A method for preparing a low-platinum-content cathode oxygen reduction catalyst and its application

Abstract

This invention discloses a method for preparing a low-platinum-content cathode oxygen reduction catalyst, comprising the following steps: dissolving a platinum metal precursor, a transition metal (M) precursor, a nitrogen-containing organic compound, and a zinc precursor in anhydrous methanol and stirring until homogeneous to obtain solution A; then dissolving dimethylimidazolium in anhydrous methanol and stirring until homogeneous to obtain solution B; mixing solutions A and B, stirring until homogeneous, centrifuging, washing with solvent, drying, and then sending to a high-temperature carbonization apparatus for high-temperature carbonization to obtain an atomically dispersed product Pt,M / NC. The Pt,M / NC catalyst prepared by this invention exhibits significantly improved performance compared to the original commercial Pt / C catalyst, possessing advantages such as higher mass activity and stability, efficient proton-charge transport capability, and enhanced electronic structure; the Pt atomic content is only 0.06 wt%, and the catalyst mass activity during the oxygen reduction reaction is 85 times that of Pt / C.

Description

Technical Field

[0001] This invention belongs to the field of new energy fuel cell technology, and particularly relates to a method for preparing a low-platinum-content cathode oxygen reduction catalyst and its application. Background Technology

[0002] With the massive consumption of fossil fuels and the increasing severity of environmental pollution and climate change, the development of green, efficient renewable energy and new energy storage and conversion devices is urgently needed. The demand for clean, green, and sustainable new energy sources is growing. Low-temperature proton exchange membrane fuel cells (PEMFCs), as a clean and sustainable energy conversion device, are widely considered a highly promising portable energy device due to their high energy conversion efficiency, convenient storage and transportation, and environmental friendliness. Furthermore, PEMFCs offer advantages such as high energy density, rapid low-temperature start-up, simple structure, excellent safety, and low noise, making them the best alternative to internal combustion engines for automobiles. They can be widely used in new energy vehicles, aerospace, ships, and other large-scale equipment, and can effectively alleviate the excessive use of traditional fossil fuels and the resulting environmental pollution and climate change problems.

[0003] The most critical aspect of low-temperature proton exchange membrane fuel cells (PEMFCs) is the use of catalysts. Currently, noble metal Pt catalysts are the most widely used catalyst materials for PEMFC cathodes, but their development and application are limited by their low reserves, high cost, and susceptibility to poisoning by intermediate products. There are also related technical studies on platinum composite catalysts in the existing technology, for example: 1. Chinese patent application CN202110398417.8 discloses a low platinum alloy catalyst with crystal facet modulation, its preparation method, and its application in fuel cells. The preparation method uses a specific transition metal carbonyl compound as a modulator and stabilizer for crystal facet modulation of the alloy catalyst. It utilizes the gas-liquid two-phase coexistence synthesis system generated by the ethylene glycol reaction liquid under critical state in the reactor to prepare a low platinum alloy catalyst with a high (111) crystal facet preferred orientation. The resulting commercial carbon black supported alloy nanoparticle composite catalyst is a black powder; the alloy particle size is 1-5 nm and it is uniformly dispersed on the carbon support surface. After modulation, the texture coefficient of the alloy crystal facet preferred orientation reaches more than 1.24. This method improves the ORR catalytic performance and activity stability of platinum alloy catalysts by modulating the crystal facets. The catalyst exhibits high electrocatalytic activity and stability for oxygen reduction reaction in acidic media, and its performance is superior to that of commercial platinum-carbon (Pt / C) catalysts. It can be applied in proton exchange membrane fuel cells to replace conventional commercial platinum-carbon catalysts.

