Gas diffusion layer and preparation method thereof

Abstract

The present invention discloses a gas diffusion layer and a preparation method thereof, which relate to the technical field of hydrogen fuel cell materials, in order to solve the shortcomings of gas diffusion layers that are prone to moisture accumulation or excessive moisture loss. A water-blocking slurry is coated on the surface of hydrophobic carbon paper to form a water-blocking layer, wherein the water-blocking slurry comprises a water-blocking coating formed by polymerization of octadecyltrichlorosilane and water; a water-retaining slurry is coated on the surface of the water-blocking layer to form a water-retaining layer to obtain a prefabricated diffusion layer; and the prefabricated diffusion layer is sintered to obtain the gas diffusion layer. The present invention provides a gas diffusion layer and a preparation method thereof, which are used to prepare a gas diffusion layer that has sufficient moisture to keep the proton membrane moist and can avoid moisture accumulation that hinders gas transmission.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen fuel cell materials, and in particular to a gas diffusion layer and a preparation method thereof. Background Art

[0002] The gas diffusion layer (GDL) is one of the core materials of proton exchange membrane fuel cells (PEMFCs). It has good electrical conductivity and corrosion resistance, supports the catalyst layer, and provides a flow channel for fluids. Therefore, the performance of the GDL material directly affects the electrochemical reaction and the efficiency of the cell.

[0003] GDL usually consists of a base layer and a microporous layer (MPL). After the base layer is hydrophobic treated, a single or multiple microporous layers are coated on it to form a gas diffusion layer. Among them, the base layer is usually composed of anisotropic stacked distribution of carbon fibers, which is in direct contact with the bipolar plate. It mainly plays the role of supporting the MPL and the catalyst layer and providing a water-electricity-gas-heat transmission channel; the microporous layer is mainly composed of a mixture of nano-carbon powder and hydrophobic material, which is in direct contact with the catalyst layer. The introduction of the microporous layer is mainly to improve the pore structure of the base layer, improve the surface flatness, reduce the contact resistance between the catalyst layer and the support layer, redistribute the gas and water to prevent "flooding", and prevent the catalyst layer from leaking into the base layer.

[0004] During hydrogen fuel cell operation, water exists as a liquid. When the water content inside the cell reaches saturation, the ionic conductivity of the proton exchange membrane increases, improving the efficiency of the hydrogen fuel cell. However, excessive water content can cause flooding of the catalyst layer, hindering the transport of reactants to the reaction sites. When designing and selecting a gas diffusion layer, balancing water management is a crucial issue: sufficient water is required to keep the proton exchange membrane moist, while also preventing water accumulation that would otherwise hinder gas transport. Summary of the Invention

[0005] The object of the present invention is to provide a gas diffusion layer and a preparation method thereof, so as to prepare a gas diffusion layer which has sufficient moisture to keep the proton membrane moist and can avoid moisture accumulation to hinder gas transmission.

[0006] In order to achieve the above object, the present invention provides a method for preparing a gas diffusion layer, comprising:

[0007] A water-blocking slurry is coated on the surface of the hydrophobic carbon paper to form a water-blocking layer, wherein the water-blocking slurry comprises a water-blocking coating formed by polymerization of octadecyltrichlorosilane and water;

[0008] Applying a water-retaining slurry on the surface of the water-blocking layer to form a water-retaining layer to obtain a prefabricated diffusion layer;

[0009] The prefabricated diffusion layer is heat-treated to obtain the gas diffusion layer.

[0010] Compared with the prior art, in the preparation method of the gas diffusion layer provided by the present invention, a water-blocking slurry is coated on the surface of the hydrophobic carbon paper to form a water-blocking layer, which can effectively improve the hydrophobicity and durability of the gas diffusion layer. The water-blocking slurry comprises a water-blocking coating formed by polymerization of octadecyltrichlorosilane and water. The hydrophilic end of the octadecyltrichlorosilane molecule faces the water droplet, and the hydrophobic chain faces outward, and nanoparticles are formed in the process of polymerization with water. The nanoparticles will eventually form micro-sized particles after continuous aggregation. The aggregates of micro-sized particles can be covalently bonded to the surface of the hydrophobic carbon paper and form a lotus leaf-shaped micro-nano hierarchical structure, which can discharge water in the gas diffusion layer in time before "flooding" occurs, thereby ensuring the normal output of the fuel cell. Next, a water-retaining slurry is applied to the surface of the water-blocking layer to form a water-retaining layer, creating a prefabricated diffusion layer. Because the water-retaining layer does not contain octadecyltrichlorosilane, its hydrophobicity is much lower than that of the water-blocking layer. This allows the proton exchange membrane to be fully wetted, preventing the membrane electrode from drying out and affecting mass transfer through the proton exchange membrane, thus ensuring normal fuel cell output. Finally, the prefabricated diffusion layer is heat-treated to obtain the gas diffusion layer.

