 in the Ar / H2 mixed atmosphere in S1 is equal to the volume ratio of Ar to H2 in the Ar / H2 mixed atmosphere in S2.

[0007] Preferably, the mass ratio of potassium molybdate, sulfur powder in S1 and sulfur powder in S2 is 1: (1~2): (1~2).

[0008] Preferably, the volume ratio of Ar to H2 in the Ar / H2 mixed atmosphere in S1 is 9:1.

[0009] Preferably, the volume ratio of Ar to H2 in the Ar / H2 mixed atmosphere in S2 is 9:1.

[0010] Preferably, the volume ratio of Ar to H2 in the Ar / H2 mixed atmosphere in S3 is 4:1.

[0011] Preferably, the sintering conditions are sintering at 450~600 °C for 1.5~3 h.

[0012] Preferably, the heating rate of the sintering is 1~5 °C / min -1 .

[0013] Preferably, the drying conditions are: drying at 60~80 °C for 12~24 h.

[0014] In the second aspect, the present invention provides a 2H-phase molybdenum disulfide crystal prepared by the above preparation method.

[0015] In the third aspect, the present invention provides an application of a 2H-phase molybdenum disulfide crystal in the field of Li-CO2 batteries, and the 2H-phase molybdenum disulfide crystal is used as a catalyst for the positive electrode material of Li-CO2 batteries.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention realizes the deep sulfidation of potassium molybdate step by step through a two-stage vulcanization sintering process. By gradually regulating the reaction kinetics, it avoids the problem of crystal phase mixing (such as the coexistence of 1T phase and 2H phase) caused by too fast sulfur volatilization or uneven local reaction in traditional single-stage sulfidation. At the same time, it promotes the step-by-step bonding of sulfur atoms and molybdenum atoms, significantly improving the purity and crystallization integrity of 2H-phase MoS2 crystals. Secondly, the present invention realizes the precise optimization of sulfidation reaction conditions by constructing a hydrogen concentration gradient environment. The increase in hydrogen concentration enhances the reducing atmosphere on the one hand, promotes the deep sulfidation of residual molybdenum oxide, and inhibits lattice distortion. On the other hand, it dynamically regulates the distribution of sulfur vacancies through hydrogen atoms, repairs lattice defects, and optimizes the interlayer spacing of 2H-phase MoS2 crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0018] Figure 1 XRD pattern of the 2H-phase MoS2 material prepared in Example 5 of the present invention; Figure 2 SEM image of the 2H-phase MoS2 material prepared in Example 5 of the present invention at 2 μm; Figure 3 SEM image of the 2H-phase MoS2 material prepared in Example 5 of the present invention at 500 nm; Figure 4 TEM image of the 2H-phase MoS2 material prepared in Example 5 of the present invention at 100 nm. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art for the present invention. In case of conflict, the definition in this specification shall prevail.

[0020] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0021] In this text, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of a numerical range or percentage range should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0022] In this text, unless otherwise specified, the terms "comprise", "include", "contain", "have", or similar terms cover the meanings of "consist of" and "consist essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0023] In this text, for the sake of concise description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as within the scope described in this specification.

[0024] The following further describes the present invention in detail with reference to the accompanying drawings: The first object of the present invention is to provide a method for preparing a 2H-phase molybdenum disulfide crystal, comprising the following steps: S1: Weigh potassium molybdate (K2MoO4) and sulfur powder (S), place them in an agate mortar and mix evenly, grind until there is no obvious particle agglomeration to obtain a mixture; transfer the mixture to a quartz boat in a tubular furnace, and sinter in an Ar / H2 mixed atmosphere (10 vol% H2) for a sulfidation reaction. After the reaction is completed, naturally cool to room temperature to obtain product A; S2: Mix product A and sulfur powder, grind and then sinter in an Ar / H2 mixed atmosphere (10 vol% H2) to ensure that the molybdenum source (potassium molybdate) is fully sulfided. After sintering is completed, naturally cool to room temperature to obtain product B; S3: Place product B in a tubular furnace and sinter in an Ar / H2 mixed atmosphere (20 vol% H2). After cooling to room temperature, obtain black 2H-phase MoS2 powder; wash the 2H-phase molybdenum disulfide (MoS2) powder with deionized water and dry it at 60 - 80 °C for 12 - 24 h to obtain the high-purity 2H-phase MoS2 crystal.

