Cathode catalyst layer structure for proton exchange membrane fuel cell

Abstract

The invention relates to a cathode catalyst layer structure for a proton exchange membrane fuel cell, which is characterized in that platinum-carbon catalysts with different average platinum particle sizes are combined in a gradient manner, so that the platinum-carbon catalysts with larger average platinum particle sizes are close to one side of a proton exchange membrane; the platinum-carbon catalyst with small average platinum particle size is close to one side of the cathode gas diffusion layer, so that the durability of the cathode catalyst layer is improved; meanwhile, the ratio (I / C) of the mass of the ionomers to the mass of carbon in the platinum-carbon catalyst is optimized to be arranged in a gradient manner, so that the platinum-carbon catalyst with larger average platinum particle size is matched with more ionomers, and the contact resistance between the catalyst layer and the proton exchange membrane is remarkably reduced while the mass transfer resistance is reduced; therefore, the catalytic activity of the platinum-carbon catalyst with larger average platinum particle size is improved. Therefore, after the cathode catalyst layer structure is applied to the proton exchange membrane fuel cell, the cell has improved durability and good electrochemical performance.

Description

Technical Field

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

[0002] Proton exchange membrane fuel cells (PEMFCs) have attracted much attention in the new energy field due to their advantages such as high energy conversion efficiency, zero pollution, and low-temperature start-up. However, their electrochemical performance and durability remain challenges in this field. One effective measure to improve electrochemical performance is to use highly active cathode catalysts. Highly active cathode catalysts typically require a small particle size to achieve high activity. However, using cathode catalysts with smaller particle sizes can lead to poorer durability of the cathode catalyst layer, resulting in a trade-off between durability and electrochemical performance. Summary of the Invention

[0003] The purpose of this application is to overcome the deficiencies in the prior art and provide a cathode catalyst layer structure for proton exchange membrane fuel cells. This cathode catalyst layer structure, when used in proton exchange membrane fuel cells, can improve the durability of the cells while also ensuring good electrochemical performance.

[0004] The first aspect of this application provides a cathode catalyst layer structure for a proton exchange membrane fuel cell, comprising: a first catalyst layer, a second catalyst layer, and so on up to an nth catalyst layer, which are stacked sequentially. The first catalyst layer is close to the cathode gas diffusion layer of the proton exchange membrane fuel cell, and the nth catalyst layer is close to the proton exchange membrane of the proton exchange membrane fuel cell, where n is a positive integer greater than or equal to 2.

[0005] Each catalyst layer contains a platinum-carbon catalyst and an ionomer; the average particle size of the platinum particles in the platinum-carbon catalyst increases sequentially from the first catalyst layer to the nth catalyst layer, and the ratio of the mass of the ionomer to the mass of carbon in the platinum-carbon catalyst is denoted as I / C, with I / C increasing sequentially from the first catalyst layer to the nth catalyst layer.

[0006] In some embodiments, the I / C ratio difference between two adjacent catalyst layers is 0.15-0.25, and the average particle size difference of the platinum particles is 1.0-1.5 nm.

[0007] In some embodiments, n is a positive integer from 2 to 5;

[0008] Alternatively, n is 2, and the ratio of platinum loading in the first catalyst layer to platinum loading in the second catalyst layer is (0.7-1.5):1, preferably (0.7-0.9):1;

[0009] Alternatively, n is 3, and the ratio of platinum loading in the first catalyst layer, platinum loading in the second catalyst layer, and platinum loading in the third catalyst layer is (0.7-0.9):(0.9-1.0):(1.0-1.3).

[0010] In some embodiments, the ionomer is a highly oxygen-permeable ionomer; the highly oxygen-permeable ionomer is a polymeric compound containing oxygen-containing heterocycles.

[0011] In some embodiments, the highly oxygen-permeable ionomer comprises at least one of the following substances:

[0012]

[0013] A second aspect of this application provides a membrane electrode assembly for a proton exchange membrane fuel cell, comprising an anode gas diffusion layer, an anode catalyst layer structure, a proton exchange membrane, a cathode catalyst layer structure, and a cathode gas diffusion layer stacked sequentially, wherein the cathode catalyst layer structure is the cathode catalyst layer structure for a proton exchange membrane fuel cell of the first aspect of this application.

