Integrated ultrathin flexible gas diffusion layer and preparation method thereof

Abstract

This invention discloses an integrated ultrathin flexible gas diffusion layer belonging to the field of fuel cells. It is a self-supporting, independent carbon fiber film composed of an electrospun carbon nanofiber network that has undergone hot-press carbonization. Conductive reinforcing materials and a matrix hydrophobic agent are uniformly dispersed within the carbon nanofiber network. The gas diffusion layer has a gradient pore structure in the thickness direction, and the first and second surfaces exhibit asymmetric wettability. This invention achieves one-way valve-type directional drainage of liquid water. In particular, the superhydrophobic surface facing the catalyst layer effectively prevents liquid water accumulation at active sites, avoiding flooding under high current densities. The moderate hydrophobicity on the back side balances drainage and moisture retention, significantly improving the oxygen transport efficiency and operational stability of the battery under different operating conditions.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, specifically an integrated ultrathin flexible gas diffusion layer and its preparation method. Specifically, it is an ultrathin flexible self-supporting gas diffusion layer with gradient pore structure and asymmetric wettability, based on a combination of electrospinning and integrated hot-pressing carbonization process, and its preparation method. Background Technology

[0002] The gas diffusion layer is one of the core components of a proton exchange membrane fuel cell, undertaking multiple functions such as conducting electrons, distributing reactant gases, removing reaction product water, providing mechanical support for the membrane electrode assembly, and transferring heat. Its performance directly affects the battery's output performance, hydrothermal management capabilities, and durability.

[0003] Traditional gas diffusion layers typically consist of a macroporous carbon paper / carbon cloth substrate and a microporous layer coated on top. This structure has the following inherent drawbacks: 1) The preparation process is cumbersome, involving multiple independent steps such as fiber preparation, papermaking, impregnation, carbonization, hydrophobic treatment, and microporous layer coating, resulting in high costs; 2) A distinct interface exists between the substrate layer and the microporous layer, increasing contact resistance and making the interface prone to peeling; 3) The carbon paper substrate itself is brittle and lacks flexibility, making it susceptible to damage during battery assembly and operation; 4) Traditional structures are relatively thick (typically >200 μm), increasing the mass transfer distance between gas and protons, which is detrimental to performance improvement.

[0004] To overcome the above problems, existing technologies have proposed various improvement schemes, but none have fundamentally solved the issues. For example, while using electrospinning technology to prepare fiber membranes (Yao Ze, Chen Chuang, Duan Feng, et al. Electrospinned carbon nanofiber membranes for gas diffusion layers in proton exchange membrane fuel cells [J]. Journal of Process Engineering, 2025, 25(6): 621-634.) can optimize the pore structure, it does not solve the problems of complex processes and interfacial resistance; the preparation of integrated gas diffusion electrodes (CN115350571B) integrates catalytic functions, but the process is complex and does not focus on improving the flexibility of the gas diffusion layer itself; The substrate gas diffusion layer solution (CN118693295A) aims to simplify the structure, but synergistically improving its mechanical strength, conductivity, and water management capabilities presents a significant challenge. Furthermore, solutions incorporating self-healing materials (CN120413688A) or free radical quenchers (CN117117209B) focus on enhancing durability but do not fundamentally revolutionize the overall structure and fabrication process of the gas diffusion layer, making it difficult to simultaneously achieve multiple objectives such as ultrathinness, flexibility, high strength, high conductivity, and excellent water vapor management. A patent (CN118867274A) uses a method of coating a microporous layer onto a traditional carbon paper substrate and then adding a hydrophilic porous fiber layer using electrospinning to improve water retention under air-cooled conditions. However, this solution still involves cumbersome process steps and is a multi-layered composite structure, posing risks of interfacial resistance and potential delamination, and also fails to achieve ultrathinness and overall flexibility in the product. Another study (CN121460599A) focuses on constructing hydrophilic and hydrophobic gradients inside the catalyst layer to optimize water management, but it targets the catalyst layer rather than the gas diffusion layer, and does not address issues such as the construction of the conductive network, mechanical support, and interface characteristics with the flow field plate required for the gas diffusion layer.

