Preparation method and application of transition metal single-atom porous carbon-based noble metal catalyst

Abstract

This application relates to the field of hydrogen production through water electrolysis and provides a method for preparing and applying a transition metal single-atom porous carbon-based noble metal catalyst. The method includes: preparing a transition metal-doped ZIF-8 precursor; adding an alcohol-water solution of a template agent to the transition metal-doped ZIF-8 precursor, grinding and drying, pyrolyzing, cooling, washing with water, and filtering to obtain a mesoporous transition metal-nitrogen-carbon composite material; mixing the mesoporous transition metal-nitrogen-carbon composite material with an ammonia source precursor and pyrolyzing it under an inert atmosphere to obtain a transition metal-nitrogen-carbon composite material rich in micropores and mesopores; and obtaining the transition metal single-atom porous carbon-based noble metal catalyst using chemical vapor deposition. The above preparation method overcomes the problems of active site agglomeration and deactivation, severe bubble exclusion, and high mass transfer polarization at the three-phase interface in existing anion exchange membrane electrolysis cathode catalysts at high current densities.

Description

Technical Field

[0001] This application relates to the field of water electrolysis for hydrogen production technology, specifically to a method for preparing and applying a transition metal single-atom porous carbon-based noble metal catalyst. Background Technology

[0002] Anion exchange membrane electrolysis combines the high current density of proton exchange membrane electrolysis with the advantages of alkaline electrolysis using non-precious metal / low-precious metal materials, and is considered a highly promising next-generation large-scale hydrogen production technology. In anion exchange membrane electrolysis, the efficiency of the cathode hydrogen evolution reaction directly determines the overall energy consumption and hydrogen production cost.

[0003] Currently, commercially available cathode catalysts mainly rely on supported nanoparticle catalysts such as carbon-supported platinum. However, under long-term high current density operation and complex alkaline electrolyte environments, traditional nanoparticle catalysts face severe problems of activity decay and stability failure. The main reasons are the weak interaction between nanoparticles and the support, leading to severe dissolution, migration, aggregation, and detachment of nanoparticles during harsh electrochemical processes; in addition, the limited porosity of the carbon support results in the accumulation of hydrogen bubbles on the electrode surface at high current densities, leading to a bubble shielding effect, which in turn causes the active sites to be covered and deactivated, as well as significant mass transfer limitation.

[0004] Chinese patent CN110201696A discloses a method for supporting noble metals on porous carbon fibers. The noble metal nanoparticles are achieved on a porous carbon substrate with a mesoporous structure through a strategy of metal-organic framework confinement and electrospinning. Although the porous structure increases the specific surface area and achieves high dispersion of nanoparticles, the nanoparticles still face severe surface energy-driven deactivation due to the weak metal-support interaction. In addition, the bubble shielding effect is still significant under high current density in a single mesoporous structure.

[0005] Chinese patent CN112421062A discloses a method for preparing a single-atom iron-dispersed / silver nanoparticle composite catalyst. It simply loads the silver nanoparticle composite catalyst onto an iron-containing single-atom carbon support. Although the interaction between the nanoparticles and the support is enhanced by the synergistic effect between the iron single atoms and the nanoparticles, the support used in this technology is mostly randomly distributed porous carbon with micropores as the main component, and it lacks a systematic porosity gradient design.

[0006] Therefore, the cathode hydrogen evolution catalysts prepared by the relevant technologies currently have poor stability in actual anion exchange membrane water electrolysis devices, especially under high current density, they are rapidly deactivated due to the aggregation and dissolution of nanoparticles. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a transition metal single-atom porous carbon-based noble metal catalyst and its application.

[0008] To achieve the above objectives, this application provides a method for preparing a transition metal single-atom porous carbon-based noble metal catalyst, comprising the following steps:

[0009] (1) A first solution is prepared by dissolving a transition metal source and zinc nitrate hexahydrate in a first solvent; a second solution is prepared by dissolving 2-methylimidazole in a second solvent; the first solution and the second solution are mixed evenly and then aged; after aging, the mixture is cooled to room temperature, the precipitate is separated and collected, and the precipitate is washed and dried to obtain the transition metal-doped zeolite imidazole ester framework-8 (ZIF-8) precursor. (2) Add an alcohol-water solution containing a template agent to the transition metal-doped ZIF-8 precursor, grind and mix it, dry it, and then pyrolyze it. After the pyrolysis treatment is completed, cool it to room temperature, wash it with water, and filter it to obtain a transition metal-nitrogen-carbon composite material rich in mesopores. (3) The mesoporous transition metal-nitrogen-carbon composite material is mixed with an ammonia source precursor and subjected to pyrolysis treatment under an inert atmosphere to obtain a transition metal-nitrogen-carbon composite material rich in micropores and mesopores. (4) Using chemical vapor deposition, platinum group metal sources are loaded onto the surface of transition metal-nitrogen-carbon composite materials rich in micropores and mesopores to obtain transition metal single-atom porous carbon-based noble metal catalysts.

