A gas diffusion layer for a low-humidification fuel cell, its preparation method, and the low-humidification fuel cell.

Abstract

This invention relates to the field of fuel cell technology, and more particularly to a gas diffusion layer for low-humidity fuel cells, its preparation method, and a low-humidity fuel cell. The gas diffusion layer for low-humidity fuel cells of this invention has an inlet end and an outlet end, comprising a substrate layer and a microporous layer stacked together. The substrate layer includes multiple substrate-level regions, and the microporous layer includes multiple microporous-level regions. From the inlet end to the outlet end, the hydrophobicity of the multiple substrate-level regions increases progressively, and the hydrophobicity of the multiple microporous-level regions also increases progressively. At the same location in the gas diffusion layer, the hydrophobicity increases from the substrate layer to the microporous layer. The gas diffusion layer of this invention coordinates moisture distribution both laterally and longitudinally, possessing a self-regulating function of water retention in low humidity and efficient drainage in high humidity. This significantly improves the output stability and electrical performance of the fuel cell under conditions without external humidification, solving the problem of poor water management under low humidity conditions.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a gas diffusion layer for low-humidification fuel cells, its preparation method, and its application. Background Technology

[0002] Water management is a core challenge for fuel cells operating under low humidity conditions. For example, air-cooled fuel cells use air as a coolant and are typically used in low-power applications, such as devices below 5kW. Air-cooled stacks have a relatively simple structure, lacking complex water-cooling systems and relying on air for heat dissipation. Due to the absence of external humidification equipment, the intake air humidity may be low, leading to easy drying of the membrane electrode assembly (MEA). However, water generated during the reaction accumulates in the flow channels, especially at the outlet. Because heat dissipation relies on air, high temperatures increase water evaporation, but airflow also carries away moisture, causing localized dryness. At the inlet, the low air humidity absorbs moisture from the membrane, causing it to dry out; while water generated during the reaction accumulates in the flow channels, especially at the outlet, water vapor condenses in cooler areas as the reaction progresses, forming liquid water. This results in less moisture near the inlet and more moisture at the outlet, creating a moisture gradient. Some air-cooled fuel cells use open flow channels, leading to significant water accumulation at the outlet. In existing technologies, the gas diffusion layer often uses homogeneous hydrophobic treatment, but its hydrophobicity is singular and cannot effectively regulate moisture distribution, causing the proton exchange membrane (PEM) to dry out and its ionic conductivity to decrease. Traditional hydrophobic diffusion layer designs suffer from high membrane resistance due to insufficient water at the inlet, while poor drainage at the outlet causes the electrodes to be "submerged," hindering gas transport. Some gas diffusion layers optimize hydrophobicity by adjusting the carbon black ratio, but lack dynamic gradient adjustment capabilities and cannot adapt to humidity fluctuations.

[0003] As commercialization progresses, gas diffusion layers suitable for low humidity conditions face higher demands in terms of drainage efficiency, temperature control, and overall performance. Therefore, the design of the gas diffusion layer needs to specifically address the issues of poor water management in fuel cells under low humidity conditions, including dry inlet and water accumulation at the outlet. Summary of the Invention

[0004] This invention provides a gas diffusion layer for low-humidity fuel cells, a method for preparing the same, and a low-humidity fuel cell, to solve the problems of poor water management, dry inlet, and water accumulation at outlet of fuel cells under low humidity conditions.

[0005] According to a first aspect of the present invention, the present invention provides a gas diffusion layer for a low-humidification fuel cell, wherein the gas diffusion layer has an inlet end and an outlet end along a first direction of the gas diffusion layer;

[0006] Along the second direction of the gas diffusion layer, the gas diffusion layer includes a substrate layer and a microporous layer stacked together, with the first direction perpendicular to the second direction; wherein, the substrate layer includes multiple substrate-level regions, with the hydrophobicity of the multiple substrate-level regions increasing progressively from the air inlet end to the air outlet end; the microporous layer includes multiple microporous-level regions, with the hydrophobicity of the multiple microporous-level regions increasing progressively from the air inlet end to the air outlet end;

[0007] Along the second direction of the gas diffusion layer, at the same location in the gas diffusion layer, from the base layer to the microporous layer, the hydrophobicity increases.

