Gas diffusion module for a fuel cell and fuel cell, method of manufacture

Abstract

The application discloses a gas diffusion module of a fuel cell, a fuel cell and a preparation method. The gas diffusion module comprises a substrate layer and a microporous layer which are arranged in sequence. The substrate layer is provided with a first hole group and a second hole group. The first hole group and the second hole group are both provided with micro-perforations. The hydrophobicity of the micro-perforations on the first surface is greater than that on the second surface. The pore diameter of the micro-perforations located in front of the air flow direction in the first hole group and the second hole group is greater than that of the micro-perforations located behind the air flow direction. Alternatively, the opening density of the micro-perforations located in front of the air flow direction in the first hole group and the second hole group is greater than that of the micro-perforations located behind the air flow direction. On any homologous line perpendicular to the air flow direction, the opening density of the micro-perforations of the first hole group is greater than that of the micro-perforations of the second hole group, and the pore diameter of the micro-perforations of the first hole group is smaller than that of the micro-perforations of the second hole group. The water in different positions of the cathode surface is kept relatively balanced, and water accumulation and excessive water loss are prevented.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a gas diffusion module for a fuel cell, a fuel cell, and a method for its fabrication. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) used in devices such as drones typically employ an open cathode structure. A fan blows ambient air into the airflow space between the cathode surface and the substrate of the gas diffusion module, simultaneously supplying oxidant and cooling the stack. This design eliminates the need for an air compressor and humidification system, significantly reducing system weight and size, making it suitable for mobile platform applications such as drones.

[0003] However, the open cathode structure presents significant challenges in water management. On the one hand, high-speed airflow carries away a large amount of moisture, causing the proton exchange membrane inside the fuel cell to dry out and the ohmic impedance to rise sharply. On the other hand, water generated by the electrochemical reaction is transferred to the cathode surface of the gas diffusion module. If it cannot be drained in time, it may cause electrode flooding on the cathode side, hindering oxygen transfer.

[0004] Traditional gas diffusion layers (GDLs) typically employ uniform hydrophobic treatment. However, on the cathode surface of a gas diffusion module, the ability of airflow to carry moisture varies at different locations. A uniform hydrophobic structure on the cathode surface can lead to different moisture retention levels at different locations, causing instability in the fuel cell reaction. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a gas diffusion module for a fuel cell, a fuel cell, and a method for its preparation, which maintains a relatively balanced distribution of moisture at different locations on the cathode surface, prevents moisture accumulation and excessive moisture loss, and improves the operational stability and reliability of the fuel cell.

[0006] According to a first aspect of the present invention, a gas diffusion module for a fuel cell is provided, wherein an airflow space is provided between the cathode surface and the substrate of the gas diffusion module, allowing air to flow; the substrate protrudes from the surface facing the gas diffusion module and is provided with a plurality of spaced-apart flow channel ridges, and a flow channel groove is formed between two adjacent flow channel ridges; the gas diffusion module includes a substrate layer and a microporous layer stacked sequentially, the first surface of the substrate layer facing the airflow space to form the cathode surface of the gas diffusion module, the second surface of the substrate layer facing the microporous layer, the ridge surfaces of the flow channel ridges being close to the first surface of the substrate layer, the substrate layer being provided with at least one set of first pore groups and at least one set of second pore groups, the first pore groups being correspondingly disposed in the regions of the substrate layer facing each of the flow channel ridges, and the second pore groups being correspondingly disposed in the regions of the substrate layer facing each of the flow channel ridges. The first and second hole groups, located in the region of the substrate layer facing each of the flow channel grooves, each have micro-perforations extending through the thickness direction. The micro-perforations on the first surface are more hydrophobic than those on the second surface. In the airflow direction, the diameter of the micro-perforations in the first and second hole groups located in front of the airflow direction is greater than the diameter of the micro-perforations located behind the airflow direction; or, the opening density of the micro-perforations in the first and second hole groups located in front of the airflow direction is greater than the opening density of the micro-perforations located behind the airflow direction. On any coaxial line perpendicular to the airflow direction, the opening density of the micro-perforations in the first hole group is greater than that in the second hole group, and the diameter of the micro-perforations in the first hole group is smaller than that in the second hole group.

