Carbon nanotube-supported nitrogen-doped catalyst and preparation method therefor

Abstract

The present invention relates to the field of water electrolysis and hydrogen production. Disclosed is a carbon nanotube-supported nitrogen-doped catalyst. The catalyst has a carbon nanotube structure as a support, and cobalt and ruthenium as active components, wherein the content of the cobalt element is 30-45w%, the content of the ruthenium element is 1-7wt%, and the proportion of the ruthenium element present in the form of RuN is 60-90wt% relative to the total ruthenium element. A graphitized structure of the catalyst is conducive to charge conduction, Ru is uniformly loaded on the surface of the support by means of a low-temperature reduction process and interaction with defect sites on the surface of the support, and then after high-temperature roasting, Ru interacts with the N element and the metal Co, thereby improving the hydrogen evolution catalytic activity of the catalyst.

Description

Carbon nanotube-supported nitrogen-doped catalyst and preparation method thereof Technical Field

[0001] The present invention relates to the field of hydrogen production by water electrolysis, and in particular to a carbon nanotube-supported nitrogen-doped catalyst, a preparation method thereof, and a method for using the catalyst to produce hydrogen by water electrolysis. Background Art

[0002] Currently, Pt-based catalysts remain the mainstream catalysts for electrocatalytic hydrogen evolution. However, the scarcity and high price of Pt in nature are major obstacles to its development. Therefore, the continuous development of highly active and low-cost catalysts is needed to reduce the production cost of electrolyzers.

[0003] Compared with traditional platinum-based HER catalyst materials, Ru-based catalysts have many advantages: 1. Ru is the cheapest Pt group metal element, and its cost is only 1 / 3 of Pt; 2. Ru has good chemical inertness under alkaline conditions and the Ru-H bond strength is close to that of Pt-H bond (Ru-H bond: 65kcal mol -1 Pt-H bond: 62 kcal mol -1 ). However, the binding energy between Ru and hydrogen intermediates is too strong, which is not conducive to the desorption of H2 during the catalytic reaction, reducing the overall reaction kinetics and being a key factor restricting its HER activity. Alloying Ru can optimize the electronic structure of the catalyst, increase the transition metal-H bond energy, and reduce the Ru-H bond energy to promote the adsorption / activation of H2O molecules and the adsorption / desorption process of H intermediates during the alkaline HER process, thereby achieving the purpose of improving the HER catalytic activity of the catalyst. However, the traditional heat treatment alloying process easily causes the particle size to increase and the metal particles to agglomerate and grow during the electrochemical process, thereby affecting the activity and stability of the catalyst. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems of high process cost, complicated operation and low activity of Ru-containing water electrolysis hydrogen evolution catalyst in the prior art.

[0005] After in-depth research, the inventors of the present invention discovered that by controlling the ratio of ruthenium in the form of RuN in a carbon nanotube-supported nitrogen-doped catalyst containing Ru and Co as active ingredients within a specific range, the resulting catalyst can solve the technical problems of existing Ru-containing catalysts and exhibit excellent hydrogen evolution catalytic activity.

[0006] Specifically, the present invention provides a carbon nanotube-supported nitrogen-doped catalyst, wherein the catalyst has a carbon nanotube structure as a carrier, and cobalt and ruthenium as active components, wherein the content of cobalt element is 30-45wt% relative to the total amount of the catalyst, the content of ruthenium element is 1-7wt%, and the proportion of ruthenium element in the form of RuN relative to all ruthenium elements is 60wt% to 90wt%, preferably 65wt% to 88wt%, and more preferably 70wt% to 85wt%.

[0007] On the other hand, the present invention provides a method for preparing a carbon nanotube-supported nitrogen-doped catalyst. The method uses a zeolite imidazole framework (ZIF) as a precursor to construct a highly active porous carbon-based support, and through nitrogen doping, in-situ reduction loading and secondary high-temperature calcination, Ru and Co form a metal nitride (metal-N), and the proportion of ruthenium elements in the form of RuN is within a specific range. The catalyst thus obtained can achieve the purpose of the present invention.

[0008] More specifically, the present invention provides a method for preparing a carbon nanotube-supported nitrogen-doped catalyst, wherein the preparation method comprises the following steps:

[0009] S1, mixing a cobalt source, a zinc source and a nitrogen-containing organic ligand in a solvent for a first reaction, and then separating and drying to obtain a CoZn-zif precursor;

[0010] S2. Carbonizing and nitrogen-doping the CoZn-zif precursor obtained in S1 in an inert gas in the presence of a nitrogen dopant to obtain a carbon nanotube-coated cobalt structural material, wherein an organic compound having three or more nitrogen atoms is used as the nitrogen dopant in the nitrogen doping;

[0011] S3, contacting the structural material obtained in S2 with a ruthenium source to load ruthenium, and reducing the ruthenium loaded on the structural material using a reducing agent;

[0012] S4. calcining the product of step S3 at 600-1000° C. to obtain a carbon nanotube-supported nitrogen-doped catalyst.

[0013] A third aspect of the present invention provides an electrolysis electrode (particularly a cathode electrode), which comprises the carbon nanotube-supported nitrogen-doped catalyst of the present invention, or the carbon nanotube-supported nitrogen-doped catalyst prepared by the method of the present invention.

[0014] A fourth aspect of the present invention provides a method for producing hydrogen by electrolysis of water, characterized in that the carbon nanotube-supported nitrogen-doped catalyst of the present invention or the carbon nanotube-supported nitrogen-doped catalyst prepared by the method of the present invention is used.

[0015] A fifth aspect of the present invention provides a method for producing hydrogen by electrolysis of water, wherein the carbon nanotube-supported nitrogen-doped catalyst of the present invention, or the carbon nanotube-supported nitrogen-doped catalyst prepared by the method of the present invention, is used in an alkaline or alkaline membrane water electrolysis reaction to produce hydrogen.

[0016] Through the above technical solution, the beneficial effects of the present invention are:

[0017] The present invention combines the advantages of two ZIF materials, Zn-based zeolitic imidazole framework materials (Zn-based ZIF materials) and Co-based zeolitic imidazole framework materials (Co-based ZIF materials), to prepare a nanosized CoZn bimetallic ZIF precursor material. Subsequently, accompanied by high-temperature treatment of carbonization and nitrogen doping, the volatilization of Zn generates a large number of defect sites. The abundant defect sites on the carbon nanotubes are conducive to the coordinated adsorption of Ru. Further low-temperature in-situ reduction is performed, so that the precious metal Ru is uniformly loaded on the carbon-based support. After a second high-temperature roasting, Ru and N elements form chemical bonds to generate active sites, and Ru and Co exert a synergistic effect. As a result, the catalyst of the present invention exhibits excellent electrocatalytic hydrogen evolution performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG1 is a scanning electron microscope photograph of Zn / Co-ZIF of Example 1;

[0019] FIG2 is a scanning electron microscope photograph of Zn / Co-ZIF after high temperature calcination in Example 1;

[0020] FIG3 is a high-resolution transmission electron micrograph of Zn / Co-ZIF after high-temperature calcination in Example 1;