[0010] In one embodiment, in step (1), the transition metal source is selected from any one of iron source, cobalt source, nickel source, and copper source; the first solvent is selected from at least one of methanol and water; and the second solvent is selected from at least one of methanol and water.

[0011] In one embodiment, in step (1), the mass ratio of zinc nitrate hexahydrate, transition metal source, and 2-methylimidazole is (5.0-8.0):(0.1-1.0):(5.0-10.0), and the molar ratio of the transition metal to zinc in zinc nitrate hexahydrate is 1:10-1:50; The volume ratio of the first solvent to the total mass of the transition metal source and zinc nitrate hexahydrate is 40-100 mL: 1 g; the volume ratio of the second solvent to the mass of 2-methylimidazole is 40-100 mL: 1 g. The aging temperature is 60 ℃ and the aging time is 6-48 h; the vacuum drying temperature is 25-80 ℃ and the drying time is 8-48 h.

[0012] In one embodiment, in step (2), the template agent is selected from any one of sodium chloride, potassium chloride, tannic acid and lithium chloride; the mass ratio of the transition metal-doped ZIF-8 precursor to the template agent is 1:0.5-1:3; The concentration of the template agent in an alcoholic aqueous solution is 20-80 mg / mL; In step (2), the pyrolysis treatment method includes: placing the mixed powder obtained by mixing the transition metal-doped ZIF-8 precursor and the template agent in a tube furnace, heating it to 950-1100℃ at a heating rate of 5℃ / min under an argon atmosphere, and holding it at that temperature for 2 h.

[0013] In one embodiment, the pyrolysis treatment method in step (3) includes: placing a mixed powder of a transition metal-nitrogen-carbon composite material rich in mesoporous material and ammonia source precursor in the heating zone of the tubular furnace, placing the ammonia source precursor in the non-heating zone of the tubular furnace, and heating the heating zone of the tubular furnace to 750-1000 ℃ at 5-20 ℃ / min under an argon atmosphere, and then pushing the ammonia source precursor in the non-heating zone of the tubular furnace into the heating zone of the tubular furnace for calcination, with a calcination time of 30-120 min.

[0014] In one embodiment, in step (3), the ammonia source precursor is selected from any one of ammonium iodide, ammonium chloride, ammonium bromide and ammonium fluoride; The mass ratio of the mesoporous transition metal-nitrogen-carbon composite material in the heating zone of the tubular furnace, the ammonia source precursor in the heating zone of the tubular furnace, and the ammonia source precursor in the non-heating zone of the tubular furnace is 1:(5-15):(5-10).

[0015] In one embodiment, in step (4), the chemical vapor deposition method includes: placing a platinum group metal source, a high-temperature resistant quartz filter membrane, and a transition metal-nitrogen-carbon composite material rich in micropores and mesopores in a ceramic boat from bottom to top. After covering, the ceramic boat is placed in a tube furnace. Under an argon atmosphere, the tube furnace is first heated to 150-300 ℃ at a rate of 5-15 ℃ / min and held for 30-60 min. Then, it is heated to 700-1000 ℃ at a rate of 5-25 ℃ / min and held for 60-120 min.

[0016] In one embodiment, the platinum group metal source is selected from any one of ruthenium source, platinum source, iridium source, and palladium source.

[0017] In one embodiment, the mass ratio of the transition metal-nitrogen-carbon composite material rich in micropores and mesopores to the platinum group metal source is 1:0.2-1:4.

[0018] Based on a general inventive concept, this invention also provides the application of the transition metal single-atom porous carbon-based noble metal catalyst prepared by the above-described method in anion exchange membrane water electrolysis for hydrogen production.

[0019] The technical principle of this invention is: the transition metal single-atom porous carbon-based noble metal catalyst prepared by this invention... By employing a bimolecular etching technique using template agents and ammonia-based precursors, the porosity of carbon carriers can be optimized and controlled. High dispersion and high exposure rate of noble metal nanoparticles can be achieved through chemical vapor deposition.

[0020] The molecular template of the template agent is used to optimize and control the mesoporous structure of the carbon support; the ammonia gas generated by the high-temperature decomposition of the ammonia source precursor is used to optimize and control the microporous structure of the carbon support, and finally the porosity of the carbon support is gradient adjustable, so as to realize the controllable construction of carbon supports with different porosities.

