Fuel Cell Catalysts, Preparation Methods and Applications

Abstract

This application discloses a fuel cell catalyst, its preparation method, and its application, belonging to the field of battery technology. The catalyst prepared in this application consists of nitrogen-doped carbon nanocages, cobalt nanoparticles, and carbon nanotubes. Carbon nanotubes are grown on the surface of the nitrogen-doped carbon nanocages, and cobalt nanoparticles are encapsulated within the carbon nanotubes and carbon nanocages. Nitrogen doping increases the catalytic active sites in the catalyst material, improving its catalytic activity. The Mott-Schottky effect between the cobalt nanoparticles and the carbon material causes electron transfer from the metal material to the carbon material; this uneven electron distribution further enhances the catalytic activity of the catalyst material. The encapsulation of the cobalt nanoparticles within the carbon material also avoids the problem of poor contact between the active metal nanoparticles and the carbon material. Furthermore, the materials used in this catalyst are inexpensive and readily available, and the preparation process is simple. Therefore, the catalyst prepared in this application has both low production cost and high catalytic activity.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a fuel cell catalyst, its preparation method, and its application. Background Technology

[0002] The oxygen reduction reaction (ORR) is the most critical technology in fuel cells, but the kinetics of the ORR at the cathode are very slow, thus requiring a suitable catalyst to promote the reaction. Pt-based catalysts, due to their high cost and limited resources, have significantly constrained the development of fuel cells. Therefore, developing efficient, long-life, non-Pt-based fuel cell catalysts is fundamental to reducing fuel cell costs and promoting the large-scale application of fuel cells.

[0003] In related technologies, either heteroatom doping modification of the nano-carbon support or the introduction of graphene composite carbon materials are employed. However, heteroatom doping modification of the nano-carbon support often leads to poor contact between the carbon material and the active metal nanoparticles, resulting in low catalytic activity of the fuel cell catalyst. Introducing graphene composite carbon materials, on the other hand, results in high production costs. Therefore, it is necessary to provide a fuel cell catalyst that can both reduce production costs and improve catalytic activity. Summary of the Invention

[0004] This application provides a fuel cell catalyst, its preparation method, and its application, which can reduce production costs and improve catalytic activity. The technical solution is as follows:

[0005] On the one hand, a method for preparing a fuel cell catalyst is provided, the method comprising:

[0006] Prepare methanol solutions of cobalt nitrate, zinc nitrate, and 2-methylimidazole respectively.

[0007] The methanol solution of cobalt nitrate, the methanol solution of zinc nitrate, and the methanol solution of 2-methylimidazole were mixed, and the mixture was allowed to stand, centrifuged, washed, and dried to obtain a metal-organic framework material.

[0008] The metal-organic framework material is placed in a tube furnace and heated to 600–1000°C under an inert protective gas atmosphere, held at that temperature for 1–4 hours, and then naturally cooled to room temperature to obtain a fuel cell catalyst.

[0009] In one possible implementation, the step of mixing the methanol solution of cobalt nitrate, the methanol solution of zinc nitrate, and the methanol solution of 2-methylimidazole, followed by standing, centrifugation, washing, and drying to obtain a metal-organic framework material includes:

[0010] The methanol solution of cobalt nitrate and the methanol solution of 2-methylimidazole were mixed and stirred until homogeneous to obtain a mixed solution.

[0011] Add the methanol solution of zinc nitrate to the mixed solution, let stand for 1-12 hours, and then centrifuge the product.

[0012] After centrifugation, the material was washed with methanol and dried to obtain the metal-organic framework material.

[0013] In another possible implementation, the methanol solution of cobalt nitrate, the methanol solution of zinc nitrate, and the methanol solution of 2-methylimidazole are mixed in a volume ratio of 1:2:3, 2:1:3, or 1:1:2.

[0014] In another possible implementation, the preparation of the methanol solutions of cobalt nitrate, zinc nitrate, and 2-methylimidazole, respectively, includes:

[0015] Prepare a 0.1–0.5 mol / L cobalt nitrate methanol solution by adding cobalt nitrate hexahydrate to methanol;

[0016] Zinc nitrate hexahydrate is added to methanol to prepare a methanol solution of 0.1–1.0 mol / L zinc nitrate.

[0017] Prepare a methanol solution of 0.5–2.0 mol / L 2-methylimidazole by adding 2-methylimidazole to methanol.

