Preparation method and application of aluminum-doped noble metal nanocatalyst

Abstract

This application belongs to the field of precious metal catalyst technology, specifically to a method for preparing an aluminum-doped precious metal nanocatalyst and its application. Specifically, a carbon source, an aluminum salt, and 2-methylimidazole are added to dimethyl sulfoxide and mixed uniformly to obtain a precursor polymer. The precursor polymer is then mixed with a precious metal solution and pyrolyzed at high temperature in a reducing atmosphere to obtain a catalyst. The catalyst is applied to fuel cell electrodes, exhibiting strong resistance to carbon monoxide poisoning and accelerating the generation of hydrogen ions in the cell, effectively improving the catalytic performance of the fuel cell.

Description

Technical Field

[0001] The present invention belongs to the technical field of noble metal catalysts, and in particular relates to a preparation method of an aluminum-doped noble metal nanocatalyst and its application. Background Art

[0002] Proton exchange membrane fuel cells have been widely used due to their low pollution and high energy characteristics. How to improve their performance has also become a research hotspot. Therefore, people have begun to turn their attention to the modification of catalysts. In proton exchange membrane fuel cells, catalysts are the core part and participate in the entire reaction process. They can accelerate the conversion of oxygen and hydrogen into ions, improve their conversion rate, and enhance the performance of the battery. However, industrial hydrogen production is inevitably accompanied by the mixing of carbon monoxide. Even at extremely low concentrations, carbon monoxide will react with the catalyst, destroying the catalyst structure and causing it to lose its catalytic performance, resulting in a decline in battery performance and loss of use value. These factors greatly limit the application scenarios of batteries. Therefore, there is an urgent need to develop catalysts that can resist carbon monoxide poisoning.

[0003] Currently, the catalyst used in hydrogen oxidation is mainly a platinum-carbon system. By loading platinum on a carbon skeleton to fix the platinum sites, the battery performance is enhanced by platinum's catalytic effect on the gas. In terms of resisting carbon monoxide poisoning, platinum-ruthenium alloy has been proven to be a very good alloy system with excellent anti-poisoning effect. However, as a precious metal, platinum-ruthenium is very expensive and difficult to industrialize. Therefore, people have gradually turned their attention to non-precious metal catalysts, improving their resistance to carbon monoxide through the interaction between non-precious metal elements and platinum, enhancing the dispersion of platinum particles, and improving the utilization rate of platinum. Summary of the Invention

[0004] To address these problems, the present invention adds a carbon source, an aluminum salt, and 2-methylimidazole to dimethyl sulfoxide, respectively, and mixes them evenly to obtain a prepolymer. The prepolymer is then mixed with a noble metal solution and pyrolyzed in a reducing atmosphere at high temperature to obtain a catalyst. This enhances the ability to resist carbon monoxide toxicity, accelerates the generation of H ions in the battery, and effectively improves the catalytic performance of the fuel cell.

[0005] In order to achieve the above object, on the one hand, the present invention provides a method for preparing aluminum-doped noble metal nanocatalysts, comprising the following steps:

[0006] (1) Adding a carbon source, 2-methylimidazole, and aluminum salt into an organic solvent, respectively, and ultrasonically dispersing the mixture, and then stirring the mixture to obtain a prepolymer mixture;

[0007] (2) centrifuging the prepolymer mixture of step (1), washing the centrifuged product, and drying it to obtain a prepolymer material;

[0008] (3) After the precursor material in step (2) is dispersed with a solvent, a certain amount of noble metal aqueous solution is added in batches and fully mixed, followed by centrifugation, washing, and drying. The dried solid product is heat-treated under a reducing gas to obtain a catalyst.

[0009] Furthermore, the noble metal element is one or more of platinum, palladium, gold, and iridium, preferably platinum.

[0010] Furthermore, the aluminum salt is one or a combination of aluminum acetylacetonate, aluminum chloride, aluminum nitrate, and aluminum acetate; preferably aluminum acetylacetonate.

