Hydrogen fuel cell gas diffusion layer with integrated structure

Abstract

The invention discloses a hydrogen fuel cell gas diffusion layer with an integrated structure, and the gas diffusion layer has a gradient change pore structure in the thickness direction, is used for realizing gas diffusion regulation and water management functions of a microporous layer, and is also used for realizing mechanical support and gas distribution functions of a diffusion substrate layer. According to the integrated structure design, an interlayer interface between the micropore layer and the diffusion substrate layer is eliminated, and then the problems of mass transfer step and instability caused by sudden change of an interface structure are avoided; and meanwhile, the thickness of a gas diffusion layer can be obviously reduced, and the gas-water transmission efficiency is improved while the mass transfer uniformity is ensured.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen fuel cell technology, specifically relating to a gas diffusion layer for a hydrogen fuel cell with an integrated structure and its preparation technology. Background Technology

[0002] Hydrogen fuel cells have broad application prospects in new energy vehicles and distributed energy systems due to their advantages such as high energy conversion efficiency, low-temperature operation, and zero pollution emissions. As a core component of hydrogen fuel cells, the gas diffusion layer undertakes multiple functions, including transporting reactant gases (oxygen and hydrogen), discharging liquid water, conducting electrons and heat, and supporting the catalyst layer. Its structural design directly affects the battery's output performance and durability. Traditional commercial gas diffusion layers are a two-layer composite structure consisting of a microporous layer and a diffusion substrate layer. The microporous layer is composed of carbon powder (such as acetylene black, Vulcan XC-72R) and a hydrophobic agent (such as PTFE), forming a very fine and dense porous structure, mainly serving to reduce contact resistance with the catalyst layer, manage water precisely, and redistribute gas. The diffusion substrate layer is usually made of carbon fiber paper or carbon fiber cloth, with large pores and a relatively loose structure, mainly serving to provide mechanical support, gas distribution, electron conduction, and hydrothermal management. While this discrete two-layer structure of traditional gas diffusion layers is effective, it also introduces problems such as interfacial resistance and interfacial mass transfer resistance.

[0003] Currently, the core defects of traditional commercial gas diffusion layers stem from the inherent contradictions of the physical interface. These defects directly restrict the power density, lifespan, and cost of hydrogen fuel cells. For example: (1) High interfacial contact resistance: The diffusion substrate layer and the microporous layer are physically coated or pressed together, resulting in microscopic gaps and poor interfacial bonding strength at the interface; (2) Low oxygen diffusion efficiency: The double-layer structure of the diffusion substrate layer and the microporous layer increases the thickness of the gas diffusion layer, prolongs the oxygen transport path, and exacerbates the oxygen transport resistance; (3) Poor mechanical stability: During long-term operation, the interfacial bonding strength gradually weakens due to thermal stress and humidity cycling; (4) Complex preparation process: The process involves multiple steps, requiring sequential completion of diffusion substrate layer carbonization, microporous layer coating, hydrophobic treatment, and other procedures.

[0004] For the reasons mentioned above, there is an urgent need to develop a gas diffusion layer with a simple structure, superior mass transfer characteristics, simple preparation process, and low cost, so as to significantly improve the mass transfer performance and power density of hydrogen fuel cells under high current density conditions. Summary of the Invention

[0005] To overcome the aforementioned problems, this invention proposes a gas diffusion layer for hydrogen fuel cells with an integrated structure. The gas diffusion layer has a gradient-varying pore structure along its thickness, serving to regulate gas diffusion and manage water within the microporous layer, as well as providing mechanical support and gas distribution for the diffusion substrate layer. This integrated structural design eliminates the interface between the microporous layer and the diffusion substrate layer, thereby avoiding mass transfer abrupt changes and instability caused by abrupt changes in interface structure. Simultaneously, it significantly reduces the thickness of the gas diffusion layer, ensuring mass transfer uniformity while improving gas-water transport efficiency.

[0006] Specifically, the object of the present invention is to provide the following aspects:

[0007] On the one hand, a gas diffusion layer for a hydrogen fuel cell is provided, wherein the gas diffusion layer has a gradient pore structure in the thickness direction, which is used to realize the gas diffusion regulation and water management functions of the microporous layer, and also to realize the mechanical support and gas distribution functions of the diffusion substrate layer.

[0008] Optionally, the gas diffusion layer has a gradient of porosity and / or fiber diameter in the thickness direction.

[0009] Optionally, the gas diffusion layer is divided into 2 to 5 layers in the thickness direction.

[0010] Optionally, the average fiber diameter of the gas diffusion layer decreases monotonically from the flow field side to the catalyst layer side, or increases first and then decreases.

[0011] Optionally, the porosity of the gas diffusion layer decreases monotonically from the flow field side to the catalyst layer side, or increases first and then decreases.

[0012] Optionally, the total porosity of the gas diffusion layer is 0.75~0.9, and the porosity of each layer is 0.72~0.93.

[0013] Optionally, the average fiber diameter of each layer of the gas diffusion layer is 0.3~1.8μm.

[0014] In a second aspect, a method for preparing the gas diffusion layer described in the first aspect is provided, the method comprising:

[0015] Step 1: Dissolve the polymer in an organic solvent to obtain a spinning solution;

[0016] Step 2: The spinning solution is stretched and solidified by electrospinning technology to deposit a nonwoven fiber mat.

