A Spiny Molybdenum Dioxide / Molybdenum Carbide / Carbon Self-Supported Nano-Electrocatalytic Hydrogen Evolution Material and Its Preparation Method and Application

Abstract

The present invention discloses a spiky molybdenum dioxide / molybdenum carbide / carbon self-supporting nano electrocatalytic hydrogen evolution material and its preparation method and application. In the present invention, a molybdenum trioxide precursor is prepared by hydrothermal method, polypyrrole is deposited on the surface of the precursor, and then carbonized in an inert atmosphere to in-situ grow a spiky molybdenum dioxide / molybdenum carbide / carbon nanoarray on a flexible carbon cloth substrate. The prepared material exhibits efficient electrocatalytic hydrogen production performance, and has advantages such as ultra-high stability and good repeatability, and has good application prospects in the fields of energy conversion and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of electrocatalytic materials, and particularly relates to a spiny molybdenum dioxide / molybdenum carbide / carbon self-supporting nano electrocatalytic hydrogen evolution material, a preparation method thereof, and an application thereof. Technical Background

[0002] In recent years, climate and environmental problems such as global warming caused by the overuse of fossil fuels have attracted wide attention. As a secondary energy source, hydrogen not only has a high calorific value when burned, but also the combustion product is water, which is clean and pollution-free. From production to use, hydrogen demonstrates a sustainable development process of natural material recycling to the world, and then becomes a crucial energy source on the world energy stage. As a zero-carbon energy source, the production, storage, transportation, and application technologies of hydrogen will also become the focus of future attention. Currently, the main method for producing hydrogen is electrolysis of water, and directly cracking water requires overcoming difficulties brought by pressure, temperature, electricity, etc. Therefore, achieving efficient and low-cost electrolysis of water remains a huge challenge.

[0003] Transition metal carbides are a class of compounds with high melting points, high hardness, high thermal stability, and high mechanical stability. Transition metal carbides are typical interstitial compounds, where carbon atoms occupy the voids in the close-packed layers of metal atoms, forming a two-dimensional layered structure. Due to the acid and alkali resistance and sulfur poisoning resistance of transition metal carbides at room temperature, they have high chemical stability and are currently widely studied in the field of energy. Transition metal compounds such as MXene have good prospects in the energy field due to their unique layered structure and large interlayer spacing. In addition, since transition metal Mo has a Pt-like d electron structure and low cost, molybdenum-based catalysts have the potential to be efficient hydrogen evolution and oxygen evolution catalysts. Molybdenum carbide, although showing high catalytic hydrogen evolution activity, is also easily oxidized to molybdenum dioxide during the hydrogen evolution process due to its high activity, which reduces the catalytic hydrogen evolution activity of molybdenum carbide and greatly reduces the catalytic stability, and the material structure is damaged. Since introducing an appropriate amount of oxygen can enhance the charge transport between atoms and at the same time make the surface of molybdenum carbide have a very negative Gibbs free energy for adsorbed hydrogen, reducing the desorption difficulty of hydrogen; on the other hand, due to the lack of hydrogen evolution stability of molybdenum carbide, a protective layer for the material needs to be provided. Therefore, the present invention in-situ prepares a spiny molybdenum dioxide / molybdenum carbide / carbon heterostructure on carbon cloth. Besides providing a heterojunction interface to enhance the charge carrier transport in the transverse and longitudinal directions, the intermediate preparation uses the method of electro-depositing a polymer to make the contact between the material and the carbon cloth substrate closer, which is beneficial to forming a tight catalytic structure, thus showing high catalytic hydrogen evolution activity and ultra-high stability. Summary of the Invention

[0004] The object of the present invention is to overcome the disadvantages of existing molybdenum carbide composites, such as easy oxidation and poor stability. The present invention discloses a thorn-like molybdenum dioxide / molybdenum carbide / carbon self-supporting nano electrocatalytic hydrogen evolution material, its preparation method and application. The preparation method hydrothermally prepares a precursor, deposits polypyrrole on the surface of the precursor, and then carbonizes it under an inert atmosphere, for the first time in-situ growing a thorn-like molybdenum dioxide / molybdenum carbide / carbon nanoarray on a flexible carbon cloth substrate. The prepared material exhibits efficient electrocatalytic hydrogen production performance and has advantages such as ultra-high stability and good repeatability.