[0004] 2. Chinese patent application CN202110202172.7 discloses a method for preparing an ordered low-platinum alloy catalyst. The method involves treating a carbon support with nitric acid in an oil bath, filtering and drying it, then adding it to deionized water and ultrasonically dispersing it to obtain a carbon support aqueous ion solution. A platinum source and a transition metal salt are dissolved in deionized water and ultrasonically dispersed to obtain a mixture I, which is then added dropwise to the carbon support aqueous ion solution. The dropping rate is controlled, and the mixture is stirred to obtain a mixture II. The solvent in mixture II is then evaporated by infrared radiation heating. After drying and grinding, an intermediate solid material is obtained. The intermediate material is placed in a microwave heating furnace and calcined in stages at different temperature ranges under a reducing / inert atmosphere to obtain ordered low-platinum alloy catalyst particles with an ordered dual-phase structure in the core and a thin layer of platinum with a stable surface structure in the shell. This method allows platinum metal to precipitate and adhere to the surface of a multiphase ordered platinum alloy, forming core-shell structured nanoparticles. The prepared catalyst particles are uniformly dispersed, have ideal particle size, and high catalytic activity. It can improve the utilization rate of platinum in the catalyst and reduce the consumption of platinum. Furthermore, the catalytic activity and stability of the platinum element located on the surface of the nanoparticles are also significantly improved by the morphology and electronic effects of the core metal, giving the catalyst both high ORR oxygen catalytic performance and good stability.

[0005] 3. Chinese patent application CN201810607646.4 discloses a method for preparing a supported, highly dispersed platinum alloy catalyst for proton exchange membrane fuel cells. The method uses a Pt and transition metal salt solution as the catalyst precursor, a polyol as the solvent and a weak reducing agent, and microwave heating in the presence of an imidazole-type ionic liquid to obtain the catalyst in one step. The PtM alloy catalyst prepared by this method has a small particle size and uniform particle size distribution, and exhibits good dispersibility on the support. It can improve the utilization rate of platinum, reduce the amount of platinum used, and show high catalytic activity for the oxygen reduction reaction. Therefore, it can be used as a cathode oxygen reduction (ORR) catalyst for proton exchange membrane fuel cells (PEMFCs).

[0006] Single-atom catalysts have attracted considerable attention from researchers due to their excellent catalytic performance and extremely high atom utilization. MNC materials exhibit activity in the oxygen reduction reaction comparable to noble metal materials, but their stability under acidic conditions remains a challenge. Therefore, to develop proton exchange membrane electrodes, it is necessary to develop an oxygen reduction catalyst with low platinum content, long lifetime, and high stability. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for preparing a low-platinum-content cathode oxygen reduction catalyst and its application. The low-platinum-content cathode oxygen reduction catalyst prepared by this invention has a Pt content of only 0.08 wt%. During oxygen reduction at the cathode of a fuel cell, the mass activity of this catalyst with Pt is 85 times that of commercial Pt / C catalysts. This catalyst exhibits significantly improved activity and excellent stability for oxygen reduction, showing considerable commercial potential. The preparation method is simple, safe, and easy to operate, and the obtained catalyst can be used as a cathode material for proton exchange membrane fuel cells.

[0008] In order to achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a low-platinum-content cathode oxygen reduction catalyst includes the following steps:

[0010] (a) Dissolve the platinum metal precursor, transition metal (M) precursor, nitrogen-containing organic compound and zinc precursor in anhydrous methanol, stir well and label it as solution A. Then dissolve dimethylimidazole in anhydrous methanol, stir well and label it as solution B.

[0011] (b) Mix the above solutions A and B, stir evenly, then centrifuge, wash with solvent, and dry to obtain the precursor product Pt,M-ZIF-8.

[0012] (c) The above-mentioned precursor product Pt,M-ZIF-8 is fed into a high-temperature carbonization device for high-temperature carbonization, and then atomically dispersed product Pt,M / NC is obtained, which is the low-platinum-content cathode oxygen reduction catalyst for fuel cells.

[0013] Further, in step (a), the platinum metal precursor is selected from one of potassium chloroplatinate, chloroplatinic acid, platinum nitrate, potassium chloroplatinate, platinum acetylacetonate, or sodium chloroplatinate.