[0007] A gas diffusion module for a fuel cell according to an embodiment of the present invention has at least the following beneficial effects: In the gas diffusion module of the fuel cell of this invention, moisture generated by the fuel cell reaction flows from the microporous layer to the substrate layer. Air flows from one side of the airflow space along the extension direction of the flow channel ridge and the flow channel groove to the other side. Since the flow channel ridge protrudes from the substrate and is close to the surface of the substrate layer, the airflow rate here is less than the airflow rate corresponding to the flow channel groove. At the same time, the airflow that just enters the airflow space is relatively dry and has a strong water absorption capacity. However, as the airflow flows in the airflow space, the moisture carried by the airflow increases, and the water absorption capacity decreases. Based on this application, the first pore group and the second... The microperforations in the two-pore group exhibit greater hydrophobicity on the first surface than on the second surface. Utilizing capillary action, water in the microporous layer more easily enters the microperforations, simultaneously enhancing the hydrophobicity of the first surface and preventing water accumulation that could hinder oxygen entry into the fuel cell. Furthermore, regardless of whether it's the first or second pore group, the pore size of the microperforations in front of the airflow direction is larger than that in the rear of the airflow direction; or, in either the first or second pore group, the pore density of the microperforations in front of the airflow direction is greater than that in the rear of the airflow direction. The pore density of the micro-perforations behind the airflow direction is equivalent to reducing the efficiency of water passing through the substrate layer by decreasing the pore size or pore density in areas with strong water absorption capacity, thereby improving the water retention capacity at that location. Conversely, in areas with weak water absorption capacity, the pore size or pore density of the micro-perforations is appropriately increased to improve the efficiency of water passing through the substrate layer. This results in a relatively balanced distribution of moisture across different locations on the cathode surface of the gas diffusion module in the airflow direction. In the areas corresponding to the flow channel ridges and grooves on the cathode surface of the gas diffusion module, moisture tends to accumulate and form water blockages in the area corresponding to the flow channel ridges. By arranging micro-perforations with a higher density and smaller pore size, capillary suction is used to actively absorb water and achieve rapid drainage. In the area corresponding to the flow channel grooves, where water vapor is relatively low, a lower density and larger pore size arrangement of micro-perforations allows for rapid water discharge and prevents excessive water loss in this area. This application maintains a relatively balanced distribution of moisture across different locations on the cathode surface, preventing water accumulation and excessive water loss.

[0008] According to some embodiments of the present invention, in the thickness direction, the hydrophobicity of the microperforations first decreases and then increases from the second surface to the first surface.

[0009] According to some embodiments of the present invention, at least a portion of the surface of the aperture edge and the inner peripheral wall of the microperforation are provided with a hydrophobic coating. The hydrophobic coating is formed by covering the surface of the microperforation with a hydrophobic agent. Specifically, the hydrophobic agent content of the hydrophobic coating near the first surface is 25-45 wt.%, and the contact angle of the microperforation near the first surface is 135-155°. The hydrophobic agent content of the hydrophobic coating at the transition position between the first and second surfaces is 2-6 wt.%, and the contact angle of the microperforation at the transition position between the first and second surfaces is 90-100°. The hydrophobic agent content of the hydrophobic coating near the second surface is 8-18 wt.%, and the contact angle of the microperforation near the second surface is 105-125°.

[0010] According to some embodiments of the present invention, the surface of the microperforation at the transition position is further provided with a hydrophilic coating.

[0011] According to a second aspect of the present invention, a fuel cell includes a gas diffusion module of a fuel cell disclosed in any of the above embodiments, wherein the microporous layer is stacked on the surface opposite to the substrate layer and attached to the catalyst layer of the fuel cell.

[0012] The fuel cell according to embodiments of the present invention has at least the following beneficial effects: The fuel cell of the present invention utilizes a gas diffusion module of a fuel cell disclosed in any of the above embodiments, thereby improving the operational stability and reliability of the fuel cell.