[0021] Micropores provide ample coordination sites for transition metal single atoms and confined anchoring sites for noble metal nanoparticles, while mesopores are used to improve the dispersion of noble metal nanoparticles and enhance mass transport during catalysis.

[0022] Compared to traditional impregnation methods, chemical vapor deposition (CVD) is advantageous for improving the dispersion of noble metal nanoparticles and their exposure rate during electrocatalytic testing. Under high-temperature conditions, ultra-small gaseous noble metal species diffuse into the hierarchical porous structure, subsequently depositing to form nanoparticles. The abundant pore structure significantly reduces the probability of aggregation and migration between noble metal particles due to the large distances between them, thus achieving spatial confinement of the nanoparticles. The presence of transition metal single atoms further anchors the noble metal nanoparticles through chemical electronic interactions, ultimately achieving high dispersion and exposure rate of the noble metal nanoparticles on the porous carbon support.

[0023] Spatial confinement utilizes the curved geometry and pore size distribution of dual continuous channels to physically confine noble metal components within a nanoscale space, effectively suppressing their migration and aggregation under the high current density scouring of water electrolysis by anion exchange membranes.

[0024] Spatial confinement enables highly efficient "liquid in, gas out" mass transport. Traditional catalysts, under high current densities, are prone to bubble aggregation, leading to difficulties in reactant entry and product exit, resulting in limited mass transfer and catalyst deterioration. This invention introduces a spatial confinement effect. On one hand, the capillary force generated by the confined channels actively draws the electrolyte into deeper sites, acting like a micro-pump, ensuring liquid entry. On the other hand, geometric constraints disrupt the equilibrium of bubble growth, forcing the generated gas to rapidly desorb in the form of microbubbles. The hierarchical porous carbon network carrier in this catalyst achieves physical separation of gas and liquid channels, ensuring rapid gas exit. The extremely low overpotential and ultra-long cycle life exhibited in the apparent activity are a direct manifestation of the mass transfer advantages brought about by this spatial confinement effect.

[0025] Interface confinement is achieved through atomically dispersed MN x The strong metal-support interaction between the sites and noble metal particles modulates the electronic structure of the active components, lowers the water dissociation energy barrier, and enhances chemical stability. A strong interaction exists between noble metal nanoparticles and transition metal single atoms; the noble metal donates electrons, and the transition metal accepts electrons, leading to a decrease in the oxidation state of the transition metal. Therefore, a strong interaction exists between the noble metal nanoparticles and the carbon support containing transition metal single atoms. Because of this electronic interaction, the intrinsic hydrogen evolution activity of the noble metal nanoparticles is optimized, and the dissolution / detachment probability of the noble metal nanoparticles is reduced, thereby enhancing device stability.

[0026] Based on the synergistic optimization of dual confinement, the spatial confinement effect of the hierarchical porous framework achieves uniform dispersion and physical isolation of active components in three-dimensional space. Simultaneously, the strong electronic coupling at the interface between transition metal single atoms and noble metals (i.e., interface confinement) synergistically optimizes the electronic structure of active sites and strengthens interfacial bonding. This dual confinement mechanism significantly reduces the adsorption energy barrier of intermediates and effectively inhibits catalyst aggregation and loss during long-term operation. Ultimately, this results in the high-efficiency performance of the composite catalyst in anion exchange membrane water electrolysis, providing a material selection for the preparation of highly active and stable anion exchange membrane water electrolysis cathode catalysts.