[0008] It should be noted that in some specific embodiments, the first direction is the length direction and the second direction is the thickness direction.

[0009] This invention discloses a gas diffusion layer for a low-humidity fuel cell. This layer features a substrate-level region and a microporous-level region with progressively increasing hydrophobicity along a first direction. The hydrophobicity increases from the substrate layer to the microporous layer in this first direction. This three-dimensional gradient hydrophobic structure allows for precise control of moisture within the fuel cell. By dynamically balancing moisture distribution, the gradient hydrophobic structure improves the battery's output stability. At the inlet, lower hydrophobicity facilitates moisture absorption and retention, preventing membrane drying; at the outlet, higher hydrophobicity helps moisture discharge, preventing excessive water accumulation from hindering gas transport. This improves battery performance and stability, enabling it to better adapt to low-humidity conditions.

[0010] Furthermore, from the air inlet end to the air outlet end, the surface contact angles of the multiple microporous regions increase progressively in a gradient difference of 2~10°. By limiting the gradient difference of the surface contact angles of the microporous layer within a reasonable range, suitable hydrophobicity is ensured in different regions of the microporous layer. This helps to further refine the distribution and transport of moisture in the microporous layer, allowing moisture to be effectively discharged while maintaining a certain degree of humidity to preserve the ionic conductivity of the proton exchange membrane, thereby improving the operating efficiency and stability of the battery.

[0011] Furthermore, the surface contact angle of the microporous layer is 140°~155°. By limiting the surface contact angle of the microporous layer to a reasonable range, it is possible to further ensure that the microporous layer has appropriate hydrophobicity in different regions, which helps to further refine the distribution and transport of moisture in the microporous layer, thereby further improving the operating efficiency and stability of the battery.

[0012] Furthermore, from the air inlet end to the air outlet end, the surface contact angles of multiple substrate-level regions increase progressively in a gradient difference of 5~20°. By limiting the gradient difference of the substrate layer surface contact angles within a reasonable range, the substrate layer can better cooperate with the microporous layer for moisture management. The lower contact angle of the substrate layer at the air inlet end is beneficial for absorbing moisture from the air, providing the necessary humidity for the membrane; the higher contact angle at the air outlet end helps to transport moisture to the microporous layer, promoting moisture expulsion and further improving the performance and stability of the battery under low humidity conditions.

[0013] Furthermore, the surface contact angle of the substrate layer is 130°~145°.

[0014] Furthermore, along the second direction of the gas diffusion layer, at the same location within the gas diffusion layer, the surface contact angle increases with a gradient difference of 5–20° from the substrate layer to the microporous layer. By limiting the surface contact angle gradient from the substrate layer to the microporous layer at the same location within a reasonable range, it is ensured that moisture can be smoothly transported from the substrate layer to the microporous layer in the vertical direction and ultimately discharged. This design helps to form a good moisture gradient, making the distribution of moisture within the gas diffusion layer more reasonable, further improving the battery's drainage efficiency and operational stability.

[0015] Furthermore, from the air inlet end to the air outlet end, the base layer includes a first base level region and a second base level region, and the microporous layer includes a first microporous level region and a second microporous level region.

[0016] Wherein, the surface contact angle of the first substrate-level region is 130°~138°, and the surface contact angle of the second substrate-level region is 142°~145°; the surface contact angle of the first micropore-level region is 143°~146°, and the surface contact angle of the second micropore-level region is 150°~153°.

[0017] The above scheme provides more specific contact angle ranges for each level of the substrate layer and microporous layer, making the hydrophobicity distribution of the gas diffusion layer more precise. This helps to better control the performance of the gas diffusion layer in actual production, ensuring that its hydrophobicity in different regions can meet the precise water management requirements of fuel cells under low humidification conditions, thereby further improving battery performance.

