Cathode transfer printing template, preparation method thereof and method for preparing fuel cell membrane electrode

Abstract

The invention relates to a cathode transfer printing template, a preparation method of the cathode transfer printing template and a method for preparing a fuel cell membrane electrode, and the cathode transfer printing template contains a high-molecular compound and a silicon-oxygen compound, so that the cathode transfer printing template has relatively good toughness and relatively high strength; and the condition that the catalyst layer is damaged due to cracks and fragmentation in the hot pressing process by using the cathode transfer printing template is avoided. Moreover, the superfine silicon-oxygen compound is uniformly distributed in the cathode transfer printing template, and particularly, the transfer printing surface of the cathode transfer printing template contains the superfine silicon-oxygen compound, so that the rubbing effect of the cathode transfer printing template and the lotus leaf can be improved, the transfer printing surface with certain roughness is formed, certain fault tolerance can be provided for the hot pressing process, and the production efficiency is improved. And the problems of large gas transmission resistance and high possibility of water logging caused by excessive compaction of the cathode catalyst layer are avoided.

Description

Technical Field

[0001] This disclosure relates to the field of fuel cells, and more specifically, to a cathode transfer template and a method for preparing the same, and a method for preparing a fuel cell membrane electrode. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) can directly convert the chemical energy of hydrogen into electrical energy, offering advantages such as cleanliness, high efficiency, and rapid start-up, making them a promising electrochemical energy conversion device. The core of a PEMFC is the membrane electrode assembly (MEA), and the core component of the MEA is the catalyst-coated membrane (CCM). The characteristics of the CCM directly affect the battery's performance, durability, and stability. The CCM consists of three parts: the cathode catalyst layer, the proton exchange membrane, and the anode catalyst layer. Conventional methods for preparing CCMs include the transfer method and the direct coating method. The transfer method involves coating a slurry onto a transfer template, then transferring the catalyst layer from the template to the proton exchange membrane via hot pressing. The direct coating method, as the name suggests, involves directly coating the catalyst onto the proton exchange membrane. Due to the unique water-swelling property of the proton exchange membrane, the direct coating method requires specialized processes and equipment; currently, most MEA manufacturers use the transfer method to prepare CCMs.

[0003] The transfer method for preparing CCM requires pressing the catalyst layer and proton exchange membrane together under high pressure and temperature, followed by the removal of the transfer template. However, most existing transfer templates are polymer films with smooth surfaces. These templates cannot balance strength and toughness, which may lead to the following problems: 1. The transfer template is prone to cracking under high temperatures, resulting in damage to the prepared catalyst layer; 2. It can easily cause over-compaction of the catalyst layer, especially the cathode catalyst layer, which reduces porosity, increases oxygen transport resistance, and affects cell efficiency; at the same time, the catalytic reaction produces a lot of water under high current density, and the reduced porosity of the catalyst layer also leads to poor water drainage, easily causing flooding. In addition, existing transfer templates have poor thermal conductivity, the hot pressing process requires a long time, and uneven heat transfer can also affect the performance of the catalyst layer. Summary of the Invention

[0004] The purpose of this disclosure is to provide a cathode transfer template and its preparation method, as well as a method for preparing a fuel cell membrane electrode, to solve the problems existing in the prior art when preparing CCM by transfer method, such as easy cracking of transfer template, damage to catalyst layer, high oxygen transport resistance of catalyst layer, and easy water flooding.

[0005] To achieve the above objectives, the first aspect of this disclosure provides a cathode transfer template, wherein the material of the cathode transfer template comprises a polymer compound and a silicon oxide compound dispersed in the polymer compound; the weight ratio of the polymer compound to the silicon oxide compound is (0.5-5):1.

[0006] Optionally, the polymer compound is a homopolymer compound; The homopolymer compound includes one or more of polystyrene, polyvinyl alcohol, carboxymethyl chitosan, polymethyl methacrylate, poly(p-phenylene terephthalate), polycarbonate, polyethylene glycol, polyacrylic acid, and polytetrafluoroethylene.

[0007] Optionally, the polymer compound is a graft copolymer; the graft copolymer comprises a rigid backbone and highly thermally conductive side chains; The rigid backbone includes one or more of the following: polystyrene backbone, polymethyl methacrylate backbone, polytetrafluoroethylene backbone, and poly(p-styrene) backbone. The high thermal conductivity side chains include one or more of the following: polyvinyl alcohol side chains, carboxymethyl chitosan side chains, polycarbonate side chains, polyethylene glycol side chains, and polyacrylic acid side chains.

[0008] Optionally, the silicon oxide compound includes silicon dioxide; the average particle size of the silicon oxide compound is 5-100 nm.

[0009] Optionally, the transfer surface of the cathode transfer template includes a plurality of transfer micropores; the density of the transfer micropores is 500-2000 per square millimeter, the average diameter of the transfer micropores is 40-100 μm, and the average depth of the transfer micropores is 20-100 μm.

[0010] Optionally, the roughness Ra of the transfer surface of the cathode transfer template is 10-100 nm.

[0011] Optionally, the cathode transfer template is square in shape; the thickness of the cathode transfer template is 0.5-2.0 mm.

[0012] A second aspect of this disclosure provides a method for preparing the cathode transfer template described in the first aspect, the method comprising: A mixture of polymer, initiator / crosslinking agent, silicon oxide and solvent is stirred to obtain a cathode transfer template mixture; the weight ratio of the polymer to the silicon oxide is (0.5-5):1; the cathode transfer template mixture is coated on the surface of a lotus leaf containing micropapillary structures to obtain a cathode transfer template.

[0013] Optionally, the initiator / crosslinking aid includes polydimethylsiloxane and / or benzoyl peroxide; The solvent includes alcohol and / or water; The solid content of the cathode transfer template mixture is 30-70% by weight.