[0018] In another possible implementation, the concentration of the cobalt nitrate methanol solution is 0.25 mol / L, the concentration of the zinc nitrate methanol solution is 0.57 mol / L, and the concentration of the 2-methylimidazole methanol solution is 1 mol / L.

[0019] In another possible implementation, the inert protective gas includes at least one of nitrogen, argon, hydrogen, and a mixture of argon and hydrogen.

[0020] In another possible implementation, the flow rate of the inert protective gas is 10–20 L / min, and the heating rate is 1–5 °C / min.

[0021] In another possible implementation, the heating temperature is 900℃ and the holding time is 2 hours.

[0022] On the other hand, a fuel cell catalyst is provided, which is prepared by any of the preparation methods described above.

[0023] On the other hand, an application of a fuel cell catalyst in the preparation of battery electrode materials is provided.

[0024] This application provides a method for preparing a fuel cell catalyst. The catalyst consists of nitrogen-doped carbon nanocages, cobalt nanoparticles, and carbon nanotubes. Carbon nanotubes are grown on the surface of the nitrogen-doped carbon nanocages, and cobalt nanoparticles are encapsulated within the carbon nanotubes and carbon nanocages. Nitrogen doping breaks the chemical inertia caused by the uniform electron distribution in the carbon network, increasing the catalytic active sites and improving catalytic activity. The Mott-Schottky effect between the cobalt nanoparticles and the carbon material causes electron transfer from the metal to the carbon material. This non-uniform electron distribution further enhances the catalytic activity of the catalyst. The encapsulation of cobalt nanoparticles within the carbon material also avoids the problem of poor contact between active metal nanoparticles and carbon material. Furthermore, the carbon nanotubes grown on the surface of the nanocages can increase the specific surface area and graphitization degree of the catalyst material. The three-dimensional network formed by the carbon nanotubes between the nanocages improves the conductivity of the material, further enhancing the catalytic activity. In addition, the materials used in this catalyst are inexpensive and readily available, and the preparation process is simple. Therefore, the catalyst prepared in this application has both low production cost and high catalytic activity.

[0025] It should be understood that the above general description and the following detailed description are merely exemplary and do not limit this disclosure. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating a method for preparing a fuel cell catalyst according to an embodiment of this application;

[0027] Figure 2 This is a morphology diagram of a catalyst prepared in Example 1, as provided in this application.

[0028] Figure 3 This is the N1s curve of the X-ray photoelectron energy spectrum of a catalyst prepared in Example 1 provided in this application;

[0029] Figure 4 This is a morphology diagram of a catalyst prepared in Example 2 provided in this application;

[0030] Figure 5 This is a Co1s curve of the X-ray photoelectron spectroscopy of a catalyst prepared in Example 2 of this application.

[0031] Figure 6 This is a morphology diagram of a catalyst prepared in Example 3 of this application.

[0032] Figure 7 This is a morphology diagram of a catalyst prepared in Example 4 of this application.

[0033] Figure 8This is a TEM image of a catalyst prepared in Example 4 of this application.

[0034] Figure 9 This is an HRTEM image of a catalyst prepared in Example 4 of this application.

[0035] Figure 10 This is an EDS diagram of a catalyst prepared in Example 4 of this application.

[0036] Figure 11 These are LSV curves of catalysts prepared in Examples 1-4 provided in this application;

[0037] Figure 12 These are the CV curves of catalysts prepared in Examples 1-4 provided in this application;

[0038] Figure 13 This is the LSV curve of a Pt / C catalyst after 10,000 ADT cycles provided in the embodiments of this application;

[0039] Figure 14 This is the LSV curve of a catalyst prepared in Example 4 of this application after 10,000 ADT cycles. Detailed Implementation

[0040] To make the technical solution and advantages of this application clearer, the embodiments of this application will be described in further detail below.

[0041] On the one hand, embodiments of this application provide a method for preparing a fuel cell catalyst, see [link to relevant documentation]. Figure 1 The preparation method includes:

[0042] Step 101: Prepare methanol solutions of cobalt nitrate, zinc nitrate, and 2-methylimidazole respectively.

[0043] Cobalt nitrate hexahydrate (Co(NO3)2·6H2O) is added to methanol to prepare a methanol solution of cobalt nitrate with a concentration of 0.1–0.5 mol / L.

