Method for preparing different phases of molybdenum carbide by one-step molten salt electrolysis and its products

Abstract

The invention discloses a method and product for preparing different phases of molybdenum carbide by a one-step molten salt electrolysis method, which belongs to the field of transition metal carbides. The method is in an air atmosphere, with a molybdenum mesh as an anode and a galvanized iron wire as a cathode. Electrolysis is carried out with a constant temperature and a constant current in a molten Li-Na-K carbonate electrolyte. The electrolysis temperature is 550°C to 800°C, and the electrolysis current is 1A to 4A. The time is 15min to 60min, and different phases of molybdenum carbide can be obtained at different electrolysis temperatures. The present invention adopts a molybdenum mesh as an anode to provide a molybdenum source, adopts a galvanized iron wire as a cathode to serve as a current collector and deposits product molybdenum carbide, adopts Li-Na-K carbonate electrolyte, changes the mobility of carbon atoms and molybdenum atoms in the electrolysis product molybdenum carbide by regulating the electrolyte temperature, thereby forming molybdenum carbide of different phase structures, and the process is simple and fast, has low requirements for experimental equipment, and has practical application value for industrialization.

Description

Technical Field

[0001] The present invention belongs to the field of transition metal carbides, and more specifically, relates to a method for preparing different phases of molybdenum carbide by a one-step molten salt electrolysis method and a product thereof. Background Art

[0002] As society continues to develop, a large amount of fossil fuels are consumed in the industrial production process, which on the one hand causes environmental pollution and on the other hand brings about an energy crisis. Environmental problems and energy problems have brought huge crises to mankind, so the vast number of scientific researchers are constantly seeking solutions. Hydrogen energy, as a clean and renewable energy source, can alleviate these two major problems to a large extent. At present, the production of hydrogen energy is mainly through the electrolysis of water. In order to reduce the electricity consumed by electrolysis of water, it is necessary to select a suitable catalyst. At present, the catalyst with the best catalytic performance is the precious metal platinum. However, the reserves of platinum are small and the price is expensive. Therefore, it is necessary to find a catalyst with abundant reserves and low price to replace platinum. Transition metal carbide, as a common catalyst, is cheap and can be used to replace the precious metal platinum.

[0003] In recent years, researchers at home and abroad have conducted in-depth research on the electrocatalytic hydrogen evolution of transition metal carbides. Molybdenum carbides have attracted the attention of researchers in this field because they share an outermost electron structure similar to that of the precious metal platinum, and because they exhibit excellent catalytic properties. Therefore, a simple, rapid, and efficient process for preparing molybdenum carbide is crucial.

[0004] Energy Environmental Science, Vol. 7, 2014, pp. 387-392, reported the preparation of a solution using ammonium molybdate as a molybdenum source and aniline as an organic carbon source. The solution was adjusted to a pH of 4-5 by dropwise addition of hydrochloric acid. The resulting precipitate was washed with deionized water and ethanol, dried at 50°C for 10 hours, and then calcined at 750°C under an argon atmosphere for 5 hours to yield the final nanoporous molybdenum carbide nanowires.

[0005] Nanoscale magazine reported in Volume 9, 2017, pages 15895-15900 that ammonium molybdate was used as a molybdenum source and dopamine was used as a carbon source. The solution was prepared into a solution, and ammonia was added to the solution to obtain a molybdenum-containing organic precursor with a three-dimensional structure. The precursor was then calcined at 900°C in a nitrogen atmosphere for 4 hours to obtain molybdenum carbide.

[0006] Advanced Materials magazine reported in Volume 31, 2019, 1900699 that a ZIF-8-MoO4 precursor was prepared by a hydrothermal method using sodium molybdate as a molybdenum source and ZIF-8 as a carbon source, and then calcined at 800°C in a nitrogen atmosphere for 2 hours to obtain dodecahedral molybdenum carbide.

