Preparation method of platinum-carbon catalyst, catalyst, application and fuel cell membrane electrode

Abstract

The present application relates to a kind of multi-particle size platinum carbon catalyst, preparation method, application and fuel cell membrane electrode, the preparation method steps are as follows: respectively preparing the small particle size platinum carbon catalyst of platinum particle average particle size 2-4nm and the large particle size platinum carbon catalyst of 5-7nm;Carbon carrier is dispersed in ethylene glycol, and chloroplatinic acid precursor is added, after being stirred uniformly by mechanical stirring, it is carried out stationary reaction;In the stationary reaction: when preparing small particle size, maintain pH=5-7, and reaction temperature is 80-100 DEG C;When preparing large particle size, maintain pH=9-13, and reaction temperature is 20-30 DEG C;Two kinds of catalysts are obtained by washing, and the mass ratio of small particle size platinum carbon catalyst / large particle size platinum carbon catalyst (4-8):1 is mixed.Its advantages are: the distribution of platinum particle size in platinum carbon catalyst is optimized, the performance advantages of different particle size platinum particles are combined, and then the activity and stability of membrane electrode are improved.

Description

Technical Field

[0001] This invention relates to the field of hydrogen fuel cell technology, specifically to a method for preparing a composite platinum-carbon catalyst loaded with platinum particles of different sizes, the platinum-carbon catalyst, the application of the catalyst, and a membrane electrode assembly (MEA) for a fuel cell using the platinum-carbon catalyst. Background Technology

[0002] Catalysts in fuel cells are typically platinum (Pt) nanoparticles due to their high catalytic activity for the oxygen reduction reaction (ORR). The catalyst slurry is made by mixing these platinum particles with a support (such as carbon) and ionomers, and then coating the electrodes. Therefore, the performance of the slurry directly affects the efficiency, durability, and cost of the fuel cell.

[0003] However, in fuel cell catalysts, the particle size distribution of platinum (Pt) nanoparticles directly affects catalytic activity and durability. Traditional platinum-carbon catalysts typically aim for a single particle size (e.g., 2-3 nm) to maximize the electrochemical active surface area (ECSA), but small particles are prone to Ostwald ripening, agglomeration, or dissolution, leading to performance degradation. Patent CN201910571287.1 improves the support stability of platinum catalysts through transition metal doping, but due to its reliance on high-temperature reduction processes and lack of optimization of platinum particle size uniformity, it fails to resolve the contradiction between high activity but easy solubility for small particles and stability but low activity for large particles. Furthermore, the preparation of strictly monodisperse small-size nanoparticles usually requires complex preparation processes, resulting in high costs and making it unsuitable for large-scale production. Patent CN111111693A discloses a method for preparing monodisperse platinum-based high-entropy alloy nanoparticle catalysts, but the process is complex and costly.

[0004] In comparison, larger particles are more stable, resisting dissolution, sintering, and agglomeration, thus reducing performance degradation during long-term operation. In polydisperse systems, large particles can act as "anchors," inhibiting the migration and agglomeration of small particles, thereby maintaining the stability of ECSA. However, larger particles have a smaller specific surface area and insufficient reactive sites, which can severely affect the performance of the catalyst.

[0005] Therefore, a method for preparing a composite multi-size platinum-carbon catalyst is provided. By mixing platinum particles of different sizes, the activity and stability are synergistically optimized, while reducing the platinum loading and preparation cost. This is of great significance for improving fuel cell performance and extending its durability. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for preparing a composite platinum-carbon catalyst loaded with platinum particles of different sizes, the platinum-carbon catalyst itself, its applications, and a membrane electrode assembly (MEA) for a fuel cell using the platinum-carbon catalyst. This method optimizes the size distribution of platinum particles in the platinum-carbon catalyst, combines the performance advantages of platinum particles of different sizes, and thereby improves the activity and stability of the MEA.