[0011] Furthermore, in step 1), the organic solvent is one or a combination of methanol, ethanol, dimethyl sulfoxide and water, preferably dimethyl sulfoxide; the carbon source is one or a combination of Ketjen black, graphene, carbon nanotubes and BP-2000.

[0012] Furthermore, the solvent used for washing in step 2) is one or a combination of methanol, ethanol, and acetone.

[0013] Furthermore, the noble metal source in the noble metal solution in step 3) is one or a combination of noble metal acetylacetonate, iodide, chloride, and the solvent for dispersing the precursor is one or a mixture of water, acetone, and ethanol.

[0014] Furthermore, the mass ratio of the precious metal to aluminum in step (3) is 1: 2.25-36; preferably 1: 4.5-18.

[0015] Furthermore, in step (1), the molar ratio of the aluminum salt to 2-methylimidazole is 1:0.5-8; preferably, the molar ratio of the aluminum salt to 2-methylimidazole is 1:1-4.

[0016] Furthermore, in step (3), the concentration of the noble metal aqueous solution is 10-60 g / L, preferably 15-25 g / L; the reducing gas is a mixture of hydrogen and argon, wherein hydrogen accounts for 5 to 10 vol%, a mixture of ammonia and argon, wherein ammonia accounts for 5 to 10 vol%, a mixture of carbon monoxide and argon, wherein carbon monoxide accounts for 5 to 10 vol% or more; the heat treatment temperature is 600 to 1000 ° C, the time is 1 to 3 hours, and the heating rate is 1-10 ° C min -1 .

[0017] Furthermore, in step (1), the ultrasonic stirring time is 20-40 min, the stirring time in step 2) is 8-20 h, preferably 12 h; the stirring time in step 1) is 8-20 h, preferably 12 h; and the stirring speed is 3000 ~ 5000 rpm.

[0018] On the other hand, the present application also provides an application of the catalyst prepared by the above preparation method in a fuel cell.

[0019] The beneficial effects of the present invention are as follows:

[0020] (1) Organic solvents and organic matter are used to introduce doping atoms, sulfur and nitrogen are doped on carbon, and the polymer skeleton formed by organic matter is used to fix the noble metal ions. After high-temperature pyrolysis, aluminum-doped noble metal carbon composite materials are prepared. The noble metal atoms and aluminum atoms agglomerate into nanoclusters and can be evenly distributed on the sulfur- and nitrogen-doped carbon carrier to maximize the active sites.

[0021] (2) Aluminum doping affects the d-band electronic structure of noble metal nanoclusters, improving their catalytic activity. The carbon structure doped with sulfur and nitrogen can reduce the absorption of carbon monoxide by adjusting the number of electrons on the carbon surface and reducing the closeness of the connection with oxygen groups, thereby enhancing the ability to resist carbon monoxide toxicity and accelerating the generation of H ions in the battery, effectively improving the catalytic performance of the fuel cell.

[0022] (3) By continuously optimizing the raw material ratio in the preparation process, the utilization rate of precious metal sites is increased, thereby reducing the amount of precious metal used, thereby achieving strong catalytic performance even with a low precious metal content. At the same time, the doped aluminum element is affordable, which can reduce industrial costs in actual production and promote the expansion of industrial scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the XRD pattern of the sulfur-nitrogen-doped carbon-supported platinum-aluminum nanoparticle material prepared in Example 1 of the present invention;

[0024] Figure 2 This is an SEM image of the sulfur-nitrogen-doped carbon-supported platinum-aluminum nanoparticle material prepared in Example 1;

[0025] Figure 3 This is a graph showing the catalytic performance of the sulfur-nitrogen-doped carbon-supported platinum-aluminum nanoparticle material prepared in Example 1 under hydrogen and nitrogen;

[0026] Figure 4 This is a comparison of the power density and current density of the sulfur-nitrogen-doped carbon-supported platinum-aluminum nanoparticle material prepared in Example 1 and the catalyst in Comparative Example 1 at different carbon monoxide concentrations;

[0027] Figure 5These are some implementation cases, including the electrochemical performance test results of Comparative Case 1 and Comparative Case 2 at a current of 10A. Specific embodiment:

[0029] To make the technical solutions and advantages of the present invention more clear, the present invention and its beneficial effects will be described in further detail below with reference to specific implementation methods and accompanying drawings, but the implementation methods of the present invention are not limited thereto.