[0005] Currently, there is still a lack of a method to directly fabricate a gas diffusion layer with ultra-thin thickness, excellent flexibility, high conductivity, self-supporting properties, and the ability to form a gradient pore structure that facilitates directional water vapor management and asymmetric wettability through a simple, integrated process. In particular, how to achieve structural densification, carbonization, conductivity, and surface functionalization of a porous precursor prepared by electrospinning in a single process to obtain a high-performance integrated gas diffusion layer remains a problem that existing technologies have not yet solved. Summary of the Invention

[0006] The gas diffusion layer of a proton exchange membrane fuel cell (PEMFC) serves as a crucial component connecting the flow field plate and the catalyst layer, simultaneously undertaking multiple functions such as reactant gas transport, product water drainage, electron conduction, and heat transfer. However, conventional gas diffusion layers in existing technologies (such as carbon paper and carbon cloth) are typically thick and bonded together with short-cut carbon fibers, resulting in insufficient flexibility. They are prone to delamination and breakage during fuel cell stack assembly or flexible operating conditions, making it difficult to meet the demands of high power density and flexible batteries. Furthermore, the uniform pore structure of conventional gas diffusion layers cannot simultaneously achieve rapid drainage under high current density and moisture retention under low current density. The demand for gas diffusion layers is high, which can lead to the accumulation of liquid water at the interface between the microporous layer and the catalyst layer, causing flooding, hindering oxygen transport, and increasing concentration polarization. In addition, the high surface roughness of traditional materials results in high interfacial contact resistance, and the preparation of high-performance products often requires a complicated multi-layer coating process, which is not only costly but also has the defects of weak interlayer bonding and easy peeling after long-term operation. Therefore, it is urgent to develop an integrated gas diffusion layer with ultra-thin self-support, excellent flexibility, gradient pore structure and asymmetric wettability, and a simplified preparation method to solve the above-mentioned technical bottlenecks such as water-gas management contradictions, poor interfacial contact and complex processes.

[0007] To achieve the above-mentioned objectives, the present invention provides an integrated ultrathin flexible gas diffusion layer, the technical solution of which includes: a self-supporting independent carbon fiber film, which is composed of an electrospun carbon nanofiber network that has undergone hot-press carbonization treatment; a conductive reinforcing material and a matrix hydrophobic agent are uniformly dispersed in the carbon nanofiber network; the gas diffusion layer has a gradient pore structure in the thickness direction, and the first surface and the second surface have asymmetric wettability.

[0008] The total thickness of the gas diffusion layer is 20-150 μm.

[0009] The asymmetric wettability is specifically manifested as follows: the side with a smaller pore size is defined as the first surface, and the side with a larger pore size is defined as the second surface; the static water contact angle of the first surface is greater than 150°, and the static water contact angle of the second surface is 120°-140°; wherein, the first surface is configured to face the catalyst layer, and the second surface is configured to face the flow field plate.

[0010] The gradient hole structure is characterized by the hole diameter gradually decreasing from the second surface to the first surface.

[0011] The conductive reinforcing material includes one or more of carbon nanotubes, graphene, Ketjen black, and acetylene black, with a mass fraction of 5%-30% in the gas diffusion layer. A surface-modified hydrophobic agent is subsequently introduced onto the first surface. Both the matrix hydrophobic agent and the surface-modified hydrophobic agent are one or more of polytetrafluoroethylene, fluorinated ethylene propylene copolymer, and polyvinylidene fluoride. The total mass fraction of the hydrophobic agent in the gas diffusion layer is 10%-40%. The surface-modified hydrophobic agent is mainly enriched on the first surface, resulting in a gradient distribution of the hydrophobic agent content in the thickness direction.

[0012] A proton exchange membrane fuel cell membrane electrode is provided, comprising an integrated ultrathin flexible gas diffusion layer.

[0013] A method for preparing an integrated ultrathin flexible gas diffusion layer is also provided, the technical solution including:

[0014] S1. Preparation of spinning solution: The high molecular polymer, conductive reinforcing material and matrix hydrophobic agent are dissolved or dispersed in an organic solvent to prepare an electrospinning precursor solution;

[0015] S2. Electrospinning: The precursor solution obtained in S1 is electrospinned to collect a self-supporting polymer composite fiber membrane.

[0016] S3. Asymmetric hydrophobic treatment: The single surface of the polymer composite fiber membrane obtained in S2 is treated with hydrophobic agent spraying or vapor deposition to introduce surface-modified hydrophobic agent to construct a wettability gradient precursor.