[0011] Moreover, since a micro-nano hierarchical structure is formed after the carbon paper surface is coated with a water-blocking slurry, its pores are smaller than those of the hydrophobic carbon paper, thereby forming stepped pores, which makes the prepared gas diffusion layer have good air permeability.

[0012] In addition, since the reaction between water and octadecyltrichlorosilane is quite mild, the amount of by-product HCl produced is small and can be recycled and reused. Therefore, the production process of water-blocking coating is not only simple and easy, but also does not pose a major threat to the environment, and can be produced on a large scale industrially.

[0013] In a second aspect, the present invention provides a gas diffusion layer prepared by the above-mentioned gas diffusion layer preparation method.

[0014] Compared with the prior art, the beneficial effects of the gas diffusion layer provided by the present invention are the same as the beneficial effects of the method for preparing the gas diffusion layer provided in the first aspect, and are not described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0016] Figure 1 The flowchart of the preparation method of the catalyst provided by the embodiment of the present invention is shown;

[0017] Figure 2The results of single cell performance testing of the gas diffusion layer product according to Example 1 of the present invention are shown. DETAILED DESCRIPTION

[0018] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined. "Several" means one or more, unless otherwise specifically defined.

[0020] Currently, water exists as a liquid during hydrogen fuel cell operation. When the water content within the cell reaches saturation, the ionic conductivity of the proton exchange membrane increases, improving the efficiency of the hydrogen fuel cell. However, excessive water content can cause flooding of the catalyst layer, hindering the transport of reactants to the reaction sites. Excessive water content can cause the membrane to dry out and crack, resulting in irreversible damage. When designing and selecting the gas diffusion layer, sufficient water is required to maintain the proton exchange membrane's moisture while preventing water accumulation that would otherwise hinder gas transport.

[0021] To address the above problems, an embodiment of the present invention provides a method for preparing a gas diffusion layer, which ensures that the prepared diffusion layer has sufficient moisture to keep the proton membrane moist while preventing moisture accumulation from hindering gas transmission. Figure 1 FIG1 shows a flow chart of a method for preparing a gas diffusion layer according to an embodiment of the present invention. Figure 1 As shown, the preparation method comprises:

[0022] Step 101: coating a water-blocking slurry on the surface of the hydrophobic carbon paper to form a water-blocking layer.

[0023] For example, a conventional hydrophobic agent (e.g., an aqueous polytetrafluoroethylene emulsion or a perfluoroethylene propylene copolymer emulsion) is applied to the carbon paper surface by a single saturation dip coating, followed by hot air drying at 100°C to 200°C for 1 to 10 minutes to form the hydrophobic carbon paper. The mass fraction of the hydrophobic agent is 5-10 wt%. It should be understood that the carbon paper used in the embodiments of the present invention can be obtained by wet papermaking or purchased as a finished product, without limitation herein.

[0024] For example, after the water-blocking slurry is coated on the surface of the hydrophobic carbon paper, it is necessary to perform hot air drying at 50°C to 180°C for 0.5min to 5min to make the water-blocking layer formed on the surface of the hydrophobic carbon paper dense. The water-blocking slurry contains a water-blocking coating formed by the polymerization of octadecyltrichlorosilane and water. The hydrophilic end of the octadecyltrichlorosilane molecule faces the water droplet, and the hydrophobic chain faces outward, forming nanoparticles in the process of polymerization with water. The nanoparticles will eventually form micro-sized particles after continuous aggregation. The aggregates of micro-sized particles can be covalently bonded to the surface of the hydrophobic carbon paper and form a lotus leaf-shaped micro-nano hierarchical structure. When the thickness of the water-blocking layer is 5μm to 20μm, it can play a good role in timely drainage, avoid the occurrence of "flooding", and ensure the normal output of the fuel cell. Furthermore, the micro-nano hierarchical structure formed after the carbon paper is coated with a water-blocking slurry has smaller pores than those of the hydrophobic carbon paper, creating a stepped pore structure that imparts excellent air permeability to the resulting gas diffusion layer. It should be understood that to prevent membrane cracking, the water-blocking layer provided in this embodiment of the present invention does not completely block water; instead, it retains some moisture within the gas diffusion layer.

