A method for preparing a high-efficiency molybdenum carbide / graphite nanosheet composite catalyst for hydrogen production by water electrolysis

Abstract

The present invention provides a preparation method of a molybdenum carbide / graphite nanosheet high-efficiency composite catalyst for producing hydrogen by electrolysis of water. The method comprises the following steps: using graphite nanosheets and ammonium molybdate as raw materials and water as solvent, calcining the catalyst by a step-by-step heating method, and preparing the molybdenum carbide / graphite nanosheet high-efficiency composite catalyst. The prepared molybdenum carbide / graphite nanosheet high-efficiency composite catalyst is in the form of flakes, and other components are uniformly grown on the surface of the graphite nanosheets. The catalyst is heated at an exchange current density of 10 mA cm ‑2 Tests were conducted and the overpotential of the highly efficient molybdenum carbide / graphite nanosheet composite catalyst reached 255mV.

Description

Technical Field

[0001] The invention relates to the field of composite catalysts, and in particular to a method for preparing a high-efficiency molybdenum carbide / graphite nanosheet composite catalyst used for electrolyzing water to produce hydrogen. Background Art

[0002] Precious metal catalysts are highly active but tend to sinter at higher temperatures, reducing their activity. Furthermore, precious metal resources are limited and expensive, making large-scale use impossible. Non-precious metal catalysts are cheaper than precious metals but have lower catalytic activity. Molybdenum carbide, with its interstitial alloy structure, exhibits excellent electrocatalytic hydrogen evolution performance, but this is limited by the number of active sites and the binding energy between the molybdenum carbide and hydrogen atoms during the hydrogen evolution process. Furthermore, the high temperatures required to form molybdenum carbide often lead to agglomeration, which compromises catalytic performance.

[0003] In the prior art, CN107694586B discloses a graphene-wrapped molybdenum carbide / carbon microsphere electrocatalyst, a preparation method thereof, and its application in water electrolysis to hydrogen production under acidic conditions. The graphene-wrapped molybdenum carbide / carbon microsphere electrocatalyst is prepared using molybdate and graphene oxide as raw materials and a solvent consisting of a mixed solution of chitosan, acetic acid, and deionized water. The prepared catalyst has a conductivity of 10 mA cm -2 The overpotential is 148mV. The catalyst preparation method also involves the application of other components and multi-step reactions. CN110575840B discloses a method for preparing a two-dimensional molybdenum carbide / graphene nanosheet composite material. The mass ratio of graphene oxide to soluble molybdenum source is 0.01-0.02:1, and the amount of cetyltrimethylammonium bromide added is 9-65 times the mass of graphene oxide. A graphene oxide ethanol dispersion containing cetyltrimethylammonium bromide is added to an aqueous solution of a soluble molybdenum source, and the mixture is hydrothermally reacted at 100-120°C for 10-12h. The reaction product is then carbonized at 800-900°C for not less than 2h to obtain a two-dimensional molybdenum carbide / graphene nanosheet composite material. This technical solution also involves a large number of raw materials and operating steps. The present invention proposes a simpler method for preparing a molybdenum carbide / graphene nanosheet high-efficiency composite catalyst with better electrocatalytic performance. Summary of the Invention

[0004] In view of this, the present invention proposes a method for preparing a high-efficiency molybdenum carbide / graphite nanosheet composite catalyst for use in electrolyzing water to produce hydrogen, thereby preparing a high-efficiency molybdenum carbide / graphite nanosheet composite catalyst with better electrical properties.

[0005] A method for preparing a high-efficiency molybdenum carbide / graphite nanosheet composite catalyst for producing hydrogen by electrolysis of water comprises the following steps:

[0006] (1) dissolving graphite nanosheets and molybdenum salt in water and stirring to prepare a mixed solution;

[0007] (2) drying the mixed solution to obtain the precursor G@(NH4)2MoO4;

[0008] (3) The precursor G@(NH4)2MoO4 is placed in a tubular furnace and sintered in steps to obtain the finished product.

