A membrane electrode, its preparation method and use

Abstract

This application belongs to the field of fuel cell technology, specifically relating to a membrane electrode assembly (MEA), its preparation method, and its application. The MEA of this application includes a proton exchange membrane, a cathode catalyst layer, and an anode catalyst layer disposed on both sides of the proton exchange membrane. The cathode catalyst layer, from the inside out, includes an inner cathode layer, a middle cathode layer, and an outer cathode layer. The anode catalyst layer, from the inside out, includes an inner anode layer and an outer anode layer. Both the inner cathode layer and the inner anode layer include a first platinum-carbon supported catalyst and a first ionomer. The middle cathode layer includes an alloy carbon supported catalyst and a second ionomer. Both the outer cathode layer and the outer anode layer include a second platinum-carbon supported catalyst, a third ionomer, and a conductive agent. The EW value of the ionomer gradually increases from the inner to the outer layers of the cathode and anode catalyst layers. The beneficial effects of this application include: the MEA of this application has high proton conductivity and hydrophilic / hydrophobic properties, while also possessing the advantages of high performance, long lifespan, and low cost.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, specifically relating to a membrane electrode, its preparation method, and its application. Background Technology

[0002] Currently, the industrialization of fuel cells still faces challenges such as high cost and short lifespan. Improving fuel cell performance and reducing system costs can be achieved through two main approaches: one is from the perspective of catalyst activity, reducing the amount of precious metal Pt used and improving catalyst activity and stability by changing the support and preparing alloy catalysts. The other is from the perspective of membrane electrode and catalyst layer structure design, improving fuel cell performance by exploring new membrane electrode preparation methods and processes.

[0003] Existing technologies disclose membrane electrodes containing multiple catalytic layers. These electrodes include a non-alloy catalyst layer and an alloy catalyst layer. The alloy catalyst layer, containing contaminants, is positioned away from the proton exchange membrane and close to the gas diffusion layer to mitigate contamination of the proton exchange membrane by transition metal leaching. However, the low platinum content in the non-alloy catalyst layer can affect the durability and performance of the membrane electrode. Existing technologies also disclose membrane electrodes with a cathode catalytic layer comprising a stacked hydrophilic catalytic layer and a hydrophobic catalytic layer. The hydrophilic catalytic layer is located between the proton exchange membrane and the hydrophobic catalytic layer, and both layers comprise hydrophilic and hydrophobic carbon nanofibers. These membrane electrodes can maintain good hydration of the perfluorosulfonic acid polymer under low-current discharge and quickly drain water to prevent cathode flooding under high-current discharge, while also maintaining good conductivity of the proton exchange membrane. However, this hydrophobic catalytic layer is obtained by adding pretreated carbon nanofibers to the slurry, involving multiple steps in the preparation process. Furthermore, introducing other components into the catalytic layer may poison the catalyst, thus affecting its activity. Therefore, designing a high-performance, long-life, and low-cost membrane electrode is currently quite challenging. Summary of the Invention

[0004] This application provides a membrane electrode, its preparation method, and its application, aiming to solve the problems of short lifespan, poor performance, and high manufacturing cost of existing membrane electrodes.

[0005] The first aspect of this application provides a membrane electrode, including a proton exchange membrane, a cathode catalyst layer and an anode catalyst layer disposed on both sides of the proton exchange membrane;

[0006] The cathode catalyst layer comprises, from the inside out, an inner cathode layer, a middle cathode layer, and an outer cathode layer;

[0007] The anode catalyst layer comprises, from the inside out, an inner anode layer and an outer anode layer;

[0008] Both the inner cathode layer and the inner anode layer comprise a first platinum-carbon supported catalyst and a first ionomer;

[0009] The cathode intermediate layer comprises an alloy carbon-supported catalyst and a second ionomer;

[0010] Both the outer cathode layer and the outer anode layer comprise a second platinum-carbon supported catalyst, a third ionomer, and a conductive agent.

[0011] From the inner to the outer layers of the cathode catalyst layer and the anode catalyst layer, the EW value of the ionomer gradually increases.

[0012] The cathode and anode catalytic layers of the membrane electrode described in this application both have multilayer structures, and the EW values ​​of the ionomers contained in the cathode and anode catalytic layers gradually increase. This gradient-designed catalytic layer structure gives it high proton conductivity and hydrophilic / hydrophobic properties, while also taking into account the advantages of high performance, long lifespan, and low cost.

[0013] According to some embodiments of the membrane electrode described in this application, the platinum loading on the cathode catalyst layer is 0.3 mg per square centimeter.

[0014] According to some embodiments of the membrane electrode described in this application, the platinum loading on the inner layer of the cathode catalyst layer is 0.01-0.1 mg per square centimeter.

[0015] According to some embodiments of the membrane electrode described in this application, the platinum loading on the intermediate layer of the cathode catalytic layer is 0.1-0.3 mg per square centimeter.

[0016] According to some embodiments of the membrane electrode described in this application, the platinum loading on the outer layer of the cathode catalyst layer is 0.01-0.1 mg per square centimeter.

