Transition metal doped epitaxial growth tubular WC catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electrocatalytic oxygen reduction reaction, and particularly relates to a transition metal doped epitaxial growth tubular WC catalyst and a preparation method and application thereof. The preparation method comprises the following steps: mixing a soluble zinc source, other transition metal salts, an organic ligand and a soluble tungsten source which are used as raw materials in a solvent system to form a mixed solution, and aging after stirring to obtain a metal tungsten doped N-C skeleton precursor; and calcining the metal tungsten doped N-C skeleton precursor in a nitrogen atmosphere to obtain the transition metal doped epitaxial growth tubular WC catalyst. A tungstate synthesis precursor is introduced in the process of synthesizing a carbon skeleton with a special structure by transition metal and an organic ligand and then is subjected to high-temperature pyrolysis, and a tubular WC structure is formed on a regular dodecahedron substrate interface, so that the content of carbon in the catalyst is increased, meanwhile, the loading capacity of the transition metal is increased, and the catalytic activity of the catalyst is improved. The intrinsic activity of the catalyst is improved. The preparation method is simple, wide in raw material source, low in preparation cost and high in catalyst activity.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic oxygen reduction reaction technology, specifically relating to transition metal-doped epitaxially grown tubular WC catalysts, their preparation methods, and applications. Background Technology

[0002] With the escalating global energy crisis and increasing environmental pollution, the development of efficient energy conversion and storage technologies has become urgent. Among these, the electrochemical oxygen reduction reaction (ORR) plays a crucial role in advancing energy conversion technologies, particularly fuel cells and metal-air batteries. However, the ORR involves complex multi-electron transfer pathways, resulting in slow kinetics, which limits the widespread development of many oxygen-dependent sustainable energy technologies. Currently, platinum (Pt)-based catalysts are widely used due to their high catalytic activity, but they face significant challenges such as limited resources, high cost, and poor stability.

[0003] In recent years, researchers have used carbon materials or non-metallic element-doped support materials as the matrix to load platinum catalysts and obtain platinum-based catalysts through reduction treatment, or further load various metals such as transition metals through precipitation method to reduce the amount of platinum used and improve catalytic activity. However, catalysts prepared in this way are prone to metal agglomeration and sintering during high-temperature pyrolysis, making it difficult to improve their catalytic performance and resulting in insufficient stability. Summary of the Invention

[0004] The present invention aims to provide a transition metal-doped epitaxially grown tubular WC catalyst, its preparation method, and its applications. A tungstate precursor is introduced during the synthesis of a carbon framework with a special structure using transition metals and organic ligands. High-temperature pyrolysis yields the transition metal-doped epitaxially grown tubular WC catalyst. By forming a tubular WC structure at the interface of a dodecahedral substrate, and by introducing a second heterometallic element to construct a bimetallic catalyst, the bimetallic catalyst effectively inhibits particle agglomeration at high temperatures, increases the density and dispersion of active sites, and simultaneously increases the loading of transition metals. The carbon content in the catalyst is increased by utilizing WC. The doping of transition elements and the synergistic effect of WC give this catalyst a high specific surface area. Furthermore, the asymmetric dual-site coordination disrupts local symmetry, and the electron coupling and synergistic effect redistribute electron density, thereby improving ORR activity and long-term stability, thus enhancing the intrinsic activity of the catalyst. The preparation method is simple, the raw materials are widely available, the preparation cost is low, and the catalyst activity is high.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] The first objective of this invention is to provide a method for preparing a transition metal-doped epitaxially grown tubular WC catalyst, comprising the following steps: Using soluble zinc source and other transition metal salts, organic ligands and soluble tungsten source as raw materials, they are mixed in a solvent system to form a mixed solution, and then aged after stirring to obtain tungsten metal-doped NC framework precursor; In a nitrogen atmosphere, a tungsten-doped NC framework precursor is calcined, the organic ligands are carbonized, the tungsten source is reduced and reacts with carbon to generate tungsten carbide, and the tungsten carbide grows along the dodecahedral matrix interface to form tubular structures, thus obtaining a transition metal-doped epitaxially grown tubular WC catalyst.

[0007] Furthermore, the molar ratio of the soluble zinc source, other transition metal soluble salts, and soluble tungsten source is 18:0.1-1:0.1-1.

[0008] Furthermore, the transition metal in other transition metal soluble salts is at least one of iron, manganese, and cobalt.

[0009] Furthermore, in the mixture, the molar ratio of total metal ions to organic ligands is 1:6 to 9.

[0010] Furthermore, the concentration of organic ligands in the mixture is 0.4 mol / L to 0.8 mol / L.

[0011] Furthermore, the organic ligand is 2-methylimidazole or 2-phenylimidazole.

[0012] Furthermore, the stirring temperature is 10℃~30℃, the time is 4h~7h, and the aging is left to stand at room temperature for 1h~4h.

[0013] Furthermore, the calcination temperature is 900℃~1000℃, the calcination rate is 5℃ / min~8℃ / min, and the holding time is 2h~3h.

