A method for preparing a fuel cell gas diffusion layer having a gradient microporous layer

Abstract

A method for preparing a fuel cell gas diffusion layer having a gradient microporous layer is disclosed. The method aims to address the technical problem of poor water vapor management capabilities of existing gradient gas diffusion layers. The preparation method includes preparing a dispersion liquid according to the volume fraction of an alcohol solvent, adding carbon powder and a hydrophobic agent to the dispersion liquid to obtain different slurries, and sequentially coating the slurries on the surface of hydrophobic carbon paper to obtain a gas diffusion layer with a multi-layer microporous layer structure. A gradient microporous layer pore structure is formed in the longitudinal direction. The porosity of the gas diffusion layer is 82.97%. A fuel cell prepared using the gas diffusion layer of the present invention and a commercial gas diffusion layer from Toray under the same conditions has a peak power density of 1659 to 1833 mW·cm. ‑2 , which is 21.99% to 34.78% higher than that of fuel cells using Toray's commercial gas diffusion layer, and can be used in the fuel cell field.

Description

Technical Field

[0001] The invention relates to a method for preparing a fuel cell gas diffusion layer, and belongs to the field of new energy battery materials. Background Art

[0002] Hydrogen energy, as a highly promising clean energy source, is widely recognized and increasingly supported. Hydrogen fuel cells are a sustainable energy conversion system, of which proton exchange membrane fuel cells are the most widely used. Their high energy conversion efficiency and long operating life make them one of the most promising devices to replace traditional energy conversion devices. A proton exchange membrane fuel cell consists of a bipolar plate, a proton exchange membrane, a catalyst layer, and a gas diffusion layer. The gas diffusion layer is one of the most important components of a proton exchange membrane fuel cell, consisting of a substrate layer and a microporous layer. During cell operation, it supports the catalyst layer and provides gas, ion, and drainage channels for the electrode reactions.

[0003] The water vapor transport mechanism within the gas diffusion layer is complex, and the gas diffusion layer may flood under long-term operation and high current density conditions. By designing a gradient pore structure in the microporous layer, the gas diffusion layer's gas transport and water management capabilities can be effectively improved, allowing for the timely removal of liquid water accumulated at the electrode interface and enhancing fuel cell performance. However, current preparation techniques for gradient gas diffusion layers often utilize carbon powder materials of varying types and particle sizes to construct a gradient microporous layer, which suffers from poor water vapor management capabilities. Summary of the Invention

[0004] The present invention aims to address the technical problem of poor water vapor management capabilities of existing gradient gas diffusion layers by providing a method for preparing a fuel cell gas diffusion layer with a gradient microporous layer. The present invention uses different dispersions to prepare different slurries and sequentially coats them on the surface of hydrophobic carbon paper to produce a gas diffusion layer with a multi-layer microporous layer structure. This layer forms a gradient microporous layer pore structure in the longitudinal direction, increasing the porosity of the gas diffusion layer. Fuel cells using this gas diffusion layer significantly improve the performance of fuel cells using commercial gas diffusion layers and traditional non-gradient uniform gas diffusion layers.

[0005] The method for preparing a fuel cell gas diffusion layer having a gradient microporous layer of the present invention is carried out according to the following steps:

[0006] 1. Preparation of carbon paper substrate: soak raw carbon paper in ethanol solution, ultrasonically clean for 30 minutes, and then vacuum dry; prepare polytetrafluoroethylene (PTFE) emulsion, soak the dried raw carbon paper in the PTFE emulsion, and sinter at high temperature in an inert atmosphere to obtain a carbon paper substrate containing polytetrafluoroethylene;

[0007] 2. Preparation of slurries of different dispersions:

[0008] According to the volume fraction V1 of the alcohol solvent being 70% to 95%, the alcohol solvent and water are uniformly mixed to obtain a dispersion A;

[0009] According to the volume fraction V2 of the alcohol solvent being 5% to 30%, the alcohol solvent and water are uniformly mixed to obtain a dispersion B;

[0010] Add carbon powder and hydrophobic agent to dispersion A at a mass ratio of (2.3-4):1, stir evenly, and obtain slurry A;

[0011] Add carbon powder and hydrophobic agent to dispersion B at a mass ratio of (2.3-4):1, stir evenly, and obtain slurry B;

[0012] The types of carbon powder and hydrophobic agent in slurry A and slurry B are the same;

[0013] 3. Preparation of the microporous layer: Slurry A prepared in step 2 is sprayed on the carbon paper base layer treated in step 1 by ultrasonic spraying to obtain microporous layer A. After the microporous layer A is dried, slurry B is sprayed on the microporous layer A to obtain microporous layer B. After spraying is completed, the layer is sintered at high temperature in an inert atmosphere to obtain a fuel cell gas diffusion layer with a gradient microporous layer.

