Composite microporous layer and preparation method and application thereof

Abstract

The invention discloses a composite microporous layer and a preparation method and application thereof. The preparation method of the composite microporous layer comprises the following steps: S1, performing carbonization treatment, hydrophobic treatment, pre-curing treatment and sintering treatment on a first woven fabric in sequence to obtain a first microporous layer precursor; s2, performing carbonization treatment, hydrophobic treatment, pre-curing treatment and sintering treatment on the second woven fabric in sequence to obtain a second microporous layer precursor; s3, superposing the first microporous layer precursor and the second microporous layer precursor, and then performing secondary curing treatment to obtain a composite microporous layer; wherein the weaving number of the first woven fabric is lower than that of the second woven fabric; the sequence of the step S1 and the step S2 is not distinguished. When the obtained composite microporous layer is used for a gas diffusion layer of a fuel cell, the performance and durability of the fuel cell can be effectively improved while good basic performance can be ensured, and the composite microporous layer is simple to prepare and beneficial to batch production.

Description

Technical Field

[0001] The invention relates to a composite microporous layer and a preparation method and application thereof. Background Art

[0002] With global energy and environmental challenges becoming increasingly severe, efficient, environmentally friendly, and clean new energy technologies are considered to be the most promising new technologies of the 21st century. Among them, proton exchange membrane fuel cells (PEMFCs), unconstrained by the Carnot cycle, have broad application prospects in aerospace, transportation, stationary power plants, and other fields. PEMFCs primarily consist of bipolar plates, gas diffusion layers (GDLs), catalyst layers, and proton exchange membranes. The GDL is one of its most critical components, supporting the catalyst layer, collecting current, providing gas and electron channels, and draining water. The presence of liquid water is unavoidable during PEMFC operation, and this water can clog the pores between the GDL and the catalyst layer, hindering reactant transport. Excessive liquid water can also cause "flooding," leading to performance degradation.

[0003] Therefore, developing a method for preparing gas diffusion layers with high permeability, simple process, and convenient batch production is of great significance for promoting the development and commercial application of proton exchange membrane fuel cells.

[0004] Existing gas diffusion layers mostly include the basic structure of a substrate and a microporous layer, but the microporous layer still has the following major defects: (1) The structure is simple and the thickness is thin, which makes it difficult to retain water; (2) It is difficult to control the gaps in the microporous layer obtained by coating, which ultimately leads to the overall quality and performance after further use in fuel cells being difficult to control, such as always being locally too dry or too wet; (3) The preparation process is relatively complicated; (4) It may affect the performance and durability of the fuel cell and reduce its service life. For example, the patent application with application number "201810201559.9" "A diffusion layer for membrane electrode and its preparation method" uses an electrochemical method to modify the surface of the diffusion layer substrate and then applies a microporous layer. This method can improve the mass transfer capacity and water flooding phenomenon under high current density, but the process requirements are complex and it is not suitable for batch preparation; for example, the patent application with application number "201910373844.3" "Preparation method of proton exchange membrane fuel cell gas diffusion layer for high current density" increases cracks on the surface of the microporous layer by baking, thereby improving the water management ability of the gas diffusion layer and thus improving the battery performance, but the increase in cracks leads to an increase in surface roughness and an increase in contact resistance, which affects the performance and durability of the fuel cell stack and reduces its service life.

[0005] Therefore, there is an urgent need for a microporous layer that is simple to prepare, has adjustable pores, excellent performance, and can effectively improve the performance and durability of fuel cells. Summary of the Invention

[0006] To address the aforementioned technical deficiencies of existing microporous layers, the present invention provides a composite microporous layer, its preparation method, and its application. When used in a gas diffusion layer for a fuel cell, this composite microporous layer simultaneously ensures excellent air permeability and water retention, effectively improving the performance and durability of the fuel cell. Furthermore, it can be produced without complex preparation processes, facilitating mass production.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows.