[0014] The second objective of this invention is to provide a transition metal-doped epitaxially grown tubular WC catalyst, which is prepared using the above-described preparation method.

[0015] The third objective of this invention is to provide the application of the above-mentioned transition metal-doped epitaxially grown tubular WC catalyst in the electrocatalytic oxygen reduction reaction in fuel cells or metal-air batteries.

[0016] Compared with the prior art, the present invention has the following advantages: This invention provides a preparation method in which a transition metal and an organic ligand are coordinated in a solvent through a simple room-temperature precipitation method to form a coordination unit that links the metal to a nitrogen-containing molecule. Self-assembly occurs through intermolecular forces, forming a regular dodecahedral catalyst precursor. This precursor is then subjected to high-temperature calcination, during which the transition metal zinc volatilizes, the organic ligand is carbonized, and the tungsten source is reduced, forming a tubular WC structure at the dodecahedral substrate interface. The introduction of tungsten metal constructs a bimetallic catalyst. The bimetallic structure effectively inhibits particle aggregation at high temperatures, increases the density and dispersion of active sites, and simultaneously increases the loading of the transition metal. The WC is used to increase the carbon content in the catalyst. The doping of transition elements and the synergistic effect of WC give this catalyst a high specific surface area. The asymmetric dual-site coordination disrupts local symmetry, and the electron coupling and synergistic effect redistribute the electron density, thereby improving ORR activity and long-term stability. The catalyst achieves an ORR onset potential of 0.98 V and a half-wave potential of 0.89 V in 0.1 M KOH electrolyte.

[0017] The preparation method provided by this invention is simple, and the raw materials used are all common materials. Compared with commercial Pt / C catalysts, it has the advantages of good stability, low cost and environmental friendliness, and is a promising oxygen reduction electrocatalyst. Attached Figure Description

[0018] Figure 1 This is a microstructure diagram of the Fe-WC / NC catalyst prepared in Example 1 of the present invention, wherein, Figure 1 In the image, (a) is a SEM image, (b) is a TEM image, (c) is a magnified view of (b), and (d) to (g) are the elemental distribution maps of the X-ray spectrum.

[0019] Figure 2 The images shown are scanning electron microscope (SEM) images of the WC / NC catalyst prepared in Comparative Example 1 and the Fe / NC catalyst prepared in Comparative Example 2 of this invention. Figure 2 (a) is a WC / NC catalyst, and (b) is an Fe / NC catalyst.

[0020] Figure 3 X-ray diffraction patterns of the Fe-WC / NC catalyst prepared in Example 1, the WC / NC catalyst prepared in Comparative Example 1, and the Fe / NC catalyst prepared in Comparative Example 2.

[0021] Figure 4 Raman scattering patterns of the Fe-WC / NC catalyst prepared in Example 1, the WC / NC catalyst prepared in Comparative Example 1, and the Fe / NC catalyst prepared in Comparative Example 2.

[0022] Figure 5The images show the X-ray photoelectron spectra of the Fe-WC / NC catalyst prepared in Example 1, the WC / NC catalyst prepared in Comparative Example 1, and the Fe / NC catalyst prepared in Comparative Example 2. Figure 5 In the diagram, (a) is the full spectrum, (b) is the fine spectrum and peak fitting diagram of W 4f, (c) is the fine spectrum and peak fitting diagram of C 1s, and (d) is the percentage content diagram of C element.

[0023] Figure 6 The image shows the adsorption performance and pore size distribution of the Fe-WC / NC catalyst prepared in Example 1 of this invention.

[0024] Figure 7 This is a diagram showing the adsorption performance and pore size distribution of the WC / NC catalyst prepared in Comparative Example 1 of this invention.

[0025] Figure 8 This is a diagram showing the adsorption performance and pore size distribution of the Fe / NC catalyst prepared in Comparative Example 2 of this invention.

[0026] Figure 9 This is a comparison chart of linear sweep voltammetry tests on the Fe-WC / NC catalyst prepared in Example 1, the WC / NC catalyst prepared in Comparative Example 1, and the Fe / NC catalyst prepared in Comparative Example 2.

[0027] Figure 10 The graphs show the linear sweep voltammetry results of the Fe-WC / NC catalysts prepared in Examples 2 to 4 of this invention.

[0028] Figure 11 Tafel slope diagrams of the Fe-WC / NC catalyst prepared in Example 1, the WC / NC catalyst prepared in Comparative Example 1, and the Fe / NC catalyst prepared in Comparative Example 2.

[0029] Figure 12 The graph shows a comparison of linear scanning voltammetry tests conducted on Fe-WC / NC prepared in Example 1 of this invention at different rotational speeds.