[0014] A third aspect of this disclosure provides a method for preparing a fuel cell membrane electrode, the method comprising: A cathode catalyst slurry is coated onto the surface of the cathode transfer template described in the first aspect, thereby obtaining a cathode catalyst layer on the surface of the cathode transfer template. A proton exchange membrane and an anode catalyst layer are sequentially stacked on the surface of the cathode catalyst layer and subjected to hot-press transfer processing. Then, the cathode transfer template is removed to obtain the fuel cell membrane electrode.

[0015] The above technical solution utilizes a cathode transfer template containing polymeric compounds and silicon oxides, which endows the template with good toughness and high strength, preventing catalyst layer damage caused by cracking and fragmentation during hot pressing. Furthermore, the uniform distribution of ultrafine silicon oxides within the cathode transfer template, particularly on its transfer surface, enhances the imprinting effect between the template and the lotus leaf. This creates a transfer surface with a certain degree of roughness, providing some tolerance for the hot pressing process and preventing problems such as excessive compaction of the cathode catalyst layer leading to high gas transport resistance and water flooding.

[0016] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0017] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a microscopic image of the surface structure of a cathode catalyst layer disclosed herein.

[0018] Figure 2 This is a schematic diagram of the surface of the cathode catalyst layer in Comparative Example 1 of this disclosure.

[0019] Figure 3 This is a schematic diagram of the surface of the cathode catalyst layer in Comparative Example 3 of this disclosure. Detailed Implementation

[0020] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0021] In this disclosure, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its normal operating state, for example, as shown in the reference. Figure 1 In the drawing orientation, "inner" and "outer" refer to their relative to the outline of the device. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature. In the description of this disclosure, "a plurality of" means two or more, unless otherwise explicitly specified.

[0022] The first aspect of this disclosure provides a cathode transfer template, the material of which includes a polymer compound and a silicon oxide compound dispersed in the polymer compound; the weight ratio of the polymer compound to the silicon oxide compound is (0.5-5):1.

[0023] The above technical solution utilizes a cathode transfer template containing polymeric compounds and silicon oxides, which endows the template with good toughness and high strength, preventing catalyst layer damage caused by cracking and fragmentation during hot pressing. Furthermore, the uniform distribution of ultrafine silicon oxides within the cathode transfer template, particularly on its transfer surface, enhances the imprinting effect between the template and the lotus leaf. This creates a transfer surface with a certain degree of roughness, providing some tolerance for the hot pressing process and preventing problems such as excessive compaction of the cathode catalyst layer leading to high gas transport resistance and water flooding.

[0024] In one embodiment, the cathode transfer template described in this disclosure is obtained by imprinting onto the surface of a lotus leaf with micropapillary structures. Therefore, the transfer surface of the cathode transfer template has multiple transfer micropores, which correspond to the micropapillary structures on the lotus leaf surface. In this embodiment, the lotus leaf is obtained after screening. The specific screening method includes: observing at least three observation points on the surface of a lotus leaf of a certain size (e.g., 6cm × 6cm) using a microscope with a magnification of 20 × 50. The observation field of view can be 0.1mm × 0.1mm. When the number of micropapillary structures in all observation points is 5-20, the average diameter of the micropapillary structures is 40-100μm, and the height of the micropapillary structures is 20-100μm, the lotus leaf is considered qualified. The average diameter of the micropapillary structures is calculated based on the maximum diameter of each micropapillary structure, and the average height of the micropapillary structures is calculated based on the maximum height of each micropapillary structure. Furthermore, fresh lotus leaves need to be washed and air-dried before use.

[0025] In one embodiment, the density of the transfer micropores is 500-2000 per square millimeter.

[0026] In some embodiments, the density of the transfer micropores can be any value within a range of any one or any two of the following: 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, and 1900 per square millimeter.

[0027] In the above embodiments, the density of transfer micropores on the transfer surface can affect the hydrophobicity of the transferred cathode catalyst, the contact area between oxygen and the catalyst layer surface, and the gas transport resistance. Specifically, the cathode catalyst surface transferred by the cathode transfer template can form a micro-papillary structure resembling a lotus leaf surface. Oxygen can flow in the depressions between the micro-papillary structures. On the one hand, this can increase the contact area between oxygen and the catalyst layer surface and reduce the oxygen transport resistance, thereby increasing the reaction rate of the cathode reaction. On the other hand, water droplets generated on the cathode catalyst layer surface come into contact with the micro-papillary structures. Since the depressions of the micro-papillary structures contain oxygen, the surface tension of oxygen and water in the depressions prevents the water droplets from wetting the catalyst layer surface, improving the hydrophobicity of the catalyst layer and avoiding flooding. Furthermore, the moisture generated by the gas reaction in the depressions can also be discharged from the depressions, improving drainage performance. In addition, if the density of the transfer micropores is too high, although it can further increase hydrophobicity, the volume of the depression between two adjacent micropapillary structures will become smaller, which will increase the oxygen transport resistance. Therefore, when the density of the transfer micropores is appropriate, it is possible to improve the contact area, hydrophobicity and drainage while ensuring low oxygen transport resistance.

[0028] In one embodiment, the average diameter of the transfer micropores is 40-100 μm.

[0029] In some embodiments, the average diameter of the transfer micropores is any value within a range formed by any one or any two of 41μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, and 95μm.

[0030] In the above embodiments, the average diameter of the transfer micropores is calculated based on the maximum diameter of the micropore profile on the surface. When the average diameter of the transfer micropores is appropriate, not only can the diameter of the micro-emulsion structure on the surface of the transferred catalyst layer be sufficient to support large water droplets generated on the surface, but it can also ensure that water generated in the recesses can be easily drained, thereby further improving the hydrophobicity of the catalyst layer. At the same time, when the average diameter of the transfer micropores is appropriate, the micro-emulsion structure on the surface of the catalyst layer is less likely to fall off, thereby improving the imprinting and separation effects between the lotus leaf and the transfer template.