[0025] Step 102: coating a water-retaining slurry on the surface of the water-blocking layer to form a water-retaining layer, thereby obtaining a prefabricated diffusion layer.

[0026] For example, because the water-retention layer does not contain octadecyltrichlorosilane, its hydrophobicity is much lower than that of the water-blocking layer, which can play a role in water retention. In particular, when the thickness of the water-retention layer is 10μm to 30μm, the proton exchange membrane can be fully wetted, avoiding the phenomenon of excessive drying of the membrane electrode affecting the mass transfer of the proton exchange membrane, thereby ensuring the normal output of the fuel cell. It should be understood that in order to prevent the occurrence of "flooding", the water-retention layer provided in the embodiment of the present invention does not completely retain water, but rather discharges some water within the gas diffusion layer.

[0027] Step 103: heat-treating the prefabricated diffusion layer to obtain a gas diffusion layer.

[0028] Exemplarily, the heat treatment includes at least drying and sintering. To prevent the prefabricated diffusion layer from cracking during sintering, a drying process is required. The drying temperature is 100°C to 200°C, and the drying time is 0.5 to 5 minutes. This allows for the formation of a dense, water-retaining layer on the surface of the water-blocking layer. The sintering temperature is 300°C to 400°C, and the sintering time is 5 to 15 minutes. At this point, the dried prefabricated diffusion layer becomes a dense, integrated whole due to intermolecular forces, ultimately forming a gas diffusion layer.

[0029] In an optional manner, before coating the water-blocking slurry on the surface of the hydrophobic carbon paper to form the water-blocking layer, the method for preparing the gas diffusion layer further comprises:

[0030] Octadecyltrichlorosilane is polymerized with water, and a water-blocking coating is obtained after dilution.

[0031] The water-blocking coating, superconductive carbon black, deionized water and additives are mixed to obtain a water-blocking slurry.

[0032] For example, octadecyltrichlorosilane (OTS) is immediately subjected to ultrasonic mechanical mixing after adding water, and then the mixture is diluted with n-hexane (5% v / v OTS / n-hexane) to obtain the coating. When the molar ratio of octadecyltrichlorosilane to water is 1: (2 to 2.5), the obtained water-blocking coating has the best performance. Too little or too much water will result in a decrease in the water contact angle of the treated surface, thereby reducing the hydrophobicity of the water-blocking coating. Since the reaction between water and octadecyltrichlorosilane is quite mild, the amount of by-product HCl produced is small and can be recycled and reused. Therefore, the production process of the water-blocking coating is not only simple and easy, but also does not pose a major threat to the environment, and can be produced on a large scale industrially.

[0033] For example, the additives used in the embodiments of the present invention include surfactants, dispersants, and viscosity modifiers. By weight, the water-blocking coating comprises 0.5 to 5 parts by weight, the surfactant comprises 0.1 to 5 parts by weight, the superconductive carbon black comprises 2 to 10 parts by weight, the dispersant comprises 0.1 to 10 parts by weight, the viscosity modifier comprises 0.1 to 5 parts by weight, and deionized water comprises 70 to 90 parts by weight.

[0034] Specifically, a water-blocking coating, a surfactant, and deionized water are mixed to form a first premix. The surfactant is used to reduce the surface tension of the first premix, allowing the highly hydrophobic water-blocking coating to be fully wetted by the deionized water, facilitating subsequent mixing steps. The surfactant is a nonionic surfactant from the polyoxyethylene ether class, including at least one of secondary alcohol polyoxyethylene ether, octylphenol polyoxyethylene ether, and distyrylphenol polyoxyethylene ether.

[0035] Specifically, superconductive carbon black, a dispersant, and a viscosity modifier are mixed to obtain a second premix. Superconductive carbon black has strong electrical conductivity and is used to impart stronger electrical conductivity to the second premix, thereby less susceptible to the conductivity of the prepared gas diffusion layer and ensuring normal fuel cell output. The superconductive carbon black comprises at least one of Ketjen Black EC-300J, Superconductive Carbon Black BP2000, and Ketjen Black EC-600JD. It should be understood that, to save costs, a mixture of superconductive carbon black and conductive carbon black may be added to the second premix. The specific amount used may be adjusted based on actual conditions and is not limited herein.

[0036] The dispersant is used to uniformly disperse the superconductive carbon black, thereby forming a stable second premix. The dispersant includes at least one of Triton X-100, sodium pyrophosphate, sodium hexametaphosphate, and sorbitol alkylate.