[0030] In this disclosure, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b and c" can refer to a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or plural.

[0031] Example 1

[0032] A sulfur-nitrogen-doped carbon-supported platinum-aluminum nanoparticle material, the preparation method of which comprises the following steps:

[0033] 1) Add 0.648 g of aluminum acetylacetonate (Ron, AR grade) to 30 ml of dimethyl sulfoxide and ultrasonically stir to obtain an aluminum acetylacetonate mixed solution. Add 0.1 g of Ketjen Black and 0.336 g of 2-methylimidazole (Aladdin, >98%) to 30 ml of dimethyl sulfoxide, stir thoroughly with a glass rod, and then slowly add the mixture to the aluminum acetylacetonate mixed solution. Ultrasonic stirring is performed for 30 min to obtain a precursor solution.

[0034] 2) The precursor solution obtained in step 2) was magnetically stirred for 12 h, the product was collected by centrifugation, washed with anhydrous ethanol, and finally dried to obtain Al@NSC material;

[0035] 3) The Al@NSC material obtained in step 2) was redispersed with anhydrous ethanol, and 240 μL of a 25 g / L platinum chloride aqueous solution was added in batches. The mixture was magnetically stirred for 3 h. The precipitate was collected by centrifugation, washed with anhydrous ethanol, and dried to obtain a Pt-Al@NSC precursor material.

[0036] 4) The precursor material obtained in step 3) was heated to 400°C under argon, kept at this temperature for 1 h, then heated to 800°C, kept at this temperature for 2 h, and cooled naturally to obtain the Pt-Al@NSC material.

[0037] Example 2

[0038] Compared with Implementation Case 1, the mass of aluminum acetylacetonate was changed to 1.296 g, and other conditions remained unchanged.

[0039] Example 3

[0040] Compared with Implementation Case 1, the mass of aluminum acetylacetonate was changed to 0.324 g, and other conditions remained unchanged.

[0041] Example 4

[0042] Compared with Implementation Case 1, the mass of aluminum acetylacetonate was changed to 2.592 g, and other conditions remained unchanged.

[0043] Example 5

[0044] Compared with Implementation Case 1, the mass of aluminum acetylacetonate was changed to 0.162 g, and other conditions remained unchanged.

[0045] Example 6

[0046] Compared with Implementation Case 1, the mass of 2-methylimidazole was changed to 0.672 g, and other conditions remained unchanged.

[0047] Example 7

[0048] Compared with Implementation Case 1, the mass of 2-methylimidazole was changed to 0.168 g, and other conditions remained unchanged.

[0049] Example 8

[0050] Compared with Implementation Case 1, the stirring time in step 2) was changed to 8 h, and the other conditions remained unchanged.

[0051] Example 9

[0052] Compared with Example 1, the volume of the added platinum chloride solution was changed to 300 μl, and the other conditions remained unchanged.

[0053] Example 10

[0054] Compared with Example 1, the volume of the added platinum chloride solution was changed to 60 μl, and the other conditions remained unchanged.

[0055] Example 11

[0056] Compared with Implementation Case 1, the proportion of platinum chloride in the solution was changed to 50 g / L, and other conditions remained unchanged.

[0057] Example 12

[0058] Compared with Implementation Case 1, the proportion of platinum chloride in the solution was changed to 12.5 g / L, and other conditions remained unchanged.

