Fuel cell cathode catalyst layer and preparation method thereof, membrane electrode assembly and proton exchange membrane fuel cell

Abstract

The invention provides a fuel cell cathode catalyst layer, a preparation method of the fuel cell cathode catalyst layer, a membrane electrode assembly and a proton exchange membrane fuel cell. The fuel cell cathode catalyst layer comprises a carbon carrier particle-ionomer composite layer, a platinum nanometer network arranged on the carbon carrier particle-ionomer composite layer and an ionomer layer arranged on the platinum nanometer network, wherein in the carbon carrier particle-ionomer composite layer, a part of ionomer at least partially coats the surfaces of the carbon carrier particles to form an ionomer film, the other part of ionomer is filled in gaps among the carbon carrier particles, and the ionomer layer does not coat platinum nano particles in the platinum nano network. The fuel cell cathode catalyst layer provided by the invention has excellent catalytic activity, electron conduction capability, stability, durability and proton conduction performance, and when the fuel cell cathode catalyst layer is applied to a proton exchange membrane fuel cell, the service life of the proton exchange membrane fuel cell can be remarkably prolonged, and the overall performance of the proton exchange membrane fuel cell can be remarkably improved.

Description

Technical Field

[0001] This invention relates to a cathode catalyst layer for a fuel cell and its preparation method, a membrane electrode assembly, and a proton exchange membrane fuel cell, belonging to the field of fuel cell technology. Background Technology

[0002] In the research and application of proton exchange membrane fuel cells (PEMFCs), the design of the cathode catalyst layer is crucial, directly affecting the power density and energy conversion efficiency of the cell. The cathode catalyst layer typically consists of active catalyst particles, a carbon support, and a polymer binder. Currently, platinum-based catalysts are widely used due to their excellent catalytic performance; however, their high cost and the effective utilization of catalytic active sites remain technical challenges.

[0003] In the design and preparation of catalysts, controlling the size of active particles is crucial. Smaller particle sizes can significantly increase the specific surface area of ​​the catalyst, creating more reactive sites and thus significantly enhancing catalytic performance. Therefore, precisely controlling the particle size within an ideal range during catalyst synthesis not only improves catalytic activity but also helps reduce the amount of platinum used, which is essential for reducing the overall catalyst cost.

[0004] The three-phase interface in PEMFC refers to the interface where the gas, liquid, and solid catalyst phases meet. This interface is a critical region where the catalytic reaction occurs, and good contact between the catalyst, proton conductor (ionomer), and reactant gas (oxygen) significantly impacts battery performance. Current technologies have limitations in optimizing the three-phase interface, making it difficult to ensure sufficient reactive sites. Furthermore, the thickness, porosity, and mechanical strength of the catalyst layer directly affect the effective conduction of protons and water during the reaction. Therefore, the design and fabrication of the cathode catalyst layer play a decisive role in improving electrochemical performance.

[0005] Traditional catalyst preparation methods mainly include wet chemical methods such as chemical reduction and sol-gel methods. In these synthesis processes, the size and morphology of Pt nanoparticles are often undesirable due to the difficulty in precisely controlling key parameters such as reducing agent concentration, pH value, and temperature. Common catalyst layer preparation methods often involve mixing a carbon-supported platinum-based catalyst, a dispersing solvent, and an ionomer to form a catalyst slurry, which is then coated onto a proton exchange membrane using processes such as ultrasonic spraying or blade coating. However, in this process, sulfonic acid groups in the ionomer readily adsorb onto the surface of the Pt-based active particles, leading to poisoning of the catalyst's active sites and significantly reducing electrochemical reaction efficiency and Pt utilization.

[0006] In recent years, successful strategies for precisely controlling the size and morphology of platinum (Pt) particles to optimize the three-phase interface have primarily focused on atomic layer deposition (ALD) technology and other advanced synthetic methods. ALD, as a precise thin-film deposition method, offers the unique advantage of controlling material growth at the atomic / molecular level. Key characteristics of ALD include precise thickness control, excellent uniformity and consistency, and tunable composition and structure.

[0007] (1) A study (RSC Adv., 2024, 14, 32358, referred to as Prior Art 1) has shown that Pt particle size can be controlled by optimizing ALD parameters: The prior art method discloses the deposition of Pt nanoparticles on powdered carbon using ALD technology, employing MeCpPtMe3 (trimethyl(methylcyclopentadienyl)platinum) as the platinum precursor, O2 as the oxygen source, and a reactor temperature of 200-300℃. This method achieves the synthesis of different platinum contents (15wt% to 40wt%) by adjusting ALD parameters, including deposition temperature and cycle number, while simultaneously obtaining highly dispersed platinum nanoparticles on the carbon support. Although the Pt nanoparticles prepared by this method have controllable size and content, and uniform distribution (see...),... Figures 1a-1d However, during the subsequent slurry coating process, the distribution of nanoparticles on the carrier surface becomes uneven, forming localized enriched or deficient areas, leading to inconsistent catalyst layer performance.

[0008] (2) To ensure the uniform distribution of Pt nanoparticles in the catalyst layer, a study (Electrochimica Acta, 177, (2015), 168-173, referred to as Prior Art II) disclosed a technical solution for depositing Pt nanoparticles on a gas diffusion layer: The prior art method discloses the preparation of Pt with a content of 0.18 mg / cm³ directly on a gas diffusion layer (GDL) using ALD technology. 2 The anode catalyst layer achieved uniform dispersion of Pt atoms on the gas diffusion layer, with an average Pt particle size of 3-4 nm. While this method provides a way to prepare a catalyst layer with high Pt dispersion, the direct deposition of Pt on the GDL without coating the GDL surface with an additional carbon layer results in the presence of a small amount of Pt agglomeration (see...). Figures 2a-2d This could lead to loose contact at the Pt / C interface, affecting electron transport efficiency. Furthermore, this method only addresses the anode catalyst layer and does not mention the preparation of the cathode catalyst layer.