[0027] Compared with the prior art, this application has the following beneficial effects: This invention utilizes the abundant hierarchical channels generated by a bimolecular etchant to achieve rapid removal of product hydrogen and rapid permeation of reactant water molecules, ensuring operation at high current densities (1000 mA cm⁻¹). -2This invention achieves long-term operational stability under various conditions. It utilizes the interfacial synergy between transition metal single-atom sites and noble metal nanoparticles to lower the water dissociation energy barrier in the alkaline environment of anion exchange membrane water electrolysis, providing intrinsic activity for the composite catalyst in the alkaline cathode hydrogen evolution reaction. Furthermore, it anchors the platinum group metal source through the spatial topological confinement of the carbon support and the electronic interaction between transition metal single atoms and noble metal nanoparticles, suppressing their aggregation, shedding, and dissolution tendencies during long-term cycling. By utilizing the synergistic effect of transition metal single atoms and noble metal nanoparticles, this invention maximizes atom utilization, achieving excellent intrinsic activity while reducing noble metal loading, providing key material support for large-scale, low-cost anion exchange membrane water electrolysis hydrogen production. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The above are bar charts showing the specific surface area and pore volume of the carbon supports in Example 1 and Comparative Example 1 of this invention. Figure 2 In Figure a, the composite catalyst Fe-HNC@Ru prepared in Example 1 of this invention is represented by an aberration-corrected electron tomography three-dimensional reconstruction. Figure 2 From left to right, in the middle a are the three-dimensional model, three-dimensional reconstruction image, three-dimensional slice image, and closest distance distribution image of the composite catalyst Fe-HNC@Ru prepared in Example 1; Figure 2 In Figure b, the aberration-corrected electron tomography three-dimensional reconstruction of the composite catalyst Fe-NC@Ru prepared in Comparative Example 1 of this invention is shown. Figure 2 From left to right in the middle b are the three-dimensional model, three-dimensional reconstruction image, three-dimensional slice image, and closest distance distribution image of the composite catalyst Fe-NC@Ru prepared in Comparative Example 1; Figure 3 In Figure a, the fine structure spectrum of iron K-edge extended X-ray absorption based on synchrotron radiation is shown in Embodiment 1 and Comparative Example 1 of the present invention. Figure 3 In Figure b, the fine structure spectra of ruthenium K-side extended X-ray absorption based on synchrotron radiation are shown in Embodiment 1, Comparative Example 1, and Comparative Example 2 of this invention. Figure 4 The linear sweep voltammetry curves of Embodiment 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention are shown below. Figure 5 The linear scan voltammetry curves for Embodiments 1, 2, and 3 of this invention are shown below. Figure 6 These are Tafel curves of Embodiment 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention; Figure 7 The bar charts for exchange current density, mass activity, and conversion frequency of Embodiment 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention at an overpotential of 100 mV are shown below. Figure 8 The polarization curves are for Embodiment 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention. Figure 9 This is a time potential curve of long-term stability in Embodiment 1 of the present invention. Detailed Implementation

[0030] To facilitate understanding of this application, the following description will be more comprehensive and detailed in conjunction with the accompanying drawings and preferred embodiments, but the scope of protection of this application is not limited to the following specific embodiments.

[0031] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of this application.

[0032] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0033] Example 1 A transition metal single-atom porous carbon-based noble metal catalyst includes the following steps: (1) Preparation of transition metal-doped zeolite imidazole ester framework-8 (ZIF-8) 6.78 g of zinc nitrate hexahydrate and 400 mg of ferric nitrate nonahydrate were dissolved in 500 mL of methanol to form the first solution. Separately, 7.88 g of 2-methylimidazole was dissolved in 500 mL of methanol to form the second solution. The first and second solutions were mixed evenly in a 2 L single-necked flask, sealed, and aged in a 60 °C oven for 24 h. After aging and cooling to room temperature, the precipitate was collected by centrifugation, washed three times with methanol solution, and then vacuum dried at 60 °C for 12 h to obtain a light yellow Fe-ZIF-8 powder.

[0034] (2) Fe-ZIF-8 treated by template method Weigh 1.2 g of Fe-ZIF-8 sample and place it in a grinding apparatus. Add 40 mg / mL of sodium chloride in methanol / water solution (30 mL in total) in batches. After thorough grinding and drying, a mixed powder is obtained. Place the mixed powder in a quartz tube in a tube furnace and heat it to 1000 ℃ at a rate of 5 ℃ / min under an argon atmosphere. Hold the temperature at 1000 ℃ for 2 h. After calcination and cooling to room temperature, remove the sample, wash it with a large amount of water, and filter the sample to obtain Fe-NC@NaCl rich in mesoporous material.

[0035] The Fe-NC@NaCl mentioned in this invention refers to an iron-nitrogen co-doped carbon-based composite material prepared using sodium chloride as a template agent, wherein Fe-NC represents the iron-nitrogen-carbon component, the @ symbol represents the composite relationship, and NaCl represents sodium chloride.

[0036] (3) Ammonia source precursor treatment Fe-NC@NaCl Weigh out 400 mg of Fe-NC@NaCl and 4000 mg of ammonium iodide mixed powder and place it in a porcelain boat. Place the porcelain boat in the quartz tube corresponding to the heating zone of the tube furnace. Place the porcelain boat containing 2000 mg of ammonium iodide in the quartz tube corresponding to the non-heating zone of the tube furnace. Under an argon atmosphere, heat the heating zone of the tube furnace at 10 °C / min to 850 °C. When the temperature reaches 850 °C, move the quartz tube so that the 2000 mg of ammonium iodide located in the non-heating zone of the tube furnace is moved to the heating zone for calcination. The porcelain boat containing the Fe-NC@NaCl and ammonium iodide mixed powder remains in the heating zone of the tube furnace. After calcination at 850 °C for 60 min, cool to room temperature and collect the fluffy sample, which is Fe-HNC rich in micropores and mesopores.

