Sn-doped Fe-N-C catalyst, preparation method and application thereof

Abstract

The application provides a Sn-doped Fe-N-C catalyst, a preparation method and application thereof. The catalyst comprises a carrier and Sn atoms and Fe atoms supported on the carrier, and the carrier is an N-doped carbon material. The application dopes the p-block metal Sn with stronger electronegativity into the Fe-N-C catalyst, forms an electron-withdrawing environment around the FeN4 site, reduces the electronegativity of the FeN4 site, and weakens the adsorption strength of the FeN4 site on the oxygen reduction intermediate. Meanwhile, the metal Sn is weaker in reactivity with hydrogen peroxide produced by the reaction of oxygen via a two-electron process than Fe, reduces the concentration of free radicals produced by the reaction, improves the stability of the carrier and active sites, and can effectively prevent the shedding of Fe. The application uses the catalyst as a cathode catalyst of a proton exchange membrane fuel cell, is low in cost, and can simultaneously meet the requirements of high catalytic activity and good stability.

Description

Technical Field

[0001] This invention relates to the field of catalysts and their preparation technology, specifically to a Sn-doped Fe-NC catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen energy is a clean and renewable energy source with advantages such as high energy density and wide application range. Currently, proton exchange membrane fuel cells (PEMFCs), as a technology that can directly convert chemical energy into electrical energy, offer highly efficient energy conversion and are a key technology for building hydrogen energy utilization systems. Typically, the kinetics of the cathode-side reaction (oxygen reduction reaction) in fuel cells are slow, requiring the use of the noble metal Pt as a catalyst. Currently, Pt-based catalysts (such as Pt / C catalysts) are the most mature, best-performing, and most stable cathode catalysts for fuel cells. However, the low resource reserves of the noble metal Pt lead to excessively high costs, significantly limiting the large-scale application of fuel cells. Therefore, developing highly active, highly stable, and low-cost non-noble metal-based oxygen reduction catalysts is crucial for reducing the cost of PEMFCs.

[0003] Non-precious metal-based catalysts are less expensive than Pt-based catalysts and have seen rapid development in recent years. Among them, metal-nitrogen-carbon (MNC) catalysts have become the most promising type of non-precious metal-based catalysts due to their high catalytic activity, attracting widespread attention from many scholars. For example, Yin et al. (Yin, S.-H. Energy & Environmental Science 2022, 15(7), 3033-3040.) used chemical vapor deposition to deposit metallic Fe onto the surface of a support, synthesizing a Fe-NC catalyst with high site density, which exhibited excellent catalytic activity. Liu et al. (Liu, S. Nature Energy 2022, 7(7), 652-663) increased the accessibility of single-atom active sites of metal by using an ammonium chloride etching strategy, significantly improving the catalytic performance of the Fe-NC catalyst, which showed activity exceeding that of commercial Pt / C catalysts in three-electrode tests. However, while the Fe-NC catalyst has excellent activity, it also exhibits significant degradation during use, resulting in poor stability. Studies have reported that the degradation mechanisms of MNC-type catalysts mainly include active site demetallization, carbon corrosion, nitrogen protonation, or micropore flooding. Among these, active site demetallization directly causes activity degradation; therefore, reducing metal detachment from active sites is crucial for improving catalyst stability. Furthermore, the active sites formed by MNC-type catalysts exhibit high adsorption strength for oxygen reduction intermediates, hindering their desorption and affecting the progress of subsequent reactions. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a Sn-doped Fe-NC catalyst, its preparation method, and its application. The catalyst, used as a cathode catalyst in a proton exchange membrane fuel cell, exhibits excellent catalytic activity and stability, and is low in cost.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a Sn-doped Fe-NC catalyst, comprising a support and Sn atoms and Fe atoms supported on the support;

[0007] The carrier is an N-doped carbon material.

[0008] Preferably, the Sn atom is a carbon-coated Sn atom, and the Sn atom includes Sn single atoms and Sn atom clusters.

[0009] Preferably, the Fe atom comprises a single Fe atom.

[0010] Preferably, the mass percentage of Fe atoms in the catalyst is 1.3% to 2.2%.

[0011] Preferably, the mass percentage of Sn atoms in the catalyst is 0.5% to 1.7%.