[0014] Further, in step (a), the transition metal (M) precursor is selected from one of ferric nitrate, ferric chloride, ferric sulfate, ferric acetylacetone, cobalt nitrate, cobalt chloride, cobalt acetylacetone, copper chloride, and copper sulfate.

[0015] Further, in step (a), the zinc metal precursor is one of zinc acetate, zinc nitrate, and zinc oxide.

[0016] Further, in step (a), the nitrogen-containing organic compound is one of melamine, guanidine salt, dicyandiamide, 1,10-phenanthroline, and urea.

[0017] Further, in step (a), the molar ratio of the platinum metal precursor, transition metal (M) precursor, zinc precursor, and nitrogen-containing organic compound is (0.5-10):(0.5-10):(1-20):(1-20); in step (a), the molar ratio of the zinc metal precursor and dimethylimidazole added is (0.5-2):(4-8); in step (a), the volume of methanol is 40-100 mL.

[0018] Further, in step (a), the molar ratio of the zinc metal precursor to the dimethylimidazole is (1-2):(4-6).

[0019] Furthermore, in step (a), the time for stirring until homogeneous is 0.5 to 1 hour.

[0020] Further, in step (b), the stirring time is 1 to 24 hours, preferably 2 hours; the washing solvent is anhydrous methanol, and the washing is performed at least three times; the drying conditions are vacuum drying: temperature is 50 to 60°C, time is 6 to 12 hours, and vacuum degree is -0.08 to -0.06 MPa.

[0021] Further, in step (c), the temperature of the high-temperature carbonization is controlled at 500℃~1200℃, the heating rate is 1~10℃ / min, and the high-temperature carbonization time is 2~5h.

[0022] Furthermore, in step (c), the high-temperature carbonization is carried out under the protection of a protective gas, which is either nitrogen or argon.

[0023] Furthermore, the application of a low-platinum-content cathode oxygen reduction catalyst prepared by the method described above in the fabrication of a proton exchange membrane fuel cell.

[0024] Because the present invention adopts the above technical solution, it has the following beneficial effects:

[0025] (1) The Pt,M / NC catalyst prepared by this invention has significantly improved performance compared with the original commercial Pt / C catalyst, with advantages such as high mass activity and stability, efficient proton-charge transport capability, and enhanced electronic structure; the Pt atomic mass content ICP test result is only 0.06wt%, and the mass activity of the Pt catalyst in the oxygen reduction reaction is 85 times that of Pt / C.

[0026] (2) The present invention adopts a one-step synthesis method, which is simple, safe and easy to operate.

[0027] (3) The Pt,M / NC catalyst prepared in this invention is applied to the preparation of proton exchange membrane fuel cells, and the resulting proton exchange membrane fuel cells have a wider range of application prospects. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings required in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some examples of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort:

[0029] Figure 1 Transmission electron microscope (TEM) images of Pt,M / NC prepared in Examples 1, 2 and 3 of this application;

[0030] Figure 2 The energy dispersive spectroscopy (EDS) spectrum of Pt,M / NC prepared in Example 1 of this application is shown.

[0031] Figure 3 The X-ray diffraction (XRD) spectra of the Pt,M / NC catalyst prepared in Example 1 of this application and the commercial Pt / C catalyst of Comparative Example 1 are shown.

[0032] Figure 4 This is a comparison chart of LSV test results of the Pt,M / NC catalysts prepared in Examples 1, 2, and 3 of this application and the commercial Pt / C catalyst of Comparative Example 1 in a mixed solution of 0.1M HClO4.

[0033] Figure 5 This is a comparison graph showing the chronoamperometry results of the Pt,M / NC catalyst prepared in Example 1 of this application and the commercial Pt / C catalyst in Comparative Example 1 in a mixed solution of 0.1M HClO4.