[0030] Figure 13 The images show cyclic voltammetry test results for the Fe-WC / NC catalyst prepared in Example 1, the WC / NC catalyst prepared in Comparative Example 1, and the Fe / NC catalyst prepared in Comparative Example 2. Figure 13 In the diagram, (a) represents the Fe-WC / NC catalyst, (b) represents the WC / NC catalyst, (c) represents the Fe / NC catalyst, and (d) represents the relationship between the current density difference and the scan rate, as well as the estimated C. dl value.

[0031] Figure 14This is a comparison of linear sweep voltammetry tests before and after 10,000 cycles of cyclic voltammetry testing of the Fe-WC / NC catalyst prepared in Example 1 of this invention.

[0032] Figure 15 The current-time curves are shown for Fe-WC / NC prepared in Example 1, WC / NC prepared in Comparative Example 1, and Fe / NC prepared in Comparative Example 2.

[0033] Figure 16 The electrochemical impedance spectroscopy Nyquist plots and fitting circuit diagrams are shown for Fe-WC / NC prepared in Example 1, WC / NC prepared in Comparative Example 1, and Fe / NC prepared in Comparative Example 2. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0036] The present invention provides a method for preparing a transition metal-doped epitaxially grown tubular WC catalyst, comprising the following steps: S1. Using soluble zinc source and other transition metal salts, organic ligands and soluble tungsten source as raw materials, they are mixed in a solvent system to form a mixed solution, and then aged after stirring to obtain tungsten metal-doped NC framework precursor.

[0037] In this invention, the molar ratio of the soluble zinc source, other transition metal salts, and the soluble tungsten source is 18:0.1-1:0.1-1. In some preferred embodiments, the transition metal in the other transition metal soluble salt is at least one of iron, manganese, and cobalt. As a preferred embodiment of this invention, the other transition metal soluble salt is a soluble iron source. The soluble zinc source, soluble iron source, and soluble tungsten source only need to be soluble in a solvent, which is one or more of water, methanol, and ethanol mixed in any proportion. The soluble zinc source is preferably zinc chloride or zinc nitrate, the soluble iron source is preferably ferric chloride hexahydrate or ferric nitrate nonahydrate, and the soluble tungsten source is preferably ammonium tungstate or sodium tungstate tetrahydrate.

[0038] In this invention, a soluble transition metal salt, an organic ligand, and a soluble tungsten source are dissolved separately in a solvent and then mixed. A simple room-temperature precipitation method is then used to coordinate the organic ligand and the zinc source in the solvent. Using methanol as the solvent, and with the simultaneous introduction of an iron source and a tungsten source, the transition metal ions in the solution coordinate with the nitrogen atoms in the organic ligand, forming coordination units that link the metal to nitrogen-containing molecules. During stirring, these coordination units self-assemble through intermolecular forces, forming a regular dodecahedral catalyst precursor. The molar ratio of total metal ions to organic ligands in the mixture is 1:6–9, the concentration of the organic ligand is 0.4 mol / L–0.8 mol / L, and the organic ligand is 2-methylimidazole or 2-phenylimidazole.

[0039] It should be noted that when a stable suspension is formed by stirring, aging is carried out at a temperature of 10℃~30℃ for 4h~7h. Aging is carried out by standing at room temperature for 1h~4h. After aging, centrifugation, washing and drying are required. The centrifugation speed is 9000r / min~11000r / min for 3min~5min. The washing solvent is the same as the washing solvent, which is one or more of water, methanol and ethanol in any proportion. The drying temperature is 50℃~60℃ for 12h~24h.

[0040] S2. In a nitrogen atmosphere, the tungsten metal-doped NC framework precursor is calcined at a rate of 5℃ / min to 8℃ / min to 900℃ to 1000℃ for 2h to 3h. The organic ligands are carbonized, the tungsten source is reduced and reacts with carbon to form tungsten carbide. The tungsten carbide grows along the dodecahedral matrix interface to form tubular structures, thus obtaining a transition metal-doped epitaxially grown tubular WC catalyst.

[0041] In this invention, during the low-temperature stage of the calcination process of the tungsten-doped NC framework precursor, the physically adsorbed water, solvent, and some uncoordinated organic matter in the precursor begin to decompose. As the temperature increases, the organic ligands begin to carbonize, releasing small carbon and nitrogen-containing molecules with reducing properties. At medium and high temperatures, iron and tungsten accelerate the breaking of Zn-N bonds, reducing Zn to metallic zinc. The metallic zinc volatilizes with nitrogen, and iron is reduced by C to metal nanoparticles. Tungsten reacts with C to generate WC and W2C. At high temperatures, N transforms into graphitization, and the graphitization of the carbon framework is also enhanced, forming a stable catalyst. This invention introduces the transition metal tungsten to construct a bimetallic catalyst. Bimetallization effectively inhibits particle agglomeration at high temperatures, increases the density and dispersion of active sites, and enhances the loading of the transition metal. WC is used to increase the carbon content in the catalyst. The doping of transition elements and the synergistic effect of WC result in a catalyst with a high specific surface area. The asymmetric dual-site coordination disrupts local symmetry, and the coupling and synergistic effect of electrons redistribute electron density, thereby improving ORR activity and long-term stability. Ultimately, a transition metal-doped epitaxially grown tubular WC catalyst is obtained. Different WC morphologies are used to increase the carbon content in the material, further enhancing the catalyst's oxygen reduction performance. This also increases the loading of the transition metal. The synergistic effect of Fe doping and WC gives this catalyst a high specific surface area, excellent ORR activity, and long-term stability. In 0.1 M KOH electrolyte, the ORR onset potential reaches 0.98 V, and the half-wave potential is 0.89 V. The catalyst preparation method provided by this invention is simple, and the raw materials used are all common materials. Compared with commercial Pt / C catalysts, it has the advantages of good stability, low cost and environmental friendliness, and is a promising oxygen reduction electrocatalyst.