[0012] Preferably, the mass ratio of N to C in the carrier is 1:100 to 3:100.

[0013] Secondly, the present invention provides a method for preparing the above-mentioned catalyst, comprising the following steps:

[0014] S1: A nitrogen-containing organic ligand solution is mixed with a solution containing zinc salt, iron salt and tin salt and reacted. After removing the solvent, an intermediate is obtained.

[0015] S2: The intermediate is pyrolyzed in an inert atmosphere to obtain a catalyst.

[0016] Preferably, step S2 is as follows: a first intermediate is placed upstream of the pyrolysis device, a second intermediate is placed downstream of the pyrolysis device, and then pyrolysis is performed in an inert atmosphere to obtain a catalyst.

[0017] Preferably, after the pyrolysis treatment is completed, the method further includes a step of treating the obtained product with an acid solution.

[0018] Preferably, the molar ratio of the organic ligand to the zinc salt, iron salt, and tin salt in the organic ligand solution is 4000:(500-1200):(9-38):(5-40).

[0019] Thirdly, the present invention provides a cathode catalyst for a proton exchange membrane fuel cell, comprising the catalysts involved in the above-mentioned technical solutions.

[0020] Fourthly, the present invention provides a proton exchange membrane fuel cell, comprising an anode, a cathode, and a proton exchange membrane;

[0021] The cathode includes the cathode catalyst involved in the above technical solution.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention provides a Sn-doped Fe-NC catalyst (i.e., Fe / Sn-NC catalyst), comprising a support (nitrogen-doped carbon material) and Sn and Fe atoms supported on the support. This invention incorporates the more electronegative p-block metal Sn into the Fe-NC catalyst, creating an electron-withdrawing environment around the FeN4 sites, thereby reducing the electronegativity of the FeN4 sites and weakening their adsorption strength for oxygen reduction intermediates. Simultaneously, compared to Fe, Sn exhibits weaker reactivity with hydrogen peroxide produced from oxygen via a two-electron process. The introduction of Sn reduces the concentration of free radicals generated by the Fenton reaction, improves the stability of the support and active sites, and effectively prevents Fe shedding. This invention utilizes the Fe / Sn-NC catalyst as a cathode catalyst for proton exchange membrane fuel cells, offering low cost and simultaneously meeting the requirements of high catalytic activity and good stability. Furthermore, the preparation method of the Fe / Sn-NC catalyst provided by this invention is simple, yields high quantities (up to gram levels), and is suitable for industrial production, which is of great significance for the large-scale preparation of low-cost, non-precious metal-based cathode catalysts for proton exchange membrane fuel cells. Attached Figure Description

[0024] Figure 1 Here is a SEM image of the Fe / Sn-NC catalyst obtained in Example 1;

[0025] Figure 2 The elemental distribution diagram of the Fe / Sn-NC catalyst obtained in Example 1 is shown below.

[0026] Figure 3 The image shows the X-ray diffraction (XRD) pattern of the Fe / Sn-NC catalyst obtained in Example 1.

[0027] Figure 4 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the Fe / Sn-NC catalyst obtained in Example 1.

[0028] Figure 5 AC-STEM image of the Fe / Sn-NC catalyst obtained in Example 1;

[0029] Figure 6 The image shows the Fourier transform X-ray absorption fine structure (FT-EXAFS) image of the Fe / Sn-NC catalyst obtained in Example 1.

[0030] Figure 7 The linear sweep voltammetry curve of the Fe / Sn-NC catalyst obtained in Example 1 in 0.5 mol / L sulfuric acid solution is shown.

[0031] Figure 8 The linear sweep voltammetry curves of the Fe / Sn-NC catalyst obtained in Example 1 after different numbers of accelerated decay cycles in 0.5 mol / L sulfuric acid solution are shown.

[0032] Figure 9 The figure shows the hydrogen-air polarization test curve of the proton exchange membrane fuel cell assembled using the Fe / Sn-NC catalyst obtained in Example 1 as the cathode catalyst.

[0033] Figure 10 The linear sweep voltammetry curves of the Fe / Sn-NC catalyst obtained in Example 4 in 0.5 mol / L sulfuric acid solution are shown initially and after 1000 cycles of accelerated decay.