[0008] The present invention provides a method for preparing a composite microporous layer, which comprises the following steps:

[0009] S1, the first woven fabric is sequentially subjected to carbonization treatment, hydrophobic treatment, pre-curing treatment and sintering treatment to obtain a first microporous layer precursor;

[0010] S2, the second woven fabric is sequentially subjected to carbonization treatment, hydrophobic treatment, pre-curing treatment and sintering treatment to obtain a second microporous layer precursor;

[0011] S3, superimposing the first microporous layer precursor and the second microporous layer precursor, and then performing a secondary curing treatment to obtain the composite microporous layer;

[0012] in,

[0013] The weave count of the first woven fabric is lower than the weave count of the second woven fabric;

[0014] Steps S1 and S2 are not sequence-dependent.

[0015] In the present invention, according to actual needs, fabrics of different thicknesses and different weave counts can be further laminated, and a multi-layer structure can be obtained by the same operation as before. The thickness and porosity can be effectively controlled from the raw material level, thereby better achieving the effects of air permeability and water retention.

[0016] In the present invention, according to actual needs, the first microporous layer precursor and the second microporous layer precursor can be stacked in the same area when being stacked, or a second microporous layer precursor of a specific size can be selected for partial area for stacking (that is, the overall situation of double-layer regional stacking), and even second microporous layer precursors of different sizes, different thicknesses and different porosities can be selected for different areas for stacking (that is, the overall situation of double-layer regional stacking with different materials).

[0017] In some embodiments, in step S1, the weave count of the first woven fabric is 100-500 weaves.

[0018] In some embodiments, in step S1 , the thickness of the first woven fabric is 50-300 μm, for example, 200 μm.

[0019] In some embodiments, in step S2, the weave count of the second woven fabric is 500-1000 weaves.

[0020] In some embodiments, in step S2, the thickness of the second woven fabric is 50-300 μm, for example, 100 μm.

[0021] In some embodiments, in steps S1 and S2, the first woven fabric and the second woven fabric are each independently pure cotton fabric.

[0022] In some embodiments, in steps S1 and S2, the first woven fabric and the second woven fabric are each independently a twill woven fabric.

[0023] In the present invention, in steps S1 and S2, the carbonization treatments can each independently obtain corresponding carbonized fiber structures, and the carbonization treatments can each independently be performed using conventional operations in the art.

[0024] In some embodiments, in steps S1 and S2, the temperature of the carbonization treatment is independently 1500-2000°C.

[0025] In some embodiments, in steps S1 and S2, the carbonization treatment time is independently 1-3 hours, for example, 2 hours.

[0026] In some embodiments, in steps S1 and S2, the carbonization treatment steps are each independently performed in a muffle furnace.

[0027] In the present invention, in steps S1 and S2, the hydrophobic treatment can be independently performed using conventional operations in the art.

[0028] In some embodiments, in steps S1 and S2, the hydrophobic treatment is each independently performed using a hydrophobic treatment liquid; the hydrophobic treatment liquid includes a hydrophobic agent, ethanol and water.

[0029] Wherein, the mass ratio of the hydrophobic agent, ethanol and water is (1-20):(20-40):(20-50), for example, 10:40:50.

[0030] The hydrophobic agent is preferably a PTFE emulsion; the solid content of the PTFE in the PTFE emulsion is, for example, 60%.

[0031] The hydrophobic treatment is preferably performed by immersing the material obtained by the carbonization treatment in the hydrophobic treatment liquid; wherein, the amount of the hydrophobic treatment liquid can be specifically selected according to actual conditions.

[0032] In some specific embodiments, in steps S1 and S2, the hydrophobic treatment liquids are independently PTFE emulsion, ethanol and water, and the mass ratios thereof are 10:40:50, respectively; and the solid content of the PTFE in the PTFE emulsion is 60%.

[0033] In some embodiments, in steps S1 and S2, the time for the hydrophobic treatment is independently 20-40 min, for example, 30 min.

[0034] In some embodiments, in steps S1 and S2, the pre-curing treatment is each independently a hot press curing treatment.

[0035] In some embodiments, in steps S1 and S2, the temperature of the pre-curing treatment is independently 150-400°C.

[0036] In some embodiments, in steps S1 and S2, the pressure of the pre-curing treatment is independently 100-400 kg / cm 2 , for example 200kg / cm 2 .

[0037] In some embodiments, in steps S1 and S2, the pre-curing treatment time is independently 20-40 minutes, for example, 30 minutes.

[0038] In some embodiments, in steps S1 and S2, the pre-curing treatment steps are each independently performed in a hot press.