[0014] Furthermore, the vacuum drying temperature in step 1 is 60-90°C.

[0015] Furthermore, the mass concentration of the PTFE emulsion described in step 1 is 10% to 20%.

[0016] Furthermore, the sintering temperature in step 1 is 300-400° C., and the sintering time is 20-60 min.

[0017] Furthermore, the alcohol solvent in step 2 is one or more of ethanol, isopropanol and n-butanol.

[0018] Furthermore, the carbon powder in step 2 is one or more of Vulcan XC-72, acetylene black, carbon nanotubes, and graphite powder.

[0019] Furthermore, the hydrophobic agent described in step 2 is one or a mixture of polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene-ethylene copolymer (ETFE) and polyvinylidene fluoride (PVDF).

[0020] Furthermore, in step 2, the relationship between the volume fraction V1 of the alcohol solvent in dispersion A and the volume fraction V2 of the alcohol solvent in dispersion B is V1 = 90%, V2 = 10%; V1 = 80%, V2 = 20%; V1 = 70%, V2 = 30%. This design ensures a significant difference in the alcohol solvent content between slurry A and slurry B.

[0021] Furthermore, in step 3, when ultrasonically spraying the slurry prepared in step 2, the spraying solid phase material loading of microporous layer A and microporous layer B is 0.5-1.0 mg / cm 2 .

[0022] Furthermore, in step 3, the drying temperature of the microporous layer A is 70-85° C., and the drying time is 5-15 min;

[0023] Furthermore, in step three, the inert atmosphere is Ar or N2.

[0024] Furthermore, in step three, the high temperature sintering has a sintering temperature of 250-400° C. and a sintering time of 20-60 minutes.

[0025] The beneficial effects of the present invention compared to the prior art are:

[0026] (1) In the present invention, the water-to-alcohol ratios in the dispersions used to prepare slurries A and B are different, resulting in significant differences in the drying rates of the slurries. The different evaporation rates will produce differentiated primary pores between the carbon powder particles. Furthermore, water and alcohol have different affinities for carbon powder and hydrophobic agent, resulting in significant differences in the dispersion effects of carbon powder and hydrophobic agent in dispersions with different water-to-alcohol ratios. Under the combined action of the hydrophobic agent and the dispersion, the carbon powder particles are subjected to different forces, forming differentiated secondary pores. Sequentially spraying slurries with different water-to-alcohol ratios will result in different pore structures, forming a gas diffusion layer with a gradient pore structure in the longitudinal direction of the gas diffusion layer.

[0027] (2) The gas diffusion layer with a gradient pore structure prepared by the present invention rationally regulates the pore distribution of the microporous layer, increases the porosity of the gas diffusion layer, reduces the resistivity, and effectively improves the water vapor management capability. When the gas diffusion layer is applied to a fuel cell, the battery performance can be improved. The fuel cell prepared using the fuel cell gas diffusion layer with a gradient microporous layer of the present invention and the Toray commercial gas diffusion layer under the same conditions has a peak power density of 1659 to 1833 mW·cm -2 , which is 21.99% to 34.78% higher than that of fuel cells using Toray's commercial gas diffusion layer, and has application prospects.