[0017] Step 3: Heat-treat the fiber felt to transform it into a conductive carbon fiber substrate, i.e., the gas diffusion layer.

[0018] In step 1, the polymer is selected from any one of polyvinyl alcohol, polyacrylonitrile, and polyimide.

[0019] Thirdly, a hydrogen fuel cell is provided, the hydrogen fuel cell including the gas diffusion layer described in the first aspect.

[0020] The beneficial effects of this invention include:

[0021] (1) The hydrogen fuel cell gas diffusion layer provided by the present invention has a pore structure with a gradient change in the thickness direction, which is used to realize the gas diffusion regulation and water management functions of the microporous layer, and also to realize the mechanical support and gas distribution functions of the diffusion substrate layer.

[0022] (2) The gas diffusion layer of the hydrogen fuel cell provided by the present invention significantly reduces the thickness of the gas diffusion layer, shortens the mass transfer path, improves the oxygen transport efficiency and distribution uniformity, reduces the mass transfer polarization loss under high current density, and improves the power density of the hydrogen fuel cell. Attached Figure Description

[0023] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0024] In the attached diagram:

[0025] Figure 1 The image shows a cross-sectional SEM image of the gas diffusion layer prepared in Example 1;

[0026] Figure 2 The image shows a SEM image of the cross-section of the gas diffusion layer prepared in Example 2;

[0027] Figure 3 The image shows a SEM image of the cross-section of the gas diffusion layer prepared in Example 3;

[0028] Figure 4 The SEM image of the cross-section of the gas diffusion layer in Comparative Example 1 is shown.

[0029] Figure 5 The diagram shows a comparison of the mass fractions of oxygen and liquid water at the interface between the cathode gas diffusion layer and the catalyst layer in hydrogen fuel cells prepared by Examples 1-3 and Comparative Example 1.

[0030] Figure 6The hydrogen fuel cells prepared by the gas diffusion layer of Examples 1-3 and Comparative Example 1 are shown, with oxygen mass fraction distribution cloud map and uniformity coefficient comparison diagram at the interface between the cathode gas diffusion layer and the catalyst layer.

[0031] Figure 7 The polarization curves and power density curves of hydrogen fuel cells prepared by the gas diffusion layer in Examples 1-3 and Comparative Example 1 are shown. Detailed Implementation

[0032] The following will refer to the appendix. Figures 1 to 7 Specific embodiments of the invention will be described in more detail below. While specific embodiments of the invention are shown in the accompanying drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0033] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0034] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship in the working state of this invention, and 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, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0035] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0036] Specifically, the object of the present invention is to provide the following aspects:

[0037] On the one hand, according to the present invention, a gas diffusion layer for a hydrogen fuel cell has a gradient pore structure in the thickness direction, which is used to realize the gas diffusion regulation and water management functions of the microporous layer, and also to realize the mechanical support and gas distribution functions of the diffusion substrate layer. That is, the gas diffusion layer realizes the integration of "microporous layer + diffusion substrate layer".

[0038] In this invention, the gas diffusion layer, while ensuring good mechanical properties, achieves a 112.5%~150% increase in oxygen mass fraction, a 1.2%~3% decrease in liquid water mass fraction, a 2.3%~13.5% increase in oxygen distribution uniformity coefficient, and a 1.4%~4.1% increase in fuel cell limiting current density compared to existing gas diffusion layers on the market.

[0039] In this invention, the gas diffusion layer is divided into 2 to 5 layers in the thickness direction.

[0040] Furthermore, the 2-5 layer gradient structure is based on the synergistic optimization requirements of oxygen transport and mechanical support in hydrogen fuel cells. The side near the catalyst layer needs to achieve uniform oxygen distribution and stable interfacial contact, thus requiring small fiber diameters and low porosity; the side near the flow field needs to achieve low-resistance gas diffusion, thus requiring large fiber diameters and high porosity; of course, the intermediate layer between the sides near the catalyst layer and the flow field selectively sandwiches the flow field, serving as a transition buffer zone for water-gas transport and avoiding interfacial abrupt changes in mass transfer. This gradient structure suppresses the tendency of gas to preferentially pass through low-resistance paths, forcing oxygen to spread throughout the entire catalyst layer; the transition from large to small fiber diameters reduces interfacial abrupt changes, avoiding localized oxygen deficiency at the reaction interface.

[0041] Furthermore, the integrated gas diffusion layer combines the traditional discrete microporous layer and diffusion substrate layer into a single whole with a continuously varying pore structure in the thickness direction, eliminating the additional material and space required for the interlayer interface. By precisely controlling the gradient structure from the flow field side (large fiber diameter, high porosity) to the catalyst layer side (small fiber diameter, low porosity), the gas mass transfer path is directly shortened while ensuring mechanical support, gas distribution, and efficient water management functions. Therefore, without sacrificing key performance, the overall thickness of the gas diffusion layer is significantly reduced, ultimately achieving the goal of improving mass transfer efficiency and battery power density.