[0007] To achieve the above-mentioned objectives, the present invention first proposes a method for preparing a multi-particle-size platinum-carbon catalyst, characterized by comprising the following steps:

[0008] Small-particle-size platinum-carbon catalysts with an average particle size of 2-4 nm and large-particle-size platinum-carbon catalysts with an average particle size of 5-7 nm were prepared respectively:

[0009] The carbon support is dispersed in ethylene glycol, and a chloroplatinic acid precursor is added. The mixture is mechanically stirred until homogeneous and then allowed to stand for reaction. During the standing reaction, the pH is maintained at 5-7 and the reaction temperature is 80-100℃ when preparing small particle sizes, and the pH is maintained at 9-13 and the reaction temperature is 20-30℃ when preparing large particle sizes.

[0010] The two catalysts were washed and mixed at a mass ratio of small-particle-size platinum-carbon catalyst to large-particle-size platinum-carbon catalyst (4-8):1.

[0011] Through the above steps, this preparation method prepares two catalysts with different particle sizes separately, and then mixes them in a specific ratio to bring about synergistic advantages. Combining the performance advantages of platinum particles with different particle sizes, it can improve the activity and stability of the membrane electrode.

[0012] More preferably, the small-particle-size platinum-carbon catalyst maintains the solution pH=7 during the static reaction, while the large-particle-size platinum-carbon catalyst maintains the solution pH=13 during the static reaction.

[0013] More preferably, in the static reaction, the pH value of the solution is maintained by adding an alkaline aqueous solution, wherein the solute in the alkaline aqueous solution is selected from one or a combination of sodium hydroxide and potassium hydroxide.

[0014] More preferably, in the static reaction: the reaction time for preparing small particle size is 2-4 hours; the reaction time for preparing large particle size is 6-10 hours.

[0015] More preferably, the mass ratio of the carbon support to ethylene glycol is 0.05-0.3:100, and the carbon support is Vulcan XC-72.

[0016] More preferably, the mechanical stirring refers to mixing using a high-speed shear disperser at a speed of 800-1000 rpm for a stirring time of 6-10 hours.

[0017] In addition, this invention also proposes a multi-particle-size platinum-carbon catalyst, which is prepared by the method described above, and is composed of a platinum-carbon catalyst with an average particle size of 2-4 nm and a platinum-carbon catalyst with an average particle size of 5-7 nm mixed at a mass ratio of (4-8):1.

[0018] In addition, this invention also proposes the application of a multi-size platinum-carbon catalyst as described above in a fuel cell.

[0019] Furthermore, this invention also proposes a fuel cell membrane electrode supported on a platinum-carbon catalyst, characterized by preparation as follows: a multi-particle-size platinum-carbon catalyst as described above is mixed with isopropanol, deionized water, and Nafion aqueous solution to form a slurry, which is then coated onto both sides of a proton exchange membrane, with a cathode loading of 0.3 mg Pt / cm². 2 Anode 0.1 mg Pt / cm 2 Hot pressing molding.

[0020] More preferably, the mass ratio of isopropanol to deionized water is 2:3; the solid content of the Nafion aqueous solution is 5%; the mass ratio of Nafion aqueous solution to platinum-carbon catalyst is 2.88:0.45; and the mass ratio of platinum-carbon catalyst to mixed solution is 0.45:29.7.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] This invention improves catalyst stability while maintaining high catalytic activity by controlling the size of platinum particles supported on a platinum-carbon catalyst. Smaller platinum particles have a higher specific surface area, providing more active sites and thus enhancing the activity of the oxygen reduction reaction. Larger particles are more stable, resisting dissolution, sintering, and agglomeration, reducing performance degradation during long-term operation. In composite multi-size platinum-carbon catalysts, larger particles can act as "anchors," inhibiting the migration and agglomeration of smaller particles, thereby maintaining stability.

[0023] Meanwhile, the dual-modal particle size distribution (2-4nm + 5-7nm) effectively improves the rheology and coating uniformity of the slurry, reduces pore blockage caused by the accumulation of single-size particles, and thus optimizes the transport path of reactants.

[0024] Secondly, under dynamic operating conditions, small, uniformly sized particles are prone to failure due to Ostwald ripening (dissolution of small particles and growth of large particles). Particles with appropriate distribution can delay this process, extending catalyst lifetime. Compared to catalysts with a single particle size, they exhibit significant advantages in stability and electrochemical activity.

