Cathode catalyst layer of proton exchange membrane fuel cell, membrane electrode assembly and preparation method thereof

Abstract

The invention relates to a cathode catalyst layer structure for a proton exchange membrane fuel cell, a membrane electrode assembly and a preparation method thereof, in the cathode catalyst layer structure, VGCF gradient addition of different catalyst layers is used, so that the catalyst layer with high VGCF content is close to one side of a proton exchange membrane, and the catalyst layer with low VGCF content is close to one side of a gas diffusion layer; on one hand, the VGCF added in the catalyst layer shows good conductivity, the internal resistance of the battery is reduced, and the performance of the battery is improved; and on the other hand, the gradient network structure formed by the VGCF enables the catalyst layer to have good gradient porosity, so that after the cathode catalyst layer structure is used for the proton exchange membrane fuel cell, water vapor conduction can be effectively promoted, generation of a three-phase reaction interface is promoted, and the performance of the cell is improved.

Description

Technical Field

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

[0002] Proton exchange membrane fuel cells (PEMFCs) offer advantages such as being green, sustainable, and high-powered, making them an important approach to solving environmental and energy problems. The membrane electrode assembly (MEA), as the core component of a fuel cell, typically consists of a gas diffusion layer, a catalyst layer, and a proton exchange membrane. The catalyst layer is the site of electrochemical reactions within the MEA assembly, and its performance and stability largely determine the MEA's electrochemical performance. The catalyst layer mainly consists of a catalyst, ionomers, and porous regions. The conductive carrier conducts electrons, the ionomers conduct protons, and the porous regions transport reactant gases. The catalyst, reactant gases, and ionomers form a three-phase reaction interface within the catalyst layer, where the consumption of reactant gases and the transport of products occur. The pores in the catalyst layer provide interstitial spaces and reaction sites for gas transport, electrochemical reactions between hydrogen and oxygen ions to generate electrons and water molecules, significantly influencing the three-phase points and playing a crucial role in fuel cell performance. Therefore, improving the porosity of the catalyst layer is essential.

[0003] Chinese patent document CN106684395A discloses a manufacturing process for a cathode catalyst layer with gradient porosity for fuel cells. Based on the traditional fuel cell cathode catalyst layer manufacturing process, and under the premise of constant platinum loading, the process optimizes the pore structure of the catalyst layer by controlling the composition of the catalyst slurry and the gradient change of platinum loading during the spraying process, thereby reducing the gas-liquid mass transfer resistance of the catalyst layer during the fuel cell reaction and improving the electrical performance of the proton exchange membrane fuel cell. However, the above technology has the following problems: the spraying process is inefficient and difficult to achieve industrial production; secondly, optimizing the pore structure by only adjusting the gradient change of platinum loading does not result in a significant difference in porosity and the effect is not obvious. Summary of the Invention

[0004] The purpose of this application is to overcome the deficiencies in the prior art and provide a cathode catalyst layer, membrane electrode assembly, and preparation method thereof for a proton exchange membrane fuel cell. The cathode catalyst layer exhibits good conductivity by adding VGCF, reducing internal resistance and improving battery performance. When this cathode catalyst layer is used to prepare a membrane electrode assembly, and further used in a proton exchange membrane fuel cell, the gradient network structure formed by VGCF gives the catalyst layer a good gradient porosity, promoting water vapor conduction and facilitating the formation of a three-phase reaction interface, thereby effectively improving battery performance.

[0005] The first aspect of this application provides a cathode catalyst layer 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.

[0006] Each catalyst layer contains a catalyst, an ionomer, and VGCF, with the VGCF content increasing sequentially from the first catalyst layer to the nth catalyst layer.

[0007] VGCF refers to vapor-grown carbon fiber, which is a fibrous carbon produced by the high-temperature pyrolysis of low-carbon hydrocarbons or carbon oxides under the action of a catalyst. The VGCF used in this invention was purchased from Showa Denko and is a two-dimensional material with a large aspect ratio. Water is conducted along the outer wall of the fiber, and the pores between the fibers can conduct gas, which can effectively promote the water-gas transport between the catalytic layers.