[0009] Furthermore, in step (1), the mass ratio of the graphite nanosheets, water and molybdenum salt is 20-5:75-15:1.

[0010] Furthermore, in step (1), the molybdenum salt is one of phosphomolybdic acid and ammonium molybdate.

[0011] Furthermore, in step (2), the drying step is to place the powder in an oven at 60-80° C. for 10-15 hours, and grind the dried powder.

[0012] Furthermore, in step (3), the precursor G@(NH4)2MoO4 is placed in a tubular furnace and sintered in steps, with the first step heating to 440-460°C and keeping warm for 1.5-2.5h, and the second step heating to 850-950°C and keeping warm for 3-4h.

[0013] The present invention employs a step-by-step heating method. The first heating step fully removes moisture and nitrogen from the sample, while an argon atmosphere is used for insulation. Further control of the argon introduction rate prevents the formation of molybdenum nitride (Mo2N). The second heating step, increasing the temperature to 850-950°C and holding it for 3-4 hours, facilitates the formation of a more stable β-phase Mo2C, improving the electrocatalytic performance of the highly efficient molybdenum carbide / graphite nanosheet composite catalyst.

[0014] Furthermore, the heating rate is 1.5-2.5°C / min.

[0015] The heating rate of the tubular furnace in the present invention can effectively reduce the high-temperature agglomeration of molybdenum carbide and make the molybdenum carbide particles evenly distributed on the graphite nanosheets, which is beneficial to improving the electrocatalytic performance of the molybdenum carbide / graphite nanosheet high-efficiency composite catalyst.

[0016] Furthermore, after the first step of heating is completed, argon gas is introduced at a rate of 1.5-2.5°C / min.

[0017] Furthermore, the mass ratio of the graphite nanosheets, water and ammonium molybdate is 20:75:1 or 10:30:1 or 5:15:1.

[0018] Furthermore, the stirring is carried out at 50-80 r / min for 11.5-12.5 hours.

[0019] The beneficial effects of the present invention are:

[0020] The present invention uses graphite nanosheets and ammonium molybdate as raw materials and water as solvent, and adopts a step-by-step heating method to calcine to produce a high-efficiency molybdenum carbide / graphite nanosheet composite catalyst. The present invention uses a reasonable heating rate to help reduce the high-temperature agglomeration of molybdenum carbide, ensuring that molybdenum carbide particles are evenly distributed on the graphite nanosheets. A high argon gas introduction rate is used to remove moisture and ammonia from the sample and prevent the formation of molybdenum nitride (Mo2N). The molybdenum carbide / graphite nanosheet composite catalyst produced by the present invention is in sheet form, with other components evenly grown on the surface of the graphite nanosheets. The exchange current density is 10 mA cm -2 Tests were conducted and the overpotential of the highly efficient molybdenum carbide / graphite nanosheet composite catalyst reached 255mV. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Example 1 Scanning electron microscope image

[0022] Figure 2 X-ray powder diffraction patterns of Mo2C / GA, Mo2C / GB and Mo2C / GC

[0023] Figure 3 LSV curves of Mo2C / GA, Mo2C / GB and Mo2C / GC. From left to right, LSV curves of Mo2C / GA, Mo2C / GC, Mo2C / GB and Pt / C DETAILED DESCRIPTION

[0024] In order to better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0025] Unless otherwise specified, the experimental methods used in the examples of the present invention are all conventional methods.

[0026] Unless otherwise specified, the materials, reagents, etc. used in the examples of the present invention can be obtained from commercial sources.

