Gas diffusion layer, preparation method thereof and fuel cell

Abstract

The invention discloses a gas diffusion layer, a preparation method thereof and a fuel cell, and relates to the technical field of cells. The gas diffusion layer comprises a substrate layer and a microporous layer coated on the substrate layer, the area median pore diameter of the gas diffusion layer is 45-150 nm, and the area median pore diameter refers to a corresponding pore diameter value when the cumulative pore surface area proportion in a pore surface area cumulative distribution curve reaches 50%; the volume median pore diameter of the gas diffusion layer is 20-50 [mu] m, and the volume median pore diameter refers to a corresponding pore diameter value when the cumulative pore volume ratio in a pore volume cumulative distribution curve reaches 50%. The gas diffusion layer is limited to have two-dimensional median aperture parameters in a specific range, the problems of water retention and gas transmission resistance increase are solved, and the method has the advantages that the gradient design of the pore structure is optimized, and the water and gas transmission efficiency and wide working condition adaptability are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a gas diffusion layer and a preparation method thereof, and a fuel cell. BACKGROUND

[0002] The gas diffusion layer (GDL) is a key component in fuel cells, and its main functions include: uniformly delivering reaction gases (hydrogen and oxygen) to the catalyst layer, and effectively discharging the water generated during the reaction process to prevent the "water flooding" phenomenon from affecting the performance of the battery. The traditional GDL structure is usually composed of a carbon paper base layer, which has micron-sized pores that are beneficial for water discharge, but has limitations in achieving uniform gas distribution.

[0003] To improve the gas distribution performance, a microporous layer (MPL) is introduced on the basis of the carbon paper base. The MPL is usually composed of nanoscale carbon materials (such as carbon black or small-particle-size graphite) and fluorine-containing binders, forming a structure with abundant nanopores, which helps to improve gas transmission efficiency and reduce the occurrence of gas short circuits and local hot spots.

[0004] However, with the development of fuel cells in high-power density application scenarios, especially under high current density operating conditions, the amount of water generated by the battery per unit time increases significantly. The lack of pore matching between the MPL and the carbon paper in the existing GDL structure leads to water accumulation, poor water discharge, increased gas transmission resistance, and thus affects the overall performance of the battery, causing voltage decay and other problems. Therefore, it is necessary to optimize the design of the GDL structure to meet the higher requirements of high-power density fuel cells for water management and gas transmission. SUMMARY

[0005] The main purpose of the present application is to provide a gas diffusion layer and a preparation method thereof, and a fuel cell, which aims to improve the problem of rapid performance degradation of the battery caused by serious water retention in the gas diffusion layer of the fuel cell under high current density.

[0006] To achieve the above-mentioned purpose, the embodiment of the present application provides a gas diffusion layer, which comprises a base layer and a microporous layer coated on the base layer.

[0007] The area median pore size of the gas diffusion layer is 45 nm-150 nm, and the area median pore size refers to the pore size corresponding to the cumulative pore surface area ratio of 50% in the cumulative distribution curve of the pore surface area.

[0008] The volume median pore size of the gas diffusion layer is 20-50 pm, and the volume median pore size refers to the pore size corresponding to the cumulative pore volume ratio of 50% in the cumulative distribution curve of the pore volume.

[0009] In some embodiments, the gas diffusion layer has an area median pore size of 50-90 nm and a volume median pore size of 25-40 pm.

[0010] In some embodiments, the gas diffusion layer has an area median pore size of 45-90 nm and a volume median pore size of 20-40 pm.

[0011] In some embodiments, the gas diffusion layer has an area median pore size of 50-150 nm and a volume median pore size of 25-50 pm.

[0012] In some embodiments, the gas diffusion layer has a thickness of 110-280 pm and a porosity of 75-90%.

[0013] In another aspect, the embodiments of the present application also provide a preparation method of a gas diffusion layer, comprising the following steps:

[0014] providing a porous conductive substrate and a microporous layer slurry, coating the microporous layer slurry on one side of the carbon paper, drying, and then sintering at 350-380°C to obtain a gas diffusion layer comprising a substrate layer and a microporous layer, wherein the carbon paper forms the substrate layer and the microporous layer slurry forms the microporous layer;

[0015] The gas diffusion layer has an area median pore size of 45-150 nm, wherein the area median pore size refers to a pore size corresponding to a cumulative pore surface area ratio of 50% in a cumulative pore surface area distribution curve.

[0016] The gas diffusion layer has a volume median pore size of 20-50 pm, wherein the volume median pore size refers to a pore size corresponding to a cumulative pore volume ratio of 50% in a cumulative pore volume distribution curve.

[0017] In some embodiments, the microporous layer slurry comprises a pore-forming agent, and the pore-forming agent has a particle size or molecular agglomeration size of 1-500 nm, preferably 5-200 nm.

[0018] The pore-forming agent is selected from at least one of polyether polyol, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyether ether ketone, cellulose, and polyether.

[0019] The pore-forming agent has a carbon residue after ablation treatment at 350°C of less than or equal to 1%.

[0020] The porous conductive substrate has a thickness of 100-260 pm, a porosity of 75-90%, and a volume median pore size of 25-50 pm.

[0021] And / or, the porous conductive substrate is selected from any one of carbon fiber paper, metal-based porous substrate.

[0022] In some embodiments, the method for preparing the microporous layer slurry comprises:

[0023] adding a dispersant and conductive carbon powder into water, and obtaining a carbon slurry after mixing;

[0024] adding a binder to the carbon slurry, and then adding a thickening agent and the pore-forming agent, and obtaining the microporous layer slurry after dispersion;

[0025] wherein the weight parts of each component of the microporous layer slurry are:

[0026]

[0027] In some embodiments, the binder comprises a fluorine-containing polymer;

[0028] And / or, the thickening agent comprises a polyether compound containing only C, H and O elements;

[0029] And / or, the dispersant comprises at least one of an aromatic non-ionic dispersant and a zwitterionic dispersant;

[0030] And / or, the conductive carbon powder comprises at least one of furnace black, acetylene black, ketjen black, graphitized carbon black, carbon nanotubes and gas-phase carbon fiber;

[0031] And / or, the binder comprises at least one of polytetrafluoroethylene, polyvinylidene fluoride, perfluorosulfonic acid resin, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer;

[0032] And / or, the thickening agent comprises at least one of polyether polyol, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyether ether ketone, cellulose and polyether.

[0033] In another aspect, the embodiments of the present application also provide a fuel cell comprising the gas diffusion layer or the gas diffusion layer prepared by the above method.

[0034] In the present application, the area median pore diameter refers to the pore diameter value corresponding to the cumulative pore surface area ratio of 50% in the cumulative pore surface area distribution curve, which is significantly affected by the small pore structure of the microporous layer. The volume median pore diameter refers to the pore diameter value corresponding to the cumulative pore volume ratio of 50% in the cumulative pore volume distribution curve, which is significantly affected by the large pore structure of the substrate layer. That is, for the gas diffusion layer for fuel cells, the adjustment of the area median pore diameter and the volume median pore diameter requires the matching design between the pore structure of the substrate layer and the pore structure of the microporous layer. In the present application, the pore structure relationship between the substrate layer and the microporous layer is controlled from the perspective of the area median pore diameter and the volume median pore diameter, and the water-gas transmission imbalance problem of the gas diffusion layer under high current density conditions is improved. Specifically, through experimental verification, it is found that when the area median pore diameter of the gas diffusion layer for fuel cells is controlled between 45nm-150nm, and the volume median pore diameter is controlled between 25μm-55μm, the gas diffusion layer can not only achieve uniform supply of reaction gas, but also ensure water discharge capacity, effectively solving the gas and water transmission imbalance problem in the existing gas diffusion layer. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained according to the structures shown in the drawings without creative labor for those skilled in the art.

[0036] Figure 1 The surface SEM image of the microporous layer of the gas diffusion layer of Example 1 of the present application.

[0037] Figure 2 The surface SEM image of the microporous layer of the gas diffusion layer of Example 2 of the present application.

[0038] Figure 3 The surface SEM image of the microporous layer of the gas diffusion layer of Example 3 of the present application.

[0039] Figure 4 The surface SEM image of the microporous layer of the gas diffusion layer of Example 4 of the present application.

[0040] Figure 5 The surface SEM image of the microporous layer of the gas diffusion layer of Comparative Example 1 of the present application.

[0041] Figure 6 The surface SEM image of the microporous layer of the gas diffusion layer of Comparative Example 2 of the present application.