[0037] The viscosity modifier is used to reduce viscosity and increase fluidity. The viscosity modifier is hydroxypropyl cellulose or hydroxymethyl cellulose.

[0038] Specifically, the first premix and the second premix are mixed to obtain a water-blocking slurry.

[0039] In an optional manner, a water-retaining slurry is coated on the surface of the water-blocking layer to form a water-retaining layer. Before forming the prefabricated diffusion layer, the method for preparing the gas diffusion layer further comprises:

[0040] Conductive carbon black, a dispersant, a viscosity regulator, a hydrophobic agent and deionized water are mixed to obtain a water-retaining slurry.

[0041] For example, the addition of conductive carbon black can make the water-retaining slurry conductive, and the conductive carbon black is at least one of VXC-72, VXC72R, and acetylene black. The hydrophobic agent is a conventional hydrophobic agent, for example, an aqueous polytetrafluoroethylene emulsion or a perfluoroethylene propylene copolymer (FEP) emulsion. In terms of weight, the weight of the conductive carbon black is 5 to 20 parts, the weight of the hydrophobic agent is 1 to 8 parts, the weight of the dispersant is 1 to 8 parts, the weight of the viscosity modifier is 0.5 to 5 parts, and the weight of the deionized water is 70 to 90 parts.

[0042] An embodiment of the present invention also provides a gas diffusion layer, produced using the aforementioned gas diffusion layer preparation method. This gas diffusion layer possesses sufficient moisture to maintain the proton membrane moist while preventing moisture accumulation from hindering gas transmission. The gas diffusion layer comprises a water-blocking layer comprising particles with a diameter of 2 to 20 μm, formed from entangled nanofibers. The nanofibers have a diameter of 150 to 200 nm and a length of 2 to 10 μm. This creates a lotus-leaf-like micro-nano hierarchical structure.

[0043] In order to verify the effect of the method for preparing the gas diffusion layer provided by the embodiment of the present invention, the embodiment of the present invention is demonstrated by comparing the embodiment with a comparative example.

[0044] Example 1

[0045] The method for preparing a gas diffusion layer provided in the first embodiment of the present invention includes the following steps:

[0046] The first step was to prepare hydrophobic carbon paper: 25 g of a 60 wt% aqueous polytetrafluoroethylene (PTFE) emulsion was mixed with 185 g of deionized water to form a hydrophobic agent. Carbon paper was then impregnated with the hydrophobic agent and dried with hot air at 160°C for 3 minutes to obtain the hydrophobic carbon paper. The mass ratio of the 60 wt% aqueous polytetrafluoroethylene (PTFE) emulsion to deionized water was 5:37.

[0047] The second step is to prepare a water-blocking layer: 2.0mL, 4.6mmol of octadecyltrichlorosilane is ultrasonically mechanically mixed with 40pL, 2.2mmol of water, and then the mixture is diluted with n-hexane (5% v / v OTS / n-hexane) to obtain 6g of water-blocking coating. Then, 6g of water-blocking coating, 2g of secondary alcohol polyoxyethylene ether and 20g of deionized water are mixed to form a first premix, and then 12g of Ketjen Black EC-600JD is mixed separately with 146g of deionized water. After Ketjen Black EC-600JD is completely immersed, 12g of Triton X-100 and 2g of hydroxymethyl cellulose are added and dispersed by high-speed shear grinding to mix them evenly to form a second premix. The first premix is ​​mixed with the second premix to obtain a water-blocking slurry. Finally, the water-blocking slurry is coated on the surface of the hydrophobic carbon paper to obtain a water-blocking layer with a thickness of 11μm, and dried at 135°C for 1min.

[0048] Among them, the mass ratio of deionized water, Ketjen Black EC-600JD, water-blocking coating, secondary alcohol polyoxyethylene ether, Triton X-100 and hydroxymethyl cellulose is 83:6:3:1:6:1.

[0049] The third step was to prepare a water-retention layer: 25g of acetylene black was mixed with 200g of deionized water. After the acetylene black was completely submerged in the deionized water, 10g of Triton X-100 and 5g of hydroxypropyl cellulose were added and uniformly dispersed by high-speed shear grinding. Subsequently, 16.7g of polytetrafluoroethylene emulsion (10g of solute) was added and mixed at medium-low speed to obtain a water-retention slurry. Finally, the water-retention slurry was applied to the surface of the water-blocking layer, resulting in a 17μm thick water-retention layer.