[0021] FIG4 is an energy spectrum scan result of Zn / Co-ZIF after high temperature calcination in Example 1;

[0022] FIG5 is a high-resolution transmission electron micrograph and Fourier transform image of the Zn / Co-ZIF sample after high-temperature calcination in Example 1;

[0023] FIG6 is a transmission electron microscope image of the Ru-loaded sample after calcination in Example 1;

[0024] FIG7 is a high-resolution transmission electron micrograph and Fourier transform image of the Ru-loaded sample after calcination in Example 1;

[0025] FIG8 is a high-resolution transmission electron micrograph and Fourier transform image of the Ru-loaded sample after calcination in Example 1;

[0026] 9 is an XPS spectrum of the sample of Zn / Co-ZIF material after high temperature calcination in Example 1;

[0027] Figure 10 is an XPS spectrum of the Ru-loaded sample after calcination in Example 1;

[0028] FIG11 is an XPS comparison chart of N element in the sample before and after Ru loading in Example 1;

[0029] FIG12 is an XRD pattern of the sample before and after Ru loading in Example 1;

[0030] FIG13 is the LSV data of the catalyst in Example 1;

[0031] FIG14 is Tafel data of the catalyst in Example 1 of the present invention;

[0032] FIG15 is a graph showing the C of the catalyst in Example 1 of the present invention. dl data;

[0033] FIG16 is the LSV data of the PtC catalyst in Comparative Example 1;

[0034] Figure 17 XPS spectrum of Ru in Comparative Example 1;

[0035] Figure 18 XPS spectrum of Ru in Comparative Example 2;

[0036] Figure 19 XPS spectrum of Ru in Comparative Example 3. DETAILED DESCRIPTION

[0037] Hereinafter, specific embodiments of the present invention will be described in detail. However, it should be noted that the protection scope of the present invention is not limited by these specific embodiments, but is determined by the appended claims.

[0038] In the context of this specification, except for the contents explicitly stated, any matters or issues not mentioned are directly applicable to those known in the art without any changes. Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the technical solutions or technical ideas formed thereby are considered part of the original disclosure or original description of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless a person skilled in the art considers that the combination is obviously unreasonable.

[0039] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this specification are based on weight, unless the weight basis does not conform to the common understanding of those skilled in the art.

[0040] The specific embodiments of the present invention are described in detail below. However, it should be noted that the protection scope of the present invention is not limited by these specific embodiments, but is determined by the claims in the appendix.

[0041] In the context of the present invention, unless otherwise specified, the physical property values ​​of a substance (such as boiling point) are all measured values ​​at normal temperature / room temperature (25° C.) and normal pressure (101325 Pa).

[0042] A first aspect of the present invention provides a carbon nanotube-supported nitrogen-doped catalyst, wherein the catalyst has a carbon nanotube structure as a carrier and cobalt and ruthenium as active components, wherein the content of cobalt element is 30-45wt% relative to the total amount of the catalyst, the content of ruthenium element is 1-7wt%, and the proportion of ruthenium element in the form of RuN relative to all ruthenium elements is 60wt% to 90wt%, preferably 65wt% to 88wt%, and more preferably 70wt% to 85wt%.

[0043] The surface of the carbon nanotube-supported nitrogen-doped catalyst of the present invention is loaded with nano-sized Ru, and the bonding of Ru with the N element in the carrier enhances its catalytic activity, and Ru and Co form a synergistic effect, effectively improving the activity of the Ru-containing water electrolysis hydrogen evolution catalyst.

[0044] In one embodiment of the present invention, in the catalyst, the proportion of ruthenium elements existing in the form of RuN relative to all ruthenium elements is 70wt%, 71wt%, 72wt%, 73wt%, 74wt%, 75wt%, 76wt%, 77wt%, 78wt%, 79wt%, 80wt%, 81wt%, 82wt%, 83wt%, 84wt%, 85wt%, 86wt%, 87wt%, 88wt% or 89wt%.

[0045] In one embodiment of the present invention, the nitrogen content of the catalyst is 2-5 wt%.

[0046] In one embodiment of the invention, the nitrogen content of the catalyst is 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt% or 5 wt%.

[0047] In one embodiment of the present invention, the nitrogen element exists in the form of at least one of metal-N, pyridinic nitrogen and graphitized nitrogen.

[0048] In the present invention, the form of cobalt and ruthenium as active ingredients is not particularly limited and can exist in the form of elemental metal, metal alloy, or metal-N. In this case, the active ingredients of cobalt and ruthenium include Co elemental metal, Ru elemental metal, RuN, CoN, and RuCo alloy, but are not limited thereto.

[0049] In one embodiment of the present invention, in the catalyst, the average particle size of metallic ruthenium is 2-5 nm.

[0050] In one embodiment of the present invention, the diameter of the carbon nanotubes in the catalyst is 30-70 nm.

[0051] In one embodiment of the present invention, the oxygen content is less than 2 wt%, preferably less than 1%, and more preferably less than 0.5%. The oxygen primarily comes from surface hydroxyl groups (O) and a small amount of vacant oxygen, but the overall oxygen content is very low. Therefore, in one embodiment of the present invention, the catalyst of the present invention is substantially free of oxygen.

[0052] In one embodiment of the present invention, the zinc content in the catalyst is 5 wt% or less, preferably 4 wt% or less, 3 wt% or less, 2 wt% or less or 1 wt% or less, and more preferably substantially no Zn is contained.

[0053] A second aspect of the present invention provides a method for preparing a carbon nanotube-supported nitrogen-doped catalyst, wherein the preparation method comprises the following steps:

[0054] S1, mixing a cobalt source, a zinc source and a nitrogen-containing organic ligand in a solvent for a first reaction, and then separating and drying to obtain a CoZn-zif precursor;

[0055] S2. Carbonizing and nitrogen-doping the CoZn-zif precursor obtained in S1 in an inert gas in the presence of a nitrogen dopant to obtain a carbon nanotube-coated cobalt structural material, wherein an organic compound having three or more nitrogen atoms is used as the nitrogen dopant in the nitrogen doping;

[0056] S3, contacting the structural material obtained in S2 with a ruthenium source to load ruthenium, and reducing the ruthenium loaded on the structural material using a reducing agent;

[0057] S4. calcining the product of step S3 at 600-1000° C. to obtain a carbon nanotube-supported nitrogen-doped catalyst.

[0058] In the present invention, the advantages of two ZIF materials, Zn-based zeolite imidazole framework materials (Zn-based ZIF materials) and Co-based zeolite imidazole framework materials (Co-based ZIF materials), are combined to prepare a nano-sized CoZn bimetallic ZIF precursor material. By high-temperature pyrolysis carbonization and nitrogen doping, a N-doped carbon nanotube-coated Co-based support material is obtained. In addition, due to the volatilization of Zn, a large number of defect sites are generated. The abundant defect sites on the carbon nanotube carbon support are conducive to the coordination adsorption of Ru. Further low-temperature in-situ reduction is performed, so that the precious metal Ru is uniformly loaded on the carbon-based support; and then after a second high-temperature calcination, Ru and N elements form a chemical bond to generate active sites. Moreover, relative to all ruthenium elements, the ratio of ruthenium elements in the form of RuN is within the specific range of the present invention. At the same time, Ru and Co exert a synergistic effect, thereby obtaining the catalyst of the present invention, which exhibits excellent electrocatalytic hydrogen evolution performance.