[0018] According to a second aspect of the present invention, the present invention also provides a method for preparing the above-described low-humidification gas diffusion layer for fuel cells, comprising the following steps:

[0019] From the inlet end to the outlet end of the gas diffusion layer, different regions of the hydrophilic substrate layer are sequentially immersed in a substrate hydrophobic treatment solution with different concentrations of substrate hydrophobic agent, and then dried to form multiple substrate level regions with progressively increasing hydrophobicity.

[0020] On each of the substrate-level regions, a microporous layer hydrophobic treatment solution with different weight ratios of hydrophilic carbon material, hydrophobic carbon material, and microporous hydrophobic agent is coated by screen printing process, and then dried to form a corresponding microporous-level region on each of the substrate-level regions, thereby obtaining a gas diffusion layer precursor.

[0021] The gas diffusion layer precursor is calcined to obtain a gas diffusion layer for low-humidification fuel cells.

[0022] The above-described method provides a way to prepare a gas diffusion layer for low-humidity fuel cells. By sequentially impregnating different regions of a substrate layer in treatment solutions with different concentrations of hydrophobic agents, and by coating the substrate layer with hydrophobic treatment solutions of different proportions of microporous layers, a three-dimensional gradient hydrophobic structure of the gas diffusion layer can be effectively achieved. This preparation method has the advantages of strong operability and ease of control, which is conducive to the preparation of high-performance gas diffusion layers in actual production and promotes the application of this technology in the field of low-humidity fuel cells.

[0023] Furthermore, in the microporous layer hydrophobic treatment liquid, from the air inlet end to the air outlet end, the content of microporous hydrophobic agent in multiple microporous grade regions increases step by step, the content of hydrophilic carbon material decreases step by step, and the content of hydrophobic carbon material increases step by step.

[0024] The hydrophilic carbon material is one or more of carbon black containing hydrophilic groups, single-walled carbon nanotubes containing hydrophilic groups, and multi-walled carbon nanotubes containing hydrophilic groups, wherein the hydrophilic groups include hydroxyl, carboxyl, or silane groups; the hydrophobic carbon material is selected from one or more of graphite, acetylene black, single-walled carbon nanotubes, and multi-walled carbon nanotubes; the microporous hydrophobic agent is one or more of polytetrafluoroethylene, polyvinylidene fluoride, and fluorinated ethylene propylene copolymer.

[0025] The aforementioned scheme specifies the types and content trends of each component in the hydrophobic treatment solution of the microporous layer, providing a concrete means for the hydrophobic gradient design of the microporous layer. By adjusting the weight ratio of hydrophilic carbon materials, hydrophobic carbon materials, and microporous hydrophobic agents, the hydrophobicity of the microporous layer in different regions can be precisely controlled, further improving the moisture management capability of the gas diffusion layer and enhancing battery performance.

[0026] Furthermore, the hydrophilic carbon material is a hydroxylated multi-walled carbon nanotube, and the hydroxylated multi-walled carbon nanotube has an inner diameter of 3~15nm, an outer diameter of 5~50nm, and a length of 0.5~30μm.

[0027] The above scheme defines the specific types and physical properties of hydrophilic carbon materials, such as the inner diameter, outer diameter, and length of hydroxylated multi-walled carbon nanotubes. These defined parameters help ensure that the hydrophilic carbon materials can play a good role in water retention and moisture transport in the microporous layer, further optimizing the performance of the microporous layer and improving the operational stability of the battery under low humidity conditions.

[0028] Furthermore, in the hydrophobic treatment liquid of the substrate layer, the content of the substrate hydrophobic agent in multiple substrate-level regions increases progressively from the air inlet end to the air outlet end; the substrate hydrophobic agent is one or more of polytetrafluoroethylene, polyvinylidene fluoride, and fluorinated ethylene propylene copolymer.