[0009] Furthermore, the dispersion process of the slurry and the treatment of catalyst particles (such as ultrasonication and ball milling) are not only complex but may also lead to structural changes in the catalyst, further reducing its catalytic performance. At the same time, the uniformity of particles in the slurry is difficult to guarantee, making it difficult to form an ideal three-phase interface, which negatively impacts the overall performance of the battery.

[0010] Therefore, avoiding the poisoning of catalyst active sites by ionomers is key to improving catalyst layer performance. When designing new catalyst preparation processes, effective strategies must be adopted to prevent the poisoning effect of ionomers on catalyst active sites. This will help maximize catalyst performance and thus improve the overall efficiency and economy of PEMFCs.

[0011] Therefore, providing a novel, high-performance fuel cell cathode catalyst layer and its preparation method, membrane electrode assembly, and proton exchange membrane fuel cell has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0012] To address the aforementioned shortcomings and deficiencies, the present invention aims to provide a fuel cell cathode catalyst layer and its preparation method, a membrane electrode assembly, and a proton exchange membrane fuel cell. The present invention introduces ionomers into the carbon support particle-ionomer composite layer of the fuel cell cathode catalyst layer. This at least solves the problems of reduced catalyst activity and stability caused by the uneven dispersion and aggregation of platinum nanoparticles, as well as the problem of complete encapsulation of platinum nanoparticles in the platinum nanonetwork by the ionomers during subsequent ionomer layer addition, which leads to poisoning of the catalyst active sites, i.e., platinum nanoparticles.

[0013] To achieve the above objectives, on the one hand, the present invention provides a fuel cell cathode catalyst layer, wherein the fuel cell cathode catalyst layer includes a carbon support particle-ionomer composite layer, a platinum nanonetwork disposed on the carbon support particle-ionomer composite layer, and an ionomer layer disposed on the platinum nanonetwork. In the carbon carrier particle-ionomer composite layer, a portion of the ionomer at least partially coats the surface of the carbon carrier particles to form an ionomer film, while another portion of the ionomer fills the gaps between the carbon carrier particles. The ionomer layer does not encapsulate the platinum nanoparticles in the platinum nanonetwork.

[0014] In one specific embodiment of the fuel cell cathode catalyst layer described above in this invention, the thickness of the carbon support particle-ionomer composite layer is 5-20 µm. Controlling the thickness of the carbon support particle-ionomer composite layer to 5-20 µm in this invention helps improve the electronic conductivity of the fuel cell cathode catalyst layer, while also helping to ensure the mechanical strength and stability of the fuel cell cathode catalyst layer.

[0015] As a specific embodiment of the fuel cell cathode catalyst layer described above in this invention, the carbon support particles include one or a combination of several of the following: solid carbon, microporous carbon, mesoporous carbon, and carbon-based composite materials.

[0016] In one specific embodiment of the fuel cell cathode catalyst layer described above in this invention, the ionomer contains sulfonic acid groups; And / or the Ew of the ionomer is 600-1200.

[0017] This invention does not specify the particular substance of the ionomer containing sulfonic acid groups, and can be selected reasonably as needed. For example, in some embodiments of this invention, the ionomer can be a perfluorosulfonic acid polymer, such as Nafion. ® Series (DuPont) (such as Nafion 117, Nafion 212, Nafion D2020, etc.), Aquivion ® Solvay, Flemion ® (Asahi Glass Co., Ltd.); sulfonated polyether ether ketone (SPEEK) or sulfonated polyimide (SPI), etc.

[0018] As a specific embodiment of the fuel cell cathode catalyst layer described above in this invention, the average particle size of the platinum nanoparticles in the platinum nanonetwork is 2-10 nm, preferably 2-3 nm. And / or the content of platinum nanoparticles in the platinum nanonetwork is 0.2-0.45 mg / cm³. 2 Its density is 100-500 mg / cm³ 3 The formulas for calculating the content and density of platinum nanoparticles are shown in Formula 1 and Formula 2, respectively: Platinum nanoparticle content = weight of platinum nanoparticles (mg) / area of ​​fuel cell cathode catalyst layer (cm²) 2 ) Formula 1); Density of platinum nanoparticles = weight of platinum nanoparticles (mg) / volume of fuel cell cathode catalyst layer (cm³) 3 ) Formula 2).

[0019] This invention improves reaction efficiency and reduces the adsorption effect of sulfonic acid groups in the ionomer on the surface of platinum nanoparticles by controlling / optimizing the thickness of the carbon support particle-ionomer composite layer and the amount of ionomer in the ionomer layer in the cathode catalyst layer of the fuel cell, i.e., the mass ratio of the ionomer to the carbon support particles used in step (1) in step (3) can ensure good contact between the catalyst, the proton conductor (ionomer) and the reaction gas (oxygen), thereby reducing poisoning.

[0020] On the other hand, the present invention also provides a method for preparing the above-described fuel cell cathode catalyst layer, wherein the preparation method includes: Step (1): Mix the carbon carrier particles and ionomer in an alcohol-water mixed solvent to obtain a slurry; coat the slurry onto a substrate to form a uniform and smooth carbon carrier particle-ionomer composite layer; Step (2): A platinum nanonetwork was constructed on the carbon support particle-ionomer composite layer using atomic layer deposition. Step (3): Coating the platinum nanonetwork with ionomer to obtain the fuel cell cathode catalyst layer.