[0007] The aforementioned methods for preparing molybdenum carbide all have drawbacks such as complex preparation processes, time-consuming reactions, and a single product phase. Therefore, developing a simple and rapid method for preparing multi-phase molybdenum carbide is of great significance. Summary of the Invention

[0008] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides a method for preparing molybdenum carbide of different phases by a one-step molten salt electrolysis method and its products. The purpose is to obtain four different phases of molybdenum carbide through a single process step of molten salt electrolysis and by regulating different electrolysis temperatures, thereby solving the technical problems of the existing molybdenum carbide preparation process being complex, time-consuming, and the resulting product having a single phase.

[0009] To achieve the above object, according to one aspect of the present invention, the following technical solution is provided:

[0010] A method for preparing different phases of molybdenum carbide by one-step molten salt electrolysis comprises the following steps:

[0011] In an air atmosphere, with a molybdenum mesh as the anode and a galvanized iron wire as the cathode, electrolysis is carried out in a molten Li-Na-K carbonate electrolyte at a constant temperature and constant current. The electrolysis temperature is 550°C to 800°C, the electrolysis current is 1A to 4A, and the time is 15min to 60min. Different phases of molybdenum carbide are obtained at different electrolysis temperatures.

[0012] Preferably, at an electrolysis temperature of 550°C to 680°C, PDF#89-2868 phase molybdenum carbide is obtained; at an electrolysis temperature of 680°C to 715°C, PDF#89-2868 and PDF#65-3494 mixed phase molybdenum carbide is obtained; at an electrolysis temperature of 715°C to 750°C, PDF#89-4305 phase molybdenum carbide is obtained; at an electrolysis temperature of 750°C to 800°C, PDF#35-0787 phase molybdenum carbide is obtained.

[0013] Preferably, the method for obtaining the molten Li-Na-K carbonate electrolyte is: drying Li-Na-K carbonate with a mass ratio of Li2CO3:Na2CO3:K2CO3=(1±0.2):(1±0.2):(1±0.2), and then heating it to 550℃~800℃ to melt it.

[0014] Preferably, the size of the molybdenum mesh is 1.5cm to 2cm wide and 3cm to 4cm long; the surface area of ​​the galvanized iron wire is 8cm 2 ~12cm 2 .

[0015] Preferably, the diameter of the galvanized iron wire is 0.9mm to 1.2mm and the length is 28cm to 32cm. The galvanized iron wire is bent into a disc shape with a single-side surface area of ​​4cm. 2 ~6cm 2 .

[0016] Preferably, the distance between the anode and the cathode is 1 cm to 1.5 cm.

[0017] Preferably, the above method further comprises: removing carbonate electrolyte on the surface of the obtained molybdenum carbide, and then drying to obtain the final molybdenum carbide.

[0018] Preferably, the method for removing the carbonate electrolyte on the surface of molybdenum carbide is specifically: soaking the molybdenum carbide in 1 mol / L to 3 mol / L hydrochloric acid for 16 h to 24 h, and then rinsing with deionized water to remove the carbonate electrolyte on the surface of the molybdenum carbide.

[0019] According to another aspect of the present invention, the following technical solution is also provided:

[0020] Molybdenum carbide is prepared by any of the above methods.

[0021] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0022] 1. The method for preparing different phases of molybdenum carbide by one-step molten salt electrolysis provided by the present invention adopts a molybdenum mesh as an anode to provide a molybdenum source, a galvanized iron wire as a cathode as a current collector and deposits the product molybdenum carbide; a Li-Na-K carbonate electrolyte is used, and a constant current is applied to both ends of the electrode for electrolysis, so that carbonate ions in the electrolyte can undergo a reduction reaction at the cathode to generate elemental carbon, and the remaining oxygen anions migrate to the anode by diffusion to undergo an oxidation reaction to generate oxygen, and the oxygen generated at the anode reacts with the molybdenum mesh to generate molybdenum trioxide, which dissolves in the electrolyte and becomes molybdenum trioxide. At this time, carbonate ions and molybdate ions are simultaneously present in the electrolyte, and these two ions are co-reduced at the cathode to generate molybdenum carbide; the mobility of carbon atoms and molybdenum atoms in the electrolysis product molybdenum carbide is changed by regulating the electrolyte temperature, thereby forming molybdenum carbide with different phase structures; the present invention adopts a single process step of molten salt electrolysis and regulates different electrolysis temperatures, and the process flow is simple and fast, and four different phases of molybdenum carbide can be obtained;