[0034] Figure 6 This is a comparison graph showing the ADT test results of the Pt,M / NC catalyst prepared in Example 1 of this application and the commercial Pt / C catalyst in Comparative Example 1 in 0.1M HClO4 solution. Detailed Implementation

[0035] The specific embodiments of the present invention will be described in further detail below, but the present invention is not limited to these embodiments. Any improvements or substitutions based on the basic spirit of these embodiments shall still fall within the scope of protection claimed by the claims of the present invention.

[0036] Example 1

[0037] like Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 As shown, a method for preparing a low-platinum-content cathode oxygen reduction catalyst includes the following steps:

[0038] (a) Dissolve platinum acetylacetonate, ferric sulfate, zinc nitrate and melamine in 50 mL of anhydrous methanol in a molar ratio of 1:1:4:3. Stir for 0.5 h to disperse the solid reagents evenly to form solution A. Then dissolve dimethylimidazole in 50 mL of anhydrous methanol in a molar ratio of 2:5 with zinc nitrate. Stir for 0.5 h to disperse the solid reagents evenly to form solution B.

[0039] (b) Mix the above solutions A and B, stir at room temperature for 6 hours, then centrifuge, wash with methanol solvent 4 times, and dry in a vacuum drying oven at 50°C for 12 hours with a vacuum degree of -0.06 MPa to obtain the precursor product Pt,M-ZIF-8.

[0040] (c) The above-mentioned dried precursor product Pt,M-ZIF-8 is fed into a high-temperature carbonization device for high-temperature carbonization. Under argon protection, the temperature is raised to 850°C at a rate of 10°C / min and held for 3 hours. Then, black atomically dispersed product Pt,Fe / NC is obtained, which is the low-platinum-content cathode oxygen reduction catalyst for fuel cells.

[0041] Figure 1 The TEM images of the Pt,Fe / NC materials prepared in Examples 1, 2, and 3 show that there are no obvious metal nanoparticles, which proves that the prepared materials are atomically dispersed. At the same time, the carbon substrate can maintain the basic morphology of MOF, which is beneficial to the improvement of the catalytic activity of the material.

[0042] Figure 2 The image shows the EDS spectrum of the Pt,Fe / NC material prepared in Example 1. The EDS spectrum reveals that the mass fractions of Pt and Fe in the material are 0.08:0.2, confirming the ultra-low loading of Pt.

[0043] Figure 3 The images show the XRD patterns of the Pt,Fe / NC material prepared in Example 1 and the commercial Pt / C catalyst of Comparative Example 1. Compared with the XRD pattern of Pt / C, no obvious metal peaks are present, indicating that Pt is dispersed on the surface of the carbon support with atomic-scale particle size.

[0044] Example 2

[0045] like Figure 1 As shown, a method for preparing a low-platinum-content cathode oxygen reduction catalyst includes the following steps:

[0046] Solution A was prepared by dissolving chloroplatinic acid, ferric chloride, zinc nitrate, and melamine in 50 mL of anhydrous methanol in a molar ratio of 2:1:6:3. Solution B was prepared by dissolving dimethylimidazolium in 50 mL of anhydrous methanol in a molar ratio of 1:3 with zinc nitrate. After stirring each solution for 1 h to ensure uniform dispersion of the solid reagents, solutions A and B were mixed and stirred at room temperature for 6 h. After centrifugation and filtration, and washing with solvent, the solutions were dried in a vacuum drying oven at 50 °C for 6 h at a vacuum degree of -0.07 MPa. The dried product was heated to 900 °C at a rate of 3 °C / min under argon protection and held at that temperature for 3 h to obtain a black product, which is Pt,Fe / NC, and thus the low platinum content cathode oxygen reduction catalyst for fuel cells.

