A fuel cell catalyst based on pH adjustment to enhance stability and a method for preparing the same

Abstract

The application belongs to the technical field of hydrogen fuel cells, and relates to a fuel cell catalyst based on pH value adjustment and enhancing stability and a preparation method thereof, which comprises the following steps: firstly, adjusting the pH value of a platinum precursor solution to 3.0-5.0; secondly, adding a carbon carrier to mix and perform impregnation treatment, and adjusting the pH value to 7.5-9.0; thirdly, uniformly dispersing the solution through ultrasonic treatment; fourthly, adjusting the pH value of the system to 6.0-7.0, and performing washing and drying; and finally, performing calcination on the impregnated product in a hydrogen argon environment to obtain the catalyst. The pH value is controlled in stages during the impregnation process, which promotes the coordination anchoring of Pt particles and oxygen-containing functional groups on the surface of the carbon carrier, forms more and more uniform nucleation sites, and avoids long-time exposure of the carrier in strong acid. The method not only improves the metal dispersion and the number of active sites of the synthesized catalyst, enhances the electrochemical stability of the catalyst, but also ensures the controllability, reproducibility and universality of the impregnation synthesis process.

Description

Technical Field

[0001] This invention relates to the field of hydrogen fuel cell catalyst technology, specifically a fuel cell catalyst with enhanced stability based on pH adjustment and its preparation method, applicable to proton exchange membrane fuel cells. Background Technology

[0002] Platinum (Pt) is currently the most efficient catalyst. However, due to its high cost, it must be fabricated into nanoparticles (2-5 nanometers in size) and dispersed on a carbon support with a large surface area to achieve the maximum active area with the least amount of material. The impregnation process aims to precisely and uniformly load the catalyst (usually platinum or platinum alloy nanoparticles) onto a conductive porous support (usually carbon black) to form a catalyst layer.

[0003] In existing technologies, the impregnation method for preparing Pt / C catalysts typically uses a single pH environment (such as strong acid or strong alkalinity), which has the following problems: 1. The metal particles are not uniformly dispersed and are prone to agglomeration on the support surface; 2. The strong acid environment leads to corrosion of the carbon support and accelerates catalyst decay; 3. The metal particles are prone to sintering during high-temperature treatment, etc.

[0004] CN120400902A discloses a platinum-carbon catalyst supported on hollow carbon nanospheres and its preparation method. By utilizing uniformly sized nanotemplates to obtain high specific surface area mesoporous carbon nanospheres, the catalyst can achieve better contact with the electrolyte, thereby enhancing catalytic activity. However, the support in the aforementioned patent is prone to carbon corrosion, leading to catalyst structural collapse. CN119674105A discloses a method for preparing a platinum-carbon catalyst and the catalyst itself. By modifying the catalyst with an amino compound solution, the interaction between platinum particles and oxygen-containing intermediates during oxygen reduction is weakened, improving the catalytic activity of the platinum-carbon catalyst. However, the weakened interaction between the support and platinum particles is detrimental to catalyst stability. Therefore, it is necessary to invent a synthesis method that can improve catalyst activity without reducing stability. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a platinum-based catalyst and its preparation method that improves stability by precisely controlling the pH value of the impregnation process, thereby improving the particle size distribution and electrochemical stability of the catalyst.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first aspect of this invention discloses a method for preparing a catalyst for a hydrogen fuel cell, comprising the following steps:

[0008] S1, Acidic Impregnation Stage: Take a solution containing platinum, adjust its pH to 3.0-5.0, and obtain the precursor solution after stabilization;

[0009] S2, Alkaline Impregnation Stage: Take the precursor solution from S1, add carbon support to it, ultrasonically disperse for 0.5-2 hours, adjust the pH of the solution to 7.5-9.0, and ultrasonically disperse for 1-6 hours to obtain a mixed solution; the ultrasonic dispersion condition is to use 40kHz ultrasonic treatment in an ice bath environment.