[0014] A third aspect of this application provides a method for fabricating a membrane electrode assembly for a proton exchange membrane fuel cell, as described in the second aspect of this application, comprising the following steps:

[0015] An anode catalyst layer structure is formed on one side of the proton exchange membrane;

[0016] A cathode catalyst layer structure is formed on the other side of the proton exchange membrane. The cathode catalyst layer structure includes a first catalyst layer, a second catalyst layer, and so on up to the nth catalyst layer, which are stacked in sequence. The average particle size of the platinum particles in the platinum-carbon catalyst increases sequentially from the first catalyst layer to the nth catalyst layer. The ratio of the mass of the ionomer to the mass of carbon in the platinum-carbon catalyst is denoted as I / C, and I / C increases sequentially from the first catalyst layer to the nth catalyst layer.

[0017] An anode gas diffusion layer is provided on the side of the anode catalyst layer structure away from the proton exchange membrane;

[0018] A cathode gas diffusion layer is provided on the side of the cathode catalytic layer structure away from the proton exchange membrane.

[0019] In some embodiments, forming a cathode catalyst layer structure on the other side of the proton exchange membrane includes:

[0020] Platinum-carbon catalysts with different average particle sizes were mixed with ionomers and solvents to prepare the first catalyst layer slurry, the second catalyst layer slurry, and so on up to the nth catalyst layer slurry.

[0021] The first catalyst layer slurry, the second catalyst layer slurry, and so on up to the nth catalyst layer slurry are subjected to nano-dispersion treatment respectively;

[0022] The cathode catalyst layer structure is formed on the proton exchange membrane using a transfer printing method or a direct coating method.

[0023] In some embodiments, the dispersion pressure is 50-150 MPa, and the dispersion times are 2-10.

[0024] The fourth aspect of this application provides a proton exchange membrane fuel cell, including the membrane electrode assembly of the fourth aspect of this application.

[0025] Compared with the prior art, the beneficial effects of this application are:

[0026] This application provides a cathode catalyst layer structure for a proton exchange membrane fuel cell. This structure utilizes a gradient combination of platinum-carbon catalysts with different average particle sizes, placing the platinum-carbon catalyst with larger average particle sizes closer to the proton exchange membrane and the platinum-carbon catalyst with smaller average particle sizes closer to the gas diffusion layer. This arrangement improves the durability of the cathode catalyst layer. Simultaneously, this application optimizes the gradient setting of the mass ratio (I / C) of the ionomer to the carbon in the platinum-carbon catalyst, allowing the platinum-carbon catalyst with larger average particle sizes to utilize a relatively larger amount of ionomer. This reduces mass transfer resistance while significantly lowering the contact resistance between the catalyst layer and the proton exchange membrane, thereby improving the catalytic activity of the platinum-carbon catalyst with larger average particle sizes. Therefore, when used in a proton exchange membrane fuel cell, the cathode catalyst layer structure of this application enables the cell to have improved durability while maintaining good electrochemical performance. Attached Figure Description

[0027] Figure 1 This is a partial structural schematic diagram of a membrane electrode assembly according to an embodiment of this application.

[0028] Explanation of reference numerals in the attached figures:

[0029] 100, First catalytic layer; 200, Second catalytic layer; 300, Gas diffusion layer; 400, Proton exchange membrane. Detailed Implementation

[0030] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0032] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0033] During operation of the membrane electrode, at a high operating potential (>0.85V), Pt atoms in the cathode platinum-carbon catalyst will be oxidized to Pt. 2+ Ions dissolve into the proton-conducting monomer, while at low potentials, Pt 2+ Ions are reduced and deposited on the surface of platinum particles or at the interface between the proton exchange membrane and the catalyst layer. Furthermore, smaller Pt catalyst particles, due to their higher surface energy, are more easily oxidized. 2+ Ions are more likely to deposit on the surface of large Pt particles. Therefore, during the variable load operation of the fuel cell, small Pt particles continuously dissolve and then deposit into large Pt particles, which continuously reduces the specific surface area of ​​the catalyst and decreases its activity, resulting in a deterioration in the durability and electrochemical performance of the proton exchange membrane fuel cell.