[0005] Another object of the present invention is to provide a modified electrode.

[0006] Another object of the present invention is to provide the application of the above-mentioned modified electrode in catalytic hydrogen production.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A thorn-like molybdenum dioxide / molybdenum carbide / carbon self-supporting nano electrocatalytic hydrogen evolution material, its preparation method and application. The method includes the following steps:

[0009] S1. Clean and dry the flexible carbon cloth substrate;

[0010] S2. Use molybdenum acetylacetonate as the molybdenum source, and use a mixed solution of acetic acid, deionized water, sodium dodecyl sulfate or cetyltrimethylammonium bromide or sodium dodecylbenzenesulfonate as the solvent. Put the mixed solution and the washed carbon cloth into a hydrothermal reaction kettle for reaction;

[0011] S3. Prepare an electrodeposition solution: Dissolve sodium perchlorate or lithium chloride or sodium chloride or potassium chloride, pyrrole monomer, ammonium persulfate or ferric trichloride in deionized water in proportion, and electrodeposit polypyrrole on the carbon cloth grown with molybdenum trioxide array;

[0012] S4. Put the carbon cloth loaded with polypyrrole and molybdenum trioxide into a tube furnace for carbonization

[0013] It should be noted that the operation of step S1 is: successively clean and dry the carbon cloth substrate with acetone, ethanol, and deionized water under ultrasonic conditions.

[0014] It should be noted that in step S2, the molar ratio of molybdenum acetylacetonate to sodium dodecyl sulfate or cetyltrimethylammonium bromide or sodium dodecylbenzenesulfonate is 75:1 to 85:1, the volume ratio of acetic acid to deionized water is 12:1 to 18:1, the reaction temperature is 130°C to 180°C, and the reaction time is 12h to 20h.

[0015] It should be noted that the step S3 is as follows: Dissolve 0.1 moL of sodium perchlorate or lithium chloride or sodium chloride or potassium chloride in a certain volume of deionized water, then add pyrrole monomer and ammonium persulfate solution or ferric chloride and stir evenly, where the volume ratio of pyrrole monomer to ammonium persulfate or ferric chloride solution is 2:1 to 5:1, and the concentration of ammonium persulfate or ferric chloride solution is 1 g / 50 mL to 3 g / 50 mL. The electro-deposition process is carried out in an electrochemical workstation, using the carbon cloth grown with molybdenum trioxide as the direct electrode, Ag / AgCl electrode as the reference electrode, and carbon rod as the counter electrode, and depositing at a constant voltage for 10 s to 40 s.

[0016] It should be noted that the step S4 is as follows: Directly heat up to 800 - 1000 °C at a heating rate of 20 °C / min to 50 °C / min, and maintain for 16 h to 40 h. The inert gas is selected from argon or nitrogen, and the gas flow rate is 50 sccm to 100 sccm.

[0017] A modified electrode is prepared by the above method.

[0018] The application of the above modified electrode in catalytic hydrogen production is also within the protection scope of the present invention.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention discloses a spiky molybdenum dioxide / molybdenum carbide / carbon self-supported nano electrocatalytic hydrogen evolution material, its preparation method and application. This method not only provides a three-dimensional molybdenum carbide composite material with a brand-new morphology, and this three-dimensional structure exposes a larger reaction active area, but also enhances the interaction between the material and the substrate by electro-depositing polypyrrole to coat the precursor, thereby greatly improving the stability of the material.