[0013] According to a second aspect of the present invention, a method for preparing a gas diffusion module is provided. The method includes: attaching a temporary sealing layer to a first surface of a substrate sheet to shield the first surface of the substrate sheet; immersing a second surface of the substrate sheet in a hydrophobic agent impregnation solution to a depth reaching a first percentage threshold of the substrate sheet thickness; removing the temporary sealing layer; immersing the first surface of the substrate sheet in the hydrophobic agent impregnation solution to a depth reaching a second percentage threshold of the substrate sheet thickness; drying and sintering the immersed substrate sheet to form a base layer, wherein the second percentage threshold is greater than the first percentage threshold; and performing a laser drilling step to form a plurality of micro-perforations on the base layer, wherein a portion of the micro-perforations constitutes a first group of perforations and another portion constitutes a second group of perforations, the first group of perforations being disposed one-to-one on the base layer facing each of the perforations. In the region of the flow channel ridge, the second hole group is correspondingly disposed in the region of the substrate layer facing each of the flow channel grooves. In the airflow direction, the diameter of the micro-perforations in the first and second hole groups located in front of the airflow direction is larger than the diameter of the micro-perforations in front of the airflow direction; or, the opening density of the micro-perforations in the first and second hole groups located in front of the airflow direction is greater than the opening density of the micro-perforations in front of the airflow direction. Furthermore, on any coaxial line perpendicular to the airflow direction, the opening density of the micro-perforations in the first hole group is greater than the opening density of the micro-perforations in the second hole group, and the diameter of the micro-perforations in the first hole group is smaller than the diameter of the micro-perforations in the second hole group. A microporous slurry is coated onto the second surface of the substrate layer and dried and sintered to form a microporous layer.

[0014] The preparation method according to embodiments of the present invention has at least the following beneficial effects: The preparation method of the present invention produces a gas diffusion module that can maintain a relatively balanced moisture content at different positions on the cathode surface, preventing moisture accumulation and excessive moisture loss.

[0015] According to some embodiments of the present invention, between the laser drilling step and the coating of the microporous slurry onto the second surface of the substrate layer and the drying and sintering treatment to form the microporous layer, the method further includes: spraying a hydrophilic agent onto the second surface of the substrate layer; using the capillary action of the microperforation to draw the hydrophilic agent into the microperforation; using compressed air to blow away the second surface of the substrate layer to remove the hydrophilic agent remaining on the second surface; and after the drying and sintering treatment, a hydrophilic coating is formed on the inner peripheral wall of the microperforation at the transition position between the first surface and the second surface.

[0016] According to some embodiments of the present invention, the hydrophobic impregnation solution is polytetrafluoroethylene, polyvinylidene fluoride, fluorinated ethylene propylene, or a tetrafluoroethylene copolymer resin, and the hydrophilic agent is one or more of polyacrylic acid, polyvinyl alcohol, titanium dioxide nanoparticles, or hydrophilic carbon nanotubes.

[0017] According to some embodiments of the present invention, the temporary sealing layer is a peelable polymer film, a heat-sensitive wax layer, or a water-soluble coating.

[0018] According to some embodiments of the present invention, the first percentage threshold ranges from 20% to 40%, and the second percentage threshold ranges from 30% to 50%.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram showing the usage state of one embodiment of the gas diffusion module of the present invention; Figure 2 This is a schematic diagram of the base layer structure of one embodiment of the gas diffusion module of the present invention; Figure 3 This is a flowchart of one embodiment of the preparation method of the present invention.

[0021] Figure label: Gas diffusion module 100; substrate layer 110; microporous layer 120; substrate 200; flow channel ridge 210; flow channel groove 220; airflow space 300; first pore group 410; second pore group 420; microperforation 430; catalyst layer 500; Detailed Implementation Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0022] In the description of this invention, it should be understood that the orientation descriptions, such as the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer", indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0023] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0024] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] like Figure 1 , 2 As shown, a gas diffusion module for a fuel cell according to a first aspect embodiment of the present invention has an airflow space between the cathode surface and the substrate of the gas diffusion module, which allows air to flow. The substrate protrudes from the surface of the gas diffusion module and is provided with a plurality of spaced-apart flow channel ridges, and a flow channel groove is formed between two adjacent flow channel ridges. The gas diffusion module includes a substrate layer and a microporous layer stacked sequentially. The first surface of the substrate layer faces the gas flow space to form the cathode surface of the gas diffusion module, and the second surface of the substrate layer faces the microporous layer. The ridge surface of the flow channel ridge is close to the first surface of the substrate layer. The substrate layer is provided with at least one set of first holes and at least one set of second holes. The first holes are correspondingly disposed in the region of the substrate layer facing each flow channel ridge, and the second holes are correspondingly disposed in the region of the substrate layer facing each flow channel groove. Both the first holes and the second holes have micro-perforations that penetrate the thickness direction. The microperforations on the first surface are more hydrophobic than those on the second surface. In the direction of airflow, the diameter of the micro-perforations located in front of the airflow direction in the first and second hole groups is greater than the diameter of the micro-perforations located behind the airflow direction, or the opening density of the micro-perforations located in front of the airflow direction in the first and second hole groups is greater than the opening density of the micro-perforations located behind the airflow direction. At any co-position line perpendicular to the direction of airflow (e.g.) Figure 2In the R group, the opening density of the micro-perforations in the first group is greater than that in the second group, and the pore diameter of the micro-perforations in the first group is smaller than that in the second group.