[0017] According to some embodiments of the membrane electrode described in this application, the platinum loading on the anode catalyst layer is 0.1 mg per square centimeter.

[0018] According to some embodiments of the membrane electrode described in this application, the platinum loading on the inner layer of the anode catalyst layer is 0.01-0.1 mg per square centimeter.

[0019] According to some embodiments of the membrane electrode described in this application, the platinum loading on the outer layer of the anode catalyst layer is 0.01-0.1 mg per square centimeter.

[0020] According to some embodiments of the membrane electrode described in this application, the first ionomer, the second ionomer, and the third ionomer are each independently selected from one or more of perfluorosulfonic acid resin, sulfonated polyarylene ether sulfone, sulfonated polyarylene (sulfur) ether, sulfonated polyether ether ketone, sulfonated polyimide, and polybenzimidazole.

[0021] According to some embodiments of the membrane electrode described in this application, the mass percentage of platinum in the first platinum-carbon supported catalyst is 30%-50%.

[0022] According to some embodiments of the membrane electrode described in this application, the mass ratio of carbon in the first ionomer and the first platinum-carbon supported catalyst is (0.9-1.1):1.

[0023] According to some embodiments of the membrane electrode described in this application, the EW value of the first ionomer is 700-750 g / mol.

[0024] According to some embodiments of the membrane electrode described in this application, the alloy carbon support catalyst includes one or more of platinum-cobalt alloy carbon support catalyst, platinum-nickel alloy carbon support, and platinum-ruthenium alloy carbon support.

[0025] According to some embodiments of the membrane electrode described in this application, the platinum mass percentage in the alloy carbon support catalyst is 50%-60%.

[0026] According to some embodiments of the membrane electrode described in this application, the mass ratio of carbon in the second ionomer and the alloy carbon support catalyst is (0.8-0.9):1.

[0027] According to some embodiments of the membrane electrode described in this application, the EW value of the second ionomer is 750-800 g / mol.

[0028] According to some embodiments of the membrane electrode described in this application, the mass percentage of platinum in the second platinum carbonaceous catalyst is 60%-70%.

[0029] According to some embodiments of the membrane electrode described in this application, the mass ratio of carbon in the third ionomer and the second platinum-carbon supported catalyst is (0.6-0.8):1.

[0030] According to some embodiments of the membrane electrode described in this application, the mass ratio of the second platinum-carbon supported catalyst to the conductive agent is (10-20):1.

[0031] According to some embodiments of the membrane electrode described in this application, the EW value of the third ionomer is 800-900 g / mol.

[0032] According to some embodiments of the membrane electrode described in this application, the conductive agent includes one or more of Ketjen black, single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

[0033] A second aspect of this application provides a method for preparing the membrane electrode described in the first aspect of this application, comprising the following steps:

[0034] (1) Preparation of inner layer slurry: The first platinum carbon support catalyst, the first ionomer and the first solvent are mixed and subjected to a first sealed ball milling to obtain the inner layer slurry;

[0035] (2) Preparation of intermediate layer slurry: The alloy carbon support catalyst, the second ionomer and the second solvent are mixed and subjected to a second sealed ball milling to obtain intermediate layer slurry;

[0036] (3) Preparation of outer layer slurry: The second platinum carbon support catalyst, the third ionomer and the third solvent are mixed and subjected to a third sealed ball milling to obtain the outer layer slurry;

[0037] (4) The outer layer slurry, the middle layer slurry and the inner layer slurry are sequentially applied to the substrate to obtain a cathode coating; the outer layer slurry and the inner layer slurry are sequentially applied to the substrate to obtain an anode coating;

[0038] (5) The cathode coating and the anode coating are transferred to both sides of the proton exchange membrane by hot pressing transfer to form a cathode catalyst layer and an anode catalyst layer.

[0039] According to some embodiments of the preparation method described in this application, the first solvent includes one or more of ethanol, isopropanol, n-propanol, ethylene glycol, and glycerol.

[0040] According to some embodiments of the preparation method described in this application, the first grinding ball used in the first sealed ball mill includes zirconium oxide.

[0041] According to some embodiments of the preparation method described in this application, the temperature of the first sealed ball mill is 20-30°C, and the time of the first sealed ball mill is 2-8 hours.

[0042] According to some embodiments of the preparation method described in this application, the second solvent includes one or more of ethanol, isopropanol, n-propanol, ethylene glycol, and glycerol.

[0043] According to some embodiments of the preparation method described in this application, the second grinding ball used in the second sealing ball mill includes zirconium oxide.

[0044] According to some embodiments of the preparation method described in this application, the temperature of the second sealed ball mill is 20-30°C, and the time of the second sealed ball mill is 2-8 hours.

[0045] According to some embodiments of the preparation method described in this application, the third solvent includes one or more of ethanol, isopropanol, n-propanol, ethylene glycol, and glycerol.

[0046] According to some embodiments of the preparation method described in this application, the third milling ball used in the third sealing mill includes zirconium oxide.