[0044] Zinc nitrate hexahydrate (Zn(NO3)2·6H2O) is added to methanol to prepare a methanol solution of 0.1–1.0 mol / L zinc nitrate.

[0045] Prepare a methanol solution of 0.5–2.0 mol / L 2-methylimidazole by adding 2-methylimidazole to methanol.

[0046] The concentrations of cobalt nitrate methanol solutions can be 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, and 0.5 mol / L. The concentrations of zinc nitrate methanol solutions can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.57 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, and 1.0 mol / L. The concentrations of 2-methylimidazole in methanol solutions can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, and 2.0 mol / L.

[0047] Furthermore, the concentration of the methanol solution of cobalt nitrate is 0.25 mol / L, the concentration of the methanol solution of zinc nitrate is 0.57 mol / L, and the concentration of the methanol solution of 2-methylimidazole is 1 mol / L.

[0048] The methanol solutions of cobalt nitrate, zinc nitrate, and 2-methylimidazole were all stored at room temperature after preparation.

[0049] In the embodiments of this application, 2-methylimidazole provides nitrogen and carbon elements, and cobalt nitrate provides cobalt element. Cobalt nitrate and zinc nitrate coordinate with 2-methylimidazole to form a metal-organic framework material, which is then subjected to a subsequent high-temperature carbonization process.

[0050] Step 102: Mix the methanol solutions of cobalt nitrate, zinc nitrate, and 2-methylimidazole, let stand, centrifuge, wash, and dry to obtain the metal-organic framework material.

[0051] A methanol solution of cobalt nitrate and a methanol solution of 2-methylimidazole were mixed and stirred until homogeneous to obtain a mixed solution. A methanol solution of zinc nitrate was added to the mixed solution, and the mixture was allowed to stand for 1–12 hours. The product was then centrifuged. After centrifugation, the product was washed with methanol and dried to obtain a metal-organic framework material. This metal-organic framework material can be represented as ZIF-67@ZIF-8.

[0052] In one possible implementation, a methanol solution of cobalt nitrate, a methanol solution of zinc nitrate, and a methanol solution of 2-methylimidazole are mixed in a volume ratio of 1:2:3, 2:1:3, or 1:1:2.

[0053] Furthermore, the methanol solutions of cobalt nitrate, zinc nitrate, and 2-methylimidazole are mixed in a volume ratio of 1:1:2.

[0054] The stirring time can be from 5 to 20 minutes, for example, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes, and 20 minutes. In this embodiment, only a stirring time of 10 minutes is used as an example for illustration.

[0055] The settling time can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours. In this embodiment, only a settling time of 4 hours is used as an example. It can be left to stand at room temperature.

[0056] The number of times methanol washing is applied can be 1 to 5 times, for example, 1, 2, 3, 4, or 5 times. In this embodiment, only 3 washes are used as an example for illustration.

[0057] The drying temperature can be set and changed as needed. For example, the drying temperature can be 50°C, 60°C, or 70°C. In this embodiment, only 60°C is used as an example for illustration.

[0058] Step 103: Place the metal-organic framework material into a tube furnace, heat it to 600-1000°C under an inert protective gas atmosphere, hold it at that temperature for 1-4 hours, and then allow it to cool naturally to room temperature to obtain the fuel cell catalyst.

[0059] The inert protective gas includes at least one of nitrogen, argon, hydrogen, and a mixture of argon and hydrogen. For example, nitrogen is the inert protective gas.

[0060] The flow rate of the inert protective gas is 10–20 L / min, for example, 10 L / min, 12 L / min, 14 L / min, 15 L / min, 16 L / min, 18 L / min, and 20 L / min. In this embodiment, only an inert protective gas flow rate of 15 L / min is used as an example for illustration.

[0061] The heating rate in the tube furnace is 1 to 5 °C / min, for example, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, and 5 °C / min. In this embodiment, only a heating rate of 2 °C / min is used as an example for illustration.

[0062] The heating temperature is 600–1000°C, for example, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, and 1000°C. In this embodiment, only a heating temperature of 900°C is used as an example for illustration.

[0063] The heat preservation time is 1 to 4 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, and 4 hours. In this embodiment, only a heat preservation time of 2 hours is used as an example for illustration.

