Gas diffusion layer for fuel cell as well as preparation method and application of gas diffusion layer

Abstract

The invention relates to the technical field of fuel cells, in particular to a gas diffusion layer for a fuel cell and a preparation method and application of the gas diffusion layer. The gas diffusion layer for the fuel cell comprises a substrate layer, a supporting layer and a microporous layer which are sequentially stacked, the substrate layer and the supporting layer are both composed of fiber filaments, the diameter of the fiber filaments of the supporting layer is smaller than that of the fiber filaments of the substrate layer, and the diameter of the fiber filaments of the supporting layer is nanoscale. According to the gas diffusion layer, the gas diffusion layer is designed to be of a three-layer structure, the supporting layer is introduced between the substrate layer and the micropore layer, meanwhile, the wire diameter of the supporting layer is limited to be smaller than that of the substrate layer, the supporting layer with the pore diameter smaller than that of the substrate layer and the porosity higher than that of the substrate layer is prepared, and meanwhile the thickness of the micropore layer is reduced; the gas diffusion layer has more excellent conductivity, reduces the resistance in the thickness direction, and is more beneficial to water and gas transmission especially under the condition of high current density.

Description

A gas diffusion layer for fuel cells, its preparation method and application Technical Field

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

[0002] Proton exchange membrane fuel cells (PEMFCs) have attracted increasing attention in recent years due to their advantages such as high thermal efficiency, no harmful gas emissions, and simultaneous power generation and energy storage, showing broad application prospects. The membrane electrode assembly (MEA) is the core component of a PEMFC, typically composed of a proton exchange membrane, catalyst, gas diffusion layer, and frame. The gas diffusion layer, acting as a transport channel for reactants, electrons, and water, directly affects the performance of the membrane electrode. Currently, the preparation of the gas diffusion layer mainly involves hydrophobizing the gas diffusion base (GDB), coating it with a microporous layer (MPL), and then heat-treating to create the gas diffusion layer. Because the substrate layer has a macroporous structure, the slurry will penetrate into the substrate layer during the microporous layer coating process, forming a transition zone that blocks the pores and affects the transport efficiency. Furthermore, its thickness is uncontrollable. In order to ensure that the carbon fiber substrate layer does not damage the proton exchange membrane under the action of assembly force, the microporous layer is usually thicker, which will further increase the transport path of electrons, fuel and water, and increase the resistance and mass transfer resistance.

[0003] As commercialization continues to advance, proton exchange membrane fuel cells are developing towards higher current density, higher power, smaller size, and lower cost. Therefore, it is necessary to specifically address the issues of low transport efficiency and high mass transfer resistance in the design of the membrane electrode assembly, especially the gas diffusion layer. Summary of the Invention

[0004] This invention provides a gas diffusion layer for fuel cells, its preparation method, and its application, in order to solve the problems of low transmission efficiency and high mass transfer resistance in existing gas diffusion layers for fuel cells.

[0005] According to a first aspect of the present invention, the present invention provides a gas diffusion layer for a fuel cell, comprising a base layer, a support layer and a microporous layer stacked sequentially, wherein the base layer and the support layer are both composed of filaments, and the diameter of the filaments of the support layer is smaller than the diameter of the filaments of the base layer, and the diameter of the filaments of the support layer is in the nanometer range.

[0006] This invention discloses a gas diffusion layer for fuel cells with a three-layer structure: a base layer, a support layer, and a microporous layer. A support layer with a finer fiber diameter is formed between the base layer and the microporous layer. This support layer prevents the microporous layer slurry from permeating into the base layer, eliminating the transition zone (blockage zone). Furthermore, the support layer also has high porosity, which, in conjunction with the finer fiber, increases the overall porosity of the gas diffusion layer, reducing mass transfer resistance. This is particularly beneficial for the rapid transport of reactant gases and generated water under high current densities.

[0007] Furthermore, the diameter of the fibers in the support layer is 100–800 nanometers. Within this range, the fibers possess sufficient mechanical strength to support the microporous layer, while also being fine enough to ensure that the support layer as a whole has high porosity and low tortuosity, facilitating smoother gas / water transport. This range of fiber diameter creates a significant gradient with the substrate layer (which typically has a fiber diameter of 5–10 micrometers), further inhibiting slurry penetration.

[0008] In this invention, the diameter of the fiber filaments in the support layer is 100~800 nanometers, for example, it can be 100 nanometers, 200 nanometers, 300 nanometers, 400 nanometers, 500 nanometers, 600 nanometers, 700 nanometers or 800 nanometers, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific values ​​included in the range.

