Molybdenum nitride loaded composite catalyst and application of molybdenum nitride loaded composite catalyst in water electrolysis hydrogen production

Abstract

The invention discloses a molybdenum nitride loaded composite catalyst and application thereof in hydrogen production by water electrolysis, and relates to the technical field of rare earth element catalysts. The preparation method comprises the following steps: dissolving molybdate in deionized water, adding pretreated fluoride and a nano nickel hydroxide additive, carrying out a hydrothermal reaction at 160-220 DEG C for 10-20 h, carrying out filtering and drying to obtain a precursor, heating the precursor to 600-800 DEG C at a speed of 4-8 DEG C / min in an ammonia / nitrogen mixed atmosphere, and carrying out heat preservation for 4-8 h to prepare the composite catalyst. A conductive network is formed through fluoride pretreatment, and the problem of poor intrinsic conductivity of MoN is solved; the d band center of MoN is optimized through nickel hydroxide, and hydrogen adsorption energy barriers are reduced; the composite fluorine additive enhances electron conduction, and the intrinsic activity is remarkably improved through the synergism of the three components. A hierarchical porous framework is constructed by a hydrothermal-nitridation process, fluoride is corroded to form pores, an active phase is refined by nickel hydroxide, rich active sites are exposed, and sintering inactivation is inhibited. The hydrogen production rate in hydrogen production through water electrolysis is increased by 60% or above compared with a comparative proportion, the performance is stable within the technological parameter range, and the industrial potential is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth element catalysts, and in particular to a loaded molybdenum nitride composite catalyst and its application in hydrogen production by water electrolysis. Background Art

[0002] With the energy crisis and environmental issues becoming increasingly prominent, the development of new and efficient energy conversion and storage technologies has become a top priority. Hydrogen production through water electrolysis has attracted widespread attention as a clean and sustainable energy production method. Hydrogen is considered an ideal energy carrier for the future, offering advantages such as high energy density and pollution-free combustion products. However, the efficiency of this process depends largely on the performance of the catalyst used.

[0003] Currently, commercial water electrolysis hydrogen production catalysts are primarily based on precious metals and their compounds, such as platinum (Pt) and ruthenium (Ru). While these precious metal catalysts possess excellent catalytic activity and stability, resource scarcity and high costs severely limit the large-scale application of water electrolysis hydrogen production technology. Therefore, the development of efficient, stable, and cost-effective non-precious metal catalysts has become a key issue in this field.

[0004] Molybdenum nitride (MoN), a novel non-precious metal catalyst, has attracted considerable attention due to its unique electronic structure and excellent catalytic performance. Compared with precious metal catalysts, MoN is abundant and low-cost, and exhibits activity comparable to that of precious metals in some catalytic reactions. However, pure MoN still has some shortcomings in practical applications, such as its conductivity needs to be improved, its small specific surface area, and its tendency to agglomerate during water electrolysis, all of which limit further improvements in its catalytic performance.

[0005] In order to solve the above problems, researchers began to try to load molybdenum nitride on different carriers to prepare supported molybdenum nitride composite catalysts. Suitable carriers can not only provide support for molybdenum nitride and increase its specific surface area, but also produce a synergistic effect with molybdenum nitride, improve its electrical conductivity and stability, thereby improving the overall catalytic performance. At present, there are many methods for preparing supported molybdenum nitride composite catalysts, but there are still problems such as complex preparation process, harsh conditions, poor repeatability and catalytic activity that needs to be further improved. Therefore, developing a simple, efficient and reproducible preparation method for supported molybdenum nitride composite catalysts is of great significance for promoting the development of electrolysis water hydrogen production technology. It is based on such background that the present invention proposes a preparation method for supported molybdenum nitride composite catalysts, which aims to overcome the defects of the prior art and provide a high-performance, low-cost catalyst to meet the needs of fields such as electrolysis water hydrogen production. Summary of the Invention