[0029] The aforementioned scheme specifies the types and content trends of the hydrophobic agent in the substrate hydrophobic treatment fluid, providing a concrete implementation method for the hydrophobicity gradient design of the substrate. By progressively increasing the content of the substrate hydrophobic agent, the hydrophobicity of the substrate in different regions can meet the water management requirements of the fuel cell, enhancing the substrate's ability to regulate moisture and thus improving the performance of the entire gas diffusion layer.

[0030] According to a third aspect of the present invention, the present invention also provides a low-humidification fuel cell, comprising the gas diffusion layer for a low-humidification fuel cell described above or a gas diffusion layer for a low-humidification fuel cell prepared by the above-described preparation method.

[0031] By employing a gas diffusion layer with a three-dimensional gradient hydrophobic structure or a gas diffusion layer prepared by the above methods, low-humidification fuel cells can achieve better water management, effectively solving the problems of inlet dryness and outlet water accumulation. This enables fuel cells to maintain high performance and stability under low-humidification conditions, extending battery life and providing strong support for their widespread application in various low-power scenarios, thus promoting the commercial development of fuel cell technology.

[0032] The beneficial effects of this invention are:

[0033] This invention provides a low-humidification gas diffusion layer for fuel cells, which achieves precise control of internal moisture levels through a three-dimensional gradient hydrophobic structure design. At the inlet, lower hydrophobicity facilitates moisture absorption and retention, preventing membrane drying; at the outlet, higher hydrophobicity aids in moisture discharge, preventing excessive water accumulation from hindering gas transport, thereby improving battery performance and stability. Without external humidification, the gradient hydrophobic structure can dynamically balance moisture distribution, enabling the fuel cell to maintain good operating conditions under low humidity, improving output stability and lifespan.

[0034] The present invention provides a low-humidification gas diffusion layer for fuel cells, which features water retention in low humidity and efficient drainage in high humidity. It can automatically adjust the moisture distribution according to the humidity changes inside the fuel cell, effectively solving the problems of traditional gas diffusion layers being prone to drying in low humidity and poor drainage in high humidity, thus improving the drainage efficiency of fuel cells.

[0035] This invention provides a low-humidification gas diffusion layer for fuel cells. Through a gradient distribution of hydrophilic and hydrophobic carbon black, the microporous layer optimizes water retention and drainage functions in different regions. The higher content of hydrophilic carbon black in the inlet region helps retain water, while the higher content of hydrophobic carbon black in the outlet region facilitates drainage, further improving the drainage performance of the fuel cell. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0037] Figure 1 is a schematic diagram of the structure of a gas diffusion layer for a low-humidification fuel cell provided in Embodiment 1 of the present invention.

[0038] Figure 2 is a comparison of the polarization curve performance of the membrane electrode assembly prepared by the gas diffusion layer in Examples 1-2 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] Example 1

[0041] This embodiment provides a gas diffusion layer for a low-humidification fuel cell, such as... Figure 1 As shown, along the length of the gas diffusion layer, the gas diffusion layer has an inlet end 101 and an outlet end 102.

[0042] Along the thickness direction of the gas diffusion layer, the gas diffusion layer includes a substrate layer 1 and a microporous layer 2 stacked together. From the inlet end 101 to the outlet end 102, the substrate layer 1 includes a first substrate level region 11 and a second substrate level region 12, and the microporous layer 2 includes a first microporous level region 21 and a second microporous level region 22.

[0043] The surface contact angle of the first substrate-level region 11 is 130.7°, and the surface contact angle of the second substrate-level region 12 is 142.6°; the surface contact angle of the first micropore-level region 21 is 143.7°, and the surface contact angle of the second micropore-level region 22 is 152.8°.