[0023] 2. The method of the present invention further provides a specific method for obtaining different phases of molybdenum carbide by regulating the electrolysis temperature, that is, at an electrolysis temperature of 550°C to 680°C, PDF#89-2868 phase molybdenum carbide is obtained; at an electrolysis temperature of 680°C to 715°C, PDF#89-2868 and PDF#65-3494 mixed phase molybdenum carbide is obtained; at an electrolysis temperature of 715°C to 750°C, PDF#89-4305 phase molybdenum carbide is obtained; at an electrolysis temperature of 750°C to 800°C, PDF#35-0787 phase molybdenum carbide is obtained;

[0024] 3. The entire process of the method of the present invention is carried out in air, and the reaction process does not require inert gas protection, which greatly reduces the requirements for reaction equipment and reaction conditions, thereby reducing costs and operational complexity;

[0025] 4. The method of the present invention uses molybdenum mesh and galvanized iron wire as electrode materials, which are cheap; and the Li-Na-K mixed carbonate electrolyte can be reused, thereby achieving the effect of saving resources and reducing production costs;

[0026] 5. The different phases of molybdenum carbide prepared by the method of the present invention have different microstructures. According to their characteristics, they can be applied in the field of catalysis and can be prepared on a large scale, with practical application value for industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 : This is the XRD pattern of PDF#89-2868 phase molybdenum carbide prepared at an electrolysis temperature of 550° C. in an embodiment of the present invention;

[0028] Figure 2 The XRD pattern of the mixed phase molybdenum carbide of PDF#89-2868 and PDF#65-3494 prepared at an electrolysis temperature of 700° C. in an embodiment of the present invention;

[0029] Figure 3 : This is the XRD pattern of PDF#89-4305 phase molybdenum carbide prepared at an electrolysis temperature of 725° C. in an embodiment of the present invention;

[0030] Figure 4 : This is the XRD pattern of PDF#35-0787 phase molybdenum carbide prepared at an electrolysis temperature of 800° C. in an embodiment of the present invention;

[0031] Figure 5 This is a SEM image of molybdenum carbide prepared at an electrolysis temperature of 550° C. in an embodiment of the present invention;

[0032] Figure 6 TEM image of molybdenum carbide prepared at an electrolysis temperature of 550° C. in an embodiment of the present invention;

[0033] Figure 7This is a SEM image of molybdenum carbide prepared at an electrolysis temperature of 700° C. in an embodiment of the present invention;

[0034] Figure 8 TEM image of molybdenum carbide prepared at an electrolysis temperature of 700° C. in an embodiment of the present invention;

[0035] Figure 9 This is a SEM image of molybdenum carbide prepared at an electrolysis temperature of 725° C. in an embodiment of the present invention;

[0036] Figure 10 TEM image of molybdenum carbide prepared at an electrolysis temperature of 725° C. in an embodiment of the present invention;

[0037] Figure 11 This is a SEM image of molybdenum carbide prepared at an electrolysis temperature of 800° C. in an embodiment of the present invention;

[0038] Figure 12 TEM image of molybdenum carbide prepared at an electrolysis temperature of 800° C. in an embodiment of the present invention;

[0039] Figure 13 This is the LSV curve of molybdenum carbide prepared at an electrolysis temperature of 550° C. used as an electrocatalytic hydrogen evolution catalyst in an embodiment of the present invention;

[0040] Figure 14 : This is the LSV curve of molybdenum carbide prepared at an electrolysis temperature of 700° C. used as an electrocatalytic hydrogen evolution catalyst in an embodiment of the present invention;

[0041] Figure 15 This is the LSV curve of molybdenum carbide prepared at an electrolysis temperature of 725° C. used as an electrocatalytic hydrogen evolution catalyst in an embodiment of the present invention;

[0042] Figure 16 This is the LSV curve of the molybdenum carbide prepared at an electrolysis temperature of 800° C. used as an electrocatalytic hydrogen evolution catalyst in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0044] The present invention provides a one-step molten salt electrolysis method for preparing different phases of molybdenum carbide. This method utilizes constant current molten salt electrolysis in an air atmosphere to deposit different phases of molybdenum carbide directly at the cathode. This method addresses the complex and long preparation cycles of molybdenum carbide, resulting in a single product phase, while also requiring minimal experimental equipment.