[0025] Furthermore, synthesizing strictly monodisperse nanoparticles typically requires complex processes and is costly. Mixed-size particles, however, improve platinum utilization: smaller particles maximize activity, while larger particles reduce degradation, thus lowering the overall platinum loading and meeting cost control requirements. Moreover, allowing for a certain distribution range of particles makes them easier to synthesize via conventional chemical reduction methods, suitable for large-scale production. Attached Figure Description

[0026] The above features and advantages of the present invention will become clearer and more readily understood from the following description of exemplary embodiments thereof in conjunction with the accompanying drawings.

[0027] Figure 1 The XRD pattern of the small-particle-size platinum-carbon catalyst prepared in Example 1;

[0028] Figure 2 The XRD pattern of the large-particle-size platinum-carbon catalyst prepared in Example 1;

[0029] Figure 3 TEM image of the composite multi-particle-size platinum-carbon catalyst prepared in this invention;

[0030] Figure 4 The polarization curves are for Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0031] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] The terms used in this specification, such as "front," "back," "left," "right," "inner," and "outer," are merely for clarity of description and are not intended to limit the scope of the invention. Any changes or adjustments to their relative relationships, without substantially altering the technical content, shall also be considered within the scope of the invention.

[0033] In the description of the following embodiments, unless otherwise expressly specified and limited, the term "connection" and other such terms should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an indirect connection through an intermediate medium; it can be the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0034] Example 1

[0035] Step 1: Stepwise preparation of platinum-carbon catalysts with different particle sizes:

[0036] Synthesis of Small-Particle-Size Platinum-Carbon Catalysts

[0037] 0.05 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was stirred at 800 rpm for 6 hours until homogeneous. The temperature was then raised to 100 °C for static reaction. During the reaction, 1 mol / L NaOH solution was dynamically added dropwise using an online pH monitoring system to maintain pH = 7. The reaction was allowed to stand for 4.0 hours. After the reaction, the mixture was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst (denoted as Pt / CS-1) with small-diameter platinum particles. The average particle size of the obtained platinum particles was 2.6 nm.

[0038] See Figure 1 The XRD pattern of platinum particles on the platinum-carbon catalyst shows that the average particle size of the platinum particles in the platinum-carbon catalyst is 2.6 nm, which can be calculated from the full width at half maximum (FWHM) of the XRD signal.

[0039] Synthesis of large-particle-size platinum-carbon catalysts

[0040] 0.05 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was stirred at 800 rpm for 6 hours until homogeneous. Then, a 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 13, and the mixture was allowed to stand at 25 °C for 6 hours. After the reaction, the solution was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst (denoted as Pt / CL-1) with large-particle platinum, exhibiting an average particle size of 5.6 nm.

[0041] See Figure 2 The XRD pattern of platinum particles on the platinum-carbon catalyst shows that the average particle size of the platinum particles in the platinum-carbon catalyst is 5.6 nm, which can be calculated from the full width at half maximum (FWHM) of the XRD signal.

[0042] The above-mentioned small-particle-size platinum-carbon catalyst and large-particle-size platinum-carbon catalyst are mixed to form a multi-particle-size platinum-carbon catalyst. To simplify the operation, in the examples, both are added to the solution and mixed thoroughly during slurry preparation.

[0043] Obviously, regardless of how the small-particle-size platinum-carbon catalyst and the large-particle-size platinum-carbon catalyst prepared by the above method are mixed, as long as they are used simultaneously and mixed evenly for the catalyst layer of the fuel cell membrane electrode, it should be understood as the use of a multi-particle-size platinum-carbon catalyst.

[0044] Step 2: Preparation of multi-particle-size platinum-carbon catalyst slurry

[0045] 10.548 g of isopropanol, 15.822 g of deionized water, and 2.88 g of Nafion solution were mixed uniformly using a high-speed shear mixer to form a homogeneous solution. Then, 0.45 g of the platinum-carbon catalyst prepared in step 1 was added to each solution. The Nafion aqueous solution had a solid content of 5%. 0.36 g of small-particle-size platinum-carbon catalyst and 0.09 g of large-particle-size platinum-carbon catalyst were mixed using a high-speed shear disperser at 5000 rpm for 30 min to obtain a uniformly dispersed catalyst slurry.

[0046] Step 3: Membrane electrode preparation

[0047] The catalyst slurry prepared in step 2 was coated on both sides of the proton exchange membrane, and the cathode catalyst loading was controlled to be 0.3 mg Pt / cm³. 2 The anodic loading is 0.1 mg Pt / cm³. 2 The membrane electrode is obtained by hot pressing and drying at 130°C and 5MPa.