[0037] The Fe-HNC mentioned in this invention refers to an iron-doped porous nitrogen-rich carbon composite material, where HNC is a highly nitrogen-doped porous carbon support, and the Fe active component is uniformly dispersed in the highly nitrogen-doped porous carbon framework.

[0038] During the heating process to 850℃, when the temperature reaches above 300℃, ammonium iodide located in the heating zone of the tubular furnace begins to decompose, generating ammonia and hydrogen iodide. Between 500℃ and 700℃, the decomposition rate of ammonium iodide in the heating zone accelerates, significantly increasing the concentrations of ammonia and hydrogen iodide within the quartz tube. This intensifies the homolytic cracking reaction of hydrogen iodide, leading to increased concentrations of hydrogen and iodine free radicals, which begin to etch the carbon support. Specifically, ammonia reacts with defective carbon to generate hydrogen cyanide and hydrogen, etching the carbon support, while hydrogen free radicals react with amorphous carbon to generate methane, producing the etching effect.

[0039] At 700 ℃-850 ℃, the ammonium iodide located in the heating zone of the tubular furnace is basically completely decomposed, while ammonia and hydrogen free radicals still react with defective carbon and amorphous carbon respectively, producing a significant etching effect on the carbon support.

[0040] When the constant temperature calcination was maintained at 850 °C for 60 min, the ammonium iodide located in the heating zone of the tube furnace was completely consumed, and the ammonia concentration in the quartz tube gradually decreased (due to the etching reaction and argon purging). At this time, the ammonium iodide located in the non-heating zone of the tube furnace was pushed to the heating zone of the tube furnace to replenish the ammonia and ensure the stability of the etching effect; during the constant temperature calcination, ammonia and hydrogen free radicals continuously etched the carbon support.

[0041] When Fe-NC@NaCl is mixed with ammonium iodide and placed in the heating zone of a tube furnace, the ammonia and hydrogen radicals generated by the decomposition of ammonium iodide can fully contact the carbon support, achieving uniform etching of the carbon support throughout the heating process. If all the ammonium iodide is placed in the non-heated zone of the tube furnace, the diffusion of ammonia during the heating stage will be delayed, easily leading to over-etching on the surface of the carbon support, insufficient internal etching, and uneven doping distribution. Therefore, a portion of ammonium iodide is reserved in the non-heated zone of the tube furnace to supplement ammonia during the 850 ℃ isothermal calcination stage, ensuring stable etching results.

[0042] Ammonium iodide located in the non-heating zone of the tubular furnace is kept at an appropriate distance from ammonium iodide located in the heating zone of the tubular furnace. During the heating stage to 850 °C, the ammonium iodide located in the non-heating zone of the tubular furnace will not undergo significant decomposition.

[0043] (4) Chemical vapor deposition of noble metal nanoparticles on porous carbon support To ensure high dispersibility of ruthenium nanoparticles, a top-to-bottom chemical vapor deposition method was employed: 10 mg of ruthenium acetylacetone was placed at the bottom of a 20 × 30 cm ceramic boat, followed by a layer of high-temperature resistant quartz filter membrane placed in the middle of the boat; finally, 20 mg of Fe-HNC was weighed and spread evenly on the filter membrane, the boat was capped, and then placed inside a quartz tube in a tube furnace. Under an argon atmosphere, the tube furnace was first heated to 200 °C at a rate of 10 °C / min and held for 30 min, then further heated to 800 °C at a rate of 10 °C / min and held for 2 h. After the reaction was complete and cooled to room temperature, the final composite catalyst Fe-HNC@Ru was obtained.

[0044] The Fe-HNC@Ru described in this invention refers to a composite catalytic material formed by loading ruthenium onto the surface or pores of Fe-HNC as a support, wherein the @ symbol represents the supported or composite structure.

[0045] The content of each metal element in the final composite catalytic material was determined by inductively coupled plasma mass spectrometry, and the element mass fraction was calculated, where Fe was 1.83 wt% and Ru was 6.18 wt%.

[0046] The principle of sequentially laying ruthenium acetylacetone, a high-temperature resistant quartz filter membrane, and an Fe-HNC support from bottom to top is as follows: The quartz filter membrane has uniform pores, allowing the vaporized noble metal precursor to pass through smoothly; the gaseous noble metal source first penetrates the filter membrane uniformly, and then seeps upwards from the bottom of the carbon support, fully entering the internal pores and interparticle gaps of the support, rather than merely skimming over the outer surface of the support. This results in a wider contact range and more thorough action, allowing for uniform contact between the vaporized noble metal source and the carbon support throughout the entire process. In traditional horizontal chemical vapor deposition, the vaporized noble metal source is easily swept away by the lateral airflow, only achieving effective contact with the surface layer of the carbon support, which can easily lead to uneven loading of the noble metal active components.