[0039] In some embodiments, in steps S1 and S2, the sintering temperature is independently 300-400°C, for example 350°C.

[0040] In some embodiments, in steps S1 and S2, the sintering treatment time is independently 20-40 minutes, for example, 30 minutes.

[0041] In some embodiments, in steps S1 and S2, the sintering treatments are each independently performed in a muffle furnace.

[0042] In some embodiments, in step S3, the secondary curing process is a hot pressing curing process.

[0043] In some embodiments, in step S3, the temperature of the secondary curing treatment is 150-250°C, for example, 200°C.

[0044] In some embodiments, in step S3, the pressure of the secondary curing process is 100-1000 kg / cm 2 .

[0045] In some embodiments, in step S3, the secondary curing treatment lasts for 5-15 minutes, for example, 10 minutes.

[0046] In some embodiments, in step S3, the secondary curing step is performed in a hot press.

[0047] In some preferred embodiments, the method for preparing the composite microporous layer comprises the following steps:

[0048] S1, the first woven fabric is sequentially carbonized at 1500-2000℃, hydrophobized in a hydrophobic treatment solution, and heated at 150-4000℃ and 100-400kg / cm 2 and sintering at 300-400° C. to obtain a first microporous layer precursor;

[0049] S2, the second woven fabric is sequentially carbonized at 1500-2000℃, hydrophobized in a hydrophobic treatment solution, and heated at 150-4000℃ and 100-400kg / cm 2 and performing a pre-curing treatment at 300-400° C. and a sintering treatment at 300-400° C. to obtain a second microporous layer precursor;

[0050] S3, the first microporous layer precursor and the second microporous layer precursor are superimposed, and then heated at 150-250 ° C and 100-1000 kg / cm 2 Performing a secondary curing treatment to obtain the composite microporous layer;

[0051] in,

[0052] The first woven fabric has a weave count of 100-500 and a thickness of 50-300 μm;

[0053] The second woven fabric has a weave count of 500-1000 and a thickness of 50-300 μm;

[0054] Steps S1 and S2 do not distinguish between the order of front and back;

[0055] In steps S1 and S2, the formula of the hydrophobic treatment solution is independently:

[0056] Hydrophobic agent: ethanol: water = (1-20): (20-40): (20-50).

[0057] In some specific embodiments, the method for preparing the composite microporous layer comprises the following steps:

[0058] S1, the first woven fabric was carbonized at 1500℃ for 2 hours, immersed in a hydrophobic treatment solution for 30 minutes for hydrophobic treatment, and heated at 150℃ and 200kg / cm 2A pre-curing treatment was performed at 350° C. for 30 minutes and a sintering treatment was performed at 350° C. for 30 minutes to obtain a first microporous layer precursor;

[0059] S2, the second woven fabric was carbonized at 1500℃ for 2 hours, immersed in a hydrophobic treatment solution for 30 minutes for hydrophobic treatment, and heated at 150℃ and 200kg / cm 2 The second microporous layer precursor was prepared by performing a pre-curing treatment at 350° C. for 30 minutes and a sintering treatment at 350° C. for 30 minutes;

[0060] S3, the first microporous layer precursor and the second microporous layer precursor are superimposed, and then heated at 200 ° C and 1000 kg / cm 2 Performing a secondary curing treatment for 10 minutes under the conditions of 400 nm to obtain the composite microporous layer;

[0061] in,

[0062] The first woven fabric has a weave count of 100 and a thickness of 200 μm;

[0063] The second woven fabric has a weave count of 500 and a thickness of 100 μm;

[0064] Steps S1 and S2 do not distinguish between the order of front and back;

[0065] In steps S1 and S2, the hydrophobic treatment liquids are independently PTFE emulsion, ethanol and water, and the mass ratios thereof are 10:40:50 respectively; the solid content of the PTFE in the PTFE emulsion is 60%.

[0066] The present invention also provides a composite microporous layer, which is prepared by the above-mentioned method for preparing the composite microporous layer;

[0067] The composite microporous layer includes a first microporous layer and a second microporous layer stacked in sequence; wherein the porosity of the first microporous layer is higher than that of the second microporous layer.

[0068] In some embodiments, the porosity of the first microporous layer is 30% to 50%, for example 35%.