[0050] The mass ratio of deionized water, acetylene black, polytetrafluoroethylene emulsion, Triton X-100 and hydroxymethyl cellulose is 40:5:2:2:1.

[0051] Step 4: Prepare the gas diffusion layer: The carbon paper, along with the water-blocking and water-retaining layers on its surface, forms a prefabricated diffusion layer. This prefabricated diffusion layer is dried at 150°C for 2 minutes and then sintered at 365°C for 5 minutes to obtain the gas diffusion layer. The technical performance test results of the gas diffusion layer product of Example 1 of the present invention are shown in Table 1.

[0052] Example 2

[0053] The method for preparing a gas diffusion layer provided in the second embodiment of the present invention includes the following steps:

[0054] The first step was to prepare hydrophobic carbon paper: 25 g of a 60 wt% aqueous polytetrafluoroethylene (PTFE) emulsion was mixed with 185 g of deionized water to form a hydrophobic agent. Carbon paper was then impregnated with the hydrophobic agent and dried with hot air at 160°C for 3 minutes to obtain the hydrophobic carbon paper. The mass ratio of the 60 wt% aqueous polytetrafluoroethylene (PTFE) emulsion to deionized water was 5:37.

[0055] The second step is to prepare a water-blocking layer: 2.0mL, 4.6mmol of octadecyltrichlorosilane is ultrasonically mechanically mixed with 40pL, 2.2mmol of water, and then the mixture is diluted with n-hexane (5% v / v OTS / n-hexane) to obtain 6g of water-blocking coating. Then, 6g of water-blocking coating, 2g of secondary alcohol polyoxyethylene ether and 20g of deionized water are mixed to form a first premix. Then, 6g of superconductive carbon black BP2000 and 6g of acetylene black are mixed separately with 146g of deionized water. After the superconductive carbon black BP2000 and acetylene black are completely immersed, 12g of Triton X-100 and 2g of hydroxymethyl cellulose are added and dispersed by high-speed shear grinding to mix them evenly to form a second premix. The first premix is ​​mixed with the second premix to obtain a water-blocking slurry. Finally, the water-blocking slurry is coated on the surface of the hydrophobic carbon paper to obtain a water-blocking layer with a thickness of 10μm, and dried at 150°C for 1min.

[0056] Among them, the mass ratio of deionized water, superconductive carbon black BP2000, acetylene black, water-blocking coating, secondary alcohol polyoxyethylene ether, Triton X-100 and hydroxymethyl cellulose is 83:6:6:3:1:6:1.

[0057] The third step was to prepare the water-retention layer: 25g of acetylene black was mixed with 200g of deionized water. After the acetylene black was completely submerged in the deionized water, 10g of Triton X-100 and 5g of hydroxypropyl cellulose were added and uniformly dispersed by high-speed shear grinding. Subsequently, 16.7g of polytetrafluoroethylene emulsion (10g of solute) was added and mixed at medium-low speed to obtain a water-retention slurry. Finally, the water-retention slurry was applied to the surface of the water-blocking layer, resulting in a 19μm thick water-retention layer.

[0058] The mass ratio of deionized water, acetylene black, polytetrafluoroethylene emulsion, Triton X-100 and hydroxymethyl cellulose is 40:5:2:2:1.

[0059] Step 4: Prepare the gas diffusion layer: The carbon paper, along with the water-blocking and water-retaining layers on its surface, forms a prefabricated diffusion layer. This prefabricated diffusion layer is dried at 150°C for 2 minutes and then sintered at 365°C for 5 minutes to obtain the gas diffusion layer. The technical performance test results of the gas diffusion layer product of Example 2 of the present invention are shown in Table 1.

[0060] Comparative Example 1

[0061] The method for preparing a gas diffusion layer provided in Comparative Example 1 of the present invention comprises the following steps:

[0062] The first step was to prepare hydrophobic carbon paper: 25 g of a 60 wt% aqueous polytetrafluoroethylene (PTFE) emulsion was mixed with 185 g of deionized water to form a hydrophobic agent. Carbon paper was then impregnated with the hydrophobic agent and dried with hot air at 160°C for 3 minutes to obtain the hydrophobic carbon paper. The mass ratio of the 60 wt% aqueous polytetrafluoroethylene (PTFE) emulsion to deionized water was 5:37.

