Molybdenum carbide with different phase structures and preparation method and application thereof

Abstract

The invention provides molybdenum carbide with different phase structures and a preparation method and application thereof, and belongs to the technical field of transition metal carbides. The preparation method is used for preparing molybdenum carbide with different phase structures based on molten salt electrolysis. According to the preparation method, molybdenum carbide with different phase structures can be selectively prepared by regulating and controlling electrolysis conditions under medium and low temperature conditions, and the preparation method has the advantages of being easy and convenient to operate, controllable in component, free of gas-phase carbon source pollution and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of transition metal carbides, and particularly relates to molybdenum carbide with different phase structures, its preparation method and application. Background Art

[0002] Molybdenum carbide (MoCx) is a typical transition metal carbide material, which has high hardness, high melting point, excellent electrical conductivity and good chemical stability, and has a wide range of applications in many fields such as electrocatalysis, energy conversion, chemical synthesis and high-temperature structures. Especially in recent years, it has been regarded as an ideal non-precious metal catalyst in clean energy technologies such as electrocatalytic hydrogen evolution (HER) because of its noble-metal-like electronic structure and catalytic performance. At present, it is known that molybdenum carbide mainly exists in various crystal structures such as α-MoC, β-MoC, η-MoC, β-Mo2C, etc. These carbides with different phases have significant differences in physical properties, thermal stability and electronic structure, thus posing higher requirements for the selective control of their synthesis methods.

[0003] At present, the preparation methods of molybdenum carbide mainly include high-temperature carbothermal reduction method, organic precursor pyrolysis method, MOF-derived method, chemical vapor deposition (CVD) method, hydrothermal method, sol-gel method, etc. Among them, although the high-temperature carbothermal reduction method has mature technology and cheap raw materials, the reaction temperature is usually higher than 1200 °C, with high energy consumption, and it is easy to cause over-carbonization or carbon residue coating on the product, resulting in a decrease in the specific surface area of molybdenum carbide and hindrance of surface active sites. The organic precursor pyrolysis method and the MOF-derived method have certain advantages in regulating the morphology of molybdenum carbide, but the preparation of the precursor is complex, the cost is high, and impurities carbon and unstable atmosphere factors are easily introduced during the pyrolysis process. Although the chemical vapor deposition method can prepare molybdenum carbide thin films with high crystal quality, the equipment requirements are high and the deposition rate is slow, which is difficult to meet the requirements of batch preparation. The hydrothermal method and the sol-gel method are mostly used for the preparation of molybdenum carbide nanoparticles, but there are many intermediate reaction steps, the product purity is low, and usually still requires secondary high-temperature treatment.

[0004] Generally speaking, the current mainstream preparation methods of molybdenum carbide generally have problems such as high energy consumption, difficult control of the phase structure of the product, unclean carbon source, complex process or difficulty in large-scale production, and there is an urgent need for a new, green, efficient and controllable technical route for synthesizing multi-phase molybdenum carbide.

[0005] The molten salt electrolysis method is a new high-temperature inorganic synthesis technology that has developed rapidly in recent years. By applying an electric field in a molten salt system, the directional migration, selective reduction and solid-phase reaction of metal ions are realized. Compared with traditional methods, the molten salt electrolysis process does not require hydrogen or an external reducing atmosphere, and the electrolysis system can serve as both a reaction medium and a carbon source, with advantages such as moderate operating temperature, strong morphology regulation ability, and green and clean reaction process. Especially in carbonate molten salt systems, the C element can be provided by CO3 2-Electrochemical reduction is provided in situ without introducing solid carbon materials such as graphite and carbon black, thus significantly reducing the source of impurities and improving the purity and crystallization quality of molybdenum carbide.

[0006] Existing studies have shown that in the Li2CO3-Na2CO3-K2CO3 ternary eutectic system, by adjusting the electrolysis temperature, current density, and electrode configuration, the control of the phase structure of molybdenum carbide and the deposition behavior can be achieved. However, at present, such technologies have not established a systematic and stable process flow suitable for the controlled synthesis of multiphase molybdenum carbide. The key lies in the lack of in-depth understanding of the electrochemical reduction mechanism, the participation path of the carbon source, and the phase formation conditions.

[0007] Therefore, developing a method for directly synthesizing molybdenum carbide with different phase structures through molten salt electrolysis using carbonate molten salt as the reaction medium and carbon source can not only reduce the synthesis energy consumption and process complexity but also provide a new path for the large-scale application of high-purity and high-activity molybdenum carbide materials, which has important scientific value and engineering application prospects. Summary of the Invention

[0008] The object of the present invention is to overcome the deficiencies in the prior art and provide molybdenum carbide with different phase structures, its preparation method, and application. The preparation method of the molybdenum carbide with different phase structures can selectively prepare molybdenum carbide with different phase structures (such as MoC, η-MoC, β-Mo2C, α-MoC) by regulating the electrolysis conditions under medium and low temperature conditions, and has the advantages of simple operation, controllable composition, and no gas-phase carbon source pollution.