[0025] Among them, the volume ratio of Ar to H2 in the Ar / H2 mixed atmosphere in S3 is less than the volume ratio of Ar to H2 in the Ar / H2 mixed atmosphere in S2; the volume ratio of Ar to H2 in the Ar / H2 mixed atmosphere in S1 is equal to the volume ratio of Ar to H2 in the Ar / H2 mixed atmosphere in S2, and the mass ratio of potassium molybdate, sulfur powder in S1 and sulfur powder in S2 is 1: (1 - 2): (1 - 2).

[0026] The present invention realizes the deep sulfidation of the molybdenum source (potassium molybdate) step by step through a two-stage sulfidation sintering process: First, in the S1 stage, potassium molybdate and sulfur powder are preliminarily mixed and sintered to generate intermediate product A; subsequently, in the S2 stage, sulfur powder is supplemented to product A and sintered again to ensure that the molybdenum source is fully sulfided to form product B. The staged sulfidation regulates the reaction kinetics step by step, avoiding the problem of crystal phase mixing (such as the coexistence of 1T phase and 2H phase) caused by too fast sulfur volatilization or uneven local reaction in traditional single-stage sulfidation. At the same time, it promotes the step-by-step bonding of sulfur atoms and molybdenum atoms, significantly improving the purity and crystallization integrity of 2H-phase MoS2 crystals.

[0027] In S3 of the present invention, by adjusting the hydrogen volume fraction in the Ar / H2 mixed atmosphere (from 10 vol% to 20 vol%), a hydrogen concentration gradient environment is constructed to achieve precise optimization of the sulfidation reaction conditions. The increase in hydrogen concentration enhances the reducing atmosphere on the one hand, promotes the deep sulfidation of residual molybdenum oxide in product B, and inhibits lattice distortion; on the other hand, it dynamically regulates the sulfur vacancy distribution through hydrogen atoms, repairs lattice defects, and optimizes the interlayer spacing of 2H-phase MoS2 crystals. Compared with the traditional process with a fixed hydrogen concentration, the gradient regulation strategy significantly improves the uniformity of the sulfur vacancy distribution by stage-matching the sulfidation reaction requirements, and at the same time inhibits the formation of non-steady crystal phases (such as 1T phase). Finally, 2H-phase MoS2 crystals with high purity and stable interlayer structure are obtained, whose electrochemical activity and catalytic stability are significantly improved and are suitable for high-performance energy storage and catalytic fields.

[0028] The sintering conditions are as follows: heating from 1 to 5 °C min -1 to 450 - 600 °C, and sintering at 450 - 600 °C for 1.5 - 3 h. Slowly heating (1 - 5 °C / min) can reduce the thermal stress generated by the material due to rapid temperature changes, thereby avoiding cracks or defects in the crystal structure and ensuring the structural integrity of 2H-phase MoS2 crystals; at the same time, it is beneficial to the uniform mixing and reaction of sulfur powder and potassium molybdate, avoiding the problem of insufficient sulfidation caused by local overheating or uneven reaction, and improving the uniformity and thoroughness of the sulfidation reaction. The temperature range of 450 - 600 °C is the optimal temperature range for the sulfidation reaction. At this temperature, sulfur powder can volatilize sufficiently and react with the molybdenum source to generate high-purity 2H-phase MoS2 crystals, while avoiding excessive sulfur volatilization or lattice distortion caused by too high temperature.

[0029] The second object of the present invention is to provide a high-purity 2H-phase molybdenum disulfide crystal. The interlayer spacing of the 2H-phase MoS2 crystal of the present invention is optimized, and the enlarged interlayer spacing can promote the interlayer migration of photo-generated carriers. Such as Figure 2 and Figure 3It can be seen that the 2H-phase MoS2 crystal prepared by the present invention has a two-dimensional sheet structure, which not only significantly increases the specific surface area of the material but also provides more active sites for the reaction, thereby effectively improving the catalytic performance and reaction efficiency of the material.