[0064] In this embodiment, the catalyst is composed of nitrogen-doped carbon nanocages, cobalt nanoparticles, and carbon nanotubes. Carbon nanotubes are grown on the surface of the nitrogen-doped carbon nanocages, and cobalt nanoparticles are encapsulated within the carbon nanotubes and carbon nanocages. The carbon nanocages have a diameter of 300–400 nm, the cobalt nanoparticles have a diameter of 10–30 nm, and the carbon nanotubes have a diameter of 30–50 nm. Nitrogen doping breaks the chemical inertia caused by the uniform electron distribution in the carbon network, increasing the catalytic active sites and improving catalytic activity. The Mott-Schottky effect between the cobalt nanoparticles and the carbon material causes electrons to transfer from the metal to the carbon material. This non-uniform electron distribution further enhances the catalytic activity of the catalyst. The encapsulation of cobalt nanoparticles within the carbon material also avoids the problem of poor contact between active metal nanoparticles and carbon. Furthermore, the carbon nanotubes grown on the surface of the nanocages can increase the specific surface area and graphitization degree of the catalyst material. The three-dimensional network formed by the carbon nanotubes between the nanocages improves the conductivity of the material, further enhancing the catalytic activity. In addition, the materials used in this catalyst are inexpensive and readily available, and the preparation process is simple. Therefore, the catalyst prepared in this application has both low production cost and high catalytic activity.

[0065] On the other hand, a fuel cell catalyst is provided, which is prepared by the above-described preparation method.

[0066] On the other hand, an application of a fuel cell catalyst in the preparation of battery electrode materials is provided.

[0067] The technical solution of this application will be described in detail below through specific embodiments.

[0068] In the following specific embodiments, unless otherwise specified, all operations shall be performed under normal conditions or conditions recommended by the manufacturer.

[0069] Example 1

[0070] Example 1 provides a catalyst, which is obtained by the following preparation method:

[0071] (1) Preparation of ZIF-8: Zn(NO3)2·6H2O was added to methanol to prepare a 0.57 mol / L methanol solution of Zn(NO3)2·6H2O, which was stored at room temperature. 2-Methylimidazole was added to methanol to prepare a 1 mol / L methanol solution of 2-methylimidazole, which was stored at room temperature. The methanol solution of Zn(NO3)2·6H2O and the methanol solution of 2-methylimidazole were mixed at a volume ratio of 1:1 and stirred for 10 min, then allowed to stand at room temperature for 4 h. The product was centrifuged, washed three times with methanol, and dried at 60 °C to obtain ZIF-8 material.

[0072] (2) Preparation of nitrogen-doped carbon catalyst: ZIF-8 material was placed in a tube furnace and heated to 900°C under an inert protective atmosphere of nitrogen. The temperature was maintained for 2 hours. The nitrogen flow rate was 15 L / min and the heating rate was 2°C / min. The catalyst was obtained by natural cooling to room temperature.

[0073] See Figure 2 , Figure 2 This is a morphology diagram of the catalyst prepared in Example 1.

[0074] See Figure 3 , Figure 3 The N1s curve of the X-ray photoelectron spectrum of the catalyst prepared in Example 1 is shown below. Figure 3 As can be seen, nitrogen has been successfully incorporated into carbon materials in the form of nitrogen-containing functional groups such as pyrrole nitrogen, pyridine nitrogen, graphitic nitrogen, and nitrogen oxide.

[0075] Example 2

[0076] Example 2 provides a catalyst, which is obtained by the following preparation method:

[0077] (1) Preparation of ZIF-67: Co(NO3)2·6H2O was added to methanol to prepare a 0.25 mol / L methanol solution of Co(NO3)2·6H2O, which was stored at room temperature. 2-Methylimidazole was added to methanol to prepare a 1 mol / L methanol solution of 2-methylimidazole, which was stored at room temperature. The methanol solution of Co(NO3)2·6H2O and the methanol solution of 2-methylimidazole were mixed at a volume ratio of 1:1 and stirred for 10 min, then allowed to stand at room temperature for 4 h. The product was centrifuged, washed three times with methanol, and dried at 60 °C to obtain ZIF-67 material.

[0078] (2) Preparation of nitrogen-doped carbon catalyst loaded with cobalt nanoparticles: ZIF-67 material was placed in a tube furnace and heated to 900℃ under an inert protective atmosphere of nitrogen. The temperature was maintained for 2 hours. The nitrogen flow rate was 15 L / min and the heating rate was 2℃ / min. The catalyst was obtained by natural cooling to room temperature.