[0017] S4. Hot-pressing and carbonization integrated treatment: The wettability gradient precursor after S3 treatment is placed in a hot-pressing device, and under a protective atmosphere, a pressure of 0.5-5 MPa is applied, and constant pressure hot-pressing treatment is performed according to a preset heating program; the preset heating program includes a pre-oxidation stage and a carbonization stage performed at a controlled heating rate, and the fiber membrane is densified and a gradient pore structure in the thickness direction is formed by utilizing the coupling effect of pressure and temperature field;

[0018] S5. Cooling and post-processing: After carbonization, cool to room temperature under maintaining pressure, and remove to obtain the integrated ultrathin flexible gas diffusion layer.

[0019] In step S4, the temperature of the pre-oxidation stage is 200-300 ℃ and the holding time is 0.5-2 h; the temperature of the carbonization stage is 800-1200 ℃ and the holding time is 0.5-2 h.

[0020] In step S4, the heating rate of the pre-oxidation stage is 1-5 ℃ / min, and the heating rate of the carbonization stage is 2-10 ℃ / min.

[0021] The polymer is one of polyacrylonitrile, polyimide, or polyacrylonitrile-co-polyvinylpyrrolidone.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. In this invention, the gradient pore structure and asymmetric wettability design work synergistically to construct an ideal capillary pressure gradient from the catalyst layer to the flow field plate, enabling unidirectional valve-like directional discharge of liquid water and forming a stable capillary pressure gradient along the thickness direction of the gas diffusion layer. In particular, the superhydrophobic surface facing the catalyst layer effectively prevents liquid water accumulation at active sites, avoiding flooding under high current density conditions. The moderate hydrophobicity on the back side balances drainage and moisture retention, significantly improving the oxygen transport efficiency and operational stability of the battery under different operating conditions. This solves the flooding problem caused by liquid water accumulation at the interface between the catalyst layer and the gas diffusion layer under high current density and high humidity operating conditions, thereby optimizing oxygen transport and alleviating concentration polarization.

[0024] 2. This invention successfully prepared a self-supporting carbon fiber membrane with a thickness of only 20-150 μm by combining electrospinning with hot-pressing carbonization technology. Its continuous long fiber network structure endows the material with excellent flexibility and mechanical strength, which not only significantly reduces the overall thickness and mass transfer resistance of the battery stack, but also effectively overcomes the defect of traditional short-cut fiber materials that are prone to delamination and breakage under repeated compression or bending conditions. It can perfectly meet the application requirements of high power density battery stacks and flexible batteries.

[0025] 3. The electrospinning-single-side modification-hot-press carbonization integrated process of this invention directly integrates the functions of the traditional microporous layer into the substrate preparation process. Through a single hot-press carbonization step, structural densification, conductive network construction, and surface functionalization are achieved, directly yielding a self-supporting, independent carbon fiber film that requires no external substrate. This not only eliminates the cumbersome microporous layer coating process, reducing production costs and the amount of fluoropolymer used, but also eliminates the risk of delamination caused by weak interlayer bonding, significantly reducing interfacial contact resistance and improving the long-term durability of the component. The process is more integrated and simpler, and the product structure is a unified whole, completely eliminating the interlayer interfaces and the resulting contact resistance and delamination risks in traditional composite structures. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of an embodiment of the integrated ultrathin flexible gas diffusion layer of the present invention.

[0027] in,

[0028] A: The first surface (top layer / microporous superhydrophobic layer) is in direct contact with the catalyst layer and has the smallest pore size.

[0029] B: The middle layer is composed of a carbon nanofiber network, whose pore size gradually and continuously decreases from the bottom layer to the top layer, forming a gradient structure;

[0030] C: Second surface (bottom layer / macroporous hydrophobic layer), facing the flow field plate, with relatively large pore size. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings.

[0032] like Figure 1 The broad embodiment of the present invention shown includes a self-supporting independent carbon fiber film composed of an electrospun carbon nanofiber network that has undergone hot-press carbonization treatment, wherein a conductive reinforcing material and a hydrophobic agent are uniformly dispersed in the carbon nanofiber network; the gas diffusion layer has a gradient pore structure in the thickness direction (the two ends of the thickness direction are the first surface and the second surface, respectively), and its first surface and second surface have asymmetrical wettability.