[0021] 2. This composite material is flexible, foldable, lightweight, has good repeatability, and is easy to recycle. It is a clean, efficient electrocatalytic hydrogen evolution material with broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 SEM image of molybdenum trioxide nanosheets grown on a carbon cloth substrate in Example 1, with a magnification of 5000 times;

[0023] Figure 2 SEM image of polypyrrole-coated molybdenum trioxide nanosheets grown on a carbon cloth substrate in Example 1, with a magnification of 5000 times;

[0024] Figure 3 SEM image of the spiky molybdenum dioxide / molybdenum carbide / carbon self-supported nano electrocatalytic hydrogen evolution material in Example 1, with a magnification of 5000 times;

[0025] Figure 4 Raman spectrum of the thorn-like molybdenum dioxide / molybdenum carbide / carbon self-supporting nano electrocatalytic hydrogen evolution material of Example 1;

[0026] Figure 5 XRD patterns of the thorn-like molybdenum dioxide / molybdenum carbide / carbon self-supporting nano electrocatalytic hydrogen evolution materials of Example 1 and Example 2;

[0027] Figure 6 Linear sweep voltammograms of Example 1 and Example 2. Detailed implementation manners

[0028] The present invention will be further described below in conjunction with embodiments. These embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. For the experimental methods without specific conditions in the following embodiments, they are usually carried out according to the conventional conditions in the art or according to the conditions recommended by the manufacturer; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as conventional markets. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention fall within the scope claimed by the present invention.

[0029] The present invention relates to a thorn-like molybdenum dioxide / molybdenum carbide / carbon self-supporting nano electrocatalytic hydrogen evolution material and its preparation method and application. The method comprises the following steps:

[0030] S1. Clean and dry the flexible carbon cloth substrate;

[0031] S2. Put the mixed solution with molybdenum acetylacetonate as the molybdenum source and the washed carbon cloth into a hydrothermal reaction kettle to grow a molybdenum trioxide nanosheet array on the carbon cloth;

[0032] S3. Prepare an electrodeposition solution and electrodeposit polypyrrole on the carbon cloth grown with the molybdenum trioxide array;

[0033] S4. Put the carbon cloth loaded with polypyrrole and molybdenum trioxide into a tube furnace for carbonization

[0034] It should be noted that the operation of step S1 is: successively clean and dry the carbon cloth substrate with acetone, ethanol, and deionized water under ultrasonic conditions.

[0035] It should be noted that in step S2, the mixed solution is a mixed solution with molybdenum acetylacetonate as the molybdenum source and acetic acid, deionized water, sodium dodecyl sulfate or cetyltrimethylammonium bromide or sodium dodecylbenzenesulfonate.

[0036] It should be noted that the step S3 is as follows: Preparation of the electrodeposition solution: Sodium perchlorate, lithium chloride, sodium chloride, or potassium chloride, pyrrole monomer, ammonium persulfate, or ferric chloride are dissolved in deionized water in a certain proportion. The electrodeposition process is carried out in an electrochemical workstation, using the carbon cloth grown with molybdenum trioxide as the working electrode, Ag / AgCl electrode as the reference electrode, and carbon rod as the counter electrode, and depositing at a constant voltage for 10 s to 40 s.′

[0037] It should be noted that the step S4 is as follows: Directly heating to 750 - 950 °C at a heating rate of 20 °C / min to 50 °C / min, maintaining for 16 h to 40 h. The inert gas is selected from argon or nitrogen, and the gas flow rate is 50 sccm to 100 sccm.

[0038] Example 1

[0039] The present invention provides a spiny molybdenum dioxide / molybdenum carbide / carbon self - supported nano - electrocatalytic hydrogen evolution material, its preparation method and application, including the following steps:

[0040] S1. Select a carbon cloth produced by Carbon Energy Co., Ltd., cut it into a size of 2 cm * 2 cm for use as the substrate for material growth. In this example, a commercially available carbon cloth is selected, which has different advantages such as being light, flexible, and high - temperature resistant, and is convenient for application in different scenarios of daily life, such as fabric, clothing fabric, masks, etc.

[0041] S2. The cut carbon cloth substrate is ultrasonically cleaned with sufficient acetone, absolute ethanol, and deionized water for 20 minutes, with an ultrasonic power of 200 W and a frequency of 40 KHz. After cleaning, it is dried with a heating table and used as the growth substrate.