[0010] S3, Neutralization adjustment stage: The pH of the mixture obtained in S2 is adjusted to 6-7, and then washed and dried to obtain the dried product;

[0011] S4. Post-treatment stage: Under a hydrogen and argon atmosphere, the dried product of S3 is heat-treated at 250-350℃ for 1-4 hours to obtain the catalyst;

[0012] In S1-S3, a buffer solution system is used to adjust and stabilize the pH value, so that the pH fluctuation range in each stage is controlled within ±0.5.

[0013] The innovation of this invention lies in setting up multiple stages: 1. Acidic stage (pH 3.0–5.0): promotes the initial coordination of Pt precursor with oxygen-containing functional groups (such as carboxyl and hydroxyl groups) on the surface of carbon support, forming anchoring sites.

[0014] 2. Alkaline stage (pH 7.5–9.0): Further promotes the uniform dispersion and nucleation of Pt species, and avoids the corrosion of the carrier caused by excessive acidity.

[0015] 3. Neutral phase (pH 6.0–7.0): Stabilizes the system, facilitates subsequent washing and drying, and avoids structural damage caused by extreme pH levels.

[0016] This invention discloses a novel method for preparing platinum-based catalysts by precisely controlling the pH value of the impregnation process and systematically improving the parameters of each stage. By precisely controlling the pH evolution of the reaction environment, the nucleation, growth and anchoring process of Pt nanoparticles is dominated thermodynamically and kinetically, and the two goals of high activity and high stability, which are often contradictory in traditional methods, are successfully achieved simultaneously.

[0017] Preferably, in S1, the solution containing platinum is selected from chloroplatinic acid solution.

[0018] Preferably, in S1, the pH is adjusted using NaOH, and sodium citrate buffer is added to stabilize the system.

[0019] Preferably, in S2, the carbon support includes Vulcan XC-72R, Ketjenblack, acetylene black, graphene, and carbon nanotubes.

[0020] Preferably, in S2, the pH is adjusted using a Na2CO3 solution.

[0021] Preferably, in step S3, the washing is performed by centrifugation at 8000 rpm for 10-30 minutes, and the drying temperature is 60-75°C for 8-15 hours.

[0022] Preferably, in S3, the pH is adjusted using an ammonia / ammonium nitrate buffer solution.

[0023] Preferably, in S4, heat treatment is carried out in a 5% H2 / Ar atmosphere at a heating rate of 2°C / min.

[0024] A second aspect of the present invention discloses a highly stable fuel cell catalyst, which is prepared by the method described above.

[0025] The third aspect of this invention discloses the application of the above-mentioned fuel cell catalyst in the membrane electrode of a proton exchange membrane fuel cell.

[0026] Compared with the prior art, the beneficial effects of this invention are as follows:

[0027] By combining the technical features of "staged pH control" and "ice bath ultrasound" into a whole, a technical solution with synergistic effects is formed.

[0028] The phased pH control during the impregnation process promotes the coordination and anchoring of oxygen-containing functional groups on the surface of Pt particles and carbon support, forming more and more uniform nucleation sites. At the same time, it avoids the long-term exposure of the support in strong acid. This invention not only improves the metal dispersion and number of active sites of the synthesized catalyst and enhances the electrochemical stability of the catalyst, but also ensures the controllability, reproducibility and universality of the impregnation synthesis process. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the impregnation process of the present invention;

[0030] Figure 2 This is a transmission electron microscope (TEM) image of the catalyst in Example 1 of the present invention;

[0031] Figure 3 The polarization curves before and after the stability test of the catalysts in Example 1 and Comparative Examples 1-2 of this invention are shown. Detailed Implementation

[0032] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but this does not limit the present invention to the scope of the described embodiments. Process parameters not specified in the embodiments of this application can be performed according to conventional methods, and all raw materials used can be obtained through commercial channels.

[0033] Example 1

[0034] Dissolve 500 mg H2PtCl6·6H2O in 25 mL of deionized water, adjust the pH to 4.0 ± 0.1 with 0.1 M NaOH, and add 1 mL of 0.5 M sodium citrate buffer (pH = 4.0) to stabilize the system to prepare the precursor solution.

[0035] Weigh 8.3 ml of precursor solution, add 50 mg of carbon support, and sonicate at 40 kHz for 20 min in an ice bath.