[0009] Preferably, the diameter of the fiber filaments in the support layer is 300-600 nanometers, more preferably 300-500 nanometers, and even more preferably 360-450 nanometers.

[0010] Furthermore, the diameter of the fibers in the base layer is 10 to 100 times the diameter of the fibers in the support layer. This specific range of difference quantifies the degree to which the "gradient structure" optimizes the suppression of permeation and reduction of contact resistance. The larger the difference, the more effectively the support layer can "seal" the large pores in the base layer; the smaller the difference, the better the mechanical bonding strength can be maintained.

[0011] Furthermore, the pore size of the support layer is 0.5–15 micrometers. Based on 100–800 nanometer-sized fibers, the 0.5–15 micrometer pore size of the support layer ensures sufficient air / water permeability while being much smaller than the typical pore size of the substrate layer, forming a "gradual pore size gradient" and reducing the risk of capillary water accumulation. The upper limit of 15 micrometers prevents an overly dense support layer from increasing gas diffusion resistance; the lower limit of 0.5 micrometers blocks the permeation of microporous carbon particles.

[0012] Furthermore, the average pore size of the substrate layer is 5 to 15 times that of the support layer. Through finer fibers, a dense and highly porous "sieve" can be formed between the substrate layer and the microporous layer. This prevents the microporous layer slurry from penetrating into the substrate layer and eliminates transitional blockage zones, while retaining sufficient gas / water transport channels. This significantly reduces the vertical resistance and mass transfer resistance of the gas diffusion layer, improving the output performance and stability of the fuel cell at high current densities.

[0013] Furthermore, the thickness of the substrate layer is 130-250 micrometers; the thickness of the support layer is 0.5-5 micrometers; and the thickness of the microporous layer is 5-60 micrometers.

[0014] By limiting the thickness of each layer within a reasonable range, better synergy can be achieved between the layers, thus improving the performance of the gas diffusion layer. Specifically, the thickness of the support layer is much smaller than that of traditionally thickened microporous layers, significantly reducing interlayer resistance and improving electron conduction efficiency. If the support layer is too thin, it will not form completely, leading to seepage of the microporous layer slurry. If the support layer is too thick, it will increase the overall thickness of the gas diffusion layer, resulting in increased gas-liquid transport resistance and consequently affecting performance.

[0015] Furthermore, the components of the fiber filaments of the support layer include one or more of the following: collagen, gelatin, chitosan, cellulose, silk fibroin, polylactic acid, polylactic acid-glycolic acid copolymer, polycaprolactone, polyvinyl alcohol, polyacrylonitrile, polyurethane, polystyrene, conductive polymer polypyrrole, polyaniline, thermosensitive polymer polyN-isopropylacrylamide, aramid, and polyimide.

[0016] Furthermore, the fiber filaments of the base layer are composed of one or more of carbon fiber and carbon cloth.

[0017] According to a second aspect of the present invention, the present invention also provides a method for preparing the above-mentioned gas diffusion layer for fuel cells, comprising the following steps: preparing a support layer on a substrate layer by electrospinning; performing pre-oxidation and heat treatment on the support layer; performing hydrophobication treatment on the substrate layer and the support layer after pre-oxidation and heat treatment; and then preparing a microporous layer on the support layer.

[0018] The preparation method of this invention involves directly constructing a nanofiber support layer on a substrate by electrospinning, followed by pre-oxidation and high-temperature heat treatment to graphitize it and enhance its conductivity. Subsequently, the entire structure is made hydrophobic and a microporous layer is screen-printed on the surface of the support layer, forming a three-layer gradient structure with clear layers and strong interface bonding. The process is simple and the thickness is controllable, effectively preventing the penetration of microporous layer slurry, significantly reducing vertical resistance and mass transfer resistance, thereby improving the power density and operational stability of fuel cells under high current density.

[0019] Furthermore, the electrospinning voltage is 10~300KV, the spinning solution flow rate is 0.05~0.5mL / min, and the spinning time is 2~6 minutes. Optimizing the electrospinning process allows for the rapid deposition of a nanofiber support layer with a thickness of 0.5~5 micrometers and a suitable filament diameter on the substrate surface. This ensures complete coverage and prevents the penetration of microporous slurry, while avoiding the additional mass transfer resistance caused by excessive thickness. This enables efficient, controllable, and low-cost continuous preparation, thereby simultaneously improving the conductivity of the gas diffusion layer and the water vapor transport performance under high current density.