[0047] According to some embodiments of the preparation method described in this application, the temperature of the third sealed ball mill is 20-30°C, and the time of the third sealed ball mill is 2-8 hours.

[0048] According to some embodiments of the preparation method described in this application, the substrate includes a polytetrafluoroethylene film.

[0049] According to some embodiments of the preparation method described in this application, the temperature of the hot pressing transfer is 140-180℃, and the pressure of the hot pressing transfer is 20-30 kg / cm². 2 .

[0050] According to some embodiments of the preparation method described in this application, the proton exchange membrane includes a tetrafluoroethylene-reinforced composite perfluorosulfonic acid proton exchange membrane.

[0051] In a third aspect, this application provides a fuel cell comprising the membrane electrode described in the first aspect of this application or the membrane electrode obtained by the preparation method described in the second aspect of this application. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the catalytic layer structure of the membrane electrode described in this application;

[0053] Figure 2 This refers to the contact angle between the outer cathode coating and water in Embodiment 1 of this application.

[0054] Figure 3 The contact angle between the cathode intermediate layer coating and water in Embodiment 1 of this application;

[0055] Figure 4 This refers to the contact angle between the cathode inner coating and water in Embodiment 1 of this application.

[0056] Figure 5 The battery performance of the membrane electrodes described in Examples 1-2 and Comparative Examples 1-4 of this application. Detailed Implementation

[0057] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0058] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0059] This application provides a membrane electrode, including a proton exchange membrane, a cathode catalytic layer and an anode catalytic layer disposed on both sides of the proton exchange membrane;

[0060] The cathode catalyst layer comprises, from the inside out, an inner cathode layer, a middle cathode layer, and an outer cathode layer;

[0061] The anode catalyst layer comprises, from the inside out, an inner anode layer and an outer anode layer;

[0062] Both the inner cathode layer and the inner anode layer comprise a first platinum-carbon supported catalyst and a first ionomer.

[0063] The cathode intermediate layer comprises an alloy carbon-supported catalyst and a second ionomer;

[0064] Both the outer layer of the cathode and the outer layer of the anode include a second platinum-carbon supported catalyst and a third ionomer conductive agent.

[0065] From the inner to the outer layers of the cathode catalyst layer and the anode catalyst layer, the EW value of the ionomer gradually increases.

[0066] The cathode and anode catalytic layers of the membrane electrode described in this application both have multilayer structures, and the EW values ​​of the ionomers contained in the cathode and anode catalytic layers gradually increase. This gradient-designed catalytic layer structure gives it high proton conductivity and hydrophilic / hydrophobic properties, while also taking into account the advantages of high performance, long lifespan, and low cost.

[0067] In the multilayer catalytic layer structure described in this application, the inner catalytic layer adopts a platinum carbon support catalyst with medium platinum mass and a high I / C ratio (I refers to the dry weight of the resin in the ionomer solution and C refers to the mass of the carbon support in the catalyst), which effectively improves the proton conductivity and low electrical density water retention. Placing the alloy layer between the two platinum carbon catalytic layers alleviates the contamination of the proton membrane by the dissolution of alloy transition metal elements.

[0068] The outermost catalytic layer of the anode and cathode uses a high-platinum-quality platinum-carbon supported catalyst and a high-EW-value ionomer. On the one hand, it provides more active sites and improves the reaction rate. On the other hand, the low I / C and high-EW-value ionomer facilitates the discharge of high-electric-density product water and permeate water. In addition, conductive and hydrophobic carbon fibers are incorporated into the outer catalytic layer to improve the conductivity and hydrophobicity of the catalytic layer. In summary, the structural design is conducive to improving the performance and durability of the membrane electrode.

[0069] In some embodiments of this application, the platinum loading on the cathode catalyst layer is 0.3 mg per square centimeter;

[0070] In some embodiments of this application, the platinum loading on the inner layer of the cathode catalyst layer per square centimeter is 0.01-0.1 mg, for example 0.01 mg, 0.05 mg, 0.08 mg, 0.1 mg, etc.

[0071] In some embodiments of this application, the platinum loading on the intermediate layer of the cathode catalyst layer per square centimeter is 0.1-0.3 mg, for example 0.1 mg, 0.15 mg, 0.2 mg, 0.22 mg, 0.28 mg, 0.3 mg, etc.

[0072] In some embodiments of this application, the platinum loading on the outer layer of the cathode catalyst layer per square centimeter is 0.01-0.1 mg, for example 0.01 mg, 0.05 mg, 0.08 mg, 0.1 mg, etc.

[0073] In some embodiments of this application, the platinum loading on the anode catalyst layer is 0.1 mg per square centimeter.

[0074] In some embodiments of this application, the platinum loading on the inner layer of the anode catalyst layer per square centimeter is 0.01-0.1 mg, for example 0.01 mg, 0.05 mg, 0.08 mg, 0.1 mg, etc.

[0075] In some embodiments of this application, the platinum loading on the outer layer of the anode catalyst layer is 0.01-0.1 mg per square centimeter, for example, 0.01 mg, 0.05 mg, 0.08 mg, 0.1 mg, etc.