[0034] Figure 11 The linear sweep voltammetry curves of the Fe / Sn-NC catalyst obtained in Example 5 in 0.5 mol / L sulfuric acid solution are shown initially and after 1000 cycles of accelerated decay. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] To address the problem of high catalytic activity but poor stability of Fe-NC catalysts used as cathode catalysts in proton exchange membrane fuel cells in existing technologies, this invention provides a Sn-doped Fe-NC catalyst (also referred to as "Fe / Sn-NC catalyst"). The Fe / Sn-NC catalyst comprises a support and Sn atoms and Fe atoms supported on the support, wherein the support is a nitrogen (N)-doped carbon (C) material. In this invention, the Sn atoms include Sn single atoms and Sn clusters, and the Fe is Fe single atoms. In some embodiments of this invention, the mass ratio of N to C in the support is 1:100 to 3:100, preferably 1.5:100 to 2.5:100, more preferably 1.5:100 to 2:100; the mass of the Fe atoms accounts for 1.3 to 2.2% of the catalyst mass, preferably 1.5 to 2%, more preferably 1.5 to 1.8%; and the mass of the Sn atoms accounts for 0.5 to 1.7% of the catalyst mass, preferably 0.7 to 1.5%, more preferably 0.7 to 1%.

[0037] Fe-NC catalysts are among the most promising non-noble metal-based catalysts. The FeN4 metal single atom is considered the active center for catalysis. Carbon supports not only provide micropores to anchor the metal single atom but also modulate the electronic structure of the active sites, affecting catalytic performance. However, the excessive adsorption of oxygen reduction intermediates at the FeN4 sites makes them difficult to dissociate, hindering subsequent reactions. Furthermore, under operating conditions, the vibration of the Fe-N bond leads to Fe loss, and the hydrogen peroxide produced by the two-electron reaction between Fe and oxygen is highly reactive, resulting in a high concentration of free radicals that corrode the support surrounding the Fe, further contributing to Fe loss. In summary, Fe-NC catalysts exhibit poor working stability. Therefore, reducing the charge density of the FeN4 sites to regulate their adsorption strength for intermediates and preventing Fe loss is an effective strategy for improving Fe-NC catalysts. Based on this, this invention incorporates the more electronegative p-block metal Sn into the Fe-NC catalyst, creating an electron-withdrawing environment around the FeN4 sites, thereby reducing the electronegativity of the FeN4 sites and weakening their adsorption strength for oxygen reduction intermediates. Meanwhile, compared to Fe, metallic Sn exhibits weaker reactivity with hydrogen peroxide produced from oxygen via a two-electron reaction. The introduction of Sn reduces the concentration of free radicals generated by the Fenton reaction, improves the stability of the support and active sites, and effectively prevents Fe shedding. This invention utilizes the Fe / Sn-NC catalyst as the cathode catalyst in a proton exchange membrane fuel cell, which is expected to simultaneously meet the requirements of high catalytic activity and good stability.

[0038] This invention also provides a method for preparing the above-mentioned Fe / Sn-NC catalyst, specifically including the following steps:

[0039] S1: A nitrogen-containing organic ligand solution is mixed with a solution containing zinc salt, iron salt and tin salt and reacted. After removing the solvent, an intermediate is obtained.

[0040] S2: The intermediate is pyrolyzed in an inert atmosphere to obtain the Fe / Sn-NC catalyst.