[0021] As a specific embodiment of the preparation method described above in this invention, in step (1), the mass ratio of ionomer to carbon carrier particles is 0.05-5.0:1, and the solid content of the slurry is 5-80%; wherein, the solid content refers to the proportion of all solid components (such as carbon carrier particles, ionomer, etc.) in the slurry to the total mass of the slurry. In the alcohol-water mixed solvent, the mass ratio of alcohol to water is 1:3 to 1:10. This invention does not specify the exact type of alcohol in the alcohol-water mixed solvent; it can be selected as needed. For example, in some embodiments of this invention, the alcohol may be methanol, ethanol, or n-propanol, etc.

[0022] As a specific embodiment of the preparation method described above in this invention, in step (1), the substrate includes polytetrafluoroethylene (PTFE), GDL (gas diffusion layer), or carbon paper, etc.

[0023] As a specific embodiment of the preparation method described above in this invention, in step (1), the uniform mixing can be achieved by one or more processes such as ultrasonication, ball milling, defoaming and stirring.

[0024] As a specific embodiment of the preparation method described above in this invention, in step (1), the coating can be achieved by processes such as scraping or spraying. In some embodiments of this invention, the scraping can be performed using a 10-100 degree wire bar, and the spraying can be ultrasonic spraying, etc.

[0025] In the uniform and smooth carbon support particle-ionomer composite layer formed in step (1) of the preparation method described above, the ionomers are uniformly distributed. The uniform distribution of the ionomers can provide an ideal substrate for the subsequent deposition of Pt nanoparticles, thereby optimizing the three-phase interface (the interface between gas, liquid and solid catalyst phases), which can help improve the transport efficiency of oxygen, protons and electrons.

[0026] The preparation method described above in this invention, step (1), successfully prepared a uniform, smooth, and uniformly thick carbon carrier particle-ionomer composite layer by precisely controlling the slurry ratio and coating process. This carbon carrier particle-ionomer composite layer can provide an ideal substrate for subsequent ALD deposition (atomic layer deposition).

[0027] As a specific embodiment of the preparation method described above in this invention, in step (2), the atomic layer deposition method includes multiple deposition cycles. Each deposition cycle includes: exposing the carbon carrier particle-ionomer composite layer to the platinum precursor and holding it for 2-20s, then reacting for 10-150s, then purging with an inert gas for 10-120s, then exposing it to the gas precursor and holding it for 10-150s, reacting for 10-120s, and then purging with an inert gas for 10-120s.

[0028] As a specific embodiment of the preparation method described above in this invention, in step (2), the temperature of atomic layer deposition is 150-300℃, and the number of deposition cycles is 10-100. And / or the platinum precursors include one or a combination of several of the following: trimethyl(methylcyclopentadienyl)platinum ((CH3)3(CH3C5H4)Pt), tri(diethylamine)tert-butamide platinum (Pt(t-BuNHC2H5)3), and platinum acetylacetonate (Pt(acac)3); The gaseous precursor includes one or a combination of several of oxygen (O2), ozone (O3), and hydrogen (H2). In some embodiments of the present invention, when the gaseous precursor is oxygen (O2), it is preferably high-purity oxygen with a volume concentration of not less than 99.999%.

[0029] As a specific embodiment of the preparation method described above in this invention, in step (2), the inert gas used for inert gas purging includes argon and the like.

[0030] In step (2) of the preparation method described above, for different carbon support particle-ionomer composite layers and precursors, the uniform distribution of platinum nanoparticles can be precisely controlled by precisely controlling the time (exposure and reaction time) and temperature during the ALD deposition process, so that the average particle size of the platinum nanoparticles is 2-10 nm, forming a dense platinum nano-network structure. The dense platinum nano-network structure helps to improve the catalytic efficiency of the fuel cell cathode catalyst layer, provides more active sites, and improves the transport efficiency of oxygen, protons, and electrons. Precise inert gas purging steps and time control can effectively suppress the aggregation of platinum nanoparticles, improving the stability and durability of the catalyst. In the platinum nano-network (platinum nano-network layer), platinum nanoparticles are uniformly distributed. The platinum nano-network layer formed by platinum nanoparticles with an average particle size of 2-10 nm not only helps to improve the activity of the catalyst, but also effectively inhibits the aggregation of platinum nanoparticles, thereby significantly improving the stability and durability of the catalyst. That is, in step (3), by precisely controlling the ALD process parameters, the size, content and density of platinum nanoparticles can be precisely controlled, and they can be evenly distributed and grown.

[0031] In a specific embodiment of the preparation method described above in this invention, in step (3), the mass ratio of the ionomer to the carbon support particles used in step (1) is 0.5-2.0:1. Step (3) optimizes the proton conduction performance by precisely controlling the amount of supplemented ionomer, thereby optimizing the MEA performance and significantly improving the overall performance of the fuel cell, providing an effective technical solution for the commercial application of PEMFC. This invention can effectively enhance the bonding force between Pt and carbon support particles and reduce the poisoning effect of the ionomer on platinum active sites by controlling the mass ratio of ionomer to carbon support particles.

[0032] As a specific embodiment of the preparation method described above in this invention, in step (3), the coating includes spraying or dipping.