[0063] The second step was to prepare the first slurry layer: 28g of acetylene black was mixed with 164g of deionized water. After the acetylene black was completely submerged in the deionized water, 11g of Triton X-100 and 4g of hydroxypropyl cellulose were added and dispersed uniformly by high-speed shear grinding. Subsequently, 15g of polytetrafluoroethylene emulsion (9g of solute) was added and mixed uniformly at medium-low speed to obtain a first slurry. Finally, the first slurry was coated on the surface of the hydrophobic carbon paper to obtain a first slurry layer with a thickness of 15μm, and then dried at 135°C for 1 minute.

[0064] The mass ratio of deionized water, acetylene black, polytetrafluoroethylene emulsion, Triton X-100 and hydroxymethyl cellulose is 164:28:9:11:4.

[0065] The third step was to prepare a second slurry layer: 25g of acetylene black was mixed with 200g of deionized water. After the acetylene black was completely submerged in the deionized water, 10g of Triton X-100 and 5g of hydroxypropyl cellulose were added and dispersed uniformly through high-speed shear grinding. Subsequently, 16.7g of polytetrafluoroethylene emulsion (10g of solute) was added and mixed uniformly at medium-low speed to obtain a second slurry. Finally, the second slurry was applied to the surface of the first slurry layer to obtain a 12μm thick water-retaining layer.

[0066] The mass ratio of deionized water, acetylene black, polytetrafluoroethylene emulsion, Triton X-100 and hydroxymethyl cellulose is 40:5:2:2:1.

[0067] Step 4: Preparation of the gas diffusion layer: The carbon paper and the first and second slurry layers on its surface formed a prefabricated diffusion layer. The prefabricated diffusion layer was dried at 150°C for 2 minutes and then sintered at 365°C for 5 minutes to obtain the gas diffusion layer. The technical performance test results of the gas diffusion layer product of Comparative Example 1 of the present invention are shown in Table 1.

[0068] Comparative Example 2

[0069] The method for preparing a gas diffusion layer provided in Comparative Example 2 of the present invention comprises the following steps:

[0070] The first step was to prepare hydrophobic carbon paper: 25 g of a 60 wt% aqueous polytetrafluoroethylene (PTFE) emulsion was mixed with 185 g of deionized water to form a hydrophobic agent. Carbon paper was then impregnated with the hydrophobic agent and dried with hot air at 160°C for 3 minutes to obtain the hydrophobic carbon paper. The mass ratio of the 60 wt% aqueous polytetrafluoroethylene (PTFE) emulsion to deionized water was 5:37.

[0071] The second step was to prepare a slurry layer: 25g of acetylene black was mixed with 200g of deionized water. After the acetylene black was completely submerged in the deionized water, 10g of Triton X-100 and 5g of hydroxypropyl cellulose were added and uniformly dispersed by high-speed shear grinding. Subsequently, 16.7g of polytetrafluoroethylene emulsion (10g of solute) was added and mixed at medium-low speed to obtain a slurry. Finally, the slurry was coated on the surface of the hydrophobic carbon paper to obtain a slurry layer with a thickness of 25μm.

[0072] The mass ratio of deionized water, acetylene black, polytetrafluoroethylene emulsion, Triton X-100 and hydroxymethyl cellulose is 40:5:2:2:1.

[0073] The third step involved preparing the gas diffusion layer: The carbon paper and the slurry layer on its surface formed a prefabricated diffusion layer. The prefabricated diffusion layer was dried at 150°C for 2 minutes and then sintered at 365°C for 5 minutes to obtain the gas diffusion layer. The technical performance test results of the gas diffusion layer product of Comparative Example 2 of the present invention are shown in Table 1.

[0074] Comparative Example 3

[0075] The method for preparing a gas diffusion layer provided in Comparative Example 3 of the present invention comprises the following steps:

[0076] The first step was to prepare hydrophobic carbon paper: 25 g of a 60 wt% aqueous polytetrafluoroethylene (PTFE) emulsion was mixed with 185 g of deionized water to form a hydrophobic agent. Carbon paper was then impregnated with the hydrophobic agent and dried with hot air at 160°C for 3 minutes to obtain the hydrophobic carbon paper. The mass ratio of the 60 wt% aqueous polytetrafluoroethylene (PTFE) emulsion to deionized water was 5:37.

[0077] The second step was to prepare a water-blocking coating layer: 2.0 mL (4.6 mmol) of octadecyltrichlorosilane and 40 μL (2.2 mmol) of water were ultrasonically mechanically mixed. The mixture was then diluted with n-hexane (5% v / v OTS / n-hexane) to produce 6 g of water-blocking coating. This 6 g of water-blocking coating was sprayed onto the surface of hydrophobic carbon paper, dried at 132°C for 1 minute, and finally sintered at 365°C for 5 minutes to obtain a 10 μm thick water-blocking coating layer.