[0044] This embodiment also provides a method for preparing the gas diffusion layer for the low-humidification fuel cell, which specifically includes the following steps:

[0045] Step (1): Immerse the hydrophilic substrate layer in a 2% solids content polytetrafluoroethylene (PTFE) emulsion for 5 minutes. After immersion, dry it in an oven at 100 degrees Celsius for 10 minutes. Divide the immersed substrate layer into two equal parts, labeled as the first substrate grade region 11 and the second substrate grade region 12. Immerse the second substrate grade region 12 in a 5% solids content polytetrafluoroethylene (PTFE) emulsion for 5 minutes. After immersion, dry it in an oven at 100 degrees Celsius for 10 minutes. After drying, calcine it at 360 degrees Celsius for 1 hour. Designate the first substrate grade region 11 as the substrate layer air inlet area and the second substrate grade region 12 as the substrate layer air outlet area.

[0046] Step (2) Preparation of the microporous layer in the air inlet region: Hydroxylated multi-walled carbon nanotubes (inner diameter 3~5nm, outer diameter 8~15nm, length 0.5~2μm), acetylene black, polytetrafluoroethylene emulsion, and isopropanol are thoroughly mixed to obtain a hydrophobic treatment solution. In the hydrophobic treatment solution, the mass ratio of hydroxylated multi-walled carbon nanotubes, acetylene black, and polytetrafluoroethylene is 7:3:4, and the mass ratio of carbon materials (including hydroxylated multi-walled carbon nanotubes and acetylene black) to isopropanol is 1:30. The hydrophobic treatment solution is screen-printed onto the first substrate level region 11 in step (1) and dried in an oven at 100 degrees Celsius for 10 minutes. This microporous layer region is designated as the first microporous level region 21, i.e., the microporous layer air inlet region.

[0047] Step (3) Preparation of the microporous layer in the exhaust outlet region: Hydroxylated multi-walled carbon nanotubes, acetylene black, polytetrafluoroethylene emulsion, and isopropanol are thoroughly mixed. In the hydrophobic treatment solution, the mass ratio of carbon materials (including hydroxylated multi-walled carbon nanotubes and acetylene black) to isopropanol is 1:30, and the mass ratio of hydroxylated multi-walled carbon nanotubes, acetylene black, and polytetrafluoroethylene is 3:7:5. The hydrophobic treatment solution is screen-printed onto the second substrate level region 12 in step (1) and dried in an oven at 100 degrees Celsius for 10 minutes. This microporous layer region is designated as the second microporous level region 22, i.e., the exhaust outlet region of the microporous layer.

[0048] Step (4) The gas diffusion layer precursor obtained in steps (1)-(3) is placed in a muffle furnace for calcination at a temperature of 360 degrees Celsius for 1 hour to prepare a gas diffusion layer with four regions.

[0049] Example 2

[0050] This embodiment provides a gas diffusion layer for a low-humidification fuel cell, which differs from Embodiment 1 in that: the surface contact angle of the first substrate-level region 11 is 137.1°, the surface contact angle of the second substrate-level region 12 is 144.3°; the surface contact angle of the first micropore-level region 21 is 145.2°, and the surface contact angle of the second micropore-level region 22 is 150.3°.

[0051] This embodiment also provides a method for preparing the gas diffusion layer for the low-humidification fuel cell, which specifically includes the following steps:

[0052] Step (1): Immerse the hydrophilic substrate layer in a 4% solids content polytetrafluoroethylene (PTFE) emulsion for 5 minutes. After immersion, dry it in an oven at 100 degrees Celsius for 10 minutes. Divide the immersed substrate layer into two equal parts, labeled as the first substrate grade region 11 and the second substrate grade region 12. Immerse the second substrate grade region 12 in a 6% solids content polytetrafluoroethylene (PTFE) emulsion for 5 minutes. After immersion, dry it in an oven at 100 degrees Celsius for 10 minutes. After drying, calcine it at 360 degrees Celsius for 1 hour. Designate the first substrate grade region 11 as the substrate layer air inlet area and the second substrate grade region 12 as the substrate layer air outlet area.