[0006] The purpose of the present invention is to address the problems in the prior art such as the complex preparation process of loaded molybdenum nitride composite catalysts and the need to improve catalytic activity, and to provide a preparation method for a loaded molybdenum nitride composite catalyst, which is simple, efficient, and highly reproducible, and the obtained catalyst has excellent catalytic performance and good stability, so as to meet the demand for high-performance, low-cost catalysts in the field of water electrolysis and hydrogen production.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a supported molybdenum nitride composite catalyst, comprising the following steps: S1. Precursor preparation: Molybdate is dissolved in deionized water, fluoride and additives are added, mixed and then subjected to hydrothermal treatment at a temperature of 160-220 ° C for 10-20 h, followed by filtration, washing and drying to obtain a precursor; S2. Nitriding preparation: The precursor is placed in a tubular furnace and nitrided in a mixed atmosphere of ammonia and nitrogen. The heating rate of the nitriding treatment is 4-8°C / min. After heating to 600-800°C, the catalyst is kept warm for 4-8 hours to obtain a loaded molybdenum nitride composite catalyst. The volume ratio of ammonia to nitrogen is 1:(0.6-0.8), and the flow rate of the mixed gas is 200sccm.

[0008] Furthermore, the molybdate is selected from at least one of ammonium molybdate, sodium molybdate and potassium molybdate.

[0009] Furthermore, the mass ratio of the molybdate to deionized water is 1:(3-5); the mass ratio of the fluoride to the additive is 1:(0.2-0.4); and the mass of the fluoride is 4-6% of the mass of the molybdate.

[0010] Furthermore, the fluoride is prepared by the following method: calcium fluoride powder, sodium fluoride powder and deionized water are mixed in a mass ratio of 1:1:(3-5), stirred at 200-300 r / min for 10-20 minutes, filtered, and the obtained solid is dried at 50-60°C for 2-4 hours, and ground to a particle size of 50nm-2μm to obtain the fluoride.

[0011] Furthermore, the calcium fluoride powder and the sodium fluoride powder are pretreated before preparing fluoride, and the pretreatment method includes: a) immersing calcium fluoride powder and sodium fluoride powder in a polyvinyl alcohol solution with a mass concentration of 0.6-1%, stirring with a magnetic force at 200-300 r / min for 1-3 hours, filtering, and drying the resulting solid at 80-100° C. for 1-3 hours; b) mixing the product obtained in step a) with a carboxymethyl cellulose binder having a mass concentration of 4-6%, wherein the mass of the carboxymethyl cellulose binder is 6-8% of the mass of the calcium fluoride powder, and stirring at 500-600 r / min for 10-20 min; c) heating the product obtained in step b) to 260-300° C. in a tube furnace at a temperature of 2-4° C. / min and maintaining the temperature for 20-30 min to complete the pretreatment; wherein the degree of polymerization of the polyvinyl alcohol is 1800-2000.

[0012] Furthermore, the additive is nickel hydroxide, which is prepared by the following method: dissolving urea and nickel nitrate in deionized water, stirring at 200-300 r / min for 10-20 minutes, adding ammonia water to adjust the pH to 9, centrifuging at 3000-5000 r / min for 6-10 minutes, washing the precipitate, drying at 60-70°C for 10-12 hours, and grinding to a particle size of less than 50 nm to prepare nickel hydroxide.

[0013] Furthermore, the drying condition in S1 is 60-80° C. for 2-4 hours.

[0014] A loaded molybdenum nitride composite catalyst is prepared by the above preparation method.

[0015] Furthermore, a loaded molybdenum nitride composite catalyst comprises a molybdenum nitride active component, a calcium fluoride or sodium fluoride promoter and a nickel hydroxide promoter, and has a porous morphology structure.

[0016] The invention discloses an application of a loaded molybdenum nitride composite catalyst in hydrogen production by water electrolysis.