[0059] In one embodiment of the present invention, the method for preparing the carbon nanotube-supported nitrogen-doped catalyst of the present invention prepares the carbon nanotube-supported nitrogen-doped catalyst of the present invention.

[0060] In one embodiment of the present invention, in step S1, the cobalt source is selected from a water-soluble cobalt salt, preferably at least one of cobalt chloride and cobalt nitrate. The cobalt source may be present with or without bound water, for example, Co(NO₃)₂·6H₂O.

[0061] In one embodiment of the present invention, in step S1, the zinc source is selected from a water-soluble zinc salt, preferably at least one of zinc nitrate, zinc sulfate, and zinc chloride. The zinc source may be present with or without bound water, for example, Zn(NO₃)₂·6H₂O.

[0062] In one embodiment of the present invention, in the above step S1, the nitrogen-containing organic ligand is selected from an optionally substituted imidazole compound, preferably 2-methylimidazole. In one embodiment of the present invention, as a "optionally substituted" substituent, it can be selected from C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, C6-C10 aryl, C6-C10 aryl optionally substituted by C1-C6 alkyl, preferably, as a "optionally substituted" substituent, it can be selected from C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, phenyl, naphthyl, phenyl optionally substituted by C1-C4 alkyl, more preferably, as a "optionally substituted" substituent, it can be selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, sec-butyl, pentyl and its isomers, hexyl and its isomers, phenyl, benzyl, xylyl. In one embodiment of the present invention, the number of "optionally substituted" is not particularly limited, and the upper limit of the positions that can be substituted is used as the maximum number of "optionally substituted", for example, it can be 1, 2, 3 or 4.

[0063] In one embodiment of the present invention, in step S1, the weight ratio of the cobalt source, the zinc source, and the nitrogen-containing organic ligand is (0.5-4):1:(2-14), preferably (0.8-3):1:(3-12). More preferably, the weight ratio of the cobalt source / zinc source is greater than 1 and less than 2.5.

[0064] In one embodiment of the present invention, in the above step S1, the solvent is selected from C1-C4 monohydric alcohol, more preferably methanol or ethanol.

[0065] In one embodiment of the present invention, in the above step S1, based on the total weight of the cobalt source, the zinc source and the nitrogen-containing organic ligand being 1 g, the amount of the solvent used is 20-60 ml, preferably 35-50 ml.

[0066] In one embodiment of the present invention, in the above step S1, the temperature of the first reaction is 20-30° C., for example, room temperature, and the reaction time of the first reaction is 10-36 h.

[0067] In one embodiment of the present invention, in the above step S1, after the first reaction, separation is performed by any one means selected from filtration and centrifugation to obtain a reaction product.

[0068] In one embodiment of the present invention, in the above step S1, the reaction product of the first reaction is dried at a temperature of 40-80° C., preferably 50-70° C., to obtain a CoZn-zif precursor.

[0069] In the present invention, in step S2, the CoZn-zif precursor obtained in step S1 is carbonized and nitrogen-doped in an inert gas in the presence of a nitrogen dopant to obtain a carbon nanotube-coated cobalt structural material, wherein an organic compound having more than three nitrogen atoms is used as a nitrogen dopant in the nitrogen doping.

[0070] In one embodiment of the present invention, in step S2 , carbonization and nitrogen doping are performed simultaneously. Specifically, carbonization and nitrogen doping are performed at high temperature in an inert gas in the presence of a nitrogen dopant.

[0071] In one embodiment of the present invention, in step S2, the conditions for carbonization and nitrogen doping are: heating to 600-1200°C at a heating rate of 1-10°C / min and maintaining for 1.5-4 hours, preferably heating at a rate of 3-8°C / min, preferably heating to 700-1100°C, and preferably maintaining for 2-3 hours.

[0072] In one embodiment of the present invention, in step S2, an organic compound having more than three nitrogen atoms is used as a nitrogen dopant. Preferably, the organic compound having more than three nitrogen atoms is a 5-10 membered cyclic organic compound having more than three ring nitrogen atoms, preferably at least one selected from triazole compounds, triazine compounds, and melamine, and more preferably at least one selected from optionally substituted 1,2,3-triazole, optionally substituted 1,2,4-triazole, optionally substituted 1,2,3-triazine, optionally substituted 1,2,4-triazine, optionally substituted 1,2,3-triazine, and melamine. In one embodiment of the present invention, as the substituent group of "optionally substituted", it can be selected from C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, C6-C10 aryl, C6-C10 aryl optionally substituted by C1-C6 alkyl, preferably, as the substituent group of "optionally substituted", it can be selected from C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, phenyl, naphthyl, phenyl optionally substituted by C1-C4 alkyl, more preferably, as the substituent group of "optionally substituted", it can be selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, sec-butyl, pentyl and its isomers, hexyl and its isomers, phenyl, benzyl, xylyl. In one embodiment of the present invention, as the number of "optionally substituted", there is no particular limitation, and the upper limit of the position that can be substituted is used as the maximum number of "optionally substituted", for example, it can be 1, 2 or 3.

[0073] In one embodiment of the present invention, in step S2, the weight ratio of the CoZn-zif precursor to the nitrogen dopant is 1:0.1-5, preferably 1:0.2-1.

[0074] In the present invention, step S2 is used to obtain a carbon nanotube-coated cobalt structural material. Step S2 can volatilize most of the Zn atoms and generate defect sites in the carbon-based structure, which can enhance the adsorption effect of Ru atoms and improve the dispersion of Ru on its surface.

[0075] In the present invention, in step S3, the carbon nanotube-coated cobalt structural material obtained in step S2 is brought into contact with a ruthenium source to load ruthenium, thereby obtaining a ruthenium-adsorbed structural material. The ruthenium supported on the structural material is then in situ reduced using a reducing agent. Specifically, step S3 includes a contacting step of bringing the carbon nanotube-coated cobalt structural material into contact with a ruthenium source to load ruthenium, thereby obtaining a ruthenium-adsorbed structural material; and a reduction step of in situ reducing the ruthenium supported on the structural material using a reducing agent.

[0076] In one embodiment of the present invention, in step S3, the weight ratio of the structural material obtained in S2 to the ruthenium source is 1-100:1, preferably 5-50:1, and more preferably 5-20:1.

[0077] In one embodiment of the present invention, in step S3, the ruthenium source is not limited and can be selected from a water-soluble ruthenium salt, preferably ruthenium chloride (RuCl3). The ruthenium source can exist in a form containing or not containing bound water, for example, ruthenium chloride can be RuCl3·3H2O,

[0078] In one embodiment of the present invention, in step S3, the contact step of the structural material with the ruthenium source is carried out in the presence of a solvent, and the solvent is preferably a nitrogen-containing organic solvent, more preferably at least one selected from pyrrole, pyrazole, imidazole, pyridine, pyrimidine, pyrrolidone, and N-vinylpyrrolidone.

