Hydrothermal preparation method of hollow CuPt alloy nanocrystals

Abstract

The invention provides a hydrothermal preparation method of a hollow CuPt alloy nanocrystal. According to the method, hydrothermal carbon nanospheres formed by hydrothermal decomposition of ascorbic acid are used as templates, hydrothermal carbon in the spheres is consumed by utilizing the Kirkendall effect, the templates are synchronously removed, and the high-purity hollow CuPt alloy nanospheres are obtained through a one-step method. According to the method, a strong reducing agent is not needed, inert gas protection and high-temperature heating treatment are not needed in the whole process, the highest preparation temperature is only 120 DEG C, the energy-saving and environment-friendly characteristics are achieved, and the influence of the preparation process on the environment is remarkably reduced. Application examples show that the obtained hollow CuPt alloy nanocrystal has activity far higher than that of commercial Pt / C on an electro-catalysis formic acid oxidation reaction, and shows excellent stability.

Description

Technical Field

[0001] The present invention relates to the field of metal nanomaterial preparation, and in particular to a hydrothermal preparation method of hollow CuPt alloy nanocrystals. Background Art

[0002] Membrane exchange fuel cells use an ion exchange membrane as an electrolyte. Through an electrochemical reaction between a fuel (such as hydrogen, methanol, or formic acid) and an oxidant (oxygen), they convert chemical energy directly into electrical energy. They are characterized by ease of operation and high safety. The reaction products are only CO2 and water, with no pollutants emitted, fully meeting green energy requirements.

[0003] In recent years, a variety of new fuel cells have emerged. Among them, formic acid fuel cells offer significant advantages: First, formic acid is far less toxic than methanol and is non-flammable, making it safer to transport and store; second, its theoretical energy density is superior to methanol, resulting in greater endurance; and third, formic acid has a low permeability in proton exchange membranes, effectively maintaining the battery's power density. As a core component, the anode of a formic acid fuel cell primarily utilizes electrocatalysts such as platinum (Pt) that catalyze the oxidation of formic acid. However, the high cost of Pt metal has become a major bottleneck to its commercialization.

[0004] To effectively address the above issues, the following key measures can be taken:

[0005] One approach is to alloy Pt metal with other inexpensive transition metals, and utilize the interfacial strain effect to regulate the center position of the d-band, significantly improving catalytic activity and stability while reducing the cost of anode catalysts. For example, after Cu and Pt form an alloy, the center position of their d-band shifts downward compared to pure Pt, significantly weakening the adsorption strength of oxygen-containing intermediates. The second approach is to cleverly utilize the size effect of nanomaterials to increase the specific surface area of ​​the electrode, thereby increasing the contact probability between formic acid molecules and the catalyst. For example, hollow structured nanomaterials have high specific surface area, short mass transfer paths, and abundant active sites, making them ideal structures for fuel cell electrodes.

[0006] In summary, if the above two strategies are used synergistically to prepare CuPt alloy nanospheres with a hollow structure, not only can the amount of precious metal Pt in the anode of formic acid fuel cells be significantly reduced, but the internal cavity can also serve as an efficient nanoreactor, greatly increasing the collision frequency of reactant molecules, thereby synergistically improving the reaction kinetics and electrocatalytic performance. However, to date, there has been no report on the preparation method of hollow structured CuPt alloy nanocrystals. There is only one study involving hollow CuPt alloy nanocrystals in the existing literature (https: / / doi.org / 10.1016 / j.cej.2021.131417), but the obtained CuPt alloy nanocrystals are encapsulated in a microporous SiO2 (silicon dioxide) shell and cannot contact the formic acid in the electrolyte, so they are not suitable as formic acid fuel cell electrode materials.

[0007] Therefore, developing a method for preparing hollow CuPt alloy nanocrystals is of great significance to reducing the cost of formic acid fuel cell anode materials. Summary of the Invention

[0008] The present invention aims to solve the problems existing in the prior art and provides a method for preparing hollow structure CuPt alloy nanocrystals.

[0009] This method uses hydrothermal carbon nanospheres, prepared after the decomposition of hexane, as templates. The Kirkendall effect consumes the hydrothermal carbon within the nanospheres, removing the template and yielding high-purity CuPt alloy nanospheres. This preparation method avoids the use of strong reducing agents and operates at a maximum temperature of only 120°C, significantly reducing the environmental impact of the process and offering energy-saving advantages. The resulting material can be used for electrocatalytic formic acid oxidation and exhibits excellent stability.