[0031] In one embodiment, the average depth of the transfer micropores is 20-100 μm.

[0032] In some embodiments, the average depth of the transfer micropores is any value within the range formed by any one or any two of the following: 23 μm, 26 μm, 29 μm, 32 μm, 35 μm, 38 μm, 41 μm, 44 μm, 47 μm, 50 μm, 53 μm, 56 μm, 59 μm, 62 μm, 65 μm, 68 μm, 71 μm, 74 μm, 77 μm, 80 μm, 83 μm, 86 μm, 89 μm, 92 μm, 95 μm, and 98 μm. In the above embodiments, when the average depth of the transfer micropores is appropriate, on the one hand, a microemulsion structure of suitable height can be obtained, providing more space for oxygen transport and drainage, further reducing oxygen transport resistance and the risk of flooding; on the other hand, it ensures that the microemulsion structure on the catalyst layer surface is not easily detached, thereby improving the separation effect between the lotus leaf and the transfer template.

[0033] In one embodiment, the average diameter of the transfer micropores is obtained by scanning electron microscopy (SEM), and the average depth is obtained by a 3D profilometer. The specific testing method includes selecting at least three detection areas on the surface of the cathode transfer template. The size of each detection area can be 0.1 mm × 0.1 mm. The average diameter parameter obtained from all detection areas is averaged, and the average depth parameter obtained from all detection areas is averaged. The average value obtained by the above testing method is the final result. In this embodiment, because the results obtained by the above testing method have a relatively large randomness, even two identical cathode transfer templates may yield different measured average diameter and average depth parameters for the transfer micropores. When the detected average diameter and average depth fall within the above-mentioned range, the parameters of the transfer micropores can be considered qualified.

[0034] In one embodiment, the polymeric compound described in this disclosure includes a homopolymer or a graft copolymer.

[0035] In one embodiment, the degree of polymerization of the polymer compound is 2000-5000, and the molecular weight of the polymer compound is 200000-250000.

[0036] In some embodiments, the degree of polymerization of the polymer is any value within the range formed by any one or any two of the following: 2200, 2400, 2600, 2800, 3000, 3200, 3400, 3600, 3800, 4000, 4200, 4400, 4600, and 4800. The molecular weight of the polymer is any molecular weight within the range formed by any one or any two of the following: 200,000, 210,000, 220,000, 230,000, and 240,000.

[0037] In one embodiment, the homopolymer compound includes any one or more of polystyrene, polyvinyl alcohol, carboxymethyl chitosan, polymethyl methacrylate, poly(p-phenylene terephthalate), polycarbonate, polyethylene glycol, polyacrylic acid, and polytetrafluoroethylene.

[0038] In one embodiment, the graft copolymer comprises a rigid backbone and highly thermally conductive side chains; wherein the rigid backbone comprises one or more of polystyrene backbone, polymethyl methacrylate backbone, polytetrafluoroethylene backbone, and poly(p-phenylene terephthalate) backbone; and the highly thermally conductive side chains comprise one or more of polyvinyl alcohol side chains, carboxymethyl chitosan side chains, polycarbonate side chains, polyethylene glycol side chains, and polyacrylic acid side chains.

[0039] In one embodiment, the weight ratio of the rigid main chain to the high thermal conductivity side chain is (5-50):1.

[0040] In some implementations, the weight ratio of the rigid main chain to the high thermal conductivity side chain is any ratio within a range formed by any one or any two of the following: 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, and 45:1.

[0041] In a preferred embodiment, the weight ratio of the rigid main chain to the high thermal conductivity side chain is (5-10):1.

[0042] In this embodiment, the rigid main chain of the graft copolymer provides excellent structural support, while the highly thermally conductive side chains exhibit good flexibility, absorbing pressure during hot pressing and achieving a balance between high strength and high toughness. The intermittent combination structure of the side chains and main chain hinders crack propagation, improves the material's tear resistance, and is suitable for the mechanical stress requirements of high-precision transfer processes. Furthermore, utilizing the high thermal conductivity of the side chains, a localized thermally conductive network can be formed within the main chain, increasing the thermal conductivity in the vertical direction, preventing thermal deformation during transfer, improving thermal conductivity, and enhancing thermal uniformity. Additionally, due to the difference in glass transition temperatures between the main chain and side chains, the hardness and softness regions of the template can be controlled via a temperature gradient, thereby adapting to the preparation and transfer of complex surfaces.

[0043] In one embodiment, the silicon oxide compound includes silicon dioxide.

[0044] In the above embodiments, adding silicon oxide compounds to the polymer can reduce the surface tension of the liquid, which helps to reduce the contact angle θ, thereby improving the wettability of the cathode transfer template mixture and enhancing the printing effect on the transfer surface. Furthermore, adding silicon oxide compounds can change the viscosity of the liquid. When the content of silicon oxide compounds in the cathode transfer template mixture is appropriate, the viscosity is suitable, which can reduce the internal frictional resistance during liquid spreading, making it easier to flow and spread on the substrate. Furthermore, since the cathode catalyst layer preparation process requires hot-press transfer at high temperatures and pressures, the cathode transfer template of this application ensures that silica is uniformly distributed within the polymer compound. On one hand, this guarantees good toughness of the cathode transfer template, avoiding cracks or breakage caused by thermal expansion and contraction. On the other hand, compared with traditional transfer templates, it enhances the strength of the cathode transfer template, preventing deformation during hot-press transfer and ensuring that the pattern on the cathode transfer template is clearly transferred to the catalyst layer surface, thus preventing damage to the catalyst layer and improving fuel cell performance. Moreover, the use of an aqueous solvent in the preparation of this cathode transfer template allows the silica compounds in the resulting template to lock in water molecules, preventing cracking caused by excessive dryness of the cathode transfer template.