[0009] The present invention is achieved by the following technical solutions: In the first aspect, the present invention provides a preparation method of molybdenum carbide with different phase structures, and the preparation method includes the following steps: In an inert gas atmosphere, using a molybdenum mesh as the anode and an iron wire as the cathode, electrolysis is carried out in a molten first electrolyte at a constant temperature and a constant current. The electrolysis temperature is 500°C to 900°C, the electrolysis current is 0.5 A to 1 A, and the electrolysis time is 30 min to 1 h. Molybdenum carbide with different phase structures is obtained at different electrolysis temperatures; wherein, the first electrolyte is a mixed molten salt of Li2CO3, Na2CO3, and K2CO3.

[0010] According to the preparation method of the molybdenum carbide with different phase structures of the present invention, when the electrolysis temperature is 500°C to 600°C, the α-MoC phase is formed; when the electrolysis temperature is 750°C to 800°C, a mixed phase of MoC and η-MoC is formed; when the electrolysis temperature is 850°C to 900°C, the β-Mo2C phase is formed.

[0011] The preparation method of molybdenum carbide with different phase structures according to the present invention, wherein the first electrolyte is obtained by the following method: mixing Li2CO3, Na2CO3 and K2CO3 in a mass ratio of 1:1:1, and then drying at 180°C to 220°C for 5h to 8h to obtain the first electrolyte.

[0012] The preparation method of molybdenum carbide with different phase structures according to the present invention, wherein the length of the molybdenum mesh is 1 cm to 10 cm, the width of the molybdenum mesh is 1 cm to 5 cm, the diameter of the iron wire is 0.8 mm to 1.2 mm, the length of the iron wire is 14 cm to 18 cm, and the iron wire is arranged in a spring shape.

[0013] The preparation method of molybdenum carbide with different phase structures according to the present invention, wherein after electrolysis, the iron wire is taken out from the electrolyte or the electrolyte. After the iron wire is cooled, the deposited product on the iron wire is peeled off to obtain the deposited product; then the deposited product is first rinsed with deionized water, and then immersed in dilute hydrochloric acid for 8 min to 15 min to obtain the acid-leached deposited product; subsequently, the acid-leached deposited product is filtered by suction to obtain the impurity-removed deposited product; the impurity-removed deposited product is placed under vacuum drying at 50°C to 100°C for 5h to 10h to obtain the molybdenum carbide.

[0014] In a second aspect, the present invention provides a preparation method of molybdenum carbide with different phase structures, and the preparation method includes the following steps: In an inert gas atmosphere, using a graphite rod as the anode and an iron wire as the cathode, electrolysis is carried out in a molten second electrolyte at a constant temperature and a constant current. The electrolysis temperature is 500°C to 850°C, the electrolysis current is 0.5 A to 1 A, and the electrolysis time is 30 min to 1 h. Molybdenum carbide with different phase structures is obtained at different electrolysis temperatures; wherein, the second electrolyte is a mixture of a mixed molten salt of Li2CO3, Na2CO3 and K2CO3 and the molybdenum source.

[0015] The preparation method of molybdenum carbide with different phase structures according to the present invention, wherein when the electrolysis temperature is 500°C to 600°C, an α-MoC phase is formed; when the electrolysis temperature is 750°C to 800°C, a mixed phase of MoC and η-MoC is formed; when the electrolysis temperature is 850°C to 900°C, a β-Mo2C phase is formed.

[0016] The preparation method of molybdenum carbide with different phase structures according to the present invention, wherein the second electrolyte is obtained by the following method: mixing Li2CO3, Na2CO3 and K2CO3 in a mass ratio of 1:1:1, and then drying at 180°C to 220°C for 5h to 8h to obtain the second electrolyte.

[0017] The preparation method of molybdenum carbide with different phase structures according to the present invention, wherein the diameter of the graphite rod is 5 mm to 8 mm, and the length of the graphite rod is 28 cm to 32 cm; and / or, the diameter of the iron wire is 0.8 mm to 1.2 mm, the length of the iron wire is 14 cm to 18 cm, and the iron wire is arranged in a spring shape.