[0008] In some embodiments, the catalyst is a platinum-carbon catalyst; the ratio of the mass of the ionomer in each catalyst layer to the mass of carbon in the platinum-carbon catalyst is denoted as I / C, and the I / C value is the same for each catalyst layer.

[0009] In some embodiments, the I / C value in each catalyst layer is 0.6-1.8;

[0010] In each catalyst layer, the content of VGCF increases sequentially from the first catalyst layer to the nth catalyst layer, and the content of VGCF is 0.05-2wt%.

[0011] In some embodiments, n is a positive integer from 2 to 5;

[0012] The catalyst is a platinum-carbon catalyst;

[0013] In different catalyst layers, the platinum content of the platinum-carbon catalyst is 20-60 wt%, preferably 50 wt%.

[0014] In different catalyst layers, the average particle size of platinum particles in platinum-carbon catalysts is 2-4 nm.

[0015] In some embodiments, the ionomer is selected from any one or a combination of several of perfluorosulfonic acid resins, sulfonated trifluorostyrene resins, polymethylphenylsulfonate siloxane resins, sulfonated polystyrene, polyethylene copolymer resins, sulfonated styrene, polyethylene, polybutene, and polystyrene resins; preferably, it is a perfluorosulfonic acid resin.

[0016] 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.

[0017] 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:

[0018] An anode catalyst layer structure is formed on one side of the proton exchange membrane;

[0019] A cathode catalytic layer structure is formed on the other side of the proton exchange membrane. The cathode catalytic layer structure includes a first catalytic layer, a second catalytic layer, and so on up to the nth catalytic layer, which are stacked in sequence. Each catalytic layer contains a catalyst, an ionomer, and VGCF. The content of VGCF in each catalytic layer increases sequentially from the first catalytic layer to the nth catalytic layer.

[0020] An anode gas diffusion layer is provided on the side of the anode catalyst layer structure away from the proton exchange membrane;

[0021] A cathode gas diffusion layer is provided on the side of the cathode catalytic layer structure away from the proton exchange membrane.

[0022] In some embodiments, forming a cathode catalyst layer structure on the other side of the proton exchange membrane includes:

[0023] The catalyst was mixed with ionomer and solvent respectively to prepare a slurry with a solid content of 8-15 wt%; then different amounts of VGCF material were added to prepare the first catalyst layer slurry, the second catalyst layer slurry, and so on up to the nth catalyst layer slurry.

[0024] 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;

[0025] The cathode catalyst layer structure is formed on the proton exchange membrane using a transfer printing method or a direct coating method.

[0026] In some embodiments, the solvent is a mixture of water and alcohol in a mass ratio of (1-9):1;

[0027] The alcohol is any one or a combination of several of methanol, ethanol, propanol, butanol, pentanol, hexanol, n-propanol, and isopropanol;

[0028] The dispersion pressure is 50-150MPa, and the dispersion times are 2-10.

[0029] 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.

[0030] Compared with the prior art, the beneficial effects of this application are:

[0031] This application provides a cathode catalyst layer structure for a proton exchange membrane fuel cell. This structure utilizes a gradient addition of VGCF to different catalyst layers, with the VGCF-rich catalyst layer positioned closer to the proton exchange membrane and the VGCF-rich catalyst layer positioned closer to the gas diffusion layer. This arrangement results in two advantages: firstly, the addition of VGCF to the catalyst layer enhances conductivity, reducing internal resistance and improving battery performance; secondly, the gradient network structure formed by VGCF provides the catalyst layer with excellent gradient porosity. Therefore, when used in a proton exchange membrane fuel cell, this cathode catalyst layer structure effectively promotes water-gas conduction, facilitates the formation of the three-phase reaction interface, and improves battery performance. Attached Figure Description

[0032] Figure 1 This is a partial structural schematic diagram of a membrane electrode assembly according to an embodiment of this application.