[0026] The substrate layer can be composed of porous substrate sheets such as carbon fiber, carbon black, carbon nanotubes, porous titanium, and porous nickel, with a thickness of 150–300 μm; the microporous layer has a thickness of 20–50 μm.

[0027] The gas diffusion module can be applied in fuel cells. The microporous layer is stacked on the surface of the substrate layer and attached to the catalyst layer of the fuel cell. The catalyst layer is stacked on the proton exchange membrane. Oxygen can enter the catalyst layer from the gas diffusion module and react with hydrogen ions passing through the proton exchange membrane to generate water. The water can pass through the catalyst layer and the gas diffusion module and finally vaporize and be output to the outside with the airflow. If the water is not discharged in time, the water accumulated on the cathode side will hinder oxygen from entering the catalyst layer. However, the fuel cell needs to have a suitable amount of water to keep the proton exchange membrane moist and reduce ohmic impedance. Therefore, the structure of the gas diffusion module of this application needs to balance the efficiency of water retention and dissipation.

[0028] The fuel cell of this application is used in open devices such as drones. The cathode surface of the gas diffusion module can be set on a substrate. The substrate has spaced-apart flow channel ridges, which are elongated and mostly straight. Correspondingly, the flow channel grooves are also elongated. The air inlet of the fuel cell is located on one side of the airflow space, corresponding to the beginning of each flow channel ridge and the flow channel groove. The air outlet of the fuel cell is located on the other side of the airflow space, corresponding to the end of each flow channel ridge and the flow channel groove.

[0029] It should be noted that although the ridge surface of the flow channel is close to the first surface of the base layer, there will still be gaps that allow airflow and moisture vaporization.

[0030] In the gas diffusion module of the fuel cell of this invention, moisture generated by the fuel cell reaction flows from the microporous layer to the substrate layer. Air flows from one side of the airflow space along the extension direction of the flow channel ridge and the flow channel groove to the other side. Since the flow channel ridge protrudes from the substrate and is close to the surface of the substrate layer, the airflow rate here is less than the airflow rate corresponding to the flow channel groove. At the same time, the airflow that just enters the airflow space is relatively dry and has a strong water absorption capacity. However, as the airflow flows in the airflow space, the moisture carried by the airflow increases, and the water absorption capacity decreases. Based on this application, the first pore group and the second... The microperforations in the two-pore group exhibit greater hydrophobicity on the first surface than on the second surface. Utilizing capillary action, water in the microporous layer more easily enters the microperforations, simultaneously enhancing the hydrophobicity of the first surface and preventing water accumulation that could hinder oxygen entry into the fuel cell. Furthermore, regardless of whether it's the first or second pore group, the pore size of the microperforations in front of the airflow direction is larger than that in the rear of the airflow direction; or, in either the first or second pore group, the pore density of the microperforations in front of the airflow direction is greater than that in the rear of the airflow direction. The pore density of the micro-perforations behind the airflow direction is equivalent to reducing the efficiency of water passing through the substrate layer by decreasing the pore size or pore density in areas with strong water absorption capacity, thereby improving the water retention capacity at that location. Conversely, in areas with weak water absorption capacity, the pore size or pore density of the micro-perforations is appropriately increased to improve the efficiency of water passing through the substrate layer. This results in a relatively balanced distribution of moisture across different locations on the cathode surface of the gas diffusion module in the airflow direction. In the areas corresponding to the flow channel ridges and grooves on the cathode surface of the gas diffusion module, moisture tends to accumulate and form water blockages in the area corresponding to the flow channel ridges. By arranging micro-perforations with a higher density and smaller pore size, capillary suction is used to actively absorb water and achieve rapid drainage. In the area corresponding to the flow channel grooves, where water vapor is relatively low, a lower density and larger pore size arrangement of micro-perforations allows for rapid water discharge and prevents excessive water loss in this area. This application maintains a relatively balanced distribution of moisture across different locations on the cathode surface, preventing water accumulation and excessive water loss.

[0031] In some embodiments of the present invention, in the thickness direction, the hydrophobicity of the microperforations first decreases and then increases from the second surface to the first surface.