[0017] The fluoride described in the present invention plays a key role in enhancing the electrical conductivity of the catalyst. The pretreatment process forms a thin and uniform carbon coating on the surface of the fluoride particles or improves their dispersion / interface contact. This conductive network or improved interface greatly improves the electronic conductivity of the entire composite catalyst, solving the problem of relatively poor conductivity of pure molybdenum nitride (MoN), which is crucial for the rapid transfer of electrons in the water electrolysis reaction. MoN provides basic hydrogen evolution active sites, and nickel hydroxide optimizes the d-band center of MoN through electronic interactions, reducing the hydrogen adsorption energy barrier, while itself serving as a synergistic active site; fluoride enhances overall conductivity and accelerates electron transfer, and the three synergistically significantly improve intrinsic activity. Fluoride acts as a structure-directing agent in the hydrothermal process, and its partial dissolution forms a porous skeleton; nanoscale nickel hydroxide is dispersed in the molybdenum nitride (MoN) matrix, refining the active particles; the hydrothermal-nitriding process synergistically constructs a hierarchical porous structure, exposing abundant active sites and promoting mass transfer. The porous structure buffers cyclic stress, and the inert skeleton of the fluoride and the anchoring effect of the nickel hydroxide inhibit the sintering deactivation of MoN.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. Significantly improved catalytic activity: The present invention achieves a breakthrough improvement in the intrinsic activity of the catalyst through the construction of a conductive network through fluoride pretreatment, and the synergistic effect of the composite fluorine additive and nickel hydroxide. The hydrogen production rate shows an order of magnitude advantage over the control examples with missing components or simplified processes.

[0019] 2. Fundamental improvement in structural stability: The hierarchical porous structure formed by the synergistic hydrothermal-nitridation process not only exposes abundant active sites, but also significantly inhibits MoN agglomeration and deactivation through the physical support of the inert fluoride skeleton and the chemical anchoring effect of nickel hydroxide, thereby ensuring long-term cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a SEM scan of a loaded molybdenum nitride composite catalyst described in the present invention. DETAILED DESCRIPTION

[0021] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Example

[0022] This embodiment provides a method for preparing a supported molybdenum nitride composite catalyst, and the specific steps are as follows: 1. Fluoride pretreatment: a) Calcium fluoride powder and sodium fluoride powder (mass ratio 1:1) were immersed in a 0.8% polyvinyl alcohol solution (DP 1900) with magnetic stirring at 250 rpm for 2 h. After filtration, the solid was dried at 90°C for 2 h.

[0023] b) The product of step a was mixed with a carboxymethyl cellulose binder having a mass concentration of 5% (the amount of binder was 7% of the mass of the calcium fluoride powder) and stirred at 550 r / min for 15 min.

[0024] c) placing the product of step b in a tube furnace, heating it to 280° C. at a rate of 3° C. / min, and keeping the temperature for 25 min to obtain a pretreated fluoride composite powder.

[0025] 2. Preparation of nickel hydroxide additive: Urea and nickel nitrate were dissolved in deionized water (molar ratio 3:1), stirred at 250 rpm for 15 minutes, and ammonia was added dropwise to adjust the pH to 9.0. The mixture was centrifuged at 4000 rpm for 8 minutes. The precipitate was washed three times with deionized water, dried at 65°C for 11 hours, and ground to a particle size of <50 nm to produce nano-nickel hydroxide.

[0026] 3. Precursor preparation (S1): Weigh 20g of ammonium molybdate and dissolve it in 80g of deionized water (1:4 by mass ratio). Stir until completely dissolved. Add 0.9g of pretreated fluoride (4.5% of the total weight of the molybdate) and 0.27g of nickel hydroxide (1:0.3 by mass ratio of fluoride to additive) and mix thoroughly. Transfer the mixture to a hydrothermal reactor and heat at 190°C for 15h. The reaction product is filtered, washed three times with deionized water, and dried at 70°C for 3h to obtain the precursor.

[0027] 4. Nitriding preparation (S2): The precursor was placed in a quartz boat in a tubular furnace and introduced with a mixture of ammonia and nitrogen (volume ratio 1:0.7, total flow rate 200 sccm). The temperature was raised to 700°C at 6°C / min, held for 6 hours, and then cooled to room temperature. A black solid product, the supported molybdenum nitride composite catalyst, was obtained.