[0033] Preferably, the total thickness of the gas diffusion layer is 20~150 μm. This ultrathin characteristic is determined by the integrated hot-press carbonization process: electrospinning forms a porous fiber network precursor, and then during the hot-press carbonization process, under the synergistic effect of pressure and temperature, the fiber network is controllably densified, thereby obtaining an ultrathin film that maintains its porous characteristics, has uniform thickness, and good mechanical strength. Because this process achieves the desired result in a simple one-step process—preparing a self-supporting polymer fiber membrane through electrospinning → single-sided asymmetric hydrophobic treatment → integrated hot-press carbonization—it overcomes the difficulty of preparing ultrathin self-supporting functional layers using traditional coating methods.

[0034] Preferably, the gradient pore structure is characterized by a pore size that gradually decreases from the second surface to the first surface. This gradient structure is formed due to the coupling effect of the pressure and temperature fields during the hot-press carbonization process, which causes a non-uniform densification effect in the fiber network along the thickness direction, ultimately solidifying into a gradient pore structure.

[0035] Preferably, the asymmetric wettability is specifically manifested as follows: the static water contact angle of the first surface is greater than 150°, and the static water contact angle of the second surface is 120°~140°.

[0036] More preferably, the first surface is a working surface with a small pore size facing the catalyst layer and has superhydrophobic properties; the second surface is a supporting surface with a large pore size facing the flow field plate and has hydrophobic properties.

[0037] Preferably, the conductive reinforcing material is selected from one or more of carbon nanotubes, graphene, Ketjen black, and acetylene black.

[0038] Preferably, the hydrophobic agent is selected from one or more of polytetrafluoroethylene, fluorinated ethylene propylene copolymer, and polyvinylidene fluoride; wherein, the hydrophobic agent located inside the carbon nanofiber network is defined as a matrix hydrophobic agent, the hydrophobic agent located in the first surface region is defined as a surface-modified hydrophobic agent, and the content of the surface-modified hydrophobic agent on the first surface is higher than the content on the second surface and inside.

[0039] Secondly, the present invention provides a method for preparing the above-mentioned integrated ultrathin flexible gas diffusion layer, characterized by comprising the following steps:

[0040] Step S1: Prepare spinning solution

[0041] A polymer, a conductive reinforcing material, and a matrix hydrophobic agent are dissolved or dispersed in an organic solvent in a certain proportion, and then heated, stirred, and / or ultrasonically treated to form a uniform and stable electrospinning precursor solution; wherein the polymer is selected from polyacrylonitrile, polyimide, and polyacrylonitrile-co-polyvinylpyrrolidone; and the organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and tetrahydrofuran.

[0042] Step S2: Electrospinning to form a film

[0043] The precursor solution obtained in step S1 is electrospun, and the ejected fibers are collected on a receiving device to obtain a self-supporting polymer composite fiber membrane. The electrospinning process parameters are: voltage 10~25 kV, receiving distance 10~20 cm, and feed speed 0.5~2.0 mL / h.

[0044] Step S3: Asymmetric hydrophobic treatment

[0045] The single surface of the polymer composite fiber membrane obtained in step S2 is treated, and a surface-modified hydrophobic agent is introduced into the surface to form a precursor with a wettability gradient.

[0046] Preferably, the treatment method is ultrasonic spraying or vapor deposition, and the penetration depth of the surface-modifying hydrophobic agent is controlled to not exceed 20% of the total thickness of the polymer composite fiber membrane.

[0047] Step S4: Integrated hot-press carbonization

[0048] The precursor processed in step S3 is placed in a hot press mold, and under inert gas protection, a pressure of 0.5~5 MPa is applied, and the following heating process is executed:

[0049] 1) Pre-oxidation stage: The temperature is increased from room temperature to 200-300 ℃ at a rate of 1-5 ℃ / min and held at that temperature for 0.5-2 h;

[0050] 2) Carbonization stage: Continue heating at a rate of 2~10 ℃ / min to 800~1200 ℃, and hold at that temperature for 0.5~2 h;

[0051] Under the combined action of the pressure and temperature fields, the polymer in the precursor is transformed into a conductive carbon network, and the fiber network is densified to form an integrated thin film with a gradient pore structure.

[0052] Step S5: Cooling and Sampling

[0053] After the carbonization stage is completed, the pressure is kept constant, the sample is cooled to room temperature, the pressure is released and the sample is taken out to obtain the integrated ultrathin flexible gas diffusion layer.