[0027] Example 1 Preparation method of high-efficiency molybdenum carbide / graphite nanosheet composite catalyst for hydrogen production by water electrolysis

[0028] (1) dissolving graphite nanosheets and ammonium molybdate in water, wherein the mass ratio of the graphite nanosheets, water, and ammonium molybdate is 20:75:1, and stirring at 60 rpm for 12 h to obtain a mixed solution;

[0029] (2) drying the mixed solution in an oven at 70° C. for 12 h, and grinding the dried powder to obtain the precursor G@(NH 4 ) 2 MoO 4 ;

[0030] (3) The precursor G@(NH4)2MoO4 is placed in a tubular furnace and sintered in steps. The first step is to heat the temperature to 450°C. After the first step is completed, argon is introduced at a rate of 2°C / min. The first step is kept warm for 2 hours. The second step is to heat the temperature to 900°C. The second step is kept warm for 3 hours. The heating rates of the first and second steps are 2°C / min to obtain the finished product.

[0031] Example 2 Preparation Method of High-Efficiency Molybdenum Carbide / Graphite Nanosheet Composite Catalyst for Hydrogen Production by Water Electrolysis

[0032] (1) dissolving graphite nanosheets and ammonium molybdate in water, wherein the mass ratio of the graphite nanosheets, water, and ammonium molybdate is 10:30:1, and stirring at 50 rpm for 11.5 hours to obtain a mixed solution;

[0033] (2) drying the mixed solution in an oven at 60° C. for 10 h, and grinding the dried powder to obtain the precursor G@(NH 4 ) 2 MoO 4 ;

[0034] (3) The precursor G@(NH4)2MoO4 was placed in a tubular furnace and sintered in steps. The first step was to heat the temperature to 440°C. After the first step was completed, argon was introduced at a rate of 1.5°C / min. The first step was kept warm for 1.5 hours. The second step was to heat the temperature to 850°C. The second step was kept warm for 3 hours. The heating rates of the first and second steps were 1.5°C / min to obtain the finished product.

[0035] Example 3 Preparation Method of High-Efficiency Molybdenum Carbide / Graphite Nanosheet Composite Catalyst for Hydrogen Production by Water Electrolysis

[0036] (1) dissolving graphite nanosheets and ammonium molybdate in water, wherein the mass ratio of the graphite nanosheets, water, and ammonium molybdate is 5:15:1, and stirring at 70 rpm for 12.5 hours to obtain a mixed solution;

[0037] (2) drying the mixed solution in an oven at 80° C. for 15 h, and grinding the dried powder to obtain the precursor G@(NH 4 ) 2 MoO 4 ;

[0038] (3) The precursor G@(NH4)2MoO4 was placed in a tubular furnace and sintered in steps. The first step was to heat the temperature to 460°C. After the first step was completed, argon was introduced at a rate of 2.5°C / min. The first step was kept warm for 2.5 hours. The second step was to heat the temperature to 950°C. The second step was kept warm for 4 hours. The heating rates of the first and second steps were 2.5°C / min to obtain the finished product.

[0039] Comparative Example 1

[0040] (1) dissolving graphite nanosheets and ammonium molybdate in water, wherein the mass ratio of the graphite nanosheets, water, and ammonium molybdate is 20:75:1, and stirring at 60 rpm for 12 h to obtain a mixed solution;

[0041] (2) drying the mixed solution in an oven at 70° C. for 12 h, and grinding the dried powder to obtain the precursor G@(NH 4 ) 2 MoO 4 ;

[0042] (3) The precursor G@(NH4)2MoO4 is placed in a tubular furnace and sintered in steps. The first step is to heat the temperature to 450°C. After the first step is completed, argon is introduced at a rate of 2°C / min. The first step is kept warm for 2 hours. The second step is to heat the temperature to 900°C. The second step is kept warm for 3 hours. The heating rates of the first and second steps are 5°C / min to obtain the finished product.

[0043] The difference between Comparative Example 1 and Example 1 is that the heating rate during the sintering process in the tubular furnace is adjusted to increase the heating rate, resulting in high-temperature agglomeration of the molybdenum carbide particles, which leads to uneven distribution of the molybdenum carbide particles on the graphite nanosheets, and the electrocatalytic performance of the obtained molybdenum carbide / graphite nanosheet high-efficiency composite catalyst is reduced.