[0048] Example 2

[0049] Step 1: Preparation of platinum-carbon catalysts with different particle sizes in steps:

[0050] Synthesis of Small-Particle-Size Platinum-Carbon Catalysts

[0051] 0.3 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was stirred at 1000 rpm for 10 h until homogeneous. The temperature was then raised to 80 °C for a static reaction. During the reaction, 1 mol / L NaOH solution was dynamically added dropwise using an online pH monitoring system to maintain the pH at 7. The reaction was allowed to stand for 2.0 h. After the reaction, the mixture was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst (denoted as Pt / CS-2) with small-diameter platinum particles. The average particle size of the platinum particles was 3.0 nm.

[0052] Synthesis of large-particle-size platinum-carbon catalysts

[0053] 0.3 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was stirred at 1000 rpm for 10 h until homogeneous. Then, 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 13, and the reaction was allowed to proceed at 25 °C for 10 h. After the reaction, the mixture was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst (denoted as Pt / CL-2) with large-particle platinum, yielding platinum particles with an average particle size of 5.9 nm.

[0054] Step 2: Preparation of multi-particle-size platinum-carbon catalyst slurry

[0055] 10.548 g of isopropanol, 15.822 g of deionized water, and 2.88 g of Nafion solution were mixed evenly using a high-speed shear mixer to form a homogeneous solution. Then, 0.45 g of the platinum-carbon catalyst prepared in step 1 was added to each solution. 0.4 g of the small-particle-size platinum-carbon catalyst and 0.05 g of the large-particle-size platinum-carbon catalyst were mixed using a high-speed shear disperser at 5000 rpm for 30 min to obtain a uniformly dispersed catalyst slurry.

[0056] Step 3: Membrane electrode preparation

[0057] The catalyst slurry prepared in step 2 was coated on both sides of the proton exchange membrane, and the cathode catalyst loading was controlled to be 0.3 mg Pt / cm³. 2 The anodic loading is 0.1 mg Pt / cm³. 2 The membrane electrode is obtained by hot pressing and drying at 130°C and 5MPa.

[0058] Example 3

[0059] Step 1: Preparation of platinum-carbon catalysts with different particle sizes in steps:

[0060] Synthesis of Small-Particle-Size Platinum-Carbon Catalysts

[0061] 0.1 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was stirred at 900 rpm for 8 hours until homogeneous. The temperature was then raised to 90 °C for static reaction. During the reaction, 1 mol / L NaOH solution was dynamically added dropwise using an online pH monitoring system to maintain pH = 7. The reaction was allowed to stand for 3.0 hours. After the reaction, the mixture was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst (denoted as Pt / CS-3) with small-diameter platinum particles. The average particle size of the platinum particles was 2.6 nm.

[0062] Synthesis of large-particle-size platinum-carbon catalysts

[0063] 0.1 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was stirred at 900 rpm for 8 hours until homogeneous. Then, a 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 13, and the mixture was allowed to stand at 25°C for 8 hours. After the reaction, the solution was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst (denoted as Pt / CL-3) with large-particle platinum. The average particle size of the platinum particles was 5.6 nm.

[0064] Step 2: Preparation of multi-particle-size platinum-carbon catalyst slurry

[0065] 10.548 g of isopropanol, 15.822 g of deionized water, and 2.88 g of Nafion solution were mixed evenly using a high-speed shear mixer to form a homogeneous solution. Then, 0.45 g of the platinum-carbon catalyst prepared in step 1 was added to each solution. 0.386 g of the small-particle-size platinum-carbon catalyst and 0.064 g of the large-particle-size platinum-carbon catalyst were mixed using a high-speed shear disperser at 5000 rpm for 30 min to obtain a uniformly dispersed catalyst slurry.

[0066] Step 3: Membrane electrode preparation

[0067] The catalyst slurry prepared in step 2 was coated on both sides of the proton exchange membrane, and the cathode catalyst loading was controlled to be 0.3 mg Pt / cm³. 2 The anodic loading is 0.1 mg Pt / cm³. 2 The membrane electrode is obtained by hot pressing and drying at 130°C and 5MPa.