[0032] Firstly, given that the hydrophobicity of the microperforations on the first surface is greater than that on the second surface, the hydrophobicity of the microperforations first decreases and then increases from the second surface to the first surface. This means that the hydrophobicity of the microperforations is minimal at the transition position between the first and second surfaces. The higher hydrophobicity of the microperforations on the first surface allows for easier water loss, which prevents excessive water accumulation in the airflow space and avoids blockage. Secondly, the water concentration on the second surface is relatively high. As a result, a gradual transition zone of capillary pressure suction is formed within the microperforations in the thickness direction, driving the generated water to be directionally transported from the catalyst layer to the airflow space side. In conjunction with the increased hydrophobicity at the transition position, water can adhere to a certain extent at this location, maintaining the membrane's hydration state and preventing excessive water loss.

[0033] Specifically, at least a portion of the surface of the microperforation's aperture edge and inner peripheral wall is provided with a hydrophobic coating. The hydrophobic coating is composed of a hydrophobic agent covering the surface of the microperforation. Specifically, the hydrophobic agent content of the hydrophobic coating near the first surface is 25–45 wt.%, and the contact angle of the microperforation near the first surface is 135–155°. The hydrophobic agent content of the hydrophobic coating at the transition position between the first and second surfaces is 2–6 wt.%, and the contact angle of the microperforation at the transition position between the first and second surfaces is 90–100°. The hydrophobic agent content of the hydrophobic coating near the second surface is 8–18 wt.%, and the contact angle of the microperforation near the second surface is 105–125°.

[0034] It should be noted that the microperforations can be divided into three segments in the thickness direction, with hydrophobic coatings formed near the first surface and near the second surface respectively. Taking the method of forming hydrophobic coatings by immersion or coating as an example, by controlling the concentration of hydrophobic agent and the penetration depth, the content of hydrophobic agent at different positions can be controlled. As a result, different contact angles are formed at different positions of the microperforations. The larger the contact angle, the stronger the hydrophobicity. It can be seen that the hydrophobicity of the microperforations first decreases and then increases from the second surface to the first surface.

[0035] To enhance the hydrophilicity of the microperforations at the transition position between the first and second surfaces, in some embodiments of the present invention, the surface of the microperforations at the transition position is further provided with a hydrophilic coating. The hydrophilic coating on the inner wall of the microperforations actively guides the water in the microperforations located on the second surface into the microperforations using capillary force, and causes the water to flow to the first surface under the concentration gradient difference, thereby accelerating the discharge.

[0036] According to a second aspect of the present invention, a fuel cell includes a gas diffusion module of a fuel cell disclosed in any of the above embodiments, wherein the microporous layer is stacked on the surface opposite to the substrate layer and attached to the catalyst layer of the fuel cell.

[0037] Fuel cells can be applied to the field of drone flight. An airflow space is formed between the first surface of the substrate and the substrate, while a catalyst layer with a microporous layer is placed on the cathode surface of the proton exchange membrane.

[0038] The fuel cell of the present invention utilizes a gas diffusion module of a fuel cell disclosed in any of the above embodiments, thereby improving the operational stability and reliability of the fuel cell.

[0039] According to the preparation method of the second aspect of the present invention, such as Figure 3 As shown, a method for preparing a gas diffusion module includes: S610. A temporary sealing layer is attached to the first surface of the substrate sheet to cover the first surface of the substrate sheet, and the second surface of the substrate sheet is immersed in a hydrophobic agent impregnation solution, with the immersion depth reaching the thickness of the substrate sheet reaching a first proportion threshold. S620. Remove the temporary sealing layer, immerse the first surface of the substrate sheet in a hydrophobic impregnation solution, and immerse the substrate sheet to a depth that reaches the thickness of the substrate sheet reaching a second proportion threshold. Dry and sinter the immersed substrate sheet to form a base layer, wherein the second proportion threshold is greater than the first proportion threshold. S630. Perform a laser drilling step to form multiple micro-perforations on the substrate layer. A portion of the micro-perforations constitute a first group of perforations, and another portion constitutes a second group of perforations. The first group of perforations is correspondingly disposed in the region of the substrate layer facing each of the flow channel ridges, and the second group of perforations is correspondingly disposed in the region of the substrate layer facing each of the flow channel grooves. In the direction of airflow, the diameter of the micro-perforations in the first group and the second group located in front of the airflow direction is larger than the diameter of the micro-perforations in front of the airflow direction. Alternatively, the opening density of the micro-perforations in the first group and the second group located in front of the airflow direction is greater than the opening density of the micro-perforations in front of the airflow direction. Furthermore, on any co-position line perpendicular to the airflow direction, the opening density of the micro-perforations in the first group is greater than the opening density of the micro-perforations in the second group, and the diameter of the micro-perforations in the first group is smaller than the diameter of the micro-perforations in the second group. S640. A microporous slurry is coated onto the second surface of the substrate and dried and sintered to form a microporous layer.