[0044] Comparative Example 2

[0045] (1) dissolving graphite nanosheets and ammonium molybdate in water, wherein the mass ratio of the graphite nanosheets, water, and ammonium molybdate is 20:75:1, and stirring at 60 rpm for 12 h to obtain a mixed solution;

[0046] (2) drying the mixed solution in an oven at 70° C. for 12 h, and grinding the dried powder to obtain the precursor G@(NH 4 ) 2 MoO 4 ;

[0047] (3) The precursor G@(NH4)2MoO4 is placed in a tubular furnace and sintered in steps. The first step is to heat the temperature to 450°C. After the first step is completed, argon is introduced at a rate of 1°C / min. The first step is kept warm for 2 hours. The second step is to heat the temperature to 900°C. The second step is kept warm for 3 hours. The heating rates of the first and second steps are 2°C / min to obtain the finished product.

[0048] The difference between Comparative Example 2 and Example 1 is that the argon introduction rate is adjusted. After testing, the electrocatalytic performance of the obtained molybdenum carbide / graphite nanosheet high-efficiency composite catalyst decreases. After analysis, it is found that reducing the argon introduction rate results in the failure to completely remove moisture and ammonia in the sample, resulting in the generation of molybdenum nitride (Mo2N), which further affects the electrocatalytic performance of the finished product.

[0049] Comparative Example 3

[0050] (1) dissolving graphite nanosheets and ammonium molybdate in water, wherein the mass ratio of the graphite nanosheets, water, and ammonium molybdate is 30:90:1, and stirring at 60 rpm for 12 h to obtain a mixed solution;

[0051] (2) drying the mixed solution in an oven at 70° C. for 12 h, and grinding the dried powder to obtain the precursor G@(NH 4 ) 2 MoO 4 ;

[0052] (3) The precursor G@(NH4)2MoO4 is placed in a tubular furnace and sintered in steps. The first step is to heat the temperature to 450°C. After the first step is completed, argon is introduced at a rate of 2°C / min. The first step is kept warm for 2 hours. The second step is to heat the temperature to 900°C. The second step is kept warm for 3 hours. The heating rates of the first and second steps are 2°C / min to obtain the finished product.

[0053] The difference between Comparative Example 3 and Example 1 is that the mass ratio of graphite nanosheets and ammonium molybdate is adjusted in Comparative Example 3, resulting in a decrease in the electrocatalytic performance of the molybdenum carbide / graphite nanosheet high-efficiency composite catalyst.

[0054] Comparative Example 4

[0055] (1) dissolving graphite nanosheets and ammonium molybdate in water, wherein the mass ratio of the graphite nanosheets, water, and ammonium molybdate is 20:75:1, and stirring at 60 rpm for 12 h to obtain a mixed solution;

[0056] (2) drying the mixed solution in an oven at 70° C. for 12 h, and grinding the dried powder to obtain the precursor G@(NH 4 ) 2 MoO 4 ;

[0057] (3) The precursor G@(NH4)2MoO4 is placed in a tubular furnace and sintered in steps. The first step is to heat the temperature to 300°C. After the first step is completed, argon is introduced at a rate of 2°C / min. The first step is kept warm for 2 hours. The second step is to heat the temperature to 750°C. The second step is kept warm for 3 hours. The heating rates of the first and second steps are 2°C / min to obtain the finished product.

[0058] The difference between Comparative Example 4 and Example 1 is that the sintering temperature is adjusted in Comparative Example 4, resulting in a decrease in the electrocatalytic performance of the high-efficiency molybdenum carbide / graphite nanosheet composite catalyst. After analysis, the sintering temperature setting in the present invention is beneficial to controlling the finished product appearance structure and removing ammonia decomposed by ammonium molybdate and moisture during the sintering process, thereby further improving the electrocatalytic performance of the catalyst.