[0042] In this invention, the pore structure parameters of the gas diffusion layer include: average fiber diameter, porosity, and permeability. The average fiber diameter monotonically decreases or first increases and then decreases from the flow field side to the catalyst layer side (in this case, the average fiber diameter near the flow field side must be greater than the average fiber diameter near the catalyst layer side); the porosity monotonically decreases or first increases and then decreases from the flow field side to the catalyst layer side (in this case, the porosity near the flow field side must be greater than the porosity near the catalyst layer side); the fiber diameter and porosity together determine the permeability.

[0043] , For penetration rate, Porosity The diameter is the fiber diameter.

[0044] In this invention, the total porosity of the gas diffusion layer is 0.75~0.9, the porosity of each layer is 0.72~0.93, and the average fiber diameter of each layer is 0.3~1.8μm.

[0045] In one embodiment, such as Figure 1 As shown, the gas diffusion layer consists of two layers. In this case, both the fiber diameter and porosity monotonically decrease from the flow field side to the catalyst layer side. The average fiber diameter on the flow field side is 1.1~1.2μm, and the porosity is 0.9~0.95; the average fiber diameter on the catalyst layer side is 0.4~0.5μm, and the porosity is 0.7~0.75. For example, the average fiber diameter on the flow field side is 1.14μm, and the porosity is 0.91; the average fiber diameter on the catalyst layer side is 0.46μm, and the porosity is 0.73.

[0046] In one embodiment, such as Figure 2 As shown, the gas diffusion layer consists of three layers. In this case, the fiber diameter and porosity increase first and then decrease from the flow field side to the catalyst layer side. The average fiber diameter on the flow field side is 0.7~0.8 μm, and the porosity is 0.85~0.9; the average fiber diameter on the middle layer is 1.4~1.5 μm, and the porosity is 0.9~0.95; the average fiber diameter on the catalyst layer side is 0.3~0.4 μm, and the porosity is 0.7~0.75. For example, the average fiber diameter near the flow field side is 0.77 μm, and the porosity is 0.87; the average fiber diameter on the middle layer is 1.43 μm, and the porosity is 0.93; the average fiber diameter on the catalyst layer side is 0.32 μm, and the porosity is 0.72.

[0047] In one embodiment, such as Figure 3As shown, the gas diffusion layer consists of five layers. In this case, both the fiber diameter and porosity monotonically decrease from the flow field side to the catalyst layer side. From the flow field side to the catalyst layer side, the average fiber diameter of the first layer is 1.3–1.4 μm, and the porosity is 0.92–0.95; the average fiber diameter of the second layer is 1.1–1.2 μm, and the porosity is 0.905–0.915; the average fiber diameter of the third layer is 1–1.1 μm, and the porosity is 0.895–0.9; the average fiber diameter of the fourth layer is 0.8–0.9 μm, and the porosity is 0.88–0.89; and the average fiber diameter of the fifth layer is 0.5–0.7 μm, and the porosity is 0.85–0.86. For example, the average fiber diameter of the first layer is 1.37 μm and the porosity is 0.92; the average fiber diameter of the second layer is 1.18 μm and the porosity is 0.91; the average fiber diameter of the third layer is 1.07 μm and the porosity is 0.90; the average fiber diameter of the fourth layer is 0.88 μm and the porosity is 0.89; and the average fiber diameter of the fifth layer is 0.60 μm and the porosity is 0.85.

[0048] In this invention, the gas diffusion layer is formed by stacking conductive fiber materials, selected from any one of carbon fiber materials, nonwoven carbon felt, and metal fiber felt, and more preferably carbon fiber materials, such as carbonized polyacrylonitrile fibers.

[0049] Among them, the above-mentioned materials have a conductive network structure, especially the polyacrylonitrile fiber which forms a highly conductive network after carbonization to meet the current collection requirements; the polyacrylonitrile fiber is precisely controlled and the pore structure is controllable; the polyacrylonitrile fiber has better corrosion resistance than metal substrates, and the biomass carbonization path is in line with the trend of green manufacturing.

[0050] Furthermore, the gas diffusion layer is made of a single material, which ensures that the multiple layers are made of the same material, eliminating the risk of peeling at the interface of traditional heterogeneous materials due to differences in thermal expansion coefficients, and increasing the structural stability in the thickness direction.

[0051] In this invention, the gas diffusion layer, while fulfilling the functions of the traditional "microporous layer + diffusion substrate layer," achieves a significant reduction in thickness through an integrated design. The thickness of the gas diffusion layer is 10~200 mm. Preferably 40~140 .

[0052] In this invention, the hydrogen fuel cell gas diffusion layer with an integrated structure is prepared by electrospinning, chopped fiber coating or sintering connection.

[0053] On the other hand, according to the method for preparing the gas diffusion layer according to the first aspect of the present invention, the gas diffusion layer is prepared by electrospinning, specifically including:

[0054] Step 1: Dissolve the polymer in an organic solvent to obtain a spinning solution;

[0055] Step 2: The spinning solution is stretched and solidified by electrospinning technology to deposit a nonwoven fiber mat.

[0056] Step 3: Heat-treat the fiber felt to transform it into a conductive carbon fiber substrate, i.e., the gas diffusion layer.

[0057] Specifically:

[0058] In step 1, the polymer is selected from any one of polyvinyl alcohol, polyacrylonitrile, and polyimide, preferably polyacrylonitrile.