[0054] Specific Example 1: Fabrication of an Integrated Ultrathin Flexible Gas Diffusion Layer

[0055] 1. Raw materials

[0056] High molecular weight polymer: Polyacrylonitrile (PAN, molecular weight 150,000)

[0057] Conductivity enhancement material: Multi-walled carbon nanotubes (MWCNTs, diameter 10-20 nm, length 10-30 μm)

[0058] Hydrophobic agent: Polytetrafluoroethylene (PTFE) emulsion (60 wt%)

[0059] Organic solvent: N,N-dimethylformamide (DMF)

[0060] 2. Preparation method

[0061] Step S1: Prepare spinning solution

[0062] Weigh 0.8 g of PAN, 0.1 g of MWCNTs, and 0.2 g of PTFE emulsion (solid content) and add them together to 9 g of DMF solvent. The mixture is magnetically stirred at 60 °C for 12 hours, followed by ultrasonic treatment for 2 hours to obtain a uniform, stable, and bubble-free electrospinning precursor solution.

[0063] Step S2: Electrospinning to form a film

[0064] The aforementioned precursor solution was injected into a syringe and installed in an electrospinning apparatus. The process parameters were set as follows: voltage 18 kV, receiving distance 15 cm, and feed rate 1.0 mL / h. Using a flat aluminum foil as the receiver, continuous spinning was performed for 8 h, and a self-supporting PAN / MWCNTs / PTFE composite fiber membrane was collected.

[0065] Step S3: Asymmetric hydrophobic treatment

[0066] The composite fiber membrane obtained in step S2 was flattened and fixed, and an ultrasonic spraying device was used to spray only its upper surface with a 5 wt% PTFE solution (solvent being an ethanol / water mixture). The spraying amount was controlled so that the PTFE penetration depth was approximately 15% of the total thickness of the fiber membrane. After spraying, it was dried in a 60 °C oven for 2 h to obtain a precursor with a wettability gradient and high PTFE content on one side.

[0067] Step S4: Integrated hot-press carbonization

[0068] The aforementioned precursor was placed in a graphite mold and then placed in a tubular autoclave. High-purity nitrogen was introduced as a protective gas. Subsequently, a constant vertical pressure of 3 MPa was applied, and the following heating program was executed:

[0069] Pre-oxidation stage: The temperature was increased from room temperature to 250 °C at a rate of 2 °C / min and held at this temperature for 1 h.

[0070] Carbonization stage: Continue heating to 1000 °C at a heating rate of 5 °C / min, and hold at this temperature for 1 h.

[0071] During this process, the precursor undergoes a transformation from polymer to conductive carbon network under the combined action of a preset pressure and a specific heating program, achieving controllable densification of the fiber network. The pressure, heating rate, and final carbonization temperature are key process parameters for synergistically controlling the final product's thickness, porosity, mechanical strength, and conductivity. Throughout the heating and holding process, the pressure remains constant at 3 MPa.

[0072] Step S5: Cooling and Sampling

[0073] After carbonization, heating was stopped, and the sample was allowed to cool naturally to room temperature while maintaining a pressure of 3 MPa. The pressure was then released, and the sample was removed, yielding the integrated ultrathin flexible gas diffusion layer sample GDL-1.

[0074] Performance Testing: GDL-1 was assembled into a membrane electrode assembly for testing in an H2 / O2 proton exchange membrane fuel cell. Under conditions of 80°C and 100% relative humidity, the battery achieved a current density of 1.5 A / cm² at 0.6 V, and no significant voltage drop occurred at this high current density, indicating excellent flood resistance and gas transport performance.

[0075] Comparative Example 1: Traditional carbon paper-based GDL

[0076] A comparative test was conducted using commercially available SIGRACET® 25BC carbon paper (approximately 235 μm thick) and a conventional PTFE hydrophobic microporous layer to assemble a GDL. Under the same test conditions, the current density at 0.6 V was 1.1 A / cm², and the voltage dropped significantly after the current density exceeded 1.2 A / cm², indicating that flooding is likely to occur at high current densities.

[0077] The foregoing description describes some exemplary embodiments of the present invention. These embodiments are merely illustrative and do not constitute a limitation on the scope of protection of the present invention. Features in these embodiments can be rearranged in a suitable manner, and the resulting solutions still fall within the scope of protection claimed by the present invention. All other embodiments obtained by those skilled in the art based on the above embodiments without inventive effort, i.e., all modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, fall within the scope of protection claimed by the present invention.