[0053] Step (2) Preparation of the microporous layer in the air inlet region: Hydroxylated multi-walled carbon nanotubes, acetylene black, polytetrafluoroethylene emulsion, and isopropanol are thoroughly mixed to obtain a hydrophobic treatment solution. The mass ratio of carbon materials (including hydroxylated multi-walled carbon nanotubes and acetylene black) to isopropanol is 1:30. In the hydrophobic treatment solution, the mass ratio of hydroxylated multi-walled carbon nanotubes, acetylene black, and polytetrafluoroethylene is 6:4:4. The solution is screen-printed onto the first substrate level region 11 in step (1) and dried in an oven at 100 degrees Celsius for 10 minutes. This microporous layer region is designated as the first microporous level region 21, i.e., the microporous layer air inlet region.

[0054] Step (3) Preparation of the microporous layer in the exhaust outlet region: Hydroxylated multi-walled carbon nanotubes, acetylene black, polytetrafluoroethylene emulsion, and isopropanol are thoroughly mixed. In the hydrophobic treatment solution, the mass ratio of carbon materials (including hydroxylated multi-walled carbon nanotubes and acetylene black) to isopropanol is 1:30, and the mass ratio of hydroxylated multi-walled carbon nanotubes, acetylene black, and polytetrafluoroethylene is 4:6:5. The mixture is screen-printed onto the second substrate level region 12 in step (1) and dried in an oven at 100 degrees Celsius for 10 minutes. This microporous layer region is designated as the second microporous level region 22, i.e., the exhaust outlet region of the microporous layer.

[0055] Step (4) The gas diffusion layer obtained in steps (1)-(3) is placed in a muffle furnace for calcination at a temperature of 360 degrees Celsius for 1 hour to prepare a gas diffusion layer with four regions.

[0056] Comparative Example 1

[0057] This comparative example provides a gas diffusion layer, the preparation method of which is as follows:

[0058] Step (1) The substrate is impregnated and hydrophobicated. The impregnation solution is polytetrafluoroethylene emulsion with a concentration of 5% and an impregnation time of 5 minutes. After impregnation, it is dried in an oven at a temperature of 100 degrees Celsius for 10 minutes. After drying, it is calcined at 360 degrees Celsius for 1 hour.

[0059] Step (2) A microporous layer is prepared on the substrate. The hydrophobic treatment solution of the microporous layer is composed of carbon powder and hydrophobic agent. The carbon powder is acetylene black and the hydrophobic agent is polytetrafluoroethylene. The mass ratio of acetylene black to polytetrafluoroethylene is 6:4. The solution is screen printed onto the substrate and dried in an oven at 100 degrees Celsius for 10 minutes. After drying, the solution is calcined at 360 degrees Celsius for 1 hour.

[0060] Comparative Example 2

[0061] This comparative example provides a gas diffusion layer, the preparation method of which is as follows:

[0062] Step (1) The substrate layer is impregnated with a hydrophobic treatment. The impregnation solution is polytetrafluoroethylene emulsion with a concentration of 5% and an impregnation time of 5 minutes. After impregnation, it is dried in an oven at 100 degrees Celsius for 10 minutes. After drying, it is calcined at 360 degrees Celsius for 1 hour. The impregnated substrate layer is divided into two equal parts according to the region, which are marked as the first region and the second region.

[0063] Step (2) Preparation of the microporous layer in the air inlet region: Hydroxylated multi-walled carbon nanotubes, acetylene black, polytetrafluoroethylene emulsion, and isopropanol are thoroughly mixed. The hydrophobic treatment solution has a mass ratio of 4:1:1 for hydroxylated multi-walled carbon nanotubes, acetylene black, and polytetrafluoroethylene. The mixture is then screen-printed onto the first region in step (1) and dried in an oven at 100 degrees Celsius for 10 minutes. This microporous layer region is designated as the microporous layer air inlet region.