[0042] The following specific examples will provide further explanation.

[0043] Example 1 A method for preparing a transition metal-doped epitaxially grown tubular WC catalyst includes the following steps: S1. Dissolve 96 mmol of 2-methylimidazole in 100 mL of methanol solution and stir for 30 min until completely dissolved to obtain a 2-methylimidazole solution; dissolve 16 mmol of zinc nitrate in 33 mL of methanol solution and stir for 30 min until completely dissolved to obtain a zinc nitrate solution; dissolve 0.2 mmol of ferric nitrate nonahydrate in 33 mL of methanol solution and stir for 30 min until completely dissolved to obtain a ferric nitrate solution; dissolve 0.6 mmol of sodium tungstate tetrahydrate in 33 mL of methanol solution and stir for 30 min until completely dissolved to obtain a sodium tungstate solution.

[0044] S2. After mixing zinc nitrate solution, ferric nitrate solution and sodium tungstate solution, add to 2-methylimidazole solution and mix. Stir at 500 rpm for 5 h at room temperature until the solution turns pale yellow to obtain the reaction solution. Let it settle at room temperature for 1 h, then centrifuge at 9000 r / min for 4 min, wash 4 times with methanol solution, and dry in an oven at 55℃ for more than 12 h to obtain the precursor.

[0045] S2. The precursor is transferred to a tube furnace, and nitrogen is introduced for 30 minutes to purge the air from the tube furnace to prevent oxygen from affecting the preparation of the catalyst. Nitrogen is continuously introduced, and the temperature is increased to 950°C at a rate of 5°C / min. The furnace is calcined for 120 minutes and then naturally cooled to room temperature to obtain a transition metal-doped epitaxially grown tubular WC catalyst, abbreviated as Fe-WC / NC.

[0046] Example 2 A method for preparing a transition metal-doped epitaxially grown tubular WC catalyst includes the following steps: S1. Dissolve 96 mmol of 2-methylimidazole in 100 mL of methanol solution and stir for 30 min until completely dissolved to obtain a 2-methylimidazole solution; dissolve 16 mmol of zinc nitrate in 33 mL of methanol solution and stir for 30 min until completely dissolved to obtain a zinc nitrate solution; dissolve 0.4 mmol of ferric nitrate nonahydrate in 33 mL of methanol solution and stir for 30 min until completely dissolved to obtain a ferric nitrate solution; dissolve 0.4 mmol of sodium tungstate tetrahydrate in 33 mL of methanol solution and stir for 30 min until completely dissolved to obtain a sodium tungstate solution.

[0047] S2. After mixing zinc nitrate solution, ferric nitrate solution and sodium tungstate solution, add to 2-methylimidazole solution and mix. Stir at 500 rpm for 5 h at room temperature until the solution turns pale yellow to obtain the reaction solution. Let it settle at room temperature for 1 h, then centrifuge at 9000 r / min for 4 min, wash 4 times with methanol solution, and dry in an oven at 55℃ for more than 12 h to obtain the precursor.

[0048] S2. The precursor is transferred to a tube furnace, and nitrogen is purged for 30 minutes to remove all air from the tube furnace and prevent oxygen from affecting the preparation of the catalyst. Nitrogen is continuously purged, and the temperature is increased to 950°C at a rate of 5°C / min. The furnace is calcined for 120 minutes and then naturally cooled to room temperature to obtain a transition metal-doped epitaxially grown tubular WC catalyst, abbreviated as Fe-WC / NC-1.

[0049] Example 3 A method for preparing a transition metal-doped epitaxially grown tubular WC catalyst includes the following steps: S1. Dissolve 96 mmol of 2-methylimidazole in 100 mL of methanol solution and stir for 30 min until completely dissolved to obtain a 2-methylimidazole solution; dissolve 16 mmol of zinc nitrate in 33 mL of methanol solution and stir for 30 min until completely dissolved to obtain a zinc nitrate solution; dissolve 0.27 mmol of ferric nitrate nonahydrate in 33 mL of methanol solution and stir for 30 min until completely dissolved to obtain a ferric nitrate solution; dissolve 0.53 mmol of sodium tungstate tetrahydrate in 33 mL of methanol solution and stir for 30 min until completely dissolved to obtain a sodium tungstate solution.