[0045] In one embodiment, the average particle size of the silicon oxide compound is 5-100 nm.

[0046] In some embodiments, the average particle size of the silicon oxide compound is any average particle size within the range formed by any one or any two of 6nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, and 95nm.

[0047] In the above embodiments, since the silicon oxide compound in the cathode transfer template can be an ultrafine and impurity-free silicon oxide compound prepared by chemical methods, the smaller the average particle size, the higher the price. Adding a silicon oxide compound with a suitable average particle size to the polymer compound can improve the uniformity of silicon oxide compound dispersion and further improve the performance of the cathode transfer template. Moreover, when the average particle size of the silicon oxide compound is suitable, the preparation cost of the transfer template can be reduced while ensuring film formation. In addition, compared with the traditional smooth surface transfer template, the transfer surface and the interior of the transfer micropores of this application form a surface with tiny unevenness, which can reduce the situation where the microemulsion structure of the lotus leaf surface is left inside the transfer micropores during the demolding stage of preparing the cathode transfer template, and can also reduce the risk of damage to the microemulsion structure during the demolding stage when preparing the cathode catalyst layer.

[0048] In one embodiment, the shape of the cathode transfer template described in this disclosure can be made into a circle, a square, or an irregular shape according to actual production needs. For example, when it is desired to prepare a square catalyst layer, the shape of the cathode transfer template can be made into a square shape.

[0049] In one embodiment, the thickness of the cathode transfer template is 0.5-2.0 mm.

[0050] In some embodiments, the thickness of the cathode transfer template can be any value within the range of any one or any two of 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, and 1.9mm. In this embodiment, using a cathode transfer template of suitable thickness ensures the strength of the template, preventing cracks and breakage during subsequent hot pressing, and also provides good thermal conductivity.

[0051] In some embodiments, the weight ratio of the polymer to the silicon oxide is any ratio within the range of any one or any two of 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, and 4.5:1.

[0052] In a preferred embodiment, the weight ratio of the polymer compound to the silicon oxide compound is (1-3):1.

[0053] In the above embodiments, when the ratio of the polymer compound to the silicon oxide compound is appropriate, a sufficient amount of nano-sized silica can be uniformly distributed in the cathode transfer template. Furthermore, ensuring a sufficient amount of nano-silica is distributed on the surface of the cathode transfer template not only guarantees the strength and toughness of the template but also improves the transfer effect and thermal conductivity, thereby further enhancing the performance of the catalyst layer. It should be noted that when the weight ratio of the polymer compound to the silicon oxide compound is less than 0.5, the cathode transfer template cannot form a film.

[0054] In one embodiment, the roughness Ra of the transfer surface of the cathode transfer template described in this disclosure is 10-100 nm.

[0055] In some embodiments, the roughness Ra of the cathode transfer template described in this disclosure is any value within the range formed by any one or any two of 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, and 95nm.

[0056] In a preferred embodiment, the roughness Ra of the transfer surface of the cathode transfer template is 20-80 nm.

[0057] In the above embodiments, roughness is mainly controlled by the surface wettability and surface energy generated by the contact between the synthesized polymer compound and the lotus leaf imprint; the smaller the wetting contact angle, the better the wetting. When the roughness Ra is suitable, the cathode catalyst slurry can have good wettability with the cathode transfer template, achieving a better transfer effect. In addition, when the roughness Ra is suitable, the surface area of ​​the prepared catalyst layer can also be increased, further improving the battery performance.

[0058] A second aspect of this disclosure provides a method for preparing the cathode transfer template described in the first aspect, the method comprising: The polymer compound, initiator / crosslinking aid, silicon oxide compound and solvent are mixed and stirred to obtain a cathode transfer template mixture; the weight ratio of the polymer compound and silicon oxide compound is (0.5-5):1; The cathode transfer template mixture is applied to the surface of a lotus leaf containing micro-papillary structures to obtain a cathode transfer template.

[0059] Through the above technical solution, the cathode transfer template prepared by the method disclosed herein can balance strength, toughness, and thermal conductivity, avoiding catalyst layer damage caused by cracking and fragmentation during the hot pressing process of the cathode transfer template, thereby improving fuel cell performance. Furthermore, using an appropriate ratio of polymeric compounds and silicon oxide compounds can improve the demolding effect during the molding process, reduce surface defects in the prepared catalyst layer, and further enhance fuel cell performance.

[0060] In one embodiment, the method further includes mixing the polymer compound, the initiator / crosslinking aid, and the solvent to form a polymer compound solution.

[0061] In this process, the polymer compound and a first solvent are first prepared into a polymer compound solution during the reaction. An initiator / crosslinking aid can be added directly, or the initiator / crosslinking aid and a second solvent can be prepared into an initiator / crosslinking aid solution before mixing. The methods and apparatus used to prepare the solution are conventional in the art, and this application does not impose special requirements. For example, a mechanical stirrer and / or ultrasonic treatment can be used. The specifications of the mechanical stirrer and the rotation speed of the stirring rod are selected according to the actual production volume, and the stirring time is 1-10 hours. The intensity of the ultrasonic treatment is selected according to the actual production situation, and the ultrasonic treatment time can be 1-2 hours.

[0062] In one embodiment, the polymeric compound described herein can be a monomer of a polymeric compound, a polymer with a low degree of polymerization, or a polymer with a high degree of polymerization.