[0020] Furthermore, the pre-oxidation treatment involves heating to 200-300°C in an oxygen environment and holding at that temperature for 80-120 minutes. The pre-oxidation treatment helps to form a thermally stable structure that can withstand the high temperatures of subsequent carbonization without melting, stabilizes the fiber morphology, and improves the carbonization yield.

[0021] Furthermore, the heat treatment temperature is 2000~3000 degrees Celsius, and the time is 2~4 hours. By heat-treating the support layer nanofibers at a high temperature of 2000~3000 degrees Celsius for 2~4 hours, the polymer fibers can be fully graphitized, significantly improving conductivity and structural stability, while maintaining high porosity and mechanical strength. This greatly reduces the vertical resistance of the gas diffusion layer and enhances the electronic conduction and durability performance of the fuel cell under high current density conditions.

[0022] Furthermore, the impregnation and hydrophobication treatment uses a polytetrafluoroethylene emulsion with a PTFE content of 15-25%, followed by calcination at 300-400 degrees Celsius for 0.5-1.5 hours. Impregnation with a 15-25% PTFE emulsion followed by calcination at 300-400 degrees Celsius for 0.5-1.5 hours can uniformly coat and moderately sinter PTFE on the fiber surfaces of the substrate and support layers. This imparts stable hydrophobicity to the gas diffusion layer, preventing water flooding, while maintaining high porosity and air and water permeability. At the same time, it avoids excessive melting of PTFE that blocks the pores, thereby significantly improving the water management capability and long-term operational stability of the fuel cell under high current density.

[0023] Furthermore, the microporous layer is prepared on the support layer by screen printing a microporous layer slurry onto the support layer, and then calcining it at 300~400 degrees Celsius for 0.5~1.5 hours; the microporous layer slurry is composed of carbon powder and a hydrophobic agent, wherein the carbon powder is acetylene black and the hydrophobic agent is polytetrafluoroethylene, and the mass ratio of acetylene black to polytetrafluoroethylene is (3~5):1.

[0024] A microporous layer slurry prepared by mixing acetylene black and PTFE in a ratio of (3~5):1 is screen-printed onto the surface of the support layer and then calcined at 300~400 ℃ for 0.5~1.5 hours. This process can quickly form a microporous layer with uniform thickness, controllable pore size, and a balanced hydrophobic-conductive network on the support layer. This process not only prevents the slurry from penetrating into the substrate layer, but also significantly reduces the interfacial resistance and the risk of flooding, thereby improving the gas mass transfer efficiency and power output stability of the fuel cell under high current density.

[0025] According to a third aspect of the present invention, the present invention also provides the application of the above-described gas diffusion layer for fuel cells or the gas diffusion layer for fuel cells prepared by the above-described method for preparing gas diffusion layers for fuel cells in proton exchange membrane fuel cells.

[0026] The beneficial effects of this invention are as follows: The gas diffusion layer for fuel cells provided by this invention is designed as a three-layer structure. A support layer is introduced between the substrate layer and the microporous layer. The support layer, with fiber diameters in the nanometer range, is prepared by electrospinning. The diameter of the support layer fiber is smaller than that of the substrate layer fiber, and the pore size of the support layer is smaller than that of the substrate layer, resulting in higher porosity. At the same time, the thickness of the microporous layer is reduced, giving the gas diffusion layer better conductivity and reducing resistance in the thickness direction. Especially under high current density conditions, it is more conducive to water and gas transport. The support layer of this invention effectively prevents the microporous layer slurry from penetrating into the substrate layer. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 is a schematic diagram of the structure of the fuel cell gas diffusion layer in Embodiment 1 of the present invention.

[0029] Figure 2 is a cross-sectional scanning electron microscope image of the gas diffusion layer in Embodiment 1 of the present invention.

[0030] Figure 3 is a scanning electron microscope image of the support layer of the gas diffusion layer in Embodiment 1 of the present invention.

[0031] Figure 4 is a scanning electron microscope image of the support layer of the gas diffusion layer in Embodiment 2 of the present invention.

[0032] Figure 5 is a comparison diagram of the vertical resistivity test of the gas diffusion layer in Embodiment 1, Embodiment 2, Comparative Example 1 and Comparative Example 2 of the present invention.

[0033] Figure 6 is a comparison of the polarization curve performance of the gas diffusion layer in Embodiment 1, Embodiment 2, Comparative Example 1 and Comparative Example 2 of the present invention.