[0036] Adjust the pH to 8.5 ± 0.1 by adding 0.5 M Na2CO3 solution dropwise, and then sonicate at 40 kHz for 120 min in an ice bath to ensure homogeneity.

[0037] Centrifuge (8000 rpm, 15 min), wash with ammonia / ammonium nitrate buffer (pH 6.8) until the filtrate pH is 6.8, and vacuum dry at 70°C for 12 h.

[0038] Heat treatment was carried out in a 5% H2 / Ar atmosphere at a temperature of 2℃ / min to 300℃ for 2 hours.

[0039] Example 2

[0040] Dissolve 500 mg H2PtCl6·6H2O in 25 mL of deionized water, adjust the pH to 3.0 ± 0.1 with 0.1 M NaOH, and add 1 mL of 0.5 M sodium citrate buffer (pH = 3.0) to stabilize the system to prepare the precursor solution.

[0041] Weigh 8.3 ml of precursor solution, add 50 mg of carbon support, and sonicate at 40 kHz for 20 min in an ice bath.

[0042] Adjust the pH to 7.5 ± 0.1 by adding 0.5 M Na2CO3 solution dropwise, and then sonicate in an ice bath at 40 kHz for 120 min to mix thoroughly.

[0043] Centrifuge (8000 rpm, 15 min), wash with ammonia / ammonium nitrate buffer (pH 6.8) until the filtrate pH is 6.8, and vacuum dry at 70°C for 12 h.

[0044] Heat treatment was carried out in a 5% H2 / Ar atmosphere at a temperature of 2℃ / min to 300℃ for 2 hours.

[0045] Comparative Example 1 (Comparative Example 1: Traditional acid impregnation, pH adjustment step omitted, other conditions the same as Example 1)

[0046] Dissolve 500 mg H₂PtCl₆·6H₂O in 25 mL of deionized water. Adjust the pH to 4.0 ± 0.1 with 0.1 M NaOH, and add 1 mL of 0.5 M sodium citrate buffer (pH = 4.0) to stabilize the system, thus preparing the precursor solution.

[0047] Weigh 8.3 ml of precursor solution, add 50 mg of carbon support, and sonicate in an ice bath at 40 kHz for 140 min to mix thoroughly.

[0048] Centrifuge (8000 rpm, 15 min), wash with ammonia / ammonium nitrate buffer (pH 6.8) until the filtrate pH is 6.8, and vacuum dry at 70°C for 12 h.

[0049] Heat treatment was carried out in a 5% H2 / Ar atmosphere at a temperature of 2℃ / min to 300℃ for 2 hours.

[0050] Comparative Example 2 (Comparative Example 1: Single alkaline impregnation, initial pH directly adjusted to 9.0, without staged adjustment)

[0051] Dissolve 500 mg H2PtCl6·6H2O in 25 ml of deionized water, and adjust the pH to 9.0 ± 0.1 with 0.1 M NaOH.

[0052] Weigh 8.3 ml of precursor solution, add 50 mg of carbon support, and sonicate in an ice bath at 40 kHz for 140 min to mix thoroughly.

[0053] Centrifuge (8000 rpm, 15 min), wash with ammonia / ammonium nitrate buffer (pH 6.8) until the filtrate pH is 6.8, and vacuum dry at 70°C for 12 h.

[0054] Heat treatment was carried out in a 5% H2 / Ar atmosphere at a temperature of 2℃ / min to 300℃ for 2 hours.

[0055] Example 3

[0056] Dissolve 500 mg H2PtCl6·6H2O in 25 mL of deionized water, adjust the pH to 3.0 ± 0.1 with 0.1 M NaOH, and add 1 mL of 0.5 M sodium citrate buffer (pH = 3.0) to stabilize the system to prepare the precursor solution.

[0057] Weigh 8.3 ml of precursor solution, add 50 mg of carbon support, and sonicate at 40 kHz for 20 min in an ice bath.