[0045] The present invention provides a method for preparing molybdenum carbide of different phases by a one-step molten salt electrolysis method, comprising the following steps: in an air atmosphere, using a molybdenum mesh as an anode and a galvanized iron wire as a cathode, electrolyzing at a constant temperature and a constant current in a molten Li-Na-K carbonate electrolyte, wherein the electrolysis temperature is 550° C. to 800° C., the electrolysis current is 1A to 4A, and the electrolysis time is 15 min to 60 min, and molybdenum carbide of different phases is obtained at different electrolysis temperatures.

[0046] Specifically, at an electrolysis temperature of 550°C to 680°C, PDF#89-2868 phase molybdenum carbide is obtained; at an electrolysis temperature of 680°C to 715°C, PDF#89-2868 and PDF#65-3494 mixed phase molybdenum carbide is obtained; at an electrolysis temperature of 715°C to 750°C, PDF#89-4305 phase molybdenum carbide is obtained; at an electrolysis temperature of 750°C to 800°C, PDF#35-0787 phase molybdenum carbide is obtained.

[0047] Optionally, the molten Li-Na-K carbonate electrolyte is obtained by placing Li-Na-K carbonates having a mass ratio of Li2CO3:Na2CO3:K2CO3 = (1±0.2):(1±0.2):(1±0.2) into a corundum crucible, drying at 200±10°C for 3±0.2 hours to remove moisture, and then heating to 550°C to 800°C to melt the Li-Na-K carbonates. The Li-Na-K carbonates are Li2CO3, Na2CO3, and K2CO3, respectively.

[0048] Optionally, the size of the molybdenum mesh is 1.5cm to 2cm wide and 3cm to 4cm long; the surface area of ​​the galvanized iron wire is 8cm 2 ~12cm 2 .

[0049] Further optionally, the diameter of the galvanized iron wire is 0.9mm to 1.2mm, and the length is 28cm to 32cm. The galvanized iron wire is bent into a disc shape with a single-side surface area of ​​4cm 2 ~6cm 2 .

[0050] Optionally, the distance between the anode and the cathode is 1 cm to 1.5 cm.

[0051] Optionally, the above method further includes: soaking the different phases of molybdenum carbide obtained above in 1 mol / L to 3 mol / L hydrochloric acid for 16 h to 24 h to remove carbonate, then rinsing with deionized water and ethanol, and drying to obtain different phases of molybdenum carbide.

[0052] The principle of the inventive method is:

[0053] The molybdenum mesh is used as the anode to provide a molybdenum source, and the galvanized iron wire of the cathode serves as a current collector and deposits the product (molybdenum carbide). Applying a constant current to electrolysis at both ends of the electrodes allows the carbonate ions in the electrolyte to undergo a reduction reaction at the cathode to produce elemental carbon. The remaining oxygen anions migrate to the anode through diffusion to undergo an oxidation reaction to produce oxygen. The oxygen produced at the anode reacts with the molybdenum mesh to produce molybdenum trioxide, which dissolves in the electrolyte and becomes molybdenum trioxide. At this time, carbonate ions and molybdenum ions exist in the electrolyte at the same time. These two ions are co-reduced at the cathode to produce molybdenum carbide. Changing the electrolysis temperature essentially changes the mobility of carbon atoms and molybdenum atoms in the electrolysis product molybdenum carbide, thereby forming molybdenum carbide with different phase structures.

[0054] The method for preparing different phases of molybdenum carbide by one-step molten salt electrolysis provided by the present invention is further described in detail below with reference to the accompanying drawings and examples.

[0055] Example 1

[0056] This example provides a method for preparing molybdenum carbide by a one-step molten salt electrolysis method. The prepared molybdenum carbide can be used as an electrocatalytic hydrogen evolution catalyst. The prepared molybdenum carbide is further characterized and performance tested. Specifically:

[0057] 50 g of Li-Na-K carbonate with a mass ratio of 1:1:1 was placed in a corundum crucible and dried at 200°C for 3 h to remove moisture. The Li-Na-K mixed carbonate was then heated to 550°C to melt.