[0050] S2. After mixing zinc nitrate solution, ferric nitrate solution and sodium tungstate solution, add to 2-methylimidazole solution and mix. Stir at 500 rpm for 5 h at room temperature until the solution turns pale yellow to obtain the reaction solution. Let it settle at room temperature for 1 h, then centrifuge at 9000 r / min for 4 min, wash 4 times with methanol solution, and dry in an oven at 55℃ for more than 12 h to obtain the precursor.

[0051] S2. The precursor is transferred to a tube furnace, and nitrogen is introduced for 30 minutes to purge the air from the tube furnace to prevent oxygen from affecting the preparation of the catalyst. Nitrogen is continuously introduced, and the temperature is increased to 950°C at a rate of 5°C / min. The furnace is calcined for 120 minutes and then naturally cooled to room temperature to obtain a transition metal-doped epitaxially grown tubular WC catalyst, abbreviated as Fe-WC / NC-2.

[0052] Example 4 A method for preparing a transition metal-doped epitaxially grown tubular WC catalyst includes the following steps: S1. Dissolve 96 mmol of 2-methylimidazole in 100 mL of methanol solution and stir for 30 min until completely dissolved to obtain a 2-methylimidazole solution; dissolve 16 mmol of zinc nitrate in 33 mL of methanol solution and stir for 30 min until completely dissolved to obtain a zinc nitrate solution; dissolve 0.16 mmol of ferric nitrate nonahydrate in 33 mL of methanol solution and stir for 30 min until completely dissolved to obtain a ferric nitrate solution; dissolve 0.64 mmol of sodium tungstate tetrahydrate in 33 mL of methanol solution and stir for 30 min until completely dissolved to obtain a sodium tungstate solution.

[0053] S2. After mixing zinc nitrate solution, ferric nitrate solution and sodium tungstate solution, add to 2-methylimidazole solution and mix. Stir at 500 rpm for 5 h at room temperature until the solution turns pale yellow to obtain the reaction solution. Let it settle at room temperature for 1 h, then centrifuge at 9000 r / min for 4 min, wash 4 times with methanol solution, and dry in an oven at 55℃ for more than 12 h to obtain the precursor.

[0054] S2. The precursor is transferred to a tube furnace, and nitrogen is introduced for 30 minutes to purge the air from the tube furnace to prevent oxygen from affecting the preparation of the catalyst. Nitrogen is continuously introduced, and the temperature is increased to 950°C at a rate of 5°C / min. The furnace is calcined for 120 minutes and then naturally cooled to room temperature to obtain a transition metal-doped epitaxially grown tubular WC catalyst, abbreviated as Fe-WC / NC-3.

[0055] Comparative Example 1 A method for preparing a WC catalyst includes the following steps: S1. Dissolve 96 mmol of 2-methylimidazole in 100 mL of methanol solution and stir for 30 min until completely dissolved to obtain a 2-methylimidazole solution; dissolve 16 mmol of zinc nitrate in 50 mL of methanol solution and stir for 30 min until completely dissolved to obtain a zinc nitrate solution; dissolve 0.8 mmol of sodium tungstate tetrahydrate in 50 mL of methanol solution and stir for 30 min until completely dissolved to obtain a sodium tungstate solution.

[0056] S2. After mixing zinc nitrate solution and sodium tungstate solution, add to 2-methylimidazole solution and mix. Stir at 500 rpm for 5 h at room temperature until the solution turns milky white to obtain the reaction solution. Let it settle at room temperature for 1 h, then centrifuge at 9000 r / min for 4 min, wash 4 times with methanol solution, and dry in an oven at 55℃ for more than 12 h to obtain the precursor.

[0057] S2. Transfer the precursor to a tube furnace, purge the air in the tube furnace with nitrogen for 30 minutes to prevent oxygen from affecting the preparation of the catalyst, continue to purge with nitrogen, heat to 950°C at a rate of 5°C / min, calcine for 120 minutes, and cool naturally to room temperature to obtain the WC catalyst, abbreviated as WC / NC.

[0058] Comparative Example 2 A method for preparing a transition metal-doped catalyst includes the following steps: S1. Dissolve 96 mmol of 2-methylimidazole in 100 mL of methanol solution and stir for 30 min until completely dissolved to obtain a 2-methylimidazole solution; dissolve 16 mmol of zinc nitrate in 50 mL of methanol solution and stir for 30 min until completely dissolved to obtain a zinc nitrate solution; dissolve 0.2 mmol of ferric nitrate nonahydrate in 50 mL of methanol solution and stir for 30 min until completely dissolved to obtain a ferric nitrate solution.

[0059] S2. After mixing zinc nitrate solution and ferric nitrate solution, add to 2-methylimidazole solution and mix. Stir at 500 rpm for 5 h at room temperature until the solution turns dark yellow to obtain the reaction solution. Let it settle at room temperature for 1 h, then centrifuge at 9000 r / min for 4 min, wash 4 times with methanol solution, and dry in an oven at 55℃ for more than 12 h to obtain the precursor.