[0042] Figure 7 Surface SEM image of the microporous layer of the gas diffusion layer of Invention Comparative Example 3.

[0043] Figure 8 Mercury intrusion porosimetry volume versus pore size plot of the samples of Invention Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3.

[0044] Figure 9 Mercury intrusion specific surface area versus pore size plot of the samples of Invention Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3.

[0045] The objectives, features and advantages of the present application will be further understood based on the following embodiments with reference to the drawings. DETAILED DESCRIPTION

[0046] The technical solutions in the embodiments of the present application will be apparently and completely described with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the present application.

[0047] The ranges disclosed herein are defined by the lower and upper limits in the form of a range. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The ranges defined in this manner can include the endpoints or not, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise stated, the numerical range "a-b" represents a shorthand notation that refers to any integer combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all the real numbers between "0-5" have been listed herein, and "0-5" is just a shorthand notation for these numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0048] If not specifically stated, all the embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0049] If there is no special indication, all the technical features of the present application and the optional technical features can be combined with each other to form new technical solutions.

[0050] If there is no special indication, all the steps of the present application can be sequentially performed or randomly performed, and preferably are sequentially performed. For example, the method comprises steps (a) and (b), which means that the method can comprise sequentially performed steps (a) and (b), or can comprise sequentially performed steps (b) and (a). For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or can comprise steps (a), (c) and (b), or can comprise steps (c), (a) and (b), etc.

[0051] In the prior art, the gas diffusion layer is a core component of the fuel cell, and the pore structure thereof directly affects the water vapor transmission efficiency. The traditional design adopts a double-layer structure, the base layer provides micrometer-level pores for water drainage, and the microporous layer provides nanometer-level pores to promote gas diffusion. However, as the power density of the fuel cell increases, the water production per unit time increases dramatically under a large current condition, and the traditional structure cannot balance the requirements of gas diffusion and water discharge, resulting in waterlogging of the catalyst layer and performance degradation.

[0052] Based on this, the embodiment of the present application proposes a gas diffusion layer, which comprises a base layer and a microporous layer coated on the base layer;

[0053] The area median pore diameter of the gas diffusion layer is 45 nm-150 nm, and the area median pore diameter refers to the pore diameter value corresponding to the cumulative pore surface area ratio of 50% in the cumulative pore surface area distribution curve;

[0054] The volume median pore diameter of the gas diffusion layer is 20 μm-50 μm, and the volume median pore diameter refers to the pore diameter value corresponding to the cumulative pore volume ratio of 50% in the cumulative pore volume distribution curve.

[0055] The technical solution analyzes the influence of pore distribution on the gas diffusion coefficient and the water transmission path, and proposes that small pores dominated by surface area and large pores dominated by volume need to be regulated respectively. Further research finds that there is a significant difference between the cumulative distribution of pore surface area and the cumulative distribution of volume, and a single pore diameter index cannot accurately represent the characteristics of the multi-level pore structure. Based on this, the technical solution introduces double control indexes of area median pore diameter and volume median pore diameter, which correspond to the functional requirements of the microporous layer and the base layer respectively, and constructs a gradient pore structure. The volume median pore diameter (VMD) and the area median pore diameter (AMD) can be obtained by mercury injection test, and the main difference between the volume median pore diameter and the area median pore diameter is due to the different influences of the pore size distribution on the volume and the surface area.

[0056] The area median pore size refers to a pore size corresponding to a cumulative pore area ratio of 50% in a cumulative pore area distribution curve. Specifically, the area median pore size (AMD) refers to a cumulative pore area distribution in which 50% of the pore area is contributed by pores having a pore size greater than the value, and the remaining 50% is contributed by pores having a pore size less than the value. Because the pore area is mainly provided by small pores, the area median pore size (AMD) is significantly affected by small-pore-size pores, and mainly reflects the small-pore-size pores dominated by MPL in a GDL material, and can be used to characterize the pore structure of the MPL.

[0057] The volume median pore size refers to a pore size corresponding to a cumulative pore volume ratio of 50% in a cumulative pore volume distribution curve. This parameter determines the water discharge efficiency. Specifically, the volume median pore size refers to a cumulative pore volume distribution in which 50% of the pore volume is contributed by pores having a pore size greater than the value, and the remaining 50% is contributed by pores having a pore size less than the value. The pore volume is mainly provided by large pores, and the volume median pore size is significantly affected by large-pore-size pores. In a GDL material, it mainly reflects the large-pore-size pores dominated by carbon paper, and can be used to characterize the water transport properties of the GDL.

[0058] Because there are two diffusion modes of water vapor in nanoscale pores, Knudsen diffusion and Fick diffusion. The average free path of water vapor gas molecules is about 70 nm under standard conditions, and in the high-temperature environment of a fuel cell, the gas molecule density decreases, and the average free path can reach more than 120 nm. When the pore size is close to or less than the average free path of gas molecule diffusion, Knudsen diffusion is dominant.

[0059] In Knudsen diffusion, the collision frequency of molecules with the pore wall increases, and the transmission rate is proportional to the pore size, following the Knudsen diffusion formula:

[0060]

[0061] where Dk is the Knudsen diffusion coefficient, d is the pore diameter, R is the gas constant, T is the temperature, and M is the molar mass of water molecules.

[0062] When the pore size is much larger than the average free path of gas molecule diffusion, Fick diffusion is dominant.

[0063] Fick diffusion is suitable for steady-state diffusion, and the diffusion flux is proportional to the concentration gradient. The diffusion coefficient is mainly affected by temperature and pressure, and is independent of pore size.

[0064]

[0065] where w is the amount of diffused water vapor per unit time (g / cm2*min), dPv is the water vapor pressure difference, Z is the diffusion distance, ε is the porosity, and τ is the tortuosity.

[0066] When the pore size of the microporous layer is close to the mean free path of water molecules, the transport mode of water vapor in the pores changes, and the diffusion rate of water vapor is positively correlated with the pore size. Specifically, in the microporous layer (MPL), the pores of the order of hundreds of nanometers and smaller are dominated by Knudsen diffusion, and the pores of the order of hundreds of nanometers to microns are in the transition region of Knudsen diffusion and Fick diffusion. Therefore, the water vapor transmission rate in the MPL is positively correlated with the pore size of the MPL, and the water vapor transmission rate can be controlled by adjusting the pore size of the MPL.

[0067] The prior art lacks an evaluation method for the pore size of the two-layer structure (substrate layer and MPL) of the GDL, which cannot guide the design of the gradient pore structure of the GDL, which leads to the fact that the commercial GDL cannot quickly discharge the water generated at a large current density, causing the waterlogging of the catalyst layer and the rapid performance degradation of the battery.

[0068] The area median diameter (AMD) and the volume median diameter (VMD) in the embodiments of the present application reflect the pore characteristics of the MPL and the substrate layer, respectively, and the accurate design of the gradient pore structure of the GDL is realized by optimizing the two parameters. There are two modes of Knudsen diffusion and Fick diffusion for the water vapor transmission in the MPL. Within the pore size range (45-150 nm) set in the present technical solution, the water vapor transmission rate is positively correlated with the pore size, which is conducive to the rapid discharge of water vapor at a large current density.

[0069] The present application controls the pore structure relationship between the microporous layer and the substrate layer from the perspective of the area median diameter and the volume median diameter. Specifically, the adjustment of the pore size range dominated by the microporous layer can improve the efficiency of the outward diffusion of water vapor and relieve the problem of water accumulation in the catalyst layer; and the substrate layer maintains a specific macroporous structure to provide a low-resistance discharge path for water. The synergistic effect enables the gas diffusion layer to maintain a suitable water content state of the catalyst layer within a wide current density range, avoiding both the waterlogging of the catalyst layer leading to the blockage of the reaction gas transmission and the excessive dehydration of the membrane electrode leading to the decrease of the proton conductivity. The overall thickness and porosity parameters of the GDL achieve the balance between the structural strength and the gas and water transmission.

[0070] In some embodiments, the area median diameter of the gas diffusion layer is 50 nm-90 nm, and the volume median diameter of the gas diffusion layer is 25 μm-40 μm.

[0071] The present technical solution further limits the preferred parameter range of the pore structure of the gas diffusion layer. The present solution limits the area median diameter to the range of 50 nm-90 nm, which represents the pore structure characteristics dominated by the microporous layer; and limits the volume median diameter to the range of 25 μm-40 μm, which reflects the pore structure characteristics dominated by the substrate layer.