[0079] See Figure 4 , Figure 4 This is a morphology diagram of the catalyst prepared in Example 2.

[0080] See Figure 5 , Figure 5 The image shows the Co 1s curve of the X-ray photoelectron spectroscopy of the catalyst prepared in Example 2. This result proves the presence of elemental cobalt and indicates that cobalt nanoparticles were successfully loaded into carbon materials.

[0081] Example 3

[0082] (1) Preparation of ZIF-67@ZIF-8: Co(NO3)2·6H2O was added to methanol to prepare a 0.25 mol / L methanol solution of Co(NO3)2·6H2O, which was stored at room temperature. Zn(NO3)2·6H2O was added to methanol to prepare a 0.57 mol / L methanol solution of Zn(NO3)2·6H2O, which was stored at room temperature. 2-Methylimidazole was added to methanol to prepare a 1 mol / L methanol solution of 2-methylimidazole, which was stored at room temperature. The methanol solutions of Co(NO3)2·6H2O, Zn(NO3)2·6H2O, and 2-methylimidazole were mixed and stirred for 10 min at a volume ratio of 1:1:2, and then allowed to stand at room temperature for 4 h. The product was centrifuged, washed three times with methanol, and dried at 60 °C to obtain ZIF-67@ZIF-8 material.

[0083] (2) Preparation of nitrogen-doped catalysts for short carbon nanotubes coated with cobalt nanoparticles: ZIF-67@ZIF-8 material was placed in a tube furnace and heated to 700℃ under an inert protective atmosphere of nitrogen. The temperature was maintained for 2 hours, the nitrogen flow rate was 15L / min, the heating rate was 2℃ / min, and the catalyst was obtained by natural cooling to room temperature.

[0084] See Figure 6 , Figure 6 Here is a morphology image of the catalyst prepared in Example 3, from... Figure 6 As can be seen, compared with the catalyst prepared in Example 2, the catalyst prepared in Example 3 has a small amount of short carbon nanotubes grown in it. The short carbon nanotubes are nitrogen-doped carbon nanomaterials that coat cobalt nanoparticles.

[0085] Example 4

[0086] (1) Preparation of ZIF-67@ZIF-8: Co(NO3)2·6H2O was added to methanol to prepare a 0.25 mol / L methanol solution of Co(NO3)2·6H2O, which was stored at room temperature. Zn(NO3)2·6H2O was added to methanol to prepare a 0.57 mol / L methanol solution of Zn(NO3)2·6H2O, which was stored at room temperature. 2-Methylimidazole was added to methanol to prepare a 1 mol / L methanol solution of 2-methylimidazole, which was stored at room temperature. The methanol solutions of Co(NO3)2·6H2O, Zn(NO3)2·6H2O, and 2-methylimidazole were mixed and stirred for 10 min at a volume ratio of 1:1:2, and then allowed to stand at room temperature for 4 h. The product was centrifuged, washed three times with methanol, and dried at 60 °C to obtain ZIF-67@ZIF-8 material.

[0087] (2) Preparation of nitrogen-doped catalysts with cobalt nanoparticles coated with long carbon nanotubes: ZIF-67@ZIF-8 material was placed in a tube furnace and heated to 900℃ under an inert protective atmosphere of nitrogen. The temperature was maintained for 2 hours, the nitrogen flow rate was 15L / min, the heating rate was 2℃ / min, and the catalyst was obtained by natural cooling to room temperature.

[0088] See Figure 7 , Figure 7 Here is a morphology image of the catalyst prepared in Example 4, from... Figure 7 As can be seen in both (a) and (b), compared with the catalyst prepared in Example 3, the catalyst prepared in Example 4 has a large number of long carbon nanotubes grown, and the long carbon nanotubes are nitrogen-doped carbon nanomaterials that coat cobalt nanoparticles.

[0089] See Figure 8 , Figure 8 The image shown is a transmission electron microscope (TEM) image of the catalyst prepared in Example 4. Figure 8 In (a), 12nm, 13nm, and 14nm are the diameters of the cobalt nanoparticles. Figure 8 In (b), 34nm, 38nm, 43nm, 45nm, and 48nm are the diameters of carbon nanotubes.