[0079] In one embodiment of the present invention, in step S3, the solvent used in the contacting step of the structural material with the ruthenium source is selected from a weakly alkaline solvent. Weakly alkaline organic solvents are conducive to the adsorption of Ru on the support surface. More preferably, the solvent is N-methylpyrrolidone (NMP).

[0080] In one embodiment of the present invention, in step S3, in order to better facilitate the adsorption of Ru ions, based on the total weight of the structural material obtained in S2 and the ruthenium source being 1 g, the amount of solvent used in the contacting step of S3 is 110-130 mL.

[0081] In one embodiment of the present invention, in step S3, the contacting conditions of the structural material and the ruthenium source are: a contact temperature of 40-80°C, preferably 50-70°C, and a contact time of 8-15 hours, preferably 10-12 hours. Preferably, the structural material and the ruthenium source are contacted under ultrasonic conditions, and the ultrasonic treatment can be performed for 1-5 hours.

[0082] In one embodiment of the present invention, in step S3, the product after contact is subjected to in-situ reduction to reduce the ruthenium salt to elemental ruthenium.

[0083] In one embodiment of the present invention, in step S3, the conditions of the reduction step are: the reducing agent is brought into contact with the structural material adsorbing ruthenium in the presence of a solvent, and the solvent is preferably a nitrogen-containing organic solvent, more preferably at least one selected from pyrrole, pyrazole, imidazole, pyridine, pyrimidine, pyrrolidone, and N-vinylpyrrolidone (NMP).

[0084] In one embodiment of the present invention, in step S3, the type of reducing agent in the reduction step is not particularly limited, as long as it can reduce Ru ions in situ. Preferably, the reducing agent is selected from NaHB4 and / or hydrogen, preferably NaHB4.

[0085] In one embodiment of the present invention, in step S3, the weight ratio of the reducing agent to the ruthenium source in the reduction step is 4-15:1, preferably 5-10:1.

[0086] In one embodiment of the present invention, in step S3, there is no particular limitation on the method for adding the reducing agent. To better mix the reducing agent with the structural material that adsorbs Ru ions so that the in-situ reduction reaction can proceed fully, the reducing agent can be first dissolved in a solvent, for example, in NMP, and then the solution containing the reducing agent is added to the feed solution containing the structural material that adsorbs ruthenium. The amount of reducing agent used in the present invention does not include the amount of solvent used to dissolve the reducing agent.

[0087] In one embodiment of the present invention, in step S3, the reduction step is performed under the following conditions: NaHB4 solution is added directly to the solution of the structural material adsorbing ruthenium obtained by contacting the structural material with the ruthenium source, and the solvent of the NaHB4 solution is the same as the solvent in the contact step.

[0088] In one embodiment of the present invention, in step S3, in the reduction step, the reduction reaction temperature is 15-40°C, preferably 20-30°C (eg room temperature), and the time is 0.5-2 hours, preferably 1-1.5 hours.

[0089] In one embodiment of the present invention, in step S3, in the reduction step, after the reduction reaction, a precipitant is further added to precipitate the reduction product, preferably the precipitant is acetone. In one embodiment of the present invention, based on 1 g of the reducing agent, the amount of acetone used is 40-60 mL.

[0090] In one embodiment of the present invention, in step S3, the product of the reduction reaction is dried under vacuum conditions at a temperature of 40-80° C., preferably 50-70° C., for 1.5-4 hours, preferably 2-3 hours.

[0091] In the present invention, in step S4, the reduction product obtained in step S3 is calcined at 600-1000°C to obtain a carbon nanotube-supported nitrogen-doped catalyst. This secondary high-temperature calcination forms highly active RuN and RuCo alloys, and the proportion of ruthenium in the form of RuN is within the range of the present invention, significantly enhancing the catalyst's activity.

[0092] In one embodiment of the present invention, in step S4, the calcination is performed under inert gas conditions.

[0093] In one embodiment of the present invention, in step S4, the calcination conditions are: heating to 600-1000°C at a heating rate of 5-20°C / min and maintaining for 1.5-4 hours, preferably at a heating rate of 8-15°C / min, preferably heating to 650-950°C, further preferably heating to 700-950°C, and preferably maintaining for 2-3 hours.

[0094] In the present invention, the product obtained from each reaction or step may be optionally washed. The solvent used for washing can be arbitrarily selected as needed and may be an aqueous solvent or an organic solvent, as long as it does not destroy the structure and morphology of the product. A readily volatile solvent is preferred, such as anhydrous ethanol. After washing, the product may be dried using conventional drying conditions in the art, such as the drying conditions described above.

[0095] In the present invention, the inert gas in step S2 and step S4 is independently selected from nitrogen and / or an inert gas, preferably selected from at least one of argon, helium and neon. Preferably, the protective gas in steps S2 and S4 is argon.

[0096] The Ru and Co contents of the prepared carbon nanotube-supported nitrogen-doped catalyst were determined by ICP characterization. Transmission electron microscopy revealed that the Ru particles were less than 5 nm in diameter and primarily distributed on the carbon nanotube surface, which is consistent with the XPS detection range. The RuN ratio was determined by fitting the peaks of high-valent Ru and zero-valent Ru in the Ru XPS spectrum using Thermo Avantage software. The ratio was calculated by integrating the peak areas.

[0097] A third aspect of the present invention provides an electrolytic electrode, which includes the carbon nanotube-supported nitrogen-doped catalyst of the present invention, or the carbon nanotube-supported nitrogen-doped catalyst prepared according to the method of the present invention.

[0098] A fourth aspect of the present invention provides a method for producing hydrogen by electrolysis of water, wherein the carbon nanotube-supported nitrogen-doped catalyst of the present invention or the carbon nanotube-supported nitrogen-doped catalyst prepared according to the method of the present invention is used. In addition, in the method for producing hydrogen by electrolysis of water of the present invention, the carbon nanotube-supported nitrogen-doped catalyst of the present invention or the carbon nanotube-supported nitrogen-doped catalyst prepared according to the method of the present invention can be used in an alkaline or alkaline membrane water electrolysis reaction to produce hydrogen.

[0099] In some embodiments of the present invention, the present invention provides the following technical solutions.

[0100] [Scheme 1] A Ru-containing catalyst for hydrogen evolution by water electrolysis, characterized in that the catalyst contains at least one of a tubular graphitized carbon structure, a layered graphitized carbon structure, and an amorphous graphitized carbon structure; the content of metallic Ru in the catalyst is 1-7wt%, and the average particle size of the metallic Ru is 2-5nm.

[0101] [Scheme 2] The catalyst according to [Scheme 1], characterized in that the content of Co element in the catalyst is 35-48wt%, and / or the content of Zn element is 0.001-2.5wt%, and / or the content of N element is 2-5wt%, and / or the content of C element is 48-60wt%;

[0102] Preferably, the average particle size of the catalyst is 200-600 nm.