[0076] In some embodiments of this application, the first ionomer, the second ionomer, and the third ionomer are each independently selected from one or more of perfluorosulfonic acid resins, sulfonated polyarylene ether sulfones, sulfonated polyarylene (sulfur) ethers, sulfonated polyether ether ketones, sulfonated polyimides, and polybenzimidazoles.

[0077] In some embodiments of this application, the mass percentage of platinum in the first platinum-carbon supported catalyst is 30%-50%, such as 30%, 35%, 38%, 40%, 43%, 49%, 50%, etc.

[0078] In some embodiments of this application, the mass ratio of carbon in the first ionomer and the first platinum-carbon supported catalyst is (0.9-1.1):1, for example, 0.9:1, 1:1, 1.1:1, etc.

[0079] In some embodiments of this application, the EW value of the first ionomer is 700-750 g / mol.

[0080] In some embodiments of this application, the alloy carbon support catalyst includes one or more of platinum-cobalt alloy carbon support catalyst, platinum-nickel alloy carbon support catalyst, and platinum-ruthenium alloy carbon support, with platinum-cobalt alloy carbon support catalyst being preferred.

[0081] In some embodiments of this application, the platinum mass percentage in the alloy carbon support catalyst is 50%-60%, such as 50%, 53%, 55%, 58%, 60%, etc.

[0082] In some embodiments of this application, the mass ratio of carbon in the second ionomer and the alloy carbon support catalyst is (0.8-0.9):1, for example, 0.8:1, 0.85:1, 0.9:1, etc.

[0083] In some embodiments of this application, the EW value of the second ionomer is 750-800 g / mol.

[0084] In some embodiments of this application, the platinum mass percentage in the second platinum-carbon supported catalyst is 60%-70%, such as 60%, 63%, 65%, 68%, 70%, etc.

[0085] In some embodiments of this application, the mass ratio of carbon in the third ionomer and the second platinum carbon supported catalyst is (0.6-0.8):1, for example, 0.6:1, 0.7:1, 0.8:1, etc.

[0086] In some embodiments of this application, the mass ratio of the second platinum-carbon supported catalyst to the conductive agent is (10-20):1, for example, 10:1, 15:1, 20:1, etc.

[0087] In some embodiments of this application, the EW value of the third ionomer is 800-900 g / mol.

[0088] In some embodiments of this application, the conductive agent includes Ketjen black, single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanofibers, etc.

[0089] This application also provides a method for preparing a membrane electrode, comprising the following steps:

[0090] (1) Preparation of inner layer slurry: The first platinum carbon support catalyst, the first ionomer and the first solvent are mixed and subjected to a first sealed ball milling to obtain the inner layer slurry;

[0091] (2) Preparation of intermediate layer slurry: The alloy carbon support catalyst, the second ionomer and the second solvent are mixed and subjected to a second sealed ball milling to obtain intermediate layer slurry;

[0092] (3) Preparation of outer layer slurry: The second platinum carbon support catalyst, the third fully ionomer and the third solvent are mixed and subjected to a third sealed ball milling to obtain the outer layer slurry;

[0093] (4) The outer layer slurry, the middle layer slurry and the inner layer slurry are sequentially applied to the substrate to obtain a cathode coating; the outer layer slurry and the inner layer slurry are sequentially applied to the substrate to obtain an anode coating;

[0094] (5) The cathode coating and the anode coating are transferred to both sides of the proton exchange membrane by hot pressing transfer to form a cathode catalyst layer and an anode catalyst layer.

[0095] In some embodiments of this application, the first solvent includes one or more of ethanol, isopropanol, n-propanol, ethylene glycol, and glycerol.

[0096] In some embodiments of this application, the first sealed ball mill uses a zirconia ball mill jar, and the first grinding beads used include zirconia.

[0097] In some embodiments of this application, the ratio of the amount of the first grinding ball added to the total amount of material in the grinding jar is (5-3):1.

[0098] In some embodiments of this application, the temperature of the first sealed ball mill is 20-30°C, and the time of the first sealed ball mill is 2-8 hours.

[0099] In some embodiments of this application, the second solvent includes one or more of ethanol, isopropanol, n-propanol, ethylene glycol, and glycerol.

[0100] In some embodiments of this application, the second sealed ball mill uses a zirconia ball mill jar, and the second grinding beads include zirconia.

[0101] In some embodiments of this application, the ratio of the amount of the second grinding ball added to the total amount of material in the grinding jar is (5-3):1.

[0102] In some embodiments of this application, the temperature of the second sealed ball mill is 20-30°C, and the time of the second sealed ball mill is 2-8 hours.

[0103] In some embodiments of this application, the third solvent includes one or more of ethanol, isopropanol, n-propanol, ethylene glycol, and glycerol.

[0104] In some embodiments of this application, the third sealed ball mill uses a zirconia ball mill jar, and the third ball mill beads include zirconia.