[0060] S2. Transfer the precursor to a tube furnace, purge the air in the tube furnace with nitrogen for 30 minutes to prevent oxygen from affecting the preparation of the catalyst, continue to purge with nitrogen, heat to 950°C at a rate of 5°C / min, calcine for 120 minutes, and cool naturally to room temperature to obtain the transition metal doped catalyst, abbreviated as Fe / NC.

[0061] The catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were subjected to structural and performance tests, and the results are shown below.

[0062] Figure 1 This is a microstructure diagram of the Fe-WC / NC catalyst prepared in Example 1 of the present invention, wherein, Figure 1 In the image, (a) is a SEM image, (b) is a TEM image, (c) is a magnified view of (b), and (d) to (g) are elemental distribution maps of the X-ray spectrum. Figure 1 As shown in (a), the microstructure of the Fe-WC / NC catalyst consists of epitaxially grown tubular WC dodecahedrons with a large number of tubular structures, uniform particle morphology, and a particle size of approximately 300 nm. Figure 1 As shown in (b) and (c), the material morphology is an epitaxially grown tubular WC dodecahedron, consistent with the scanning electron microscopy results. Figure 1 From (d) to (g), it can be seen that the metallic Fe and W elements are uniformly distributed in the material, proving that the elements were successfully doped and uniformly distributed.

[0063] Figure 2 The images shown are scanning electron microscope (SEM) images of the WC / NC catalyst prepared in Comparative Example 1 and the Fe / NC catalyst prepared in Comparative Example 2 of this invention. Figure 2 In the example, (a) is a WC / NC catalyst, and (b) is an Fe / NC catalyst. Figure 2 As shown in (a), the WC / NC catalyst has a dodecahedral microstructure with few epitaxial tubular structures and a particle size of approximately 150 nm. Figure 2 As shown in (b), the microstructure of the Fe / NC catalyst is also dodecahedral, but the particle morphology is slightly different, with a particle size of about 500 nm.

[0064] Figure 3X-ray diffraction patterns of the Fe-WC / NC catalyst prepared in Example 1, the WC / NC catalyst prepared in Comparative Example 1, and the Fe / NC catalyst prepared in Comparative Example 2. Figure 3 As shown, the XRD pattern of Fe-WC / NC exhibits a series of diffraction peaks between 20° and 80°, corresponding to WC (PDF#51-0939), confirming successful WC growth on the substrate. The diffraction peaks in the WC / NC XRD pattern correspond to W₂C(C,O), while the diffraction peaks in Fe / NC are mainly characteristic peaks of carbon, without any Fe metal-related diffraction peaks or impurity peaks. All three findings show good agreement with the results obtained from scanning electron microscopy.

[0065] Figure 4 Raman scattering patterns of the Fe-WC / NC catalyst prepared in Example 1, the WC / NC catalyst prepared in Comparative Example 1, and the Fe / NC catalyst prepared in Comparative Example 2. Figure 3 As shown, the I of the Fe-WC / NC catalyst D :I G The value is 0.47, which is less than the I of WC / NC and Fe / NC. D :I G The value indicates that it has a high degree of graphitization, low internal resistance, and fast electron transport rate, which makes the ORR process kinetics better. In addition, the graphitized structure is stable, which significantly improves the stability of the catalyst.

[0066] Figure 5 The images show the X-ray photoelectron spectra of the Fe-WC / NC catalyst prepared in Example 1, the WC / NC catalyst prepared in Comparative Example 1, and the Fe / NC catalyst prepared in Comparative Example 2. Figure 5 In the image, (a) is the full spectrum, (b) is the fine spectrum and peak fitting plot of W 4f, (c) is the fine spectrum and peak fitting plot of C 1s, and (d) is the percentage content plot of C element. Figure 5 As shown in Figure (a), the Fe-WC / NC catalyst exhibits characteristic peaks for C, N, O, Fe, and W, confirming the presence of these elements. Figure 5 As shown in (b) and (c), the W 4f peak of Fe-WC / NC shows WC 4f2 / 7 at 32.2 eV, WC 4f2 / 5 at 34.3 eV, and W at 35.6 eV. 6+ 4f2 / 7, displaying W at 37.5eV 6+ The peak fitting plots of C 1s for 4f2 / 7, Fe-WC / NC, and WC / NC show that it has a WC peak. For example... Figure 5As shown in Figure (d) and Table 1, inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis revealed that the Fe content (1.24%) and W content (1.47%) in Fe-WC / NC were significantly higher than those in Fe / NC (0.08%) and W content (1.44%) in WC / NC, respectively. Carbon content is shown in Table 2.