[0058] A molybdenum mesh with a width of 1.5 cm and a length of 4 cm was used as the anode; a galvanized iron wire with a diameter of 1 mm and a length of 32 cm was bent into a disk as the cathode, with a specific surface area of ​​10 cm 2 , the surface area on one side is 5cm 2 The cathode and anode were assembled with a spacing of 1.5 cm between them and then inserted into a molten electrolyte for electrolysis at a current of 1 A for 60 minutes at a temperature of 550°C. After the electrolysis was complete, the product on the cathode was soaked in 2 mol / L hydrochloric acid for 24 hours to remove carbonates. The product was then rinsed with deionized water and ethanol and dried for 12 hours to obtain molybdenum carbide.

[0059] Figure 1 This is the XRD of molybdenum carbide prepared at 550°C. It can be seen that the phase corresponding to the molybdenum carbide obtained at 550°C is PDF#89-2868. Figure 5 The corresponding SEM image is shown in Figure 2. Figure 6 is the corresponding TEM image. Figure 6 It can be seen that the molybdenum carbide obtained by electrolysis at this temperature is granular at the microscopic level.

[0060] The prepared molybdenum carbide was formulated into an ink for electrocatalytic hydrogen evolution testing: 5 mg of sample was mixed with 470 μL of anhydrous ethanol, 470 μL of deionized water, and 60 μL of 5% Nafion film. Ultrasonication was then applied for 1 hour to obtain a uniform ink. LSV testing was performed using a CHI 760 electrochemical workstation in a 1 mol / L KOH solution, using a glassy carbon electrode with the ink as the working electrode, a saturated calomel electrode as the reference electrode, and a graphite rod as the counter electrode.

[0061] Depend on Figure 13 The LSV curve of the material used as an electrocatalytic hydrogen evolution catalyst shows that when the current density is -10mA / cm 2 When the overpotential is -171mV, it shows better catalytic performance.

[0062] Example 2

[0063] The steps of this embodiment are the same as those of embodiment 1, except that:

[0064] In the one-step molten salt electrolysis process, the electrolysis temperature is 680°C.

[0065] 55 g of Li-Na-K carbonate with a mass ratio of 1.2:1.2:1.2 was placed in a corundum crucible and dried at 210° C. for 2.8 h to remove moisture. The Li-Na-K mixed carbonate was then heated to 680° C. to melt.

[0066] A molybdenum mesh with a width of 2 cm and a length of 4 cm was used as the anode; a galvanized iron wire with a diameter of 0.9 mm and a length of 28 cm was bent into a disk as the cathode, with a specific surface area of ​​8 cm 2 , with a single-sided surface area of ​​4 cm 2 The cathode and anode were assembled with a spacing of 1.5 cm between them and then inserted into a molten electrolyte for electrolysis at a current of 2 A for 30 minutes at a temperature of 680°C. After the electrolysis was complete, the product on the cathode was soaked in 1 mol / L hydrochloric acid for 24 hours to remove carbonates. The product was then rinsed with deionized water and ethanol and dried for 12 hours to obtain molybdenum carbide.

[0067] The molybdenum carbide phase obtained at this temperature has the same phase structure as the molybdenum carbide obtained in Example 1. The standard card corresponding to the molybdenum carbide is PDF#89-2868. The XRD diffraction peaks corresponding to the product are Figure 1 Similar to Figure 5 and Figure 6 resemblance.

[0068] Example 3

[0069] The steps of this embodiment are the same as those of embodiment 1, except that:

[0070] In the one-step molten salt electrolysis process, the electrolysis temperature is 700°C.

[0071] 55 g of Li-Na-K carbonate with a mass ratio of 1.2:1.2:1.2 was placed in a corundum crucible and dried at 210° C. for 2.8 h to remove moisture. The Li-Na-K mixed carbonate was then heated to 700° C. to melt.