[0072] The preferred range is further targeted at the fine-tuning control requirement of water vapor transport balance under high power operating conditions. In the 50-90 nm interval, the microporous layer pore size is close to the mean free path of water molecules, and the water vapor diffusion rate is positively correlated with the pore size, which helps to improve the water vapor transport efficiency across the microporous layer. At the same time, the 25-40 μm substrate layer pore provides a low-resistance discharge path for water, reducing water retention in the catalytic interface. This synergistic effect optimizes the water management dynamic balance under high current density, both alleviating the reaction gas transport obstruction caused by catalyst layer flooding and reducing the risk of excessive drying of the membrane electrode. By narrowing the design range of the pore parameters, the gas diffusion layer can have stronger adaptability under different humidity conditions, which is conducive to maintaining the match between gas transport efficiency and proton conduction capacity under a wide humidity range. This configuration is suitable for low to high humidity wide range, high current operating conditions, such as: in a 30-100% RH wide humidity range environment @ 2A / cm -2 A single cell voltage higher than 0.6V can be obtained under a current density, and a single cell voltage higher than 0.6V can be maintained under a high current density in a wide humidity range environment. -2 A single cell voltage higher than 0.6V can be obtained under a current density, and a single cell voltage higher than 0.6V can be maintained under a high current density in a wide humidity range environment.

[0073] In some embodiments, the area median pore size of the gas diffusion layer is 45-90 nm, and the volume median pore size of the gas diffusion layer is 20-40 μm. This configuration is suitable for medium-low humidity, high current operating conditions. For example: in a 30-60% RH medium-low humidity environment @ 2A / cm -2 A single cell voltage higher than 0.64V can be obtained under a current density, and a single cell voltage higher than 0.64V can be maintained under a high current density in a 30-60% RH medium-low humidity environment. -2 A single cell voltage higher than 0.64V can be obtained under a current density, and a single cell voltage higher than 0.64V can be maintained under a high current density in a 30-60% RH medium-low humidity environment.

[0074] In some embodiments, the area median pore size of the gas diffusion layer is 50-150 nm, and the volume median pore size of the gas diffusion layer is 25-50 μm. This configuration is suitable for medium-high humidity, high current operating conditions. For example: in a 60-100% RH medium-high humidity environment @ 2A / cm -2 A single cell voltage higher than 0.64V can be obtained under a current density, and a single cell voltage higher than 0.64V can be maintained under a high current density in a high humidity environment. -2 A single cell voltage higher than 0.64V can be obtained under a current density, and a single cell voltage higher than 0.64V can be maintained under a high current density in a high humidity environment.

[0075] In some embodiments, the thickness of the gas diffusion layer is 110-280 μm, and the porosity is 75-90%.

[0076] In the technical solution, the thickness range of the GDL is determined by balancing the structural strength and the transmission path, and the porosity range is set by coordinating the electrical conductivity and permeability. The thickness of the substrate layer refers to the vertical dimension of the carbon paper without the microporous layer. The porosity refers to the proportion of the pore volume in the total volume in the substrate layer, which can be achieved by adjusting the carbon fiber diameter, arrangement density, and binder content.

[0077] The substrate layer, as a key structural layer supporting the microporous layer and transmitting water, needs to meet multiple physical design requirements under high-power working conditions: the thickness needs to be thin enough to reduce the resistance of the transmission path for water discharge, and the thickness cannot be too thin to support the catalyst layer for structural strength; high porosity is needed to form an unobstructed channel for rapid water permeation, but too high porosity will weaken the carbon fiber skeleton structure; when the porosity is less than 75%, a dense fiber network may be formed, hindering the migration efficiency of water under capillary action.

[0078] In the design of thickness and porosity, the thickness range of 110 μm-280 μm controls the water transmission distance and maintains sufficient mechanical support strength; the porosity range of 75%-90% ensures the capacity of the water transmission channel while maintaining the structural stability of the carbon fiber skeleton. This parameter combination enables the substrate layer to quickly discharge large droplets under the impact of strong water pressure generated by high current density, avoiding water flooding of the catalyst layer, and preventing pore deformation that causes microporous layer leakage or structural collapse. The optimization of the substrate layer provides a structural basis for the microporous layer to achieve precise gas distribution, and together forms a gradient-porosity cooperative drainage mechanism.

[0079] On the other hand, the application also provides a preparation method of a gas diffusion layer, comprising the following steps:

[0080] A porous conductive substrate and a microporous layer slurry are provided, the microporous layer slurry is coated on one side of the carbon paper, and after drying, a sintering treatment at 350-380°C is performed to obtain a gas diffusion layer comprising a substrate layer and a microporous layer; the carbon paper forms the substrate layer, and the microporous layer slurry forms the microporous layer;

[0081] The area median pore size of the gas diffusion layer is 45-150 nm, and the area median pore size refers to the pore size corresponding to the cumulative pore surface area proportion of 50% in the cumulative distribution curve of the pore surface area;

[0082] The volume median pore size of the gas diffusion layer is 20-50 μm, and the volume median pore size refers to the pore size corresponding to the cumulative pore volume proportion of 50% in the cumulative distribution curve of the pore volume.

[0083] In some embodiments, the microporous layer slurry comprises a pore-forming agent, and the particle size or molecular agglomeration size of the pore-forming agent is 1-500 nm, preferably 5-200 nm.

[0084] In some embodiments, the pore-forming agent is selected from at least one of polyether polyol, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyether ether ketone, cellulose, and polyether.

[0085] In some embodiments, the pore-forming agent has a carbon residue after ablation treatment at 350°C of ≤1%.

[0086] In some embodiments, the pore-forming agent has a carbon residue after ablation treatment at 350°C of ≤1%.

[0087] Specifically, by selecting an organic macromolecule of a specific size as the pore-forming agent, a uniform dispersion of temporary pore templates is formed in the microporous layer slurry. During subsequent sintering, the pore-forming agent decomposes under heat to form nanoscale pores, the size of which is determined by the original particle size of the pore-forming agent. Polyether polyol materials contain hydrophilic groups and can be stably dispersed in aqueous slurry, avoiding the agglomeration problem of traditional hydrophobic organic particles. Cellulose materials form nanoscale agglomerates through intermolecular hydrogen bonding, and form a network of through pores after sintering. The linear molecular structure of polypropylene oxide produces uniformly distributed slit-shaped pores when it decomposes, which is conducive to the construction of gas diffusion paths.

[0088] The technical solution controls the pore structure of the microporous layer by using a specific pore-forming agent. An organic pore-forming agent with a particle size or molecular agglomeration size in the range of 1 nm to 500 nm is selected, and the material type includes polyether polyol, polyethylene glycol, and other polymers containing carbon, hydrogen, and oxygen elements. The pore-forming agent forms a template during the processing of the microporous layer slurry and forms permanent pores after high-temperature sintering and decomposition. Inorganic pore-forming agents in existing technologies have stability defects, and organic polymer microspheres are too large to form nanoscale pores, but the selected pore-forming agent material has controllable nanoscale and thermal decomposition characteristics.

[0089] The size range of 1 nm to 500 nm forms submicron pores that match the target after sintering, directly expanding the mass transfer pore diameter of the microporous layer. Polyether and cellulose materials have very low carbon residue when they decompose at temperatures above 350°C, avoiding the blockage of new pores by residual materials. These organic materials have good solubility and dispersibility in aqueous slurry, which helps to form a template structure with uniform size. The generated pore structure shifts the water vapor diffusion mode towards the Knudsen diffusion mechanism, improving the efficiency of water molecule migration in a high-humidity environment, while maintaining the uniform distribution function of the microporous layer for reaction gas. The material selection scheme cooperates with the sintering process to achieve controllable preparation of the pore structure of the microporous layer.

[0090] In some embodiments, the pore-forming agent has a carbon residue after ablation treatment at 350°C of ≤1%.

[0090]

[0091] Further, the 5nm-200nm size enables the pore-forming agent to form a pore structure within the microporous layer in a target pore size range, directly optimizing the water vapor transmission efficiency in the Knudsen diffusion mechanism dominant interval. Residual carbon content control is achieved through material selection, and polyether and cellulose organic matter completely breaks the molecular chain during thermal decomposition, producing almost no solid residue.

[0092] Compared with the prior art, traditional pore-forming agents such as inorganic ammonium salts easily produce residues to pollute the pores, and organic polymer microspheres have a particle size that is too large, resulting in a pore size that exceeds the standard. The present solution forms a gradient distribution of pore networks in the microporous layer by controlling the size and decomposition characteristics of the pore-forming agent, thereby maintaining the gas diffusion efficiency and balancing the water blocking ability.

