Self-supporting molybdenum / molybdenum nitride composite catalyst and preparation method and application thereof

Abstract

The invention provides a preparation method of a self-supporting molybdenum / molybdenum nitride composite catalyst. The preparation method mainly comprises the following steps: 1) growing a molybdenum oxide nano array as a precursor on carbon cloth through high-temperature reflux reaction; 2) carrying out nitridation reaction on the molybdenum oxide nano array to obtain molybdenum nitride; and 3) carrying out eddy current heating reduction reaction on the molybdenum nitride in a mixed reducing atmosphere of hydrogen and argon to partially reduce the molybdenum nitride into elemental molybdenum, thereby preparing the self-supporting molybdenum / molybdenum nitride composite catalyst. In the self-supporting molybdenum / molybdenum nitride composite catalyst prepared by the invention, molybdenum and molybdenum nitride coexist in the form of a heterogeneous interface, and abundant heterogeneous interfaces exist. And meanwhile, the electron transmission rate of the molybdenum / molybdenum nitride composite catalyst is increased by introducing the metal molybdenum elementary substance, so that the hydrogen evolution reaction kinetics in the water electrolysis process is enhanced. The composite catalyst prepared by the method has a wide application prospect in the field of hydrogen production by electrolysis of water.

Description

Technical Field

[0001] This invention belongs to the field of water electrolysis for hydrogen production technology, specifically relating to a self-supporting molybdenum / molybdenum nitride composite catalyst, its preparation method, and its application. Background Technology

[0002] Electrolysis of water to produce hydrogen is considered a promising key technology for producing clean hydrogen energy, but its reaction efficiency is still largely limited by the use of efficient electrocatalysts. Commercially available noble metal catalysts mainly employ Pt / C catalysts. However, due to the high activation energy involved in the water splitting step, the kinetics of the hydrogen evolution reaction are significantly slowed down, and the cost is high. Therefore, developing non-noble metal catalysts that combine low cost and high catalytic performance has become a key direction for promoting the development of hydrogen production through water electrolysis. Currently, transition metals and their oxides and nitrides, among other non-noble metal materials, have been extensively studied and have shown great potential for high-efficiency hydrogen evolution performance.

[0003] Molybdenum nitride (MoN) exhibits unique physicochemical properties, a tunable crystal structure, and high catalytic activity, enabling it to efficiently promote reactions at relatively low overpotentials. Furthermore, its excellent electrical conductivity, due to its noble metal-like electronic structure, facilitates rapid electron transfer on the catalyst surface, enhancing reaction kinetics, which is particularly important for electrocatalytic processes. Crucially, MoN exhibits high corrosion resistance in harsh reaction environments, including acidic and alkaline conditions, effectively inhibiting catalyst dissolution and structural degradation during long-term operation and significantly improving the material's cycle stability and lifespan. Therefore, MoN, as a non-noble metal catalyst possessing both high activity and stability, holds great potential as a replacement for noble metal catalysts.

[0004] Compared to their single-component counterparts, heterogeneous structures, through structural engineering to adjust size and microstructure, are key to increasing the number of active sites and constructing active interfaces, thereby effectively improving the hydrogen evolution activity of catalysts. However, during prolonged high-temperature heat treatment, the crystal structure of molybdenum nitride is prone to melting, leading to a significant reduction in the material's specific surface area and severely restricting the full exposure of active sites. Simultaneously, component control remains significantly challenging, particularly the lack of effective strategies for achieving lattice matching and interface control in heterostructures. These challenges severely limit the further development of molybdenum-based heterostructure catalysts in terms of microstructure control and surface activity optimization.