Claims

1. An integrated ultrathin flexible gas diffusion layer, characterized in that, The self-supporting independent carbon fiber film is composed of an electrospun carbon nanofiber network that has undergone hot-press carbonization treatment; the carbon nanofiber network contains a uniformly dispersed conductive reinforcing material and a matrix hydrophobic agent; the gas diffusion layer has a gradient pore structure in the thickness direction, and the first and second surfaces have asymmetric wettability.

2. The integrated ultrathin flexible gas diffusion layer according to claim 1, characterized in that, The total thickness of the gas diffusion layer is 20-150 μm.

3. The integrated ultrathin flexible gas diffusion layer according to claim 1, characterized in that, The asymmetric wettability is specifically manifested as follows: the side with a smaller pore size is defined as the first surface, and the side with a larger pore size is defined as the second surface; the static water contact angle of the first surface is greater than 150°, and the static water contact angle of the second surface is 120°-140°; wherein, the first surface is configured to face the catalyst layer, and the second surface is configured to face the flow field plate.

4. The integrated ultrathin flexible gas diffusion layer according to claim 1 or 3, characterized in that, The gradient hole structure is characterized by the hole diameter gradually decreasing from the second surface to the first surface.

5. The integrated ultrathin flexible gas diffusion layer according to claim 4, characterized in that, The conductive reinforcing material includes one or more of carbon nanotubes, graphene, Ketjen black, and acetylene black, with a mass fraction of 5%-30% in the gas diffusion layer. A surface-modified hydrophobic agent is subsequently introduced onto the first surface. Both the matrix hydrophobic agent and the surface-modified hydrophobic agent are one or more of polytetrafluoroethylene, fluorinated ethylene propylene copolymer, and polyvinylidene fluoride. The total mass fraction of the hydrophobic agent in the gas diffusion layer is 10%-40%. The surface-modified hydrophobic agent is mainly enriched on the first surface, resulting in a gradient distribution of the hydrophobic agent content in the thickness direction.

6. A membrane electrode assembly for a proton exchange membrane fuel cell, characterized in that, It includes an integrated ultrathin flexible gas diffusion layer as described in any one of claims 1-5.

7. A method for preparing an integrated ultrathin flexible gas diffusion layer according to claim 1, characterized in that, include: S1. Preparation of spinning solution: The high molecular polymer, conductive reinforcing material and matrix hydrophobic agent are dissolved or dispersed in an organic solvent to prepare an electrospinning precursor solution; S2. Electrospinning: The precursor solution obtained in S1 is electrospinned to collect a self-supporting polymer composite fiber membrane. S3. Asymmetric hydrophobic treatment: The single surface of the polymer composite fiber membrane obtained in S2 is treated with hydrophobic agent spraying or vapor deposition to introduce surface-modified hydrophobic agent to construct a wettability gradient precursor. S4. Hot-pressing and carbonization integrated treatment: The wettability gradient precursor after S3 treatment is placed in a hot-pressing device, and under a protective atmosphere, a pressure of 0.5-5 MPa is applied, and constant pressure hot-pressing treatment is performed according to a preset heating program; the preset heating program includes a pre-oxidation stage and a carbonization stage performed at a controlled heating rate, and the fiber membrane is densified and a gradient pore structure in the thickness direction is formed by utilizing the coupling effect of pressure and temperature field; S5. Cooling and post-processing: After carbonization, cool to room temperature under maintaining pressure, and remove to obtain the integrated ultrathin flexible gas diffusion layer.

8. The method for preparing the integrated ultrathin flexible gas diffusion layer according to claim 7, characterized in that, In step S4, the temperature of the pre-oxidation stage is 200-300 ℃ and the holding time is 0.5-2 h; the temperature of the carbonization stage is 800-1200 ℃ and the holding time is 0.5-2 h.

9. The method for preparing the integrated ultrathin flexible gas diffusion layer according to claim 7, characterized in that, In step S4, the heating rate of the pre-oxidation stage is 1-5 ℃ / min, and the heating rate of the carbonization stage is 2-10 ℃ / min.

10. The method for preparing the integrated ultrathin flexible gas diffusion layer according to claim 7, characterized in that, The polymer is one of polyacrylonitrile, polyimide, or polyacrylonitrile-co-polyvinylpyrrolidone.

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