[0059] Comparative Example 5

[0060] (1) dissolving graphite nanosheets and ammonium molybdate in water, wherein the mass ratio of the graphite nanosheets, water, and ammonium molybdate is 20:75:1, and stirring at 60 rpm for 12 h to obtain a mixed solution;

[0061] (2) drying the mixed solution in an oven at 70° C. for 12 h, and grinding the dried powder to obtain the precursor G@(NH 4 ) 2 MoO 4 ;

[0062] (3) The precursor G@(NH4)2MoO4 was placed in a tubular furnace for sintering at a high temperature and calcined in an argon atmosphere at a rate of 2°C / min. The temperature was raised to 900°C at a rate of 2°C / min and kept at that temperature for 3 hours.

[0063] The difference between Comparative Example 5 and Example 1 is that the adjustment of the sintering method leads to a decrease in the electrocatalytic performance of the high-efficiency molybdenum carbide / graphite nanosheet composite catalyst. After analysis, in the present invention, the precursor G@(NH4)2MoO4 is placed in a tubular furnace and sintered in steps by increasing the temperature, which is beneficial to controlling the finished product appearance structure and improving the electrocatalytic performance of the catalyst.

[0064] Test Example 1

[0065] The sample of Example 1 was analyzed by SEM electron microscopy, X-ray diffraction, and exchange current density of 10 mA cm -2 The samples of Examples 1 to 3 were analyzed. The finished products of Examples 1 to 3 were labeled as Mo2C / GA, Mo2C / GB and Mo2C / GC, respectively.

[0066] See also Figure 1 , the scanning electron microscope photograph of the sample in Example 1, the obtained product is in flaky form, mainly due to the layered structure of the graphite nanosheets and the preparation process of the present invention, and the other components are uniformly grown on the surface of the graphite nanosheets.

[0067] See also Figure 2 The X-ray powder diffraction patterns of Mo2C / GA, Mo2C / GB and Mo2C / GC show that the peaks at around 26°, 54° and 77° are attributed to the characteristic peaks of graphite (G), while the remaining diffraction peaks are attributed to Mo2C. This indicates that the synthesized product is a composite of Mo2C and G.

[0068] See also Figure 3 , LSV curves of Mo2C / GA, Mo2C / GB and Mo2C / GC. At an exchange current density of 10 mA cm -2When the overpotentials of Mo2C / GA, Mo2C / GB and Mo2C / GC reached 255, 136 and 183 mV, respectively, showing good electrocatalytic performance, indicating that the Mo2C / G series composites have more active sites, which is beneficial to the electrocatalytic hydrogen evolution reaction.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. 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 a highly efficient molybdenum carbide / graphite nanosheet composite catalyst for hydrogen production by electrolysis of water, characterized in that: The following steps are involved: Dissolving graphite nanosheets and ammonium molybdate in water at a mass ratio of 20-5:75-15:1, stirring to prepare a mixed solution; The mixed solution was placed in an oven at 60-80°C and dried for 10-15h to obtain the precursor G@(NH4)2MoO4; The precursor G@(NH4)2MoO4 is placed in a tubular furnace and sintered in steps to obtain a finished product; the precursor G@(NH4)2MoO4 is placed in a tubular furnace and sintered in steps, the first step of heating the temperature to 440-460°C, argon is introduced after the first heating step is completed, the argon introduction rate is 2°C / min, the insulation time is 1.5-2.5h, the second step of heating the temperature to 850-950°C, the insulation time is 3-4h; the heating rate is 1.5-2.5°C / min.

2. The method for preparing a highly efficient composite catalyst of molybdenum carbide / graphite nanosheets for producing hydrogen by electrolysis of water as claimed in claim 1, wherein: The mass ratio of the graphite nanosheets, water and ammonium molybdate is 20:75:1 or 10:30:1 or 5:15:

1.

3. The method for preparing a high-efficiency molybdenum carbide / graphite nanosheet composite catalyst for hydrogen production by electrolysis of water according to claim 1, wherein in step (1), the stirring is performed at 50-80 r / min for 11.5-12.5 hours.

Images