A method for preparing a platinum-carbon catalyst and the catalyst itself.

Abstract

This invention discloses a method for preparing a platinum-carbon catalyst and the catalyst itself, relating to the field of catalyst preparation technology. It provides a simple method for preparing a platinum-carbon catalyst with excellent stability. The method includes: placing solid polyacrylamide in pure water and uniformly dispersing it until it is completely dissolved to obtain an aqueous solution of polyacrylamide; preparing an aqueous solution of platinum salt in pure water; raising the temperature of the polyacrylamide aqueous solution and adding the platinum salt aqueous solution, then homogenizing and dispersing it; placing the dispersed mixture in a cold trap for solidification, and then freeze-drying it in a low-temperature dryer; calcining and carbonizing the dried sample in a tube furnace, reducing platinum ions with carbon to obtain the desired platinum-carbon catalyst. This invention features simple and easy-to-operate steps, easy control, and easy mass production. The resulting platinum-carbon catalyst exhibits tight bonding between platinum and the carbon support, uniform platinum distribution on the carbon support, uniform platinum size, and is not prone to agglomeration, resulting in excellent electrochemical performance and long-term stability.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, specifically to a method for preparing a platinum-carbon catalyst and the catalyst itself. Background Technology

[0002] Platinum-carbon catalysts, as catalyst materials with platinum nanoparticles dispersed on the surface of carbon materials, are among the most common noble metal carbon catalysts. They possess a high active specific surface area and are therefore frequently used in aerospace and pharmaceutical product development. Membrane electrode arrays (MEAs) are the core components of proton exchange membrane fuel cells (PEMFCs), and the platinum-carbon catalysts required for their fabrication typically have a platinum loading exceeding 20%. Furthermore, the activity of platinum-carbon catalysts plays a crucial role in the operating efficiency of fuel cells.

[0003] The size of platinum-carbon catalysts, the uniformity of platinum nanoparticle dispersion in carbon materials, and the amount of impurities inside the catalyst all significantly affect their electrochemical activity. Furthermore, due to the weak interaction between platinum particles and carbon materials, platinum may detach or agglomerate under prolonged high temperature and humidity conditions in fuel cells, affecting their long-term stability. The invention patent application CN116344852A, entitled "A Carbon-Supported Platinum Nanoparticle Electrocatalyst and Its Preparation Method," discloses a method of dissolving a platinum-containing precursor compound and a compound that assists in the controlled hydrolysis of the platinum precursor in water, then adding a carbon support and sonicating it. The mixed slurry is heated and held at that temperature for a period of time, then cooled to room temperature, filtered, washed, dried, and ground. Finally, it is heat-treated in a reducing gas atmosphere to obtain a carbon-supported platinum nanoparticle electrocatalyst. One of the purposes of this method is to improve its long-term operational stability. Although this method is relatively simple, and the catalyst prepared in Example 1 showed a 23% decrease in electrochemical active area after 10,000 cycles of accelerated durability testing, which is a significant improvement compared to the platinum-carbon catalyst from JM Company in the UK, the effect is still not ideal. Therefore, this invention aims to find a simple synthesis method while further improving the long-term stability of platinum-carbon catalysts. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a platinum-carbon catalyst and the catalyst itself, so as to prepare a platinum-carbon catalyst with excellent stability through a simple method.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a platinum-carbon catalyst, comprising the following steps: placing solid polyacrylamide in pure water and uniformly dispersing it until it is completely dissolved to obtain an aqueous solution of polyacrylamide; placing a platinum salt in pure water to prepare an aqueous solution of platinum salt; raising the temperature of the aqueous solution of polyacrylamide, adding the aqueous solution of platinum salt, and homogenizing and dispersing it; placing the dispersed mixed solution in a cold trap for solidification, and then freeze-drying it in a low-temperature dryer; placing the dried sample in a tube furnace for calcination and carbonization, reducing platinum ions through carbon to obtain the desired platinum-carbon catalyst.

[0006] Preferably, the polyacrylamide has a molecular weight of 4 million to 12 million, and is one or more of anionic, cationic, and nonionic types, with an aqueous solution concentration of 10.5 to 28.5 g / L.