[0063] In one embodiment, if the polymer compound is a homopolymer, the polymer compound may be a polymer monomer, which includes, but is not limited to, one or more of polystyrene monomer, polyvinyl alcohol monomer, carboxymethyl chitosan monomer, polymethyl methacrylate monomer, poly(p-styrene) monomer, polycarbonate monomer, polyethylene glycol monomer, polyacrylic acid monomer, and polytetrafluoroethylene monomer.

[0064] In one embodiment, if the polymer compound is a graft copolymer, the rigid backbone can be a rigid backbone monomer, which includes one or more of polystyrene monomer, polymethyl methacrylate monomer, polytetrafluoroethylene monomer, and poly(p-styrene) monomer; the high thermal conductivity side chain can be a high thermal conductivity side chain monomer, which includes one or more of polyvinyl alcohol monomer, carboxymethyl chitosan monomer, polycarbonate monomer, polyethylene glycol monomer, and polyacrylic acid monomer.

[0065] In one embodiment, the first solvent includes, but is not limited to, water and / or alcohol, as long as it can dissolve or disperse the polymer monomer therein.

[0066] In one embodiment, the initiator / crosslinking aid includes polydimethylsiloxane emulsion and / or benzoyl peroxide; the second solvent includes, but is not limited to, water and / or alcohol solvents.

[0067] In one embodiment, when the initiator / crosslinking aid is benzoyl peroxide, the content of the initiator / crosslinking aid in the initiator / crosslinking aid solution is 1-3% by weight; when the initiator / crosslinking aid is polydimethylsiloxane, the content of the initiator / crosslinking aid in the initiator / crosslinking aid solution is 1-30% by weight.

[0068] In one embodiment, the solid content of the polymer compound solution is 10-40% by weight. In this embodiment, the solid content of the polymer compound solution can be flexibly adjusted according to the type of polymer compound. For example, the solid content of the polymer compound solution can be any value within the range of any one or any two of 10% by weight, 15% by weight, 20% by weight, 25% by weight, 30% by weight, 35% by weight, and 40% by weight.

[0069] In one embodiment, the method further includes dispersing the silicon oxide compound in a third solvent to obtain a silicon oxide compound suspension.

[0070] In one embodiment, the silicon oxide compound comprises silicon dioxide; the third solvent comprises an alcohol.

[0071] In the above embodiments, the dispersion treatment can be a conventional choice in the art, as long as it enables the nano-sized silica to be dispersed in the alcohol; this application does not impose any special requirements. The nano-sized silica can be obtained by chemical methods.

[0072] In one embodiment, mixing and stirring the polymer compound solution and the silicon oxide compound suspension is also a conventional choice in the art. It should be noted that the mixing and stirring needs to uniformly disperse the silicon oxide compound in the polymer compound.

[0073] In the above embodiments, the alcohols described herein can be selected from C1-C5 alcohols, preferably ethanol.

[0074] In one embodiment, the weight ratio of the polymer compound, initiator / crosslinking aid, and silicon oxide compound in the cathode transfer template mixture is (0.5-5):(0.0001-0.015):1.

[0075] In a preferred embodiment, the weight ratio of the polymer compound, initiator / crosslinking aid, and silicon oxide compound in the cathode transfer template mixture is (1-3):(0.0004-0.012):1.

[0076] In this embodiment, since the initiator / crosslinking aid only plays an auxiliary role in the initial stage of the polymerization reaction, and is present in very small amounts compared to the polymer and silicon oxide compounds, the weight of the initiator / crosslinking aid is usually ignored when calculating the weight ratio of polymer and silicon oxide compounds in the cathode transfer template. When the weight ratio of polymer, initiator / crosslinking aid, and silicon oxide compounds in the cathode transfer template mixture is appropriate, the resulting cathode transfer template can balance strength, toughness, and thermal conductivity. This not only avoids cracking and breakage during hot pressing using the cathode transfer template, but also reduces the hot pressing process time and improves the hot pressing effect.

[0077] In one embodiment, the solid content of the cathode transfer template mixture is 30-70% by weight. Preferably, the solid content of the cathode transfer template mixture can be any solid content within the range of any one or any two of 35% by weight, 40% by weight, 45% by weight, 50% by weight, 55% by weight, 60% by weight, and 65% by weight. In this embodiment, the cathode transfer template mixture with a suitable solid content has good fluidity and wettability on the lotus leaf surface, thereby improving the imprinting effect and better imprinting the micropapillary structure on the lotus leaf surface.

[0078] In some embodiments, the lotus leaves used in this disclosure are clean, flat, and freshly dried lotus leaves prepared in advance.

[0079] In one embodiment, the method further includes applying the cathode transfer template mixture onto the surface of a lotus leaf and then drying it at a temperature below 80°C. The drying time is adjusted according to the liquid content in the cathode transfer template mixture, as long as it is sufficiently dried. After drying, the lotus leaf is peeled off to obtain the cathode transfer template.

[0080] In one embodiment, the method for preparing a cathode transfer template includes: The polymer compound and the first solution are mixed to obtain a polymer compound solution; Mix the initiator / crosslinking aid and the second solution to obtain an initiator / crosslinking aid solution; The polymer compound solution and the initiator / crosslinking aid solution are subjected to mechanical stirring and ultrasonic treatment in sequence to obtain a polymer compound solution with a solid content of 10-40% by weight; wherein the stirring time of the mechanical stirrer is 1-10h and the ultrasonic treatment time is 1-2h. The silicon oxide compound is dispersed in a third solution, and then added to a polymer compound solution to obtain a cathode transfer template mixture with a solid content of 30-70% by weight, wherein the weight ratio of polymer compound to silicon oxide compound in the cathode transfer template mixture is (0.5-5):1; Take a clean, flat, and air-dried fresh lotus leaf, fix it on the vacuum adsorption platform of a tabletop doctor blade coater, adjust the doctor blade height, and apply the cathode transfer template mixture to the surface of the lotus leaf containing micro-papillary structures. Then dry it at a temperature below 80°C until the cathode transfer template mixture is completely dry, and then peel off the lotus leaf to obtain the cathode transfer template.