[0033] In the preparation method described above in this invention, step (1) involves first mixing carbon carrier particles and ionomers uniformly in an alcohol-water mixed solvent to obtain a slurry; then coating the slurry onto a substrate to form a uniform and smooth carbon carrier particle-ionomer composite layer; during the uniform mixing process, a portion of the ionomers adsorbs onto the surface of the carbon carrier particles, so that this portion of the ionomers at least partially coats the surface of the carbon carrier particles to form an ionomer film, while another portion of the ionomers partially fills the gaps between the carbon carrier particles, that is, some of the gaps between the carbon carrier particles are occupied by the ionomers, and because the surface of the carbon carrier particles has functional groups such as hydroxyl and carboxyl groups, these functional groups... Under the influence of the energy group, the sulfonic acid groups in the ionomer have strong interactions with the surface of the carbon support particles (such as hydrogen bonding or electrostatics, especially hydrogen bonding). In addition, the carbon support particles usually have a large specific surface area and complex pore structure, which can provide more adsorption sites and space for the ionomer. These factors make the ionomer tend to be uniformly distributed around the carbon support particles (including at least partially covering the surface of the carbon support particles and the voids between the carbon support particles) in the manner shown above, rather than agglomerating in a certain area. Furthermore, during the mixing process, the ionomer is more easily adsorbed and fixed on the surface of the carbon support particles and in their voids.

[0034] Platinum nanoparticles are small in size and are usually dispersed in the catalyst layer. The area on their surface available for ionomer adsorption is relatively limited. Moreover, during the preparation process, the preferential adsorption and distribution of ionomers on the carbon support particles will create a steric hindrance, which will further limit the ionomers from covering the platinum nanoparticles. When ionomers are added in step (3) by coating the platinum nano network, the interaction between the carbon support particles and the ionomers in the carbon support particle-ionomer composite layer is stronger. The added ionomers will preferentially fill the gaps in the carbon support particle-ionomer composite layer that were not occupied by the ionomers added in step (1), rather than completely covering the platinum nanoparticles in the platinum nano network. This can avoid poisoning of the catalyst active sites, i.e., platinum nanoparticles, due to the ionomers completely covering the platinum nanoparticles.

[0035] The ionomer added in step (3) can not only provide the necessary structural support and electrical conductivity for the catalyst, thereby improving the proton conduction capability of the cathode catalyst layer of the fuel cell, but also will not form a complete coating structure on the catalyst, thus avoiding Pt agglomeration and reducing the chance of contact between the ionomer and Pt, thereby reducing the risk of poisoning caused by the adsorption of sulfonic acid groups in the ionomer on the surface of Pt nanoparticles.

[0036] The order of steps (2) and (3) in the preparation method described above is irreplaceable, and steps (2) and (3) are the core steps of this invention. By adjusting the conditional parameters in these steps, the uniformity and homogeneity of platinum nanoparticles can be controlled, while ensuring efficient proton conduction.

[0037] In another aspect, the present invention also provides a membrane electrode assembly, including a proton exchange membrane, a cathode catalyst layer, an anode catalyst layer, a cathode gas diffusion layer, and an anode gas diffusion layer. The cathode catalyst layer and the anode catalyst layer are respectively disposed on both sides of the proton exchange membrane, and the cathode gas diffusion layer and the anode gas diffusion layer are respectively disposed on the side of the cathode catalyst layer and the anode catalyst layer opposite to the proton exchange membrane. The cathode catalyst layer is the fuel cell cathode catalyst layer described above.

[0038] In another aspect, the present invention also provides a proton exchange membrane fuel cell, wherein the proton exchange membrane fuel cell includes the membrane electrode assembly described above.

[0039] Compared with the prior art, the technical effects that the technical solution of the present invention can achieve include at least the following: 1) The fuel cell cathode catalyst layer provided by the present invention includes a carbon support particle-ionomer composite layer, which is uniform, smooth and of uniform thickness. It not only provides an ideal substrate for subsequent ALD deposition, but also significantly improves the electronic conductivity of the fuel cell cathode catalyst layer, provides a good electronic transport path for the catalytic reaction, and plays a crucial role in the subsequent ionomer replenishment process, greatly improving the uniformity and consistency of the overall structure.

[0040] Specifically, in the carbon support particle-ionomer composite layer, a portion of the ionomers at least partially coats the surface of the carbon support particles to form an ionomer film, while another portion fills the voids between the carbon support particles. When ionomers are subsequently added, this later-added portion preferentially fills the voids in the carbon support particle-ionomer composite layer that were not occupied by the portion of ionomers added in step (1), rather than completely encapsulating the platinum nanoparticles in the platinum nanonetwork. This avoids the poisoning of the catalyst active sites, i.e., the platinum nanoparticle active sites, caused by the ionomers completely encapsulating the platinum nanoparticles, as is common in conventional methods. This innovative design enables the platinum nanoparticle active sites in the catalyst layer to participate in electrochemical reactions more efficiently, significantly improving the catalyst activity. Furthermore, since sulfonic acid group poisoning is effectively avoided, the catalyst will exhibit higher stability during long-term operation, thereby extending the lifespan of the fuel cell, while also providing a good proton conduction channel.

[0041] 2) The fuel cell cathode catalyst layer provided by the present invention includes a platinum nano-network layer, wherein the platinum nanoparticles are highly uniformly distributed. These platinum nanoparticles do not exist in isolation, but form a continuous nano-network structure, which is interconnected to form a three-dimensional channel. This can not only improve catalytic activity, but also effectively inhibit the aggregation of platinum nanoparticles.

[0042] 3) The fuel cell cathode catalyst layer provided by this invention comprises a carbon support particle-ionomer composite layer, a platinum nano-network layer, and an ionomer layer. This invention significantly optimizes the three-phase interface through a multi-layer structure design, thereby improving the transport efficiency of oxygen, protons, and electrons.

[0043] In summary, the fuel cell cathode catalyst layer provided by this invention is a high-performance catalyst layer with excellent catalytic activity, electron conductivity, stability, durability, and proton conductivity. Using it in a proton exchange membrane fuel cell can significantly improve the service life and overall performance of the proton exchange membrane fuel cell. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figures 1a-1d This is an electron microscope image of the cathode catalyst prepared by ALD with optimized parameters in the prior art.

[0046] Figures 2a-2d This is an electron microscope image of the anode GDE prepared by ALD in the prior art.