[0068] Example 4

[0069] Step 1: Preparation of platinum-carbon catalysts with different particle sizes in steps:

[0070] Synthesis of Small-Particle-Size Platinum-Carbon Catalysts

[0071] 0.1 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was stirred at 900 rpm for 8 hours until homogeneous. The temperature was then raised to 90 °C for static reaction. During the reaction, 1 mol / L NaOH solution was dynamically added dropwise using an online pH monitoring system to maintain the pH at 5. The reaction was allowed to stand for 4.0 hours. After the reaction, the mixture was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst (denoted as Pt / CS-4) with small-diameter platinum particles. The average particle size of the platinum particles was 4.0 nm.

[0072] Synthesis of large-particle-size platinum-carbon catalysts

[0073] 0.1 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was stirred at 900 rpm for 8 hours until homogeneous. Then, a 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 9, and the mixture was allowed to stand at 25 °C for 10 hours. After the reaction, the mixture was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst (denoted as Pt / CL-4) with large-particle platinum. The average particle size of the platinum particles was 7.0 nm.

[0074] Example 5

[0075] Step 1: Preparation of platinum-carbon catalysts with different particle sizes in steps:

[0076] Synthesis of Small-Particle-Size Platinum-Carbon Catalysts

[0077] 0.1 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was stirred at 900 rpm for 8 hours until homogeneous. The temperature was then raised to 90 °C for static reaction. During the reaction, 1 mol / L NaOH solution was dynamically added dropwise using an online pH monitoring system to maintain the pH at 5. The reaction was allowed to stand for 4.0 hours. After the reaction, the mixture was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst (denoted as Pt / CS-4) with small-diameter platinum particles. The average particle size of the platinum particles was 4.0 nm.

[0078] Synthesis of large-particle-size platinum-carbon catalysts

[0079] 0.1 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was stirred at 900 rpm for 8 hours until homogeneous. Then, a 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 13, and the mixture was allowed to stand at 30 °C for 6 hours. After the reaction, the solution was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst (denoted as Pt / CL-5) with large-particle platinum. The average particle size of the platinum particles was 5.8 nm.

[0080] Example 6

[0081] Step 1: Preparation of platinum-carbon catalysts with different particle sizes in steps:

[0082] Synthesis of Small-Particle-Size Platinum-Carbon Catalysts

[0083] 0.1 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was stirred at 900 rpm for 8 hours until homogeneous. The temperature was then raised to 90 °C for static reaction. During the reaction, 1 mol / L NaOH solution was dynamically added dropwise using an online pH monitoring system to maintain the pH at 5. The reaction was allowed to stand for 4.0 hours. After the reaction, the mixture was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst (denoted as Pt / CS-4) with small-diameter platinum particles. The average particle size of the platinum particles was 4.0 nm.

[0084] Synthesis of large-particle-size platinum-carbon catalysts

[0085] 0.1 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was stirred at 900 rpm for 8 hours until homogeneous. Then, a 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 13, and the mixture was allowed to stand at 20 °C for 10 hours. After the reaction, the mixture was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst (denoted as Pt / CL-6) with large-particle platinum. The average particle size of the platinum particles was 6.5 nm.

[0086] Examples 4-6 above illustrate the preparation of small-particle-size and large-particle-size platinum-carbon catalysts at different reaction pH and temperature within the scope of the claims.

[0087] Comparative Example 1

[0088] Step 1: Preparation of platinum-carbon catalyst:

[0089] Synthesis of Small-Particle-Size Platinum-Carbon Catalysts

[0090] 0.1 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.1 g of chloroplatinic acid precursor. The mixture was stirred at 800 rpm for 6 hours until homogeneous. The temperature was then raised to 100 °C for static reaction. During the reaction, 1 mol / L NaOH solution was dynamically added dropwise using an online pH monitoring system to maintain the pH at 7. The reaction was allowed to stand for 4.0 hours. After the reaction, the mixture was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst with small-diameter platinum particles. The average particle size of the obtained platinum particles was 2.1 nm.