[0105] In some embodiments of this application, the ratio of the amount of the third grinding ball added to the total amount of material in the grinding jar is (5-3):1.

[0106] In some embodiments of this application, the temperature of the third sealing ball mill is 20-30°C, and the time of the third sealing ball mill is 2-8 hours.

[0107] In some embodiments of this application, the substrate includes a polytetrafluoroethylene film.

[0108] In some embodiments of this application, the temperature of the hot pressing transfer is 140-180°C, and the pressure of the hot pressing transfer is 20-30 kg / cm². 2 .

[0109] In some embodiments of this application, the proton exchange membrane is a polytetrafluoroethylene-reinforced perfluorosulfonic acid proton exchange membrane with a thickness of 8-18 μm. The polytetrafluoroethylene-reinforced perfluorosulfonic acid proton exchange membrane described in this application was purchased from Gore, model number Gore M788.12.

[0110] This application also provides a fuel cell, including the membrane electrode described in the first aspect of this application or the membrane electrode obtained by the preparation method described in the second aspect of this application.

[0111] Example 1

[0112] A method for preparing a membrane electrode includes the following steps:

[0113] S1: Slurry for preparing the inner cathode layer and inner anode layer

[0114] Weigh out a platinum-carbon supported catalyst with a platinum content of 50% by mass. Weigh out ultrapure water and n-propanol at a mass ratio of 1:4. Weigh out a perfluorosulfonic acid resin solution with an I / C ratio of 1 (I refers to the dry weight of the resin in the perfluorosulfonic acid resin solution, and C refers to the mass of the carbon support in the catalyst). The solid content in the inner slurry is controlled at 8%. The EW value of the perfluorosulfonic acid resin is 720 g / mol, and the solid content of the perfluorosulfonic acid resin is 25%.

[0115] The weighed materials were added to the ball mill jar in the following order: platinum-carbon carrier catalyst, ultrapure water, n-propanol, and perfluorosulfonic acid resin. The platinum-carbon carrier catalyst was fully wetted with water before the n-propanol was added, and the perfluorosulfonic acid resin was added last. After mixing and stirring for 1 hour, zirconia grinding beads were added, with the mass ratio of grinding beads to the total material in the ball mill jar being 3:1. The jar was sealed and ball milled at 25°C for 4 hours. The grinding beads were then filtered out to obtain the inner slurry.

[0116] S2 Preparation of cathode intermediate layer slurry

[0117] Weigh out a platinum-cobalt alloy carbon support catalyst with a platinum content of 50%. Weigh out ultrapure water and n-propanol at a mass ratio of 1:4. Weigh out perfluorosulfonic acid resin with an I / C ratio of 0.85 (I refers to the dry weight of the resin in the perfluorosulfonic acid resin solution, and C refers to the mass of the carbon support in the catalyst). The solid content of the intermediate layer slurry is controlled at 9%. The EW value of the perfluorosulfonic acid resin is 790 g / mol, and the solid content of the perfluorosulfonic acid resin is 25%.

[0118] The weighed materials were added to a ball mill jar in the following order: platinum-cobalt alloy carbon carrier catalyst, ultrapure water, n-propanol, and perfluorosulfonic acid resin. The platinum-cobalt alloy carbon carrier catalyst was fully wetted with water before the n-propanol was added, and the perfluorosulfonic acid resin was added last. After mixing and stirring for 1 hour, zirconia grinding beads were added. The mass ratio of the grinding beads to the total material in the ball mill jar was 3:1. The jar was sealed and ball milled at 25°C for 4 hours. The grinding beads were then removed by filtration to obtain the intermediate layer slurry.

[0119] S3 prepares the slurry for the outer cathode layer and outer anode layer.

[0120] Weigh platinum-carbon supported catalyst and carbon nanofibers with a platinum content of 60% at a mass ratio of 20:1. Weigh ultrapure water and n-propanol at a mass ratio of 1:4. Weigh perfluorosulfonic acid resin with an I / C ratio of 0.7 (I refers to the dry weight of the perfluorosulfonic acid resin solution, and C refers to the mass of the carbon support in the catalyst). The solid content of the outer slurry is controlled at 8%. The EW value of the perfluorosulfonic acid resin is 830 g / mol, and the solid content of the perfluorosulfonic acid resin is 25%.

[0121] The weighed materials were added to a ball mill jar in the following order: platinum-carbon carrier catalyst, ultrapure water, n-propanol, and perfluorosulfonic acid resin. The platinum-carbon carrier catalyst was fully wetted with water before the n-propanol was added, and the perfluorosulfonic acid resin was added last. After stirring for 1 hour, zirconia grinding beads were added. The mass ratio of the grinding beads to the total material in the ball mill jar was 3:1. The jar was sealed and ball milled at 25°C for 4 hours. The outer slurry was obtained by filtering the grinding beads.