[0005] Therefore, finding a simple and efficient method to prepare molybdenum-based composite catalysts is of significant research value and application importance. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a self-supporting molybdenum / molybdenum nitride composite catalyst, its preparation method, and its application. This invention uses a molybdenum oxide nanoarray grown on carbon cloth prepared by a high-temperature reflux method as a precursor, combined with nitriding reaction and reduction treatment to prepare the molybdenum / molybdenum nitride composite catalyst.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing a self-supporting molybdenum / molybdenum nitride composite catalyst, comprising the following steps: (1) Ammonium molybdate was dissolved in ethanol and then refluxed at high temperature to grow molybdenum oxide nanoarrays on carbon cloth, and used as a precursor. (2) The molybdenum oxide nanoarray precursor obtained in step (1) was subjected to nitridation in a closed system under an atmosphere of ammonia as the reaction gas. After cooling to room temperature, it was taken out to obtain the molybdenum nitride precursor. (3) The molybdenum nitride precursor prepared in step (2) is placed in a reducing atmosphere of mixed hydrogen and argon for eddy current heating reduction reaction. After cooling to room temperature, it is taken out to obtain the self-supported molybdenum / molybdenum nitride composite catalyst.

[0008] Preferably, in step (1), a molybdenum oxide nanoarray is uniformly grown on carbon cloth by reflow at 130-220°C.

[0009] Preferably, the nitriding reaction temperature in step (2) is 500-700 °C.

[0010] Preferably, the heating rate in step (2) is 5-10 ℃ / min.

[0011] Preferably, the nitriding reaction time in step (2) is 3-8 h.

[0012] Preferably, the concentration of ammonia in step (2) is 20-100%.

[0013] Preferably, the ammonia gas flow rate in step (2) is 50-200 Sccm.

[0014] Preferably, the reduction power in step (3) is 1-20 kW.

[0015] Preferably, the reduction reaction time in step (3) is 1-20 s.

[0016] Preferably, the concentration of hydrogen in the hydrogen and argon mixture in step (3) is 5-15%.

[0017] Preferably, the flow rate of the hydrogen and argon mixture in step (3) is 50-150 Sccm.

[0018] The present invention also provides the application of the above-mentioned composite catalyst in electrocatalytic water splitting for hydrogen production.

[0019] The composite catalyst obtained in this invention exhibits abundant heterogeneous interfaces where molybdenum and molybdenum nitride coexist as a heterogeneous interface. At these interfaces, electrons migrate from molybdenum to molybdenum nitride, thereby enhancing the occupancy of the molybdenum 4d antibonding orbitals in molybdenum nitride, weakening the molybdenum-hydrogen bond strength, and thus improving water adsorption / dissociation, optimizing hydrogen adsorption / desorption, and increasing the overall hydrogen evolution efficiency of the catalyst. Simultaneously, the introduction of elemental molybdenum accelerates the electron transport rate of the molybdenum / molybdenum nitride composite catalyst, thereby enhancing the hydrogen evolution reaction kinetics of the water electrolysis process.

[0020] The technical effects achieved by this invention are as follows: 1. The self-supporting molybdenum / molybdenum nitride composite catalyst prepared by the present invention presents a heterostructure nanoarray in which molybdenum and molybdenum nitride phases coexist. The abundant heterostructure between the two phases provides rich catalytic active sites for the composite catalyst in the hydrogen evolution reaction.

[0021] 2. The introduction of elemental molybdenum in this invention accelerates the electron transport rate of the nanoarray, optimizes water adsorption on the nanoarray surface, and promotes mass transfer, thereby uniformly and effectively releasing H2 bubbles.

[0022] 3. Electron migration at the heterostructure interface of this invention shifts the center of the d-band of the nanoarray downwards, increases the occupancy of antibonding orbitals of molybdenum nitride, weakens the strength of molybdenum-hydrogen bonds, optimizes the adsorption / desorption process of H*, and enhances the hydrogen evolution reaction kinetics of the self-supporting molybdenum / molybdenum nitride composite catalyst. Attached Figure Description

[0023] Figure 1 This is a SEM image of the self-supporting molybdenum oxide nanoarray precursor prepared in Example 1 of the present invention; Figure 2 This is a SEM image of the self-supporting molybdenum / molybdenum nitride composite catalyst prepared in Example 1 of this invention; Figure 3 This is a mapping diagram of the self-supporting molybdenum / molybdenum nitride composite catalyst prepared in Example 1 of the present invention; Figure 4 The XRD pattern of the self-supporting molybdenum / molybdenum nitride composite catalyst prepared in Example 1 of this invention; Figure 5 The catalysts prepared for Example 1 and Comparative Example 1 of this invention were used in 1 mol L... 1 Polarization curves and Tafel slope values ​​in KOH solution. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available.