[0028] (3) The method and reagents used in the present invention are simple, the manufacturing process cost is low, the time is short, the economic benefit is high, and there is good application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a surface SEM image of a fuel cell gas diffusion layer having a gradient microporous layer prepared in Example 1;

[0030] Figure 2 is a cross-sectional SEM image of a fuel cell gas diffusion layer having a gradient microporous layer prepared in Example 1;

[0031] Figure 3 is a surface SEM image of a fuel cell gas diffusion layer having a gradient microporous layer prepared in Example 2;

[0032] Figure 4 This is a comparison of the porosity of the gas diffusion layer of the battery of Example 1 and Comparative Examples 1 and 2;

[0033] Figure 5 1 is a comparison diagram of contact angles of gas diffusion layers of batteries of Example 1, Comparative Example 1, and Comparative Example 2;

[0034] Figure 6 This is a comparison chart of the resistivity of the battery gas diffusion layer of Example 1, Comparative Example 1, Comparative Example 2, and the commercial TGP-H-060 gas diffusion layer;

[0035] Figure 7 1 is a comparison chart of fuel cell performance using Example 1, Comparative Example 1, Comparative Example 2, and commercial TGP-H-060 gas diffusion layer;

[0036] Figure 8 1 is a graph comparing the performance of fuel cells using Example 2, Comparative Example 1, Comparative Example 2, and commercial TGP-H-060 gas diffusion layers. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments so that those skilled in the art can better understand the present invention and implement it. Obviously, the embodiments described are only a part of the embodiments of the present invention, rather than all the embodiments. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments do not limit the content and scope of the present invention. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0038] Example 1: The preparation method of the fuel cell gas diffusion layer having a gradient microporous layer of this embodiment is carried out according to the following steps:

[0039] 1. Preparation of carbon paper substrate: Commercial TGP-H-060 raw carbon paper was cut into 2.25 × 2.25 cm squares, soaked in ethanol solution, ultrasonically cleaned for 30 min, and then dried in a vacuum drying oven at 60°C for 8 h. 12.5 g of 60% PTFE emulsion and 37.5 g of deionized water were stirred and mixed. The dried raw carbon paper was soaked in the mixture for 2 min, then removed and heated in an Ar atmosphere at 2°C / min to 350°C and maintained for 60 min. The mixture was then cooled to room temperature to obtain a PTFE-containing carbon paper substrate.

[0040] 2. Preparation of slurries of different dispersions:

[0041] 18 mL of isopropyl alcohol and 2 mL of deionized water were mixed and stirred for 10 min to obtain dispersion A;

[0042] Mix 2 mL of isopropanol and 18 mL of deionized water and stir for 10 min to obtain dispersion B;

[0043] 0.143 g of 60% PTFE emulsion and 0.2 g of Vulcan XC-72 carbon powder were added to dispersion A, and the mixture was sheared and dispersed using a high shear emulsifier for 30 min to obtain slurry A.

[0044] 0.143 g of 60% PTFE emulsion and 0.2 g of Vulcan XC-72 carbon powder were added to dispersion B, and the mixture was sheared and dispersed using a high shear emulsifier for 30 min to obtain slurry B.

[0045] Preparation of microporous layer: Slurry A prepared in step 2 was sprayed on the carbon paper substrate treated in step 1 by ultrasonic spraying, and the sprayed solid phase was controlled to be 0.7 mg / cm 2 , and dried at 75 ° C for 5 minutes to obtain microporous layer A; continue to spray slurry B on the microporous layer A, and control the spraying load to 0.7 mg / cm 2 , and dried at 75°C for 5 minutes to obtain microporous layer B. After spraying, it was placed in a furnace and heated to 350°C at 5°C / min in an Ar atmosphere and maintained for 30 minutes, and then naturally cooled to room temperature to obtain a fuel cell gas diffusion layer with a gradient microporous layer.

[0046] Example 2: The preparation method of the fuel cell gas diffusion layer having a gradient microporous layer of this embodiment is carried out according to the following steps:

[0047] 1. Preparation of the hydrophobic base layer: This step is the same as the method in step 1 of Example 1;

[0048] 2. Preparation of microporous layer slurry:

[0049] Mix 24 mL of isopropyl alcohol and 6 mL of deionized water and stir for 10 min to obtain dispersion A;

[0050] Mix 6 mL of isopropanol and 24 mL of deionized water and stir for 10 min to obtain dispersion B;

[0051] 0.215 g of 60% PTFE emulsion and 0.3 g of Vulcan XC-72 carbon powder were added to dispersion A, and the mixture was sheared and dispersed for 30 min using a high shear emulsifier to obtain slurry A.