[0122] S4 coated cathode and anode catalyst layers

[0123] The outer slurry prepared in step S3, the intermediate slurry prepared in step S2, and the inner slurry prepared in step S1 were sequentially coated onto a polytetrafluoroethylene (PTFE) vinyl material using a small vacuum coating machine to obtain a three-layer cathode coating. During the coating process, each layer was allowed to dry completely before applying the next layer to avoid damaging the coating structure. The platinum coating amount for the outer layer of the cathode catalyst was 0.05 mg / cm³. 2 The platinum coating amount of the intermediate layer of the cathode catalyst is 0.2 mg / cm². 2 The inner platinum coating of the cathode catalyst layer is 0.05 mg / cm². 2 The platinum coating amount in the cathode catalyst layer is 0.3 mg / cm². 2 .

[0124] Similarly, the outer slurry prepared in step S3 and the inner slurry prepared in step S1 are sequentially coated onto the polytetrafluoroethylene vinyl material using a small vacuum coating machine to obtain a two-layer anodic coating. During the coating process, the first layer is ensured to dry completely before the second layer is applied. The coating amount of platinum in the outer layer of the anodic catalyst layer is 0.05 mg / cm³. 2 The inner platinum coating of the anode catalyst layer is 0.05 mg / cm². 2 The platinum coating amount in the anode catalyst layer is 0.1 mg / cm². 2 .

[0125] S5 Fabrication of Membrane Electrodes

[0126] The cathode and anode coatings on a polytetrafluoroethylene (PTFE) membrane were transferred to both sides of a 12µm Gore expanded PTFE (ePTFE) reinforced perfluorosulfonic acid proton exchange membrane using a hot-press transfer method to form multilayer cathode and anode catalyst layers. The hot-pressing temperature was 170°C and the hot-pressing pressure was 25 kg / cm². 2 The structure of the catalyst layer after transfer is as follows Figure 1 As shown.

[0127] The inner layers of both the cathode and anode catalysts are close to the proton exchange membrane. A frame and a gas diffusion layer are attached to the outer layers of the cathode and anode catalysts, respectively, to obtain the membrane electrode.

[0128] Example 2

[0129] The only difference between the membrane electrode in Example 2 and that in Example 1 is that the amount of platinum coated on the outer layer of the cathode catalyst is 0.1 mg / cm². 2 The platinum coating amount of the intermediate layer of the cathode catalyst is 0.1 mg / cm². 2 The inner platinum coating of the cathode catalyst layer is 0.1 mg / cm². 2 .

[0130] Comparative Example 1

[0131] The membrane electrode described in Comparative Example 1 differs from that in Example 1 only in that the anodic catalyst layer of the membrane electrode described in Comparative Example 1 consists only of an inner layer, and the platinum coating amount of this inner layer is 0.1 mg / cm². 2 The cathode catalytic layer of the membrane electrode described in Comparative Example 1 consists only of an outer layer, and the platinum coating amount of this outer layer is 0.3 mg / cm². 2 .

[0132] Comparative Example 2

[0133] The membrane electrode described in Comparative Example 2 differs from that in Example 1 only in that the cathode catalytic layer of the membrane electrode described in Comparative Example 2 consists of only an inner layer and an outer layer, and the platinum coating amount of the inner layer is 0.15 mg / cm². 2 The outer platinum coating amount is 0.15 mg / cm². 2 .

[0134] Comparative Example 3

[0135] The only difference between the membrane electrode described in Comparative Example 3 and that in Example 1 is that the inner and outer layers of the cathode catalytic layer of the membrane electrode described in Comparative Example 3 are interchanged with respect to the cathode catalytic layer of the membrane electrode described in Example 1, that is, the outer layer of the cathode catalytic layer of the membrane electrode described in Comparative Example 3 is closer to the proton exchange membrane; and the inner and outer layers of the anode catalytic layer of the membrane electrode described in Comparative Example 3 are interchanged with respect to the anode catalytic layer of the membrane electrode described in Example 1, that is, the outer layer of the anode catalytic layer of the membrane electrode described in Comparative Example 3 is closer to the proton exchange membrane.

[0136] Comparative Example 4

[0137] The membrane electrode described in Comparative Example 4 differs from that described in Example 1 only in that the cathode catalytic layer of the membrane electrode described in Comparative Example 4 consists only of an intermediate layer and an outer layer, and the platinum coating amount of the intermediate layer of the cathode catalytic layer is 0.2 mg / cm³. 2 The platinum coating on the outer layer of the cathode catalyst is 0.1 mg / cm². 2 .

[0138] Performance tests of the membrane electrodes described in Examples 1-2 and Comparative Examples 1-4 of this application.

[0139] The membrane electrodes (active area > 280 cm²) prepared in Examples 1-2 and Comparative Examples 1-4 2 A single-cell test was conducted. The anode and cathode gases of the membrane electrode were air and hydrogen, respectively. The test cell temperature was 80℃, and the humidity at the anode and cathode was 35% and 15%, respectively. The back pressure of both the anode and cathode was 100 kPa, and the stoichiometric ratio of H2 to air was 1.4:1.7.