[0069] In some embodiments, the porosity of the second microporous layer is 10%-20%, for example 15%.

[0070] In some embodiments, the thickness of the first microporous layer is 5-20 μm, for example, 15 μm.

[0071] In some embodiments, the second microporous layer has a thickness of 10-40 μm, for example 30 μm.

[0072] In some embodiments, the carbon loading of the first microporous layer is 0.5-1 mg / cm 2 .

[0073] In some embodiments, the carbon loading of the second microporous layer is 1-2 mg / cm 2 .

[0074] In some embodiments, the resistivity of the first microporous layer is 0.4-0.6 Ω·cm.

[0075] In some embodiments, the resistivity of the second microporous layer is 0.4-0.8 Ω·cm, for example 0.6 Ω·cm.

[0076] In some specific embodiments, the composite microporous layer comprises a first microporous layer and a second microporous layer stacked in sequence; wherein,

[0077] The porosity of the first microporous layer is 30%-50%, the thickness is 5-20 μm, and the carbon loading is 0.5-1 mg / cm 2 , resistivity is 0.4-0.6Ω·cm;

[0078] The porosity of the second microporous layer is 10%-20%, the thickness is 10-40 μm, and the carbon loading is 1-2 mg / cm 2 , the resistivity is 0.4-0.8Ω·cm.

[0079] In some specific embodiments, the composite microporous layer comprises a first microporous layer and a second microporous layer stacked in sequence; wherein,

[0080] The porosity of the first microporous layer is 35%, the thickness is 15 μm, and the carbon loading is 1 mg / cm 2 , the resistivity is 0.4Ω·cm;

[0081] The porosity of the second microporous layer is 15%, the thickness is 30 μm, and the carbon loading is 1 mg / cm 2 , the resistivity is 0.6Ω·cm.

[0082] The present invention also provides an application of the composite microporous layer as described above in a fuel cell.

[0083] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0084] The reagents and raw materials used in the present invention are commercially available.

[0085] The positive progress effect of the present invention is:

[0086] The present invention uses different woven fabrics to produce a composite microporous layer with a multi-layer structure, and different layers and different areas of the same layer can have different porosities. When actually used in the gas diffusion layer of a fuel cell, it can simultaneously ensure excellent air permeability and water retention effects, and effectively improve the performance and durability of the fuel cell.

[0087] In addition, the composite microporous layer preparation method of the present invention has the following advantages: 1) simple operation, no need to prepare microporous layer slurry, and no coating process; 2) low cost, no heavy equipment, and conducive to scale-up production; 3) customizable, and can be customized for different flow field structures of fuel cells. Multi-layer microporous layers with different transverse and longitudinal porosities can be customized, effectively improving the mass transfer process and facilitating water and gas transport in fuel cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 This is an electron microscope image of the local surface of the composite microporous layer obtained in Example 1 of the present invention.

[0089] Figure 2 This is a cross-sectional view of the gradient pore structure of the composite microporous layer obtained in Example 1 of the present invention.

[0090] The reference numerals are as follows:

[0091] 1-first microporous layer; 2-second microporous layer.

[0092] Figure 3 This is a performance diagram of the composite microporous layer obtained in Example 1 of the present invention and a conventional microporous layer after being used in a fuel cell. DETAILED DESCRIPTION

[0093] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0094] In the following examples and effect examples, the measured results of thickness, porosity, carbon loading, etc. may refer to the average measured results of the corresponding layers.

[0095] Example 1

[0096] The composite microporous layer of this embodiment was prepared using the following process:

[0097] S1. Preparation of the first microporous layer precursor:

[0098] 1. Place the first woven fabric (specifically twill fabric with a weave count of 100 and a thickness of 200 μm) in a muffle furnace and set the temperature to 1500° C. for 2 hours for carbonization treatment.

[0099] 2. Prepare a hydrophobic treatment solution according to 10g of 60% PTFE emulsion, 40g of ethanol, and 50g of deionized water.

[0100] 3. Soak the carbonized material in the hydrophobic treatment solution for 30 minutes, take it out and dry it, then perform pre-curing treatment (hot pressing curing). The hot press temperature is 150℃ and the pressure is 200kg / cm 2 , pre-curing for 30 minutes.