[0034] Studies have shown that increasing the average particle size of platinum particles can reduce their surface energy, decrease platinum dissolution and agglomeration, and improve stability. Layering small-particle-size, highly active catalysts with large-particle-size, highly durable catalysts can improve durability. However, the catalytic activity of large-particle-size platinum particles is lower than that of small-particle-size particles, which can lead to a decrease in the electrochemical performance of the battery. In order to improve durability while maintaining electrochemical performance, this application also optimized the mass ratio (I / C) of ionomer to carbon in the platinum-carbon catalyst. This allows the platinum-carbon catalyst with a larger average particle size to use a relatively larger amount of ionomer. This reduces mass transfer resistance and significantly lowers the contact resistance between the catalyst layer and the proton exchange membrane, thereby improving the catalytic activity of the platinum-carbon catalyst with a larger average particle size.

[0035] Specifically, the first aspect of this application provides a cathode catalyst layer structure for a proton exchange membrane fuel cell, comprising: a first catalyst layer, a second catalyst layer, and so on up to an nth catalyst layer, which are stacked sequentially. The first catalyst layer is close to the cathode gas diffusion layer of the proton exchange membrane fuel cell, and the nth catalyst layer is close to the proton exchange membrane of the proton exchange membrane fuel cell, where n is a positive integer greater than or equal to 2.

[0036] Each catalyst layer contains a platinum-carbon catalyst and an ionomer; the average particle size of the platinum particles in the platinum-carbon catalyst increases sequentially from the first catalyst layer to the nth catalyst layer, and the ratio of the mass of the ionomer to the mass of carbon in the platinum-carbon catalyst is denoted as I / C, with I / C increasing sequentially from the first catalyst layer to the nth catalyst layer.

[0037] By optimizing the average particle size of platinum particles and the gradient distribution of I / C, the battery's durability is effectively improved, while also ensuring good electrochemical performance.

[0038] In some embodiments, n can be a positive integer from 2 to 5, for example, 2, 3, 4, or 5; preferably, n can be 2 or 3. When n is 2, the cathode catalytic layer structure includes a first catalytic layer and a second catalytic layer; when n is 3, the cathode catalytic layer structure includes a first catalytic layer, a second catalytic layer, and a third catalytic layer; when n is 4, the cathode catalytic layer structure includes a first catalytic layer, a second catalytic layer, a third catalytic layer, and a fourth catalytic layer; and so on.

[0039] The platinum-carbon catalyst comprises a carbon support and platinum particles supported on the carbon support. In this application, the average particle size of the platinum particles in the first catalyst layer is smaller than the average particle size of the platinum particles in the second catalyst layer; the average particle size of the platinum particles in the second catalyst layer is smaller than the average particle size of the platinum particles in the third catalyst layer; and so on.

[0040] In this application, the I / C ratio in the first catalyst layer is less than that in the second catalyst layer; the I / C ratio in the second catalyst layer is less than that in the third catalyst layer; and so on.

[0041] Figure 1 A partial structural schematic diagram of a membrane electrode assembly according to an embodiment of this application is provided. For example... Figure 1 As shown, the cathode catalyst layer structure includes a first catalyst layer 100 and a second catalyst layer 200; both the first catalyst layer 100 and the second catalyst layer 200 contain a platinum-carbon catalyst and an ionomer; the average particle size of the platinum particles in the first catalyst layer 100 is smaller than the average particle size of the platinum particles in the second catalyst layer 200; the I / C ratio in the first catalyst layer 100 is smaller than the I / C ratio in the second catalyst layer 200. The first catalyst layer 100 is located near the gas diffusion layer 300, and the second catalyst layer is located near the proton exchange membrane 400.

[0042] In some embodiments, the I / C difference between two adjacent catalyst layers can be 0.15-0.25, and the difference in the average particle size of platinum particles can be 1.0-1.5 nm.

[0043] Optimizing the I / C ratio difference between two adjacent catalyst layers and the average particle size difference of platinum particles can help improve battery durability while also taking into account the battery's electrochemical performance.

[0044] like Figure 1 The difference between the I / C ratio of the second catalyst layer and the first catalyst layer can be 0.15-0.25, and the difference between the average particle size of the platinum particles in the second catalyst layer and the average particle size of the platinum particles in the first catalyst layer can be 1.0-1.5 nm.

[0045] In some specific embodiments, the I / C difference between two adjacent catalyst layers may be, for example, 0.15, 0.18, 0.2, 0.22 or 0.25, preferably, the I / C difference may be 0.18-0.22.

[0046] In some specific embodiments, the difference in average particle size of platinum particles in two adjacent catalyst layers may be, for example, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5 nm, and preferably, the difference in average particle size of platinum particles may be 1.0-1.2 nm.