[0093] Through the above technical solution, the present application realizes fine regulation of the pore structure of the microporous layer, further balances the water vapor diffusion and water blocking requirements under wide humidity conditions of the fuel cell, avoids water flooding of the catalyst layer or drying of the proton membrane, and improves the performance stability of the battery under high current density.

[0094] In some embodiments, the thickness of the porous conductive substrate is 100μm-260μm, the porosity is 75%-90%, and the volume median pore size is 25μm-50μm.

[0095] In some embodiments, the porous conductive substrate is selected from any one of carbon fiber paper, metal-based porous substrate. Specifically, the metal base can be titanium base, iron base (carbon can be plated on the surface of the iron base), copper, gold, silver, etc.

[0096] The technical solution provides a method for preparing a gas diffusion layer by a specific pore-forming agent and a sintering process. The method adds an organic pore-forming agent with a size of 1nm-500nm to the microporous layer slurry, selects polyether polyol, cellulose, and other carbon-containing hydrogen and oxygen polymers, and performs sintering treatment at 350℃-380℃ to completely decompose the pore-forming agent and form a permanent pore structure in the microporous layer.

[0097] The present process mainly addresses the limitations of traditional pore-forming techniques in precisely regulating nanoscale pores. Existing inorganic pore-forming agents produce gas by-products during thermal decomposition, leading to a decrease in slurry stability; organic polymer microspheres have a molecular size that is too large, resulting in pores that exceed the effective nanoscale range. The selected pore-forming agent material in the present solution has solubility and dispersibility in aqueous systems, and its thermal decomposition characteristics avoid the blockage of newly formed pores by residues.

[0098] Within the defined temperature range, the pore-forming agent molecular chain breaks to generate gaseous products, and its original space is converted into pores. The 1nm-500nm scale corresponds to the average free range of water molecules, and the size of the formed pores promotes the shift of water vapor transmission to Knudsen diffusion mechanism. The carbon residual rate of polyether and cellulose materials is extremely low at this temperature, reducing the possibility of pore blockage. The lower limit of the sintering temperature allows the pore-forming agent to fully decompose, and the upper limit prevents damage to the carbon fiber substrate structure. The final formed pore structure coordinates the gas diffusion and water vapor transmission efficiency, while maintaining the function of uniform distribution of the microporous layer gas, and enhancing the outward migration ability of the catalyst layer water in a high humidity environment.

[0099] Compared with the prior art, when the traditional method uses inorganic ammonium salt or large-size organic particles as a pore-forming agent, there are defects such as environmental pollution by decomposition products, poor slurry stability, or excessively large pore size. The method selects a specific size of polyether high molecular material, which has good dispersibility in the slurry, no harmful residue after sintering, and can accurately control the pore size to the nanometer level.

[0100] Through the above technical solution, the present application solves the problem of pore structure regulation caused by improper selection of pore-forming agent, and realizes accurate control of the pore size of the microporous layer. The stability of the slurry is improved, and the problem of gas emission caused by the decomposition of inorganic salts is avoided. The gradient pore structure formed takes into account the gas diffusion efficiency and water discharge capacity, and inhibits the waterlogging phenomenon of the catalyst layer under high current density.

[0101] In some embodiments, the method of preparing the microporous layer slurry comprises: adding a dispersant and conductive carbon powder to water, and mixing to obtain a carbon slurry; adding a binder to the carbon slurry, and then adding a thickening agent and a pore-forming agent, and dispersing to obtain a microporous layer slurry;

[0102] In the above technical solution, the weight parts of each component of the microporous layer slurry are as follows:

[0103]

[0104] The technical solution optimizes the preparation of the microporous layer slurry through a specific feeding sequence. First, the conductive carbon powder is mixed with water in the presence of a dispersant to form a primary dispersion; then the binder is added to coat the carbon particles; finally, the thickening agent and the pore-forming agent are introduced to complete the construction of the slurry. This feeding sequence forms a stable dispersion structure in stages.

[0105] This process improves the uniformity of the slurry. If the conductive carbon powder and the pore-forming agent are added simultaneously, agglomeration may occur due to differences in surface energy. If the binder is added too early, it may wrap the active sites on the surface of the carbon powder, hindering the uniform distribution of the pore-forming agent. Stepwise feeding allows each component to combine in a balanced state of interfacial forces.

[0106] The initial carbon slurry stage is fully wetted by the dispersant on the surface of the carbon powder, reducing the interfacial tension of the subsequent added components. The binder is added after the carbon slurry is stabilized, forming a binder coating layer to avoid the pore-forming agent molecules directly adsorbing on the surface of the carbon powder. The thickening agent is finally added to achieve a uniform spatial distribution of the pore-forming agent in the stabilized system. This sequence allows the pore-forming agent molecules to remain discrete in the slurry, and the size distribution of the pores formed after sintering and decomposition is closer to the original molecular size. The process design optimizes the pore formation mechanism by controlling the timing of component contact, improving the structural integrity and mass transfer efficiency of the final microporous layer.

[0107] The present technical solution defines the ratio range of each functional component of the microporous layer slurry. 5-20 parts of conductive carbon powder form a continuous conductive path while retaining pore space; 0.2-10 parts of dispersant balances between stabilizing the suspension system and maintaining interfacial activity; 1-20 parts of binder builds a moderate hydrophobic network without closing the pore channel; 0.1-10 parts of thickening agent makes the slurry have both coating applicability and deformation recovery force; 1-100 parts of pore-forming agent precisely controls the pore size distribution through the template effect. This ratio system makes the microporous layer after sintering form a gradient pore structure, optimizing the transmission efficiency of water vapor while maintaining the uniformity of the gas diffusion path. Each component forms a complementary effect at a limited ratio, improving the mechanical stability and functional reliability of the coating structure.

[0108] In some embodiments, the binder includes a fluorine-containing polymer,

[0109] In some embodiments, the thickening agent includes a polyether compound containing only C, H, and O elements, and the dispersant includes at least one of an aromatic non-ionic dispersant and a zwitterionic dispersant.

[0110] The fluorine-containing polymer refers to a high molecular compound containing fluorine atoms in the main chain or side chain, which forms a three-dimensional network structure after high-temperature sintering, enhancing the bonding strength of the microporous layer and the substrate layer. The polyether compound refers to a polymer connected by ether bonds between repeating units, which adjusts the slurry viscosity through hydrogen bonding and completely decomposes during high-temperature sintering to avoid impurity elements remaining and blocking the pores. The aromatic non-ionic dispersant refers to a surfactant containing a benzene ring structure and no charge, which adsorbs on the surface of the carbon powder through a hydrophobic group to form steric hindrance; the zwitterionic dispersant refers to a surfactant carrying both positive and negative charge groups, which maintains the dispersion stability of the slurry through charge balance.

[0111] Specifically, the fluorine-containing polymer forms a stable hydrophobic network during sintering, ensuring the barrier function of the microporous layer to moisture, while its molecular chain flexibility keeps the pore structure open. The polyether compound does not contain nitrogen, sulfur and other heteroatoms, and its thermal decomposition products are gaseous substances, reducing the physical blockage of carbon residues to the newly formed pores. The aromatic non-ionic or zwitterionic dispersant maintains the uniform dispersion of nano-carbon particles and pore-forming agent molecules through steric hindrance or electrostatic repulsion, making the pore size distribution after sintering closer to the design target. This combination of materials maintains the integrity of the pore structure while enhancing the durability of the coating in high temperature and high humidity environments, providing a long-term stable water vapor transport channel for the gas diffusion layer.

[0112] In some embodiments, the conductive carbon powder includes at least one of furnace black, acetylene black, ketjen black, graphitized carbon black, carbon nanotube, vapor grown carbon fiber. As an example, commercially available conductive carbon powder can be listed as: Cabot XC72R furnace black, Japan Electric Chemical denka series acetylene black, Lion EC series ketjen black, BTR BGD series graphitized carbon black, etc.

[0113] In some embodiments, the binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, perfluorosulfonic acid resin, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer.

[0114] The thickening agent includes at least one of polyether polyol, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyether ether ketone, cellulose, polyether.