[0033] Figure 2 The graph shows the electrochemical performance test results of the membrane electrodes prepared based on the cathode catalyst layers described in Examples 1-4 and the comparative examples of this application.

[0034] Explanation of reference numerals in the attached figures:

[0035] 100, First catalytic layer; 200, Second catalytic layer; 300, Gas diffusion layer; 400, Proton exchange membrane. Detailed Implementation

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] Each catalyst layer contains a catalyst, an ionomer, and VGCF, with the VGCF content increasing sequentially from the first catalyst layer to the nth catalyst layer.

[0041] 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.

[0042] In this application, the catalyst is a platinum-carbon catalyst, which includes a carbon support and platinum particles supported on the carbon support, with a platinum content of 20wt%-60wt%; preferably, the platinum content in the platinum-carbon catalyst is 50wt%.

[0043] In some specific embodiments, n is 2, and the platinum content in the platinum-carbon catalyst is 50 wt% in both the first and second catalyst layers.

[0044] In some specific embodiments, n is 3, and the platinum content in the platinum-carbon catalyst is 50 wt% in the first catalyst layer, the second catalyst layer, and the third catalyst layer.

[0045] The ratio of the mass of ionomers in each catalyst layer to the mass of carbon in the platinum-carbon catalyst is denoted as I / C.

[0046] In this application, the I / C values ​​in each catalyst layer are the same, and are all between 0.6 and 1.8.

[0047] In some specific embodiments, n is 2, and the I / C ratio in both the first and second catalyst layers is 1.0.

[0048] In some specific embodiments, n is 3, and the I / C ratio is 1 in the first catalyst layer, the second catalyst layer, and the third catalyst layer.

[0049] In this application, the VGCF content in each catalyst layer is 0.05-2 wt%, the VGCF content in the first catalyst layer is less than the VGCF content in the second catalyst layer; the VGCF content in the second catalyst layer is less than the VGCF content in the third catalyst layer; and so on.

[0050] In some specific embodiments, n is 2, the VGCF content in the first catalyst layer is 0.05-0.35 wt%, and the VGCF content in the second catalyst layer is 0.35-0.65 wt%; or, the VGCF content in the first catalyst layer is 0.05-0.35 wt%, and the VGCF content in the second catalyst layer is 0.65-0.95 wt%; or, the VGCF content in the first catalyst layer is 0.35-0.65 wt%, and the VGCF content in the second catalyst layer is 0.65-0.95 wt%.

[0051] In some specific embodiments, n is 3, the VGCF content in the first catalyst layer is 0.05-0.35 wt%, the VGCF content in the second catalyst layer is 0.35-0.65 wt%, and the VGCF content in the third catalyst layer is 0.65-0.95 wt%.

[0052] Excessive VGCF addition can negatively impact mass transfer in the catalyst layer, increasing resistance and affecting performance. Conversely, insufficient addition fails to improve porosity. By optimizing the VGCF content in the catalyst layer, the content increases sequentially from the first to the nth layer. Layers with high VGCF content are located closer to the proton exchange membrane, while those with low content are closer to the gas diffusion layer. This arrangement achieves two benefits: firstly, the addition of VGCF to the catalyst layer enhances conductivity, reducing internal resistance and improving performance; secondly, the gradient network structure formed by VGCF provides excellent gradient porosity. Therefore, the cathode catalyst layer structure of this application, when used in a proton exchange membrane fuel cell, effectively promotes water-gas conduction, facilitates the formation of the three-phase reaction interface, and enhances battery performance.

[0053] In this application, the ionomer in each catalyst layer is selected from any one or a combination of several of perfluorosulfonic acid resin, sulfonated trifluorostyrene resin, polymethylphenylsulfonate siloxane resin, sulfonated polystyrene, polyethylene copolymer resin, sulfonated styrene, polyethylene, polybutene, and polystyrene resin; in some specific embodiments, the ionomer in each catalyst layer is perfluorosulfonic acid resin.