[0059] Among them, the cyano group (-CN) in the polyacrylonitrile molecular chain forms a heat-resistant ladder structure through cyclization, and the carbonization yield is as high as 50% or more, which is much higher than that of polyvinyl alcohol and polyimide. This characteristic ensures that the carbon fiber substrate has high conductivity and mechanical strength. Moreover, polyacrylonitrile can easily form nanofibers with uniform diameter in electrospinning, which meets the requirements for controlling the porosity and permeability of the gas diffusion layer.

[0060] In step 1, the organic solvent is selected from any one of N,N-dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran, preferably N,N-dimethylformamide.

[0061] N,N-Dimethylformamide has strong polarity and high efficiency in dissolving polyacrylonitrile to form a uniform spinning solution, thus avoiding fiber defects such as beading. The N,N-Dimethylformamide has low toxicity and a low freezing point, making it suitable for wide-temperature-range spinning processes.

[0062] In step 1, the polymer mass fraction in the spinning solution is 10-15 wt%. The constraints for selecting this concentration are: below 10 wt%, the viscosity is insufficient, the jet is unstable and will lead to beading defects; above 15 wt%, the viscosity is too high, the fiber diameter will exceed the standard and the nozzle will be easily clogged.

[0063] Furthermore, the fiber diameter is positively correlated with the mass fraction of polymer in the spinning solution. Low concentration forms fine fiber accumulation with slightly lower porosity, while high concentration forms a coarse fiber network with higher porosity. By controlling the concentration, the differentiated requirements of the catalyst layer side (low porosity) and the flow field side (high porosity) can be achieved.

[0064] In one embodiment, polyacrylonitrile is dissolved in N,N-dimethylformamide to form spinning solutions with mass fractions of 14 wt% and 10 wt%, respectively, to prepare a bilayer fiber mat with an average fiber diameter of 1.14 μm and a porosity of 0.91 on the flow field side and an average fiber diameter of 0.46 μm and a porosity of 0.73 on the catalyst layer side.

[0065] In one embodiment, polyacrylonitrile is dissolved in N,N-dimethylformamide to form spinning solutions with mass fractions of 11 wt%, 15 wt%, and 10 wt%, respectively, to prepare a three-layer fiber mat with an average fiber diameter of 0.77 μm and a porosity of 0.87 on the flow field side; an average fiber diameter of 1.43 μm and a porosity of 0.93 on the intermediate layer; and an average fiber diameter of 0.32 μm and a porosity of 0.72 on the catalyst layer side.

[0066] In one embodiment, polyacrylonitrile is dissolved in N,N-dimethylformamide to form spinning solutions with mass fractions of 15 wt%, 14 wt%, 13 wt%, 12 wt%, and 11 wt%, respectively. From the flow field side to the catalyst layer side, the first layer has an average fiber diameter of 1.37 μm and a porosity of 0.92; the second layer has an average fiber diameter of 1.18 μm and a porosity of 0.91; the third layer has an average fiber diameter of 1.07 μm and a porosity of 0.90; the fourth layer has an average fiber diameter of 0.88 μm and a porosity of 0.89; and the fifth layer has an average fiber diameter of 0.60 μm and a porosity of 0.85, forming a five-layer fiber mat.

[0067] In step 2, the electrospinning pressure is 10~20kV, for example, 15kV. The constraint for choosing this parameter is that electrospinning requires a high-voltage electric field to overcome the surface tension of the polymer droplets, forming Taylor cones, and further stretching them into jets. Experiments show that when the voltage is below 10kV, the electric field force is insufficient to effectively overcome the surface tension of the solution, resulting in the droplets failing to form stable jets and easily causing droplet splashing or fiber breakage; while when the voltage is above 20kV, the jet velocity is too fast and unstable, easily producing multiple jets or uneven fiber diameter distribution, affecting structural uniformity.

[0068] In step 3, the heat treatment sequentially includes pre-oxidation and carbonization.

[0069] Further, the pre-oxidation includes: heating from room temperature to 200-300°C at a heating rate of 1-5°C / min, holding at this temperature for 1-3 hours, and then naturally cooling with the furnace. For example, heating from room temperature to 240°C at a heating rate of 1°C / min, holding at this temperature for 2 hours, and then naturally cooling with the furnace.

[0070] Polymers such as polyacrylonitrile are easily melted at high temperatures. Pre-oxidation, achieved by heating in an air atmosphere, causes the molecular chains to undergo cyclization and dehydrogenation reactions, preventing fiber melting or breakage during subsequent carbonization. Pre-oxidation significantly increases the oxygen content of the fibers, forming oxygen-containing functional groups such as carbonyl and hydroxyl groups, enhancing the fibers' thermal stability and corrosion resistance during carbonization, thus adapting them to the acidic environment of fuel cells. The constraints on the temperature and time are as follows: too low a temperature or too short a time results in insufficient oxidation; too high a temperature or too long a time leads to over-oxidation, increasing surface defects and reducing carbon fiber strength.

[0071] In step 3, the carbonization includes: heating to 800-1200°C at a heating rate of 5-10°C / min under an inert atmosphere, holding at this temperature for 0.3-2 hours, and then allowing the furnace to cool naturally. For example, heating to 1000°C at a heating rate of 5°C / min under nitrogen protection, holding at this temperature for 1 hour, and then allowing the furnace to cool naturally.