[0081] A third aspect of this disclosure provides a method for preparing a fuel cell membrane electrode, the method comprising: A cathode catalyst slurry is coated onto the surface of the cathode transfer template described in the first aspect, thereby obtaining a cathode catalyst layer on the surface of the cathode transfer template. A proton exchange membrane and an anode catalyst layer are sequentially stacked on the surface of the cathode catalyst layer and subjected to hot-press transfer processing. Then, the cathode transfer template is removed to obtain the fuel cell membrane electrode.

[0082] Through the above technical solution, the surface of the cathode catalyst layer prepared by the cathode transfer template prepared in the first aspect has a micro-papillary structure similar to the surface of a lotus leaf. This not only increases the contact area between oxygen and the surface of the catalyst layer and accelerates the reaction rate, but also improves the hydrophobicity of the catalyst layer surface and avoids water flooding.

[0083] In one embodiment, the cathode catalyst slurry comprises a platinum-carbon catalyst and a Nafion solution; wherein the platinum content in the platinum-carbon catalyst is 30-70% by weight; and the Nafion content in the Nafion solution is 5-20% by weight. In this embodiment, the Nafion solution refers to a perfluorosulfonic acid resin solution conventional in the art.

[0084] In one embodiment, the solid content of the cathode catalyst slurry is 5-20% by weight, preferably 8-15% by weight. In this embodiment, when the solid content of the cathode catalyst slurry is appropriate, during the hot pressing process, the transfer micropores of the cathode transfer template can be filled with the cathode catalyst slurry, forming more microemulsion structures, thereby increasing the surface area and hydrophobicity of the cathode catalyst layer.

[0085] In one embodiment, the thickness of the cathode catalyst slurry coated on the cathode transfer template can be flexibly set according to actual production needs. For example, in this disclosure, the cathode catalyst slurry coated on the transfer surface of the cathode transfer template is 0.5-2 mm.

[0086] In one embodiment, the temperature of the hot press transfer process is 80-200℃, the pressure is 5-50MPa, and the time is 0.5-10min.

[0087] In one embodiment, the static water contact angle on the surface of the cathode catalyst layer described in this disclosure is above 125°.

[0088] In some embodiments, the static water contact angle of the cathode catalyst layer surface described in this disclosure is any contact angle within the range formed by any one or any two of 130°, 140°, 145°, 150°, 155°, 160°, 165°, 170° and 175°.

[0089] The present invention will be illustrated by the following examples, which are illustrative and should not be construed as limiting the scope of the invention.

[0090] Preparation Example 1 Mix 2.5g of polyvinyl alcohol and 20mL of ethanol until the polyvinyl alcohol dissolves, then add 2mL of 1% benzoyl peroxide solution. The mixture is then subjected to mechanical stirring and ultrasonic treatment in sequence to obtain 20mL of a polymer compound solution with a solid content of 13% by weight. The mechanical stirring time is 2h, and the ultrasonic treatment time can be 1.5h. 2.5g of silica with an average particle size of 10nm was dispersed in ethanol and then added to a polymer compound solution. The mixture was stirred thoroughly to obtain a cathode transfer template mixture with a solid content of 30% by weight. The weight ratio of polymer compound, initiator / crosslinking aid and silica compound in the cathode transfer template mixture was 1:0.0004:1. Clean, flat, and air-dried fresh lotus leaves were prepared beforehand and fixed on the vacuum adsorption platform of a tabletop doctor blade coater. The doctor blade height was adjusted to 3 mm, allowing the cathode transfer template mixture to be applied to the surface of the lotus leaf containing micropapillary structures. The leaves were then dried at 80°C for 24 hours until the cathode transfer template mixture was completely dry. After drying, the lotus leaves were removed to obtain the cathode transfer template S1. The density of the micropapillary structures on the surface of the fresh lotus leaf was 1800±200 per square millimeter, with an average diameter of 90 μm and an average height of 100 μm.

[0091] The parameters of the obtained cathode transfer template are shown in Table 1.

[0092] Preparation Example 2 The method for preparing the cathode transfer template S2 is the same as in Example 1, except that the amount of polyvinyl alcohol added is 7.5 g, and the concentration of the benzoyl peroxide solution is 3% by weight. The weight ratio of the polymer compound, initiator / crosslinking aid, and silicon oxide compound in the cathode transfer template mixture was 3:0.012:1. The parameters of the obtained cathode transfer template are shown in Table 1.

[0093] Preparation Example 3 The method for preparing the cathode transfer template S3 is the same as in Example 1, except that 2.5g of polystyrene is used instead of 2.5g of polyvinyl alcohol. The parameters of the obtained cathode transfer template are shown in Table 1.

[0094] Preparation Example 4 The method for preparing the cathode transfer template S4 is the same as in Example 1, except that 2.5g of polystyrene (2g) and polyvinyl alcohol (0.5g) are used instead of polyvinyl alcohol. The parameters of the obtained cathode transfer template are shown in Table 1.

[0095] Preparation of Comparative Example 1 The method for preparing the cathode transfer template D1 is the same as in Example 1, except that no silicon dioxide is added during the preparation of the cathode transfer template D1. The parameters of the obtained cathode transfer template are shown in Table 1.

[0096] Preparation of Comparative Example 2 The method for preparing the cathode transfer template D2 is the same as in Example 1, except that the amount of silicon dioxide added is 0.25 g, and the weight ratio of the polymer compound to the silicon oxide compound is 10:1. The parameters of the obtained cathode transfer template are shown in Table 1.