[0018] The preparation method of molybdenum carbide with different phase structures according to the present invention, wherein after electrolysis is completed, the iron wire is taken out from the electrolyte or the electrolyte. After the iron wire is cooled, the deposition product on the iron wire is peeled off to obtain a deposition product; then the deposition product is first rinsed with deionized water, and then immersed in dilute hydrochloric acid for 8 min to 15 min to obtain an acid-leached deposition product; subsequently, the acid-leached deposition product is filtered by suction to obtain a deposition product after impurity removal; the deposition product after impurity removal is placed under vacuum drying at 50 °C to 100 °C for 5 h to 10 h to obtain the molybdenum carbide.

[0019] In a third aspect, the present invention provides molybdenum carbide with different phase structures, and the molybdenum carbide is obtained by the preparation method described in the first aspect or the second aspect.

[0020] In a third aspect, the present invention provides an application of the molybdenum carbide with different phase structures described in the first aspect or the second aspect in an electrocatalytic hydrogen evolution catalyst.

[0021] Beneficial effects The preparation method of molybdenum carbide with different phase structures provided by the present invention belongs to the carbonate molten salt electrolysis method, and can realize the synthesis of molybdenum carbide materials with different crystal structures under medium and low temperature conditions without using traditional gas-phase carbon sources or solid carbon reducing agents. Compared with existing traditional preparation routes such as high-temperature carbothermal reduction method, organic precursor pyrolysis method, MOF-derived method, chemical vapor deposition (CVD) method, hydrothermal method, sol-gel method, etc., the preparation method of the present invention has significant technical advantages and practical application effects: 1. The preparation method of the present invention can complete the one-step synthesis of molybdenum carbide in the temperature range of 500 °C to 900 °C, significantly reducing energy consumption and avoiding the problem of high-temperature roasting above 1200 °C in the traditional carbothermal reduction method, and has higher economy and safety.

[0022] 2. The preparation method of the present invention utilizes CO3 2-In-situ electroreduction of anions as a carbon source enables precise control of the crystal phase structure of molybdenum carbide by adjusting the electrolysis temperature, current density, and molybdenum source supply method. Experiments show that α-MoC phase can be prepared when the electrolysis temperature is controlled at 500 °C - 600 °C, a mixed structure of MoC and η-MoC can be formed in the range of 750 °C - 800 °C, and β-Mo2C phase can be stably obtained when the temperature reaches 850 °C - 900 °C. This multiphase selective synthesis ability is difficult to achieve with existing organic precursor pyrolysis and chemical vapor deposition methods.

[0023] 3. The preparation method of the present invention uses spring-shaped iron wire as the cathode, and the prepared molybdenum carbide product has strong controllability in terms of morphology, and can obtain various microstructures including reed-like, spherical, needle-like, flake-like, cluster-like, granular, etc., providing wide adaptability for its applications in catalysis, electrode materials, and porous composite structures. Through characterization and analysis, the molybdenum carbide material prepared by the preparation method of the present invention has high crystal form purity, complete structure, and large specific surface area, and has good subsequent loading and dispersion performance.

[0024] 4. The reaction process of the preparation method of the present invention is clean and environmentally friendly, without using organic solvents, toxic gases throughout the process, and there is no dust escape and waste gas emission. The electrolytic molten salt can be recycled, greatly improving the raw material utilization rate and environmental friendliness, and meeting the urgent needs of future high-performance material preparation for green processes. Detailed implementation manners

[0025] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following further elaborates on the present invention in combination with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] In the first aspect, the present invention provides a preparation method of molybdenum carbide with different phase structures, and the preparation method includes the following steps: In an inert gas atmosphere, using a molybdenum mesh as the anode and an iron wire as the cathode, electrolyze in a molten first electrolyte at a constant temperature and a constant current. The electrolysis temperature is 500 °C - 900 °C, the electrolysis current is 0.5 A - 1 A, and the electrolysis time is 30 min - 1 h, and molybdenum carbide with different phase structures is obtained at different electrolysis temperatures; wherein, the first electrolyte is a mixed molten salt of Li2CO3, Na2CO3, and K2CO3.

[0027] The key technology of the present invention realizes the low-temperature one-step electrochemical synthesis of molybdenum carbide by constructing a comprehensive process path combining a carbonate molten salt system, electrode configuration, electrolysis parameter regulation, and product post-treatment. The specific key points are as follows: 1. The preparation method of the present invention uses a carbonate (ternary eutectic) molten salt system as both an electrolyte and a carbon source. This molten salt system not only provides an ionic conduction environment, but also the CO3 in it 2- can be directly electrochemically reduced at the cathode to release active carbon, realizing the electrically controlled input of the carbon source, which is different from the solid carbon source that is difficult to precisely control in the traditional carbothermal reduction method. This design enables the reaction process to avoid introducing gaseous carbon sources (such as CH4, CO) or adding solid carbon such as graphite, thus avoiding by-product pollution and carbon coating problems.