[0047] In some specific embodiments, n is 2, the I / C ratio in the first catalyst layer can be 0.95-1.05, and the average particle size of the platinum particles can be 2.3-2.8 nm; in the second catalyst layer, the I / C ratio can be 1.15-1.25, and the average particle size of the platinum particles can be 3.6-4.1 nm.

[0048] In some specific embodiments, n is 3. In the first catalyst layer, the I / C ratio can be 0.75-0.85, and the average particle size of the platinum particles can be 2.0-2.4 nm; in the second catalyst layer, the I / C ratio can be 0.95-1.05, and the average particle size of the platinum particles can be 3.0-3.4 nm; in the third catalyst layer, the I / C ratio can be 1.15-1.25, and the average particle size of the platinum particles can be 4.0-4.5 nm.

[0049] In some embodiments, n is 2, and the ratio of platinum loading in the first catalyst layer to platinum loading in the second catalyst layer is (0.7-1.5):1, preferably (0.7-0.9):1.

[0050] Optimizing the platinum loading ratio in the catalyst layer is beneficial for further improving battery durability while maintaining electrochemical performance. Since large-diameter platinum particles have lower catalytic activity than small-diameter particles but significantly improved durability, to achieve a balance between catalytic activity and durability, preferably, the platinum loading of larger average-diameter platinum particles is higher than that of smaller average-diameter platinum particles. In this application, the unit for platinum loading is mg / cm³. 2 .

[0051] In some specific embodiments, n is 2, and the ratio of platinum loading in the first catalyst layer to platinum loading in the second catalyst layer can be 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1.

[0052] In some embodiments, n is 3, and the ratio of platinum loading in the first catalyst layer, platinum loading in the second catalyst layer, and platinum loading in the third catalyst layer is (0.7-0.9):(0.9-1.0):(1.0-1.3).

[0053] Optimizing the platinum loading ratio in the catalyst layer can further improve battery durability while maintaining electrochemical performance. In the oxygen reduction reaction, protons are transported from the anode across the proton exchange membrane to the cathode catalyst layer via electrolyte channels, while oxygen diffuses from the gas diffusion layer to the cathode catalyst layer via gas channels. Therefore, in the cathode catalyst layer, the proton concentration decreases from the side closer to the proton exchange membrane to the side farther from the proton exchange membrane, while the oxygen concentration increases. To balance the electrochemical performance of the cathode catalyst layer, a platinum loading gradient is applied, with a higher platinum loading near the proton exchange membrane than near the gas diffusion layer. This facilitates proton conduction, oxygen diffusion, liquid water removal, and a reduction in charge transfer resistance.

[0054] In some specific embodiments, n is 3, and the ratio of platinum loading in the first catalyst layer, platinum loading in the second catalyst layer, and platinum loading in the third catalyst layer is 0.7:0.9:1.0, 0.8:0.95:1.2, 0.9:1:1.1, or 0.9:1:1.3.

[0055] In some embodiments, the ionomer is a highly oxygen-permeable ionomer. The highly oxygen-permeable ionomer is a polymeric compound containing oxygen-containing heterocycles.

[0056] In this application, the term "high oxygen permeability ionomer" has the same meaning as commonly understood by those skilled in the art, referring to an ionomer with high oxygen permeability. Commonly used high oxygen permeability ionomers in the art can be used in this application and can achieve the same or similar effects. In some specific embodiments, the high oxygen permeability ionomer is a polymer compound containing an oxygen-containing heterocycle, such as a perfluorosulfonic acid resin containing an oxygen-containing heterocycle, a sulfonated trifluorostyrene resin containing an oxygen-containing heterocycle, or a polymethylphenylsulfonate siloxane resin containing an oxygen-containing heterocycle. In some specific embodiments, the oxygen-containing heterocycle is a five-membered heterocycle containing two oxygen atoms. The cyclic structural framework matrix of these high oxygen permeability ionomers avoids repetitive coating of the ionomer framework onto the surface of the platinum-carbon catalyst. The high oxygen permeability of the high oxygen permeability ionomer benefits from its high oxygen solubility, increasing the oxygen permeability at the interface between the ionomer and platinum particles. This reduces mass transfer resistance while significantly reducing the contact resistance between the catalyst layer and the proton exchange membrane, thereby further improving the activity of the platinum-carbon catalyst, especially the catalytic activity of large-diameter platinum particles. Meanwhile, the sulfonate anion group reduces catalyst poisoning and enhances the activity of oxygen reduction reaction.