[0047] Figure 3 The figure shows the cathodic polarization curves of MEA sample 4#, MEA sample 1#, MEA sample 2#, MEA sample 3# and MEA sample 5# obtained in performance test example 1 of the present invention. The 150 / 150kPa in the figure refers to the pressure of the anode and cathode being 150kPa.

[0048] Figure 4 This is a comparison of the cathodic polarization curves of MEA sample 4# and MEA sample 6# obtained in performance test example 1 of the present invention. The 150 / 150kPa in the figure refers to the pressure of the anode and cathode being 150kPa.

[0049] Figure 5 The above are ECSA images of MEA sample 4# and MEA sample 6# obtained in performance test example 1 of this invention.

[0050] Figure 6 The figure shows the cathodic polarization curves of MEA sample 4# and MEA sample 7# obtained in performance test example 1 of the present invention. The 150 / 150kPa in the figure refers to the pressure of the anode and cathode being 150kPa.

[0051] Figures 7a-7cThese are transmission electron microscopy annular dark-field images of the platinum nanonetwork layer at different resolutions in the intermediate product obtained in step (2) of this embodiment of the invention.

[0052] Figures 8a-8b The image shows a ring-shaped dark field image of the platinum nanonetwork layer at different resolutions in the intermediate product obtained in step (2) of Comparative Example 2. Detailed Implementation

[0053] It should be noted that the term "comprising" and any variations thereof in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0054] The "range" disclosed in this invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges defined in this way are composable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is also expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if the listed minimum range values ​​are 1 and 2, and the listed maximum range values ​​are 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0055] In this invention, unless otherwise specified, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this invention, and "0-5" is simply a shortened representation of these numerical combinations.

[0056] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in this invention can be combined with each other to form new technical solutions.

[0057] In this invention, unless otherwise specified, all technical features and preferred features mentioned in this invention can be combined with each other to form new technical solutions.

[0058] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The embodiments described below are some, but not all, embodiments of this invention, and are only used to illustrate the invention, and should not be considered as limiting the scope of the invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0059] Examples and Comparative Examples of Fuel Cell Cathode Catalyst Layers

[0060] Example 1

[0061] This embodiment provides a fuel cell cathode catalyst layer, which is prepared by a method including the following specific steps: Step (1) Preparation of carbon carrier particle-ionomer composite layer: Mesoporous carbon particles (BMC-5, BTR New Materials Group Co., Ltd.) and ionomer (Nafion D2020) are added to a mixed solvent of n-propanol and water and then subjected to ultrasonication, stirring, ball milling and defoaming to mix the system evenly to obtain a slurry; wherein, the mass ratio of ionomer to mesoporous carbon particles is 0.8:1 (i.e. I1 / C value = 0.8, where I and C are ionomer and mesoporous carbon particles respectively), the solid content of mesoporous carbon particles in the slurry is 0.1, and the mass ratio of n-propanol to water in the mixed solvent is 1:5; The slurry is coated onto a polytetrafluoroethylene (PTFE) substrate using a 50-degree wire rod coating method to form a uniform, smooth, and uniformly thick carbon carrier particle-ionomer composite layer with a thickness of approximately 10µm.

[0062] Step (2) Construction of the platinum nanonetwork: A platinum nanonetwork was constructed on the carbon support particle-ionomer composite layer using atomic layer deposition (ALD). The ALD process consisted of 50 deposition cycles, performed at 250°C. Each deposition cycle included: exposing the carbon support particle-ionomer composite layer to the platinum precursor (trimethyl(methylcyclopentadienyl)platinum) for 10 seconds, followed by a reaction for 100 seconds, and then... The process involves purging with argon for 120 seconds, then exposing the product to a gaseous precursor (oxygen pulse, high-purity oxygen, 99.995 v%) for 60 seconds, reacting for 60 seconds, and then purging with argon for another 120 seconds. This deposition cycle can be summarized as follows: Trimethyl(methylcyclopentadienyl)platinum (10 seconds) → reaction (100 seconds) → argon purging (120 seconds) → O2 pulse (high-purity oxygen, 99.995 v%), 60 seconds → reaction (60 seconds) → argon purging (120 seconds). The average particle size of the platinum nanoparticles in the platinum nanonetwork is 2-3 nm; and the area of ​​the fuel cell cathode catalyst layer in this embodiment is 5. 5cm 2 The thickness (referring to the thickness of the carbon support particle-ionomer composite layer and the fuel cell cathode catalyst layer, which can be considered to be the same) is approximately 10 µm, and the content of platinum nanoparticles in the platinum nanonetwork is 0.3 mg / cm³. 2 Its density is 300 mg / cm³ 3 .

[0063] Step (3): Ionomers are coated onto the platinum nanonetwork by processes such as spraying or impregnation to precisely replenish the ionomers and form an ionomer layer, thereby obtaining the cathode catalyst layer of the fuel cell; The ionomer used in step (3) is Nafion D2020, with Ew=980, and its mass ratio with the mesoporous carbon particles used in step (1) is 2.0:1 (i.e., I2 / C value=2.0, where I and C are the ionomer and mesoporous carbon particles, respectively). The fuel cell cathode catalyst layer provided in this embodiment includes a carbon support particle-ionomer composite layer, a platinum nanonetwork disposed on the carbon support particle-ionomer composite layer, and an ionomer layer disposed on the platinum nanonetwork. In the carbon carrier particle-ionomer composite layer, a portion of the ionomer at least partially coats the surface of the carbon carrier particles to form an ionomer film, while another portion of the ionomer fills the gaps between the carbon carrier particles. The ionomer layer does not encapsulate the platinum nanoparticles in the platinum nanonetwork.