[0072] A molybdenum mesh with a width of 2 cm and a length of 4 cm was used as the anode; a galvanized iron wire with a diameter of 0.9 mm and a length of 28 cm was bent into a disk as the cathode, with a specific surface area of ​​8 cm 2 , with a single-sided surface area of ​​4 cm 2 The cathode and anode were assembled with a spacing of 1.5 cm between them and then inserted into a molten electrolyte for electrolysis at a current of 2 A for 30 minutes at a temperature of 700°C. After the electrolysis was complete, the product on the cathode was soaked in 1 mol / L hydrochloric acid for 24 hours to remove carbonates. The product was then rinsed with deionized water and ethanol and dried for 12 hours to obtain molybdenum carbide.

[0073] Figure 2 This is the XRD of molybdenum carbide prepared at 700°C. It can be seen that the phases corresponding to the molybdenum carbide obtained at 700°C are PDF#89-2868 and PDF#65-3494. Figure 7 The corresponding SEM image is shown in Figure 2. Figure 8 is the corresponding TEM image.

[0074] The prepared molybdenum carbide was formulated into an ink for electrocatalytic hydrogen evolution testing: 5 mg of sample was mixed with 470 μL of anhydrous ethanol, 470 μL of deionized water, and 60 μL of 5% Nafion film. Ultrasonication was then applied for 1 hour to obtain a uniform ink. LSV testing was performed using a CHI 760 electrochemical workstation in a 1 mol / L KOH solution, using a glassy carbon electrode with the ink as the working electrode, a saturated calomel electrode as the reference electrode, and a graphite rod as the counter electrode.

[0075] Depend on Figure 14 The LSV curve of the material used as an electrocatalytic hydrogen evolution catalyst shows that when the current density is -10mA / cm 2 When , the overpotential is -205mV.

[0076] Example 4

[0077] The steps of this embodiment are the same as those of embodiment 1, except that:

[0078] During the one-step molten salt electrolysis process, the electrolysis temperature is 715°C.

[0079] 55 g of Li-Na-K carbonate with a mass ratio of 1.2:1.2:1.2 was placed in a corundum crucible and dried at 210° C. for 2.8 h to remove moisture. The Li-Na-K mixed carbonate was then heated to 715° C. to melt.

[0080] A molybdenum mesh with a width of 2 cm and a length of 4 cm was used as the anode; a galvanized iron wire with a diameter of 0.9 mm and a length of 28 cm was bent into a disk as the cathode, with a specific surface area of ​​8 cm 2 , with a single-sided surface area of ​​4 cm 2 The cathode and anode were assembled with a spacing of 1.5 cm between them and then inserted into a molten electrolyte for electrolysis at a current of 2 A for 30 minutes at a temperature of 715°C. After the electrolysis was complete, the product on the cathode was soaked in 1 mol / L hydrochloric acid for 24 hours to remove carbonates. The product was then rinsed with deionized water and ethanol and dried for 12 hours to obtain molybdenum carbide.

[0081] The molybdenum carbide phase obtained at this temperature has the same phase structure as the molybdenum carbide obtained in Example 3. The standard cards corresponding to the molybdenum carbide are PDF#89-2868 and PDF#65-3494. Figure 2 Similar XRD diffraction peaks and microscopic morphology are also similar to Figure 7 and Figure 8 resemblance.

[0082] Example 5

[0083] The steps of this embodiment are the same as those of embodiment 1, except that:

[0084] In the one-step molten salt electrolysis process, the electrolysis temperature is 725°C.

[0085] 60 g of Li-Na-K carbonate with a mass ratio of 0.8:0.8:0.8 was placed in a corundum crucible and dried at 190° C. for 3.2 h to remove moisture. The Li-Na-K mixed carbonate was then heated to 725° C. to melt.

[0086] A molybdenum mesh with a width of 1.5 cm and a length of 3 cm was used as the anode; a galvanized iron wire with a diameter of 1.2 mm and a length of 32 cm was bent into a disk as the cathode, with a specific surface area of ​​12 cm. 2 , with a single-sided surface area of ​​6 cm 2 The cathode and anode were assembled with a 2cm gap between them and then inserted into a molten electrolyte for electrolysis at a current of 4A for 15 minutes at a temperature of 725°C. After the electrolysis was complete, the product on the cathode was soaked in 3mol / L hydrochloric acid for 16 hours to remove carbonates. The product was then rinsed with deionized water and ethanol and dried for 12 hours to obtain molybdenum carbide.