[0047] Example 3

[0048] like Figure 1 As shown, a method for preparing a low-platinum-content cathode oxygen reduction catalyst includes the following steps:

[0049] Solution A was prepared by dissolving platinum nitrate, ferric sulfate, zinc nitrate, and dicyandiamide in a molar ratio of 1:2:10:3 in 50 mL of anhydrous methanol. Solution B was prepared by dissolving dimethylimidazole in a molar ratio of 1:4 with zinc nitrate in 50 mL of anhydrous methanol. After stirring for 1 h to ensure uniform dispersion of the solid reagents, solutions A and B were mixed and stirred at room temperature for 12 h. After centrifugation, filtration, and washing with solvent, the product was dried in a vacuum drying oven at 60 °C for 12 h at a vacuum degree of -0.08 MPa. The dried product was then heated to 1000 °C at a rate of 4 °C / min under nitrogen protection and held at this temperature for 3 h to obtain a black product, which is Pt,Fe / NC, and thus the low-platinum-content cathode oxygen reduction catalyst for fuel cells.

[0050] Comparative Example 1

[0051] like Figure 1 , Figure 3 , Figure 4 , Figure 5 , Figure 6 As shown, a commercial catalyst Pt / C with a Pt loading of 20% was purchased from Johnson-Matthery.

[0052] To further illustrate that the present invention can achieve the aforementioned technical effects, the following experiments were conducted:

[0053] Performance testing

[0054] The cathode oxygen reduction catalysts prepared in Examples 1-3 and Comparative Example 1 of this application were used for performance testing. A three-electrode system was employed, with a 5 mm diameter glassy carbon electrode coated with either the Pt,M / NC prepared in the examples of this application or the commercial Pt / C prepared in Comparative Example 1 as the working electrode, an Ag / AgCl electrode as the reference electrode, and a platinum sheet (1 cm × 1 cm) as the counter electrode. The materials were subjected to LSV testing in an oxygen-saturated 0.1 M perchloric acid solution, with a potential range of 0.05–1.1 V vs. RHE. The results are as follows: Figure 4 As shown. A chronoamperometry test was performed on the material at 0.7V vs. RHE for 12 hours. The test results are as follows. Figure 5 As shown. An ADT test was performed on the material in 0.1M perchloric acid solution, and the results are as follows. Figure 6 As shown.

[0055] Figure 4 The graph shows a comparison of the LSV (Laser Vapor Potential) of the Pt,Fe / NC catalyst prepared in Example 1 and the commercial Pt / C catalyst in Comparative Example 1 in 0.1 M perchloric acid solution. It can be seen that, compared to the commercial Pt / C catalyst, the Pt,Fe / NC catalyst has the same half-wave potential as the commercial Pt / C catalyst.

[0056] Figure 5 This is a comparison graph showing the chronoamperometry results of the Pt,Fe / NC catalyst prepared in Example 1 and the commercial Pt / C catalyst in Comparative Example 1 in 0.1 M perchloric acid solution. It can be seen that after 12 hours, the Pt,Fe / NC catalyst still maintains 54% of its current density. In contrast, the commercial Pt / C catalyst retains only 6% after 12 hours, indicating that the Pt,Fe / NC catalyst exhibits excellent stability.

[0057] Figure 6 The graph shows a comparison of the ADT (Active Thermal Expansion) results of the Pt,Fe / NC catalyst prepared in Example 1 and the commercial Pt / C catalyst in Comparative Example 1 in 0.1 M perchloric acid solution. It can be seen that after 8000 cycles of ADT testing, the half-wave potential of Pt,Fe / NC decreased by only 16 mV. In contrast, the commercial Pt / C catalyst showed a significant decrease in half-wave potential after 8000 cycles of ADT testing, indicating that the Pt,Fe / NC catalyst exhibits excellent stability under acidic conditions.

[0058] The excellent activity and stability of the Pt,Fe / NC catalyst obtained in Example 1 are attributed to the synergistic effect of its material composition and structure. Firstly, the advantages of the material's structure include high electrical conductivity, high specific surface area, more contact points with the carbon support, and enhanced atomic interactions, which not only promote proton / charge transfer between oxygen and the catalyst surface but also suppress the formation of the intermediate product H₂O₂. Secondly, the introduction of M atoms significantly improves the electronic structure of Pt atoms, reduces its solubility in acidic electrolytes, and thus increases the catalyst lifetime.