[0064] Step (3) Preparation of the microporous layer in the air inlet and outlet area: Acetylene black, polytetrafluoroethylene emulsion, and isopropanol are thoroughly mixed. The hydrophobic treatment solution ratio is 6:4 (mass ratio of acetylene black to polytetrafluoroethylene). The mixture is then screen-printed onto the second area in step (1) and dried in an oven at 100 degrees Celsius for 10 minutes. This microporous layer area is designated as the air inlet and outlet area of ​​the microporous layer.

[0065] Step (4) The gas diffusion layer is placed in a muffle furnace and calcined at a temperature of 360 degrees Celsius for 1 hour to prepare a gas diffusion layer with four regions.

[0066] Comparative Example 3

[0067] This comparative example provides a gas diffusion layer, the preparation method of which is as follows:

[0068] Step (1) Immerse the hydrophilic substrate layer in a 1% polytetrafluoroethylene (PTFE) emulsion for 5 minutes. After immersion, dry it in an oven at 100 degrees Celsius for 10 minutes. Divide the immersed substrate layer into two equal parts, labeled as Region 1 and Region 2. Immerse Region 2 in a 5% polytetrafluoroethylene (PTFE) emulsion for 5 minutes. After immersion, dry it in an oven at 100 degrees Celsius for 10 minutes. After drying, calcine it at 360 degrees Celsius for 1 hour. Designate Region 1 as the substrate layer air inlet area and Region 2 as the substrate layer air outlet area.

[0069] Step (2) A microporous layer is prepared on the substrate. The hydrophobic treatment solution of the microporous layer is composed of carbon powder and hydrophobic agent. The carbon powder is acetylene black and the hydrophobic agent is polytetrafluoroethylene. The mass ratio of acetylene black to polytetrafluoroethylene is 6:4. The solution is screen printed onto the substrate and dried in an oven at 100 degrees Celsius for 10 minutes. After drying, the solution is calcined at 360 degrees Celsius for 1 hour.

[0070] The hydrophilic substrate used in the comparative and example examples was Toray TGP~H~060 carbon paper.

[0071] Gas diffusion layers were fabricated using the methods provided in the embodiments and comparative examples for fabricating fuel cell gas diffusion layers. The first substrate-level region 11 and the first region of the gas diffusion layer correspond to the air inlet direction of the flow field, while the second substrate-level region 12 and the second region of the gas diffusion layer correspond to the air outlet direction of the flow field. Film-coated electrode assemblies were then fabricated, and performance tests were performed. The test items and results are compared below:

[0072] Performance testing

[0073] The polarization curves of the membrane electrode assembly in the test embodiment and comparative example were obtained using an industry-standard fuel cell fixture. The test conditions were: battery temperature set at 60 degrees Celsius, hydrogen / air ratio: RH 15%, outlet back pressure 100 kPa, and metering ratio H2: 1.5, air: 2.5. The test results are as follows: Figure 2 As shown in Table 1, the battery performance is as follows. It can be seen that the single cell assembled with the gas diffusion layer prepared by the preparation method of the present invention has higher performance than the membrane electrode of other comparative gas diffusion layers.

[0074] Table 1

[0075]

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A gas diffusion layer for a low-humidification fuel cell, characterized in that, Along a first direction of the gas diffusion layer, the gas diffusion layer has an inlet end and an outlet end; Along the second direction of the gas diffusion layer, the gas diffusion layer includes a substrate layer and a microporous layer stacked together, with the first direction perpendicular to the second direction; wherein, the substrate layer includes multiple substrate-level regions, with the hydrophobicity of the multiple substrate-level regions increasing progressively from the air inlet end to the air outlet end; the microporous layer includes multiple microporous-level regions, with the hydrophobicity of the multiple microporous-level regions increasing progressively from the air inlet end to the air outlet end; Along the second direction of the gas diffusion layer, at the same location in the gas diffusion layer, the hydrophobicity increases from the substrate layer to the microporous layer; From the air inlet end to the air outlet end, the surface contact angles of the multiple micropore-level regions increase progressively with a gradient difference of 2 to 10°. The surface contact angle of the microporous layer is 140°~155°; From the air inlet end to the air outlet end, the surface contact angles of the multiple base-level regions increase progressively with a gradient difference of 5~20°. The surface contact angle of the substrate layer is 130°~145°; Along the second direction of the gas diffusion layer, at the same location in the gas diffusion layer, from the substrate layer to the microporous layer, the surface contact angle increases with a gradient difference of 5 to 20°.