[0078] The third step is to prepare a water-retaining slurry layer: 25g of acetylene black is mixed with 200g of deionized water. Once the acetylene black is completely submerged in the deionized water, 10g of Triton X-100 and 5g of hydroxypropyl cellulose are added and uniformly dispersed by high-speed shear grinding. Subsequently, 16.7g of polytetrafluoroethylene emulsion (10g of solute) is added and mixed at medium-low speed to obtain a water-retaining slurry. Finally, the water-retaining slurry is applied to the surface of the water-blocking layer, resulting in a 17μm thick water-retaining layer.

[0079] The mass ratio of deionized water, acetylene black, polytetrafluoroethylene emulsion, Triton X-100 and hydroxymethyl cellulose is 40:5:2:2:1.

[0080] Step 4: Preparation of the gas diffusion layer: The carbon paper, along with the water-blocking coating and water-retaining slurry layers on its surface, formed a prefabricated diffusion layer. The prefabricated diffusion layer was dried at 155°C for 2 minutes and then sintered at 365°C for 5 minutes to obtain the gas diffusion layer. The technical performance test results of the gas diffusion layer product of Comparative Example 3 of the present invention are shown in Table 1.

[0081] Next, the technical performances of the gas diffusion layer products of Examples 1 to 2 and Comparative Examples 1 to 3 of the present invention were tested.

[0082] Test method:

[0083] Parallel resistivity: The resistivity in the plane direction of the gas diffusion layer is tested using a four-probe resistivity tester. The unit is mΩ·cm.

[0084] Vertical resistivity: A vertical resistivity tester is used to test the vertical resistivity of the gas diffusion layer. The unit is mΩ·cm.

[0085] Air permeability: The air permeability of the gas diffusion layer was measured using a Gurley air permeability tester. The unit is s / 100cc.

[0086] Porosity: The porosity of the gas diffusion layer is measured using a mercury intrusion porosimeter, unit: %.

[0087] Surface roughness: Use a roughness meter to test the surface roughness of the microporous layer of the gas diffusion layer. Unit: m.

[0088] Surface contact angle: Use a contact angle tester to test the water contact angle on the material surface, unit: °.

[0089] Single-cell performance testing: A membrane electrode (MEA) was assembled from a homemade gas diffusion layer, proton exchange membrane, and catalyst. Test conditions: H2 / Ar, 100kPa air back pressure, 100% humidity, and a cell operating temperature of 70°C.

[0090] Table 1 shows the technical performance test results of the gas diffusion layer products of Examples 1 to 2 and Comparative Examples 1 to 3 of the present invention.

[0091] Table 1

[0092]

[0093] As shown in Table 1, the parallel resistivity test results and the perpendicular resistivity test results of the gas diffusion layer products according to Examples 1 to 2 of the present invention are much lower than the test results of the gas diffusion layer products according to Comparative Examples 1 to 3. It can be seen that the gas diffusion layer products according to Examples 1 to 2 of the present invention have lower resistance and are more conducive to the normal output of the fuel cell. The porosity of the gas diffusion layer products according to the embodiments of the present invention is greater than that of the comparative example, indicating that after coating the water-blocking slurry on the hydrophobic carbon paper, a micro-nano hierarchical structure is constructed in the water-blocking layer formed, and its pores are smaller than the pores of the hydrophobic carbon paper, thereby forming stepped pores, so that the prepared gas diffusion layer has a larger porosity and good air permeability. The surface roughness of the gas diffusion layer products according to Examples 1 to 2 of the present invention is less than that of the gas diffusion layer products according to the comparative example, indicating that the surface of the gas diffusion layer products according to Examples 1 to 2 of the present invention is relatively smooth, so that the catalyst utilization rate in the catalyst layer is relatively high. In addition, according to the comparison of the surface contact angles of the gas diffusion layer products according to Examples 1 and 2 of the present invention, it can be seen that the gas diffusion layer product containing the water-blocking slurry or the water-blocking coating has better hydrophobicity.