[0054] Figure 1A 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, an ionomer, and VGCF; the VGCF content in the first catalyst layer 100 is less than the VGCF content 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.

[0055] 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.

[0056] 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:

[0057] An anode catalyst layer structure is formed on one side of the proton exchange membrane;

[0058] A cathode catalytic layer structure is formed on the other side of the proton exchange membrane. The cathode catalytic layer structure includes a first catalytic layer, a second catalytic layer, and so on up to the nth catalytic layer, which are stacked in sequence. Each catalytic layer contains a catalyst, an ionomer, and VGCF. The content of VGCF in each catalytic layer increases sequentially from the first catalytic layer to the nth catalytic layer.

[0059] An anode gas diffusion layer is provided on the side of the anode catalyst layer structure away from the proton exchange membrane;

[0060] A cathode gas diffusion layer is provided on the side of the cathode catalytic layer structure away from the proton exchange membrane.

[0061] The preparation method of this application is simple and the materials are inexpensive, making it very suitable for widespread application in industrial production.

[0062] In some embodiments, forming a cathode catalyst layer structure on the other side of the proton exchange membrane includes:

[0063] The catalyst was mixed with ionomer and solvent respectively to prepare a slurry with a solid content of 8-15 wt%; then different amounts of VGCF material were added to prepare the first catalyst layer slurry, the second catalyst layer slurry, and so on up to the nth catalyst layer slurry.

[0064] 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;

[0065] The cathode catalyst layer structure is formed on the proton exchange membrane using a transfer printing method or a direct coating method.

[0066] This application improves the dispersion uniformity of platinum-carbon catalyst, ionomer, and VGCF material 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.

[0067] In this application, the amount of VGCF material added to each catalyst layer slurry is different, and the amount of VGCF material added increases sequentially from the first catalyst layer slurry to the nth catalyst layer slurry, thereby making the content of VGCF material in the first catalyst layer to the nth catalyst layer increase sequentially. In addition, the I / C ratio is the same in each catalyst layer slurry, so that the I / C ratio is the same from the first catalyst layer to the nth catalyst layer.

[0068] 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.

[0069] In some embodiments, the dispersion pressure is 50-150 MPa, and the dispersion times are 2-10.

[0070] By controlling the dispersion conditions, the dispersion uniformity of platinum-carbon catalyst, ionomer, and VGCF material in the solvent can be further improved, allowing them to be evenly distributed in each catalyst layer, thereby enhancing the catalytic activity of the platinum-carbon catalyst and the durability and electrochemical performance of the battery.

[0071] In some embodiments, the solvent comprises water and an alcohol. The alcohol includes at least one of methanol, ethanol, propanol and its isomers, propanol and its isomers and stereoisomers, butanol and its isomers and stereoisomers, pentanol and its isomers and stereoisomers, and hexanol and its isomers and stereoisomers.

[0072] In some embodiments, the preparation of the slurry may include: first, dissolving the platinum-carbon catalyst in water to obtain n catalyst solutions; then adding alcohol and ionomer to the n catalyst solutions respectively, stirring, adding different amounts of VGCF material respectively, and stirring to perform nano-dispersion treatment on the n slurries respectively.

[0073] 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.

[0074] The present application will be further described below with reference to specific embodiments, but the present application is not limited thereto.

[0075] 1. Preparation of slurry

[0076] Step 1: Dissolve 5g of a 50% by weight platinum-carbon catalyst (with an average particle size of 3nm) in 37.31g of water. Then, add 5.77g of n-propanol and 9.62g of perfluorosulfonic acid resin sequentially according to an I / C ratio of 1.0 to obtain a slurry with a solid content of 26wt%. Stir the obtained slurry evenly on a magnetic stirrer, then add 0.25wt% of VGCF material (purchased from Showa Denko). After stirring continuously for 60min, use a nano-dispersant to nano-disperse the mixed slurry at a dispersion pressure of 100MPa for 5 times to obtain slurry A.