[0030] The third object of the present invention is to provide an application of a 2H-phase molybdenum disulfide crystal in the field of Li-CO2 batteries. The 2H-phase molybdenum disulfide crystal, as a catalyst for the positive electrode material of the Li-CO2 battery, can efficiently catalyze the CO2 reduction and precipitation reactions of the positive electrode material of the Li-CO2 battery. Specifically, in the CO2 reduction and precipitation reactions, due to the expanded interlayer spacing of the 2H-phase MoS2 crystal of the present invention, it is beneficial to the rapid transmission of CO2 molecules, protons (H + +) and electrons between the layers, thereby increasing the reaction rate; in addition, due to the two-dimensional sheet structure of the 2H-phase MoS2 crystal prepared by the present invention, more edge active sites (molybdenum and sulfur atoms at the edge of the 2H-phase MoS2 crystal) are exposed on the surface, thereby significantly improving the efficiency of the catalytic reaction; at the same time, since more active sites participate in the reaction, it can accelerate the reaction kinetics and reduce the energy required for the reaction.

[0031] The present invention constructs an efficient photo-electrochemical synergistic catalytic interface by controllably synthesizing high-purity 2H-phase MoS2 crystals and using their excellent photosensitive properties and stable layered structure, and uses it as a catalyst for the positive electrode material of the Li-CO2 battery, effectively solving the problems of low catalyst activity, insufficient light energy utilization rate and poor cycle stability in the prior art, and significantly improving the electrochemical performance and energy conversion efficiency of the Li-CO2 battery.

[0032] In addition, the stable 2H-phase structure of the present invention forms electron-hole pairs under light illumination. Its moderate band gap width (~1.8 eV) can efficiently utilize visible light, synergistically reduce the reaction energy barrier of the Li-CO2 battery, and inhibit the degradation of the material caused by photocorrosion, thereby achieving a double improvement in photo-assisted catalysis and electrochemical cycle stability.

[0033] The following further elaborates the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0034] Conventional instruments and equipment in the art are used in the following examples. For the experimental methods without specific conditions noted in the following examples, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following examples. Unless otherwise specified, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0035] Example 1 Step 1: Weigh 100 mg of potassium molybdate and 100 mg of sulfur powder, place them in an agate mortar and mix evenly, grind until there is no obvious particle aggregation to obtain a mixture. Step 2: Transfer the mixture to a quartz boat in a tube furnace. Under an Ar / H2 mixed atmosphere (10 vol% H2), heat it to 450 °C at a rate of 5 °C·min -1 and sinter for 1.5 h for the sulfidation reaction. After the reaction is completed, cool it to room temperature with the furnace to obtain product A. Step 3: Mix and grind product A with 100 mg of sulfur powder. Under an Ar / H2 mixed atmosphere (10 vol% H2), heat it to 450 °C at a rate of 5 °C·min -1 and sinter for 1.5 h to ensure sufficient sulfidation of the molybdenum source. After natural cooling, obtain product B. Step 4: Place product B in a tube furnace. Under an Ar / H2 mixed atmosphere (20 vol% H2), heat it to 450 °C at a rate of 5 °C·min -1 and sinter for 2 h to promote the stable formation of the 2H phase. Then, cool it to room temperature naturally to obtain black 2H-phase MoS2 powder. Step 5: Wash the obtained 2H-phase MoS2 powder with deionized water once, and dry it in a vacuum oven at 60 °C for 24 h to obtain high-purity 2H-phase MoS2 crystals.