[0058] Adjust the pH to 8.5 ± 0.1 by adding 0.5 M Na2CO3 solution dropwise, and then sonicate at 40 kHz for 120 min in an ice bath to ensure homogeneity.

[0059] Centrifuge (8000 rpm, 15 min), wash with ammonia / ammonium nitrate buffer (pH 6.8) until the filtrate pH is 6.8, and vacuum dry at 70°C for 12 h.

[0060] Heat treatment was carried out in a 5% H2 / Ar atmosphere at a temperature of 2℃ / min to 300℃ for 2 hours.

[0061] Example 4

[0062] Dissolve 500 mg H2PtCl6·6H2O in 25 mL of deionized water, adjust the pH to 4.0 ± 0.1 with 0.1 M NaOH, and add 1 mL of 0.5 M sodium citrate buffer (pH = 4.0) to stabilize the system to prepare the precursor solution.

[0063] Weigh 8.3 ml of precursor solution, add 50 mg of carbon support, and sonicate at 40 kHz for 20 min in an ice bath.

[0064] Adjust the pH to 7.5 ± 0.1 by adding 0.5 M Na2CO3 solution dropwise, and then sonicate in an ice bath at 40 kHz for 120 min to mix thoroughly.

[0065] Centrifuge (8000 rpm, 15 min), wash with ammonia / ammonium nitrate buffer (pH 6.8) until the filtrate pH is 6.8, and vacuum dry at 70°C for 12 h.

[0066] Heat treatment was carried out in a 5% H2 / Ar atmosphere at a temperature of 2℃ / min to 300℃ for 2 hours.

[0067] The Pt particles in Example 1 were the smallest (2.8 nm), indicating that its staged pH control strategy (acidic → alkaline → neutral) was the most effective in controlling the nucleation and growth of Pt particles.

[0068] The particle size of Examples 2, 3, and 4 is slightly larger than that of Example 1, but still significantly smaller than that of Comparative Examples 1 and 2, indicating that the pH combination of Example 1 is superior to other pH combinations.

[0069] The morphology of the catalyst synthesized in Example 1 was characterized by TEM, such as... Figure 2 As shown. The catalyst metal particles synthesized in Example 1 using a staged pH control strategy are uniformly dispersed on a carbon support, and the minimum platinum particle size is 2.8 nm. Furthermore, the platinum particle size of the catalyst synthesized using the staged pH control strategy is significantly lower than that of the catalyst synthesized by traditional acid impregnation (3.7 nm) and the catalyst synthesized by single alkaline impregnation (4.5 nm).

[0070] Table 1. Platinum particle size of catalysts in Examples 1-4 and Comparative Examples 1-2

[0071]

[0072]

[0073] Stability test

[0074] Polarization test: 80℃, 100%RH, anode / cathode gas metering ratio 1.5 / 2.5, back pressure 150Kpa.

[0075] Accelerated durability testing: 0.6 (3s) - 0.95V (3s) vs. RHE, 10,000 square wave cycles, membrane electrode active area is 5×5cm. 2 The platinum loading at the anode and cathode is 0.4 / 0.1 mg / cm³. 2 .

[0076] The membrane electrodes prepared with the catalysts of Example 1 and Comparative Examples 1-2 of this invention were subjected to durability tests at 80°C and 100% RH. Figure 3 As shown in Table 2, the catalyst synthesized using a staged pH control strategy after 10,000 potential cycles has a pH of 0.8 A / cm. 2 It exhibits the least voltage change (8mV) and the best stability.

[0077] Table 2. Voltage changes before and after membrane electrode stability of catalysts in Examples 1 and Comparative Examples 1-2.

[0078] <![CDATA[BOL(V@0.8A / cm 2 )]]> <![CDATA[EOL(V@0.8A / cm 2 )]]> △(mV) Example 1 0.756V 0.748V 8mV Comparative Example 1 0.753V 0.737V 16mV Comparative Example 2 0.752V 0.735V 17mV

[0079] As can be seen from the data in Tables 1 and 2: 1. The phased pH control strategy proposed in this invention is superior to the traditional single pH environment impregnation method (whether it is a strong acid or a strong base) in terms of reducing the size of platinum (Pt) particles, improving the dispersion and significantly enhancing electrochemical stability.