[0042] S3. Weigh 0.5 g of molybdenum acetylacetonate (purity 99.9%, purchased from aladin) as the molybdenum source, weigh 5 mg of sodium dodecyl sulfate (purity 99.99%, purchased from aladin), the volume ratio of acetic acid to deionized water is 12:1 to 18:1, preferably 16:1. After mixing evenly, transfer it to a 50 mL reaction kettle, the reaction temperature is 130 °C to 180 °C, preferably 140 °C, the reaction time is 12 h to 20 h, preferably 15 h. After the reaction, take out the sample and dry it overnight at 60 °C in a vacuum drying oven.

[0043] S4. Dissolve 0.1 moL of sodium perchlorate or lithium chloride or sodium chloride or potassium chloride in a certain volume of deionized water, then add pyrrole monomer and ammonium persulfate solution or ferric chloride and stir evenly. The volume ratio of pyrrole monomer to ammonium persulfate or ferric chloride solution is 2∶1 - 5∶1, preferably 3∶1. The concentration of ammonium persulfate or ferric chloride solution is 1 g / 50 mL - 3 g / 50 mL, preferably 2 g / 50 mL. The electrodeposition process is carried out in an electrochemical workstation, using the carbon cloth grown with molybdenum trioxide as the working electrode, Ag / AgCl electrode as the reference electrode, and carbon rod as the counter electrode. Deposit at a constant voltage for 10 s - 40 s, and the time is preferably 30 s.

[0044] S5. After the electrodeposition is completed, take out the sample to obtain a polypyrrole-coated molybdenum trioxide nanosheet array material grown on a flexible carbon cloth substrate, and dry it overnight at 60 °C in a vacuum drying oven.

[0045] S6. Put the carbon cloth grown with the polypyrrole-coated molybdenum trioxide nanosheet array material into a tubular furnace, and directly heat it to 750 - 950 °C at a heating rate of 20 °C / min - 50 °C / min, and maintain it for 16 h - 40 h. The preferred heating rate is 30 °C / min. The inert gas is selected from argon or nitrogen, and the gas flow rate is 50 sccm - 100 sccm, and the flow rate is preferably 50 sccm.

[0046] S7. Take out the sample to obtain a spiny molybdenum dioxide / molybdenum carbide / carbon nano electrocatalytic hydrogen evolution material grown on a flexible carbon cloth substrate.

[0047] Figure 1 is the SEM image of the molybdenum trioxide nanosheets grown on the flexible carbon cloth substrate in the embodiment of the present invention. It can be seen from the figure that the molybdenum trioxide nanosheets grow uniformly, vertically and densely on the flexible carbon cloth substrate, and present serrated edges;

[0048] Figure 2 is the SEM image of the polypyrrole-coated molybdenum trioxide nanosheet array material grown on the flexible carbon cloth substrate in the embodiment of the present invention. It can be seen from the figure that the polypyrrole layer uniformly coats the surface of the molybdenum trioxide nanosheets, forming a core-shell structure. While the polypyrrole vertically coats the molybdenum trioxide nanosheets, it also increases the contact interface with the flexible carbon cloth substrate, strengthening the combination of the material and the substrate. It can be predicted that after high-temperature carbonization, the interaction between the carbon atoms of this material and the substrate will be greatly enhanced, and the bonding will be firm, greatly improving the stability of the material.

[0049] Figure 3In the embodiment of the present invention, it is the SEM image of the thorn-like molybdenum dioxide / molybdenum carbide / carbon self-supporting nano electrocatalytic hydrogen evolution material after high-temperature carbonization at 950 °C. The material forms a unique vertical multi-thorn structure aggregated by nanosheets. The adjacent nanosheets are cross-connected and folded, showing a three-dimensional structure, which enhances the electron transport in the horizontal and vertical directions.

[0050] Figure 4 In the embodiment of the present invention, it is the Raman image of the thorn-like molybdenum dioxide / molybdenum carbide / carbon self-supporting nano electrocatalytic hydrogen evolution material obtained after high-temperature carbonization at 950 °C. It can be seen from the figure that the D peak in the carbon peak moves towards the low wavenumber band, showing a red shift, indicating that the van der Waals interaction between molecules increases with the increase of temperature. After comparing the intensities of the D peak and the G peak, I D ∶I G = 1.200, indicating an increase in the crystal defects of carbon atoms and a tendency towards disorder. At the same time, the introduction of nitrogen atoms also increases the degree of defects.