[0025] Example 1 A method for preparing a self-supporting molybdenum / molybdenum nitride composite catalyst (1) Weigh 0.5 g of ammonium molybdate and measure 50 mL of ethanol. Stir to dissolve it completely. Then transfer it to a 100 mL single-necked flask. Place the carbon cloth of appropriate size into the flask. Then reflux at 180 °C for 12 h. After cooling to room temperature, remove it, filter it, and wash it with deionized water to obtain the precursor for growing molybdenum oxide nanoarrays on carbon cloth.

[0026] (2) The precursor of molybdenum oxide nanoarrays grown on carbon cloth prepared in step (1) is tilted in a corundum crucible and the system is sealed. Under the atmosphere of ammonia as the reaction gas, it is heated to 600 °C for low-temperature nitriding reaction for 5 h. The heating rate is 5 °C / min, the ammonia concentration is controlled at 50%, and the gas flow rate is controlled at 100 Sccm. After cooling to room temperature, the molybdenum nitride precursor can be obtained.

[0027] (3) The molybdenum nitride precursor obtained in step (2) is placed in a reducing atmosphere of mixed hydrogen and argon for eddy current heating reaction. The eddy current power is 10 kW and the eddy current time is 5 seconds. The hydrogen concentration is controlled at 10% and the flow rate of the argon-hydrogen mixed gas is controlled at 100 Sccm. After cooling to room temperature, it is taken out to obtain the self-supported molybdenum / molybdenum nitride composite catalyst.

[0028] Figure 1 The image shows a SEM image of the self-supporting molybdenum oxide nanoarray precursor prepared in Example 1 of this invention. As can be seen from the image, the molybdenum oxide nanoribbons are uniformly grown on the surface of the carbon cloth in an array.

[0029] Figure 2 The image shows a SEM image of the self-supporting molybdenum / molybdenum nitride composite catalyst prepared in Example 1 of this invention. As can be seen from the image, after nitriding and reduction reactions, the morphology of the nanoarray remains intact, and the nanoarray is still uniformly grown on the surface of the carbon cloth. The magnified SEM image shows that no particles are generated.

[0030] Figure 3 The image shows the mapping diagram of the self-supporting molybdenum / molybdenum nitride composite catalyst prepared in Example 1 of this invention; as can be seen from the image, Mo and N elements are uniformly distributed in the nanoarray.

[0031] Figure 4The image shows the XRD pattern of the self-supporting molybdenum / molybdenum nitride composite catalyst prepared in Example 1 of this invention. As can be seen from the image, the peaks at 31.9°, 36.2° and 49.0° are diffraction peaks of molybdenum nitride with relatively high peak intensities. The peak at 40.5° corresponds to the peak of elemental molybdenum with relatively weak peak intensity. This indicates that the catalyst is a self-supporting molybdenum / molybdenum nitride composite catalyst with molybdenum nitride as the main phase.

[0032] Example 2 A method for preparing a self-supporting molybdenum / molybdenum nitride composite catalyst Weigh 0.5 g of ammonium molybdate and measure 50 mL of ethanol. Stir to dissolve the mixture completely. Then transfer the mixture to a 100 mL single-necked flask. Place a carbon cloth of suitable size into the flask and then reflux the mixture at 180 °C for 12 h. After cooling to room temperature, remove the flask, filter it, and wash it with deionized water to obtain the precursor for growing molybdenum oxide nanoarrays on carbon cloth.

[0033] (2) The precursor of molybdenum oxide nanoarrays grown on carbon cloth prepared in step (1) is tilted in a corundum crucible and the system is sealed. Under the atmosphere of ammonia as the reaction gas, it is heated to 600 °C for low-temperature nitriding reaction for 5 h. The heating rate is 5 °C / min, the ammonia concentration is controlled at 50%, and the gas flow rate is controlled at 100 Sccm. After cooling to room temperature, the molybdenum nitride precursor can be obtained.