[0040] The substrate sheet can be made of porous materials such as carbon fiber, carbon black, carbon nanotubes, porous titanium, and porous nickel. A temporary sealing layer is first attached to the first surface of the substrate sheet. A hydrophobic coating can be formed on the second surface of the substrate sheet by immersion. The second surface is then brought into contact with the hydrophobic impregnation liquid. At the same time, vacuum or positive pressure can be selectively applied to control the penetration driving force and control the penetration depth of the hydrophobic impregnation liquid from the second surface to reach a first percentage threshold of the thickness of the substrate sheet. The first percentage threshold ranges from 20% to 40%.

[0041] Then, the temporary sealing layer is removed, and the substrate sheet is flipped over so that the first surface is immersed in the hydrophobic agent impregnation solution with the first surface facing down. The immersion depth reaches the thickness of the substrate sheet and reaches the second proportion threshold. The second proportion threshold ranges from 30% to 50%. It can be understood that the immersion depth of the second proportion threshold needs to be greater than the first proportion threshold. For example, if the first proportion threshold is 35%, then the second proportion threshold is 50%, thereby ensuring that the hydrophobicity of the first surface is greater than that of the second surface.

[0042] Then, the soaked substrate sheet is dried and sintered at 340–380°C for 20–40 minutes to form the base layer.

[0043] In addition, this application uses a laser drilling process to form multiple micro-perforations on the substrate layer. Compared with the previous drilling method using drip etching, laser drilling can ensure that the diameter of the micro-perforations remains roughly consistent in the penetration direction, and can control the diameter of the opening relatively accurately. It can also control the moving laser to drill relatively accurately at the corresponding position to form a first group and a second group of holes with different opening densities and different diameters. It can also form micro-perforations with different diameters in the airflow direction or form different opening densities at different positions.

[0044] In some embodiments of the present invention, the temporary sealing layer is a peelable polymer film, a heat-sensitive wax layer, or a water-soluble coating, such as a polyimide film. These materials do not react with the substrate layer, can adhere to the surface of the substrate layer, and can be easily detached and removed under external force.

[0045] The preparation method of the present invention produces a gas diffusion module that can maintain a relatively balanced moisture content at different positions on the cathode surface, preventing moisture accumulation and excessive moisture loss.

[0046] In some embodiments of the present invention, the step of performing laser drilling and the step of coating the microporous slurry onto the second surface of the substrate and performing drying and sintering to form the microporous layer further include: The hydrophilic agent is sprayed onto the second surface of the substrate layer; The hydrophilic agent is drawn into the microperforations by the capillary action of the microperforations. Compressed air is used to blow away the second surface of the substrate to remove the residual hydrophilic agent on the second surface. After drying and sintering, a hydrophilic coating is formed on the inner peripheral wall of the micro-perforation at the transition position between the first and second surfaces.

[0047] After laser drilling, a hydrophilic agent can be sprayed onto the second surface of the substrate layer to ensure that the hydrophobicity of the second surface is less than that of the first surface. During the immersion step, a small area in the center of the substrate sheet is not immersed in the hydrophobic agent. The capillary action of the microperforations draws the hydrophilic agent into the microperforations, removing the residual hydrophilic agent from the second surface. This ensures that the hydrophilicity in the center of the microperforations is higher than that on the second surface (i.e., the hydrophobicity in the center of the microperforations is lower than that on the second surface). Finally, after drying and sintering, a hydrophilic coating is formed at the transition position of the inner peripheral wall of the microperforations. Specifically, the hydrophobic impregnation liquid is polytetrafluoroethylene, polyvinylidene fluoride, fluorinated ethylene propylene, or a tetrafluoroethylene copolymer resin, and the hydrophilic agent is one or more of polyacrylic acid, polyvinyl alcohol, titanium dioxide nanoparticles, or hydrophilic carbon nanotubes.