[0115] The aromatic non-ionic dispersant includes at least one of alkyl phenol polyoxyethylene ether (such as nonyl phenol polyoxyethylene ether Tergitol NP-40, distyryl phenol polyoxyethylene ether), phenyl modified polyethylene glycol (such as polyethylene glycol octyl phenyl ether Triton X-100, polyethylene glycol nonyl phenyl ether op-4, ethyl phenyl polyethylene glycol), phenoxy dispersant (such as R-methyl p-hydroxyphenoxypropionate).

[0116] The zwitterionic dispersant includes at least one of amino acid type (such as N-acyl amino acid, lauroyl lysine, alkoxy (2-hydroxypropyl) arginine, Gemini type amino acid surfactant, Bola type amino acid surfactant), betaine type (such as lauryl betaine, 3-sulfidodecyl dimethyl betaine, 3-sulfotetradecyl dimethyl betaine, cocamide propyl betaine).

[0117] Among the above-mentioned materials, carbon materials such as furnace black and acetylene black form a three-dimensional conductive network, and the surface characteristics thereof promote the interface combination with other components; fluorine-containing polymers such as polytetrafluoroethylene form a chemically stable hydrophobic skeleton after sintering, thereby maintaining the durability of the pore structure in an acidic environment; polyether polyols and cellulose-based thickening agents regulate the viscosity of the slurry through hydrogen bonding, and the complete decomposition characteristics thereof avoid the blockage of new pores by carbon residues. The selection and combination of the above-mentioned materials enable the slurry to maintain a uniformly dispersed state during the coating stage, and the microporous layer formed after sintering has continuous conductive paths, gradient pore distribution and structural integrity.

[0118] In another aspect, the embodiments of the present application also provide a fuel cell comprising the above-mentioned gas diffusion layer or the gas diffusion layer prepared by the above-mentioned preparation method. Since the above-mentioned gas diffusion layer has a physical structure that coordinates water vapor transmission, the fuel cell integrated with the gas diffusion layer exhibits sustainable operation capability under high power output conditions.

[0119] The following will be described in conjunction with specific embodiments.

[0120] Embodiment 1

[0121] The embodiment provides a gas diffusion layer, and structural parameters of the gas diffusion layer are as follows: thickness 200 μm, porosity 85%, volume median pore diameter 32 μm, and area median pore diameter 72 nm. The preparation method of the gas diffusion layer is as follows:

[0122] S1: 100 parts of deionized water are taken, 8 parts of a dispersant are added, and stirring is performed until complete dispersion; then 10 parts of graphitized conductive carbon black is added while stirring, and stirring is performed until uniform dispersion, and then high-speed homogenization dispersion is performed by a homogenizer at 20,000 rpm to obtain a carbon slurry.

[0123] S2: In the above-mentioned carbon slurry of S1, 6 parts of a binder (60 wt% PTFE emulsion) is added while stirring, and then stirring and dispersion are performed to obtain a slurry of PTFE uniformly coated carbon powder material;

[0124] S3: In the above-mentioned slurry of S2, 0.2 parts of a thickening agent and 30 parts of 50 nm particle size methyl polyethylene glycol pore-forming agent are added while stirring, and then stirring and dispersion are performed to obtain a stable, uniform and highly dispersed MPL slurry;

[0125] S4: The above-mentioned slurry of S3 is coated on one side of a carbon paper with a thickness of 180 μm, a porosity of 80%, and a volume median pore diameter of 42 μm after PTFE hydrophobization by a silk screen coating method, and after drying at 80°C, a fuel cell gas diffusion layer is prepared by sintering at 360°C.

[0126] Embodiment 2

[0127] The embodiment provides a gas diffusion layer, and structural parameters of the gas diffusion layer are as follows: thickness 200 μm, porosity 85%, volume median pore diameter 32 μm, and area median pore diameter 72 nm. The preparation method of the gas diffusion layer is as follows:

[0128] S1: Take 100 parts of deionized water, add 5 parts of dispersant, stir until completely dispersed; then add 5 parts of porous carbon black while stirring, stir until evenly dispersed, then pass through a homogenizer at 10000 rpm for high-speed homogenization and dispersion to obtain a carbon slurry.

[0129] S2: In the above S1 carbon slurry, 3 parts of binder (60wt% PTFE emulsion) are added under stirring, then stirred and dispersed to obtain a slurry of PTFE uniformly coated carbon powder material;

[0130] S3: In the above S2 slurry, 1 part of thickening agent and 90 parts of 3 nm particle size polyoxyethylene-octyl phenyl ether pore former are added under stirring, then stirred and dispersed to obtain a stable, uniform and highly dispersed MPL slurry;

[0131] S4: The above S3 slurry is coated on one side of the carbon paper with a thickness of 240 μm, a porosity of 76%, and a volume median pore size of 25 μm after PTFE hydrophobization, dried at 120°C, and sintered at 350°C to obtain a gas diffusion layer for fuel cells.

[0132] Example 3

[0133] This example provides a gas diffusion layer, the structural parameters of which are shown in Table 1. The preparation method of the gas diffusion layer comprises the following steps:

[0134] S1: Take 100 parts of deionized water, add 0.3 parts of dispersant (Triton X-100), stir until completely dispersed; then add 12 parts of acetylene black while stirring, stir until evenly dispersed, then pass through a disperser at 5000 rpm for high-speed homogenization and dispersion to obtain a carbon slurry.

[0135] S2: In the above S1 carbon slurry, 18 parts of binder (60wt% PTFE emulsion) are added under stirring, then stirred and dispersed to obtain a slurry of PTFE uniformly coated carbon powder material;

[0136] S3: In the above S2 slurry, 5 parts of thickening agent (polyethylene glycol) and 30 parts of 20 nm particle size polyethylene oxide pore former are added under stirring, then stirred and dispersed to obtain a stable, uniform and highly dispersed MPL slurry;

[0137] S4: The above S3 slurry is coated on one side of the carbon paper with a thickness of 200 μm, a porosity of 82%, and a volume median pore size of 39 μm after PTFE hydrophobization, dried at 110°C, and sintered at 380°C to obtain a gas diffusion layer for fuel cells.

[0138] Example 4

[0139] The embodiment provides a kind of gas diffusion layer, its structural parameter refers to Table 1.The preparation method of the gas diffusion layer includes the following steps:

[0140] S1: take 100 parts of deionized water, add 0.3 parts of dispersant (Triton X-100), stir until completely dispersed;Then add 12 parts of acetylene black while stirring, stir until evenly dispersed, then homogenously dispersed by disperser 5000 rpm high speed, obtain carbon slurry.

[0141] S2: in the above S1 carbon slurry, 18 parts of binder (60wt% PTFE emulsion) are added under stirring, then stirring and dispersing, obtain the slurry of PTFE evenly coated carbon powder material;

[0142] S3: in the above S2 slurry, 5 parts of thickening agent (polyethylene glycol) and 30 parts of 20nm particle size polyethylene oxide pore former are added under stirring, then stirring and dispersing to obtain stable, uniform and highly dispersed MPL slurry;

[0143] S4: the above S3 slurry is coated on one side of carbon paper with thickness of 180 μm, porosity of 85% and volume median pore diameter of 42 μm after PTFE hydrophobization by spraying, dried at 110 ℃, and sintered at 380 ℃ to obtain a gas diffusion layer for fuel cell.

[0144] Example 5

[0145] The embodiment provides a kind of gas diffusion layer, its structural parameter refers to Table 1.The preparation method of the gas diffusion layer includes the following steps:

[0146] S1: take 100 parts of deionized water, add 8 parts of dispersant, stir until completely dispersed;Then add 10 parts of graphitized conductive carbon black while stirring, stir until evenly dispersed, then homogenously dispersed by homogenizer 20000 rpm high speed, obtain carbon slurry.

[0147] S2: in the above S1 carbon slurry, 6 parts of binder (60wt% PTFE emulsion) are added under stirring, then stirring and dispersing, obtain the slurry of PTFE evenly coated carbon powder material;

[0148] S3: in the above S2 slurry, 0.2 parts of thickening agent and 2 parts of 50nm particle size methyl glucose polyether pore former are added under stirring, then stirring and dispersing to obtain stable, uniform and highly dispersed MPL slurry;

[0149] S4: the above S3 slurry is coated on one side of carbon paper with thickness of 180 μm, porosity of 80% and volume median pore diameter of 42 μm after PTFE hydrophobization by silk screen coating, dried at 80 ℃, and sintered at 360 ℃ to obtain a gas diffusion layer for fuel cell.