[0010] The steps of the proposed method for preparing hollow structure CuPt alloy nanospheres are as follows:

[0011] (1) Using deionized water as the solvent, ascorbic acid solutions with concentrations of 4 mmol / L (low concentration) and 500 mmol / L (high concentration) and a hydrochloric acid solution with a concentration of 1 mol / L were prepared respectively;

[0012] (2) Add polyvinyl pyrrolidone powder to a pre-prepared low-concentration ascorbic acid solution (4 mmol / L) in proportion, and stir at room temperature to obtain a mixed solution 1;

[0013] (3) Add the pre-prepared hydrochloric acid solution to the mixed solution 1 in proportion, and stir evenly at room temperature to obtain the mixed solution 2;

[0014] (4) Transferring the mixed solution 2 to a hydrothermal reactor, performing a hydrothermal reaction at 120° C. for 8 hours, and then naturally cooling to room temperature to obtain a mixed solution 3;

[0015] (5) The mixed solution 3 was ultrasonically treated for 10-20 minutes, and then deionized water was added to dilute it to 2.0-2.2 times the original volume to obtain a mixed solution 4;

[0016] (6) KCl powder and CuCl2 powder were added to the mixed solution 4 in proportion, and the mixture was stirred again. Then, 26 mL of a high concentration of ascorbic acid (500 mmol / L) aqueous solution was added and stirred at room temperature to obtain a mixed solution 5.

[0017] (7) Add 7 mmol / L H2PtCl6 solution to the mixed solution 5 and react at 60°C for 6 hours;

[0018] (8) After the reaction, the precipitate was filtered, washed with ethanol 1 to 2 times, and dried with air for several hours to obtain hollow CuPt alloy nanocrystals;

[0019] In step (2), the amount of polyvinyl pyrrolidone powder added to each milliliter of the low-concentration ascorbic acid solution is 1.16 to 1.20 mg;

[0020] In step (3), the volume of hydrochloric acid added per milliliter of mixed solution 1 is 0.22 to 0.25 mL;

[0021] In step (6), the mass of KCl powder added per milliliter of mixed solution 4 is 8.0 to 9.0 mg, and the mass of CuCl2 powder added per milliliter of mixed solution 4 is 2.6 to 2.8 mg;

[0022] In step (7), the volume ratio of the added H2PtCl6 solution to the mixed solution 5 is 1:6-1:5.

[0023] In the above preparation process, the low concentration of ascorbic acid used in step (2) is decomposed at 120°C to form a hydrothermal carbon nanosphere carrier, and polyvinyl pyrrolidone is used to improve the dispersibility of the hydrothermal carbon carrier. The CuCl2 and H2PtCl6 used in step (6) are used to provide the Cu source and Pt source for forming the CuPt alloy. Through the Kirkendall effect, the carbon hydrothermal carbon nanospheres consume the CuCl2 and H2PtCl6 nanospheres and are co-reduced to CuPt alloy nanocrystals, while the template is removed. KCl and high concentration of ascorbic acid are used to suppress the formation of oxides during the co-reduction process.

[0024] The preparation method provided by the present invention can achieve the following positive effects.

[0025] (1) The hydrothermal preparation is completed in one step without the need for highly toxic reagents and is suitable for industrial production.

[0026] The present invention provides a one-step liquid-phase method for preparing hollow CuPt alloy nanocrystals. This method eliminates the tedious steps of intermediate product separation, washing, and drying, significantly shortening the production cycle. This method uses hydrothermal carbon nanospheres as a self-sacrificial template to form hollow spheres, reducing raw material costs while increasing yield, making it suitable for industrial production.

[0027] (2) The creation and removal of the hollow template does not require gas protection and high-temperature annealing, which is safer.

[0028] The hydrothermal preparation method provided by this invention decomposes ascorbic acid at 120°C to form hydrothermal carbon nanosphere carriers. The Kirkendall effect removes the template to form a hollow structure. The entire preparation process does not require inert gas protection or high-temperature heating, significantly improving safety.

[0029] (3) The product is of high purity and does not require further purification.

[0030] X-ray diffraction analysis confirmed that the hollow CuPt alloy nanocrystals prepared in this patent exhibited excellent crystallinity, with no detectable oxides or other impurities. The resulting product can be used directly as an electrode material for fuel cells without the need for subsequent purification, such as acid washing.

[0031] (4) The obtained hollow structure can resist agglomeration and significantly enhance the intrinsic electrocatalytic activity.