[0064] Example 2

[0065] This embodiment provides a fuel cell cathode catalyst layer, the only difference between its preparation method and the preparation method provided in Example 1 is: In step (3), the I2 / C value is 0.8.

[0066] Example 3

[0067] This embodiment provides a fuel cell cathode catalyst layer, the only difference between its preparation method and the preparation method provided in Example 1 is: In step (3), the I2 / C value is 0.4.

[0068] Example 4

[0069] This embodiment provides a fuel cell cathode catalyst layer, the only difference between its preparation method and the preparation method provided in Example 1 is: In step (3), the I2 / C value is 3.0.

[0070] Comparative Example 1

[0071] This comparative example provides a fuel cell cathode catalyst layer, the only difference between its preparation method and the preparation method provided in Example 1 is: In step (3), the I2 / C value is 0, meaning that no ionomer was added in Comparative Example 1.

[0072] Comparative Example 2

[0073] This comparative example provides a fuel cell cathode catalyst layer, the only difference between its preparation method and the preparation method provided in Example 1 is: In step (2) during the construction of the platinum nanonetwork, the atomic layer deposition method includes 60 deposition cycles. Each deposition cycle includes trimethyl (methylcyclopentadienyl)platinum (25s) → reaction (100s) → argon purging (120s) → O2 pulse (medical oxygen, 99.5v%, 100s) → reaction (60s) → argon purging (120s).

[0074] Comparative Example 3

[0075] This comparative example provides a fuel cell cathode catalyst layer, which is prepared by a method including the following specific steps: First, the same powdered mesoporous carbon material as in the embodiments of the present invention is selected as the carbon support particle, i.e., the base material of the catalyst. Next, Pt nanoparticles are uniformly deposited on the carbon support particle using the same ALD technology as in the embodiments of the present invention to form a supported Pt catalyst. In this supported Pt catalyst, the Pt content is 40% based on 100% of the total weight of the supported Pt catalyst. Subsequently, the supported Pt catalyst is mixed with a mixed solvent of n-propanol and water, and an ionomer is added to obtain a slurry (the mass ratio of n-propanol to water in the mixed solvent is 1:5; the solid content of the ionomer and supported Pt catalyst in the slurry is 0.15%; the mass ratio of the ionomer to the powdered mesoporous carbon material is 2.0:1; the ionomer is Nafion D2020 with Ew=980). This allows the ionomer to coat the outer layer of the supported Pt catalyst, forming a coating structure, thus preparing an ink composition containing an ionomer-coated supported Pt catalyst. Finally, the ink composition is uniformly coated onto the PTFE substrate using a blade coating process to obtain a cathode catalyst coating layer containing an ionomer-coated supported Pt catalyst, which is the fuel cell cathode catalyst layer.

[0076] Comparative Example 4

[0077] This comparative example provides a fuel cell cathode catalyst layer, the only difference between its preparation method and the preparation method provided in Example 1 is: In step (1), no ionomer is added, and conventional polyacrylic acid is used as the binder.

[0078] Examples and comparative examples of membrane electrode assemblies and proton exchange membrane fuel cells

[0079] The cathode catalyst layer and anode catalyst layer are respectively disposed on both sides of the proton exchange membrane, and the cathode gas diffusion layer and anode gas diffusion layer are respectively disposed on the side of the cathode catalyst layer and anode catalyst layer away from the proton exchange membrane. The fuel cell cathode catalyst layers provided in Examples 1-4 and Comparative Examples 1-4 of this invention are respectively bonded to a proton exchange membrane (Gore membrane, 8µm) and a commercial anode catalyst layer (0.1mg / cm²) by transfer hot pressing. 2 40% TKK was transferred onto the proton exchange membrane), the cathode gas diffusion layer and the anode gas diffusion layer (both of which are German SIG GREE 29BC) were assembled to form a stable membrane electrode assembly structure, namely MEA, in order to explore the effect of different ionomer supplementation amounts on MEA performance. Among them, the MEAs made from the fuel cell cathode catalyst layers provided by Example 1 (I2 / C value = 2.0), Comparative Example 1 (I2 / C value = 0), Example 3 (I2 / C value = 0.4), Example 2 (I2 / C value = 0.8), Example 4 (I2 / C value = 3.0), Comparative Example 3 (supported Pt catalyst and ionomer directly mixed) and Comparative Example 4 (no ionomer was added in step (1), and conventional polyacrylic acid was used as a binder) were respectively designated as 4#, 1#, 2#, 3#, 5#, 6# and 7#; then the MEAs were assembled between a pair of flow plates to form a proton exchange membrane fuel cell.

[0080] Performance Test Example 1

[0081] This performance test example measured the polarization curves of samples 4#, 1#, 2#, 3#, 5#, 6#, and 7#, and the ECSA of samples 4# and 6#, under an environment of 80℃, 100%RH, 150kPa-H2 (pure hydrogen, volume concentration 99.99%) / Air, to evaluate the exposure level of platinum nanoparticles and the performance of the MEA. The cathodic polarization curves of MEA samples 4#, 1#, 2#, 3#, and 5# are shown in the figure below. Figure 3 As shown in the figure, the comparison of the cathodic polarization curves of MEA sample 4# and MEA sample 6# is as follows. Figure 4 As shown, the ECSA images of MEA sample 4# and MEA sample 6# are as follows. Figure 5 The following are the cathodic polarization curves of MEA sample 4# and MEA sample 7#. Figure 6 As shown.