[0101] 4. The material after the pre-curing treatment in step 3 is placed in a muffle furnace, and the temperature is set to 350° C. for 30 minutes for sintering to obtain the first microporous layer precursor.

[0102] S2. Preparation of the first microporous layer precursor:

[0103] 6. Place the second woven fabric (specifically, twill fabric with a weave count of 500 and a thickness of 100 μm) in a muffle furnace and set the temperature to 1500° C. for 2 hours for carbonization treatment.

[0104] 7. Prepare a hydrophobic treatment solution according to 10g of 60% PTFE emulsion, 40g of ethanol, and 50g of deionized water.

[0105] 8. Soak the carbonized material in the hydrophobic treatment solution for 30 minutes. After the surface is dried, pre-curing treatment (hot pressing curing) is carried out. The hot press temperature is 150 ° C, the pressure is 200 kg / cm², and the curing time is 30 minutes.

[0106] 9. Place the material after the pre-curing treatment in step 8 into a muffle furnace, set the temperature to 350° C., and sinter for 30 minutes to obtain the second microporous layer precursor.

[0107] S3. Preparation of composite microporous layer:

[0108] 10. Directly stack the first microporous layer precursor and the second microporous layer precursor.

[0109] 11. Perform secondary curing (hot press curing) in a hot press with a pressure of 1000kg / cm 2 , temperature is 200℃, time is 10min.

[0110] That is, the composite microporous layer of this embodiment is obtained, and the composite microporous layer includes a first microporous layer and a second microporous layer stacked in sequence.

[0111] Effect embodiment

[0112] 1. Microstructure characterization

[0113] The composite microporous layer obtained in Example 1 was characterized by scanning electron microscopy.

[0114] The results are as follows Figure 1 and Figure 2 shown.

[0115] in, Figure 1 The electron microscope image of the local surface of the composite microporous layer shows that the surface of the composite microporous layer can have pore structures with different microstructures in different areas.

[0116] Figure 2 This is a cross-sectional view of the local gradient pore structure of the composite microporous layer. The results show that the composite microporous layer as a whole has a two-layer structure, namely the first microporous layer 1 and the second microporous layer 2. The second microporous layer 2 is relatively dense, and the first microporous layer 1 is relatively fluffy, and the overall structure is similar to a gradient structure.

[0117] 2. Characterization of physical and chemical parameters such as porosity, thickness, carbon loading, and resistivity

[0118] The composite microporous layer obtained in Example 1 was characterized for porosity, thickness, and resistivity according to GB / T 20042.7-2014, Proton Exchange Membrane Fuel Cells, Part 7: Test Methods for Carbon Paper Characteristics. Carbon loading can be measured using conventional testing methods in the art (gravimetric method).

[0119] The measured physical and chemical parameters of each layer structure are as follows:

[0120] (1) The porosity of the first microporous layer is 35%;

[0121] (2) The porosity of the second microporous layer is 15%;

[0122] (3) The thickness of the first microporous layer is 15 μm;

[0123] (4) The thickness of the second microporous layer is 30 μm;

[0124] (5) The carbon loading of the first microporous layer is 1 mg / cm 2 ;

[0125] (6) The carbon loading of the second microporous layer is 1 mg / cm 2 ;

[0126] (7) The resistivity of the first microporous layer is 0.4Ω·cm;

[0127] (8) The resistivity of the second microporous layer is 0.6Ω·cm.

[0128] 3. Battery performance characterization

[0129] The composite microporous layer obtained in Example 1 was prepared into a membrane electrode assembly (MEA) and placed on a fuel cell platform for evaluation. A membrane electrode assembly obtained with a conventional microporous layer (a standard microporous layer, i.e., a microporous layer formed by coating a coating slurry with carbon powder and PTFE as the main materials and then coating it on carbon paper) was used for comparison. Specifically, the conventional fuel cell single cell test in the art was used to test the membrane electrode polarization curve (test parameters such as Figure 3 shown).

[0130] The results are as follows Figure 3 As shown in the results, when the composite microporous layer obtained in Example 1 was used to prepare a membrane electrode for single cell testing, when the current density was higher than 1000 mA / cm 2 Afterwards, the polarization performance is significantly improved compared with the membrane electrode obtained with a conventional microporous layer, indicating that the optimization of the microporous layer helps to reduce mass transfer losses.