[0140] Square wave durability test: The active area is 25cm² 2The membrane electrode assembly was performed with the cell temperature controlled at 80℃, H2 / N2 flow rates at 0.2 / 0.1 NLPM, back pressure at 0 / 0 kPa, and the anode and cathode of the membrane electrode humidified at 35% / 20%. The positive electrode of an electrochemical potentiostat was connected to the cathode of the cell, and the negative electrode to the anode. A square wave cycle was performed between 0.6V (3s) and 0.95V (3s) on the potentiostat, with a potential switching time of less than 0.5s and each cycle lasting 6s. The square wave cycle was tested for 30,000 times at 0.8 A / cm². 2 The voltage decay, current density at 0.65V, and electrochemical active area decay were measured, and the results are shown in Table 1.

[0141] Table 1

[0142] <![CDATA[Voltage decay mV @ 0.8 A / cm 2 > <![CDATA[Current density mA / cm 2 @ 0.65V]]> ECSA attenuation rate Example 1 18 2.2 26％ Example 2 17 2.1 25％ Comparative Example 1 16 1.8 22％ Comparative Example 2 16 1.9 23％ Comparative Example 3 20 2.0 25％ Comparative Example 4 38 2.0 37％

[0143] As shown in Table 1, in Comparative Example 2, both the inner and outer layers used platinum-carbon supported catalysts. After 30,000 square wave cycles, the membrane electrode exhibited a capacitance of 0.8 A / cm. 2 The voltage decay and ECSA decay were slightly better than in Example 1, but due to the low catalytic activity of platinum-carbon, a high-performance membrane electrode could not be obtained. Comparative Example 4 used an optimized combination of alloy and platinum-carbon supported catalyst, which was beneficial to improving the performance of the membrane electrode. However, due to the contamination of the proton membrane caused by cobalt ion migration during cycling, the proton conductivity was reduced, and the membrane electrode reached 0.8 A / cm after 30,000 square wave cycles. 2 The voltage decay and ECSA decay are significant. However, the membrane electrode prepared using Example 1 of this invention can balance high performance and long lifespan.

[0144] Figure 2 , Figure 3 and Figure 4 Contact angle tests of the outer, middle, and inner layers of the cathode catalyst layer structure are presented. The contact angle of the alloy middle layer is 130.6°C. Doping with high EW value perfluorosulfonic acid resin and hydrophobic conductive agent improves the hydrophobicity of the catalyst layer, increasing the contact angle to 149.7°C. This increased contact angle increases the additional pressure. In this embodiment, the additional pressure of the cathode catalyst layer gradually increases from the proton exchange membrane side to the diffusion layer side. At low current densities, a pressure gradient is formed that promotes water backflow to the anode side, ensuring the proton conductivity of the proton exchange membrane. At high current densities, the contact angle of the outermost layers of the anode and cathode is relatively large, acting similarly to the microporous layer in the diffusion layer, promoting the discharge of excess water from the inner to the outer layers of the catalyst layer, and preventing flooding.

[0145] Figure 5The battery performance curves of the membrane electrode in the embodiments and comparative examples of this application are given. The test results of Examples 1, 2 and the comparative examples show that appropriately adjusting the platinum loading of the cathode platinum-carbon catalyst layer and the alloy catalyst layer has little effect on the membrane electrode. The test results of Examples 1, 2 and 3 show that the cathode containing only an inner layer and an inner / outer layer structure, or changing the position of the inner and outer layers, are not conducive to the performance of the membrane electrode. The results of Examples 1 and 4 show that the cathode containing only an intermediate layer and an outer layer does not have a significant impact on the initial performance of the membrane electrode, but it will affect the durability of the membrane electrode.

[0146] Although the EW of the inner layer in the embodiment was relatively low, no flooding occurred under high current. This indicates that the high EW of the outermost layer and the hydrophobic conductive agent effectively drained water, ensuring the mass transfer performance of the battery. The performance of the embodiment was significantly higher than that of the comparative example. This is because, under low relative humidity conditions, the three-layer cathode and the double-layer anode structure design established an effective capillary pressure gradient, causing water in the reaction to diffuse towards the anode, thus reducing the film resistivity under low relative humidity. Secondly, the introduction of hydrophobic conductive agents into the outer layers of the anode and cathode effectively prevented battery flooding under high humidity conditions.

[0147] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A membrane electrode, characterized in that, It includes a proton exchange membrane, a cathode catalyst layer and an anode catalyst layer disposed on both sides of the proton exchange membrane; The cathode catalyst layer comprises, from the inside out, an inner cathode layer, a middle cathode layer, and an outer cathode layer; The anode catalyst layer comprises, from the inside out, an inner anode layer and an outer anode layer; Both the inner cathode layer and the inner anode layer comprise a first platinum-carbon supported catalyst and a first ionomer; The cathode intermediate layer comprises an alloy carbon-supported catalyst and a second ionomer; Both the outer cathode layer and the outer anode layer comprise a second platinum-carbon supported catalyst, a third ionomer, and a conductive agent. From the inner to the outer layers of the cathode catalyst layer and the anode catalyst layer, the EW value of the ionomer gradually increases; The EW value of the first ionomer is 700-750 g / mol, the EW value of the second ionomer is 750-800 g / mol, and the EW value of the third ionomer is 800-900 g / mol.