[0028] 2. The preparation method of the present invention uses a molybdenum metal mesh anode to provide a controllable molybdenum source. Through anodic oxidation, Mo species dissolve and migrate, and the amount and distribution of molybdenum reduction are controlled by the electric field drive. The preparation method of the present invention is different from the passive reduction mode of directly mixing salts with the molybdenum source MoO3, and has an electrochemical reaction path of dissolution-migration-reduction in three stages, which can precisely regulate the supply rate of Mo ions, thereby enabling repeatable control of the generated phase structure.

[0029] 3. In the preparation method of the present invention, the electrolysis temperature is the core variable for regulating the crystal form. By setting the molten salt electrolysis temperature in the range of 500 °C to 900 °C, the present invention realizes the directional synthesis of various molybdenum carbide phases such as α-MoC, MoC, η-MoC, and β-Mo2C, solving the problem of uncontrollable crystal forms of products in the traditional carbothermal reduction method and organic precursor pyrolysis method. This "temperature-phase selectivity" response relationship constitutes one of the core regulation mechanisms of the preparation method of the present invention.

[0030] 4. Cathode electrode structure and control of molybdenum carbide morphology. The preparation method of the present invention uses iron wire as the cathode, which not only enhances the deposition surface area, but also forms a local non-uniform electric field, promoting local nucleation, growth control, and phase distribution regulation of the deposit, and is the key to controlling the microscopic morphology of the product (such as structures like reed flower shape, spherical shape, needle shape, flake shape, cluster shape, granular shape, etc.).

[0031] According to the preparation method of molybdenum carbide with different phase structures described in the present invention, when the electrolysis temperature is 500 °C to 600 °C, such as 500 °C, 520 °C, 540 °C, 560 °C, 580 °C, 600 °C, etc., the α-MoC phase is formed; when the electrolysis temperature is 750 °C to 800 °C, such as 750 °C, 760 °C, 770 °C, 780 °C, 790 °C, 800 °C, etc., a mixed phase of MoC and η-MoC is formed; when the electrolysis temperature is 850 °C to 900 °C, such as 850 °C, 860 °C, 870 °C, 880 °C, 890 °C, 900 °C, etc., the β-Mo2C phase is formed.

[0032] In the method for preparing molybdenum carbide with different phase structures according to the present invention, the electrolysis current is 0.5 A to 1 A, such as 0.5 A, 0.6 A, 0.7 A, 0.8 A, 0.9 A, 1 A, etc. The current density also has a regulating effect on the product morphology and phase composition. When the electrolysis current is too small, the formation rate of molybdenum carbide is too slow, which is not conducive to improving production efficiency. When the electrolysis current is too large, it is easy to form a structure with small and disordered particles.

[0033] In the method for preparing molybdenum carbide with different phase structures according to the present invention, the electrolysis time is 30 min to 1 h, such as 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 1 h, etc. The electrolysis time also has a regulating effect on the product morphology and phase composition. The longer the electrolysis time, α-MoC starts from dot-shaped nuclei and gradually evolves into flocculent and flower-shaped structures, indicating that the electrolysis time dominates the two-dimensional / three-dimensional morphology expansion of the crystal. When the electrolysis time is less than 30 min, the formation rate of molybdenum carbide is too slow, which is not conducive to improving production efficiency. When the electrolysis time is greater than 1 h, it is not conducive to the formation of single-phase carbide.

[0034] In the method for preparing molybdenum carbide with different phase structures according to the present invention, the electrolysis process is carried out under the protection of an inert atmosphere to prevent the product and intermediate products from being oxidized. If it is carried out in air, stable oxides such as MoO3 or MoO2 will be formed, and the product composition will change.

[0035] According to the method for preparing molybdenum carbide with different phase structures of the present invention, wherein, the first electrolyte is obtained by the following method: mixing Li2CO3, Na2CO3 and K2CO3 in a mass ratio of 1:1:1, and then drying at 180 °C to 220 °C for 5 h to 8 h to obtain the first electrolyte.

[0036] According to the method for preparing molybdenum carbide with different phase structures of the present invention, wherein. The length of the molybdenum mesh is 1 cm to 10 cm, and the width of the molybdenum mesh is 1 cm to 5 cm.

[0037] According to the method for preparing molybdenum carbide with different phase structures of the present invention, wherein, the diameter of the iron wire is 0.8 mm to 1.2 mm, and the length of the iron wire is 14 cm to 18 cm. The cathode electrode structure affects the morphology of molybdenum carbide. For example, when the iron wire is in a spring shape, the generated molybdenum carbide is spherical; when the iron wire is in a mosquito coil shape, the generated molybdenum carbide is in a reed flower shape; when the iron wire is in a rod shape or a planar shape, it is easier to form sheet-like or regular crystal plane molybdenum carbide.