[0034] Figure 7 is a scanning electron microscope image of the support layer fiber filaments of the gas diffusion layer in Embodiment 1 of the present invention.

[0035] Reference numerals: 1: base layer; 2: support layer; 3: microporous layer. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0037] Example 1 This example provides a gas diffusion layer for a fuel cell with a support layer, as shown in Figure 1. The gas diffusion layer includes a base layer 1, a support layer 2, and a microporous layer 3 stacked sequentially. The thickness of the base layer 1 is 200 micrometers, and the diameter of the fibers in the base layer 1 is 5-10 micrometers. The pore size of the support layer is 0.5-15 micrometers, with an average pore size of 7.75 micrometers. The pore size of the base layer is 30-150 micrometers, with an average pore size of 90 micrometers. The thickness of the support layer 2 is 1.5 micrometers, and the thickness of the microporous layer 3 is 10 micrometers.

[0038] This embodiment also provides a method for preparing the gas diffusion layer for the fuel cell, including the following steps: first, measuring the diameter and pore size of the base layer fiber, and then preparing a support layer on the base layer. The support layer is prepared by electrospinning, the fiber is polyacrylonitrile, the fiber diameter is 360~450 nanometers, the electrospinning voltage is 20KV, the flow rate of the spinning solution is 0.1mL / min, and the spinning time is 2 minutes.

[0039] The support layer was pre-oxidized by heating to 250°C in an oxygen environment and holding for 100 minutes, then heating to 2500°C and holding for 3 hours.

[0040] The gas diffusion layer of the above double-layer structure was impregnated and hydrophobically treated. The impregnation solution was polytetrafluoroethylene emulsion with a PTFE content of 20%, and then calcined at 350 degrees Celsius for 1 hour.

[0041] A microporous layer was prepared on the support layer. The microporous layer slurry was composed of carbon powder and a hydrophobic agent. The carbon powder was selected as acetylene black and the hydrophobic agent was selected as polytetrafluoroethylene. The mass ratio of acetylene black to PTFE was 4:1. The slurry was screen printed onto the support layer and then calcined at 350 degrees Celsius for 1 hour.

[0042] Example 2 This example provides a gas diffusion layer for a fuel cell with a support layer, which differs from Example 1 in that the thickness of the support layer 2 is 5 micrometers.

[0043] This embodiment also provides a method for preparing the gas diffusion layer for the fuel cell, which differs from Embodiment 1 in that the electrospinning time is 6 minutes.

[0044] Comparative Example 1 This comparative example provides a gas diffusion layer for a fuel cell without a support layer, which differs from Example 1 in that it does not include a support layer 2.

[0045] This comparative example also provides a method for preparing the gas diffusion layer, including the following steps: impregnating the substrate layer to make it hydrophobic, using polytetrafluoroethylene emulsion as the impregnation solution with a concentration of 20%, and calcining it at 350 degrees Celsius for 1 hour after impregnation.

[0046] A microporous layer was prepared on the substrate. The microporous layer slurry consisted of carbon powder and a hydrophobic agent. The carbon powder was acetylene black and the hydrophobic agent was polytetrafluoroethylene. The mass ratio of acetylene black to PTFE was 4:1. The slurry was screen-printed onto the substrate and then calcined at 350 degrees Celsius for 1 hour.

[0047] Comparative Example 2 provides a gas diffusion layer for a fuel cell with a support layer, which differs from Example 1 in that the thickness of the support layer 2 is 7 micrometers.

[0048] This comparative example also provides a method for preparing the gas diffusion layer for the fuel cell, which differs from Example 1 in that the electrospinning time is 8 minutes.

[0049] The carbon paper used in the comparative examples and the embodiments was Toray TGP-H-060.

[0050] The performance of the gas diffusion layers provided in the examples and comparative examples was tested respectively. The test items and test results are compared as follows: (1) Cross-sectional scanning electron microscope image: The cross-section of Example 1 was observed using a scanning electron microscope. The result is shown in Figure 2. The microporous layer of the gas diffusion layer prepared by the present invention did not penetrate into the interior of the substrate layer.

[0051] (2) Scanning electron microscopy images of the support layer. The results of the observation of Example 1 and Example 2 using scanning electron microscopy are shown in Figures 3 and 4. The surface of the base layer of the gas diffusion layer prepared by the present invention has a layer of nanofibers as a support layer.