[0059] Example 13

[0060] Compared with Implementation Case 1, the stirring time in step 2) was changed to 20 h, and the other conditions remained unchanged.

[0061] Comparative Example 1

[0062] Compared with Example 1, a commercial platinum-carbon catalyst (Hesen, 20% wt) was used for the electrochemical test, and other conditions remained unchanged.

[0063] Comparative Example 2

[0064] Compared with Example 1, the aluminum salt was replaced with an equimolar amount of aluminum chloride, and other conditions remained unchanged.

[0065] The SEM image of Example 1 of the present invention is as follows Figure 2 As shown, the material forms a dispersed ZIF structure, and the particles interact with each other, which makes it have good dispersion and improves the utilization of Pt.

[0066] The catalyst obtained in Example 1 was tested with hydrogen and nitrogen in a conventional three-electrode test. The results are as follows: Figure 3 As shown, the catalyst obtained in Example 1 has high catalytic ability.

[0067] The catalysts obtained in Example 1 and Comparative Example 1 were subjected to membrane electrode tests. The anode gas was pure H2, 1000ppm CO / H2, 2000ppm CO / H2, 5000ppm CO / H2 and 10000ppm CO / H2, respectively, and the cathode gas was air. The results are shown in the figure. Figure 4 The catalytic performance of the catalyst obtained in Example 1 in the presence of carbon monoxide is higher than that of ordinary commercial catalysts.

[0068] The catalysts obtained in Examples 1 to 2 of Example 1, Example 6, Example 8, Example 9 and Example 11 were tested on membrane electrodes. When the anode gas was a mixture of hydrogen and a certain concentration of carbon monoxide and the cathode gas was air, the results were as follows: Figure 5 As shown, a comparison shows that Example 1 exhibits superior catalytic performance compared to the other examples. The doping of nitrogen and sulfur elements with carbon forms a composite support, which synergizes with the PtAl alloy, reducing carbon monoxide adsorption and improving the catalyst's resistance to carbon monoxide poisoning. Furthermore, when adding the same molar amount of aluminum, the aluminum salt formed by the reduction of aluminum acetylacetonate exhibits stronger adhesion, maintaining the catalyst's monoatomic structure and preventing clustering. This enhances the aluminum salt's dispersing effect, ensuring greater contact area between platinum and the gas, and ultimately improving catalytic performance.

[0069] Table 1 shows the half-wave unit performance of the catalysts prepared in Examples 1-13. Comparison of the electrochemical performance of the catalysts in Examples 1-5 shows that when the mass ratio of aluminum to platinum metal is 4.5-18:1, the catalyst has a higher half-wave potential and exhibits better catalytic performance. Aluminum and platinum in this range are more conducive to the formation of aluminum-platinum nanoclusters and more conducive to the dispersion of single atoms of platinum and aluminum. At the same time, it was found through Examples 1-7 that changes in the addition amount of aluminum acetylacetonate and 2-methylimidazole also affect the formation of nanoclusters and the dispersion of single atoms of platinum and aluminum in the clusters. The formation of acetylacetonate aluminum and 2-methylimidazole finally brought about a change in catalyst performance. When the molar ratio of aluminum acetylacetonate to 2-methylimidazole was 1:1-4, the catalyst had a higher half-wave potential. It was also found that the length of the stirring time of the aluminum atoms also directly affected the formation of platinum and aluminum single atoms in the nanoclusters. It can be seen from Examples 8 and 13 that compared with Example 1, a stirring time that was too long or too short also caused a decrease in catalyst performance. It can be seen that the implementation conditions of Example 1 are the best conditions, and its half-wave potential reached 8.83V, which is much higher than that of other examples. The catalyst of Example 1 not only has a better addition ratio, but also has excellent hydrogen oxidation catalytic performance and resistance to carbon monoxide poisoning, and has better commercial value.