[0038] The preparation method of molybdenum carbide with different phase structures according to the present invention, wherein, after electrolysis is completed, the iron wire is taken out from the electrolyte or electrolytes. After the iron wire is cooled, the deposition product on the iron wire is peeled off to obtain the deposition product; then the deposition product is first rinsed with deionized water, and then soaked in dilute hydrochloric acid for 8 min to 15 min to obtain the acid-leached deposition product; subsequently, the acid-leached deposition product is filtered by suction to obtain the impurity-removed deposition product; the impurity-removed deposition product is placed under vacuum drying at 50°C to 100°C for 5 h to 10 h to obtain the molybdenum carbide.

[0039] Elution and drying of the product obtained after electrolysis can effectively remove by-product salts and unreacted molybdenum sources. The combined elution step of deionized water-dilute hydrochloric acid, supplemented by low-temperature vacuum drying, ensures the purity and structural integrity of the final molybdenum carbide, which is an integrated post-treatment strategy to guarantee the material performance.

[0040] In a second aspect, the present invention provides a preparation method of molybdenum carbide with different phase structures, and the preparation method includes the following steps: In an inert gas atmosphere, using a graphite rod as the anode and a spring-shaped iron wire as the cathode, electrolysis is carried out in a molten second electrolyte at a constant temperature and a constant current. The electrolysis temperature is 500°C to 850°C, the electrolysis current is 0.5 A to 1 A, and the electrolysis time is 30 min to 1 h. Molybdenum carbide with different phase structures is obtained at different electrolysis temperatures; wherein, the second electrolyte is a mixture of a mixed molten salt of Li2CO3, Na2CO3 and K2CO3 and the molybdenum source.

[0041] The key technology of the present invention is to realize the low-temperature one-step electrochemical synthesis of molybdenum carbide through an integrated process path combining the construction of a carbonate molten salt system, electrode configuration, electrolysis parameter regulation and product post-treatment. The specific key points are as follows: 1. The preparation method of the present invention uses a carbonate (ternary eutectic) molten salt system as both the electrolyte and the carbon source. This molten salt system not only provides an ion conduction environment, but also the CO3 2- at the cathode can directly electro-reduce and release active carbon, realizing the electrically controlled input of the carbon source, which is different from the solid carbon source that is difficult to accurately control in the traditional carbothermal reduction method. This design enables the reaction process to avoid introducing gaseous carbon sources (such as CH4, CO) or adding solid carbon such as graphite, thus avoiding by-product pollution and carbon coating problems.

[0042] 2. The preparation method of the present invention uses the molybdenum source in the electrolyte to provide a controllable molybdenum source. The dissolution and migration of Mo species are realized through the oxidation of the molybdenum source in the electrolyte, and the reduction amount and distribution of molybdenum are controlled by the electric field drive. The preparation method of the present invention has an electrochemical reaction path of three stages: dissolution-migration-reduction, which can accurately regulate the supply rate of Mo ions, so as to reproducibly control the generated phase structure.

[0043] 3. In the preparation method of the present invention, the electrolysis temperature is the core variable for regulating the crystal form. By setting the molten salt electrolysis temperature in the range of 500°C to 900°C, the present invention realizes the directional synthesis of various molybdenum carbide phases such as α-MoC, MoC, η-MoC, and β-Mo2C, and solves the problem of uncontrollable crystal forms of products in traditional carbothermal reduction method and organic precursor pyrolysis method. This "temperature-phase selectivity" response relationship constitutes one of the core regulation mechanisms of the preparation method of the present invention.

[0044] 4. Cathode electrode structure and molybdenum carbide morphology control. The preparation method of the present invention uses iron wire as the cathode, which not only enhances the deposition surface area, but also forms a local non-uniform electric field, promoting local nucleation, growth control and phase distribution regulation of the deposit, and is the key to controlling the microscopic morphology of the product (such as structures like reed flower-shaped, spherical, needle-shaped, flake-shaped, cluster-shaped, granular, etc.).

[0045] In the preparation method of molybdenum carbide with different phase structures according to the present invention, when the electrolysis temperature is 500°C to 600°C, such as 500°C, 520°C, 540°C, 560°C, 580°C, 600°C, etc., the α-MoC phase is formed; when the electrolysis temperature is 750°C to 800°C, such as 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, etc., a mixed phase of MoC and η-MoC is formed; when the electrolysis temperature is 850°C to 900°C, such as 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, etc., the β-Mo2C phase is formed.