[0048] In actual preparation processes, the following methods can be used: 1. Take carbon paper (190 μm thick), cut it to the required size, prepare a 20 wt.% PTFE aqueous emulsion, attach a polyimide film to the first surface of the carbon paper as a temporary sealing layer, place it in a Buchner funnel with the first surface facing down in contact with the porous plate and the second surface facing up. Start the vacuum pump, and after the vacuum level stabilizes at -0.07 MPa, pour the PTFE aqueous emulsion onto the second surface and allow it to permeate for 30 seconds.

[0049] Remove the carbon paper, remove the temporary sealing layer, and dry at 60°C for 10 minutes.

[0050] Flip the carbon paper and pour the PTFE aqueous emulsion onto the first surface. Vacuum can be used; capillary penetration can be performed for 20 seconds. After drying, weigh the emulsion to ensure that the total PTFE content of the substrate layer is 20 wt.%. Sinter at 360℃ for 40 minutes.

[0051] A UV laser drilling machine with a laser power of 10 W and a pulse frequency of 5 kHz is used to process micro-perforations.

[0052] Based on the cathode flow channel structure, an opening ratio of 4% and a pore diameter of 100 μm are set in the corresponding flow channel ridge region; and an opening ratio of 2% and a pore diameter of 150 μm are set in the corresponding flow channel groove region. The perforations are distributed in an array, with a total opening ratio of approximately 3%.

[0053] A 1 wt.% Nafion aqueous solution was prepared and sprayed onto the surface of perforated carbon paper (spraying distance 20 cm, pressure 0.2 MPa, 2 coats). After standing for 30 seconds, the surface was blown off with compressed air at 0.3 MPa and dried at 60℃ for 30 minutes. Acetylene black, PTFE emulsion, and ethylene glycol were ball-milled at a mass ratio of 2:1:10 for 4 hours to obtain a microporous slurry. This slurry was then coated onto the side of the carbon paper with a lower PTFE content, to a thickness of 30 μm. After drying at 120℃, it was sintered at 350℃ to obtain a gas diffusion layer.

[0054] Second, the difference from the first method is that by controlling the permeation time, vacuum permeation is performed on the second surface for 15 seconds, capillary permeation is performed on the first surface for 15 seconds, and the substrate is dried and weighed to make the total PTFE content of the substrate layer 10 wt.%, while the remaining steps are the same.

[0055] The difference from the first method is that by controlling the permeation time, the permeation is carried out on the second surface for 60 seconds and on the first surface by capillary permeation for 40 seconds. After drying, the product is weighed to make the total PTFE content of the substrate layer 30 wt.%, while the other steps are the same.

[0056] Fourth, the difference from the first method is that the hydrophobic agent is replaced by FEP emulsion (60 wt.% diluted to 20 wt.%) instead of PTFE emulsion, and the total FEP content is controlled at 20 wt.%, while the other steps are the same.

[0057] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0058] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A gas diffusion module for a fuel cell, wherein an airflow space is provided between the cathode surface and the substrate of the gas diffusion module, allowing air to flow, and the substrate protrudes from the surface facing the gas diffusion module with a plurality of spaced-apart flow channel ridges, and a flow channel groove is formed between two adjacent flow channel ridges; characterized in that, The gas diffusion module includes a substrate layer and a microporous layer stacked sequentially. The first surface of the substrate layer faces the gas flow space to form the cathode surface of the gas diffusion module, and the second surface of the substrate layer faces the microporous layer. The ridge surface of the flow channel ridge is close to the first surface of the substrate layer. The substrate layer is provided with at least one set of first holes and at least one set of second holes. The first holes are correspondingly disposed in the region of the substrate layer facing each flow channel ridge, and the second holes are correspondingly disposed in the region of the substrate layer facing each flow channel groove. Both the first holes and the second holes have micro-perforations that penetrate the thickness direction. Specifically, the hydrophobicity of the microperforations on the first surface is greater than that on the second surface; in the airflow direction, the diameter of the microperforations located in front of the airflow direction in the first and second hole groups is greater than the diameter of the microperforations located behind the airflow direction, or the opening density of the microperforations located in front of the airflow direction in the first and second hole groups is greater than the opening density of the microperforations located behind the airflow direction; on any coaxial line perpendicular to the airflow direction, the opening density of the microperforations in the first hole group is greater than the opening density of the microperforations in the second hole group, and the diameter of the microperforations in the first hole group is smaller than the diameter of the microperforations in the second hole group.