[0070] Table 1

[0071]

[0072] Compared to commercial Pt / C catalysts, the Pt-Al@NSC composite catalyst prepared in the present invention separates platinum atoms through the doping of aluminum salts, forming nanoclusters with aluminum atoms. Furthermore, the catalyst achieves further dispersion on the sulfur- and nitrogen-doped carbon support, increasing the contact between platinum and the gas, maximizing the catalytic effect of platinum in the reaction, improving platinum utilization, reducing platinum metal input, and lowering costs. Furthermore, due to the unique structure formed by the aluminum salts and nitrogen and sulfur, the catalyst can maintain good performance even when the anode gas contains a certain amount of carbon monoxide, significantly improving its carbon monoxide resistance compared to commercial catalysts. In practical applications, the catalyst can well adapt to relatively harsh environments and has certain practical significance in the field of proton exchange membrane fuel cells.

[0073] Based on the disclosure and teachings of the above description, those skilled in the art will be able to make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments. Any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention fall within the scope of protection of the present invention. In addition, although certain specific terms are used in this description, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A method for preparing aluminum-doped noble metal nanocatalyst, characterized in that: The steps include: (1) adding a carbon source, 2-methylimidazole, and an aluminum salt into an organic solvent, performing ultrasonic dispersion, and then stirring to obtain a prepolymer mixture; the aluminum salt is aluminum acetylacetonate; and the organic solvent is dimethyl sulfoxide; (2) centrifuging the prepolymer mixture of step (1), washing the centrifuged product, and drying it to obtain a prepolymer material; (3) After the precursor material of step (2) is dispersed with a solvent, a certain amount of precious metal aqueous solution is added in batches and fully mixed, and then centrifuged, washed, and dried. The dried solid product is heat-treated under a reducing gas to obtain a catalyst. The heat treatment temperature is 600 ~ 1000 ° C and the time is 1 ~ 3 hours.

2. The preparation method according to claim 1, characterized in that The noble metal element is one or more of platinum, palladium, gold and iridium.

3. The preparation method according to claim 2, characterized in that The noble metal element is platinum.

4. The preparation method according to claim 1, characterized in that In step (1), the carbon source is one or a combination of Ketjen black, graphene, carbon nanotubes, and BP-2000.

5. The preparation method according to claim 1, characterized in that The noble metal source in the noble metal aqueous solution in step (3) is one or a combination of acetylacetonate, iodide, and chloride of the noble metal, and the solvent for dispersing the precursor is one or a mixture of water, acetone, and ethanol.

6. The preparation method according to claim 1, characterized in that The mass ratio of the precious metal element to the aluminum element in step (3) is 1: 2.25-36.

7. The preparation method according to claim 6, characterized in that The mass ratio of the noble metal element to the aluminum element in step (3) is 1:4.5-18.

8. The preparation method according to claim 1, characterized in that In step (1), the molar ratio of the aluminum salt to 2-methylimidazole is 1:0.5-8.

9. The preparation method according to claim 8, characterized in that In step (1), the molar ratio of the aluminum salt to 2-methylimidazole is 1:1-4.

10. The preparation method according to claim 1, characterized in that In step (3), the concentration of the noble metal aqueous solution is 10-60 g / L; the reducing gas is a mixture of hydrogen and argon, a mixture of ammonia and argon, a mixture of carbon monoxide and argon, or a mixture of several thereof; the heating rate of the heat treatment is 1-10 ° C·min -1 .

11. The preparation method according to claim 10, characterized in that: In step (3), the concentration of the noble metal aqueous solution is 15-25 g / L.

12. The preparation method according to claim 1, characterized in that In step (1), the ultrasonic dispersion time is 20-40 min; the stirring time in step (1) is 8-20 h; and the stirring speed is 3000 ~ 5000 rpm.

13. The preparation method according to claim 12, characterized in that The stirring time in step (1) is 12 h.

14. Use of the catalyst prepared by the preparation method according to any one of claims 1 to 10 in a fuel cell.

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