[0097] Preparation of Comparative Example 3 The method for preparing the cathode transfer template D3 is the same as in Example 1, except that it is not molded with a lotus leaf. The parameters of the obtained cathode transfer template are shown in Table 1.

[0098] Preparation of Comparative Example 4 The method for preparing the cathode transfer template D4 is the same as that in Example 1, except that a cathode transfer template mixture with a solid content of 80% by weight is obtained. The parameters of the obtained cathode transfer template are shown in Table 1.

[0099] Preparation of Comparative Example 5 The method for preparing the cathode transfer template D5 is the same as in Example 1, except that the height of the scraper is adjusted by 1 mm, resulting in a cathode transfer template thickness of 0.4 mm. The parameters of the obtained cathode transfer template are shown in Table 1.

[0100] Test case The surface roughness Ra and the average depth of the transfer micropores were determined using a conventional 3D profilometer in the art; the density and average diameter of the transfer micropores were measured using a conventional scanning electron microscope (SEM) in the art; the density, average diameter, and average depth of the transfer micropores are actually average values, and the testing method is the same as the measurement method used when screening lotus leaves; specifically, 10 observation areas of 0.1 mm × 0.1 mm were randomly selected on the cathode transfer template, and after obtaining 10 sets of density, 10 sets of diameter, and 10 sets of depth statistics, the average values ​​of the 10 sets of density, 10 sets of diameter, and 10 sets of depth were calculated respectively.

[0101] The thermal conductivity of the cathode transfer template is measured using the fixed steady-state hot plate method. The thermal conductivity is affected by the thickness and material of the cathode transfer template. Different materials of cathode transfer templates have different thermal conductivity, and the greater the thickness, the smaller the thermal conductivity.

[0102] The thickness of the cathode transfer template was measured using an optical microscope.

[0103] Table 1 Parameters of the cathode transfer template

[0104] Since the weight of the initiator / crosslinking aid is very small compared to that of the polymer and silicon oxide compounds, the weight ratio of polymer to silicon oxide compounds in the table can be calculated based on the weight of the polymer. As shown in Table 1, a comparison of the data from Preparation Examples 1-4 and Preparation Comparative Examples 1-2 shows that when the weight ratio of the polymer compound to the silicon oxide compound is (0.5-5):1, the wettability of the cathode transfer template mixture can be improved, ensuring that the density, average diameter, average depth, and surface roughness of the transfer micropores on the cathode transfer template are within acceptable ranges.

[0105] Comparing the data from Preparation Example 1 and Preparation Example 2, it can be seen that the silica content in the cathode transfer template S2 is low, and the wettability of the mixture of cathode transfer template S2 and cathode transfer template S1 is poor. Therefore, the density and surface roughness of cathode transfer template S2 are lower than those of cathode transfer template S1.

[0106] Comparing the data from Preparation Example 1, Preparation Example 2, Comparative Example 5, and Preparation Example 4, even though the thicknesses of cathode transfer templates S1 and S2 are smaller than that of S4, their thermal conductivity is still smaller. This indicates that, compared to homopolymers, graft copolymers can significantly improve the thermal conductivity of cathode transfer templates while ensuring transfer effectiveness. Comparing the data from Preparation Example 1, Comparative Example 4, and Comparative Example 5, it is evident that using a cathode transfer template mixture with an appropriate solid content can maintain the thickness of the cathode transfer template at 0.5-2 μm, thus balancing the strength and thermal conductivity of the cathode transfer template.

[0107] Examples 1-4 Methods for preparing fuel cell membrane electrodes include: Cathode transfer templates S1~S4 were cut into 100mm×100mm sizes and adsorbed onto the doctor blade coating in reverse. The doctor blade distance was adjusted to coat the cathode catalyst slurry on the surface of the cathode transfer templates S1~S4. The slurry was then dried at 110℃ and finally cooled to obtain a cathode catalyst layer with a thickness of 2mm. A proton exchange membrane and an anode catalyst layer are sequentially stacked on the surface of the cathode catalyst layer and subjected to hot-press transfer processing. After cooling, the cathode transfer template is removed, and finally, the membrane electrode assembly is performed according to conventional procedures to obtain a fuel cell membrane electrode assembly (CCMS1~CCMS4). The cathode catalyst loading is 0.4 mg / cm³. 2 The cathode active area is 7cm × 7cm, and the anode catalyst loading is 0.1mg / cm². 2 .

[0108] The parameters of the obtained cathode catalyst layer and fuel cell membrane electrode are shown in Table 2.

[0109] Comparative Examples 1-5 The method for preparing the fuel cell membrane electrode is the same as in Examples 1-9, except that cathode transfer templates D1-D5 are used to obtain fuel cell membrane electrodes CCMD1-CCMD5. The parameters of the obtained cathode catalyst layer and fuel cell membrane electrode are shown in Table 2.

[0110] Test case The surface morphology of the cathode catalyst layer was observed using scanning electron microscopy. The microscopic image of the surface morphology of the cathode catalyst layer in Example 1 is shown below. Figure 1 As shown in the figure, the surface of the cathode catalyst layer has a stable micropapillary structure.

[0111] The surface morphology of the cathode catalyst layer in Comparative Example 1 is as follows: Figure 2 As shown in the figure, the cathode catalyst layer surface has near-circular spots and obvious cracks. These near-circular spots are traces formed after the micro-papillary structures on the cathode catalyst layer surface are flattened. Because CCMD1 requires a graphite structure to clamp the cathode catalyst layer during testing, the cathode transfer template D1 of this application has poor thermal conductivity. The cathode catalyst layer surface structure obtained after hot pressing is relatively soft. After testing, the formed micro-papillary structures are flattened, resulting in near-circular spots. Furthermore, the cracks on the cathode catalyst layer surface are due to the absence of silica in the cathode transfer template D1 during hot pressing, resulting in poor strength and toughness. Under the action of the pressure components, the cathode transfer template D1 cracks or warps, leading to cracks on the cathode catalyst layer surface.