[0082] from Figure 3As can be seen, the voltage of each MEA sample gradually decreases with increasing current density, exhibiting typical polarization characteristics. MEA sample 1# (I2 / C=0) shows the lowest performance, indicating the worst catalytic activity. This is because MEA sample 1# lacks suitable ionomers, preventing the formation of an effective three-phase interface in the catalyst layer. MEA samples 2# and 3# (I2 / C=0.4 and 0.8) show improved performance, with relatively higher voltages at the same current density, and MEA sample 3# outperforming MEA sample 2#. This indicates that adding an appropriate amount of ionomer can improve the conductivity and proton conductivity of the catalyst layer. MEA sample 4# (I2 / C=2.0) exhibits the best performance, maintaining a good voltage at high current densities, showing strong catalytic activity and good electrochemical stability. MEA sample 5# (I2 / C=3) shows the most significant voltage drop at high current densities, exhibiting a relatively low output voltage. This is because excessive ionomers cause pore blockage, affecting gas diffusion and the effective reaction area.

[0083] Therefore, the amount of ionomer added has a significant impact on the performance of proton exchange membrane fuel cells. Too little or too much ionomer will negatively affect the catalytic effect, indicating that the ratio of ionomers needs to be precisely controlled in the design of the catalyst layer to achieve optimal electrochemical performance.

[0084] from Figure 4 It can be clearly seen that, under the same test conditions, the voltages of both MEA samples 4# and 6# show a decreasing trend with increasing current density, but the degree of decrease differs significantly. Specifically, compared to MEA sample 4#, the voltage of MEA sample 6# decreases significantly across the entire current density range (especially at high current densities), eventually approaching 0.4V (1.5A / cm). 2 This indicates a significant performance degradation. This further confirms the poisoning effect of existing ionomer-coated supported Pt catalyst structures in the catalyst layer, which restricts the active sites of Pt and reduces catalytic efficiency. Figure 4 It can also be seen that the HFR value of MEA sample 6# (e.g. Figure 4 The overall resistance is relatively high (as shown by the dashed line in the figure), which indicates that the existing ionomer-coated supported Pt catalyst structure in this field exhibits a larger resistance during the current density test. This further verifies the catalyst poisoning problem caused by the ionomer-coated supported Pt catalyst structure.

[0085] Figure 4The experimental results demonstrate the significant advantages of the multi-layered fuel cell cathode catalyst layer provided in this invention compared to existing fuel cell cathode catalyst layers, highlighting the crucial importance of careful consideration of the use of ionomers when designing fuel cell catalyst layers. Through rational catalyst design, this invention can effectively avoid poisoning effects, thereby improving catalytic performance and ensuring the sustainable performance of the fuel cell under high-load conditions.

[0086] Figure 5 Two curves are shown, representing the ECSA changes of MEA sample 4# and MEA sample 6#, respectively. From Figure 5 It is evident that the curve for MEA sample 4# is generally higher than that for MEA sample 6#, indicating that MEA sample 4# has a larger ECSA value, meaning it has a larger electrochemically active surface area. This suggests that the platinum nanoparticles in MEA sample 4# are less encapsulated by ionomers, resulting in more active sites. Furthermore, the curve for MEA sample 4# exhibits higher peak values ​​within certain potential ranges, implying better electrochemical activity or more active sites at these potentials. Additionally, the curve for MEA sample 4# shows a more stable trend with potential changes, while the curve for MEA sample 6# may exhibit larger fluctuations in certain regions, which is related to the catalyst structure or preparation process of both samples.

[0087] Calculations show that the ECSA of MEA sample #4 is 82.4 cm. 2 / mgPt, while the ECSA of MEA sample 6# was only 28cm. 2 / mgPt. This experimental result shows that the platinum nanoparticles in the catalyst layer of MEA sample 4# are less encapsulated by ionomers and have a higher electrochemical active surface area. This further indicates that the catalyst layer in MEA sample 4# forms more uniform or more efficient active sites during the preparation process, which can improve the efficiency of the catalytic reaction.

[0088] For the catalyst layer in MEA sample 4#, the preparation process employed a multilayer structure design and precise ionomer control, enabling platinum nanoparticles to participate in the electrochemical reaction more efficiently and avoiding poisoning of active sites by ionomers, thereby significantly improving the ECSA value. However, for the catalyst layer in MEA sample 6#, a similar multilayer structure design and / or precise ionomer control were not used during preparation, resulting in the active sites of platinum nanoparticles being encapsulated by ionomers, thus reducing the ECSA value.

[0089] Figure 6 Two curves are shown, representing the polarization curves of MEA samples 4# and MEA7#, respectively. From Figure 6As can be seen, the curve of MEA sample 4# is higher than that of MEA sample 7#, which indicates that MEA sample 4# has a higher voltage output at the same current density, that is, MEA sample 4# has better performance. Figure 6 The curve also shows the change in HFR. MEA sample 7# has a relatively high HFR value, indicating a larger resistance at high frequencies. In the low current density region (0.5 A / cm²), the voltage of MEA sample 4# is approximately 0.8 V, while that of MEA sample 7# is approximately 0.7 V. This indicates that MEA sample 4# also has better performance under low load conditions. Meanwhile, as the current density increases, the curve of MEA sample 7# shows better performance in the high current density region (1.5 A / cm²). 2 The voltage drop was more pronounced, which means that MEA sample 7# had lower efficiency under high load conditions, which is related to the choice of catalyst layer binder.

[0090] Depend on Figure 6 The results show that, because Comparative Example 4 used polyacrylic acid as a binder instead of an ionomer, while polyacrylic acid provides hygroscopicity, water permeability, and conductivity, it is not as effective as an ionomer (such as Nafion) in proton conduction. Nafion, as an ionomer, not only has good binding properties but also provides excellent proton conduction performance, which is crucial for the efficient operation of fuel cells.