[0034] (3) The molybdenum nitride precursor obtained in step (2) is placed in a reducing atmosphere of mixed hydrogen and argon for eddy current heating reaction. The eddy current power is 5 kW and the eddy current time is 5 seconds. The hydrogen concentration is controlled at 10% and the flow rate of the argon-hydrogen mixed gas is controlled at 100 Sccm. After cooling to room temperature, it is taken out to obtain the self-supported molybdenum / molybdenum nitride composite catalyst.

[0035] Example 3 A method for preparing a self-supporting molybdenum / molybdenum nitride composite catalyst (1) Weigh 0.5 g of ammonium molybdate and measure 50 mL of ethanol. Stir to dissolve it completely. Then transfer it to a 100 mL single-necked flask. Place the carbon cloth of appropriate size into the flask. Then reflux at 180 °C for 12 h. After cooling to room temperature, remove it, filter it, and wash it with deionized water to obtain the precursor for growing molybdenum oxide nanoarrays on carbon cloth.

[0036] (2) The precursor of molybdenum oxide nanoarrays grown on carbon cloth prepared in step (1) is tilted in a corundum crucible and the system is sealed. Under the atmosphere of ammonia as the reaction gas, it is heated to 600 °C for low-temperature nitriding reaction for 5 h. The heating rate is 5 °C / min, the ammonia concentration is controlled at 50%, and the gas flow rate is controlled at 100 Sccm. After cooling to room temperature, the molybdenum nitride precursor can be obtained.

[0037] (3) The molybdenum nitride precursor obtained in step (2) is placed in a reducing atmosphere of mixed hydrogen and argon for eddy current heating reaction. The eddy current power is 20 kW and the eddy current time is 5 seconds. The hydrogen concentration is controlled at 10% and the flow rate of the argon-hydrogen mixed gas is controlled at 100 Sccm. After cooling to room temperature, it is taken out to obtain the self-supported molybdenum / molybdenum nitride composite catalyst.

[0038] Example 4 A method for preparing a self-supporting molybdenum / molybdenum nitride composite catalyst (1) Weigh 0.5 g of ammonium molybdate and measure 50 mL of ethanol. Stir to dissolve it completely. Then transfer it to a 100 mL single-necked flask. Place the carbon cloth of appropriate size into the flask and then reflux at 130 °C for 12 h. After cooling to room temperature, remove it, filter it, and wash it with deionized water to obtain the precursor for growing molybdenum oxide nanoarrays on carbon cloth.

[0039] (2) The precursor of molybdenum oxide nanoarrays grown on carbon cloth prepared in step (1) is tilted in a corundum crucible and the system is sealed. Under the atmosphere of ammonia as the reaction gas, it is heated to 600 °C for low-temperature nitriding reaction for 5 h. The heating rate is 5 °C / min, the ammonia concentration is controlled at 50%, and the gas flow rate is controlled at 100 Sccm. After cooling to room temperature, the molybdenum nitride precursor can be obtained.

[0040] (3) The molybdenum nitride precursor obtained in step (2) is placed in a reducing atmosphere of mixed hydrogen and argon for eddy current heating reaction. The eddy current power is 10 kW and the eddy current time is 10 seconds. The hydrogen concentration is controlled at 10% and the flow rate of the argon-hydrogen mixed gas is controlled at 100 Sccm. After cooling to room temperature, it is taken out to obtain the self-supported molybdenum / molybdenum nitride composite catalyst.

[0041] Example 5 A method for preparing a self-supporting molybdenum / molybdenum nitride composite catalyst (1) Weigh 0.5 g of ammonium molybdate and measure 50 mL of ethanol. Stir to dissolve it completely. Then transfer it to a 100 mL single-necked flask. Place the carbon cloth of appropriate size into the flask and then reflux at 220 °C for 12 h. After cooling to room temperature, remove it, filter it, and wash it with deionized water to obtain the precursor for growing molybdenum oxide nanoarrays on carbon cloth.