[0047] Example 2 The preparation method of the transition metal single-atom porous carbon-based noble metal catalyst in this embodiment is the same as that in Example 1, except that the mass ratio of Fe-HNC rich in micropores and mesopores to ruthenium acetylacetone is 1:0.2.

[0048] Example 3 The preparation method of the transition metal single-atom porous carbon-based noble metal catalyst in this embodiment is the same as that in Example 1, except that the mass ratio of Fe-HNC rich in micropores and mesopores to ruthenium acetylacetone is 1:2.

[0049] Comparative Example 1 A method for preparing a transition metal single-atom carbon-based noble metal catalyst includes the following steps: (1) Weigh 6.78 g of zinc nitrate hexahydrate and 400 mg of ferric nitrate nonahydrate and dissolve them in 500 mL of methanol solution to form the first solution; separately weigh 7.88 g of 2-methylimidazole and dissolve it in 500 mL of methanol solution to form the second solution; mix the first solution and the second solution evenly in another 2L single-necked flask, seal it well and place it in a 60 ℃ oven for aging for 24 h. After cooling to room temperature, centrifuge to collect the precipitate, wash it three times with methanol solution and then vacuum dry it at 60 ℃ for 12 h to finally obtain light yellow Fe-ZIF-8 powder.

[0050] (2) After the Fe-ZIF-8 powder is fully ground, it is placed in a quartz tube in a tube furnace and heated to 1000 ℃ at 5 ℃ / min under an argon atmosphere. It is then kept at 1000 ℃ for 2 h. After the calcination is completed and the temperature is lowered to room temperature, the collected sample is the Fe-NC support without porous structure.

[0051] (3) Ruthenium nanoparticles were loaded using chemical vapor deposition. Specifically, 10 mg of ruthenium acetylacetone was placed at the bottom of a 20×30 cm ceramic boat, and a layer of high-temperature resistant quartz filter membrane was placed in the middle of the boat. Finally, 20 mg of Fe-NC support was placed on the filter membrane, the boat was capped, and the ceramic boat was placed in a quartz tube in a tube furnace. Under an argon atmosphere, the tube furnace was first heated to 200 °C at a rate of 10 °C / min and held for 30 min, and then heated to 800 °C at a rate of 10 °C / min and held for 2 h. After the program ran out and cooled to room temperature, the final composite catalyst Fe-NC@Ru was obtained.

[0052] Comparative Example 2 A method for preparing a porous carbon-based noble metal catalyst includes the following steps: (1) Weigh 6.78g of zinc nitrate hexahydrate and dissolve it in 500mL of methanol solution to form the first solution; separately weigh 7.88g of 2-methylimidazole and dissolve it in 500mL of methanol solution to form the second solution; mix the first and second solutions evenly in another 2L single-necked flask, seal it, and place it in a 60℃ oven for aging for 24h. After cooling to room temperature, centrifuge to collect the precipitate, wash it three times with methanol solution, and then vacuum dry it at 60℃ for 12h to finally obtain white ZIF-8 powder.

[0053] (2) The prepared ZIF-8 powder was etched with sodium chloride and ammonium iodide. The etching process of sodium chloride and ammonium iodide was the same as steps (2) and (3) in Example 1. The collected sample was the porous carbon carrier HNC without single-atom iron.

[0054] (3) Ruthenium nanoparticles were loaded using chemical vapor deposition. Specifically, 10 mg of ruthenium acetylacetone was placed at the bottom of a 20 x 30 cm ceramic boat, and a layer of high-temperature resistant quartz filter membrane was placed in the middle of the boat. Finally, 20 mg of HNC was weighed and spread evenly on the filter membrane. After capping, the ceramic boat was placed in a quartz tube in a tube furnace. Under an argon atmosphere, the tube furnace was first heated to 200 °C at a rate of 10 °C / min and held for 30 min, and then heated to 800 °C at a rate of 10 °C / min and held for 2 h. After the reaction was completed and cooled to room temperature, the final composite catalyst HNC@Ru was obtained.

[0055] Comparative Example 3 A method for preparing a transition metal single-atom porous carbon-based noble metal catalyst includes the following steps: (1) Preparation of transition metal-doped zeolite imidazole framework materials 6.78 g of zinc nitrate hexahydrate and 400 mg of ferric nitrate nonahydrate were dissolved in 500 mL of methanol to form the first solution. Separately, 7.88 g of 2-methylimidazole was dissolved in 500 mL of methanol to form the second solution. The first and second solutions were mixed evenly in a 2 L single-necked flask, sealed, and aged in a 60 °C oven for 24 h. After aging and cooling to room temperature, the precipitate was collected by centrifugation, washed three times with methanol solution, and then vacuum dried at 60 °C for 12 h to obtain a light yellow Fe-ZIF-8 powder.