[0032] Compared to solid, small-sized CuPt alloy nanocrystals, which tend to agglomerate, resulting in a reduction in exposed active sites and lower precious metal utilization, hollow CuPt alloy nanocrystals, with their dual internal and external surfaces and abundant pores, significantly increase the material's specific surface area. Their abundant pores shorten ion diffusion pathways and accelerate charge transfer, enabling them to exhibit excellent intrinsic electrocatalytic activity without the need for composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the X-ray diffraction result of the product obtained in Example 1.

[0034] Figure 2 This is a transmission electron microscope image of the hydrothermal carbon support generated after decomposition of ascorbic acid obtained in Example 1.

[0035] Figure 3 This is a transmission electron microscope image of the hollow CuPt alloy nanocrystals obtained in Example 1.

[0036] Figure 4 1 is the cyclic voltammetry curve of the hollow CuPt alloy nanocrystal obtained in Example 1 in a 0.5 mol / L H2SO4 solution and a H2SO4 solution containing 400 mmol / L formic acid.

[0037] Figure 5 1 is a chrono-response current density curve of the hollow CuPt alloy nanocrystals obtained in Example 1 and commercial Pt / C in an H2SO4 electrolyte containing 400 mmol / L formic acid. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail below with reference to the accompanying drawings.

[0039] Example 1: Preparation of hollow CuPt alloy nanocrystals by hydrothermal method

[0040] (1) Using deionized water as the solvent, ascorbic acid solutions with concentrations of 4 mmol / L (low concentration) and 500 mmol / L (high concentration) and a hydrochloric acid solution with a concentration of 1 mol / L were prepared respectively;

[0041] (2) 43 mL of low-concentration (4 mmol / L) ascorbic acid solution was added with 0.05 g of polyvinylpyrrolidone and stirred thoroughly at room temperature to prepare mixed solution 1;

[0042] (3) Add 10 mL of a pre-prepared 1 mol / L hydrochloric acid solution to the mixed solution 1 and stir evenly at room temperature to obtain a mixed solution 2;

[0043] (4) Transferring the mixed solution 2 to a hydrothermal reactor, performing a hydrothermal reaction at 120° C. for 8 hours, and then naturally cooling to room temperature to obtain a mixed solution 3;

[0044] (5) After ultrasonicating the mixed solution 3 for 10 minutes, 58.3 mL of deionized water was added to dilute it to 2.1 times the original volume to obtain mixed solution 4;

[0045] (6) 960 mg of KCl powder and 306 mg of CuCl2 powder were added to the mixed solution 4, and the mixture was stirred for another 20 minutes. Subsequently, 26 mL of a 500 mmol / L ascorbic acid aqueous solution was added and stirred for 10 minutes to obtain a mixed solution 5;

[0046] (7) Add 21.0 mL of 7 mmol / L H2PtCl6 solution to the mixed solution 5 and react at 60°C for 6 hours;

[0047] (8) After the reaction is completed, the precipitate is filtered, washed twice with ethanol, and dried at 60 °C for 6 h to obtain a powder, which is hollow CuPt alloy nanocrystals.

[0048] In order to analyze the composition of the product, we conducted an X-ray diffraction test on the obtained sample, and the results are shown in the attached manual. Figure 1 As shown. Figure 1 It can be observed that the X-ray diffraction pattern of the obtained product has diffraction peaks at 40.6°, 47.2°, 69.4° and 83.6° located between the face-centered cubic Pt (JCPDS card: 89-2838) and Cu (JCPDS card: 04-0802) (111), (200), (220) and (311) crystal phases, respectively. In addition, no peaks corresponding to oxides or corresponding to individual metal components were observed, indicating that high-purity CuPt nanoalloys were successfully synthesized. In this embodiment, the precipitate in the mixed solution 3 obtained after heating in step (4) is the hydrothermal carbon template after decomposition of ascorbic acid. To verify this inference, we performed transmission electron microscopy on the precipitate.

[0049] As the instruction manual Figure 2As shown, the intermediate product appears as a solid spherical structure with a diameter of approximately 600 nm. Elemental analysis reveals that the spherical structure is primarily composed of carbon and oxygen. Therefore, we infer that the solid sphere is a decomposition product of ascorbic acid. Since this product is insoluble in water, it can serve as a template for the subsequent formation of hollow structures.

[0050] To verify that the product obtained in Example 1 is indeed a hollow structure, we conducted a transmission electron microscopy test on the product collected in step (8) (see the attached manual for details). Figure 3 The results showed that the product was spherical and had a diameter of Figure 2 The intermediate product increased slightly, and there was a significant difference in light transmittance between its edge and center. The wall thickness was measured to be about 21 nm, proving that the product was a spherical hollow structure. Combined with the X-ray diffraction pattern analysis results, it was finally determined that the product of Example 1 was a hollow CuPt alloy nanocrystal.