[0041] According to the present invention, a nitrogen-containing organic ligand solution is first mixed with a solution containing zinc salt, iron salt, and tin salt and reacted. After removing the solvent, an intermediate is obtained. The nitrogen-containing organic ligand solution is obtained by mixing a nitrogen-containing organic ligand with a solvent. The nitrogen-containing organic ligand is selected from any one or more of 2-methylimidazole, imidazole-2-carboxaldehyde, or 4-cyanopyridine, preferably 2-methylimidazole. The solvent can be methanol, ethanol, or water, preferably methanol. In some embodiments of the present invention, the organic ligand is preferably dissolved in a solvent and stirred at room temperature for 0.1–0.5 h to obtain a clear and transparent organic ligand solution. The solution containing zinc salt, iron salt, and tin salt is obtained by mixing the zinc salt, iron salt, tin salt, and a solvent. The zinc salt is selected from zinc nitrate, zinc acetate, or zinc chloride; the iron salt is selected from ferric nitrate, ferric chloride, or ferric acetylacetone; the tin salt is selected from stannous chloride or stannous tetrachloride; the solvent can be methanol, ethanol, or water, preferably methanol. In some embodiments of the present invention, zinc salt, iron salt, and tin salt are preferably dissolved in a solvent and ultrasonically dispersed at room temperature for 0.1–0.5 h to obtain a yellow transparent solution. Since a coordination reaction occurs when the organic ligand solution is mixed with the solution containing zinc salt, iron salt, and tin salt, the resulting intermediate has a metal-organic framework (MOF) structure. Therefore, the organic ligand, zinc salt, iron salt, and tin salt should be considered as a whole. In some embodiments of the present invention, the molar ratio of the organic ligand, zinc salt, iron salt, and tin salt is 4000:(500–1200):(9–38):(5–40), more preferably 4000:(700–1000):(11–18):(7–18), and even more preferably 4000:(900–950):(14–16):(12–15). In some embodiments of the present invention, the organic ligand solution is preferably mixed with a solution containing zinc salt, iron salt, and tin salt according to the above proportions. More preferably, the solution containing zinc salt, iron salt, and tin salt is added to the organic ligand solution, and the reaction is carried out for 20-30 hours, preferably 20-25 hours. After removing the solvent, the intermediate is obtained. The solvent removal is preferably carried out by centrifugal washing. In the present invention, after the reaction is completed, ethanol is added to the reaction system as a washing reagent, and the mixture is centrifuged and washed 4-5 times to remove impurities. In some embodiments of the present invention, the centrifugal washing is preferably followed by drying. The drying treatment is preferably carried out at 50-70°C for 5-10 hours, more preferably at 55-60°C for 6-8 hours, and preferably by vacuum drying. It should be noted that the intermediate obtained in the present invention has a MOF structure, wherein the metal framework is composed of Zn atoms, and some Zn atoms are replaced by Fe atoms or Sn atoms, which exist in the form of clusters.

[0042] After obtaining the intermediate, it is pyrolyzed in an inert atmosphere to obtain the Fe / Sn-NC catalyst. During the pyrolysis process, Zn volatilizes, forming numerous micropores, and some Fe or Sn existing in cluster form gradually forms FeN. X or SnN X The metal single-atom active sites are anchored in the micropores. In this invention, the inert atmosphere is an atmosphere well known to those skilled in the art, preferably nitrogen or argon. The pyrolysis temperature is preferably 900–1100°C, more preferably 950–1000°C, and the time is 0.5–4 h, more preferably 1–2 h. To ensure that Zn volatilizes quickly and forms micropores as soon as possible during the pyrolysis process, the heating rate of the pyrolysis process is preferably 5–10°C / min, more preferably 6–8°C / min. The pyrolysis process is preferably carried out in a tube furnace.

[0043] It should be noted that Sn will also volatilize during the pyrolysis process. Therefore, in some embodiments of the present invention, it is preferable to place a first intermediate and a second intermediate upstream and downstream of the pyrolysis device (i.e., a tubular furnace) during the pyrolysis process. This allows the vapor generated after the Zn in the upstream first intermediate volatilizes, carrying carbon and the volatilized Sn downstream. This vapor deposits carbon onto the downstream second intermediate and provides a Sn source, resulting in a carbon-coated Sn in the final Fe / Sn-NC catalyst. The mass of the first intermediate is generally lower than that of the second intermediate to ensure more complete volatilization of the first intermediate during pyrolysis. The present invention preferably controls the mass ratio of the first intermediate to the second intermediate to be 1:(1-10), more preferably 1:(3-10), and even more preferably 1:(5-8). In some embodiments of the present invention, after the pyrolysis treatment is completed, the product is preferably allowed to cool naturally, and then treated with an acid solution to remove the Fe clusters formed during the pyrolysis treatment, preventing the Fe clusters from reacting with hydrogen peroxide to generate excessive free radicals, corroding the support, and causing Fe to detach. In this step, since the Sn is carbon-coated Sn, the acid solution will not remove the Sn clusters. In some embodiments of the present invention, the acid solution treatment is preferably performed by: dispersing the product in the acid solution, ultrasonically dispersing, stirring for 8-12 hours, then filtering with a water washing solution 1-3 times, and drying to obtain the Fe / Sn-NC catalyst. The drying is preferably vacuum drying, and the drying temperature is preferably 50-70°C. In the present invention, the acid solution is any one or more of hydrochloric acid, sulfuric acid, or nitric acid. The present invention does not have a particular limitation on the concentration of the acid solution, but the concentration of hydrogen ions in the acid solution is preferably 1-3 mol / L, more preferably 1.5-2.5 mol / L.