[0057] In some specific embodiments, the highly oxygen-permeable ionomer includes at least one of the following substances:

[0058]

[0059] In some specific embodiments, highly oxygen-permeable ionomers The synthesis steps include polymerization and hydrolysis, specifically: first, perfluoro-(2,2-dimethyl-1,3-dioxane) (PDD) and perfluoro(3-oxopent-4-ene)sulfonyl fluoride (PSVE) are mixed and distilled; PDD, PSVE and polymerization initiator [CF3(CF2)2C(=O)O-]2 are stirred under an inert atmosphere to induce polymerization; then the product liquid is heated to remove monomers, yielding a copolymer with SO2F group side chain ends; the copolymer is mixed with NaOH aqueous solution for reaction; after solvent removal, the remaining solid polymer is immersed in HCl aqueous solution, heated, washed with water several times and dried to obtain a highly oxygen-permeable ionomer with SO3H group side chain ends.

[0060] In some embodiments, the platinum content of the platinum-carbon catalyst may be 20%-60%, for example, 20%, 3%, 40%, 50% or 60%.

[0061] A second aspect of this application provides a membrane electrode assembly for a proton exchange membrane fuel cell, comprising an anode gas diffusion layer, an anode catalyst layer structure, a proton exchange membrane, a cathode catalyst layer structure, and a cathode gas diffusion layer stacked sequentially, wherein the cathode catalyst layer structure is the cathode catalyst layer structure for a proton exchange membrane fuel cell of the first aspect of this application.

[0062] A third aspect of this application provides a method for fabricating a membrane electrode assembly for a proton exchange membrane fuel cell, as described in the second aspect of this application, comprising the following steps:

[0063] An anode catalyst layer structure is formed on one side of the proton exchange membrane;

[0064] A cathode catalyst layer structure is formed on the other side of the proton exchange membrane. The cathode catalyst layer structure includes a first catalyst layer, a second catalyst layer, and so on up to the nth catalyst layer, which are stacked in sequence. The average particle size of the platinum particles in the platinum-carbon catalyst increases sequentially from the first catalyst layer to the nth catalyst layer. The ratio of the mass of the ionomer to the mass of carbon in the platinum-carbon catalyst is denoted as I / C, and I / C increases sequentially from the first catalyst layer to the nth catalyst layer.

[0065] An anode gas diffusion layer is provided on the side of the anode catalyst layer structure away from the proton exchange membrane;

[0066] A cathode gas diffusion layer is provided on the side of the cathode catalytic layer structure away from the proton exchange membrane.

[0067] The preparation method of this application is simple and easy to operate, making it very suitable for widespread application in industrial production.

[0068] In some embodiments, forming a cathode catalyst layer structure on the other side of the proton exchange membrane includes:

[0069] Platinum-carbon catalysts with different average particle sizes were mixed with ionomers and solvents to prepare the first catalyst layer slurry, the second catalyst layer slurry, and so on up to the nth catalyst layer slurry.

[0070] The first catalyst layer slurry, the second catalyst layer slurry, and so on up to the nth catalyst layer slurry are subjected to nano-dispersion treatment respectively;

[0071] The cathode catalyst layer structure is formed on the proton exchange membrane using a transfer printing method or a direct coating method.

[0072] This application improves the dispersion uniformity of platinum-carbon catalyst and ionomer in solvent by performing nano-dispersion treatment on the slurry of each catalyst layer, so that they are evenly distributed in each catalyst layer, thereby improving the catalytic activity of platinum-carbon catalyst and the durability and electrochemical performance of battery.

[0073] In this application, the average particle size of the platinum particles in the platinum-carbon catalyst in each catalyst layer slurry is different, and the average particle size of the platinum particles increases sequentially from the first catalyst layer slurry to the nth catalyst layer slurry, thereby resulting in a sequential increase in the average particle size of the platinum particles in the first catalyst layer to the nth catalyst layer. Furthermore, the I / C ratio in each catalyst layer slurry is different, and the I / C ratio increases sequentially from the first catalyst layer slurry to the nth catalyst layer slurry, thereby resulting in a sequential increase in the I / C ratio in the first catalyst layer to the nth catalyst layer.