[0112] The surface morphology of the cathode catalyst layer in Comparative Example 3 is as follows: Figure 3As shown in the figure, the cathode catalyst layer has a smooth and flat surface without micro-papillary structures and cracks. This is because the cathode catalyst layer was prepared using a cathode transfer template D3, which was not subjected to a molding process with a lotus leaf, resulting in a smooth and flat surface. Furthermore, the cathode transfer template D3 has a suitable weight ratio of polymer to silica, exhibiting good strength, toughness, and thermal conductivity, preventing crack formation on the cathode catalyst layer surface after hot pressing.

[0113] The contact angles between the cathode catalyst layers obtained in Examples 1-4 and Comparative Examples 1-5 and water were measured using the method of GB / T 30693-2014.

[0114] The fuel cell membrane electrodes CCMS1-CCMS4 obtained in Examples 1-4 and CCMD1-CCMD5 obtained in Comparative Examples 1-5 were subjected to an A / cm ratio of 2A / cm. 2 The battery generates electricity at a current density during this period. The output voltage of the membrane electrode is monitored, and the output voltage reflects the drainage performance. The lower the output voltage, the less water generated in the cathode catalyst layer is discharged in time, resulting in some areas where gas cannot contact the catalyst, thus indicating poor drainage performance. The measurement conditions include: temperature 75℃, P=170 / 160Kpa, ST=1.5 / 2.0.

[0115] Table 2 Parameters of hot pressing transfer treatment and cathode catalyst layer

[0116] As shown in Table 2, a comparison of the data from Examples 1-4 and Comparative Examples 1-2 reveals that the cathode transfer template prepared using the method of this disclosure balances strength and toughness, avoiding damage to the cathode catalyst layer caused by cracking, breakage, or warping of the cathode transfer template during hot pressing. Furthermore, the cathode catalyst layer prepared using the cathode transfer template of this disclosure exhibits good drainage properties, reducing the risk of water flooding of the cathode catalyst layer under high-power operating conditions.

[0117] A comparison of the data from Examples 1-4 and Comparative Example 3 shows that the cathode transfer template disclosed herein can provide a certain degree of tolerance for the hot pressing process, avoiding the problems of high gas transmission resistance and easy water flooding caused by excessive compaction of the cathode catalyst layer.

[0118] A comparison of the data from Examples 1 and 4 shows that using a cathode transfer template with good thermal conductivity can reduce the time required for hot pressing transfer processing.

[0119] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0120] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0121] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A cathode transfer template, characterized in that, The material of the cathode transfer template includes a polymer compound and a silicon oxide compound dispersed in the polymer compound; The weight ratio of the polymer compound to the silicon oxide compound is (0.5-5):

1.

2. The cathode transfer template according to claim 1, characterized in that, The polymer compound is a homopolymer compound; The homopolymer compound includes one or more of polystyrene, polyvinyl alcohol, carboxymethyl chitosan, polymethyl methacrylate, poly(p-phenylene terephthalate), polycarbonate, polyethylene glycol, polyacrylic acid, and polytetrafluoroethylene.

3. The cathode transfer template according to claim 1, characterized in that, The polymer compound is a graft copolymer; The graft copolymer comprises a rigid backbone and highly thermally conductive side chains; The rigid backbone includes one or more of the following: polystyrene backbone, polymethyl methacrylate backbone, polytetrafluoroethylene backbone, and poly(p-styrene) backbone. The high thermal conductivity side chains include one or more of the following: polyvinyl alcohol side chains, carboxymethyl chitosan side chains, polycarbonate side chains, polyethylene glycol side chains, and polyacrylic acid side chains.

4. The cathode transfer template according to claim 1, characterized in that, The silicon oxide compound includes silicon dioxide; the average particle size of the silicon oxide compound is 5-100 nm.

5. The cathode transfer template according to claim 1, characterized in that, The transfer surface of the cathode transfer template includes multiple transfer micropores; the density of the transfer micropores is 500-2000 per square millimeter, the average diameter of the transfer micropores is 40-100 μm, and the average depth of the transfer micropores is 20-100 μm.

6. The cathode transfer template according to claim 1, characterized in that, The surface roughness Ra of the cathode transfer template is 10-100 nm.

7. The cathode transfer template according to claim 1, characterized in that, The cathode transfer template is square in shape; The thickness of the cathode transfer template is 0.5-2.0 mm.

8. A method for preparing a cathode transfer template according to any one of claims 1-7, characterized in that, The method includes: The polymer compound, initiator / crosslinking aid, silicon oxide compound and solvent are mixed and stirred to obtain a cathode transfer template mixture; the weight ratio of the polymer compound and silicon oxide compound is (0.5-5):1; The cathode transfer template mixture is applied to the surface of a lotus leaf containing micro-papillary structures to obtain a cathode transfer template.

9. The method according to claim 8, characterized in that, The initiator / crosslinking aid includes polydimethylsiloxane and / or benzoyl peroxide; The solvent includes alcohol and / or water; The solid content of the cathode transfer template mixture is 30-70% by weight.

10. A method for preparing a fuel cell membrane electrode, characterized in that, The method includes: A cathode catalyst slurry is scraped onto the surface of the cathode transfer template according to any one of claims 1-7, thereby obtaining a cathode catalyst layer on the surface of the cathode transfer template; A proton exchange membrane and an anode catalyst layer are sequentially stacked on the surface of the cathode catalyst layer and subjected to hot-press transfer processing. Then, the cathode transfer template is removed to obtain the fuel cell membrane electrode.

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