[0036] Example 2 Step 1: Weigh 200 mg of potassium molybdate and 200 mg of sulfur powder, place them in an agate mortar and mix evenly, grind until there is no obvious particle aggregation to obtain a mixture. Step 2: Transfer the mixture to a quartz boat in a tube furnace. Under an Ar / H2 mixed atmosphere (10 vol% H2), heat it to 450 °C at a rate of 1 °C·min -1 and sinter for 1.5 h for the sulfidation reaction. After the reaction is completed, cool it to room temperature with the furnace to obtain product A. Step 3: Mix and grind product A with 200 mg of sulfur powder. Under an Ar / H2 mixed atmosphere (10 vol% H2), heat it to 450 °C at a rate of 1 °C·min -1Heat to 450 °C and sinter for 1.5 h to ensure sufficient sulfidation of the molybdenum source, obtaining Product B; Step 4. Place Product B in a tube furnace and, under an Ar / H2 mixed atmosphere (20 vol% H2), at a rate of 1 °C·min -1 Heat to 450 °C and sinter for 3 h to promote the stable formation of the 2H phase, and then naturally cool to room temperature to obtain black 2H-phase MoS2 powder; Step 5. Wash the obtained 2H-phase MoS2 powder once with deionized water and dry it in a vacuum oven at 65 °C for 20 h to obtain high-purity 2H-phase MoS2 crystals.

[0037] Example 3 Step 1. Weigh 300 mg of potassium molybdate and 600 mg of sulfur powder, place them in an agate mortar and mix evenly, grind until there is no obvious particle agglomeration to obtain a mixture; Step 2. Transfer the mixture to a quartz boat in a tube furnace and, under an Ar / H2 mixed atmosphere (10 vol% H2), at a rate of 2 °C·min -1 Heat to 450 °C and sinter for 1.5 h for the sulfidation reaction. After the reaction ends, cool to room temperature with the furnace to obtain Product A; Step 3. Mix and grind Product A with 600 mg of sulfur powder and, under an Ar / H2 mixed atmosphere (10 vol% H2), at a rate of 2 °C·min -1 Heat to 450 °C and sinter for 1.5 h to ensure sufficient sulfidation of the molybdenum source, obtaining Product B; Step 4. Place Product B in a tube furnace and, under an Ar / H2 mixed atmosphere (20 vol% H2), at a rate of 2 °C·min -1 Heat to 500 °C and sinter for 3 h to promote the stable formation of the 2H phase, and then naturally cool to room temperature to obtain black 2H-phase MoS2 powder; Step 5. Wash the obtained 2H-phase MoS2 powder once with deionized water and dry it in a vacuum oven at 70 °C for 18 h to obtain high-purity 2H-phase MoS2 crystals.

[0038] Example 4 Step 1. Weigh 400 mg of potassium molybdate and 600 mg of sulfur powder, place them in an agate mortar and mix evenly, grind until there is no obvious particle agglomeration to obtain a mixture; Step 2. Transfer the mixture to a quartz boat in a tube furnace and, under an Ar / H2 mixed atmosphere (10 vol% H2), at a rate of 3 °C·min -1 Heat to 500 °C and sinter for 2.5 h for the sulfidation reaction. After the reaction ends, cool to room temperature with the furnace to obtain Product A; Step 3: Mix and grind product A with 600 mg of sulfur powder. Under an Ar / H2 mixed atmosphere (10 vol% H2), heat it at 3 °C·min -1 to 500 °C and sinter for 2.5 h to ensure sufficient sulfidation of the molybdenum source, obtaining product B; Step 4: Place product B in a tube furnace. Under an Ar / H2 mixed atmosphere (20 vol% H2), heat it at 3 °C·min -1 to 550 °C and sinter for 2.5 h to promote the stable formation of the 2H phase. Then, naturally cool it to room temperature to obtain black 2H-phase MoS2 powder; Step 5: Wash the obtained 2H-phase MoS2 powder once with deionized water and dry it in a vacuum oven at 70 °C for 18 h to obtain high-purity 2H-phase MoS2 crystals.