[0052] 0.215 g of 60% PTFE emulsion and 0.3 g of Vulcan XC-72 carbon powder were added to dispersion B, and the mixture was sheared and dispersed using a high shear emulsifier for 30 min to obtain slurry B.

[0053] 3. Preparation of gas diffusion layer: This step is the same as the method in step 3 of Example 1.

[0054] Comparative Example 1: The preparation method of the gas diffusion layer of this comparative example is carried out according to the following steps:

[0055] 1. Preparation of the hydrophobic base layer: This step is the same as the method in step 1 of Example 1;

[0056] Preparation of Microporous Layer Slurry: 18 mL of isopropyl alcohol and 2 mL of deionized water were stirred for 10 minutes to obtain Dispersion A. 0.143 g of 60% PTFE emulsion and 0.2 g of Vulcan XC-72 carbon powder were added to Dispersion A and dispersed using a high shear emulsifier for 30 minutes to obtain Slurry A.

[0057] Preparation of gas diffusion layer: Slurry A was evenly sprayed on the hydrophobic treated carbon paper substrate using ultrasonic spraying method, and the spraying load was controlled to be 1.4 mg / cm 2 , and dried at 75°C for 5 minutes, then placed in a furnace, heated to 350°C at 5°C / min in an Ar atmosphere and maintained for 30 minutes, and then naturally cooled to room temperature to obtain a gas diffusion layer with a gradient-free uniform microporous layer.

[0058] Comparative Example 2: The preparation method of the gas diffusion layer of this comparative example is carried out according to the following steps:

[0059] 1. Preparation of the hydrophobic base layer: This step is the same as the method in step 1 of Example 1;

[0060] Preparation of Microporous Layer Slurry: 24 mL of isopropyl alcohol and 6 mL of deionized water were stirred for 10 minutes to obtain Dispersion A. 0.215 g of 60% PTFE emulsion and 0.3 g of Vulcan XC-72 carbon powder were added to Dispersion A and dispersed using a high shear emulsifier for 30 minutes to obtain Slurry A.

[0061] Preparation of gas diffusion layer: Slurry A was evenly sprayed on the hydrophobic treated carbon paper substrate using ultrasonic spraying method, and the spraying load was controlled to be 1.4 mg / cm 2 , and dried at 75°C for 5 minutes, then placed in a furnace, heated to 350°C at 5°C / min in an Ar atmosphere and maintained for 30 minutes, and then naturally cooled to room temperature to obtain a gas diffusion layer with a gradient-free uniform microporous layer.

[0062] The surface morphology of the fuel cell gas diffusion layer with gradient microporous layer prepared in Example 1 is as follows: Figure 1 As shown, from Figure 1 It can be seen that micropores and mesopores with different pore sizes are distributed alternately on the surface.

[0063] Figure 2 This is a scanning electron microscope photograph of the cross section of the fuel cell gas diffusion layer with a gradient microporous layer prepared in Example 1. Figure 2 It can be seen that there are two microporous layers on the surface of the carbon paper substrate. The upper layer has a larger pore size, and the lower layer has a smaller pore size, forming a gradient. This is formed by sequentially spraying slurries prepared from dispersions with different water-to-alcohol ratios onto the carbon paper substrate. Dispersions with different water-to-alcohol ratios have significant differences in drying rates, and different evaporation rates will produce differentiated primary pores between the carbon powder particles. In addition, water and alcohol have different affinities for carbon powder and hydrophobic agents, and the dispersion effects of carbon powder and hydrophobic agents in dispersions with different water-to-alcohol ratios are significantly different. Under the combined action of the hydrophobic agent and dispersion, the carbon powder particles are subjected to different forces, forming differentiated secondary pores. Sequentially spraying slurries with different water-to-alcohol ratios will form a gas diffusion layer with a gradient pore structure in the longitudinal direction of the gas diffusion layer.

[0064] The surface morphology of the fuel cell gas diffusion layer with gradient microporous layer prepared in Example 2 is as follows: Figure 3 As shown, from Figure 3 It can be seen that there are a large number of small holes distributed on the surface, and the pore diameter is slightly smaller than that of Example 1.