[0072] The carbonization temperature (800~1200℃) is much higher than the material's oxidation threshold, and the inert gas isolates oxygen, preventing the carbon fiber from being oxidized and ablated. If the holding time is too short, the carbonization reaction will not reach equilibrium, and the excessive residual oxygen content will lead to a decrease in corrosion resistance; if the holding time is too long, the fiber will shrink excessively.

[0073] Furthermore, the inert atmosphere is high-purity nitrogen (purity ≥ 99.999%) or argon.

[0074] In this invention, the fiber diameter and porosity of the gas diffusion layer are gradient-distributed from the catalyst layer side to the flow field side. The side closer to the catalyst layer uses low porosity and small fiber diameter to form a dense network, increasing the capillary pressure of liquid water and the gas diffusion resistance. This drives the liquid water out of the catalyst layer and forces oxygen molecules to distribute evenly to the active sites of the catalyst layer, avoiding localized oxygen-deficient areas. On the flow field side, high porosity and large fiber diameter reduce mass transfer resistance, ensuring efficient gas supply and rapid discharge of generated water. This gradient structure, through the synergistic regulation of the water-gas transport process, achieves a balance optimization between oxygen diffusion rate and distribution uniformity, thereby realizing the gas diffusion regulation and water management functions of the microporous layer.

[0075] Furthermore, the integrated structure is composed of a continuous conductive fiber network. The small fiber diameter and low porosity region on the catalyst layer side is equivalent to a microporous layer, realizing gas diffusion and water management and control. The large fiber diameter and high porosity region on the flow field side provides mechanical support and electronic conduction functions, equivalent to a diffusion substrate layer. Moreover, the porous structure realizes the gas distribution function of a traditional diffusion substrate layer. That is, the gradient transition layer in the middle acts as a buffer zone, further smoothing the gas velocity distribution and ensuring that the gas is uniformly distributed at the macroscopic level before entering the catalyst layer. This design eliminates the interfacial contact resistance of traditional layered structures and significantly reduces the thickness. This integrated structure design of "microporous layer + diffusion substrate layer" improves the mass fraction and uniformity coefficient of oxygen at the catalyst layer interface, ultimately improving the battery mass transfer efficiency and output performance.

[0076] In another aspect, according to a hydrogen fuel cell provided by the present invention, the hydrogen fuel cell includes the gas diffusion layer described in the first aspect. Preferably, from the anode to the cathode, it sequentially includes: an anode end plate, an anode current collector, an anode flow field plate, an anode gas diffusion layer (GDL), a membrane electrode, a cathode gas diffusion layer (GDL), a cathode flow field plate, a cathode current collector, and a cathode end plate.

[0077] The membrane electrode assembly comprises an anode catalyst layer, a proton exchange membrane, and a cathode catalyst layer. The anode GDL is located between the anode flow field plate and the anode catalyst layer, and the cathode GDL is located between the cathode catalyst layer and the cathode flow field plate. The cathode GDL adopts the structural design described in the second aspect of this invention to optimize gas transport, electron conduction, and water management performance.

[0078] Furthermore, the proton exchange membrane is preferably Nafion; the anode catalyst layer and the cathode catalyst layer are typically Pt / C.

[0079] The present invention is further described below through specific examples; however, these examples are merely exemplary and do not constitute any limitation on the scope of protection of the present invention.

[0080] Example 1

[0081] like Figure 1 As shown, the gas diffusion layer is composed of carbonized polyacrylonitrile (PAN) fibers, with an overall thickness of 40 mm. It is divided into two layers along the thickness direction. The gas diffusion layer is made by electrospinning, specifically:

[0082] (1) Polyacrylonitrile (PAN) is dissolved in solvent N,N-dimethylformamide (DMF) to form homogeneous spinning solutions with mass fractions of 10wt% and 14wt%, respectively, for later use;

[0083] 10 mL of 14 wt% PAN / DMF solution was loaded into a syringe, the spinning voltage was set to 15 kV, and spinning was carried out at room temperature of 25°C and relative humidity of 20%. The spinning solution was stretched into nanofibers, and the fibers were deposited on the aluminum foil collector to form Region I.

[0084] While maintaining Region I, replace the syringe and load 10 mL of 10 wt% PAN / DMF solution into the syringe. Set the spinning voltage to 15 kV and spin at room temperature of 25°C and relative humidity of 20%. The spinning solution is stretched into nanofibers, which are deposited on the aluminum foil collector to form Region II, thus obtaining a double-layer PAN nanofiber felt.

[0085] (2) The fiber felt is heated from 25°C to 240°C in air at a heating rate of 1°C / min and kept at this temperature for 2 hours to complete the pre-oxidation; then it is transferred to a tube furnace and heated to 1000°C at a heating rate of 5°C / min under nitrogen protection, and kept at this temperature for 1 hour to fully carbonize the fiber and transform it into a conductive carbon fiber substrate, i.e., the gas diffusion layer.

[0086] Figure 1 The SEM image of the cross-section of the fabricated gas diffusion layer is shown. It can be seen that the fabricated gas diffusion layer is divided into two regions along the thickness direction (region I and region II correspond to...). Figure 1 (① and ② in the text), ① is closer to the flow field side, and ② is closer to the catalyst layer side.