[0077] Step 2: Dissolve 5g of a 50% by weight platinum-carbon catalyst (with an average particle size of 3nm) in 37.31g of water. Then, add 5.77g of n-propanol and 9.62g of perfluorosulfonic acid resin sequentially according to an I / C ratio of 1.0 to obtain a slurry with a solid content of 26wt%. Stir the obtained slurry evenly on a magnetic stirrer, then add 0.55wt% of VGCF material (purchased from Showa Denko). After stirring continuously for 60min, use a nano-dispersant to nano-disperse the mixed slurry at a dispersion pressure of 100MPa for 5 times to obtain slurry B.

[0078] Step 3: Dissolve 5g of a 50% by weight platinum-containing platinum-carbon catalyst (with an average particle size of 3nm) in 37.31g of water. Then, add 5.77g of n-propanol and 9.62g of perfluorosulfonic acid resin sequentially according to an I / C ratio of 1.0 to obtain a slurry with a solid content of 26wt%. Stir the obtained slurry evenly on a magnetic stirrer, then add 0.85wt% of VGCF material (purchased from Showa Denko). After stirring continuously for 60min, use a nano-dispersant to nano-disperse the mixed slurry at a dispersion pressure of 100MPa for 5 times to obtain slurry C.

[0079] 2. Preparation of cathode catalyst layer structure based on the slurry

[0080] Example 1

[0081] The above-mentioned nano-dispersed slurry AC was prepared according to the following three slurries, each containing 0.4 mg / cm³ of total platinum. 2 One-third of the coating is scraped onto the base film to obtain the cathode catalyst layer.

[0082] Example 2

[0083] The above-mentioned nano-dispersed slurries A and B were prepared according to a ratio of 0.4 mg / cm³ of total platinum in each slurry. 2Half of it is scraped onto the base film to obtain the cathode catalyst layer.

[0084] Example 3

[0085] The above-mentioned nano-dispersed slurries A and C were prepared according to a ratio of 0.4 mg / cm³ of total platinum in each slurry. 2 Half of it is scraped onto the base film to obtain the cathode catalyst layer.

[0086] Example 4

[0087] The above-mentioned nano-dispersed slurries B and C were prepared according to a ratio of 0.4 mg / cm³ of total platinum in each slurry. 2 Half of it is scraped onto the base film to obtain the cathode catalyst layer.

[0088] Comparative Example

[0089] 5 g of a platinum-carbon catalyst with a platinum content of 50 wt% (average particle size of platinum particles of 3 nm) was dissolved in 37.31 g of water. Then, 5.77 g of n-propanol and 9.62 g of perfluorosulfonic acid resin were added sequentially according to an I / C ratio of 1.0 to obtain a slurry with a solid content of 26 wt%. The obtained slurry was continuously stirred on a magnetic stirrer for 60 min, and then the mixed slurry was nano-dispersed using a nano-disperser at a dispersion pressure of 100 MPa for 5 times, to obtain a slurry with a total platinum content of 0.4 mg / cm³. 2 The cathode catalyst layer is obtained by scraping it onto the base film.

[0090] The cathode catalyst layer structures obtained after transfer printing in Examples 1-4 and the comparative example were assembled with a commercially available Toray TGL-0550 gas diffusion layer to form a membrane electrode for testing. The first catalyst layer was located near the gas diffusion layer, and the second catalyst layer was located near the proton exchange membrane. Detailed testing methods are as follows:

[0091] The test conditions were Greenlight 25cm. 2 Fixture, test conditions: temperature 75℃, humidity (anode 40% / cathode 50%), pressure (anode 260KPa / cathode 250KPa), metering ratio (anode 1.5 / cathode 1.9).