[0074] Both "transfer printing" and "direct coating" are conventional methods used in the field for coating catalyst slurries. The transfer printing method involves first coating the slurry onto a base membrane, and then transferring it onto the proton exchange membrane. The direct coating method involves directly coating the slurry onto the proton exchange membrane. Coating methods may include blade coating, spray coating, etc.

[0075] In some embodiments, the dispersion pressure is 50-150 MPa, and the dispersion times are 2-10.

[0076] By controlling the dispersion conditions, the dispersion uniformity of platinum-carbon catalyst and ionomer in the solvent can be further improved, so that they are evenly distributed in each catalyst layer, thereby improving the catalytic activity of platinum-carbon catalyst and the durability and electrochemical performance of battery.

[0077] In some embodiments, the solvent comprises water and an alcohol. The alcohol includes at least one of methanol, ethanol, propanol and its isomers, n-propanol and its isomers and stereoisomers, isopropanol and its isomers and stereoisomers, butanol and its isomers and stereoisomers, pentanol and its isomers and stereoisomers, and hexanol and its isomers and stereoisomers.

[0078] In some embodiments, the preparation of the slurry may include: first, dissolving n different platinum-carbon catalysts with different average particle sizes in water to obtain n different catalyst solutions; then, adding alcohol and ionomer to the n different catalyst solutions respectively, and performing nano-dispersion treatment on the n slurries after stirring.

[0079] The fourth aspect of this application provides a proton exchange membrane fuel cell, including the membrane electrode assembly of the second aspect of this application.

[0080] The present application will be further described below with reference to specific embodiments, but the present application is not limited thereto.

[0081] The membrane electrodes prepared in the examples were subjected to electrochemical performance and durability tests. The detailed test methods are as follows.

[0082] (1) Electrochemical performance test: The test conditions were Greenlight 25cm 2Fixture, test conditions: temperature 75℃, humidity (anode 40% / cathode 50%), pressure (anode 260KPa / cathode 250KPa), metering ratio (anode 1.5 / cathode 1.9).

[0083] (2) Durability test: The catalyst stability test was conducted according to the US DOE 2016 standard (0.6-0.95V, 80℃, 30,000 cycles).

[0084] Preparation of high oxygen permeability ionomers

[0085] High oxygen permeability ionomer The synthesis steps included: PDD (97%, P&M) and perfluoro(3-oxopent-4-ene)sulfonyl fluoride (PSVE) were distilled before use. PDD (4.0 g, 16.4 mmol), PSVE (13.7 g, 48.9 mmol), and polymerization initiator [CF3(CF2)2C(=O)O-]2 (0.08 cm⁻¹) were stirred under an inert atmosphere. 3 0.08 mol dm -3 The product liquid was polymerized at 15°C for 3 days. The monomer was then removed by heating the liquid product at 100°C, yielding a copolymer (2.5 g) with SO2F group-terminated side chains. The copolymer (1.03 g) was then reacted with NaOH (1 mol dm³). -3 The aqueous solution was mixed in a polytetrafluoroethylene crucible and reacted at 130°C for 12 hours. After removing the solvent, the remaining solid polymer was immersed in an aqueous HCl solution (1 mol dm⁻³), heated at 80°C, washed several times with ultrapure water, and dried at 80°C to obtain a highly oxygen-permeable ionomer (0.86 g) with SO₃H group side chain ends. The dried highly oxygen-permeable ionomer was added to a solvent to obtain a highly oxygen-permeable ionomer solution with a solid content of 25%.

[0086] Preparation of membrane electrodes

[0087] Example 1

[0088] (1) Dissolve 5g of a small-particle-size platinum-carbon catalyst with a platinum content of 50% by weight (the average particle size of the platinum particles is 2.7nm) in 14g of water, and then add 50g of alcohol and 10g of the prepared high-oxygen-permeable ionomer solution (solid content 25%) according to an I / C ratio of 1.0. After stirring the resulting slurry continuously on a magnetic stirrer for 60min, the mixed slurry is nano-dispersed using a nano-disperser at a dispersion pressure of 100MPa and a dispersion number of 5 times to obtain the first catalyst layer slurry.