[0044] The "room temperature" referred to in this invention is generally between 20 and 30°C, preferably 25°C.

[0045] The preparation method of the Fe / Sn-NC catalyst provided by this invention is simple, has a high yield, and can achieve gram-level preparation, making it suitable for industrial production. It is of great significance for the mass production of low-cost non-precious metal-based catalysts for proton exchange membrane fuel cell cathodes.

[0046] The present invention employs linear sweep voltammetry to test the Fe / Sn-NC catalyst in the above-mentioned technical solution in a 0.5 mol / L sulfuric acid solution, and finds that the catalyst exhibits superior activity compared to the Fe-NC catalyst. Accelerated degradation tests in the 0.5 mol / L sulfuric acid solution show no significant degradation after 10,000, 20,000, and 30,000 cycles, indicating that the catalyst possesses excellent stability.

[0047] Based on this, the present invention also provides a catalyst slurry comprising the above-mentioned Fe / Sn-NC catalyst, a binder, and a solvent. The present invention does not impose any particular limitation on the binder and solvent; they can be selected according to the conventional methods used by those skilled in the art. The binder can be selected from any one or more of perfluorosulfonic acid resin, polytetrafluoroethylene, or polyvinylidene fluoride-hexafluoropropylene copolymer; the solvent can be selected from any one or more of isopropanol, water, ethanol, N-methylpyrrolidone, N-dimethylformamide, dimethyl sulfoxide, or glycerol.

[0048] This invention also provides a membrane electrode, comprising an anode gas diffusion layer, an anode catalyst layer, a cathode catalyst layer, a cathode gas diffusion layer, and a proton exchange membrane located between the anode catalyst layer and the cathode catalyst layer. The cathode catalyst layer can be formed from the aforementioned cathode catalyst slurry, specifically by ultrasonic spraying or blade coating. This invention does not impose any particular limitations on the anode gas diffusion layer, anode catalyst layer, cathode gas diffusion layer, and proton exchange membrane; any conventional choices made by those skilled in the art are acceptable. For example, the anode catalyst layer can be obtained by ultrasonic spraying from a slurry including an anode catalyst (platinum-based catalyst), and the proton exchange membrane can be either Nafion 115 or Nafion 212 proton exchange membrane.

[0049] The present invention also provides a proton exchange membrane fuel cell, including the Fe / Sn-NC catalyst, cathode catalyst slurry, or membrane electrode involved in the above technical solutions.

[0050] This invention provides a specific proton exchange membrane fuel cell, comprising a positive electrode, a negative electrode, and a proton exchange membrane. The positive electrode can be selected from JM Pt / C (20% Pt), the negative electrode is selected from the prepared Fe / Sn-NC catalyst, and the proton exchange membrane is selected from Nafion 212. Studies have shown that by using the above-mentioned Fe / Sn-NC as the cathode catalyst and assembling it into a proton exchange membrane fuel cell, the catalyst exhibits excellent catalytic activity.

[0051] To further illustrate the present invention, the following examples provide a detailed description. The experimental materials used in the following examples can all be purchased commercially or prepared using conventional methods.