[0092] Test results are as follows Figure 1As shown, the performance of the catalyst layer in Example 1 > Example 4 > Example 3 > Example 2 > Comparative Example is superior to that in the comparative example. The addition of VGCF results in higher performance in all examples, indicating that the gradient network structure formed by the addition of VGCF gives the catalyst layer a good gradient porosity. This allows the cathode catalyst layer structure of this application, when used in a proton exchange membrane fuel cell, to effectively promote water vapor conduction, facilitate the formation of the three-phase reaction interface, and improve battery performance. The superior performance of the three-gradient VGCF addition compared to the two-gradient addition indicates a more uniform porosity distribution in the catalyst layer and more efficient water vapor transport. The performance of the catalyst layer in Example 4 > Example 3 > Example 2 demonstrates that as the amount of VGCF added increases, the porosity of the resulting catalyst layer increases, and the performance improves accordingly.

[0093] The porosity of the catalyst layer in Examples 1-4 and the comparative examples was tested using the mercury intrusion porosimetry method. Table 1 shows the test results.

[0094] sample Porosity Example 1 56.4％ Example 2 45.2％ Example 3 49.5％ Example 4 54.2％ Comparative Example 20.4％

[0095] Table 1 shows that the comparative catalyst layer without VGCF has the lowest porosity, indicating a denser catalyst layer that is not conducive to water vapor transport. The catalyst layers obtained in Examples 1-4 show significantly increased porosity due to the addition of VGCF, with the catalyst layer in Example 1 exhibiting the highest porosity. Combined with the membrane electrode performance, this demonstrates that the gradient network structure formed by VGCF provides the catalyst layer with excellent gradient porosity, effectively promoting water vapor conduction, facilitating the formation of the three-phase reaction interface, and improving battery performance.

[0096] 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 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 catalyst, an ionomer, and VGCF, with the VGCF content 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, The catalyst is a platinum-carbon catalyst; the ratio of the mass of the ionomer in each catalyst layer to the mass of carbon in the platinum-carbon catalyst is denoted as I / C, and the I / C value is the same for each catalyst layer.

3. The cathode catalyst layer structure according to claim 2, characterized in that, In each catalyst layer, the I / C ratio is 0.6-1.8, and the VGCF content is 0.05-2 wt%.

4. The cathode catalyst layer structure according to claim 1, characterized in that, n is a positive integer between 2 and 5; The catalyst is a platinum-carbon catalyst; In different catalyst layers, the platinum content of the platinum-carbon catalyst is 20-60 wt%, preferably 50 wt%. In different catalyst layers, the average particle size of platinum particles in platinum-carbon catalysts is 2-4 nm.

5. The cathode catalyst layer structure according to claim 1, characterized in that, The ionomer is selected from any one or a combination of several of the following: perfluorosulfonic acid resin, sulfonated trifluorostyrene resin, polymethylphenylsulfonate siloxane resin, sulfonated polystyrene, polyethylene copolymer resin, sulfonated styrene, polyethylene, polybutene, and polystyrene resin; preferably, it is a perfluorosulfonic acid resin.

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 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 catalytic layer structure is formed on the other side of the proton exchange membrane. The cathode catalytic layer structure includes a first catalytic layer, a second catalytic layer, and so on up to the nth catalytic layer, which are stacked in sequence. Each catalytic layer contains a catalyst, an ionomer, and VGCF. The content of VGCF in each catalytic layer increases sequentially from the first catalytic layer to the nth catalytic 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: The catalyst was mixed with ionomer and solvent respectively to prepare a slurry with a solid content of 8-15 wt%; then different amounts of VGCF material were added 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 solvent is a mixture of water and alcohol in a mass ratio of (1-9):1; The alcohol is any one or a combination of several of methanol, ethanol, propanol, butanol, pentanol, hexanol, n-propanol, and isopropanol; The dispersion pressure is 50-150MPa, and the dispersion times are 2-10.

10. A proton exchange membrane fuel cell, characterized in that, The membrane electrode assembly includes the membrane electrode assembly of claim 6 or the membrane electrode assembly prepared by the method of any one of claims 7-9.

Images