[0046] In the preparation method of molybdenum carbide with different phase structures according to the present invention, the electrolysis current is 0.5A to 1A, such as 0.5A, 0.6A, 0.7A, 0.8A, 0.9A, 1A, etc. The current density also has a regulating effect on the product morphology and phase composition. When the electrolysis current is less than 0.5A, the formation rate of molybdenum carbide is too slow, which is not conducive to improving production efficiency. When the electrolysis current is greater than 1A, it leads to grain refinement and may induce the formation of different structures.

[0047] In the preparation method of molybdenum carbide with different phase structures according to the present invention, the electrolysis time is 30 min to 1 h, such as 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 1 h, etc. The electrolysis time also has a regulating effect on the product morphology and phase composition. The longer the electrolysis time, the α-MoC starts from dot-shaped nuclei and gradually evolves into flocculent and flower-shaped structures, indicating that time dominates the two-dimensional / three-dimensional morphology expansion of the crystal. When the electrolysis time is less than 30 min, the formation rate of molybdenum carbide is too slow, which is not conducive to improving production efficiency. When the electrolysis time is greater than 1 h, it is not conducive to the formation of single-phase carbides.

[0048] In the preparation method of molybdenum carbide with different phase structures according to the present invention, the electrolysis process is carried out under the protection of an inert atmosphere to prevent the products and intermediate products from being oxidized. If it is carried out in air, stable oxides such as MoO3 or MoO2 will be formed, and the composition of the products will change.

[0049] According to the preparation method of molybdenum carbide with different phase structures according to the present invention, wherein the second electrolyte is obtained by the following method: mixing Li2CO3, Na2CO3 and K2CO3 according to a mass ratio of 1:1:1, and then drying at 180 °C to 220 °C for 5 h to 8 h to obtain the second electrolyte.

[0050] According to the preparation method of molybdenum carbide with different phase structures according to the present invention, wherein the diameter of the graphite rod is 5 mm to 8 mm, and the length of the graphite rod is 28 cm to 32 cm.

[0051] According to the preparation method of molybdenum carbide with different phase structures according to the present invention, wherein the diameter of the iron wire is 0.8 mm to 1.2 mm, and the length of the iron wire is 14 cm to 18 cm. The cathode electrode structure affects the morphology of molybdenum carbide. For example, when the iron wire is in a spring shape, the generated molybdenum carbide is spherical; when the iron wire is in a mosquito coil shape, the generated molybdenum carbide is in a reed flower shape; when the iron wire is in a rod shape or a planar shape, it is easier to form flaky or regular crystal plane molybdenum carbide.

[0052] According to the preparation method of molybdenum carbide with different phase structures according to the present invention, after electrolysis is completed, the iron wire is taken out from the electrolyte or electrolytes. After the iron wire is cooled, the deposited product on the iron wire is peeled off to obtain the deposited product; then the deposited product is first rinsed with deionized water, and then soaked in dilute hydrochloric acid for 8 min to 15 min to obtain the acid-leached deposited product; subsequently, the acid-leached deposited product is filtered by suction to obtain the deposited product after impurity removal; the deposited product after impurity removal is placed under vacuum drying at 50 °C to 100 °C for 5 h to 10 h to obtain the molybdenum carbide.

[0053] Eluting and drying the products obtained after electrolysis can effectively remove by-product salts and unreacted molybdenum sources. The combined elution step of deionized water-dilute hydrochloric acid, supplemented by low-temperature vacuum drying, ensures the purity and structural integrity of the final molybdenum carbide, and is an integrated post-treatment strategy to ensure the material performance.

[0054] In the third aspect, the present invention provides molybdenum carbide with different phase structures, and the molybdenum carbide is obtained by the preparation method described in the first aspect or the second aspect.

[0055] Due to the adoption of the preparation method described in the first aspect or the second aspect, the present invention selectively prepares molybdenum carbide with different phase structures (such as α-MoC, MoC, η-MoC, β-Mo2C) by regulating the electrolysis conditions.

[0056] In a fourth aspect, the present invention provides the application of molybdenum carbide with different phase structures in the first aspect or the second aspect in an electrocatalytic hydrogen evolution catalyst.

[0057] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. The experimental methods without specific conditions noted in the following examples are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions or parts are by weight.

[0058] The reagents and raw materials used in the embodiments of the present invention can be obtained through commercial channels without special instructions.

[0059] Example 1 A preparation method for molybdenum carbide with different phase structures based on molten salt electrolysis includes the following steps: 1: Preparation and pretreatment of molten salt electrolyte Mix Li2CO3, Na2CO3 and K2CO3 with a mass ratio of 1:1:1 evenly as the basic salt system of the electrolyte, and weigh a total of 45 grams. The obtained mixture is placed in a corundum crucible and dried in an oven at 200 °C for 6 hours to remove moisture.