[0087] The total porosity of the gas diffusion layer was measured to be 0.84; the thickness of region ① was 24 μm, and the average fiber diameter was [not specified]. The porosity is 1.14 μm. The value is 0.91, and the penetration rate K is 5.5 × 10⁻⁶. -12 m 2 The thickness of region ② is 16 μm, and the average fiber diameter is... The porosity is 0.46 μm. The value is 0.73, and the permeability K is 5.5 × 10⁻⁶. -14 m 2 Because each layer is composed of micron-scale fibers, there is good contact and transition between the layers.

[0088] Example 2

[0089] like Figure 2 As shown, the gas diffusion layer is composed of carbonized polyacrylonitrile (PAN) fibers, with an overall thickness of 59 mm. The structure is divided into three layers along its thickness direction. The gas diffusion layer is prepared by electrospinning. Specifically:

[0090] (1) Polyacrylonitrile (PAN) is dissolved in solvent N,N-dimethylformamide (DMF) to form homogeneous spinning solutions with mass fractions of 10wt%, 11wt% and 15wt%, respectively.

[0091] 10 mL of 11 wt% PAN / DMF solution was loaded into a syringe, the spinning voltage was set to 15 kV, and spinning was carried out at room temperature of 25℃ and relative humidity of 20%. The spinning solution was stretched into nanofibers, and the fibers were deposited on the aluminum foil collector to form Region I.

[0092] While maintaining Region I, replace the syringe and load 10 mL of 15 wt% PAN / DMF solution into the syringe. Set the spinning voltage to 15 kV and spin at room temperature of 25°C and relative humidity of 20%. The spinning solution is stretched into nanofibers, which are deposited on the aluminum foil collector to form Region II.

[0093] While maintaining region II, replace the syringe and load 10 mL of 10 wt% PAN / DMF solution into the syringe. Set the spinning voltage to 15 kV and spin at room temperature 25°C and relative humidity 20%. The spinning solution is stretched into nanofibers, which are deposited on the aluminum foil collector to form region III, thus obtaining a three-layer PAN nanofiber felt.

[0094] (2) The fiber felt is heated from 25°C to 240°C in air at a heating rate of 1°C / min and kept at this temperature for 2 hours to complete the pre-oxidation; then it is transferred to a tube furnace and heated to 1000°C at a heating rate of 5°C / min under nitrogen protection, and kept at this temperature for 1 hour to fully carbonize the fiber and transform it into a conductive carbon fiber substrate, i.e., the gas diffusion layer.

[0095] Figure 2 The SEM image of the cross-section of the fabricated gas diffusion layer is shown. It can be seen that the fabricated gas diffusion layer is divided into three regions along the thickness direction (region I, region II, and region III correspond to...). Figure 2 (In the diagram, ①, ②, and ③), ① is closer to the flow field side, and ③ is closer to the catalyst layer side.

[0096] The total porosity of the gas diffusion layer was measured to be 0.87; the thickness of region ① was 12 μm, and the average fiber diameter was [not specified]. The porosity is 0.77 μm. The value is 0.87, and the penetration rate K is 1.1 × 10⁻⁶. -12 m 2 The thickness of region ② is 33 μm, and the average fiber diameter is... The porosity is 1.43 μm. The value is 0.93, and the penetration rate K is 1.5 × 10⁻⁶.-11 m 2 The thickness of region ③ is 14 μm, and the average fiber diameter is... The porosity is 0.32 μm. The value is 0.72, and the permeability K is 2.4 × 10⁻⁶. -14 m 2 Because each layer is composed of micron-scale fibers, there is good contact and transition between the layers.

[0097] Example 3

[0098] The gas diffusion layer is composed of carbonized polyacrylonitrile (PAN) fibers, with an overall thickness of 136. The gas diffusion layer is divided into five layers along its thickness direction and is prepared by electrospinning. Specifically:

[0099] (1) Polymer polyacrylonitrile (PAN) is dissolved in solvent N,N-dimethylformamide (DMF) to form homogeneous spinning solutions with mass fractions of 15wt%, 14wt%, 13wt%, 12wt% and 11wt%, respectively.

[0100] 10 mL of 15 wt% PAN / DMF solution was loaded into a syringe, the spinning voltage was set to 15 kV, and spinning was carried out at room temperature of 25℃ and relative humidity of 20%. The spinning solution was stretched into nanofibers, and the fibers were deposited on the aluminum foil collector to form Region I.

[0101] While maintaining Region I, replace the syringe and load 10 mL of 14 wt% PAN / DMF solution into the syringe. Set the spinning voltage to 15 kV and spin at room temperature of 25°C and relative humidity of 20%. The spinning solution is stretched into nanofibers, which are deposited on the aluminum foil collector to form Region II.

[0102] While maintaining Region II, replace the syringe and load 10 mL of 13 wt% PAN / DMF solution into the syringe. Set the spinning voltage to 15 kV and spin at room temperature of 25°C and relative humidity of 20%. The spinning solution is stretched into nanofibers, which are deposited on the aluminum foil collector to form Region III.

[0103] While maintaining region III, replace the syringe and load 10 mL of 12 wt% PAN / DMF solution into the syringe. Set the spinning voltage to 15 kV and spin at room temperature of 25°C and relative humidity of 20%. The spinning solution is stretched into nanofibers, which are deposited on the aluminum foil collector to form region IV.