[0051] Combined with the experimental results in the accompanying figures, it can be seen that in steps (6-7), the CuCl2 and H2PtCl6 involved in the reaction are reduced to form CuPt alloy nanocrystals. Simultaneously, the decomposition of ascorbic acid causes the hydrothermal carbon inside the nanospheres to gradually consume. Due to the concentration gradient, the hydrothermal carbon layer continues to diffuse outward, eventually removing the template and forming a structurally intact hollow CuPt alloy nanocrystal.

[0052] The hollow structure significantly increases the actual specific surface area of ​​CuPt alloy nanocrystals. Through a triple mechanism of exposed inner and outer surfaces, a porous shell design, and a lightweight spatial arrangement, it transcends the geometric limitations of solid materials and achieves a doubling of the specific surface area. This characteristic enables them to exhibit strong catalytic performance in the electrocatalytic formic acid oxidation process. To verify this concept, we investigated the feasibility of hollow CuPt alloy nanocrystals in the electrocatalytic formic acid oxidation reaction through Application Example 1.

[0053] Application Example 1: Study on the electrocatalytic activity of formic acid oxidation using hollow CuPt alloy nanocrystals

[0054] The present invention adopts a three-electrode system and uses a hollow CuPt alloy nanocrystal modified working electrode to detect its cyclic voltammetry curve in formic acid solution. The specific detection method is as follows:

[0055] (1) A glassy carbon electrode modified with hollow CuPt alloy nanocrystals was used as the working electrode (12 μg of a hollow CuPt alloy nanocrystal suspension was added dropwise to the glassy carbon working electrode. After the liquid evaporated, 6 μL of a 0.05% perfluorosulfonic acid polymer solution was added dropwise. After the liquid evaporated, the modification was completed). Ag / AgCl was used as the reference electrode, and a Pt wire electrode was used as the counter electrode. The electrodes were connected to an electrochemical workstation.

[0056] (2) Using 0.5 mol / L H2SO4 as the electrolyte, set the operating parameters (scan rate 10 mV / s) and collect cyclic voltammetry curve 1;

[0057] (3) Formic acid was added to the electrolyte to make the formic acid concentration in the solution reach 400 mmol / L, the operating parameters were set (scan rate 10 mV / s), and cyclic voltammetry curve 2 was collected.

[0058] As the instruction manual Figure 3 As shown, in a 0.5 mol / L H₂SO₄ electrolyte, the hollow CuPt alloy nanocrystals exhibited no distinct oxidation or reduction peaks, indicating no significant redox reaction. When 400 mmol / L formic acid was introduced into the solution, two new oxidation peaks emerged in the forward scan cyclic voltammetry curve: the first peak at 0.76 V vs. Ag / AgCl corresponds to the direct oxidation of formic acid; the second peak at 1.12 V vs. Ag / AgCl is attributed to the indirect catalytic oxidation process. These results demonstrate that the hollow CuPt alloy nanocrystals can efficiently catalyze the oxidation of formic acid.

[0059] Based on the peak current density ratio of the first and second oxidation peaks in the forward scan cyclic voltammetry curve, it can be preliminarily determined that the hollow CuPt alloy nanocrystals mainly undergo indirect electrocatalytic formic acid oxidation.

[0060] Application Example 2: Study on the Stability of Formic Acid Oxidation Reaction Using Hollow CuPt Alloy Nanocrystals

[0061] To evaluate the stability of the hollow CuPt alloy nanocrystals obtained in Example 1 in the electrocatalytic formic acid oxidation reaction, we used chronoamperometry to test in a H2SO4 solution containing 400 mmol / L formic acid (working potential: 0.76 V vs Ag / AgCl). As a control, the same test was performed on a commercial Pt / C catalyst. Figure 5 As shown, the hollow CuPt alloy nanocrystals obtained in Example 1 of the present invention exhibited a higher response current density than commercial Pt / C, indicating that the catalyst possesses superior electrocatalytic activity. Furthermore, the response current density did not change significantly as the catalytic oxidation reaction proceeded, demonstrating the excellent stability of the hollow CuPt alloy nanocrystals during the electrocatalytic formic acid oxidation process and their suitability as electrode materials for formic acid fuel cells.