[0042] (2) The precursor of molybdenum oxide nanoarrays grown on carbon cloth prepared in step (1) is tilted in a corundum crucible and the system is sealed. Under the atmosphere of ammonia as the reaction gas, it is heated to 600 °C for low-temperature nitriding reaction for 5 h. The heating rate is 5 °C / min, the ammonia concentration is controlled at 50%, and the gas flow rate is controlled at 100 Sccm. After cooling to room temperature, the molybdenum nitride precursor can be obtained.

[0043] (3) The molybdenum nitride precursor obtained in step (2) is placed in a reducing atmosphere of mixed hydrogen and argon for eddy current heating reaction. The eddy current power is 15 kW and the eddy current time is 10 seconds. The hydrogen concentration is controlled at 10% and the flow rate of the argon-hydrogen mixed gas is controlled at 100 Sccm. After cooling to room temperature, it is taken out to obtain the self-supported molybdenum / molybdenum nitride composite catalyst.

[0044] Example 6 A method for preparing a self-supporting molybdenum / molybdenum nitride composite catalyst (1) Weigh 0.5 g of ammonium molybdate and measure 50 mL of ethanol. Stir to dissolve it completely. Then transfer it to a 100 mL single-necked flask. Place the carbon cloth of appropriate size into the flask and then reflux at 220 °C for 12 h. After cooling to room temperature, remove it, filter it, and wash it with deionized water to obtain the precursor for growing molybdenum oxide nanoarrays on carbon cloth.

[0045] (2) The precursor of molybdenum oxide nanoarrays grown on carbon cloth prepared in step (1) is tilted in a corundum crucible and the system is sealed. Under the atmosphere of ammonia as the reaction gas, it is heated to 600 °C for low-temperature nitriding reaction for 5 h. The heating rate is 5 °C / min, the ammonia concentration is controlled at 50%, and the gas flow rate is controlled at 100 Sccm. After cooling to room temperature, the molybdenum nitride precursor can be obtained.

[0046] (3) The molybdenum nitride precursor obtained in step (2) is placed in a reducing atmosphere of mixed hydrogen and argon for eddy current heating reaction. The eddy current power is 10 kW and the eddy current time is 20 seconds. The hydrogen concentration is controlled at 10% and the flow rate of the argon-hydrogen mixed gas is controlled at 100 Sccm. After cooling to room temperature, it is taken out to obtain the self-supported molybdenum / molybdenum nitride composite catalyst Mo / MoN.

[0047] Comparative Example 1 A method for preparing a self-supporting molybdenum nitride catalyst (1) Weigh 0.5 g of ammonium molybdate and measure 50 mL of ethanol. Stir to dissolve it completely. Then transfer it to a 100 mL single-necked flask. Place the carbon cloth of appropriate size into the flask. Then reflux at 180 °C for 12 h. After cooling to room temperature, remove it, filter it, and wash it with deionized water to obtain the precursor for growing molybdenum oxide nanoarrays on carbon cloth.

[0048] (2) The precursor of molybdenum oxide nanoarrays grown on carbon cloth prepared in step (1) is tilted in a corundum crucible and the system is sealed. Under the atmosphere of ammonia as the reaction gas, it is heated to 600 °C for low-temperature nitriding reaction for 5 h. The heating rate is 5 °C / min, the ammonia concentration is controlled at 50%, and the gas flow rate is controlled at 100 Sccm. After cooling to room temperature, the molybdenum nitride precursor can be obtained.

[0049] (3) Place the molybdenum nitride precursor obtained in step (2) in a crucible and seal the system. Under an argon atmosphere, heat to 750 °C for a reduction reaction for 3 h at a heating rate of 5 °C / min. After cooling to room temperature, take it out to obtain the self-supported molybdenum nitride catalyst MoN.