[0103] [Scheme 3] A method for preparing a Ru-containing water electrolysis hydrogen evolution catalyst, characterized in that the preparation method comprises the following steps:

[0104] S1. In the presence of a first solvent, a cobalt source, a zinc source, and a nitrogen-containing organic ligand are first mixed and reacted to obtain a precursor;

[0105] S2. In the presence of a protective gas, calcining the precursor for the first time;

[0106] S3. In the presence of a second solvent, the product obtained in S2 and a ruthenium source are mixed for a second time, and then the mixed materials and a reducing agent are mixed for a third time and subjected to an in-situ reduction reaction;

[0107] S4. In the presence of a protective gas, the solid phase product obtained in S3 is subjected to a second calcination at 700-900°C.

[0108] [Scheme 4] The preparation method according to [Scheme 3] is characterized in that, in S1, the cobalt source, the zinc source and the nitrogen-containing organic ligand are first mixed in a weight ratio of (1.5-3):1:(4-12);

[0109] Preferably, the temperature of the first reaction is 20-30°C and the time is 10-36h;

[0110] Preferably, based on the total weight of the cobalt source, the zinc source and the nitrogen-containing organic ligand being 1 g, the amount of the first solvent used is 35-50 mL;

[0111] Preferably, the cobalt source is selected from water-soluble cobalt salts, preferably cobalt chloride and / or cobalt nitrate;

[0112] Preferably, the zinc source is selected from water-soluble zinc salts, preferably at least one selected from zinc nitrate, zinc sulfate and zinc chloride;

[0113] Preferably, the nitrogen-containing organic ligand is selected from 2-methylimidazole, preferably 2-methylimidazole;

[0114] Preferably, the first solvent is selected from C1-C4 monohydric alcohols, preferably methanol.

[0115] [Scheme 5] The preparation method according to [Scheme 3] or [Scheme 4] is characterized in that, in S2, the conditions of the first calcination include: heating to 700-900°C at a rate of 3-8°C / min, and maintaining at 700-900°C for 1.5-4h.

[0116] [Scheme 6] The preparation method according to any one of [Scheme 3] to [Scheme 5], characterized in that in S3, the product obtained in S2 and the ruthenium source are mixed in a weight ratio of (5-15):1;

[0117] Preferably, the temperature of the second mixing is 55-85°C and the time is 10-15h;

[0118] Preferably, based on the total weight of the product obtained in S2 and the ruthenium source being 1 g, the amount of the second solvent used is 110-130 mL;

[0119] Preferably, the ruthenium source is selected from water-soluble ruthenium salts, preferably RuCl3;

[0120] Preferably, the second solvent is selected from weakly alkaline organic solvents, preferably N-methylpyrrolidone.

[0121] [Scheme 7] The preparation method according to any one of [Scheme 3] to [Scheme 6], characterized in that the reducing agent is selected from NaHB4 and / or hydrogen, preferably NaHB4;

[0122] Preferably, based on the weight of the ruthenium source being 1 g, the amount of the reducing agent used is 4-8 g;

[0123] Preferably, the temperature of the in-situ reduction reaction is 20-30° C. and the time is 0.5-2 h.

[0124] [Scheme 8] The preparation method according to any one of [Scheme 3] to [Scheme 7] is characterized in that in S4, the conditions for the second calcination include: heating to 700-900°C at a rate of 8-15°C / min, and maintaining at 700-900°C for 1.5-4h.

[0125] [Scheme 9] A Ru-containing water electrolysis hydrogen evolution catalyst prepared by the preparation method described in any one of [Scheme 3] to [Scheme 8].

[0126] [Scheme 10] A method for producing hydrogen by electrolysis of water, characterized in that the method comprises: in the presence of a Ru-containing water electrolysis hydrogen evolution catalyst, electrifying an electrolyte to produce hydrogen; wherein the Ru-containing water electrolysis hydrogen evolution catalyst is the Ru-containing water electrolysis hydrogen evolution catalyst described in any one of [Scheme 1], [Scheme 2], and [Scheme 9].

[0127] Example

[0128] The present invention will be described in detail below through examples and comparative examples. In the following examples, unless otherwise specified, conventional methods are used; and the reagents and materials used, unless otherwise specified, can be obtained from commercial sources.

[0129] The contents of Co, Zn, Ru, N, and O were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an iCAP 6300 instrument, ThermoFisher.

[0130] X-ray photoelectron spectroscopy (XPS) was obtained using a PHIQuantera SXM instrument with a monochromated Al target (E = 1486.68 eV), 200 eV (Survey) (full spectrum), 50 eV (fine spectrum), energy steps: 1.000 eV (full spectrum), 0.100 eV (fine spectrum), and the bond energy was corrected by the C1s peak (284.8 eV).

[0131] The following examples are used to illustrate the preparation of the carbon nanotube-supported nitrogen-doped catalyst of the present invention.

[0132] Example 1

[0133] S1. Weigh 0.3 g of zinc nitrate (Zn(NO3)2·6H2O, 1 mmol) and 0.6 g of cobalt nitrate (Co(NO3)2·6H2O, 2.06 mmol) in 50 mL of methanol to obtain solution A. Then, dissolve 1.64 g of 2-methylimidazole (20 mmol) in 50 mL of methanol to obtain solution B. The two solutions are evenly mixed and stirred at room temperature for 12 hours. The product is centrifuged and washed with ethanol and dried at 60°C for later use. Figure 1 shows a scanning electron microscope image of the sample, which shows a regular dodecahedral morphology with an average size of 500 nm.

[0134] S2. Weigh 1g of the dried sample and grind it with 0.5g of melamine and place it in a tube furnace. Under argon conditions, the argon flow rate is adjusted to 20mL / min, and the temperature is raised to 950℃ at a heating rate of 5℃ / min, maintained for 2h, and naturally cooled to room temperature to obtain a black powder. Its microscopic morphology can be seen in Figure 2. After calcination, the original polyhedral morphology is transformed into a carbon tube structure. From the transmission electron microscopy characterization in Figure 3, it can be seen that the carbon tubes are coated with black particles, and the carbon tube diameter is 10-20nm. Further STEM energy spectrum scanning results (as shown in Figure 4) show that the black particles are cobalt particles, and the Co particle size is about 10nm. As shown in Figure 5, Fourier transform of the transmission electron microscopy characterization of the carbon tube structure can clearly see a large number of dislocation structures, indicating that the calcined carbon tube material is rich in surface defects. ICP was used to determine the element content. According to the ICP results, the composition of the Zn / Co-ZIF material after high-temperature calcination was C: 52wt%, Co: 42.5wt%, Zn: 2.5wt%, N: 3wt%, and a small amount of O element.

[0135] S3. Weigh 30 mg of RuCl3 and dissolve it in 40 ml of NMP. Then add 0.3 g of the above black powder, ultrasonicate for 2 hours, then heat and stir at 60°C for 12 hours, then slowly add 2 ml of NaHB4 / NMP solution (NaHB4 concentration is 0.1 g / mL), stir at room temperature for 1 hour, then add 10 ml of acetone solution, centrifuge, then wash three times with ethanol solution, and vacuum dry at 60°C for 2 hours.

[0136] S4. The catalyst was heated to 700°C under Ar gas at a heating rate of 10°C / min, maintained for 2 hours, and naturally cooled to room temperature to obtain a catalyst having a catalyst composition of 51 wt% C, 41.7 wt% Co, 0.5 wt% Zn, 2.8 wt% N, and 4 wt% Ru. The proportion of ruthenium in the form of RuN was 83.6 wt%.