[0028] Catalyst characterization: Scanning electron microscopy (SEM) Figure 1 ) observed that the catalyst exhibited a hierarchical porous structure with a pore size range of 50-500 nm, molybdenum nitride (MoN) particles uniformly loaded on the fluoride skeleton, and nickel hydroxide nanoparticles dispersed on the surface. Example

[0029] This example provides a method for preparing a supported molybdenum nitride composite catalyst. Referring to the preparation method of Example 1, the hydrothermal temperature, nitridation temperature, and fluoride addition amount are modified, while the remaining steps remain the same as in Example 1. Specific modifications are as follows: Precursor preparation (S1): The hydrothermal temperature is adjusted to 160°C, and the treatment time is 20 hours. The fluoride addition amount is 4% of the mass of the molybdate. Nitridation preparation (S2): The nitridation temperature is adjusted to 600°C, and the holding time is 8 hours. Example

[0030] This embodiment provides a preparation method for a loaded molybdenum nitride composite catalyst. Referring to the preparation method of Example 1, the fluoride pretreatment parameters, nickel hydroxide preparation conditions, and hydrothermal / nitriding time are replaced, and the rest remain the same as Example 1. Specific adjustments are as follows: Fluoride pretreatment: a): The mass concentration of the polyvinyl alcohol solution is adjusted to 0.6%, the drying temperature is 80°C, and magnetic stirring is performed for 1 hour; b): The mass concentration of the carboxymethyl cellulose adhesive is 4%, and the amount is 6% of the mass of the calcium fluoride powder; c): The heating rate is 2°C / min to 260°C and kept warm for 30 minutes. Nickel hydroxide preparation: centrifugal speed 3000r / min, drying temperature 60°C, and centrifugal time 10 minutes. Precursor preparation (S1): The hydrothermal time is adjusted to 10 hours. Nitriding preparation (S2): The nitriding holding time is adjusted to 4 hours.

[0031] Comparative Example 1 This comparative example provides a preparation method of a loaded molybdenum nitride composite catalyst. Referring to the preparation method of Example 1, the calcium fluoride powder and the sodium fluoride powder were not pretreated in this comparative example.

[0032] Comparative Example 2 This comparative example provides a method for preparing a supported molybdenum nitride composite catalyst. Referring to the preparation method of Example 1, an equal amount of calcium fluoride is used to replace fluoride in this comparative example.

[0033] Comparative Example 3 This comparative example provides a method for preparing a loaded molybdenum nitride composite catalyst, referring to the preparation method of Example 1, except that this comparative example does not contain fluoride.

[0034] Comparative Example 4 This comparative example provides a preparation method of a loaded molybdenum nitride composite catalyst, referring to the preparation method of Example 1, but does not contain any additives.

[0035] Performance testing: The performance test of a loaded molybdenum nitride composite catalyst prepared in the embodiment and the comparative example was carried out: a loaded molybdenum nitride composite catalyst prepared in the embodiment and the comparative example was loaded on a carbon-based electrode (loading amount 1 mg / cm 2 ), with platinum as the counter electrode and Ag / AgCl as the reference electrode. Test system: 0.5M H2SO4 electrolyte, scan rate 5mV / s. Test 10mA / cm 2 The obtained test data are recorded in Table 1.

[0036] Table 1. 10 mA / cm2 of a supported molybdenum nitride composite catalyst prepared in Examples and Comparative Examples 2 Overpotential data.

[0037]

[0038] The catalytic activity of the example group using the complete preparation method of the present invention (containing fluoride pretreatment, composite fluorine auxiliary agent and nickel hydroxide additive) is significantly higher than that of all comparative examples. Among them, the activity decreases most dramatically when the fluoride pretreatment is missing. Replacing the composite auxiliary agent with a single component or completely lacking the fluoride / additive leads to a significant decrease in activity, highlighting the necessity of the synergistic effect of the three to enhance the intrinsic activity. At the same time, the different parameter combinations within the example group all maintain high efficiency and stability.