[0150] Example 6

[0151] This example provides a gas diffusion layer, the structural parameters of which are shown in Table 1. The preparation method of the gas diffusion layer comprises the following steps:

[0152] S1: Take 100 parts of deionized water, add 8 parts of dispersant, and stir until completely dispersed; then add 10 parts of graphitized conductive carbon black while stirring, stir until uniformly dispersed, and then pass through a homogenizer at 20000 rpm for high-speed homogenization and dispersion to obtain a carbon slurry.

[0153] S2: In the carbon slurry of S1 above, 6 parts of a binder (60 wt% PTFE emulsion) are added while stirring, and then stirred and dispersed to obtain a slurry of PTFE uniformly coated carbon powder material;

[0154] S3: In the slurry of S2 above, 0.2 parts of a thickening agent and 100 parts of a 50 nm particle size methyl glucose polyether pore former are added while stirring, and then stirred and dispersed to obtain a stable, uniform and highly dispersed MPL slurry;

[0155] S4: The slurry of S3 above is coated on one side of a carbon paper with a thickness of 180 μm, a porosity of 80%, and a volume median pore diameter of 42 μm after PTFE hydrophobization by means of silk screen coating, dried at 80°C, and sintered at 360°C to obtain a gas diffusion layer for fuel cells.

[0156] Example 7

[0157] This example provides a gas diffusion layer, the structural parameters of which are shown in Table 1. The preparation method of the gas diffusion layer comprises the following steps:

[0158] S1: Take 100 parts of deionized water, add 8 parts of dispersant, and stir until completely dispersed; then add 10 parts of graphitized conductive carbon black while stirring, stir until uniformly dispersed, and then pass through a homogenizer at 20000 rpm for high-speed homogenization and dispersion to obtain a carbon slurry.

[0159] S2: In the carbon slurry of S1 above, 6 parts of a binder (60 wt% PTFE emulsion) are added while stirring, and then stirred and dispersed to obtain a slurry of PTFE uniformly coated carbon powder material;

[0160] S3: In the slurry of S2 above, 0.2 parts of a thickening agent and 30 parts of a 50 nm particle size methyl glucose polyether pore former are added while stirring, and then stirred and dispersed to obtain a stable, uniform and highly dispersed MPL slurry;

[0161] S4: The S3 slurry is coated on one side of the carbon paper with a thickness of 160 μm, porosity of 87%, and volume median pore diameter of 45 μm after PTFE hydrophobization by silk screen coating, dried at 80°C, and sintered at 360°C to obtain a gas diffusion layer for fuel cells.

[0162] Example 8

[0163] This example provides a gas diffusion layer, the structural parameters of which are shown in Table 1. The preparation method of the gas diffusion layer comprises the following steps:

[0164] S1: 100 parts of deionized water are taken, 10 parts of a dispersant are added, and stirred until completely dispersed; then 18 parts of Super P conductive carbon black are added while stirring, and stirred until uniformly dispersed, and then high-speed homogenized and dispersed by a homogenizer at 150,000 rpm to obtain a carbon slurry.

[0165] S2: In the carbon slurry of S1 above, 15 parts of a binder (60 wt% PTFE emulsion) are added while stirring, and then stirred and dispersed to obtain a slurry of PTFE uniformly coated carbon powder material;

[0166] S3: In the slurry of S2 above, 2 parts of a thickening agent and 10 parts of a 350 nm particle size hydroxypropyl methylcellulose pore former are added while stirring, and then stirred and dispersed to obtain a stable, uniformly highly dispersed MPL slurry;

[0167] S4: The S3 slurry is coated on one side of the carbon paper with a thickness of 160 μm, porosity of 87%, and volume median pore diameter of 45 μm after PTFE hydrophobization by silk screen coating, dried at 120°C, and sintered at 350°C to obtain a gas diffusion layer for fuel cells.

[0168] Example 9

[0169] This example provides a gas diffusion layer, the structural parameters of which are shown in Table 1. The preparation method of the gas diffusion layer comprises the following steps:

[0170] S1: 100 parts of deionized water are taken, 10 parts of a dispersant are added, and stirred until completely dispersed; then 18 parts of Super P conductive carbon black are added while stirring, and stirred until uniformly dispersed, and then high-speed homogenized and dispersed by a homogenizer at 150,000 rpm to obtain a carbon slurry.

[0171] S2: In the carbon slurry of S1 above, 15 parts of a binder (60 wt% PTFE emulsion) are added while stirring, and then stirred and dispersed to obtain a slurry of PTFE uniformly coated carbon powder material;

[0172] S3: In the slurry of S2 above, 2 parts of thickening agent and 3 parts of 800 nm particle size hydroxypropyl methyl cellulose pore-forming agent were added under stirring, and then the slurry was stirred and dispersed to obtain a stable, uniform and highly dispersed MPL slurry;

[0173] S4: The slurry of S3 above was coated on one side of the carbon paper after PTFE hydrophobization, with a thickness of 110 μm, a porosity of 89%, and a volume median pore size of 48 μm, by means of silk screen coating, dried at 120°C, and sintered at 350°C to obtain a gas diffusion layer for fuel cells.

[0174] Example 10

[0175] This example provides a gas diffusion layer, the structural parameters of which are shown in Table 1. The preparation method of the gas diffusion layer comprises the following steps:

[0176] S1: 100 parts of deionized water were taken, 0.3 parts of dispersant (Triton X-100) was added, and stirred until completely dispersed; then 12 parts of acetylene black was added while stirring, and stirred until uniformly dispersed, and then high-speed homogenized by a dispersing machine at 5000 rpm to obtain a carbon slurry.

[0177] S2: In the carbon slurry of S1 above, 18 parts of binder (60 wt% PTFE emulsion) was added under stirring, and then stirred and dispersed to obtain a slurry of PTFE uniformly coated carbon powder material;

[0178] S3: In the slurry of S2 above, 5 parts of thickening agent (polyethylene glycol) and 30 parts of 20 nm particle size polyethylene oxide pore-forming agent were added under stirring, and then the slurry was stirred and dispersed to obtain a stable, uniform and highly dispersed MPL slurry;

[0179] S4: The slurry of S3 above was coated on one side of the carbon paper after PTFE hydrophobization, with a thickness of 160 μm, a porosity of 87%, and a volume median pore size of 45 μm, by means of silk screen coating, dried at 80°C, and sintered at 360°C to obtain a gas diffusion layer for fuel cells.

[0180] Comparative Example 1

[0181] The preparation method of the gas diffusion layer of Comparative Example 1 is different from that of Example 1 in that no pore-forming agent was added to the microporous layer slurry of Comparative Example 1.

[0182] Comparative Example 2

[0183] The preparation method of the gas diffusion layer of Comparative Example 2 is different from that of Example 1 in that the pore-forming agent in the microporous layer slurry of Comparative Example 2 was 1.8 μm particle size polymethyl methacrylate microspheres.

[0184] Comparative Example 3

[0185] The preparation method of the gas diffusion layer of Comparative Example 3 is different from that of Example 1 in that the pore-forming agent in the microporous layer slurry of Comparative Example 2 is erythritol with a particle size of 0.8 nm.

[0186] Comparative Example 4

[0187] The gas diffusion layer of Comparative Example 4 is different from that of Example 1 in that the carbon paper is replaced by a carbon paper with a thickness of 180 μm, a porosity of 70%, and a volume median pore diameter of 38 μm.

[0188] Comparative Example 5

[0189] The gas diffusion layer of Comparative Example 5 is different from that of Example 1 in that the carbon paper is replaced by a carbon paper with a thickness of 220 μm, a porosity of 79%, and a volume median pore diameter of 21 μm.

[0190] Comparative Example 6

[0191] The gas diffusion layer of Comparative Example 6 is different from that of Example 1 in that the carbon paper is replaced by a carbon paper with a thickness of 160 μm, a porosity of 85%, and a volume median pore diameter of 53 μm.

[0192] Comparative Example 7

[0193] The gas diffusion layer of Comparative Example 7 is different from that of Example 1 in that the carbon paper is replaced by a carbon paper with a thickness of 280 μm, a porosity of 77%, and a volume median pore diameter of 37 μm.

[0194] Material performance test

[0195] In order to verify the progressiveness of the embodiments of the present application, the samples of the examples and comparative examples were respectively tested as follows:

[0196] 1. Thickness test

[0197] A thickness tester with an accuracy of ±1 μm was used for testing.