[0094] Figure 2 The results of single cell performance test of the gas diffusion layer product of Example 1 of the present invention are shown. Figure 2 As shown, the current density is 200mA / cm 2 When the corresponding voltage is 0.83V and the current density is 600mA / cm 2 When the corresponding voltage is 0.73V and the current density is 1000mA / cm 2When the voltage is 0.7V, the membrane electrode performance is relatively excellent. The above is only a specific embodiment of the present invention. Obviously, various modifications and combinations can be made thereto without departing from the spirit and scope of the present invention. Accordingly, this specification and the drawings are merely exemplary illustrations of the present invention as defined by the appended claims, and are deemed to have covered any and all modifications, changes, combinations or equivalents within the scope of the present invention. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is intended to include these changes and variations. Any person skilled in the art who can easily think of changes or substitutions within the technical scope disclosed by the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a gas diffusion layer, characterized in that: include: A water-blocking slurry is coated on the surface of the hydrophobic carbon paper to form a water-blocking layer, wherein the water-blocking slurry comprises a water-blocking coating formed by polymerization of octadecyltrichlorosilane and water; the water-blocking layer has a micro-nano hierarchical structure, wherein the pores of the micro-nano hierarchical structure are smaller than the pores of the hydrophobic carbon paper, forming a stepped pore; the water-blocking layer comprises particles with a diameter of 2 μm to 20 μm, wherein the particles are formed by entangled nanofibers, wherein the nanofibers have a diameter of 150 nm to 200 nm and a length of 2 μm to 10 μm; A water-retaining slurry is applied on the surface of the water-blocking layer to form a water-retaining layer, thereby obtaining a prefabricated diffusion layer; the thickness of the water-blocking layer is 11 μm, and the thickness of the water-retaining layer is 17 μm; The prefabricated diffusion layer is heat-treated to obtain the gas diffusion layer.

2. The method for preparing a gas diffusion layer according to claim 1, wherein: Before coating the water-blocking slurry on the surface of the hydrophobic carbon paper to form the water-blocking layer, the preparation method further comprises: The water-blocking coating is obtained by polymerizing octadecyltrichlorosilane with water and then diluting the mixture; the molar ratio of the octadecyltrichlorosilane to the water is 1:(2-2.5); Mixing the water-blocking coating, superconductive carbon black, deionized water and an additive to obtain a water-blocking slurry; The superconductive carbon black includes at least one of Ketjen Black EC-300J, superconductive carbon black BP2000 and Ketjen Black EC-600JD; the auxiliary agent includes a surfactant, a dispersant and a viscosity modifier.

3. The method for preparing a gas diffusion layer according to claim 2, wherein: In terms of mass, the mass portion of the water-blocking coating is 0.5 to 5 parts, the mass portion of the surfactant is 0.1 to 5 parts, the mass portion of the superconductive carbon black is 2 to 10 parts, the mass portion of the dispersant is 0.1 to 10 parts, the mass portion of the viscosity modifier is 0.1 to 5 parts, and the mass portion of the deionized water is 70 to 90 parts.

4. The method for preparing a gas diffusion layer according to claim 2, wherein: The water-blocking coating, superconductive carbon black and additives are mixed to obtain a water-blocking slurry, comprising: Mixing the water-blocking coating, the surfactant, and the deionized water to obtain a first premix; mixing the superconductive carbon black, the dispersant, and the viscosity modifier to obtain a second premix; The first premix and the second premix are mixed to obtain a water-blocking slurry.

5. The method for preparing a gas diffusion layer according to claim 1, wherein: Before coating the surface of the water-blocking layer with a water-retaining slurry to form the water-retaining layer and forming the prefabricated diffusion layer, the preparation method further comprises: Conductive carbon black, a dispersant, a viscosity regulator, a hydrophobic agent and deionized water are mixed to obtain a water-retaining slurry, wherein the conductive carbon black includes at least one of conductive carbon black VXC-72, conductive carbon black VXC72R and acetylene black.

6. The method for preparing a gas diffusion layer according to claim 5, characterized in that: In terms of mass, the mass portion of the conductive carbon black is 5 to 20 parts, the mass portion of the hydrophobic agent is 1 to 8 parts, the mass portion of the dispersant is 1 to 8 parts, the mass portion of the viscosity regulator is 0.5 to 5 parts, and the mass portion of the deionized water is 70 to 90 parts.

7. The method for preparing a gas diffusion layer according to claim 1, wherein: The heat treatment includes drying and sintering. The drying temperature is 100° C. to 200° C., the drying time is 0.5 min to 5 min, the sintering temperature is 300° C. to 400° C., and the sintering time is 5 min to 15 min.

8. A gas diffusion layer prepared by the method for preparing a gas diffusion layer according to any one of claims 1 to 7.

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