[0059] In summary, this invention provides a low-platinum-content cathode oxygen reduction catalyst: Pt,M / NC. This catalyst achieves atomic-level dispersion of Pt metal on a carbon support. The preparation method is simple, safe, and easy to operate. This catalyst can be used in the oxygen reduction process at the cathode of fuel cells, exhibiting significantly enhanced electrochemical activity and stability. Compared with commercial Pt / C, the Pt,M / NC prepared using this invention exhibits significantly improved electrochemical activity, stability, and extremely high Pt metal mass activity for oxygen reduction reactions under acidic conditions, and can be used as a cathode oxygen reduction catalyst for proton exchange membrane fuel cells.

[0060] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the equivalent meaning and scope of the claims be included within the protection scope of the present invention.

Claims

1. A method for preparing a low-platinum-content cathode oxygen reduction catalyst, characterized in that, Includes the following steps: (a) Dissolve the platinum metal precursor, transition metal (M) precursor, nitrogen-containing organic compound and zinc precursor in anhydrous methanol, stir until homogeneous, and label as solution A. Then dissolve dimethylimidazole in anhydrous methanol, stir until homogeneous, and label as solution B. The molar ratio of the platinum metal precursor, transition metal (M) precursor, zinc precursor and nitrogen-containing organic compound is (0.5-10):(0.5-10):(1-20):(1-20). In step (a), the molar ratio of the zinc precursor and dimethylimidazole added is (0.5-2):(4-8). (b) Mix the above solutions A and B, stir evenly, then centrifuge, wash with solvent, and dry to obtain the precursor product Pt,M-ZIF-8. (c) The above-mentioned precursor product Pt,M-ZIF-8 is fed into a high-temperature carbonization device for high-temperature carbonization, and then atomically dispersed product Pt,M / NC is obtained, which is the low-platinum-content cathode oxygen reduction catalyst for fuel cells. In step (a), the platinum metal precursor is selected from one of potassium chloroplatinate, chloroplatinic acid, platinum nitrate, potassium chloroplatinate, platinum acetylacetonate, or sodium chloroplatinate. In step (a), the transition metal (M) precursor is selected from one of ferric nitrate, ferric chloride, ferric sulfate, ferric acetylacetone, cobalt nitrate, cobalt chloride, cobalt acetylacetone, copper nitrate, copper chloride, and copper sulfate. In step (a), the zinc precursor is selected from one of zinc acetate, zinc nitrate, zinc oxide, or zinc chloride; In step (a), the nitrogen-containing organic compound is one of melamine, guanidine salt, dicyandiamide, 1,10-phenanthroline, and urea.

2. The method for preparing a low-platinum-content cathode oxygen reduction catalyst according to claim 1, characterized in that: In step (b), the stirring time is 1 to 24 hours; the solvent is anhydrous methanol; and the washing is performed at least three times. The drying conditions are vacuum drying: temperature is 50 to 60°C, time is 6 to 12 hours, and vacuum degree is -0.08 to -0.05 MPa.

3. The method for preparing a low-platinum-content cathode oxygen reduction catalyst according to claim 1, characterized in that: In step (c), the temperature of the high-temperature carbonization is controlled at 500℃~1200℃, the heating rate is 1~10℃ / min, and the high-temperature carbonization time is 2~5h.

4. The method for preparing a low-platinum-content cathode oxygen reduction catalyst according to claim 1, characterized in that: In step (c), the high-temperature carbonization is carried out under the protection of a protective gas, which is one of nitrogen, argon, or helium.

5. The application of a low-platinum-content cathode oxygen reduction catalyst prepared by any one of claims 1-4 in the fabrication of a proton exchange membrane fuel cell.

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