[0065] Figure 4 is a comparison chart of the porosity of Example 1, Comparative Example 1 and Comparative Example 2. Figure 4It can be seen that the porosity of the fuel cell gas diffusion layer with a gradient microporous layer in Example 1 is 82.97%, while the porosity of the gas diffusion layer prepared in Comparative Example 1 is 56.54%. The preparation process of Comparative Example 1 is a traditional ultrasonic spraying method, and the gas diffusion layer prepared has only one uniform microporous layer. Compared with the gas diffusion layer with a uniform non-gradient microporous layer in Comparative Example 1, the porosity of the fuel cell gas diffusion layer with a gradient microporous layer in Example 1 is increased by 26%, and compared with the gas diffusion layer with a uniform non-gradient microporous layer prepared in Comparative Example 2, it is increased by 16%. The fuel cell gas diffusion layer with a gradient microporous layer prepared in Example 1 has more water vapor transmission channels.

[0066] Figure 5 : is a contact angle comparison diagram of Example 1, Comparative Example 1 and Comparative Example 2, Figure 5 It shows that the contact angle of the gas diffusion layer prepared in Example 1 is 149.8°, which is larger than the contact angle of the gas diffusion layer of the uniform non-gradient microporous layer prepared in Comparative Example 1 and Comparative Example 2, indicating that the hydrophobicity of the diffusion layer surface prepared in Example 1 is stronger. When used in fuel cells, the liquid water generated on the surface of the microporous layer during the electrochemical reaction process can be removed more quickly, and the "water flooding" phenomenon under high current density can be effectively suppressed.

[0067] Figure 6 The resistivity comparison diagram of Example 1, Comparative Example 1, Comparative Example 2 and commercial TGP-H-060 gas diffusion layer is shown in FIG. Figure 6 It can be seen that the electrical conductivity of the gas diffusion layer of Experimental Example 1 is 5.9 mΩ·cm, which is 0.21 mΩ·cm lower than that of the diffusion layer of Comparative Example 1, 0.61 mΩ·cm lower than that of the diffusion layer of Comparative Example 2, and 3.72 mΩ·cm lower than that of Toray's commercial gas diffusion layer. In comparison, the gas diffusion layer prepared in Example 1 has a lower resistivity and improves the electron conductivity.

[0068] Example 1, Example 2, Comparative Example 1, Comparative Example 2, and commercial TGP-H-060 gas diffusion layer were applied to the battery, and the cathode Pt catalyst loading was 0.3 mg / cm prepared by ultrasonic spraying. 2 , the anode Pt catalyst loading is 0.1 mg / cm 2 Fuel cells were assembled using a proton exchange membrane and commercial TGP-H-060 as the anode gas diffusion layer. Example 1, Example 2, Comparative Example 1, Comparative Example 2, and a commercial TGP-H-060 gas diffusion layer were used as the cathode gas diffusion layer. The anode and cathode test gases were air (flow rate 2 ml / min) and hydrogen (flow rate 0.5 ml / min), respectively. Cell polarization curve and power density performance tests were conducted with a test voltage sweep from 1.0 V to 0.2 V at a sweep rate of 0.05 V / min.

[0069] Figure 7 The fuel cell performance comparison chart of Example 1, Comparative Example 1, Comparative Example 2 and commercial TGP-H-060 gas diffusion layer is shown in Figure 1. Figure 7 It can be seen that the peak power density of the fuel cell prepared with the gas diffusion layer of Example 1 is 1833 mW·cm -2 The peak power density value is increased by 46.52% compared with the fuel cell prepared with the gas diffusion layer of Comparative Example 1, by 64.99% compared with the fuel cell prepared with the gas diffusion layer of Comparative Example 2, and by 34.78% compared with the fuel cell using the commercial TGP-H-060 gas diffusion layer.

[0070] Figure 8 The fuel cell performance comparison chart of Example 2, Comparative Example 1, Comparative Example 2, and commercial TGP-H-060 gas diffusion layer is shown in FIG. Figure 8 It can be seen that the peak power density of the fuel cell prepared with the gas diffusion layer of Example 2 is 1659 mW·cm -2 The peak power density value is increased by 32.61% compared with the fuel cell prepared with the gas diffusion layer of Comparative Example 1, by 49.32% compared with the fuel cell prepared with the gas diffusion layer of Comparative Example 2, and by 21.99% compared with the fuel cell prepared with the commercial TGP-H-060 gas diffusion layer.