[0091] Step 2: Preparation of multi-particle-size platinum-carbon catalyst slurry

[0092] 10.548 g of isopropanol, 15.822 g of deionized water and 2.88 g of Nafion solution were mixed evenly using a high-speed shear mixer to form a homogeneous solution. Then, 0.45 g of the small-particle-size platinum-carbon catalyst prepared in step 1 was added to each solution and mixed using a high-speed shear disperser at 5000 rpm for 30 min to obtain a uniformly dispersed catalyst slurry.

[0093] Step 3: Membrane electrode preparation

[0094] The catalyst slurry prepared in step 2 was coated on both sides of the proton exchange membrane, and the cathode catalyst loading was controlled to be 0.3 mg Pt / cm³. 2 The anodic loading is 0.1 mg Pt / cm³. 2 The membrane electrode is obtained by hot pressing and drying.

[0095] Comparative Example 2

[0096] Step 1: Preparation of platinum-carbon catalyst:

[0097] Synthesis of large-particle-size platinum-carbon catalysts

[0098] 0.1 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.1 g of chloroplatinic acid precursor. The mixture was stirred at 800 rpm for 6 hours until homogeneous. Then, a 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 13, and the mixture was allowed to stand at 25°C for 10 hours. After the reaction, the solution was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst with large-particle platinum. The average particle size of the obtained platinum particles was 5.9 nm.

[0099] Step 2: Preparation of multi-particle-size platinum-carbon catalyst slurry

[0100] 10.548 g of isopropanol, 15.822 g of deionized water, and 2.88 g of Nafion solution were mixed evenly using a high-speed shear mixer to form a homogeneous solution. Then, 0.45 g of the large-particle-size platinum-carbon catalyst prepared in step 1 was added to each solution. The mixture was then mixed using a high-speed shear disperser at 5000 rpm for 30 min to obtain a uniformly dispersed catalyst slurry.

[0101] Step 3: Membrane electrode preparation

[0102] The catalyst slurry prepared in step 2 was coated on both sides of the proton exchange membrane, and the cathode catalyst loading was controlled to be 0.3 mg Pt / cm³. 2 The anodic loading is 0.1 mg Pt / cm³. 2 The membrane electrode is obtained by hot pressing and drying.

[0103] Comparative Example 3

[0104] Step 1: Preparation of platinum-carbon catalysts with different particle sizes in steps:

[0105] Synthesis of Small-Particle-Size Platinum-Carbon Catalysts

[0106] 0.05 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was stirred at 800 rpm for 6 hours until homogeneous. The temperature was then raised to 100 °C for static reaction. During the reaction, 1 mol / L NaOH solution was dynamically added dropwise using an online pH monitoring system to maintain pH = 7. The reaction was allowed to stand for 4.0 hours. After the reaction, the mixture was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst (denoted as Pt / CS-1) with small-diameter platinum particles. The average particle size of the obtained platinum particles was 2.1 nm.

[0107] Synthesis of large-particle-size platinum-carbon catalysts

[0108] 0.05 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was stirred at 800 rpm for 6 hours until homogeneous. Then, a 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 13, and the mixture was allowed to stand at 25 °C for 6 hours. After the reaction, the solution was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst (denoted as Pt / CL-1) with large-particle platinum, exhibiting an average particle size of 4.6 nm.

[0109] Step 2: Preparation of multi-particle-size platinum-carbon catalyst slurry

[0110] 10.548 g of isopropanol, 15.822 g of deionized water, and 2.88 g of Nafion solution were mixed evenly using a high-speed shear mixer to form a homogeneous solution. Then, 0.45 g of the platinum-carbon catalyst prepared in step 1 was added to each solution. 0.225 g of the small-particle-size platinum-carbon catalyst and 0.225 g of the large-particle-size platinum-carbon catalyst were mixed using a high-speed shear disperser at 5000 rpm for 30 min to obtain a uniformly dispersed catalyst slurry.

[0111] Step 3: Membrane electrode preparation

[0112] The catalyst slurry prepared in step 2 was coated on both sides of the proton exchange membrane, and the cathode catalyst loading was controlled to be 0.3 mg Pt / cm³. 2 The anodic loading is 0.1 mg Pt / cm³. 2 The membrane electrode is obtained by hot pressing and drying.