[0137] The microscopic morphology of the catalyst is shown in Figure 6. After being loaded with Ru and calcined twice, the carbon tube structure becomes thicker, with a tube diameter of about 50nm, and is distributed with two metal particles of different sizes. From the STEM energy spectrum scan results in Figure 7, it can be seen that the large particles are Co structures with a size of about 50nm, and the small particles are Ru, with a size of about 2nm, and are evenly dispersed on the surface of the carbon tubes. Fourier transform of the layered structure of the carbon tubes shows that the carbon tube structure is a well-crystallized graphitized structure with obvious defect structures. The presence of defect sites in the carbon carrier increases the interaction between Ru and the carrier, and increases the adsorption amount and dispersion of Ru on its surface. In order to explore the existence state of the active components of the catalyst, XPS characterization was performed on the materials before and after loading Ru, and the characterization results are shown in Figures 9 and 10. Figure 9 shows that Co exists in various valence states, including zero and high valence states. Nitrogen exists in the more active forms of pyridinic N and metal-N, with inert graphitized N accounting for a very small fraction. The XPS results for carbon also reveal distinct CN bonds, indicating that Co exists in the forms of CoN and metallic Co (elemental Co and Co-Ru alloy). The XPS results for oxygen (O) primarily show surface hydroxyl groups (O) and a small amount of vacant oxygen, but the overall O content is low. Comparing the XPS results for the Ru-loaded sample (Figure 11), the Ru XPS spectrum (Figure 10) reveals that Ru exists in both zero and high valence states. The N XPS spectrum exhibits a significant shift, particularly in the peak position of the metal-N. The CN binding energy in the C XPS spectrum also shifts accordingly. These results indicate that the addition of Ru binds to nitrogen, leading to changes in the binding energy of nitrogen with both metal and carbon. Furthermore, XRD characterization before and after Ru loading (Figure 12) reveals a shift in the Co peak position and a relative broadening after Ru loading, indicating the presence of a RuCo alloy.

[0138] Example 2

[0139] A catalyst was prepared according to the method of Example 1, except that in step S2, the condition "heating to 950°C at a heating rate of 5°C / min" was replaced with "heating to 800°C at a heating rate of 5°C / min." The resulting catalyst was obtained. ICP analysis revealed that the catalyst composition was 51.5 wt% C, 41 wt% Co, 1.2 wt% Zn, 2.5 wt% N, and 3.5 wt% Ru. The proportion of ruthenium, in the form of RuN, was 85.2 wt%.

[0140] Example 3

[0141] A catalyst was prepared according to the method of Example 1, except that in S2, the condition "heating to 950°C at a heating rate of 5°C / min" was replaced with "heating to 700°C at a heating rate of 5°C / min." The resulting catalyst had a composition of 49 wt% C, 44.7 wt% Co, 2.5 wt% Zn, 2 wt% N, and 2.8 wt% Ru. The proportion of ruthenium, in the form of RuN, was 84.3 wt%.

[0142] Example 4

[0143] A catalyst was prepared according to the method of Example 1, except that in S2, the condition "heating to 950°C at a heating rate of 5°C / min" was replaced with "heating to 1100°C at a heating rate of 5°C / min." The resulting catalyst had a composition of 54.5 wt% C, 38 wt% Co, 3 wt% N, and 4.5 wt% Ru. The proportion of ruthenium, in the form of RuN, was 84.1 wt%.

[0144] Example 5

[0145] A catalyst was prepared according to the method of Example 1, except that in S4, the condition "heating to 900°C at a heating rate of 10°C / min" was replaced with "heating to 700°C at a heating rate of 10°C / min." The catalyst was prepared. The catalyst composition was C: 57.5wt%, Co: 35wt%, N: 3wt%, and Ru: 4.8wt%. Although the proportion of supported Ru was high, the increase in the secondary calcination temperature resulted in an increase in the Ru particle size. The proportion of ruthenium element in the form of RuN was 75.6wt%.

[0146] Example 6

[0147] The catalyst was prepared according to the method of Example 1, except that the amounts of zinc nitrate and cobalt nitrate were different. Specifically, in S1, the condition "Weigh 0.3 g of zinc nitrate (Zn(NO3)2·6H2O, 1 mmol) and 0.6 g of cobalt nitrate (Co(NO3)2·6H2O, 2.06 mmol) in 50 mL of methanol to obtain solution A" was replaced with "Weigh 0.15 g of zinc nitrate (Zn(NO3)2·6H2O, 0.5 mmol) and 0.3 g of cobalt nitrate (Co(NO3)2·6H2O, 1.03 mmol) in 50 mL of methanol to obtain solution A." The particle size of the Zn / Co-ZIF material was approximately 250 nm. According to ICP analysis, the composition of the prepared catalyst was C: 53.8 wt%, Co: 39 wt%, Zn: 0.1 wt%, N: 3 wt%, and Ru: 4.3 wt%. The proportion of ruthenium in the form of RuN was 85.8 wt%.

[0148] Example 7

[0149] A catalyst was prepared according to the method of Example 1, except that in S4, the condition "heating to 700°C at a heating rate of 10°C / min" was replaced with "heating to 950°C at a heating rate of 10°C / min." ICP analysis revealed that the Ru loading in the catalyst was 3.0 wt%. The proportion of ruthenium in the form of RuN was 70.3 wt%.

[0150] Example 8

[0151] A catalyst was prepared according to the method of Example 1, except that in S4, the condition "heating to 700°C at a heating rate of 10°C / min" was replaced with "heating to 800°C at a heating rate of 10°C / min." ICP analysis revealed that the Ru loading in the catalyst was 3.8 wt %. The proportion of ruthenium in the form of RuN was 78.6 wt %.

[0152] Example 9

[0153] The catalyst was prepared according to the method of Example 1, except that the ratio of zinc nitrate to cobalt nitrate was different. Specifically, in S1, the condition "0.3 g zinc nitrate (Zn(NO3)2·6H2O, 1 mmol) and 0.6 g cobalt nitrate (Co(NO3)2·6H2O, 2.06 mmol) were weighed in 50 mL of methanol to obtain solution A" was replaced with "0.45 g zinc nitrate (Zn(NO3)2·6H2O, 1.55 mmol) and 0.45 g cobalt nitrate (Co(NO3)2·6H2O, 1.55 mmol) were weighed in 50 mL of methanol to obtain solution A" to obtain the catalyst. After loading Ru, the catalyst composition was C: 62 wt%, Co: 26 wt%, Zn: 3.6 wt%, N: 3.7 wt%, and the Ru loading was 4.7 wt%. The proportion of ruthenium element in the form of RuN was 86.9 wt%.

[0154] Example 10

[0155] A catalyst was prepared according to the method of Example 1, except that in S2, the condition "weighing 1 g of the dry sample and grinding it with 1 g of melamine" was substituted for "weighing 1 g of the dry sample and grinding it with 0.5 g of melamine." ICP analysis revealed that the Ru loading in the catalyst was 1.8 wt %. The proportion of ruthenium in the form of RuN was 86.2 wt %.