[0007] Preferably, the platinum salt is one or more of chloroplatinic acid, sodium chloroplatinate, ammonium chloroplatinate, and potassium hydrogen chloroplatinate, and the concentration of the platinum salt solution is 0.08–0.21 mol / L.

[0008] Preferably, the cold trap temperature is -40℃ to -20℃, the processing time is 3 to 6 hours, and the freeze-drying conditions are -60℃ to -30℃, with a processing time of 20 to 30 hours.

[0009] Preferably, the calcination and carbonization are carried out in an inert gas atmosphere at a temperature range of 300℃ to 450℃ for a processing time of 4 to 8 hours.

[0010] A platinum-carbon catalyst was prepared using the method described above.

[0011] Preferably, the platinum in the catalyst is tightly bonded to the carbon support, the platinum is uniformly distributed on the carbon support, and the platinum is of uniform size and does not easily agglomerate.

[0012] Preferably, after 30,000 cycles of ADT aging test, the ECSA loss rate of the above catalyst is less than 12%.

[0013] Compared with the prior art, the beneficial effects of the present invention are:

[0014] 1. The preparation method of this platinum-carbon catalyst involves uniformly dispersing polyacrylamide and platinum salt, freeze-drying the solution and calcining it. It does not require the use of traditional carbon materials, and the steps are simple, easy to operate and control, and easy to mass-produce.

[0015] 2. The preparation method and catalyst of this platinum-carbon catalyst utilize a water-soluble polymer as a support. Its water solubility allows it to completely dissolve with platinum salt in water, effectively improving the uniformity of platinum ion distribution with the support material. Simultaneously, the carbonyl and carbon atoms of the amide group in the polymer possess lone pairs of electrons, which can interact with platinum ions to form complexes. Utilizing the coordination of the amide group with platinum ions, the product obtained after freeze-drying and calcination exhibits stronger interaction forces between platinum and carbon materials. After calcination, the platinum and support are tightly bound. Compared to traditional methods, the platinum-carbon catalyst obtained in this invention exhibits a more uniform distribution of platinum on the carbon material surface and stronger interaction forces, thus demonstrating higher electrochemical performance and superior long-term stability. Attached Figure Description

[0016] Figure 1 These are microscopic images of the platinum nanometal products in Example 1 and Comparative Example 1 of the present invention, taken using a transmission electron microscope (TEM).

[0017] Figure 2 This is a comparison of cyclic voltammetry curves before and after accelerated aging tests of the 60% Pt / C catalyst in Example 1 of this invention.

[0018] Figure 3 This is a comparison of the cyclic voltammetry curves of the 60% Pt / C catalyst before and after accelerated aging test in Comparative Example 1 of this invention. Detailed Implementation

[0019] A method for preparing a platinum-carbon catalyst, comprising the following:

[0020] Solid polyacrylamide is placed in pure water and uniformly dispersed to completely dissolve it to obtain an aqueous solution of polyacrylamide. Preferably, the molecular weight of polyacrylamide is 4 million to 12 million, and the type can be one or more of anionic, cationic, and nonionic polyacrylamide. The concentration of the aqueous solution of polyacrylamide is preferably 10.5 to 28.5 g / L.

[0021] Platinum salt is placed in pure water to prepare an aqueous solution of platinum salt; preferably, the platinum salt is one or more of chloroplatinic acid, sodium chloroplatinate, ammonium chloroplatinate, and potassium hydrogen chloroplatinate, which are soluble in water, and the concentration of the platinum salt solution is preferably 0.08 to 0.21 mol / L.

[0022] The temperature of the polyacrylamide aqueous solution was increased, and a platinum salt aqueous solution was added for homogeneous dispersion.

[0023] The dispersed mixture is placed in a cold trap for curing. For reference, the cold trap temperature is set to -40℃ to -20℃, and the treatment time is 3 to 6 hours. After curing, it is placed in a low-temperature dryer for freeze drying. For reference, the freeze drying conditions are set to -60℃ to -30℃, and the treatment time is 20 to 30 hours.