[0067] Table 1. Fe and W content of catalysts in Example 1, Comparative Examples 1 to 2 Table 2. Percentage C content of catalysts in Examples 1 and Comparative Examples 1-2 Figure 6 This is a diagram showing the adsorption performance and pore size distribution of the Fe-WC / NC catalyst prepared in Example 1 of this invention. Figure 6 As shown, the prepared Fe-WC / NC catalyst has a specific surface area of ​​823.29 m². 2 / g, mesopores exist at 2nm.

[0068] Figure 7 This diagram shows the adsorption performance and pore size distribution of the WC / NC catalyst prepared in Comparative Example 1 of this invention. Figure 7 As shown, the specific surface area of ​​the prepared catalyst reaches 647.05 m². 2 / g, mesopores exist at 2nm.

[0069] Figure 8 This diagram shows the adsorption performance and pore size distribution of the Fe / NC catalyst prepared in Comparative Example 2 of this invention. Figure 8 As shown, the specific surface area of ​​the prepared catalyst reaches 867.65 m². 2 / g, mesopores exist at 2nm.

[0070] The electrochemical performance of the pyridine catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 2 was tested, specifically including the following steps: Weigh 5 mg of the catalyst prepared in Examples 1 to 4 and Comparative Examples 1 to 2 after thorough grinding, add 1.5 mL of anhydrous ethanol and 0.5 mL of 0.5% naphthol solution to each, and place them in a 1000W ultrasonic machine for ultrasonication until uniformly dispersed. Take 6 μL to 10 μL of the sample and drop it onto the platinum carbon electrode of the rotating disk, and dry it at room temperature.

[0071] A three-electrode system was constructed using a standard hydrogen electrode as the reference electrode, a platinum sheet as the counter electrode, and a platinum-carbon electrode coated with slurry as the working electrode. The electrolyte used was 0.1M KOH, and high-purity oxygen was continuously introduced into the electrolyte to keep the oxygen in the electrolyte saturated. A series of ORR performance tests were conducted using a Shanghai Chenhua electrochemical workstation.

[0072] Figure 9 This is a comparison graph showing the linear sweep voltammetry test results of the Fe-WC / NC catalyst prepared in Example 1, the WC / NC catalyst prepared in Comparative Example 1, and the Fe / NC catalyst prepared in Comparative Example 2. Figure 9 As shown in Table 3, the onset potential of the oxygen reduction reaction of the Fe-WC / NC catalyst is 0.98V and the half-wave potential is 0.89V, which is higher than that of the WC / NC catalyst (0.96V) and the half-wave potential (0.85V) and the Fe / NC catalyst (0.97V) and the half-wave potential (0.85V).

[0073] Table 3. Onset potential and half-wave potential of catalysts in the examples and comparative examples Figure 10 This is a comparison chart of linear sweep voltammetry tests on the Fe-WC / NC catalysts prepared in Examples 2 to 4 of this invention. Figure 10 As shown in Table 3, the onset potential of the oxygen reduction reaction of the Fe-WC / NC-1 catalyst was 0.94V and the half-wave potential was 0.83V, the onset potential of the Fe-WC / NC-2 catalyst was 1.02V and the half-wave potential was 0.83V, and the onset potential of the Fe-WC / NC-3 catalyst was 0.97V and the half-wave potential was 0.86V. The overall performance of all of them was lower than that of the Fe-WC / NC catalyst prepared in Example 1.

[0074] The linear sweep voltammetry results of the obtained Fe-WC / NC catalyst, WC / NC catalyst, and Fe / NC catalyst were analyzed, and Tafel slope plots were plotted. Figure 11 The Tafel slope diagrams are for the Fe-WC / NC catalyst prepared in Example 1, the WC / NC catalyst prepared in Comparative Example 1, and the Fe / NC catalyst prepared in Comparative Example 2. Figure 11 As shown, the Tafel slope of Fe-WC / NC is 70.12 mV·dec -1 Less than WC / NC (80.71V·dec) -1 ) and Fe / NC (82.29V·dec -1 This indicates that Fe-WC / NC has better electrocatalytic kinetics.

[0075] The Fe-WC / NC catalyst obtained above was tested using linear sweep cyclic voltammetry at different rotational speeds. Figure 12 The graph shows a comparison of linear sweep voltammetry tests conducted on the Fe-WC / NC prepared in Example 1 of this invention at different rotational speeds. Figure 12As shown, the results were fitted using the KL equation, and the electron transfer number of Fe-WC / NC was approximately 3.9, verifying the near-four-electron oxygen reduction reaction.