[0039] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a supported molybdenum nitride composite catalyst, characterized in that: The following steps are involved: S1. Precursor preparation: Molybdate is dissolved in deionized water, fluoride and additives are added, mixed and then subjected to hydrothermal treatment at a temperature of 160-220 ° C for 10-20 h, followed by filtration, washing and drying to obtain a precursor; S2. Nitriding preparation: The precursor is placed in a tubular furnace and nitrided in a mixed atmosphere of ammonia and nitrogen. The heating rate of the nitriding treatment is 4-8°C / min. After heating to 600-800°C, the catalyst is kept warm for 4-8 hours to obtain a loaded molybdenum nitride composite catalyst. The volume ratio of ammonia to nitrogen is 1:(0.6-0.8), and the flow rate of the mixed gas is 200sccm.

2. The method for preparing a supported molybdenum nitride composite catalyst according to claim 1, wherein: The molybdate is selected from at least one of ammonium molybdate, sodium molybdate and potassium molybdate.

3. The method for preparing a supported molybdenum nitride composite catalyst according to claim 1, wherein: The mass ratio of the molybdate to deionized water is 1:(3-5); the mass ratio of the fluoride to the additive is 1:(0.2-0.4); and the mass of the fluoride is 4-6% of the mass of the molybdate.

4. The method for preparing a supported molybdenum nitride composite catalyst according to claim 1, wherein: The fluoride is prepared by the following method: calcium fluoride powder, sodium fluoride powder and deionized water are mixed in a mass ratio of 1:1:(3-5), stirred at 200-300 r / min for 10-20 minutes, filtered, and the obtained solid is dried at 50-60° C. for 2-4 hours and ground to a particle size of 50 nm-2 μm to obtain the fluoride.

5. The method for preparing a supported molybdenum nitride composite catalyst according to claim 4, wherein: The calcium fluoride powder and the sodium fluoride powder are pretreated before preparing fluoride, and the pretreatment method includes: a) immersing calcium fluoride powder and sodium fluoride powder in a polyvinyl alcohol solution with a mass concentration of 0.6-1%, stirring with a magnetic force at 200-300 r / min for 1-3 hours, filtering, and drying the resulting solid at 80-100° C. for 1-3 hours; b) mixing the product obtained in step a) with a carboxymethyl cellulose binder having a mass concentration of 4-6%, wherein the mass of the carboxymethyl cellulose binder is 6-8% of the mass of the calcium fluoride powder, and stirring at 500-600 r / min for 10-20 min; c) heating the product obtained in step b) to 260-300° C. in a tube furnace at a temperature of 2-4° C. / min and maintaining the temperature for 20-30 min to complete the pretreatment; wherein the degree of polymerization of the polyvinyl alcohol is 1800-2000.

6. The method for preparing a supported molybdenum nitride composite catalyst according to claim 1, wherein: The additive is nickel hydroxide, which is prepared by the following method: dissolving urea and nickel nitrate in deionized water, stirring at 200-300 r / min for 10-20 minutes, adding ammonia water to adjust the pH to 9, centrifuging at 3000-5000 r / min for 6-10 minutes, washing the precipitate, drying at 60-70°C for 10-12 hours, and grinding to a particle size of less than 50 nm to prepare nickel hydroxide.

7. The method for preparing a supported molybdenum nitride composite catalyst according to claim 1, wherein: The drying condition in S1 is drying at 60-80° C. for 2-4 hours.

8. A supported molybdenum nitride composite catalyst, characterized in that Prepared by the preparation method according to any one of claims 1 to 7.

9. A supported molybdenum nitride composite catalyst according to claim 8, characterized in that: A loaded molybdenum nitride composite catalyst comprises a molybdenum nitride active component, a calcium fluoride or sodium fluoride promoter and a nickel hydroxide promoter, and has a porous morphology structure.

10. Use of the supported molybdenum nitride composite catalyst according to claim 8 in hydrogen production by water electrolysis.

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