[0113] Comparative Example 4

[0114] Step 1: Preparation of platinum-carbon catalysts with different particle sizes in steps:

[0115] Synthesis of Small-Particle-Size Platinum-Carbon Catalysts

[0116] 0.05 g of Vulcan XC-72 carbon support was added to 100 g of ethylene glycol, along with 0.2 g of chloroplatinic acid precursor. The mixture was mechanically stirred at 800 rpm for 6 hours until homogeneous. The mixture was then allowed to stand at 70°C for further reaction. During the reaction, 1 mol / L NaOH solution was dynamically added dropwise using an online pH monitoring system to maintain the pH at 7. The reaction was allowed to stand for 4.0 hours. After the reaction, the mixture was repeatedly washed with deionized water and filtered to obtain a platinum-carbon catalyst with supported platinum particles. The average particle size of the obtained catalyst was 1.7 nm. The filtrate was a pale yellow liquid. ICP analysis showed that the platinum content in the platinum-carbon catalyst was less than 60%.

[0117] The performance data of the platinum-carbon catalysts in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0118]

[0119] See Figure 4 As shown, the results of the membrane electrode performance test are as follows. By comparison, it can be seen that when only small particle size is used, the catalyst performs well under low charge density, but the performance degrades significantly under high charge density. When only large particle size is used, the catalyst performs poorly under low charge density and even worse under high charge density. When large and small particle sizes are combined, the performance under both low and high charge density is improved, and the performance is best within the optimal ratio range.

[0120] In the above scheme, the reason for choosing pH = 5-7 and pH = 9-13 respectively for the solution during the static reaction when manufacturing the two platinum-carbon catalysts is:

[0121] pH = 9-13: This is because in an alkaline environment, OH- promotes the oxidation of ethylene glycol to aldehydes / acids, releasing more electrons (enhanced reactivity). PtCl62 - The reduction potential shifts positively, making it easier to reduce. This leads to the rapid reduction of platinum precursors, generating a large number of platinum particles in a short time. However, the high temperature and alkaline conditions result in excessively strong reducing power. A large amount of chloroplatinic acid aggregates and is reduced using the generated platinum particles as seed crystals, resulting in large-sized platinum particles. By controlling the reaction time, reaction temperature (25℃), and reaction conditions (pH = 9-13), a platinum-carbon catalyst loaded with large-sized platinum particles was prepared, with particle sizes ranging from 5-7 nm.

[0122] pH = 5-7: This is because chloroplatinic acid solution is acidic. When the solution is within the pH range of 5-7, the influence of an alkaline environment on the reduction process can be effectively avoided, preventing the precursor from being reduced too quickly. By increasing the temperature, the reduction reaction rate can be effectively controlled, thereby enabling the preparation of small-sized platinum particles.

[0123] Platinum-carbon catalysts mainly rely on platinum particles on a carbon support for catalysis. Small-diameter platinum particles help improve the performance of the catalyst, but their own stability is insufficient. While large-diameter platinum particles do not perform as well as small-diameter particles, they have better stability, especially in maintaining system stability during long cycles.

[0124] Experimental comparisons revealed that the optimal ratio range is (4–8):1. When there is too little small-particle-size catalyst, the catalyst performance is low and cannot meet practical applications; when there is too much small-particle-size catalyst, although the initial performance is good, after cycle stability testing, the stability is insufficient and the performance degradation is obvious.

[0125] Compared with the prior art, the present invention has the following beneficial technical effects:

[0126] This invention improves catalyst stability while maintaining high catalytic activity by controlling the size of platinum particles supported on a platinum-carbon catalyst. Smaller platinum particles have a higher specific surface area, providing more active sites and thus enhancing the activity of the oxygen reduction reaction. Larger particles are more stable, resisting dissolution, sintering, and agglomeration, reducing performance degradation during long-term operation. In composite multi-size platinum-carbon catalysts, larger particles can act as "anchors," inhibiting the migration and agglomeration of smaller particles, thereby maintaining stability.

[0127] Meanwhile, the dual-modal particle size distribution (2-4nm + 5-7nm) effectively improves the rheology and coating uniformity of the slurry, reduces pore blockage caused by the accumulation of single-size particles, and thus optimizes the transport path of reactants.