[0089] (2) Dissolve 5g of a 50% by weight platinum-containing large-particle-size platinum-carbon catalyst (with an average particle size of 4.1nm) in 14.4g of water. Then, add 52.8g of alcohol and 12g of the prepared high-oxygen-permeable ionomer solution (25% solid content) sequentially according to an I / C ratio of 1.2. After stirring the resulting slurry continuously on a magnetic stirrer for 60min, the mixed slurry is nano-dispersed using a nano-disperser at a dispersion pressure of 100MPa and for 5 dispersion cycles to obtain the second catalyst layer slurry.

[0090] (3) With a total platinum loading of 0.3 mg / cm³ at the cathode. 2 The two slurries were coated onto the base membrane to form a first catalytic layer and a second catalytic layer (with a platinum loading ratio of 0.9:1). After being cut to a size of 6cm x 6cm, the slurries were transferred onto a 12-micron-thick Gore proton exchange membrane at a transfer temperature of 150℃ and a transfer pressure of 14 kgf / cm². 2 After transfer printing, the catalyst was assembled with a commercially available Toray TGL-0550 gas diffusion layer to form a membrane electrode for electrochemical performance and durability testing. The first catalyst layer was located near the gas diffusion layer, and the second catalyst layer was located near the proton exchange membrane. The test results are shown in Table 1 below.

[0091] Examples 2-6

[0092] The membrane electrode was prepared according to the method described in Example 1, except that the difference in I / C ratio and the difference in average particle size of platinum particles were different from those in Example 1. The test results of the membrane electrode are shown in Table 1 below.

[0093] Table 1

[0094]

[0095] Examples 7-9

[0096] The membrane electrode was prepared according to the method described in Example 1, except that the ratio of platinum loading in the first catalyst layer to platinum loading in the second catalyst layer was different from that in Example 1. The test results of the membrane electrode are shown in Table 2 below.

[0097] Table 2

[0098]

[0099]

[0100] Examples 10-11

[0101] The membrane electrode was prepared according to the method described in Example 1, except that the type of ionomer was different from that in Example 1. The test results of the membrane electrode are shown in Table 3 below.

[0102] Table 3

[0103]

[0104] Examples 12-16

[0105] The membrane electrode was prepared according to the method described in Example 1, except that the dispersion pressure and dispersion times in steps (1) and (2) were different from those in Example 1. The test results of the membrane electrode are shown in Table 4 below.

[0106] Table 4

[0107]

[0108]

[0109] Comparative Example 1

[0110] The membrane electrode was prepared according to the method described in Example 1, except that only the second catalyst layer slurry was prepared, and the second catalyst layer slurry was prepared with a cathode platinum loading of 0.3 mg / cm³. 2 The coating was applied to a substrate film, transferred, and then assembled with a commercially available Toray TGL-0550 gas diffusion layer to form a film electrode for testing. The test results are shown in Table 5 below.

[0111] Comparative Example 2

[0112] The membrane electrode was prepared according to the method described in Example 1, except that only the first catalyst layer slurry was prepared, and the first catalyst layer slurry was prepared with a cathode platinum loading of 0.3 mg / cm³. 2 The coating was applied to a substrate film, transferred, and then assembled with a commercially available Toray TGL-0550 gas diffusion layer to form a film electrode for testing. The test results are shown in Table 5 below.

[0113] Table 5

[0114]

[0115]

[0116] Comparative Example 3

[0117] The membrane electrode was prepared according to the method described in Example 1, except that the coating order of the first and second catalyst layer slurries in step (3) was reversed, so that the first catalyst layer was closer to the proton exchange membrane and the second catalyst layer was closer to the gas diffusion layer. The test results are shown in Table 6 below.

[0118] Table 6

[0119]

[0120] As shown in Examples 1 and Comparative Examples 1-2, the electrochemical performance of Comparative Example 1, which uses only a platinum-carbon catalyst with a larger average particle size, is lower than that of Comparative Example 2, which uses only a platinum-carbon catalyst with a smaller average particle size. Example 1, by gradient combining a platinum-carbon catalyst with a larger average particle size and a platinum-carbon catalyst with a smaller average particle size, exhibits electrochemical performance comparable to that of directly using the platinum-carbon catalyst with a smaller average particle size, indicating a good combination and a stable catalyst layer structure. Furthermore, Example 1 demonstrates higher durability than Comparative Examples 1 and 2, indicating a stable catalyst layer structure and that the prepared catalyst layer balances battery electrochemical performance and durability, resulting in excellent overall performance.