[0062] Example 2: Preparation of hollow CuPt alloy nanocrystals by hydrothermal method

[0063] (1) Using deionized water as the solvent, ascorbic acid solutions with concentrations of 4 mmol / L (low concentration) and 500 mmol / L (high concentration) and a hydrochloric acid solution with a concentration of 1 mol / L were prepared;

[0064] (2) Take 14.3 mL of low-concentration (4 mmol / L) ascorbic acid solution, add 16.7 mg of polyvinylpyrrolidone, and stir thoroughly at room temperature to prepare mixed solution 1;

[0065] (3) Add 3.3 mL of pre-prepared 1 mol / L hydrochloric acid solution to the mixed solution 1, and stir evenly at room temperature to obtain a mixed solution 2;

[0066] (4) Transferring the mixed solution 2 to a hydrothermal reactor, performing a hydrothermal reaction at 120° C. for 8 hours, and then naturally cooling to room temperature to obtain a mixed solution 3;

[0067] (5) Mixed solution 3 was ultrasonicated for 20 minutes, and then 21.12 mL of deionized water was added to dilute it to 2.2 times the original volume to obtain mixed solution 4;

[0068] (6) 320 mg of KCl powder and 102 mg of CuCl2 powder were added to the mixed solution 4, and the mixture was stirred for 20 minutes. Subsequently, 26 mL of a 500 mmol / L ascorbic acid aqueous solution was added, and the mixture was stirred at room temperature for 10 minutes to obtain a mixed solution 5;

[0069] (7) Add 7.0 mL of 7 mmol / L H2PtCl6 solution to the mixed solution 5 and react at 60°C for 6 hours;

[0070] (8) After the reaction is completed, the precipitate is filtered, washed twice with ethanol, and dried at 60°C for 6 hours to obtain a powder, which is a hollow CuPt alloy nanosphere.

[0071] In summary, the present invention proposes a simple and efficient hydrothermal method for preparing hollow CuPt alloy nanocrystals. The resulting hollow CuPt alloy nanocrystals demonstrate remarkable performance in electrocatalytic formic acid oxidation, as demonstrated through application examples. It should be noted that the foregoing is a preferred embodiment of the invention. Those skilled in the art will readily appreciate that improvements and modifications can be made without departing from the principles of the present invention, and such improvements and modifications are considered within the scope of protection of the present invention.

Claims

1. A hydrothermal preparation method for hollow CuPt alloy nanocrystals, characterized in that: The preparation method of hollow CuPt alloy nanocrystals is as follows: (1) Using deionized water as the solvent, prepare ascorbic acid solutions with concentrations of 4 mmol / L (low concentration) and 500 mmol / L (high concentration), and a hydrochloric acid solution with a concentration of 1 mol / L; (2) Add polyvinyl pyrrolidone powder to a pre-prepared low-concentration ascorbic acid solution (4 mmol / L) in proportion, and stir at room temperature to obtain a mixed solution 1; (3) Add the pre-prepared hydrochloric acid solution to the mixed solution 1 in proportion, and stir evenly at room temperature to obtain the mixed solution 2; (4) Transferring the mixed solution 2 to a hydrothermal reactor, performing a hydrothermal reaction at 120° C. for 8 hours, and then naturally cooling to room temperature to obtain a mixed solution 3; (5) The mixed solution 3 was ultrasonically treated for 10-20 minutes, and then deionized water was added to dilute it to 2.0-2.2 times the original volume to obtain a mixed solution 4; (6) KCl powder and CuCl2 powder were added to the mixed solution 4 in proportion, and the mixture was stirred again. Then, 26 mL of a high concentration of ascorbic acid (500 mmol / L) aqueous solution was added and stirred at room temperature to obtain a mixed solution 5. (7) Add 7 mmol / L H2PtCl6 solution to the mixed solution 5 and react at 60°C for 6 hours; (8) After the reaction, the precipitate was filtered, washed with ethanol 1 to 2 times, and dried with air for several hours to obtain hollow CuPt alloy nanocrystals; In step (2), the amount of polyvinyl pyrrolidone powder added to each milliliter of the low-concentration ascorbic acid solution is 1.16 to 1.20 mg; In step (3), the volume of hydrochloric acid added per milliliter of mixed solution 1 is 0.22 to 0.25 mL; In step (6), the mass of KCl powder added per milliliter of mixed solution 4 is 8.0 to 9.0 mg, and the mass of CuCl2 powder added per milliliter of mixed solution 4 is 2.6 to 2.8 mg; In step (7), the volume ratio of the added H2PtCl6 solution to the mixed solution 5 is 1:6 to 1:

5.

2. A hollow CuPt alloy nanocrystal, characterized in that: The hollow CuPt alloy nanocrystal is obtained by the hydrothermal preparation method of claim 1.

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