2. The gas diffusion layer for a low-humidification fuel cell according to claim 1, characterized in that, From the air inlet end to the air outlet end, the base layer includes a first base level region and a second base level region, and the microporous layer includes a first microporous level region and a second microporous level region. Wherein, the surface contact angle of the first substrate-level region is 130°~138°, and the surface contact angle of the second substrate-level region is 142°~145°; the surface contact angle of the first micropore-level region is 143°~146°, and the surface contact angle of the second micropore-level region is 150°~153°.

3. The method for preparing the gas diffusion layer for a low-humidification fuel cell according to claim 1 or 2, characterized in that, Includes the following steps: From the inlet end to the outlet end of the gas diffusion layer, different regions of the hydrophilic substrate layer are sequentially immersed in a substrate hydrophobic treatment solution with different concentrations of substrate hydrophobic agent, and then dried to form multiple substrate level regions with progressively increasing hydrophobicity. On each of the substrate-level regions, a microporous layer hydrophobic treatment solution with different weight ratios of hydrophilic carbon material, hydrophobic carbon material, and microporous hydrophobic agent is coated by screen printing process, and then dried to form a corresponding microporous-level region on each of the substrate-level regions, thereby obtaining a gas diffusion layer precursor. The gas diffusion layer precursor is calcined to obtain a gas diffusion layer for low-humidification fuel cells.

4. The method for preparing a gas diffusion layer for a low-humidification fuel cell according to claim 3, characterized in that, In the microporous layer hydrophobic treatment liquid, from the air inlet end to the air outlet end, the content of microporous hydrophobic agent in multiple microporous grade regions increases step by step, the content of hydrophilic carbon material decreases step by step, and the content of hydrophobic carbon material increases step by step. The hydrophilic carbon material is one or more of carbon black containing hydrophilic groups, single-walled carbon nanotubes containing hydrophilic groups, and multi-walled carbon nanotubes containing hydrophilic groups, wherein the hydrophilic groups include hydroxyl, carboxyl, or silane groups; the hydrophobic carbon material is selected from one or more of graphite, acetylene black, single-walled carbon nanotubes, and multi-walled carbon nanotubes; the microporous hydrophobic agent is one or more of polytetrafluoroethylene, polyvinylidene fluoride, and fluorinated ethylene propylene copolymer.

5. The method for preparing a gas diffusion layer for a low-humidification fuel cell according to claim 4, characterized in that, The hydrophilic carbon material is a hydroxylated multi-walled carbon nanotube, with an inner diameter of 3-15 nm, an outer diameter of 5-50 nm, and a length of 0.5-30 μm.

6. The method for preparing a gas diffusion layer for a low-humidification fuel cell according to claim 3, characterized in that, In the hydrophobic treatment solution of the substrate layer, the content of the substrate hydrophobic agent in multiple substrate-level regions increases progressively from the air inlet end to the air outlet end; the substrate hydrophobic agent is one or more of polytetrafluoroethylene, polyvinylidene fluoride, and fluorinated ethylene propylene copolymer.

7. A low-humidification fuel cell, characterized in that, The gas diffusion layer for a low-humidity fuel cell, as described in claim 1 or 2, or prepared by the method for preparing a low-humidity fuel cell gas diffusion layer as described in any one of claims 3-6, includes the gas diffusion layer for a low-humidity fuel cell described in claim 1 or 2.

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