[0090] See Figure 9 , Figure 9 Here is a high-resolution transmission electron microscope (HRTEM) image of the catalyst prepared in Example 4. Figure 9 (a) The middle framed part is cobalt nanoparticles, and the part pointed to by the arrow is the carbon wall of carbon nanotubes. Figure 9 (b) is for Figure 9 (a) An enlarged view of the framed area, from... Figure 9 As can be seen from (b): the lattice spacing d of cobalt 111=0.21nm, the lattice spacing d of carbon 002 =0.34nm. And from Figure 9 As can be seen in (b), carbon is on the outside of cobalt, which also shows that the catalyst prepared in Example 4 is indeed a carbon nanotube-coated cobalt nanoparticle catalyst.

[0091] See Figure 10 , Figure 10 The image shows the energy dispersive X-ray (EDS) spectrum of the catalyst prepared in Example 4. Figure 10 (a) is a schematic diagram of the distribution of elements on the catalyst surface. Figure 10 (b) is a schematic diagram of the carbon element distribution in the catalyst. Figure 10 (c) is a schematic diagram of the nitrogen distribution in the catalyst. Figure 10 (d) is a schematic diagram of the distribution of cobalt in the catalyst.

[0092] Combination Figures 7 to 10 This demonstrates that Example 4 successfully prepared a nitrogen-doped carbon catalyst with cobalt nanoparticles coated with carbon nanotubes.

[0093] It should be noted that the catalyst prepared by carbonization of ZIF-8 synthesized in Example 1 with the addition of zinc nitrate and 2-methylimidazole did not grow carbon nanotubes due to the lack of cobalt catalyst. The catalyst prepared by carbonization of ZIF-67 synthesized in Example 2 with the addition of cobalt nitrate and 2-methylimidazole lacked sufficient carbon source for carbon nanotube growth due to the absence of ZIF-8 coating; therefore, no carbon nanotubes grew in the catalyst. However, in Examples 3 and 4, ZIF-67@ZIF-8 was synthesized by simultaneously adding cobalt nitrate, zinc nitrate, and 2-methylimidazole. ZIF-67 provided cobalt catalyst for carbon nanotube growth, and ZIF-8 provided sufficient carbon source; therefore, carbon nanotubes grew in the catalyst. It is evident that the necessary conditions for carbon nanotube growth are a nanomaterial with a ZIF-8 shell providing sufficient carbon source and a ZIF-67 core providing cobalt catalyst.

[0094] In addition, although carbon nanotubes were grown in Example 3, the grown carbon nanotubes were short and the quantity was small. This is because the heating temperature (700°C) in Example 3 was low, while the heating temperature (900°C) in Example 4 was high, which was suitable for the growth of carbon nanotubes. Therefore, the grown carbon nanotubes were long and the quantity was large.

[0095] Application Examples

[0096] All ORR tests in this experiment were performed on a CHI760e electrochemical workstation manufactured by Shanghai Chenhua Instruments Co., Ltd. A three-electrode testing system was used, with a glassy carbon electrode as the working electrode, and a 1cm depth. 2A platinum sheet was used as the counter electrode, mercury / mercury oxide (Hg / HgO) was used as the reference electrode, and 0.1 mol / L KOH was selected as the electrolyte. All electrochemical tests were performed in a constant temperature water bath at 25°C.

[0097] Slurry preparation: Accurately weigh 5 mg of the ground catalyst and uniformly disperse it in a mixed solution consisting of 995 μL ethanol and 5 μL Nafion. Then, place the mixed solution in an ultrasonic machine and sonicate for 1 hour to ensure uniform dispersion of the catalyst. This uniformly dispersed catalyst is used to prepare the working electrode.

[0098] The activity of the catalyst in ORR was investigated using linear sweep voltammetry (LSV). LSV measurements were performed in an O2-saturated KOH electrolyte at a scan rate of 20 mV·s. -1 The scanning voltage range is -0.9 to 0.3V, and the rotation speed of the ring disk electrode is 1600 rpm.

[0099] The CV curve (O2) test conditions for the catalyst were: in 0.1 mol / L KOH electrolyte, within a set voltage range of -0.9 to 0.3 V and 50 mV·s. -1 Cyclic voltammetry (CV) curves were performed at a scan rate until a stable curve was obtained.