[0091] Performance Test Example 2

[0092] This performance test example performs transmission electron microscopy (TEM) analysis at different resolutions on the platinum nanonetwork layer in the intermediate product obtained in step (2) of the present invention and the platinum nanonetwork layer in the intermediate product obtained in step (2) of Comparative Example 2. The TEM annular dark-field images of the platinum nanonetwork layer in the intermediate product obtained in step (2) of the present invention at different resolutions are shown below. Figures 7a-7c As shown, the annular dark-field images of the platinum nanonetwork layer in the intermediate product obtained in step (2) of Comparative Example 2 at different resolutions are as follows: Figures 8a-8b As shown.

[0093] from Figures 7a-7c As can be seen from the figure, the size (average particle size) of the Pt nanoparticles in the platinum nano-network layer of the present invention is 2-3 nm. The Pt nanoparticles are dispersed into a uniformly distributed network structure, and the main exposed surface is the (111) crystal plane, which is the key active site for the cathode side reaction.

[0094] from Figures 8a-8b As can be seen, the size (average particle size) of the Pt nanoparticles in the platinum nanonetwork layer of Comparative Example 2 is 5 nm, and there are some particles with a size greater than 10 nm. The overall distribution is uneven, and local aggregation occurs, failing to form a dense nanonetwork structure.

[0095] By comparison Figures 7a-7c and Figures 8a-8b The specific time parameters and O2 concentration parameters used in the atomic layer deposition method of this invention can be clearly demonstrated for their importance in forming a dense platinum nanonetwork. These parameters are not only technically innovative, but also significantly improve catalyst performance in practical applications.

[0096] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical inventions, and technical inventions in this invention can be freely combined and used.

Claims

1. A cathode catalyst layer for a fuel cell, characterized in that, The fuel cell cathode catalyst layer includes a carbon support particle-ionomer composite layer, a platinum nanonetwork disposed on the carbon support particle-ionomer composite layer, and an ionomer layer disposed on the platinum nanonetwork. In the carbon carrier particle-ionomer composite layer, a portion of the ionomer at least partially coats the surface of the carbon carrier particles to form an ionomer film, while another portion of the ionomer fills the gaps between the carbon carrier particles. The ionomer layer does not encapsulate the platinum nanoparticles in the platinum nanonetwork.

2. The fuel cell cathode catalyst layer according to claim 1, characterized in that, The thickness of the carbon carrier particle-ionomer composite layer is 5-20µm.

3. The fuel cell cathode catalyst layer according to claim 1 or 2, characterized in that, The carbon carrier particles include one or a combination of several of the following: solid carbon, microporous carbon, mesoporous carbon, and carbon-based composite materials.

4. The fuel cell cathode catalyst layer according to claim 1, characterized in that, The ionomer contains sulfonic acid groups; And / or the Ew of the ionomer is 600-1200.

5. The fuel cell cathode catalyst layer according to claim 1, characterized in that, The average particle size of the platinum nanoparticles in the platinum nanonetwork is 2-10 nm. And / or the content of platinum nanoparticles in the platinum nanonetwork is 0.2-0.45 mg / cm³. 2 Its density is 100-500 mg / cm³ 3 .

6. The method for preparing the cathode catalyst layer of the fuel cell according to any one of claims 1-5, characterized in that, The preparation method includes: Step (1): Mix the carbon carrier particles and ionomer in an alcohol-water mixed solvent to obtain a slurry; coat the slurry onto a substrate to form a uniform and smooth carbon carrier particle-ionomer composite layer; Step (2): A platinum nanonetwork is constructed on the carbon support particle-ionomer composite layer using atomic layer deposition. Step (3): Coating the platinum nanonetwork with ionomer to obtain the fuel cell cathode catalyst layer.

7. The preparation method according to claim 6, characterized in that, In step (1), the mass ratio of ionomer to carbon carrier particles is 0.05-5.0:1, and the solid content of the slurry is 5-80%. In the alcohol-water mixed solvent, the mass ratio of alcohol to water is 1:3 to 1:

10.

8. The preparation method according to claim 6 or 7, characterized in that, In step (1), the substrate includes polytetrafluoroethylene, GDL, or carbon paper.

9. The preparation method according to claim 6, characterized in that, In step (2), the atomic layer deposition method includes multiple deposition cycles. Each deposition cycle includes: exposing the carbon support particle-ionomer composite layer to the platinum precursor and holding it for 2-20s, then reacting for 10-150s, then purging with an inert gas for 10-120s, then exposing it to the gas precursor and holding it for 10-150s, reacting for 10-120s, and then purging with an inert gas for 10-120s.

10. The preparation method according to claim 6 or 9, characterized in that, In step (2), the temperature of atomic layer deposition is 150-300℃, and the number of deposition cycles is 10-100. And / or the platinum precursor includes one or a combination of several of trimethyl(methylcyclopentadienyl)platinum, tri(diethylamine)tert-butyramide platinum and acetylacetonate platinum; The gaseous precursor includes one or a combination of oxygen, ozone, and hydrogen.

11. The preparation method according to claim 6, characterized in that, In step (3), the mass ratio of the ionomer to the carbon carrier particles used in step (1) is 0.5-2.0:

1.

12. A membrane electrode assembly, comprising a proton exchange membrane, a cathode catalyst layer, an anode catalyst layer, a cathode gas diffusion layer, and an anode gas diffusion layer, wherein the cathode catalyst layer and the anode catalyst layer are respectively disposed on opposite sides of the proton exchange membrane, and the cathode gas diffusion layer and the anode gas diffusion layer are respectively disposed on the side of the cathode catalyst layer and the anode catalyst layer opposite to the proton exchange membrane, characterized in that, The cathode catalyst layer is the fuel cell cathode catalyst layer according to any one of claims 1-5.

13. A proton exchange membrane fuel cell, characterized in that, The proton exchange membrane fuel cell includes the membrane electrode assembly as described in claim 12.

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