[0060] 2: Electrode construction and device assembly Use a molybdenum mesh with a length of 5 cm and a width of 1.5 cm as the anode, and bend a wire with a diameter of 1 mm and a length of 16 cm into a "spring shape" as the cathode. Fix the anode and cathode in graphite conductive clamps respectively, and insert them into a corundum crucible filled with the electrolyte. Place the device in a resistance furnace. The electrolysis system is filled with high-purity argon as a protective atmosphere to prevent oxidation.

[0061] 3: Execution of electrolysis reaction Raise the temperature of the resistance furnace to the predetermined set value of 550 °C to fully melt the mixed molten salt. Carry out electrolysis in a constant current control mode, with the current set at 0.8 A and the electrolysis time at 40 min. During the electrolysis process, molybdenum in the anode dissolves into the molten salt system and migrates to the cathode region in the form of MoO4²⁻ or MoO3, and undergoes an electrochemical reduction reaction with CO3 2- ions together to generate molybdenum carbide. The molybdenum carbide is in the α-MoC phase, and the morphology of the molybdenum carbide is spherical.

[0062] 4: Collection and treatment of electrolysis products After electrolysis is completed, the cathode iron wire is taken out from the molten salt. After cooling, the deposited product is peeled off, rinsed with deionized water, and then soaked in 5 wt% dilute hydrochloric acid for 10 min to remove the residual electrolyte and by-products on the surface. Subsequently, the product is collected by suction filtration and dried in a vacuum drying oven at 60 °C for 6 hours to obtain the final molybdenum carbide powder sample.

[0063] Example 2 The preparation method of this example is the same as that of Example 1, except that the electrolysis temperature is 780 °C, and the generated molybdenum carbide is a mixed phase of MoC and η-MoC.

[0064] Example 3 The preparation method of this example is the same as that of Example 1, except that the electrolysis temperature is 860 °C, and the generated molybdenum carbide is the β-Mo2C phase.

[0065] Example 4 A preparation method for molybdenum carbide with different phase structures based on molten salt electrolysis includes the following steps: 1: Preparation and pretreatment of molten salt electrolyte Mix Li2CO3, Na2CO3, and K2CO3 with a mass ratio of 1:1:1 evenly as the basic salt system of the electrolyte. Weigh a total of 45 grams and add 10 g of the molybdenum source MoO3 to supply Mo elements. The obtained mixture is placed in a corundum crucible and dried in an oven at 200 °C for 6 hours to remove moisture.

[0066] 2: Electrode construction and device assembly Use a graphite rod with a diameter of 6 mm and a length of 30 cm as the anode, and bend a wire with a diameter of 1 mm and a length of 16 cm into a "spring shape" as the cathode. They are respectively fixed in a graphite conductive fixture and inserted into a corundum crucible filled with the electrolyte. The device is placed in a resistance furnace. The electrolysis system is filled with high-purity argon as a protective atmosphere to prevent oxidation.

[0067] 3: Execution of electrolysis reaction Raise the temperature of the resistance furnace to the predetermined set value of 750 °C to fully melt the mixed molten salt. Electrolysis is carried out in a constant current control mode, with the current set at 0.8 A and the electrolysis time at 40 min. During electrolysis, MoO3 in the molten salt system migrates to the cathode region and undergoes an electrochemical reduction reaction with CO3 2- ions together to generate molybdenum carbide. The molybdenum carbide is the α-MoC phase, and the morphology of the molybdenum carbide is spherical.

[0068] 4: Collection and treatment of electrolysis products After electrolysis is completed, the cathode iron wire is taken out from the molten salt. After cooling, the deposited product is peeled off, rinsed with deionized water, and then soaked in 5 wt% dilute hydrochloric acid for 10 min to remove the residual electrolyte and by-products on the surface. Subsequently, the product is collected by suction filtration and dried in a vacuum drying oven at 60 °C for 6 hours to obtain the final molybdenum carbide powder sample.

[0069] Example 5 The preparation method of this example is the same as that of Example 4, except that in step 3, the electrolysis temperature is 800 °C, and the generated molybdenum carbide is a mixed phase of MoC and η-MoC.

[0070] Example 6 The preparation method of this example is the same as that of Example 4, except that in step 3, the electrolysis temperature is 850 °C, and the generated molybdenum carbide is the β-Mo2C phase.

[0071] Performance test: (1) The molybdenum carbide prepared in each of the above examples was subjected to XRD testing, and the test results are shown in Table 1.