[0100] To evaluate the stability of the obtained catalyst, the difference in half-wave potential in the LSV curves of the catalyst material before and after accelerated durability testing (ADT) was compared. This experiment was conducted in a 0.1 mol / L KOH electrolyte environment, with continuous O2 introduction and a flow rate of 100 mV·s. -1 The catalyst sample was subjected to a CV test at a scan rate of 10,000 cycles.

[0101] like Figure 11 As shown, the O2-saturated system at 1600 rpm and 10 mV·s -1 The LSV curves below show the half-wave potential (E) of different catalysts in 0.1 mol / L KOH electrolyte. 1 / 2 As can be seen, the catalyst prepared in Example 4 exhibits a higher half-wave potential, i.e., E 1 / 2 The voltage is 0.78V (vs RHE), indicating that it has good performance.

[0102] like Figure 12 As shown in the CV curves under O2 saturation, the catalyst prepared in Example 4 exhibits stronger oxygen reduction activity compared to the catalysts prepared in Examples 1-3.

[0103] To verify the durability of the catalyst prepared in Example 4, an accelerated durability test (ADT) was used for evaluation. Figure 13 and Figure 14 As shown, the half-wave potential of the Pt / C catalyst decreased by 32 mV, while the half-wave potential of the catalyst prepared in Example 4 decreased by only 20 mV. This indicates that the catalyst prepared in Example 4 has higher durability.

[0104] The above description is only for the purpose of enabling those skilled in the art to understand the technical solution of this application, and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a fuel cell catalyst, characterized in that, The preparation method includes: Prepare a 0.1-0.5 mol / L cobalt nitrate methanol solution by adding cobalt nitrate hexahydrate to methanol; Zinc nitrate hexahydrate is added to methanol to prepare a 0.1-1.0 mol / L zinc nitrate methanol solution; Prepare a 0.5~2.0 mol / L 2-methylimidazole methanol solution by adding 2-methylimidazole to methanol; The methanol solution of cobalt nitrate, the methanol solution of zinc nitrate, and the methanol solution of 2-methylimidazole are mixed in a volume ratio of 1:2:3, 2:1:3, or 1:1:2, and then allowed to stand, centrifuged, washed, and dried to obtain a metal-organic framework material. The metal-organic framework material is placed in a tube furnace and heated to 600~1000℃ under an inert protective gas atmosphere, held for 1~4 hours, and then naturally cooled to room temperature to obtain a fuel cell catalyst. The fuel cell catalyst is composed of nitrogen-doped carbon nanocages, cobalt nanoparticles, and carbon nanotubes. The carbon nanotubes are grown on the surface of the nitrogen-doped carbon nanocages, and the cobalt nanoparticles are coated inside the carbon nanotubes and the nitrogen-doped carbon nanocages.

2. The preparation method according to claim 1, characterized in that, The process involves mixing the methanol solutions of cobalt nitrate, zinc nitrate, and 2-methylimidazole, followed by standing, centrifugation, washing, and drying to obtain a metal-organic framework material, comprising: The methanol solution of cobalt nitrate and the methanol solution of 2-methylimidazole were mixed and stirred until homogeneous to obtain a mixed solution. Add the methanol solution of zinc nitrate to the mixed solution, let stand for 1-12 hours, and then centrifuge the product. After centrifugation, the material was washed with methanol and dried to obtain the metal-organic framework material.

3. The preparation method according to claim 1, characterized in that, The concentration of the cobalt nitrate methanol solution is 0.25 mol / L, the concentration of the zinc nitrate methanol solution is 0.57 mol / L, and the concentration of the 2-methylimidazole methanol solution is 1 mol / L.

4. The preparation method according to claim 1, characterized in that, The inert protective gas includes at least one of nitrogen, argon, hydrogen, and a mixture of argon and hydrogen.

5. The preparation method according to claim 1, characterized in that, The flow rate of the inert protective gas is 10~20 L / min, and the heating rate is 1~5℃ / min.

6. The preparation method according to claim 1, characterized in that, The heating temperature is 900℃, and the holding time is 2 hours.

7. A fuel cell catalyst, characterized in that, The fuel cell catalyst is prepared using the preparation method described in any one of claims 1 to 6.

8. The application of the fuel cell catalyst according to claim 7 in the preparation of battery electrode materials.

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