[0051] Figure 5 In the embodiment of the present invention, it is the XRD image of the thorn-like molybdenum dioxide / molybdenum carbide / carbon self-supporting nano electrocatalytic hydrogen evolution material obtained after high-temperature carbonization at 950 °C. Compared with the standard card PDF#32-0671 of molybdenum dioxide, the three diffraction peaks at 26.03°, 37.02°, and 53.51° correspond to the (-111), (-211), and (-312) crystal planes respectively. Compared with the standard card PDF#35-0787 of molybdenum carbide, the 39.39° corresponds to the (101). The peaks of the carbon cloth appear at 26° and 43°. The carbon peak at 26° coincides with the 26.03° peak of molybdenum dioxide, while the carbon peak at 43° shows a broad peak.

[0052] Figure 6 It is the linear sweep voltammogram of Example 1 and Example 2. It can be seen that the material at 950 °C shows higher catalytic hydrogen evolution activity in 0.5 M dilute sulfuric acid, and is 72 mV at a current density of -10 mA / cm 2 . This is because with the increase of temperature, the content of active molybdenum carbide increases, the activity increases, and the crystallinity of the material rises, and the Mo-O-C interaction is enhanced.

[0053] Example 2

[0054] The difference between Example 2 and Example 1 is that:

[0055] S6. Other conditions remain unchanged, and the holding temperature is changed to 900 °C.

[0056] For those skilled in the art, various corresponding changes and modifications can be made based on the above technical solutions and concepts, and all such changes and modifications should be included within the protection scope of the claims of the present invention.

Claims

1. A preparation method of a spiny molybdenum dioxide / molybdenum carbide / carbon self-supporting nano electrocatalytic hydrogen evolution material, characterized in that, the method comprises the following steps: S1. Clean and dry the flexible carbon cloth substrate; S2. Put the mixed solution with molybdenum acetylacetonate as the molybdenum source and the washed carbon cloth into a hydrothermal reaction kettle to grow molybdenum trioxide nanosheet arrays on the carbon cloth; S3. Prepare an electrodeposition solution and electrodeposit polypyrrole on the carbon cloth grown with molybdenum trioxide arrays; S4. Put the carbon cloth loaded with polypyrrole and molybdenum trioxide into a tubular furnace for carbonization; wherein the mixed solution in step S2 is obtained by mixing molybdenum acetylacetonate as the molybdenum source with acetic acid, deionized water, sodium dodecyl sulfate or cetyltrimethylammonium bromide or sodium dodecylbenzenesulfonate; step S3 is: Preparation of the electrodeposition solution: Dissolve sodium perchlorate or lithium chloride or sodium chloride or potassium chloride, pyrrole monomer, ammonium persulfate or ferric trichloride in deionized water in proportion. The electrodeposition process is carried out in an electrochemistry workstation CHI 660, using the carbon cloth grown with molybdenum trioxide as the working electrode, Ag / AgCl electrode as the reference electrode, and carbon rod as the counter electrode, and depositing at a constant voltage for 10 s - 40 s; step S4 is: Directly heat up to 800 °C - 1000 °C at a heating rate of 20 °C / min - 50 °C / min and maintain for 16 h - 40 h. The inert gas is selected from argon or nitrogen, and the gas flow rate is 50 sccm - 100 sccm.

2. The preparation method of the spiny molybdenum dioxide / molybdenum carbide / carbon self-supporting nano electrocatalytic hydrogen evolution material according to claim 1, characterized in that: the operation of step S1 is: successively clean and dry the carbon cloth substrate with acetone, ethanol, and deionized water under ultrasonic conditions.

3. A spiny molybdenum dioxide / molybdenum carbide / carbon self-supporting nano electrocatalytic hydrogen evolution material prepared by the method according to any one of claims 1 to 2.

4. Application of the spiny molybdenum dioxide / molybdenum carbide / carbon self-supporting nano electrocatalytic hydrogen evolution material obtained according to claim 3 in catalytic hydrogen production.

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