[0104] While maintaining region IV, replace the syringe and load 10 mL of 11 wt% PAN / DMF solution into the syringe. Set the spinning voltage to 15 kV and spin at room temperature of 25°C and relative humidity of 20%. The spinning solution is stretched into nanofibers, which are deposited on the aluminum foil collector to form region V, thus obtaining a five-layer PAN nanofiber felt.

[0105] (2) The fiber felt is heated from 25°C to 240°C in air at a heating rate of 1°C / min and kept at this temperature for 2 hours to complete the pre-oxidation; then it is transferred to a tube furnace and heated to 1000°C at a heating rate of 5°C / min under nitrogen protection, and kept at this temperature for 1 hour to fully carbonize the fiber and transform it into a conductive carbon fiber substrate, i.e., the gas diffusion layer.

[0106] Figure 3 The SEM image of the cross-section of the fabricated gas diffusion layer is shown. It can be seen that the fabricated gas diffusion layer is divided into five regions along the thickness direction (regions I, II, III, IV, and V correspond to...). Figure 3 (In the diagram, ①, ②, ③, ④, ⑤), ① is closer to the flow field side, and ⑤ is closer to the catalyst layer side.

[0107] The total porosity of the gas diffusion layer was measured to be 0.89; the thickness of region ① was 20 μm, and the average fiber diameter was [not specified]. The porosity is 1.37 μm. The value is 0.92, and the penetration rate K is 1.0 × 10⁻⁶. -11 m 2 The thickness of region ② is 35 μm, and the average fiber diameter is... The porosity is 1.18 μm. The value is 0.91, and the penetration rate K is 5.9 × 10⁻⁶. -12 m 2 The thickness of region ③ is 23 μm, and the average fiber diameter is... The porosity is 1.07 μm. The value is 0.90, and the penetration rate K is 3.8 × 10⁻⁶. -12 m 2 The thickness of region ④ is 30 μm, and the average fiber diameter is... The porosity is 0.88 μm. The value is 0.89, and the penetration rate K is 2.1 × 10⁻⁶. -12 m 2 The thickness of region ⑤ is 28 μm, and the average fiber diameter is... The porosity is 0.60 μm. The value is 0.85, and the penetration rate K is 4.5 × 10⁻⁶. -13 m 2Because each layer is composed of micron-scale fibers, there is good contact and transition between the layers.

[0108] Comparative Example 1

[0109] Using a traditional commercial double-layer gas diffusion layer as a control group, model YLS-30T, which consists of a "microporous layer" and a "diffusion substrate layer". Figure 4 The image shows a SEM image of its cross-section. The microporous layer (…) Figure 4 The average particle size (shown as ①) is 30 nm, the porosity is 0.6, and the thickness is 30 μm; the diffusion substrate layer ( Figure 4 The average fiber diameter (shown in ②) is 8 μm, the porosity is 0.78, and the thickness is 190 μm. From Figure 4 It is evident that the microporous layer and the diffuse substrate layer exhibit abrupt changes in their interface structure due to differences in microscale.

[0110] To verify the effect of the gas diffusion layer with the integrated structure of "microporous layer + diffusion substrate layer" of the present invention on improving gas-water transport efficiency and hydrogen fuel cell performance, three-dimensional numerical simulation analysis was performed on the gas diffusion layers of Examples 1-3 and Comparative Example 1. The anode and cathode single-channel geometric units of the hydrogen fuel cell were used as the computational domain, and a multiphysics numerical model of the hydrogen fuel cell was constructed using the computational fluid dynamics software ANSYS Fluent. The output performance and oxygen distribution characteristics of the hydrogen fuel cell were obtained through calculation.

[0111] The hydrogen fuel cell is composed of gas diffusion layers from Examples 1-3 and Comparative Example 1, all of which serve as the cathode gas diffusion layer. The aforementioned commercial gas diffusion layer (model: YLS-30T) serves as the anode gas diffusion layer. Except for differences in fiber diameter, porosity, and thickness structural parameters of the cathode gas diffusion layer, the structural and physical property parameters of other hydrogen fuel cell components are consistent. In the fuel cell, a proton exchange membrane (CCM) coated with a catalyst layer (a mixture of carbon-supported platinum and perfluorosulfonic acid polymer solution) is placed between the anode GDL and the cathode GDL, ensuring that the micropores of the GDL are tightly attached to the catalyst layer. A "sandwich" structure (GDL-CCM-GDL) is placed between the bipolar plates, with the macropores of the GDL facing the flow field channels of the bipolar plates.

[0112] The operating parameters of the four hydrogen fuel cells are as follows: the battery operating temperature is 80℃, the operating pressure is 1 atmosphere, the anode and cathode air inlet metering ratios are 2.0 and 1.5 respectively, and the anode and cathode air inlet humidity is 100%.

[0113] The uniformity of oxygen distribution is characterized by an oxygen distribution cloud map and a uniformity coefficient. Specifically, the oxygen distribution in the calculation results is selected, and the interface between the hydrogen fuel cell cathode gas diffusion layer and the catalyst layer is used as the object. An oxygen mass fraction distribution cloud map of this interface is plotted, and the uniformity coefficient is calculated. The formula for calculating the uniformity coefficient is as follows:

[0114]

[0115] Where U is the uniformity coefficient, and the closer its value is to 1, the more uniform the distribution; A i Let be the area of ​​the i-th grid point, in cm. 2 ;X i X represents the oxygen mass fraction at the i-th grid point; A denoted as the average mass fraction of oxygen on the surface, and n as the total number of grid cells.