[0071] The fuel cell gas diffusion layer with a gradient microporous layer of the present invention is provided with two microporous layers on the surface of a carbon paper base layer. The pore size of the upper layer is large, and the pore size of the lower layer is small, forming a gradient distribution, which has stronger hydrophobicity, improves the water vapor management ability, and thus improves the performance of the fuel cell.

Claims

1. A method for preparing a fuel cell gas diffusion layer having a gradient microporous layer, characterized in that The method proceeds as follows:

1. Preparation of carbon paper substrate: soak raw carbon paper in ethanol solution, ultrasonically clean for 30 minutes, and then vacuum dry; prepare polytetrafluoroethylene emulsion, soak the dried raw carbon paper in the PTFE emulsion, and sinter at high temperature in an inert atmosphere to obtain a carbon paper substrate containing polytetrafluoroethylene; 2. Preparation of slurries of different dispersions: According to the volume fraction V1 of the alcohol solvent being 70% to 95%, the alcohol solvent and water are uniformly mixed to obtain a dispersion A; According to the volume fraction of the alcohol solvent V2 = 5% to 30%, the alcohol solvent and water are mixed uniformly to obtain a dispersion B; Add carbon powder and hydrophobic agent to dispersion A at a mass ratio of (2.3-4):1, stir evenly, and obtain slurry A; Add carbon powder and hydrophobic agent to dispersion B at a mass ratio of (2.3-4):1, stir evenly, and obtain slurry B; The types of carbon powder and hydrophobic agent in slurry A and slurry B are the same; 3. Preparation of the microporous layer: Slurry A prepared in step 2 is sprayed on the carbon paper base layer treated in step 1 by ultrasonic spraying to obtain microporous layer A. After the microporous layer A is dried, slurry B is sprayed on the microporous layer A to obtain microporous layer B. After spraying is completed, the layer is sintered at high temperature in an inert atmosphere to obtain a fuel cell gas diffusion layer with a gradient microporous layer.

2. The method for preparing a fuel cell gas diffusion layer having a gradient microporous layer according to claim 1, characterized in that: The vacuum drying temperature in step 1 is 60-90°C.

3. The method for preparing a fuel cell gas diffusion layer having a gradient microporous layer according to claim 1 or 2, characterized in that: The mass percentage concentration of the PTFE emulsion described in step 1 is 10% to 20%.

4. The method for preparing a fuel cell gas diffusion layer having a gradient microporous layer according to claim 1 or 2, characterized in that: The sintering temperature in step 1 is 300-400° C., and the sintering time is 20-60 minutes.

5. The method for preparing a fuel cell gas diffusion layer having a gradient microporous layer according to claim 1 or 2, characterized in that: The alcohol solvent described in step 2 is one or more of ethanol, isopropanol and n-butanol.

6. The method for preparing a fuel cell gas diffusion layer having a gradient microporous layer according to claim 1 or 2, characterized in that: The carbon powder in step 2 is one or more of Vulcan XC-72, acetylene black, carbon nanotubes, and graphite powder.

7. The method for preparing a fuel cell gas diffusion layer having a gradient microporous layer according to claim 1 or 2, characterized in that: The hydrophobic agent in step 2 is one or a mixture of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polychlorotrifluoroethylene, tetrafluoroethylene-ethylene copolymer and polyvinylidene fluoride.

8. The method for preparing a fuel cell gas diffusion layer having a gradient microporous layer according to claim 1 or 2, characterized in that: In step 3, when ultrasonically spraying the slurry prepared in step 2, the spraying solid phase material loading of microporous layer A and microporous layer B is 0.5-1.0 mg / cm 2 .

9. The method for preparing a fuel cell gas diffusion layer having a gradient microporous layer according to claim 1 or 2, characterized in that: In step 3, the drying temperature of the microporous layer A is 70-85° C., and the drying time is 5-15 minutes.

10. The method for preparing a fuel cell gas diffusion layer having a gradient microporous layer according to claim 1 or 2, characterized in that: In step three, the high-temperature sintering is performed at a temperature of 250 to 400° C. and a sintering time of 20 to 60 minutes.

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