2. The gas diffusion module for a fuel cell according to claim 1, characterized in that: In the thickness direction, the hydrophobicity of the microperforations first decreases and then increases from the second surface to the first surface.

3. The gas diffusion module for a fuel cell according to claim 2, characterized in that: At least a portion of the surface of the microperforation's aperture edge and inner peripheral wall is provided with a hydrophobic coating. The hydrophobic coating is composed of a hydrophobic agent covering the surface of the microperforation. Specifically, the hydrophobic agent content of the hydrophobic coating near the first surface is 25–45 wt.%, and the contact angle of the microperforation near the first surface is 135–155°. The hydrophobic agent content of the hydrophobic coating at the transition position between the first and second surfaces is 2–6 wt.%, and the contact angle of the microperforation at the transition position between the first and second surfaces is 90–100°. The hydrophobic agent content of the hydrophobic coating near the second surface is 8–18 wt.%, and the contact angle of the microperforation near the second surface is 105–125°.

4. The gas diffusion module for a fuel cell according to claim 3, characterized in that: The microperforations are further provided with a hydrophilic coating on the surface at the transition position.

5. A fuel cell, characterized in that, The gas diffusion module of a fuel cell as described in any one of claims 1 to 4 is wherein the microporous layer is stacked on the surface of the substrate layer opposite to the substrate layer and attached to the catalyst layer of the fuel cell.

6. A preparation method for preparing a gas diffusion module, characterized in that, The preparation method includes: A temporary sealing layer is attached to the first surface of the substrate sheet to cover the first surface of the substrate sheet, and the second surface of the substrate sheet is immersed in a hydrophobic agent impregnation solution, with the immersion depth reaching the thickness of the substrate sheet reaching the first proportion threshold. Remove the temporary sealing layer, immerse the first surface of the substrate sheet in a hydrophobic impregnation solution, and immerse the substrate sheet to a depth that reaches the thickness of the substrate sheet to a second proportion threshold. Dry and sinter the immersed substrate sheet to form a base layer, wherein the second proportion threshold is greater than the first proportion threshold. A laser drilling step is performed to form multiple micro-perforations on a substrate layer. A portion of the micro-perforations constitute a first group of perforations, and another portion constitutes a second group of perforations. The first group of perforations is disposed in a corresponding manner in the region of the substrate layer facing each of the flow channel ridges, and the second group of perforations is disposed in a corresponding manner in the region of the substrate layer facing each of the flow channel grooves. In the direction of airflow, the diameter of the micro-perforations in the first and second groups that are located in front of the airflow direction is larger than the diameter of the micro-perforations in the airflow direction. Alternatively, the opening density of the micro-perforations in the first and second groups that are located in front of the airflow direction is greater than the opening density of the micro-perforations in the airflow direction. Furthermore, on any coaxial line perpendicular to the airflow direction, the opening density of the micro-perforations in the first group is greater than the opening density of the micro-perforations in the second group, and the diameter of the micro-perforations in the first group is smaller than the diameter of the micro-perforations in the second group. A microporous slurry is coated onto the second surface of the substrate and then dried and sintered to form a microporous layer.

7. The preparation method according to claim 6, characterized in that, Between the laser drilling step and the coating of the microporous slurry onto the second surface of the substrate and the drying and sintering process to form the microporous layer, the following steps are also included: The hydrophilic agent is sprayed onto the second surface of the substrate layer; The hydrophilic agent is drawn into the microperforations by the capillary action of the microperforations. Compressed air is used to blow away the second surface of the substrate to remove the residual hydrophilic agent on the second surface. After drying and sintering, a hydrophilic coating is formed on the inner peripheral wall of the micro-perforation at the transition position between the first and second surfaces.

8. The preparation method according to claim 7, characterized in that, The hydrophobic impregnation solution is polytetrafluoroethylene, polyvinylidene fluoride, fluorinated ethylene propylene, or tetrafluoroethylene copolymer resin, and the hydrophilic agent is one or more of polyacrylic acid, polyvinyl alcohol, titanium dioxide nanoparticles, or hydrophilic carbon nanotubes.

9. The preparation method according to claim 6, characterized in that, The temporary sealing layer is a peelable polymer film, a heat-sensitive wax layer, or a water-soluble coating.

10. The preparation method according to claim 6, characterized in that, The first percentage threshold ranges from 20% to 40%, and the second percentage threshold ranges from 30% to 50%.

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