[0080] Traditional acidic method (Comparative Example 1): An acidic environment is conducive to the adsorption of Pt precursors, but strong acidity severely corrodes the carbon support, resulting in poor long-term stability.

[0081] Single alkaline method (Comparative Example 2): The lack of effective anchoring in the acidic stage leads to uneven nucleation of Pt precursors on the support, easy aggregation, the largest particle size (4.5 nm), and the worst stability (17 mV decay).

[0082] The present invention (Examples 1-4) achieved smaller particle size (2.8 vs 3.7 nm) and better stability (8 vs 16 mV decay) by shortening the strong acid exposure time and transferring to an alkaline environment.

[0083] 2. The Pt particle size result (2.8 nm) in Example 1 demonstrates that staged pH regulation effectively creates more and more uniform nucleation sites, significantly inhibiting particle aggregation and growth, and achieving a minimal and uniform particle size distribution. The voltage decay (8 mV) in Example 1 demonstrates the stability of the catalyst prepared according to this invention, thanks to its minimal particle size and strongest metal-support interaction (MSI). Strong MSI firmly "anchors" the Pt particles to the carbon support, effectively inhibiting the dissolution, migration, and aggregation of Pt particles during potential cycling.

[0084] This invention is not limited to the above-described embodiments. Any changes in shape or structure are within the scope of protection of this invention. The scope of protection of this invention is defined by the appended claims. Those skilled in the art can make various changes, modifications, substitutions, combinations, and simplifications to these embodiments without departing from the principles and essence of this invention. All such changes and simplifications should be considered equivalent substitutions and fall within the scope of protection of this invention.

Claims

1. A method for preparing a catalyst for hydrogen fuel cells, characterized in that, Includes the following steps: S1, Acidic Impregnation Stage: Take a solution containing platinum, adjust its pH to 3.0-5.0, and obtain the precursor solution after stabilization; S2, Alkaline Impregnation Stage: Take the precursor solution from S1, add carbon support to it, ultrasonically disperse for 0.5-2 hours, adjust the pH of the solution to 7.5-9.0, and ultrasonically disperse for 1-6 hours to obtain a mixed solution; the ultrasonic dispersion condition is to use 40kHz ultrasonic treatment in an ice bath environment. S3, Neutralization adjustment stage: The pH of the mixture obtained in S2 is adjusted to 6-7, and then washed and dried to obtain the dried product; S4. Post-treatment stage: Under a hydrogen and argon atmosphere, the dried product of S3 is heat-treated at 250-350℃ for 1-4 hours to obtain the catalyst; In S1-S3, a buffer solution system is used to adjust and stabilize the pH value, so that the pH fluctuation range in each stage is controlled within ±0.

5.

2. The preparation method according to claim 1, characterized in that, The solution containing platinum in S1 is selected from chloroplatinic acid solution.

3. The preparation method according to claim 1, characterized in that, In S1, the pH was adjusted using NaOH, and sodium citrate buffer was added to stabilize the system.

4. The preparation method according to claim 1, characterized in that, In S2, the carbon support includes Vulcan XC-72R, Ketjenblack, acetylene black, graphene, and carbon nanotubes.

5. The preparation method according to claim 1, characterized in that, In S2, the pH is adjusted using Na2CO3 solution.

6. The preparation method according to claim 1, characterized in that, In S3, the washing is performed by centrifugation at 8000 rpm for 10-30 minutes, and the drying temperature is 60-75℃ for 8-15 hours.

7. The preparation method according to claim 1, characterized in that, In S3, the pH is adjusted using an ammonia / ammonium nitrate buffer solution.

8. The preparation method according to claim 1, characterized in that, In S4, heat treatment was carried out in a 5% H2 / Ar atmosphere at a heating rate of 2℃ / min.

9. A highly stable fuel cell catalyst, characterized in that, It is prepared by the method described in any one of claims 1-8.

10. The use of the fuel cell catalyst as described in claim 9 in the membrane electrode assembly of a proton exchange membrane fuel cell.

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