2. The membrane electrode according to claim 1, characterized in that, The platinum loading on the cathode catalyst layer is 0.3 mg per square centimeter; The platinum loading on the inner layer of the cathode catalyst is 0.01-0.1 mg per square centimeter; The platinum loading on the intermediate layer of the cathode catalyst layer is 0.1-0.3 mg per square centimeter; The platinum loading on the outer layer of the cathode catalyst per square centimeter is 0.01-0.1 mg; And / or, the platinum loading on the anode catalyst layer is 0.1 mg per square centimeter; The platinum loading on the inner layer of the anode catalyst layer is 0.01-0.1 mg per square centimeter; The platinum loading on the outer layer of the anode catalyst layer is 0.01-0.1 mg per square centimeter; And / or, the first ionomer, the second ionomer, and the third ionomer are each independently selected from one or more of perfluorosulfonic acid resins, sulfonated polyarylene ether sulfones, sulfonated polyarylene sulfides, sulfonated polyether ether ketones, sulfonated polyimides, and polybenzimidazoles.

3. The membrane electrode according to claim 1, characterized in that, The platinum mass percentage in the first platinum-carbon supported catalyst is 30%-50%; And / or, the mass ratio of carbon in the first ionomer and the first platinum-carbon supported catalyst is (0.9-1.1):

1.

4. The membrane electrode according to claim 1, characterized in that, The alloy carbon support catalyst includes one or more of platinum-cobalt alloy carbon support catalyst, platinum-nickel alloy carbon support catalyst, and platinum-ruthenium alloy carbon support catalyst. And / or, the platinum content in the alloy carbon-supported catalyst is 50%-60% by mass; And / or, the mass ratio of carbon in the second ionomer and the alloy carbon support catalyst is (0.8-0.9):

1.

5. The membrane electrode according to claim 1, characterized in that, The platinum content in the second platinum-carbon supported catalyst is 60%-70% by mass; And / or, the mass ratio of carbon in the third ionomer and the second platinum-carbon supported catalyst is (0.6-0.8):1; And / or, the mass ratio of the second platinum-carbon supported catalyst to the conductive agent is (10-20):1; And / or, the conductive agent includes one or more of Ketjenblack, single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

6. The method for preparing the membrane electrode according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Preparation of inner layer slurry: The first platinum carbon support catalyst, the first ionomer and the first solvent are mixed and subjected to a first sealed ball milling to obtain the inner layer slurry; (2) Preparation of intermediate layer slurry: The alloy carbon support catalyst, the second ionomer and the second solvent are mixed and subjected to a second sealed ball milling to obtain intermediate layer slurry; (3) Preparation of outer layer slurry: The second platinum carbon support catalyst, the third ionomer and the third solvent are mixed and subjected to a third sealed ball milling to obtain the outer layer slurry; (4) The outer layer slurry, the intermediate layer slurry and the inner layer slurry are sequentially applied to the substrate to obtain a cathode coating; the outer layer slurry and the inner layer slurry are sequentially applied to the substrate to obtain an anode coating; (5) The cathode coating and the anode coating are transferred to both sides of the proton exchange membrane by hot pressing to form a cathode catalyst layer and an anode catalyst layer.

7. The method for preparing the membrane electrode according to claim 6, characterized in that, The first solvent includes one or more of ethanol, isopropanol, n-propanol, ethylene glycol, and glycerol; And / or, the first grinding ball used in the first sealed ball mill comprises zirconium oxide; And / or, the temperature of the first sealed ball mill is 20-30℃, and the time of the first sealed ball mill is 2-8h.

8. The method for preparing the membrane electrode according to claim 6, characterized in that, The second solvent includes one or more of ethanol, isopropanol, n-propanol, ethylene glycol, and glycerol; And / or, the second grinding balls used in the second sealed ball mill include zirconium oxide; And / or, the temperature of the second sealed ball mill is 20-30℃, and the time of the second sealed ball mill is 2-8h; And / or, the third solvent includes one or more of ethanol, isopropanol, n-propanol, ethylene glycol, and glycerol; And / or, the third ball milling beads used in the third sealing ball mill include zirconium oxide; And / or, the temperature of the third sealed ball mill is 20-30℃, and the time of the third sealed ball mill is 2-8h.

9. The method for preparing the membrane electrode according to claim 6, characterized in that, The substrate includes a polytetrafluoroethylene film; And / or, the temperature of the hot pressing transfer is 140-180℃, and the pressure of the hot pressing transfer is 20-30 kg / cm². 2 ; And / or, the proton exchange membrane comprises a polytetrafluoroethylene-reinforced composite perfluorosulfonic acid proton exchange membrane.

10. A fuel cell, characterized in that, The membrane electrode includes the membrane electrode according to any one of claims 1-5 or the membrane electrode obtained by the preparation method according to any one of claims 6-9.

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