[0024] The dried sample is placed in a tube furnace for calcination. During the high-temperature calcination, polyacrylamide is carbonized. Part of the carbon acts as a reducing agent to reduce divalent platinum ions, while the other part acts as a catalyst support to obtain the desired platinum-carbon catalyst. The calcination and carbonization should preferably be carried out in an inert gas atmosphere, with a calcination temperature of 300℃ to 450℃ and a treatment time of 4 to 8 hours.

[0025] In the above method, both the carbonyl group and carbon atom of the polymer lactam group have lone pairs of electrons, which can interact with platinum ions to form a complex, resulting in a tight bond between platinum and the support in the catalyst obtained after calcination. The catalyst prepared by the above sol-gel freeze-drying and calcination method exhibits uniform platinum distribution on the carbon support, with uniform platinum size and low agglomeration. (See reference...) Figure 1 Because platinum forms a relatively uniform dispersion in an aqueous solution of polyacrylamide, and the complexes are tightly bound and not easily displaced or agglomerated, they can also maintain a uniform and non-agglomerated distribution structure after calcination.

[0026] Example 1:

[0027] 19.5 g of polyacrylamide (Mw≈4 million, anionic) was completely dissolved in 1000 mL of pure water. Then, 0.05 mol (25.89 g) of chloroplatinic acid was dissolved in 300 mL of pure water. After the two were mixed evenly, the mixture was placed in a -30℃ cold trap for 4 h and then dried in a freeze dryer at -50℃ for 21 h to obtain a solid sample.

[0028] The solid was placed in a tube furnace and heated to 300°C within 40 minutes under high-concentration nitrogen protection. It was then held at that temperature for 6 hours and cooled to room temperature before being taken out and recorded as sample 1.

[0029] Example 2:

[0030] 17.8 g of polyacrylamide (Mw≈11 million, anionic) was completely dissolved in 1000 mL of pure water. Then, 0.04 mol (20.71 g) of chloroplatinic acid was dissolved in 300 mL of pure water. After the two were mixed evenly, the mixture was placed in a -40℃ cold trap for 3.5 h and then dried in a freeze dryer at -60℃ for 20 h to obtain a solid sample.

[0031] The solid was placed in a tube furnace and heated to 400°C within 40 minutes under high-concentration nitrogen protection. It was then held at that temperature for 4.5 hours and cooled to room temperature before being taken out and recorded as sample 2.

[0032] Example 3:

[0033] 12.3 g of polyacrylamide (Mw≈8 million, non-ionic) was completely dissolved in 1000 mL of pure water. Then, 0.03 mol (15.53 g) of chloroplatinic acid was dissolved in 300 mL of pure water. After the two were mixed evenly, the mixture was placed in a -20℃ cold trap for 3 h and then dried in a freeze dryer at -40℃ for 28 h to obtain a solid sample.

[0034] The solid was placed in a tube furnace and heated to 450°C within 40 minutes under high-concentration nitrogen protection. It was then held at that temperature for 7 hours and cooled to room temperature before being taken out and recorded as sample 3.

[0035] Example 4:

[0036] 27.3 g of polyacrylamide (Mw≈4 million, anionic) was completely dissolved in 1000 mL of pure water. Then, 0.05 mol (25.89 g) of chloroplatinic acid was dissolved in 250 mL of pure water. After the two were mixed evenly, the mixture was placed in a -40℃ cold trap for 5 h and then dried in a freeze dryer at -40℃ for 24 h to obtain a solid sample.

[0037] The solid was placed in a tube furnace and heated to 350°C within 40 minutes under high-concentration nitrogen protection. It was then held at that temperature for 5 hours and cooled to room temperature before being taken out and recorded as sample 4.

[0038] Comparative Example 1:

[0039] 19.5g of carbon black was dispersed in 1000mL of pure water. Then, 0.05mol (25.89g) of chloroplatinic acid was dissolved in 300mL of pure water. The two were mixed and ultrasonically dispersed to form a suspension. The suspension was placed in a -30℃ cold trap for 4h and then dried in a freeze dryer at -50℃ for 21h to obtain a solid sample.