[0050] Figure 5 The samples prepared in Example 1 and Comparative Example 1 of this invention are shown in 1 mol L⁻¹ 1 The polarization curves and Tafel slopes in the KOH solution were consistent across all samples with the same loading. Figure 5 As shown in Figure a, the self-supported molybdenum / molybdenum nitride composite catalyst exhibits the best hydrogen evolution performance and the lowest overpotential, slightly worse than the Pt / C electrode. In contrast, single-phase molybdenum nitride exhibits the highest overpotential and the worst hydrogen evolution performance.

[0051] In addition, such as Figure 5 As shown in b, the Tafel slope of the self-supported molybdenum / molybdenum nitride composite catalyst is as high as 45.6 mV dec. 1 Slightly higher than the 34.2 mV dec of Pt / C. 1 The worst Tafel slope for single-phase molybdenum nitride was 123.2 mV dec. 1 Generally, the Tafel slope is an important parameter for evaluating the kinetic performance of electrocatalysts in the hydrogen evolution reaction. A smaller Tafel slope indicates a faster increase in current density per unit overpotential and a higher reaction rate, implying superior charge transfer efficiency during the catalytic process. Based on this, it can be inferred that the self-supporting molybdenum / molybdenum nitride composite catalyst possesses the optimal electrocatalytic hydrogen evolution performance.

[0052] The self-supporting molybdenum / molybdenum nitride composite catalyst prepared in this invention exhibits abundant heterogeneous interfaces where elemental molybdenum and molybdenum nitride coexist in the form of heterogeneous interfaces. At these interfaces, electrons migrate from molybdenum to molybdenum nitride, thereby enhancing the occupancy of the molybdenum 4d antibonding orbitals and weakening the molybdenum-hydrogen bond strength. This improves water adsorption / dissociation, optimizes hydrogen adsorption / desorption, and increases the overall hydrogen evolution efficiency of the catalyst. Simultaneously, the introduction of elemental molybdenum accelerates the electron transport rate of the molybdenum / molybdenum nitride composite catalyst, thus enhancing the hydrogen evolution reaction kinetics of the water electrolysis process.

[0053] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A method for preparing a self-supporting molybdenum / molybdenum nitride composite catalyst, characterized in that, The preparation method steps are as follows: (1) Ammonium molybdate was dissolved in ethanol and then refluxed at high temperature to grow molybdenum oxide nanoarrays on carbon cloth, and used as a precursor. (2) The molybdenum oxide nanoarray precursor obtained in step (1) was subjected to nitridation in a closed system under an atmosphere of ammonia as the reaction gas. After cooling to room temperature, it was taken out to obtain the molybdenum nitride precursor. (3) The molybdenum nitride precursor prepared in step (2) is placed in a reducing atmosphere of mixed hydrogen and argon for eddy current heating reaction. After cooling to room temperature, it is taken out to obtain the self-supported molybdenum / molybdenum nitride composite catalyst.

2. The preparation method according to claim 1, characterized in that, In step (1), a molybdenum oxide nanoarray is uniformly grown on carbon cloth by reflow at 130-220℃.

3. The preparation method according to claim 1, characterized in that, The nitriding reaction temperature in step (2) is 500-700 ℃; the reaction time is 3-8 h.

4. The preparation method according to claim 1, characterized in that, The heating rate in step (2) is 5-10 ℃ / min.

5. The preparation method according to claim 1, characterized in that, In step (2), the concentration of ammonia is 20-100% and the flow rate of ammonia is 50-200 Sccm.

6. The preparation method according to claim 1, characterized in that, The eddy current heating power in step (3) is 1-20kW.

7. The preparation method according to claim 1, characterized in that, The eddy current heating reaction time in step (3) is 1-20 s.

8. The preparation method according to claim 1, characterized in that, In step (3), the concentration of hydrogen in the hydrogen and argon mixture is 5-15%; the flow rate of the hydrogen and argon mixture is 50-150 Sccm.

9. The self-supporting molybdenum / molybdenum nitride composite catalyst obtained by the preparation method according to any one of claims 1-8.

10. The application of the self-supporting molybdenum / molybdenum nitride composite catalyst as described in claim 9 in electrocatalytic water splitting for hydrogen production.

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