[0156] Comparative Example 1

[0157] A catalyst was prepared according to the method of Example 1, except that melamine was not added during the primary calcination of S2. ICP analysis revealed a nitrogen loading of 1.1 wt %. As the nitrogen content decreased, the RuN content decreased, with more of the Ru present as an alloy of metallic Ru and RuCo. The proportion of ruthenium present as RuN was 4.3 wt %.

[0158] Comparative Example 2

[0159] A catalyst was prepared according to the method of Example 1, except that urea was used instead of melamine in the primary calcination step S2. ICP analysis revealed that the catalyst had a nitrogen loading of 1.3 wt %. The proportion of ruthenium in the form of RuN was 15.3 wt %.

[0160] Comparative Example 3

[0161] A catalyst was prepared according to the method of Example 1, except that the low-temperature reduction and loading of Ru was omitted from the secondary calcination at high temperature in S4. ICP analysis revealed that the catalyst had a Ru loading of 4.2 wt %. The proportion of ruthenium in the form of RuN was 6.4 wt %.

[0162] Comparative Example 4

[0163] A catalyst was prepared according to the method of Example 1, except that no zinc was added to the precursor in S1, and only Co was added to obtain Co-zif as the precursor. The obtained catalyst had a Ru loading of 0.2 wt % according to ICP analysis.

[0164] Test Example 1

[0165] Scanning electron microscopy was used to measure the SEM images of Zn / Co-ZIF materials and samples of Zn / Co-ZIF materials after high-temperature calcination; transmission electron microscopy was used to measure the TEM images of Zn / Co-ZIF materials and catalysts after high-temperature calcination; high-resolution transmission electron microscopy was used to measure the HRTEM images of Zn / Co-ZIF materials and catalysts after high-temperature calcination; and X-ray photoelectron spectroscopy was used to measure the XPS spectra of Co, N or C elements in samples of Zn / Co-ZIF materials after high-temperature calcination.

[0166] Test Example 2

[0167] The catalysts prepared in each embodiment and comparative example were fully ground, 10 mg of the catalyst was weighed, 1 mL of an ethanol solution containing Nafion (the volume content of Nafion was 4%) and 1 mL of an isopropanol solution were added, and the mixture was uniformly dispersed by ultrasound. 20 μL of the above dispersion (0.2 mg of catalyst) was measured and added dropwise to a rotating disk electrode for HER performance measurement. The electrochemical test experiment used a Shanghai Chenhua 760E electrochemical workstation. Before the test, N2 was passed through the electrolyte for about 30 minutes to saturate the electrolyte with N2. Subsequently, the three-electrode test system was assembled so that the voltage test range was set to (-0.1 to 0.1 V (vs. RHE)) and the number of test cycles was set to 20 cycles to fully activate the sample and fully expose the active sites; then, H2 was passed through the electrolyte using a hydrogen generator for 30 minutes to fully saturate the electrolyte with H2, and an LSV test was performed at -0.6 to 0 V. With 1 mol / L KOH as electrolyte, at 10 mA cm -2 The HER overpotentials of the catalysts prepared in various examples and comparative examples at current density are shown in Table 1. The LSV curves of the hydrogen evolution performance of the sample and catalyst of the Zn / Co-ZIF material calcined at high temperature in Example 1 of the present invention are shown in FIG13 .

[0168] Electrochemically active surface area (ECSA) is a key characteristic parameter for describing, analyzing, and comparing electrocatalysts. The determination of the mass activity of a given catalyst is linked to this parameter, thus enabling material benchmarking. In ECSA testing, the current-voltage curve is measured in the non-Faraday region. Its magnitude can be directly expressed as electrochemical double layer capacitance (Cdl).

[0169] When calculating the electrochemically active area (ECSA) of the electrode using cyclic voltammetry, nitrogen was continuously introduced for 20 min. During the test, nitrogen was continuously introduced at different scan rates (10-100 mV s -1 ) to obtain a CV curve. A linear fit is performed, with half the current difference at the midpoint of the potential range as the vertical axis and the scan rate as the horizontal axis. The slope of the resulting line is the double-layer capacitance of the electrode. The effective electrochemical active area can be calculated using the following formula.

[0170] ECSA=C dl / C s

[0171] Table 1

[0172] As can be seen from Figure 13, a small amount of Ru (Ru loading 0.1 mg cm -2 ) after which the catalyst was exposed to 10 mA cm -2 The hydrogen evolution overpotential is 43 mV at a current density of 100 mA cm -2 The overpotential is 130 mV at a current density close to that of commercial PtC (Pt loading 0.4 mg cm -2 ) catalyst (as shown in Figure 15).

[0173] The overpotential of the electrolytic water hydrogenation catalyst obtained by Examples 1-10 and Comparative Examples 1-4 is within 70mV, and Comparative Example 1 does not adopt nitrogen doping agent, and Comparative Example 2 adopts urea as nitrogen doping agent. After doping, nitrogen element is less, and it is confirmed that only a small amount of Ru-N is formed through characterization. As a result, the overpotential of the electrolytic water hydrogenation catalyst obtained by Comparative Examples 1 and 2 is significantly increased, indicating that the interaction between nitrogen element and metal (particularly between nitrogen element and ruthenium element) can significantly improve the hydrogen evolution activity of the catalyst. Comparative Example 3 does not adopt secondary high-temperature roasting after loading Ru, and it is confirmed that only a small amount of Ru-N is formed through characterization. As a result, hydrogen evolution performance is significantly lower than the sample of secondary roasting. Studies have shown that after high-temperature roasting, Ru can form better interactions with carrier and Co by forming nitride and alloy, thereby improving the intrinsic activity of the catalyst. In Comparative Example 4, no Zn element was added to the synthetic carrier precursor, and Co-ZIF was synthesized. Since no more defect sites were formed after the first high-temperature calcination, it was difficult for the Ru element to be loaded onto the carrier through a low-temperature reduction process, and thus the Ru loading amount was very low.

[0174] In addition, although the ratio of loaded Ru in Example 5 is high, the utilization efficiency of Ru is not high because the increase in secondary temperature will cause the particle size of Ru to increase.

[0175] Examples 6 and 9 both adjusted the amount and ratio of the zinc source and the cobalt source. Compared with Example 1, in the catalyst obtained in Example 6, due to the reduced amount, the synthesized CoZn-ZIF particle size was smaller, the high-temperature carbonization process was more sufficient, and the loaded Ru content was improved. Accordingly, Example 9 increased the ratio of Zn and the ratio of Co, and more defect sites were obtained, thereby increasing the loading rate of Ru, but the content of Co was reduced. This shows that when the ratio of the amount of zinc source and the cobalt source meets the preferred conditions, the hydrogen evolution activity of the catalyst can be further improved. Example 10 increases the addition ratio of the nitrogen dopant, and the results show that the nitrogen dopant has an effect on the hydrogen evolution activity of the catalyst.