[0198] 2. Carbon residue test

[0199] 2 g of the sample was placed in a crucible and ablated at 350℃ for 2 h in an air atmosphere, and the weight W of the residual material was measured. The carbon residue was:

[0200]

[0201] 3. Pore-forming agent particle size test

[0202] The pore-forming agent sample was dispersed in a water medium and treated with ultrasonic waves to remove agglomerates, according to the national standard method of GB / T 29022-2021 “Particle size analysis dynamic light scattering method (DLS)”. The data was collected at a scattering angle of 173° and a temperature of 25℃ using a dynamic light scattering instrument, and each sample was tested repeatedly for 3 times.

[0203] 4. GDL electrode sheet pore structure test method

[0204] The pore structure of the GDL is tested by mercury intrusion method. The electrode sheet is cut into a 10 mm x 10 mm sample, vacuum dried and loaded into a sample tube. The pore distribution of the electrode sheet is tested by an AutoPore IV 9500 mercury intrusion instrument in a pressure range of 0.00 to 61000.00 psia.

[0205] Pore rate test method:

[0206]

[0207] The pressure-volume data is converted to pore diameter-volume data according to the following Washburn equation.

[0208]

[0209] Where d is the pore diameter, γ is the surface tension of mercury, and θ is the contact angle.

[0210] The pore diameter corresponding to the cumulative volume of 50% is taken, i.e. the volume median pore diameter.

[0211] According to the following formula, the pore volume increment corresponding to each pore diameter is converted to the corresponding surface area increment.

[0212]

[0213] The pore diameter corresponding to the cumulative area of 50% is taken, i.e. the area median pore diameter.

[0214] 5. Test method for coating electrode sheet MPL apparent morphology

[0215] The morphology of the MPL coating surface of the electrode sheet is observed by scanning electron microscopy (SEM).

[0216] Battery performance test

[0217] The performance of the GDL prepared from the carbon material is tested by a battery test bench. The anode catalyst loading of the membrane electrode is 0.1 mg·cm -2 , the cathode catalyst loading is 0.4 mg·cm -2 , the battery operating temperature is 80°C, the battery back pressure is 150 kPa / 150 kPa, the three-snake flow field, under three different humidity conditions of 100 RH%, 60% RH, and 30 RH%, the battery voltage at 2 A / cm 2 and 3 A / cm 2 current density is recorded.

[0218] Performance results

[0219] Table 1 is a table of relevant characterization data of the gas diffusion layers obtained in various embodiments and comparative examples.

[0220] Table 1

[0221]

[0222] Table 2 is a table showing the battery performance data of the gas diffusion layers prepared in various embodiments and comparative examples under different humidity environments and different current densities.

[0223] Table 2

[0224]

[0225] Combining the data in Table 1 and Table 2, it can be seen that in Examples 1 to 10, by adding a suitable pore-forming agent to the microporous layer and selecting carbon paper with suitable porosity, thickness and volume median pore diameter as the substrate, the GDL prepared meets the following requirements: the area median pore diameter is in the range of 45nm-150nm and the volume median pore diameter is in the range of 20μm-50μm. The GDL prepared in Examples 1 to 10 meets the following requirements: @2A / cm -2 The single cell voltage can be higher than 0.6V under high voltage, and @3A / cm2 in a wide humidity range environment -2 The single cell voltage can be maintained above 0.5V at high electrical density.

[0226] Among them, in Examples 1, 4-7, a moderate pore-forming agent is added to the microporous layer, and carbon paper with a moderate porosity, thickness and volume median pore diameter is selected as the substrate. The prepared GDL satisfies the area median pore diameter range of 50nm-90nm and the volume median pore diameter range of 25μm-40μm. The GDL prepared in Examples 1, 4-7 is in an environment with a wide humidity range of 30-100% RH @2A / cm -2 The single cell voltage can be higher than 0.64V under high density and @3A / cm2 in a wide humidity range environment. -2 The single cell voltage can be maintained above 0.53V under high electrical density. Even under 60% RH humidity conditions, at @2A / cm -2 The single cell voltage can be higher than 0.65V under high current density, and @3A / cm -2 It can maintain above 0.56V under high electrical density.

[0227] The GDLs prepared in Examples 1-7 meet the requirements of an area median pore size in the range of 45 nm-90 nm and a volume median pore size in the range of 20 μm-40 μm. The GDLs prepared in Examples 1-7 have a single cell voltage of more than 0.64 V at a low current density of 2 A / cm -2 The GDLs prepared in Examples 1-7 have a single cell voltage of more than 0.64 V at a low current density of 2 A / cm -2 The GDLs prepared in Examples 1-7 have a single cell voltage of more than 0.64 V at a low current density of 2 A / cm

[0228] The GDLs prepared in Examples 1-7 meet the requirements of an area median pore size in the range of 45 nm-90 nm and a volume median pore size in the range of 20 μm-40 μm. The GDLs prepared in Examples 1-7 have a single cell voltage of more than 0.64 V at a low current density of 2 A / cm -2 The GDLs prepared in Examples 1-7 have a single cell voltage of more than 0.64 V at a low current density of 2 A / cm -2 The GDLs prepared in Examples 1-7 have a single cell voltage of more than 0.64 V at a low current density of 2 A / cm

[0229] The data above show that the technical solution provided by the present application can precisely control the pore structure of the MPL layer, and obtain a GDL with a smooth surface and a uniform multi-level pore distribution. The GDL has high battery performance in a wide humidity range of 30% RH-100% RH and a wide current density range of 0-3 A / cm 3 The data above show that the technical solution provided by the present application can precisely control the pore structure of the MPL layer, and obtain a GDL with a smooth surface and a uniform multi-level pore distribution. The GDL has high battery performance in a wide humidity range of 30% RH-100% RH and a wide current density range of 0-3 A / cm

[0230] Comparative Examples 1 and 3 do not add a pore-forming agent to the microporous layer or add a small-size pore-forming agent. Compared with Example 1, the volume median pore size and the area median pore size of the GDLs decrease, resulting in poor drainage performance at a large current density, especially in a high humidity environment of 100% RH.

[0231] Comparative Example 2 adds a large-size pore-forming agent to the microporous layer. The MPL pores increase, and the volume and area provided by the MPL in the GDL increase. Compared with Example 1, the volume median pore size and the area median pore size of the GDLs increase, resulting in excessive drainage performance in a low humidity environment of 30% RH, and a decrease in the battery performance of the membrane dryness.

[0232] Comparative Example 4: Low porosity carbon paper was selected as the substrate. Compared to Example 1, the GDL porosity was lower, and the slight MPL infiltration during GDL preparation led to a decrease in both the volume median pore diameter and the area median pore diameter. The decreased GDL porosity resulted in insufficient drainage, leading to flooding and a sharp decrease in battery performance.

[0233] Comparative Example 5: Low volume median pore diameter carbon paper was selected as the substrate. Compared to Example 1, the GDL had a smaller macropore diameter. Large droplets of water accumulated under high humidity and high current conditions could not be quickly drained, leading to blocked gas transport and decreased battery performance.

[0234] Comparative Example 6: High volume median pore diameter carbon paper was selected as the substrate. Due to the excessively large carbon paper pore diameter, MPL leakage into the substrate was likely to occur during MPL coating. Compared to Example 1, the GDL volume median pore diameter and area median pore diameter decreased significantly, leading to decreased overall performance. However, there were still large pores, so large droplets of water could still be drained.

[0235] Comparative Example 7: Thick carbon paper was selected as the substrate. Compared to Example 1, the GDL was thicker, and the volume median pore diameter of the carbon paper was also difficult to increase. The prepared GDL had a low pore diameter, leading to insufficient drainage. Excessive water accumulated under high current conditions, leading to blocked gas transport and decreased battery performance.

[0236] Figure 1 SEM image of the surface of the microporous layer of the gas diffusion layer of Example 1 of the present application. The image shows the surface morphology of the gas diffusion layer microporous layer (MPL) prepared using 50 nm methyl polyethylene glycol pore-forming agent. The scanning electron microscope (SEM) image shows that the MPL surface forms a uniform distribution of submicron pore networks, with a pore size that closely matches the original particle size of the pore-forming agent (50 nm).

[0237] Figure 2 SEM image of the surface of the microporous layer of the gas diffusion layer of Example 2 of the present application. The image shows the surface morphology of the MPL using a 3 nm polyoxyethylene-octylphenyl ether pore-forming agent. The SEM image shows that the pores are highly dense but the pore size is significantly smaller (nanoscale dominant).