[0040] The solid was placed in a tube furnace and heated to 300°C within 40 minutes under high-concentration nitrogen protection. It was then held at that temperature for 6 hours and removed after cooling to room temperature. This was recorded as Comparative Example 1.

[0041] Test results:

[0042] 1) Electron microscopy results

[0043] like Figure 1 The image shows transmission electron microscopy (TEM) images of the platinum-carbon nanoparticles synthesized in Example 1 and Comparative Example 1. As can be seen from the image, the platinum on the carbon support in Example 1 has more uniform dispersion and smaller nanoscale size.

[0044] 2) Results of oxygen reduction activity test

[0045] Further tests on the active specific surface area of ​​the synthesized examples and comparative samples of this patent were conducted primarily using electrochemical methods, such as... Figure 2 and 3The electrochemical activity curves of the platinum-carbon particles in Example 1 and Comparative Example 1 were tested using cyclic voltammetry (CV).

[0046] Table 1: ECSA and ADT test results of the examples and comparative examples

[0047]

[0048] Depend on Figure 2 , Figure 3 As shown in Table 1, after 30,000 cycles of ADT aging test, the platinum-carbon CV curve of Example 1 showed less change compared to Comparative Example 1. Comparing the corresponding ECSA, the ECSA of the Example 1 samples before the aging test was higher than that of the Comparative Example, and the ECSA loss rate of the Example 1 samples after the aging test was around 10%, far lower than the 28.59% in Comparative Example 1. Furthermore, this invention conducted a larger number of experiments. The tests showed that after 30,000 cycles of ADT aging test, the ECSA loss rate of the catalyst was less than 12%. These tests demonstrate that the platinum-carbon catalyst prepared by the sol-gel freeze-drying calcination method using polyacrylamide as a support for platinum ion coordination in this invention can effectively improve the electrochemical activity and stability of synthesized platinum-carbon.

[0049] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

[0050] Any aspects of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A method for preparing a platinum-carbon catalyst, characterized in that, The process includes the following steps: placing solid polyacrylamide in pure water and dispersing it uniformly until it is completely dissolved to obtain an aqueous solution of polyacrylamide; preparing an aqueous solution of platinum salt in pure water; raising the temperature of the polyacrylamide aqueous solution, adding the aqueous solution of platinum salt, and dispersing it homogeneously; placing the dispersed mixture in a cold trap for solidification, and then freeze-drying it in a low-temperature dryer; calcining and carbonizing the dried sample in a tube furnace, reducing platinum ions through carbon to obtain the desired platinum-carbon catalyst; wherein the polyacrylamide has a molecular weight of 4 million to 12 million, and is one or both anionic and nonionic types, and the concentration of the polyacrylamide aqueous solution is 10.5 to 28.5 g / L.

2. The method for preparing a platinum-carbon catalyst according to claim 1, characterized in that: The platinum salt is one or more of chloroplatinic acid, sodium chloroplatinate, ammonium chloroplatinate, and potassium hydrogen chloroplatinate, and the concentration of the platinum salt solution is 0.08–0.21 mol / L.

3. The method for preparing a platinum-carbon catalyst according to claim 1, characterized in that: The cold trap temperature is -40℃ to -20℃, and the processing time is 3 to 6 hours. The freeze-drying conditions are -60℃ to -30℃, and the processing time is 20 to 30 hours.

4. The method for preparing a platinum-carbon catalyst according to claim 1, characterized in that: The calcination and carbonization are carried out in an inert gas atmosphere, with a temperature range of 300℃ to 450℃ and a processing time of 4 to 8 hours.

5. A platinum-carbon catalyst, characterized in that: It is prepared by any one of the preparation methods described in claims 1 to 4.

6. The platinum-carbon catalyst according to claim 5, characterized in that: The platinum in the catalyst is tightly bonded to the carbon support, and the platinum is uniformly distributed and sized on the carbon support.

7. The platinum-carbon catalyst according to claim 5, characterized in that: After undergoing 30,000 cycles of ADT aging test, the catalyst showed an ECSA loss rate of less than 12%.

Images