[0072] (2) The molybdenum carbide prepared in each of the above examples was subjected to SEM testing, and the test results are shown in Table 1.

[0073] Table 1. XRD and SEM results of molybdenum carbide prepared in each of the above examples

[0074] The present invention discloses a method for preparing molybdenum carbide materials with different phase structures by molten salt electrolysis in a carbonate molten salt system, which can achieve the directional synthesis of different crystal forms of molybdenum carbide (including α-MoC, MoC, η-MoC, β-Mo2C) according to the electrolysis temperature, electrode type, current density, and molybdenum source concentration. This method has the characteristics of simple process flow, controllable morphology, and environmental friendliness. The prepared molybdenum carbide materials can be used as electrocatalytic hydrogen evolution catalysts, with excellent catalytic performance and stability.

[0075] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Preparation method of molybdenum carbide with different phase structures, characterized in that, It includes the following steps: In an inert gas atmosphere, using a molybdenum mesh as the anode and an iron wire as the cathode, electrolysis is carried out in a molten first electrolyte at a constant temperature and a constant current. The electrolysis temperature is 500°C to 900°C, the electrolysis current is 0.5 A to 1 A, and the electrolysis time is 30 min to 1 h. Molybdenum carbides with different phase structures are obtained at different electrolysis temperatures. Among them, the first electrolyte is a mixed molten salt of Li2CO3, Na2CO3, and K2CO3.

2. Preparation method of molybdenum carbide with different phase structures, characterized in that, It includes the following steps: In an inert gas atmosphere, using a graphite rod as the anode and an iron wire as the cathode, electrolysis is carried out in a molten second electrolyte at a constant temperature and a constant current. The electrolysis temperature is 500°C to 900°C, the electrolysis current is 0.5 A to 1 A, and the electrolysis time is 30 min to 1 h. Molybdenum carbides with different phase structures are obtained at different electrolysis temperatures. Among them, the second electrolyte is a mixture of a mixed molten salt of Li2CO3, Na2CO3, and K2CO3 and the molybdenum source.

3. The preparation method of molybdenum carbide with different phase structures according to claim 1 or 2, characterized in that, When the electrolysis temperature is 500°C to 600°C, the α-MoC phase is formed; when the electrolysis temperature is 750°C to 800°C, the MoC and η-MoC mixed phase is formed; when the electrolysis temperature is 850°C to 900°C, the β-Mo2C phase is formed.

4. The preparation method of molybdenum carbide with different phase structures according to claim 1, characterized in that, The first electrolyte is obtained by the following method: Using one or more of carbonates (Li2CO3, Na2CO3, K2CO3) as the electrolyte and carbon source, and then drying at 180°C to 220°C for 5 h to 8 h to obtain the first electrolyte.

5. The method for preparing molybdenum carbide with different phase structures according to claim 2, wherein The second electrolyte is obtained by the following method: Mixing one or more of carbonates (Li2CO3, Na2CO3, K2CO3) as the electrolyte and carbon source, and then drying at 180°C to 220°C for 5 h to 8 h to obtain the second electrolyte.

6. The preparation method of molybdenum carbide with different phase structures according to claim 1, characterized in that, The length of the molybdenum mesh is 1 cm to 10 cm, the width of the molybdenum mesh is 1 cm to 5 cm, the diameter of the iron wire is 0.8 mm to 1.2 mm, the length of the iron wire is 14 cm to 18 cm, and the iron wire is arranged in a spring shape.

7. The preparation method of molybdenum carbide with different phase structures according to claim 2, characterized in that, The diameter of the graphite rod is 5 mm to 8 mm, the length of the graphite rod is 28 cm to 32 cm; and / or, the diameter of the iron wire is 0.8 mm to 1.2 mm, the length of the iron wire is 14 cm to 18 cm, and the iron wire is arranged in a spring shape.

8. The method for preparing molybdenum carbide with different phase structures according to claim 1 or 2, characterized in that, After electrolysis is completed, take out the iron wire from the electrolyte or electrolytes. After the iron wire cools, peel off the deposition product on the iron wire to obtain the deposition product; then first rinse the deposition product with deionized water, and then soak the deposition product in dilute hydrochloric acid for 8 min to 15 min to obtain the acid-leached deposition product; Subsequently, filter the acid-leached deposition product by suction to obtain the impurity-removed deposition product; Place the impurity-removed deposition product under vacuum drying at 50°C to 100°C for 5 h to 10 h to obtain the molybdenum carbide.

9. Molybdenum carbide with different phase structures, characterized in that, Obtained by the preparation method according to any one of claims 1 to 8.

10. Application of the molybdenum carbide with different phase structures according to claim 9 in an electrocatalytic hydrogen evolution catalyst.

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