[0052] Example 1

[0053] This embodiment provides a Fe / Sn-NC catalyst, the preparation method of which is as follows:

[0054] At room temperature, 39 mmol of 2-methylimidazole was dissolved in 100 mL of methanol and stirred for 0.1 h to obtain a clear and transparent solution A. Simultaneously, 5 mmol of zinc nitrate, 0.11 mmol of ferric chloride, and 0.1 mmol of stannous chloride were dissolved in 80 mL of methanol to obtain a yellow and transparent solution B. Under stirring conditions, solution B was uniformly mixed with solution A and stirred for 24 h. The mixture was washed four times by centrifugation with ethanol as the washing solution, and then dried in a drying oven at 55 °C for 8 h to obtain a pale yellow powder. 110 mg of the pale yellow powder was placed 10 mg upstream and 100 mg downstream of a tube furnace, respectively. The furnace was then heated to 950 °C at a rate of 10 °C / min and heat-treated in an argon atmosphere for 1 h. After cooling to room temperature, a black powder was obtained. The black powder was dispersed in a mixed acid of hydrochloric acid and nitric acid with a hydrogen ion concentration of approximately 2 mol / L, stirred for 10 h, filtered three times with the washing solution, and dried at 55 °C for 10 h to obtain the Fe / Sn-NC catalyst.

[0055] The surface morphology and elemental distribution of the Fe / Sn-NC catalyst obtained in Example 1 were characterized using scanning electron microscopy, and the results are as follows: Figure 1 and Figure 2 As shown, where Figure 1 Here are SEM images of the Fe / Sn-NC catalyst. Figure 2 This is the elemental distribution diagram of the Fe / Sn-NC catalyst. Figure 1 It can be seen that the Fe / Sn-NC catalyst has a polyhedral structure and is uniformly dispersed, combining... Figure 2 It can be seen that the framework of the polyhedron is composed of nitrogen-doped carbon, and the Sn, Fe, N and C elements are evenly distributed in the catalyst.

[0056] X-ray diffraction analysis was performed on the Fe / Sn-NC catalyst obtained in Example 1, and the results are as follows: Figure 3 As shown, it can be seen that it has obvious diffraction peaks of elemental Sn, proving that it contains Sn nanoclusters with zero valence.

[0057] X-ray photoelectron spectroscopy analysis was performed on the Fe / Sn-NC catalyst obtained in Example 1, and the results are as follows: Figure 4 As shown, the presence of 0-valent Sn in the Fe / Sn-NC catalyst also proves the presence of Sn nanoclusters.

[0058] The Fe / Sn-NC catalyst obtained in Example 1 was characterized by spherical aberration electron microscopy and synchrotron radiation, and the results are as follows: Figure 5 and Figure 6 As shown, Figure 5 The image shown is an AC-STEM image of the Fe / Sn-NC catalyst obtained in Example 1. Figure 6 This is a Fourier transform X-ray absorption fine structure (FT-EXAFS) image of the Fe / Sn-NC catalyst obtained in Example 1. Figure 5 It can be seen that the large black circle contains carbon-coated Sn clusters, the small black circle contains Sn single atoms, and the small white circle contains Fe single atoms. This indicates that Sn exists in both single-atom and cluster forms, specifically carbon-coated Sn, while Fe exists in single-atom form. Figure 6 It can be seen that the Fe / Sn-NC catalyst provided by this invention has Fe-N coordination bonds at 1.6 Å and no Fe-Fe bonds at about 2.3 Å, which further proves that Fe exists in the form of single atoms.

[0059] Linear sweep voltammetry was performed on the Fe / Sn-NC catalyst of Example 1 in 0.5 mol / L sulfuric acid solution, and the results are as follows: Figure 7 As shown, the obtained catalyst exhibits superior activity compared to the Fe-NC catalyst.

[0060] Accelerated degradation tests were conducted on the FeSn-NC catalyst of Example 1 in 0.5 mol / L sulfuric acid solution, and the results are as follows: Figure 8 As shown, no significant degradation was observed after 10,000, 20,000, and 30,000 cycles, indicating that the obtained catalyst has excellent stability.

[0061] Using the Fe / Sn-NC catalyst from Example 1 as the cathode catalyst, a proton exchange membrane fuel cell was assembled, and its polarization curve is shown below. Figure 9 As shown, it can exhibit excellent activity.