[0087] Figure 3 This is the XRD of molybdenum carbide prepared at 725°C. It can be seen that the phase corresponding to the molybdenum carbide obtained at 725°C is PDF#89-4305. Figure 9 The corresponding SEM image is shown in Figure 2. Figure 10 is the corresponding TEM image.

[0088] The prepared molybdenum carbide was formulated into an ink for electrocatalytic hydrogen evolution testing: 5 mg of sample was mixed with 470 μL of anhydrous ethanol, 470 μL of deionized water, and 60 μL of 5% Nafion film. Ultrasonication was then applied for 1 hour to obtain a uniform ink. LSV testing was performed using a CHI 760 electrochemical workstation in a 1 mol / L KOH solution, using a glassy carbon electrode with the ink as the working electrode, a saturated calomel electrode as the reference electrode, and a graphite rod as the counter electrode.

[0089] Depend on Figure 15 The LSV curve of the material used as an electrocatalytic hydrogen evolution catalyst shows that when the current density is -10mA / cm 2 When , the overpotential is -233mV.

[0090] Example 6

[0091] The steps of this embodiment are the same as those of embodiment 1, except that:

[0092] In the one-step molten salt electrolysis process, the electrolysis temperature is 750°C.

[0093] 60 g of Li-Na-K carbonate with a mass ratio of 1:1:1 was placed in a corundum crucible and dried at 190°C for 3.2 hours to remove moisture. The Li-Na-K mixed carbonate was then heated to 750°C to melt.

[0094] A molybdenum mesh with a width of 1.5 cm and a length of 3 cm was used as the anode; a galvanized iron wire with a diameter of 1 mm and a length of 32 cm was bent into a disk as the cathode, with a specific surface area of ​​10 cm 2 , the surface area on one side is 5cm 2 The cathode and anode were assembled with a 2cm gap between them and then inserted into a molten electrolyte for electrolysis at a current of 4A for 15 minutes at a temperature of 750°C. After the electrolysis was complete, the product on the cathode was soaked in 2mol / L hydrochloric acid for 20 hours to remove carbonates. The product was then rinsed with deionized water and ethanol and dried for 12 hours to obtain molybdenum carbide.

[0095] The main corresponding standard card for molybdenum carbide obtained at this temperature is PDF#35-0787. Figure 4 have similar XRD diffraction peaks and their microstructures are similar to Figure 11 and Figure 12 resemblance.

[0096] Example 7

[0097] The steps of this embodiment are the same as those of embodiment 1, except that:

[0098] In the one-step molten salt electrolysis process, the electrolysis temperature is 800°C.

[0099] 60 g of Li-Na-K carbonate with a mass ratio of 1:1:1 was placed in a corundum crucible and dried at 190°C for 3.2 hours to remove moisture. The Li-Na-K mixed carbonate was then heated to 800°C to melt.

[0100] A molybdenum mesh with a width of 1.5 cm and a length of 3 cm was used as the anode; a galvanized iron wire with a diameter of 1 mm and a length of 32 cm was bent into a disk as the cathode, with a specific surface area of ​​10 cm 2 , the surface area on one side is 5cm 2 The cathode and anode were assembled with a 2cm gap between them and then inserted into the melted electrolyte for electrolysis at a current of 4A for 15 minutes at a temperature of 800°C. After the electrolysis was complete, the product on the cathode was soaked in 2mol / L hydrochloric acid for 20 hours to remove carbonates. The product was then rinsed with deionized water and ethanol and dried for 12 hours to obtain molybdenum carbide.

[0101] Figure 4 This is the XRD of molybdenum carbide prepared at 800°C. It can be seen that the phase corresponding to the molybdenum carbide obtained at 800°C is PDF#35-0787. Figure 11 The corresponding SEM image is shown in Figure 2. Figure 12 is the corresponding TEM image.