[0131] In summary, the present invention can realize a multi-layer microporous layer structure with different overall transverse and longitudinal porosities by orderly stacking woven fabrics with different weave counts. By regulating the porosity of different areas of each layer, the ultimate excellent air permeability and water retention effects are achieved, and the performance and durability of the fuel cell are effectively improved.

Claims

1. A method for preparing a composite microporous layer, characterized in that: The preparation method of the composite microporous layer comprises the following steps: S1, the first woven fabric is sequentially subjected to carbonization treatment, hydrophobic treatment, pre-curing treatment and sintering treatment to obtain a first microporous layer precursor; S2, the second woven fabric is sequentially subjected to carbonization treatment, hydrophobic treatment, pre-curing treatment and sintering treatment to obtain a second microporous layer precursor; S3, superimposing the first microporous layer precursor and the second microporous layer precursor, and then performing a secondary curing treatment to obtain the composite microporous layer; in, The weave count of the first woven fabric is lower than the weave count of the second woven fabric; Steps S1 and S2 are performed in no particular order.

2. The method for preparing the composite microporous layer according to claim 1, wherein: In step S1, the weave number of the first woven cloth is 100-500; and / or, in step S1, the thickness of the first woven fabric is 50-300 μm; and / or, in step S2, the weave count of the second woven fabric is 500-1000 weaves; And / or, in step S2, the thickness of the second woven fabric is 50-300 μm.

3. The method for preparing the composite microporous layer according to claim 1, wherein: In steps S1 and S2, the temperature of the carbonization treatment is independently 1500-2000°C; And / or, in steps S1 and S2, the carbonization treatment time is independently 1-3 hours.

4. The method for preparing the composite microporous layer according to claim 1, wherein: In steps S1 and S2, the hydrophobic treatment is independently performed using a hydrophobic treatment liquid; the hydrophobic treatment liquid includes a hydrophobic agent, ethanol and water; Wherein, the mass ratio of the hydrophobic agent, ethanol and water is (1-20):(20-40):(20-50); And / or, in steps S1 and S2, the time of the hydrophobic treatment is independently 20-40 minutes.

5. The method for preparing the composite microporous layer according to claim 1, wherein: In steps S1 and S2, the pre-curing treatment is independently a hot pressing curing treatment; and / or, in steps S1 and S2, the temperature of the pre-curing treatment is independently 150-400° C.; And / or, in steps S1 and S2, the pressure of the pre-curing treatment is independently 100-400 kg / cm 2 ; And / or, in steps S1 and S2, the pre-curing treatment time is independently 20-40 minutes.

6. The method for preparing the composite microporous layer according to claim 1, wherein: In steps S1 and S2, the sintering temperature is independently 300-400°C; And / or, in steps S1 and S2, the sintering treatment time is independently 20-40 minutes.

7. The method for preparing the composite microporous layer according to claim 1, wherein: In step S3, the secondary curing process is a hot pressing curing process; and / or, in step S3, the temperature of the secondary curing treatment is 150-250° C.; And / or, in step S3, the pressure of the secondary curing treatment is 100-1000 kg / cm 2 ; And / or, in step S3, the secondary curing treatment time is 5-15 minutes.

8. A composite microporous layer, characterized in that: The composite microporous layer is prepared by the preparation method of the composite microporous layer according to any one of claims 1 to 7; The composite microporous layer includes a first microporous layer and a second microporous layer stacked in sequence; wherein the porosity of the first microporous layer is higher than that of the second microporous layer.

9. The composite microporous layer according to claim 8, wherein The composite microporous layer satisfies one or more of the following conditions: (1) The porosity of the first microporous layer is 30%-50%; (2) The porosity of the second microporous layer is 10%-20%; (3) The thickness of the first microporous layer is 5-20 μm; (4) The thickness of the second microporous layer is 10-40 μm; (5) The carbon loading of the first microporous layer is 0.5-1 mg / cm 2 ; (6) The carbon loading of the second microporous layer is 1-2 mg / cm 2 ; (7) The resistivity of the first microporous layer is 0.4-0.6Ω·cm; (8) The resistivity of the second microporous layer is 0.4-0.8Ω·cm.

10. Use of the composite microporous layer according to claim 8 or 9 in a fuel cell.

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