[0062] Example 2

[0063] This embodiment provides a Fe / Sn-NC catalyst, the preparation method of which is as follows:

[0064] At room temperature, 32 mmol of 2-methylimidazole was dissolved in 350 mL of methanol and stirred for 0.1 h to obtain a clear and transparent solution A. Simultaneously, 7.5 mmol of zinc nitrate, 0.319 mmol of ferric chloride, and 0.27 mmol of stannous chloride were dissolved in 80 mL of methanol to obtain a yellow and transparent solution B. Under stirring conditions, solution B was uniformly mixed with solution A and stirred for 24 h. The mixture was washed four times by centrifugation with ethanol as the washing solution, and then dried in a drying oven at 55 °C for 8 h to obtain a pale yellow powder. 170 mg of the pale yellow powder was placed in tubular furnaces at 20 mg and 150 mg respectively, and then heated to 950 °C at a rate of 10 °C / min and heat-treated in an argon atmosphere for 1 h. After cooling to room temperature, a black powder was obtained. The black powder was dispersed in hydrochloric acid with a hydrogen ion concentration of approximately 2.5 mol / L, stirred for 10 h, filtered three times with water as the washing solution, and dried at 55 °C for 10 h to obtain the Fe / Sn-NC catalyst.

[0065] The Fe / Sn-NC catalyst obtained in Example 2 was characterized by electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical performance testing. The results were similar to those in Example 1.

[0066] Example 3

[0067] This embodiment provides a Fe / Sn-NC catalyst, the preparation method of which is as follows:

[0068] At room temperature, 21 mmol of 2-methylimidazole was dissolved in 60 mL of methanol and stirred for 0.1 h to obtain a clear and transparent solution A. Simultaneously, 5 mmol of zinc nitrate, 0.17 mmol of ferric chloride, and 0.17 mmol of stannous chloride were dissolved in 200 mL of methanol to obtain a yellow and transparent solution B. Under stirring conditions, solution B was uniformly mixed with solution A and stirred for 24 h. The mixture was washed four times by centrifugation with ethanol as the washing solution, and then dried in a drying oven at 55 °C for 8 h to obtain a pale yellow powder. 170 mg of the pale yellow powder was placed 10 mg upstream and 100 mg downstream of a tube furnace, respectively. The furnace was then heated to 950 °C at a rate of 10 °C / min and heat-treated in an argon atmosphere for 1 h. After cooling to room temperature, a black powder was obtained. The black powder was dispersed in hydrochloric acid with a hydrogen ion concentration of approximately 2 mol / L, stirred for 10 h, filtered three times with water as the washing solution, and dried at 55 °C for 10 h to obtain the Fe / Sn-NC catalyst.

[0069] The Fe / Sn-NC catalyst obtained in Example 3 was characterized by electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical performance testing. The results were similar to those in Example 1.

[0070] Example 4

[0071] This embodiment provides a Fe / Sn-NC catalyst, the preparation method of which is as follows:

[0072] At room temperature, 39 mmol of 2-methylimidazole was dissolved in 100 mL of methanol and stirred for 0.1 h to obtain a clear and transparent solution A. Simultaneously, 5 mmol of zinc nitrate, 0.1 mmol of ferric chloride, and 0.06 mmol of stannous chloride were dissolved in 80 mL of methanol to obtain a yellow and transparent solution B. Under stirring, solution B was uniformly mixed with solution A and stirred for 24 h. The mixture was washed four times by centrifugation with ethanol as the washing solution, and then dried in a drying oven at 55 °C for 8 h to obtain a pale yellow powder. 110 mg of the pale yellow powder was placed 10 mg upstream and 100 mg downstream of a tube furnace, respectively. The furnace was then heated to 950 °C at a rate of 10 °C / min and heat-treated in an argon atmosphere for 1 h. After cooling to room temperature, a black powder was obtained. The black powder was dispersed in hydrochloric acid and stirred for 10 h. It was then filtered three times with the washing solution and dried at 55 °C for 10 h to obtain the Fe / Sn-NC catalyst.

[0073] The Fe / Sn-NC catalyst obtained in Example 4 was characterized by electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical performance testing. It was found that the Sn clusters formed by this catalyst had smaller particle sizes and exhibited higher catalytic activity, but poorer stability.

[0074] The Fe / Sn-NC catalyst obtained in Example 4 was subjected to linear sweep voltammetry and stability testing in 0.5 mol / L sulfuric acid solution. The results are as follows: Figure 10 As shown, the obtained catalyst exhibits better activity than the catalyst in Example 1, but its stability is lower than that of Example 1.