[0076] The Fe-WC / NC catalyst, WC / NC catalyst, and Fe / NC catalyst obtained above were tested by cyclic voltammetry at scan rates ranging from 5 mV to 25 mV. Figure 13 The images show cyclic voltammetry test results for the Fe-WC / NC catalyst prepared in Example 1, the WC / NC catalyst prepared in Comparative Example 1, and the Fe / NC catalyst prepared in Comparative Example 2. Figure 13 In the diagram, (a) represents the Fe-WC / NC catalyst, (b) represents the WC / NC catalyst, (c) represents the Fe / NC catalyst, and (d) shows the relationship between the current density difference and the scan rate, along with the estimated Cdl value. Figure 13 Images (a) to (c) show the cyclic voltammetry results of the Fe-WC / NC catalyst, WC / NC catalyst, and Fe / NC catalyst at scan rates ranging from 5 mV to 25 mV, respectively. The results were fitted to the obtained data, as shown in the figure. Figure 13 As shown in (d), the capacitance density of the Fe-WC / NC catalyst is approximately 140.07 mF·cm⁻¹. -2 Greater than WC / NC (109.06 mF·cm) -2 ) and Fe / NC (82.78 mF·cm -2 ).

[0077] The stability of the Fe-WC / NC catalyst obtained above was tested. Figure 14 This is a comparison of linear sweep voltammetry results of the Fe-WC / NC catalyst prepared in Example 1 of this invention before and after 10,000 cycles of cyclic voltammetry testing. Figure 14 As shown, after 10,000 cycles of cyclic voltammetry, the performance of linear scanning voltammetry was tested, and the half-wave potential only decreased by 23mV.

[0078] The stability of the obtained Fe-WC / NC catalyst, WC / NC catalyst, and Fe / NC catalyst was tested. Figure 15 The images show the current-time curves of Fe-WC / NC prepared in Example 1, WC / NC prepared in Comparative Example 1, and Fe / NC prepared in Comparative Example 2. Figure 15 As shown, after 30 hours of oxygen reduction reaction stability testing, the performance of Fe-WC / NC decreased by only 4.06%, maintaining an activity of 95.94%, which is higher than that of WC / NC (90.49%) and Fe / NC (77.56%).

[0079] The Fe-WC / NC catalyst, WC / NC catalyst, and Fe / NC catalyst obtained above were characterized. Figure 16 The table shows the Nyquist plots and fitting circuit diagrams of the Fe-WC / NC prepared in Example 1, the WC / NC prepared in Comparative Example 1, and the Fe / NC prepared in Comparative Example 2. Table 4 shows the Nyquist plot fitting results of the Fe-WC / NC prepared in Example 1, the WC / NC prepared in Comparative Example 1, and the Fe / NC prepared in Comparative Example 2. Figure 16 As shown in Table 4, the R of Fe-WC / NC ct (233.20Ω) and R s (57.14Ω) are all less than the R of WC / NC ct (332.10Ω) and R s (67.79Ω) and R of Fe / NC ct (466.70Ω) and R s (61.54Ω).

[0080] Table 4. Nyquist plot fitting results It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0081] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a transition metal-doped epitaxially grown tubular WC catalyst, characterized in that, Includes the following steps: Using soluble zinc source and other transition metal salts, organic ligands and soluble tungsten source as raw materials, they are mixed in a solvent system to form a mixed solution, and then aged after stirring to obtain a tungsten-doped precursor with an NC framework. In a nitrogen atmosphere, the NC framework precursor doped with metal tungsten is calcined, the organic ligands are carbonized, the tungsten source is reduced and reacts with carbon to generate tungsten carbide, and the tungsten carbide grows along the interface of the dodecahedral matrix to form tubular structures, thus obtaining a transition metal doped epitaxially grown tubular WC catalyst.

2. The method for preparing a transition metal-doped epitaxially grown tubular WC catalyst according to claim 1, characterized in that, The molar ratio of soluble zinc source, other transition metal soluble salts and soluble tungsten source is 18:0.1-1:0.1-1.

3. The method for preparing a transition metal-doped epitaxially grown tubular WC catalyst according to claim 2, characterized in that, Other transition metal soluble salts contain at least one of iron, manganese, and cobalt as the transition metal.

4. The method for preparing a transition metal-doped epitaxially grown tubular WC catalyst according to claim 1, characterized in that, In the mixed solution, the molar ratio of total metal ions to organic ligands is 1:6 to 9.

5. The method for preparing a transition metal-doped epitaxially grown tubular WC catalyst according to claim 1, characterized in that, The concentration of organic ligands in the mixture is 0.4 mol / L to 0.8 mol / L.

6. The method for preparing a transition metal-doped epitaxially grown tubular WC catalyst according to claim 1, characterized in that, The organic ligand is 2-methylimidazole or 2-phenylimidazole.

7. The method for preparing a transition metal-doped epitaxially grown tubular WC catalyst according to claim 1, characterized in that, The stirring temperature is 10℃~30℃, the time is 4h~7h, and the aging is left to stand at room temperature for 1h~4h.

8. The method for preparing a transition metal-doped epitaxially grown tubular WC catalyst according to claim 1, characterized in that, The calcination temperature is 900℃~1000℃, the calcination rate is 5℃ / min~8℃ / min, and the holding time is 2h~3h.

9. A transition metal-doped epitaxially grown tubular WC catalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the transition metal-doped epitaxially grown tubular WC catalyst of claim 9 in the electrocatalytic oxygen reduction reaction in a fuel cell or metal-air battery.

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