[0128] Secondly, under dynamic operating conditions, small, uniformly sized particles are prone to failure due to Ostwald ripening (dissolution of small particles and growth of large particles). Particles with appropriate distribution can delay this process, extending catalyst lifetime. Compared to catalysts with a single particle size, they exhibit significant advantages in stability and electrochemical activity.

[0129] Furthermore, synthesizing strictly monodisperse nanoparticles typically requires complex processes and is costly. Mixed-size particles, however, improve platinum utilization: smaller particles maximize activity, while larger particles reduce degradation, thus lowering the overall platinum loading and meeting cost control requirements. Moreover, allowing for a certain distribution range of particles makes them easier to synthesize via conventional chemical reduction methods, suitable for large-scale production.

[0130] The foregoing embodiments have provided a detailed description of the inventive intent and implementation of the present invention. However, those skilled in the art will understand that the above embodiments are merely preferred embodiments of the present invention. Due to space limitations, not all embodiments can be listed here. Any implementation that embodies the technical solution of the claims of the present invention is within the protection scope of the present invention.

[0131] It should be noted that the above content is a further detailed description of the present invention in conjunction with specific embodiments, and it should not be considered that the specific embodiments of the present invention are limited to this. Under the guidance of the above embodiments, those skilled in the art can make various improvements and modifications based on the above embodiments, and these improvements or modifications fall within the protection scope of the present invention.

Claims

1. A method for preparing a multi-particle size platinum carbon catalyst, characterized by The method is as follows: Small particle size platinum carbon catalyst with average particle size of 2-4 nm and large particle size platinum carbon catalyst with average particle size of 5-7 nm are prepared respectively: The carbon carrier is dispersed in ethylene glycol, the chloroplatinic acid precursor is added, and mechanical stirring is performed for uniform mixing, followed by standing reaction; in the standing reaction, for preparation of small particle size, pH is maintained at 5-7, and reaction temperature is 80-100°C; for preparation of large particle size, pH is maintained at 9-13, and reaction temperature is 20-30°C; The two catalysts are washed, and mixed according to mass ratio of small particle size platinum carbon catalyst / large particle size platinum carbon catalyst (4-8):

1.

2. The method of claim 1, wherein the method is characterized by: In the standing reaction, the solution pH is maintained at 7 for the small particle size platinum carbon catalyst, and the solution pH is maintained at 13 for the large particle size platinum carbon catalyst.

3. The method of claim 2, wherein the method further comprises: In the standing reaction, the solution pH is maintained by adding an alkaline aqueous solution, and the solute in the alkaline aqueous solution is selected from one or a combination of sodium hydroxide and potassium hydroxide.

4. The method of claim 1, wherein the method is characterized by In the standing reaction, the reaction time is 2-4 h for preparation of small particle size, and the reaction time is 6-10 h for preparation of large particle size.

5. The method of claim 1, wherein the method is characterized by: The mass ratio of the carbon carrier to ethylene glycol is 0.05-0.3:100, and the carbon carrier is Vulcan XC-72.

6. The method of claim 1, wherein the method is characterized by: The mechanical stirring refers to mixing by using a high-speed shearing disperser at a speed of 800-1000 rpm for 6-10 h.

7. A multi-particle size platinum carbon catalyst, which is prepared by the method according to any one of claims 1-6, and is obtained by mixing platinum carbon catalyst with average particle size of 2-4 nm and platinum carbon catalyst with average particle size of 5-7 nm according to mass ratio (4-8):

1.

8. Use of the multi-particle size platinum carbon catalyst according to claim 7 in a fuel cell.

9. A fuel cell membrane electrode loaded with a platinum carbon catalyst, characterized by The multi-particle size platinum carbon catalyst according to claim 7 is added to a slurry of isopropyl alcohol, deionized water and Nafion aqueous solution, and coated on both sides of a proton exchange membrane, with cathode loading of 0.3 mg Pt / cm 2 , anode 0.1 mg Pt / cm 2 , hot press molding.

10. A fuel cell membrane electrode with a supported platinum carbon catalyst according to claim 9, characterized in that: The mass ratio of the isopropyl alcohol to deionized water is 2:3; the solid content of the Nafion aqueous solution is 5%, the mass ratio of the Nafion aqueous solution to the platinum carbon catalyst is 2.88:0.45; and the mass ratio of the platinum carbon catalyst to the mixed solution is 0.45:29.7.

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