[0039] Example 5 Step 1: Weigh 500 mg of potassium molybdate and 1000 mg of sulfur powder, place them in an agate mortar and mix evenly, grind until there is no obvious particle agglomeration to obtain a mixture; Step 2: Transfer the mixture to a quartz boat in a tube furnace. Under an Ar / H2 mixed atmosphere (10 vol% H2), heat it at 4 °C·min -1 to 550 °C and sinter for 1.5 h for the sulfidation reaction. After the reaction ends, cool it to room temperature with the furnace to obtain product A; Step 3: Mix and grind product A with 500 mg of sulfur powder. Under an Ar / H2 mixed atmosphere (10 vol% H2), heat it at 4 °C·min -1 to 550 °C and sinter for 1.5 h to ensure sufficient sulfidation of the molybdenum source, obtaining product B; Step 4: Place product B in a tube furnace. Under an Ar / H2 mixed atmosphere (20 vol% H2), heat it at 4 °C·min -1 to 550 °C and sinter for 2 h to promote the stable formation of the 2H phase. Then, naturally cool it to room temperature to obtain black 2H-phase MoS2 powder; Step 5: Wash the obtained 2H-phase MoS2 powder once with deionized water and dry it in a vacuum oven at 75 °C for 14 h to obtain high-purity 2H-phase MoS2 crystals.

[0040] Example 6 Step 1: Weigh 500 mg of potassium molybdate and 500 mg of sulfur powder, place them in an agate mortar and mix evenly, grind until there is no obvious particle agglomeration to obtain a mixture; Step 2: Transfer the mixture to a quartz boat in a tube furnace. Under an Ar / H2 mixed atmosphere (10 vol% H2), heat it at 5 °C·min -1Heat to 600 °C and sinter for 1.5 h to carry out the sulfidation reaction. After the reaction is completed, cool to room temperature with the furnace to obtain product A; Step 3: Mix and grind product A with 1000 mg of sulfur powder. Under an Ar / H2 mixed atmosphere (10 vol% H2), at a rate of 5 °C·min -1 Heat to 600 °C and sinter for 1.5 h to ensure sufficient sulfidation of the molybdenum source, obtaining product B; Step 4: Place product B in a tube furnace. Under an Ar / H2 mixed atmosphere (20 vol% H2), at a rate of 5 °C·min -1 Heat to 600 °C and sinter for 2 h to promote the stable formation of the 2H phase. Then, cool naturally to room temperature to obtain black 2H-phase MoS2 powder; Step 5: Wash the obtained 2H-phase MoS2 powder once with deionized water and dry it in a vacuum oven at 75 °C for 14 h to obtain high-purity 2H-phase MoS2 crystals.

[0041] Example 7 Step 1: Weigh 500 mg of potassium molybdate and 500 mg of sulfur powder, place them in an agate mortar and mix evenly, grind until there is no obvious particle agglomeration to obtain a mixture; Step 2: Transfer the mixture to a quartz boat in a tube furnace. Under an Ar / H2 mixed atmosphere (10 vol% H2), at a rate of 5 °C·min -1 Heat to 450 °C and sinter for 2.5 h to carry out the sulfidation reaction. After the reaction is completed, cool to room temperature with the furnace to obtain product A; Step 3: Mix and grind product A with 600 mg of sulfur powder. Under an Ar / H2 mixed atmosphere (10 vol% H2), at a rate of 5 °C·min -1 Heat to 450 °C and sinter for 2.5 h to ensure sufficient sulfidation of the molybdenum source, obtaining product B; Step 4: Place product B in a tube furnace. Under an Ar / H2 mixed atmosphere (20 vol% H2), at a rate of 5 °C·min -1 Heat to 550 °C and sinter for 3 h to promote the stable formation of the 2H phase. Then, cool naturally to room temperature to obtain black 2H-phase MoS2 powder; Step 5: Wash the obtained 2H-phase MoS2 powder once with deionized water and dry it in a vacuum oven at 80 °C for 12 h to obtain high-purity 2H-phase MoS2 crystals.

[0042] Perform XRD experiments on the sample prepared in Example 5: Grind the prepared sample into a powder with uniform particles, spread the powder evenly in the groove of the XRD sample stage, flatten the surface with a glass slide to ensure that the sample surface is flat and consistent with the plane of the sample stage. Turn on the X-ray diffractometer and calibrate it, set parameters such as the scanning angle range, speed, and step size, fix the sample on the sample stage and adjust the optical path alignment, start scanning to collect diffraction data, analyze the data and draw the XRD pattern. As Figure 1 shown, the XRD diffraction peaks of the sample prepared in this example correspond one by one to the diffraction peaks of the 2H-phase MoS2 crystal, proving that the synthesized product is the 2H-phase MoS2 crystal.