[0176] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. Carbon nanotube-supported nitrogen-doped catalyst, wherein: The catalyst has a carbon nanotube structure as a carrier, and cobalt and ruthenium as active components, wherein the content of cobalt element is 30-45wt% relative to the total amount of the catalyst, the content of ruthenium element is 1-7wt%, and the proportion of ruthenium element in the form of RuN relative to all ruthenium elements is 60wt% to 90wt%, preferably 65wt% to 88wt%, and more preferably 70wt% to 85wt%.

2. The catalyst according to claim 1, wherein The ruthenium element also exists in the form of metallic ruthenium and cobalt-ruthenium alloy.

3. The catalyst according to claim 1 or 2, wherein The content of nitrogen is 2-5 wt %, and the nitrogen exists in the form of at least one of metal-N, pyridinic nitrogen and graphitized nitrogen.

4. The catalyst according to any one of claims 1 to 3, wherein The catalyst satisfies at least one of the following conditions: The average particle size of metallic ruthenium is 2-5nm; The diameter of the carbon nanotube is 30-70nm; The carbon nanotubes have defect sites; The oxygen content is 2 wt% or less, preferably 1% or less, and more preferably 0.5% or less; The zinc content is 5 wt% or less, preferably 4% or less.

5. A method for preparing a carbon nanotube-supported nitrogen-doped catalyst, wherein: The preparation method comprises the following steps: S1, mixing a cobalt source, a zinc source and a nitrogen-containing organic ligand in a solvent for a first reaction, and obtaining a CoZn-zif precursor after separation and drying; S2. In an inert gas and in the presence of a nitrogen dopant, the CoZn-zif precursor obtained in S1 is carbonized and nitrogen-doped to obtain a carbon nanotube-coated cobalt structural material, wherein an organic compound having more than 3 nitrogen atoms is used as a nitrogen dopant in the nitrogen doping; S3, contacting the structural material obtained in S2 with a ruthenium source to load ruthenium, and using a reducing agent to reduce the ruthenium loaded on the structural material; S4, calcining the product of step S3 at 600-1000° C. to obtain a carbon nanotube-supported nitrogen-doped catalyst.

6. The preparation method according to claim 5, wherein: The condition of step S1 satisfies at least one of the following conditions: The cobalt source is selected from water-soluble cobalt salts, preferably at least one selected from cobalt chloride and cobalt nitrate; The zinc source is selected from water-soluble zinc salts, preferably at least one selected from zinc nitrate, zinc sulfate and zinc chloride; The nitrogen-containing organic ligand is selected from optionally substituted imidazole compounds, preferably 2-methylimidazole; The weight ratio of the cobalt source, the zinc source and the nitrogen-containing organic ligand is (0.5-4):1:(2-14), preferably (0.8-3):1:(3-12); The solvent is selected from C1-C4 monohydric alcohol, preferably methanol or ethanol, and the total weight of the cobalt source, the zinc source and the nitrogen-containing organic ligand is 1g, and the amount of the solvent is 20-60ml, preferably 35-50ml; The temperature of the first reaction is 20-30°C and the time is 10-36h; The separation is performed by any one means selected from filtration and centrifugation; The drying temperature is 40-80°C, preferably 50-70°C.

7. The preparation method according to claim 5 or 6, characterized in that: The condition of step S2 satisfies at least one of the following conditions: The conditions for carbonization and nitrogen doping are: heating at a heating rate of 1-10°C / min, heating to 600-1200°C and maintaining for 1.5-4 hours, preferably heating at a rate of 3-8°C / min, preferably heating to 700-1100°C, and preferably maintaining for 2-3 hours; The organic compound having 3 or more nitrogen atoms is a 5-10-membered cyclic organic compound having 3 or more ring nitrogen atoms, preferably at least one selected from triazole compounds, triazine compounds, and melamine, and more preferably at least one selected from optionally substituted 1,2,3-triazole, optionally substituted 1,2,4-triazole, optionally substituted 1,2,3-triazine, optionally substituted 1,2,4-triazine, optionally substituted 1,2,3-triazine, and melamine; The weight ratio of the CoZn-zif precursor to the nitrogen dopant is 1:0.1-5, preferably 1:0.2-1.

8. The preparation method according to any one of claims 5 to 7, wherein The condition of step S3 satisfies at least one of the following conditions: The weight ratio of the structural material obtained in S2 to the ruthenium source is 1-100:1, preferably 5-50:1, and more preferably 5-20:1; The ruthenium source is selected from water-soluble ruthenium salts, preferably ruthenium chloride (RuCl3); The contacting is carried out in the presence of a solvent, and the solvent is preferably a nitrogen-containing organic solvent, and more preferably at least one selected from pyrrole, pyrazole, imidazole, pyridine, pyrimidine, pyrrolidone, and N-vinylpyrrolidone; The contact conditions are: contact temperature of 40-80°C, preferably 50-70°C, contact time of 8-15 hours, preferably 10-12 hours, and ultrasonic treatment is optionally performed during contact; The weight ratio of the reducing agent to the ruthenium source is 4-15:1, preferably 5-10:1; The conditions of the reduction step are: contacting the reducing agent with the structural material loaded with ruthenium in the presence of a solvent, the solvent is preferably a nitrogen-containing organic solvent, more preferably at least one selected from pyrrole, pyrazole, imidazole, pyridine, pyrimidine, pyrrolidone, and N-vinylpyrrolidone, the reducing agent is NaHB4 or hydrogen, and the conditions of the reduction step are preferably: adding a NaHB4 solution to the solution of the structural material loaded with ruthenium, the solvent of the NaHB4 solution is preferably the same as the solvent in the contacting step; after the reduction, further adding a precipitant to precipitate the reduction product, preferably the precipitant is acetone; The reduction reaction temperature is 15-40°C, preferably 20-30°C, and the time is 0.5-2 hours, preferably 1-1.5 hours; The product of the reduction reaction is dried under vacuum conditions at a temperature of 40-80° C., preferably 50-70° C., for a drying time of 1.5-4 hours, preferably 2-3 hours.

9. The preparation method according to any one of claims 5 to 8, wherein The roasting conditions of step S4 are: Under inert gas conditions, the temperature is increased to 600-1000°C at a heating rate of 5-20°C / min and maintained for 1.5-4 hours, preferably at a heating rate of 8-15°C / min, preferably increased to 650-950°C, further preferably increased to 700-950°C, and preferably maintained for 2-3 hours.

10. An electrolytic electrode comprising the carbon nanotube-supported nitrogen-doped catalyst according to any one of claims 1 to 4, or the carbon nanotube-supported nitrogen-doped catalyst prepared by the method according to any one of claims 5 to 9.

11. A method for producing hydrogen by electrolysis of water, characterized in that: The carbon nanotube-supported nitrogen-doped catalyst according to any one of claims 1 to 4 is used, or the carbon nanotube-supported nitrogen-doped catalyst prepared by the method according to any one of claims 5 to 9 is used.

12. A method for producing hydrogen by electrolysis of water, characterized in that: In an alkaline or alkaline membrane water electrolysis reaction to produce hydrogen, the carbon nanotube-supported nitrogen-doped catalyst according to any one of claims 1 to 4 is used, or the carbon nanotube-supported nitrogen-doped catalyst prepared by the method according to any one of claims 5 to 9 is used.

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