[0075] Example 5

[0076] This embodiment provides a Fe / Sn-NC catalyst, the preparation method of which is as follows:

[0077] At room temperature, 39 mmol of 2-methylimidazole was dissolved in 100 mL of methanol and stirred for 0.1 h to obtain a clear and transparent solution A. Simultaneously, 5 mmol of zinc nitrate, 0.1 mmol of ferric chloride, and 0.15 mmol of stannous chloride were dissolved in 80 mL of methanol to obtain a yellow and transparent solution B. Under stirring conditions, solution B was uniformly mixed with solution A and stirred for 24 h. The mixture was washed four times by centrifugation with ethanol as the washing solution, and then dried in a drying oven at 55 °C for 8 h to obtain a pale yellow powder. 110 mg of the pale yellow powder was placed 10 mg upstream and 100 mg downstream of a tube furnace, respectively. The furnace was then heated to 950 °C at a rate of 10 °C / min and heat-treated in an argon atmosphere for 1 h. After cooling to room temperature, a black powder was obtained. The black powder was dispersed in hydrochloric acid and stirred for 10 h. It was then filtered three times with the washing solution and dried at 55 °C for 10 h to obtain the Fe / Sn-NC catalyst.

[0078] The Fe / Sn-NC catalyst obtained in Example 5 was characterized by electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical performance testing. It was found that the Sn clusters formed by this catalyst had larger particle sizes and exhibited higher stability, but poorer catalytic activity.

[0079] The Fe / Sn-NC catalyst obtained in Example 5 was subjected to linear sweep voltammetry and stability testing in 0.5 mol / L sulfuric acid solution. The results are as follows: Figure 11 As shown, the obtained catalyst exhibits better stability than the catalyst in Example 1, but its activity is lower than that of Example 1.

[0080] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A Sn-doped Fe-NC catalyst, characterized in that, Includes the support and Sn and Fe atoms loaded on the support; The carrier is an N-doped carbon material; The Sn atom is a carbon-coated Sn atom, and the Sn atom includes Sn single atoms and Sn atom clusters; The Fe atom includes a single Fe atom; The method for preparing the catalyst includes the following steps: S1: A nitrogen-containing organic ligand solution is mixed with a solution containing zinc salt, iron salt and tin salt and reacted. After removing the solvent, an intermediate is obtained. S2: The intermediate is pyrolyzed in an inert atmosphere to obtain a catalyst; In step S2, a first intermediate is placed upstream of the pyrolysis device and a second intermediate is placed downstream of the pyrolysis device. Then, the pyrolysis is carried out in an inert atmosphere to obtain a catalyst.

2. The catalyst according to claim 1, characterized in that, The catalyst contains 1.3% to 2.2% Fe atoms by mass. The catalyst contains 0.5% to 1.7% Sn atoms by mass.

3. The catalyst according to claim 1, characterized in that, The mass ratio of N to C in the carrier is 1:100 to 3:

100.

4. The method for preparing the catalyst according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1: A nitrogen-containing organic ligand solution is mixed with a solution containing zinc salt, iron salt and tin salt and reacted. After removing the solvent, an intermediate is obtained. S2: The intermediate is pyrolyzed in an inert atmosphere to obtain a catalyst; In step S2, a first intermediate is placed upstream of the pyrolysis device and a second intermediate is placed downstream of the pyrolysis device. Then, the pyrolysis is carried out in an inert atmosphere to obtain a catalyst.

5. The preparation method according to claim 4, characterized in that, After the pyrolysis treatment is completed, the process further includes the step of treating the obtained product with an acid solution.

6. The preparation method according to claim 4, characterized in that, The molar ratio of the organic ligand to the zinc salt, iron salt, and tin salt in the organic ligand solution is 4000:(500~1200):(9~38):(5~40).

7. A cathode catalyst for a proton exchange membrane fuel cell, characterized in that, The catalyst includes any one of claims 1 to 3 or a catalyst prepared by any one of claims 4 to 6.

8. A proton exchange membrane fuel cell, characterized in that, Includes the anode, cathode, and proton exchange membrane; The cathode comprises the cathode catalyst of claim 7.

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