[0056] (2) The prepared ZIF-8 powder was etched with sodium chloride and ammonium iodide. The etching treatment of sodium chloride and ammonium iodide was the same as step (2) and step (3) in Example 1. The collected sample was Fe-HNC carrier rich in micropores and mesopores.

[0057] (3) Impregnation method: 100 mg of Fe-HNC support was weighed and dispersed in a mixed solvent of ethanol and water (50 mL, ethanol and water volume ratio of 1:1). After sonication for 30 min, 30 mg of ruthenium acetylacetone was added, and sonication was continued for another 30 min. After stirring at room temperature for 24 h, the solvent was evaporated by rotary evaporation to obtain a mixed powder. The mixed powder sample was then thoroughly ground and vacuum dried at 60 ℃ for 12 h. Finally, the mixed powder was placed in a quartz tube in a tube furnace and heated to 800 ℃ at a heating rate of 10 ℃ / min under an argon atmosphere. The temperature was then maintained for 2 hours, and after natural cooling, the target product Fe-HNC@Ru-i was obtained. The Fe-HNC@Ru-i is a composite catalyst obtained by impregnation method with a hierarchical porous carbon support (Fe-HNC) containing transition metal single atoms. It is distinguished from the Fe-HNC@Ru obtained by chemical vapor deposition in Example 1, and is therefore named Fe-HNC@Ru-i.

[0058] Depend on Figure 1 As can be seen, in this Example 1, the molecular template of sodium chloride is used to optimize and control the mesoporous structure of the carbon support, and the ammonia gas generated by the high-temperature decomposition of ammonium iodide is used to optimize and control the microporous structure of the carbon support. This makes the carbon support of Example 1 have both rich microporous and mesoporous structures. Therefore, the specific surface area of ​​Example 1 is much larger than that of Comparative Example 1 (the small amount of micropores and mesopores in Comparative Example 1 are due to the characteristics of the ZIF system itself).

[0059] Depend on Figure 2 It can be seen that the composite catalyst Fe-HNC@Ru prepared in Example 1 has a spatial confinement effect, with nanoparticles uniformly distributed inside the rich porous carbon support, and has the characteristics of high dispersion and low particle size.

[0060] Figure 3This verifies that the Fe species in the composite catalyst Fe-HNC@Ru prepared in Example 1 exist in the form of transition metal single atoms and the Ru species exist in the form of nanoparticles.

[0061] Figures 4-8 It can be seen that the alkaline cathode hydrogen evolution reaction activity of the composite catalyst Fe-HNC@Ru prepared in Example 1 was evaluated in a three-electrode system. The results show that it has excellent alkaline cathode hydrogen evolution reaction activity, with a 10 mA cm⁻¹ activity. -2 The overpotential is only 17 mV, and the Tafel slope is 35.09 mV dec. -1 ( Figure 6 (As shown); the mass activity at a 100 mV overpotential is 6.02 A mg. -1 ( Figure 7 As shown), the conversion frequency is 3.29 s. -1 ( Figure 7 As shown in the figure, it is significantly superior to Comparative Examples 1, 2, and 3, indicating that the Fe-HNC@Ru prepared in Example 1 has excellent intrinsic activity. Figure 4 , Figure 5 As can be seen from the curves, the Fe-HNC@Ru prepared in Examples 1, 2, and 3 have superior intrinsic activity compared to Comparative Examples 1, 2, and 3.

[0062] pass Figure 8 The performance of the composite catalyst Fe-HNC@Ru prepared in Example 1 in the electrolysis of water using anion exchange membranes was evaluated: at 80 °C, it only requires 1.57 V to reach 1.0 A cm⁻¹. -2 The current density. Furthermore, from... Figure 9 It can be seen that the composite catalyst Fe-HNC@Ru prepared in Example 1 can achieve a flux of 1.0 Acm. -2 It operated stably for more than 5000 h at a current density, verifying that the dual synergistic effect of "spatial confinement" and "interfacial confinement" enhances the activity and stability of the catalyst in anion exchange membrane water electrolysis.

[0063] The above are merely preferred embodiments of this application. It should be noted that this application is not limited to the above embodiments. For those skilled in the art, several improvements and modifications can be made without departing from the principles of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should also be considered within the scope of protection of this application.