[0121] As can be seen from Example 1 and Comparative Example 3, when the average particle size of platinum particles in the catalyst layer structure and the I / C gradient change, the electrochemical performance and durability of the battery will be severely degraded.

[0122] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A cathode catalyst layer structure for a proton exchange membrane fuel cell, characterized in that, include: The first catalyst layer, the second catalyst layer, and so on up to the nth catalyst layer are stacked in sequence. The first catalyst layer is close to the cathode gas diffusion layer of the proton exchange membrane fuel cell, and the nth catalyst layer is close to the proton exchange membrane of the proton exchange membrane fuel cell. n is a positive integer greater than or equal to 2. Each catalyst layer contains a platinum-carbon catalyst and an ionomer; the average particle size of the platinum particles in the platinum-carbon catalyst increases sequentially from the first catalyst layer to the nth catalyst layer, and the ratio of the mass of the ionomer to the mass of carbon in the platinum-carbon catalyst is denoted as I / C, with I / C increasing sequentially from the first catalyst layer to the nth catalyst layer.

2. The cathode catalyst layer structure according to claim 1, characterized in that, In two adjacent catalyst layers, the I / C ratio difference is 0.15-0.25, and the average particle size difference of platinum particles is 1.0-1.5 nm.

3. The cathode catalyst layer structure according to claim 1, characterized in that, n is a positive integer between 2 and 5; Alternatively, n is 2, and the ratio of platinum loading in the first catalyst layer to platinum loading in the second catalyst layer is (0.7-1.5):1, preferably (0.7-0.9):1; Alternatively, n is 3, and the ratio of platinum loading in the first catalyst layer, platinum loading in the second catalyst layer, and platinum loading in the third catalyst layer is (0.7-0.9):(0.9-1.0):(1.0-1.3).

4. The cathode catalyst layer structure according to claim 1, characterized in that, The ionomer is a highly oxygen-permeable ionomer; the highly oxygen-permeable ionomer is a polymeric compound containing oxygen-containing heterocycles.

5. The cathode catalyst layer structure according to claim 4, characterized in that, The highly oxygen-permeable ionomer includes at least one of the following substances:

6. A membrane electrode assembly for a proton exchange membrane fuel cell, characterized in that, The device comprises an anode gas diffusion layer, an anode catalyst layer structure, a proton exchange membrane, a cathode catalyst layer structure, and a cathode gas diffusion layer stacked sequentially, wherein the cathode catalyst layer structure is the cathode catalyst layer structure for a proton exchange membrane fuel cell as described in any one of claims 1-5.

7. The method for preparing the membrane electrode assembly for a proton exchange membrane fuel cell according to claim 6, characterized in that, Includes the following steps: An anode catalyst layer structure is formed on one side of the proton exchange membrane; A cathode catalyst layer structure is formed on the other side of the proton exchange membrane. The cathode catalyst layer structure includes a first catalyst layer, a second catalyst layer, and so on up to the nth catalyst layer, which are stacked in sequence. The average particle size of the platinum particles in the platinum-carbon catalyst increases sequentially from the first catalyst layer to the nth catalyst layer. The ratio of the mass of the ionomer to the mass of carbon in the platinum-carbon catalyst is denoted as I / C, and I / C increases sequentially from the first catalyst layer to the nth catalyst layer. An anode gas diffusion layer is provided on the side of the anode catalyst layer structure away from the proton exchange membrane; A cathode gas diffusion layer is provided on the side of the cathode catalytic layer structure away from the proton exchange membrane.

8. The preparation method according to claim 7, characterized in that, The formation of a cathode catalyst layer structure on the other side of the proton exchange membrane includes: Platinum-carbon catalysts with different average particle sizes were mixed with ionomers and solvents to prepare the first catalyst layer slurry, the second catalyst layer slurry, and so on up to the nth catalyst layer slurry. The first catalyst layer slurry, the second catalyst layer slurry, and so on up to the nth catalyst layer slurry are subjected to nano-dispersion treatment respectively; The cathode catalyst layer structure is formed on the proton exchange membrane using a transfer printing method or a direct coating method.

9. The preparation method according to claim 8, characterized in that, The dispersion pressure is 50-150MPa, and the dispersion times are 2-10.

10. A proton exchange membrane fuel cell, characterized in that, Includes the membrane electrode assembly as described in claim 6.

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