[0238] Figure 3 SEM image of the surface of the microporous layer of the gas diffusion layer of Example 3 of the present application. Figure 4 SEM image of the surface of the microporous layer of the gas diffusion layer of Example 4 of the present application. Both images are based on a 20 nm polyethylene oxide pore-forming agent, but Figure 4 the pore-forming agent addition amount is doubled (60 parts vs. 30 parts). Figure 3 uniform submicron pores are present; whereas Figure 4 due to the increased amount of pore-forming agent, the pore density is significantly increased and the average pore size is slightly increased.

[0239] Figure 5 This is a surface SEM image of the microporous layer of the gas diffusion layer of Comparative Example 1 of the present invention. The figure shows the surface morphology of MPL without any pore-forming agent. The SEM image shows that the surface is exceptionally dense and smooth, with almost no effective pores. This closed structure severely hinders the migration of water molecules, leading to severe flooding of the catalyst layer under high humidity.

[0240] Figure 6 This is a surface SEM image of the microporous layer of the gas diffusion layer of Comparative Example 2 of the present invention. This sample uses 1.8μm polymethyl methacrylate microspheres (far exceeding the 1-500nm range specified in this application). The SEM image shows irregular pores >1μm. These large pores destroy the structural integrity of the MPL, causing two defects: first, direct short circuiting of the gas through the large pores, preventing uniform diffusion to the catalyst layer; second, excessive drainage causing membrane electrode drying. Its performance data is shown at 30% RH@2A / cm 2 The voltage is only 0.542V and 3A / cm 2 Complete failure.

[0241] Figure 7 This is a surface SEM image of the microporous layer of the gas diffusion layer of comparative example 3 of the present invention. This image uses 0.8nm erythritol as a pore-forming agent (the particle size is far below the preferred range). The SEM image shows that its surface is different from the sample without pore-forming agent ( Figure 5 ), with almost no visible pores. This is because the pore-forming agent molecules are too small to form a stable template during the sintering process, and the pore structure is ultimately not effectively established.

[0242] Figure 8 The relationship between the pore size and pore volume per unit mass of the samples was measured by mercury intrusion porosimetry, and the samples included the carbon papers used in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, and the prepared GDL samples.

[0243] The figure shows that all samples contribute very limited pore volume in pores below 500 nm. The pore volume is primarily provided by micron-sized pores, primarily from the carbon paper (square marks), which contribute to pores between 20 and 50 μm. After preparation into GDL, both pore volume and pore size decrease to varying degrees, but the pore volume distribution trend remains unchanged.

[0244] Example 1 is similar to Comparative Examples 1 and 3, with no obvious pores in the middle. Comparative Example 2 (pentagonal symbol) adds a 1.8 μm large-size pore former to the microporous layer, and a clear pore distribution appears near 2 μm in the figure, which provides some pore volume.

[0245] Figure 9 The relationship between the pore size and pore specific surface area per unit mass of the sample was measured by mercury intrusion porosimetry. The samples included the carbon papers used in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, and the prepared GDL samples.

[0246] The carbon paper (square symbol) has a low value of the specific surface area, indicating that the pores of the carbon paper provide a very limited specific surface area.

[0247] The GDL samples of Example 1, Comparative Example 1 and Comparative Example 3 provide a very limited specific surface area in the pore size of 1 μm or more. The specific surface area is mainly provided by the nano-sized pores on the microporous layer. The distribution of the specific surface area is different for the different sizes of the pore-forming agent used. Comparative Example 1 (triangle symbol) and Comparative Example 3 (pentagram symbol) which do not use or use a small size of pore-forming agent decrease rapidly at the pore size of more than 60 nm, indicating that the pores of 60-200 nm are relatively lacking.

[0248] Comparative Example 2 (pentagon symbol) adds a large size of pore-forming agent of 1.8 μm to the microporous layer, and the figure shows a clear pore distribution near 2 μm, and provides part of the specific surface area, while the small pore part has a low specific surface area.

[0249] The above merely describes exemplary embodiments of the present application, and is not intended to limit the patent scope of the present application. Any equivalent structural transformation made according to the technical concept of the present application, or direct / indirect application in other related technical fields, is included in the patent protection scope of the present application.

Claims

1. A gas diffusion layer, characterized in that: The gas diffusion layer includes a base layer and a microporous layer coated on the base layer; The area median pore diameter of the gas diffusion layer is 45 nm to 150 nm, and the area median pore diameter refers to the pore diameter value corresponding to when the cumulative pore surface area accounts for 50% in the cumulative pore surface area distribution curve; The volume median pore diameter of the gas diffusion layer is 20 μm-50 μm, and the volume median pore diameter refers to the pore diameter value corresponding to when the cumulative pore volume accounts for 50% in the pore volume cumulative distribution curve.

2. The gas diffusion layer according to claim 1, wherein The area median pore diameter of the gas diffusion layer is 50 nm to 90 nm, and the volume median pore diameter of the gas diffusion layer is 25 μm to 40 μm.

3. The gas diffusion layer according to claim 1, wherein The area median pore diameter of the gas diffusion layer is 45 nm to 90 nm, and the volume median pore diameter of the gas diffusion layer is 20 μm to 40 μm.

4. The gas diffusion layer according to claim 1, wherein The area median pore diameter of the gas diffusion layer is 50 nm to 150 nm, and the volume median pore diameter of the gas diffusion layer is 25 μm to 50 μm.

5. The gas diffusion layer according to any one of claims 1 to 4, characterized in that The thickness of the gas diffusion layer is 110 μm-280 μm, and the porosity is 75%-90%.

6. A method for preparing a gas diffusion layer, characterized in that: The steps include: Providing a porous conductive substrate and a microporous layer slurry, coating the microporous layer slurry on one side of the carbon paper, drying, and sintering at 350°C-380°C to obtain a gas diffusion layer including a base layer and a microporous layer, wherein the carbon paper forms the base layer and the microporous layer slurry forms the microporous layer; The area median pore diameter of the gas diffusion layer is 45 nm to 150 nm, and the area median pore diameter refers to the pore diameter value corresponding to when the cumulative pore surface area accounts for 50% in the cumulative pore surface area distribution curve; The volume median pore diameter of the gas diffusion layer is 20 μm-50 μm, and the volume median pore diameter refers to the pore diameter value corresponding to when the cumulative pore volume accounts for 50% in the pore volume cumulative distribution curve.

7. The method for preparing a gas diffusion layer according to claim 6, wherein: The microporous layer slurry includes a pore-forming agent, and the particle size or molecular agglomeration size of the pore-forming agent is 1 nm to 500 nm, preferably 5 nm to 200 nm; and / or, the pore-forming agent is selected from at least one of polyether polyol, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyetheretherketone, cellulose, and polycyclic ether; and / or, the carbon residue of the pore-forming agent after ablation treatment at 350° C. is ≤1%; And / or, the porous conductive substrate has a thickness of 100 μm to 260 μm, a porosity of 75% to 90%, and a volume median pore diameter of 25 μm to 50 μm; And / or, the porous conductive substrate is selected from any one of carbon fiber paper and metal-based porous substrate.

8. The method for preparing a gas diffusion layer according to claim 7, wherein: The method for preparing the microporous layer slurry comprises: adding a dispersant and conductive carbon powder to water and mixing to obtain a carbon slurry; Adding a binder to the carbon slurry, then adding a thickener and the pore-forming agent, and dispersing them to obtain the microporous layer slurry; Wherein, the weight parts of each component of the microporous layer slurry are: 5-20 parts of the conductive carbon powder; 0.2-10 parts of the dispersant; 1-20 parts of the binder; 0.1-10 parts of the thickener; 1-100 parts of the pore-forming agent; 100 parts of water.

9. The method for preparing a gas diffusion layer according to claim 8, wherein: The binder includes a fluoropolymer; And / or, the thickener comprises a polyether compound containing only three elements: C, H, and O; And / or, the dispersant includes at least one of an aromatic nonionic dispersant and a zwitterionic dispersant; And / or, the conductive carbon powder includes at least one of furnace black, acetylene black, Ketjen black, graphitized carbon black, carbon nanotubes, and vapor-phase carbon fibers; And / or, the binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, perfluorosulfonic acid resin, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer; And / or, the thickener includes at least one of polyether polyol, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyetheretherketone, cellulose, and polycyclic ether.

10. A fuel cell, characterized in that: The gas diffusion layer comprises the gas diffusion layer according to any one of claims 1 to 5 or the gas diffusion layer prepared by the preparation method according to any one of claims 6 to 9.

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