Claims

1. A method for preparing a transition metal single atom porous carbon-based noble metal catalyst, characterized in that, Includes the following steps: (1) Dissolve the transition metal source and zinc nitrate hexahydrate in a first solvent to prepare a first solution; dissolve 2-methylimidazole in a second solvent to prepare a second solution; mix the first solution and the second solution evenly, and then perform an aging treatment; After aging treatment, the sample was cooled to room temperature, separated and collected, and then washed and dried to obtain the transition metal-doped zeolite imidazole ester framework-8 precursor. (2) Add an alcohol-water solution containing a template agent to the transition metal-doped zeolite imidazole ester framework-8 precursor, grind and mix, dry, pyrolyze, cool to room temperature after pyrolysis, wash with water and filter to obtain a mesoporous transition metal-nitrogen-carbon composite material. (3) The mesoporous transition metal-nitrogen-carbon composite material is mixed with an ammonia source precursor and subjected to pyrolysis treatment under an inert atmosphere to obtain a transition metal-nitrogen-carbon composite material rich in micropores and mesopores. (4) Using chemical vapor deposition, platinum group metal sources are loaded onto the surface of transition metal-nitrogen-carbon composite materials rich in micropores and mesopores to obtain transition metal single-atom porous carbon-based noble metal catalysts.

2. The preparation method according to claim 1, characterized in that, In step (1), the transition metal source is selected from any one of iron source, cobalt source, nickel source, and copper source; the first solvent is selected from at least one of methanol and water; and the second solvent is selected from at least one of methanol and water.

3. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of zinc nitrate hexahydrate, transition metal source, and 2-methylimidazole is (5.0-8.0):(0.1-1.0):(5.0-10.0), and the molar ratio of transition metal to zinc in zinc nitrate hexahydrate is 1:10-1:

50. The volume ratio of the first solvent to the total mass of the transition metal source and zinc nitrate hexahydrate is 40-100 mL: 1 g; the volume ratio of the second solvent to the mass of 2-methylimidazole is 40-100 mL: 1 g. The aging temperature is 60℃ and the aging time is 6-48h; the vacuum drying temperature is 25-80℃ and the drying time is 8-48h.

4. The preparation method according to claim 1, characterized in that, In step (2), the template agent is selected from any one of sodium chloride, potassium chloride, tannic acid and lithium chloride; the mass ratio of the transition metal-doped zeolite imidazole ester framework-8 precursor to the template agent is 1:0.5-1:3; The concentration of the template agent in an alcoholic aqueous solution is 20-80 mg / mL; In step (2), the pyrolysis treatment method includes: placing the mixed powder obtained by mixing the transition metal-doped zeolite imidazole ester framework-8 precursor and the template agent in a tube furnace, heating it to 950-1100℃ at a heating rate of 5℃ / min under an argon atmosphere, and holding it at that temperature for 2h.

5. The preparation method according to claim 1, characterized in that, In step (3), the pyrolysis treatment method includes: placing a mixed powder of a transition metal-nitrogen-carbon composite material rich in mesoporous material and ammonia source precursor in the heating zone of the tube furnace, placing the ammonia source precursor in the non-heating zone of the tube furnace, and heating the heating zone of the tube furnace to 750-1000℃ at 5-20℃ / min under an argon atmosphere, and then pushing the ammonia source precursor in the non-heating zone of the tube furnace into the heating zone of the tube furnace for calcination for 30-120min.

6. The preparation method according to claim 5, characterized in that, In step (3), the ammonia source precursor is selected from any one of ammonium iodide, ammonium chloride, ammonium bromide and ammonium fluoride; The mass ratio of the mesoporous transition metal-nitrogen-carbon composite material in the heating zone of the tubular furnace, the ammonia source precursor in the heating zone of the tubular furnace, and the ammonia source precursor in the non-heating zone of the tubular furnace is 1:(5-15):(5-10).

7. The preparation method according to claim 1, characterized in that, In step (4), the chemical vapor deposition method includes: placing a platinum group metal source, a high-temperature resistant quartz filter membrane, and a transition metal-nitrogen-carbon composite material rich in micropores and mesopores in a ceramic boat from bottom to top. After covering, the ceramic boat is placed in a tube furnace. Under an argon atmosphere, the tube furnace is first heated to 150-300℃ at a rate of 5-15℃ / min and held for 30-60min. Then, it is heated to 700-1000℃ at a rate of 5-25℃ / min and held for 60-120min.

8. The preparation method according to claim 1, characterized in that, The platinum group metal source is selected from any one of ruthenium source, platinum source, iridium source, and palladium source.

9. The preparation method according to claim 1, characterized in that, The mass ratio of the transition metal-nitrogen-carbon composite material rich in micropores and mesopores to the platinum group metal source is 1:0.2-1:

4.

10. The application of the transition metal single-atom porous carbon-based noble metal catalyst prepared by any one of claims 1-9 in anion exchange membrane water electrolysis for hydrogen production.

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