[0102] The prepared molybdenum carbide was formulated into an ink for electrocatalytic hydrogen evolution testing: 5 mg of sample was mixed with 470 μL of anhydrous ethanol, 470 μL of deionized water, and 60 μL of 5% Nafion film. Ultrasonication was then applied for 1 hour to obtain a uniform ink. LSV testing was performed using a CHI 760 electrochemical workstation in a 1 mol / L KOH solution, using a glassy carbon electrode with the ink as the working electrode, a saturated calomel electrode as the reference electrode, and a graphite rod as the counter electrode.

[0103] Depend on Figure 16 The LSV curve of the material used as an electrocatalytic hydrogen evolution catalyst shows that when the current density is -10mA / cm 2 When , the overpotential is -266mV.

[0104] The present invention provides a method for preparing different phases of molybdenum carbide by a one-step molten salt electrolysis method. In an air atmosphere, a molybdenum mesh is used as an anode and a galvanized iron wire is used as a cathode. A molten Li-Na-K carbonate electrolyte is used and a constant current molten salt electrolysis method is adopted to directly deposit different phases of molybdenum carbide at the cathode. Four different phases of molybdenum carbide can be obtained by regulating the electrolysis temperature. This method solves the problems of complex molybdenum carbide preparation process, long preparation cycle, and single product phase. In addition, the method has low requirements for experimental equipment.

[0105] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing different phases of molybdenum carbide by one-step molten salt electrolysis, characterized in that: The steps include: In an air atmosphere, with a molybdenum mesh as the anode and a galvanized iron wire as the cathode, electrolysis was carried out in a molten Li-Na-K carbonate electrolyte at a constant temperature and constant current. The electrolysis temperature was 550°C to 800°C, the electrolysis current was 1 A to 4 A, and the electrolysis time was 15 min to 60 min. Different phases of molybdenum carbide were obtained at different electrolysis temperatures. The molten Li-Na-K carbonate electrolyte is obtained by drying Li-Na-K carbonate having a mass ratio of Li2CO3:Na2CO3:K2CO3=(1±0.2):(1±0.2):(1±0.2), and then heating it to 550°C to 800°C to melt it; At an electrolysis temperature of 550℃~680℃, PDF# 89-2868 phase molybdenum carbide is obtained; at an electrolysis temperature of 680℃~715℃, PDF# 89-2868 and PDF# 65-3494 mixed phase molybdenum carbide is obtained; at an electrolysis temperature of 715℃~750℃, PDF# 89-4305 phase molybdenum carbide is obtained; at an electrolysis temperature of 750℃~800℃, PDF# 35-0787 phase molybdenum carbide is obtained.

2. The method for preparing different phases of molybdenum carbide by one-step molten salt electrolysis according to claim 1, characterized in that: The size of the molybdenum mesh is 1.5 cm to 2 cm wide and 3 cm to 4 cm long; the surface area of ​​the galvanized iron wire is 8 cm 2 ~12cm 2 .

3. The method for preparing different phases of molybdenum carbide by one-step molten salt electrolysis according to claim 2, characterized in that: The galvanized iron wire has a diameter of 0.9 mm to 1.2 mm and a length of 28 cm to 32 cm. The galvanized iron wire is bent into a disk shape with a single-side surface area of ​​4 cm. 2 ~6cm 2 .

4. The method for preparing different phases of molybdenum carbide by one-step molten salt electrolysis according to claim 1, characterized in that: The distance between the anode and the cathode is 1 cm to 1.5 cm.

5. The method for preparing different phases of molybdenum carbide by one-step molten salt electrolysis according to claim 1, characterized in that: Also includes: The obtained molybdenum carbide is subjected to removal of carbonate electrolyte on its surface and then dried to obtain the final molybdenum carbide.

6. The method for preparing different phases of molybdenum carbide by one-step molten salt electrolysis according to claim 5, characterized in that: The method for removing the carbonate electrolyte on the surface of molybdenum carbide is specifically as follows: soaking the molybdenum carbide in 1 mol / L~3 mol / L hydrochloric acid for 16h~24h, and then rinsing with deionized water to remove the carbonate electrolyte on the surface of the molybdenum carbide.

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