[0043] Perform SEM experiments on the sample prepared in Example 5: Clean the sample powder prepared in this example and spray it with gold, disperse the powder on the conductive tape, load it onto the sample stage and evacuate, set the acceleration voltage and detector parameters, adjust the focal length and contrast for imaging, and the obtained SEM images are as shown in Figure 2 and Figure 3 shown.

[0044] Perform TEM experiments on the sample prepared in Example 5: Disperse the sample powder prepared in this example in ethanol by ultrasonic treatment and then drop it on a copper grid, insert the sample rod into the electron microscope, adjust the electron beam parameters, and obtain high-resolution images after low-magnification positioning. The obtained TEM images are as shown in Figure 4 shown.

[0045] It can be seen from Figures 2 to 4 that the sample prepared in this example presents a two-dimensional sheet structure, thereby increasing the specific surface area of the material, exposing more edge active sites (molybdenum and sulfur atoms at the edge of the 2H-phase MoS2 crystal) on the surface, which is beneficial to improving the performance of the photo-assisted Li-CO2 battery.

[0046] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing 2H phase molybdenum disulfide crystals, characterized in that: The following steps are involved: S1: Potassium molybdate and sulfur powder are mixed, ground, sintered in an Ar / H2 mixed atmosphere, and cooled to room temperature to obtain product A; S2: Mix product A and sulfur powder, grind them, sinter them in an Ar / H2 mixed atmosphere, and cool them to room temperature to obtain product B; S3: sintering the product B in an Ar / H2 mixed atmosphere, cooling it to room temperature, and then washing and drying it to obtain the 2H phase molybdenum disulfide crystal; Among them, the volume ratio of Ar and H2 in the Ar / H2 mixed atmosphere described in S3 is less than the volume ratio of Ar and H2 in the Ar / H2 mixed atmosphere described in S2; the volume ratio of Ar and H2 in the Ar / H2 mixed atmosphere described in S1 is equal to the volume ratio of Ar and H2 in the Ar / H2 mixed atmosphere described in S2.

2. The method for preparing a 2H phase molybdenum disulfide crystal according to claim 1, characterized in that: The mass ratio of the potassium molybdate and sulfur powder in S1 to the sulfur powder in S2 is 1:(1~2):(1~2).

3. The method for preparing a 2H phase molybdenum disulfide crystal according to claim 1, characterized in that: The volume ratio of Ar to H2 in the Ar / H2 mixed atmosphere described in S1 is 9:

1.

4. The method for preparing a 2H phase molybdenum disulfide crystal according to claim 1, characterized in that: The volume ratio of Ar to H2 in the Ar / H2 mixed atmosphere described in S2 is 9:

1.

5. The method for preparing a 2H phase molybdenum disulfide crystal according to claim 1, characterized in that: The volume ratio of Ar to H2 in the Ar / H2 mixed atmosphere described in S3 is 4:

1.

6. The method for preparing a 2H phase molybdenum disulfide crystal according to claim 1, characterized in that: The sintering conditions are sintering at 450-600°C for 1.5-3 h.

7. The method for preparing a 2H phase molybdenum disulfide crystal according to claim 6, characterized in that: The heating rate of the sintering is 1-5 °C min -1 .

8. The method for preparing a 2H phase molybdenum disulfide crystal according to claim 1, characterized in that: The drying conditions are: drying at 60-80° C. for 12-24 hours.

9. A 2H phase molybdenum disulfide crystal, characterized in that: The method is prepared by any one of claims 1 to 8.

10. The use of a 2H phase molybdenum disulfide crystal in the field of Li-CO2 batteries according to claim 9, characterized in that: The 2H phase molybdenum disulfide crystal is used as a catalyst for a positive electrode material of a Li-CO2 battery.

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