[0116] Figure 5 The diagram shows the mass fractions of oxygen and liquid water at the interface between the cathode gas diffusion layer and the catalyst layer of the hydrogen fuel cells prepared in Examples 1-3 and Comparative Example 1, with an output voltage of 0.3V. It can be seen that, compared with Comparative Example 1, the oxygen mass fraction of the three integrated gas diffusion layers in Examples 1-3 increased by 125%, 112.5%, and 150%, respectively, while the liquid water mass fraction decreased by 1.6%, 1.2%, and 3%, respectively. This proves that the integrated gas diffusion layer can enhance oxygen transport and promote the discharge of liquid water, with Example 3 showing the best effect.

[0117] Figure 6 The hydrogen fuel cells prepared by the gas diffusion layers of Examples 1-3 and Comparative Example 1 are shown. At an output voltage of 0.3V, the oxygen mass fraction distribution cloud map and uniformity coefficient comparison diagram at the interface between the cathode gas diffusion layer and the catalyst layer are shown. It can be seen that, compared with Comparative Example 1, the oxygen distribution uniformity coefficient of the three integrated gas diffusion layers in Examples 1-3 is improved by 6.7%, 2.3%, and 13.5%, respectively. This indicates that the oxygen distribution uniformity on the surface of the catalyst layer is improved, which improves the utilization rate of the catalyst and is beneficial to improving the performance of the fuel cell. Among them, Example 3 has the best effect.

[0118] Figure 7The diagram shows the polarization curves and power density curves of hydrogen fuel cells fabricated using gas diffusion layers in Examples 1-3 and Comparative Example 1. It can be seen that, compared to Comparative Example 1, the limiting current density of the hydrogen fuel cells corresponding to the three integrated gas diffusion layer structures in Examples 1-3 increased by 4.1%, 2.7%, and 1.4%, respectively. This indicates that the integrated gas diffusion layer structure designed in this patent can improve the output performance of hydrogen fuel cells, with Example 1 showing the best effect. This is mainly due to the increased interfacial resistance resulting from the increased number of layers in Examples 2 and 3, which lengthens the mass transfer path. Therefore, the structure of Example 1 is more suitable for applications requiring high power density, while the strategy of Example 3 is more suitable for high-stability scenarios with stringent requirements for oxygen distribution uniformity.

[0119] In summary, the integrated gas diffusion layer for hydrogen fuel cells designed in this patent improves oxygen distribution uniformity and transport efficiency by optimizing the distribution of pore structure characteristics within the gas diffusion layer. Further optimization of the gradient characteristic parameters of the gas diffusion layer ultimately leads to a significant improvement in the performance of hydrogen fuel cells using this invention's gas diffusion layer.

[0120] The present invention has been described in detail above with reference to preferred embodiments and exemplary examples. However, it should be noted that these specific embodiments are merely illustrative explanations of the invention and do not constitute any limitation on the scope of protection of the invention. Various improvements, equivalent substitutions, or modifications can be made to the technical content and embodiments of the present invention without departing from the spirit and scope of protection of the invention, and all such modifications fall within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A hydrogen fuel cell gas diffusion layer, characterized by, The gas diffusion layer has a gradient change of porosity structure in the thickness direction, for realizing the gas diffusion regulation and water management functions of the microporous layer, and for realizing the mechanical support and gas distribution functions of the diffusion substrate layer.

2. The gas diffusion layer according to claim 1, wherein Preferably, the gas diffusion layer has a gradient change of porosity and / or fiber diameter in the thickness direction.

3. The gas diffusion layer according to claim 2, wherein The gas diffusion layer is divided into 2-5 layers in the thickness direction.

4. The gas diffusion layer according to claim 2, wherein The average fiber diameter of the gas diffusion layer monotonously decreases or first increases and then decreases from the flow field side to the catalyst layer side.

5. The gas diffusion layer according to claim 2, wherein The porosity of the gas diffusion layer monotonously decreases or first increases and then decreases from the flow field side to the catalyst layer side.

6. The gas diffusion layer according to claim 5, wherein The total porosity of the gas diffusion layer is 0.75-0.9, and the porosity of each layer is 0.72-0.

93.

7. The gas diffusion layer according to claim 4, wherein The average fiber diameter of each layer of the gas diffusion layer is 0.3-1.8 μm.

8. A method for producing the gas diffusion layer according to any one of claims 1 to 7, characterized by, The method comprises: Step 1: dissolving a polymer in an organic solvent to obtain a spinning solution; Step 2: stretching and solidifying the spinning solution by electrospinning technology to deposit a non-woven structure of fiber felt; Step 3: heat treating the fiber felt to convert it into a conductive carbon fiber substrate, i.e. the gas diffusion layer.

9. The method of claim 8, wherein, In step 1, the polymer is selected from any one of polyvinyl alcohol, polyacrylonitrile and polyimide.

10. A hydrogen fuel cell, characterized by The hydrogen fuel cell comprises the gas diffusion layer according to any one of claims 1-7.

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