[0052] (3) Vertical resistivity test: Vertical resistivity test was performed on the examples and comparative examples. By comparison, it was found that, as shown in Figure 5, the gas diffusion layer prepared by the method of the present invention has a lower resistivity.

[0053] (4) The polarization curves of the two membrane electrode assemblies were tested using the industry-standard fuel cell fixture. The test results are shown in Figure 6. The performance of the single cell with the gas diffusion layer prepared by the method described in this invention is higher than that of the membrane electrode prepared with the gas diffusion layer that exceeds the thickness range of the support layer and the membrane electrode using the conventional gas diffusion layer.

[0054] (5) The diameter of the support layer fiber filaments in the gas diffusion layer of Example 1 of the present invention was measured by scanning electron microscopy. The results are shown in Figure 7. It can be seen that the diameter of some support layer fiber filaments is between 360-450 nanometers.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A gas diffusion layer for a fuel cell, characterized in that, It includes a base layer, a support layer and a microporous layer stacked in sequence. The base layer and the support layer are both made of fiber filaments, and the diameter of the fiber filaments in the support layer is smaller than that in the base layer. The diameter of the fiber filaments in the support layer is in the nanometer range.

2. The gas diffusion layer for fuel cells according to claim 1, characterized in that, The diameter of the fiber filaments in the support layer is 100-800 nanometers, preferably 300-600 nanometers.

3. The gas diffusion layer for fuel cells according to claim 1 or 2, characterized in that, The diameter of the fiber filaments in the base layer is 10 to 100 times the diameter of the fiber filaments in the support layer.

4. The gas diffusion layer for a fuel cell according to any one of claims 1-3, characterized in that, The thickness of the support layer is 0.5 to 5 micrometers.

5. The gas diffusion layer for a fuel cell according to any one of claims 1-4, characterized in that, The pore size of the support layer is 0.5 to 15 micrometers; the average pore size of the substrate layer is 5 to 15 times that of the average pore size of the support layer.

6. The gas diffusion layer for a fuel cell according to any one of claims 1-5, characterized in that, The thickness of the substrate layer is 130-250 micrometers, and the thickness of the microporous layer is 5-60 micrometers.

7. The gas diffusion layer for a fuel cell according to any one of claims 1-6, characterized in that, The components of the supporting layer fibers include one or more of collagen, gelatin, chitosan, cellulose, silk fibroin, polylactic acid, polylactic acid-glycolic acid copolymer, polycaprolactone, polyvinyl alcohol, polyacrylonitrile, polyurethane, polystyrene, conductive polymer polypyrrole, polyaniline, thermosensitive polymer polyN-isopropylacrylamide, aramid, and polyimide; and / or, the components of the base layer fibers are one or more of carbon fiber and carbon cloth.

8. The method for preparing a gas diffusion layer for a fuel cell according to any one of claims 1-7, characterized in that, The process includes the following steps: preparing a support layer on a substrate layer by electrospinning; pre-oxidizing and heat-treating the support layer; impregnating the substrate layer and the pre-oxidized and heat-treated support layer with hydrophobicity; and then preparing a microporous layer on the support layer.

9. The method for preparing a gas diffusion layer for a fuel cell according to claim 8, characterized in that, The electrospinning voltage is 10~300KV, the spinning solution flow rate is 0.05~0.5mL / min, and the spinning time is 2~6 minutes; and / or, the pre-oxidation treatment involves heating to 200~300℃ in an oxygen environment and holding at that temperature for 80~120 minutes; and / or, the heat treatment temperature is 2000~3000℃, and the time is 2~4 hours; and / or, the impregnation hydrophobication treatment uses PTFE with a content of 15~25%. The process involves preparing a polytetrafluoroethylene (PTFE) emulsion and then calcining it at 300-400 degrees Celsius for 0.5-1.5 hours; and / or, preparing a microporous layer on the support layer involves screen printing a microporous layer slurry onto the support layer and then calcining it at 300-400 degrees Celsius for 0.5-1.5 hours; the microporous layer slurry is composed of carbon powder and a hydrophobic agent, wherein the carbon powder is acetylene black and the hydrophobic agent is polytetrafluoroethylene, and the mass ratio of acetylene black to polytetrafluoroethylene is (3-5):

1.

10. The application of the gas diffusion layer for fuel cells according to any one of claims 1-7, or the gas diffusion layer for fuel cells prepared by the preparation method of the gas diffusion layer for fuel cells according to claim 8 or 9, in a proton exchange membrane fuel cell.

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