A bilayer microporous layer for fuel cells, its preparation method, gas diffusion layer and fuel cell

Abstract

This invention provides a bilayer microporous layer for fuel cells, its preparation method, a gas diffusion layer, and a fuel cell. The bilayer microporous layer comprises a first microporous layer and a second microporous layer stacked together. The porosity and average pore size of the first microporous layer are both larger than those of the second microporous layer. Both the first and second microporous layers contain a conductive agent and a benzene-based polymer, wherein the benzene-based polymer has tertiary amine groups or sulfonic acid groups. In this invention, on the one hand, the gradient porosity and gradient pore size of the first and second microporous layers optimize water vapor transport; on the other hand, the fact that both the first and second microporous layers contain benzene-based polymers with tertiary amine groups or sulfonic acid groups effectively regulates the humidity of the membrane electrode assembly (MEA) due to their hydrophilic and hydrophobic properties; furthermore, the benzene-based polymers with sulfonic acid groups can also adsorb metal ions through ionic interactions, reducing metal ion contamination of the MEA. Therefore, the fuel cell containing the bilayer microporous layer exhibits excellent electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, and relates to a double-layer microporous layer for fuel cells, and more particularly to a double-layer microporous layer for fuel cells, its preparation method, a gas diffusion layer, and a fuel cell. Background Technology

[0002] Fuel cells have broad development prospects in transportation, backup power, and distributed power stations due to their advantages such as high energy conversion efficiency, low emissions, and zero pollution. The core component of a fuel cell is the membrane electrode assembly (MEA), which is the site of electrochemical reactions. Its performance directly determines the application of the fuel cell. It typically consists of a gas diffusion layer, a catalyst layer, and a proton exchange membrane. The gas diffusion layer is usually composed of a conductive porous substrate such as carbon fiber paper or carbon cloth, with a microporous layer (MPL) attached to it. The microporous layer mainly functions to facilitate drainage, ventilation, and enhance electron transport; therefore, it must have a suitable pore structure to ensure gas and water transport and prevent flooding.

[0003] Currently, the mainstream method for preparing microporous layers involves uniformly mixing conductive carbon black with a hydrophobic agent (PTFE), coating it onto the surface of a hydrophobically treated support layer (such as carbon paper, carbon cloth, or carbon felt), and then calcining it at high temperature to obtain the microporous layer. Microporous layers prepared in this way typically have discontinuous electron transport channels, and the porosity and pore size distribution are difficult to control, affecting the transport of electrons, gases, and water, leading to a decline in fuel cell performance.

[0004] CN101325259A discloses a method for preparing a gas diffusion layer for proton exchange membrane fuel cells. The polytetrafluoroethylene (PTFE) in the gas diffusion layer is uniformly dispersed, and the diffusion layer exhibits relatively low electronic resistance and gas mass transfer resistance. The preparation method is as follows: a microporous layer slurry is mixed with carbon powder using a low-boiling-point organic solvent that easily wets the carbon powder. A fluorosurfactant is added to the PTFE aqueous dispersion before it is added. The microporous layer slurry is then uniformly dispersed on a support layer of the diffusion layer, and heat-treated to form the gas diffusion layer. The gas diffusion layer prepared by this method can be applied to batteries, electrolytic cells, and sensors with gas diffusion electrode structures. However, the disclosed preparation method does not use a pore-forming agent and only produces a single-layer microporous layer, therefore it does not have high porosity and a gradient pore size distribution. Furthermore, the use of the hydrophobic polymer PTFE does not improve low-humidity performance.

[0005] CN118057637A discloses a microporous layer and its preparation method. The preparation method includes: forming a slurry comprising a conductive material, a binder, a pore-forming agent, and a solvent; and coating the slurry onto a substrate surface, then calcining it at 60-350°C until the pore-forming agent is completely decomposed, followed by further calcination to obtain the microporous layer. However, the disclosed preparation method uses two binders, one a hydrophilic polymer and the other a hydrophobic polymer. These two types of polymers have significantly different hydrophilicity and hydrophobicity, and one of the binders cannot be completely dissolved in the solvent. This makes it difficult to uniformly disperse the binder in the slurry used to prepare the microporous layer, resulting in poor consistency of the prepared microporous layer and affecting its hydrophilicity / hydrophobicity and water management capabilities. Furthermore, neither binder added in this preparation method can adsorb metal ions, thus failing to prevent metal ions from entering the catalyst layer and failing to mitigate the adverse effects of metal ions entering the catalyst layer on battery performance.

[0006] CN106299398A discloses a method for preparing a bilayer microporous layer to improve fuel cell performance, comprising the following steps: preparing a first slurry with uniform composition by stirring a highly conductive material, a pore-forming agent, a hydrophobic agent, and a dispersion; coating the prepared first slurry onto hydrophobically treated carbon paper or carbon cloth by screen printing to form a first coating layer; spraying a second slurry of a predetermined thickness, composed of a highly conductive material, a hydrophobic agent, and a dispersion, onto the surface of the carbon paper or carbon cloth to form a second sprayed layer; and heat-treating the layer to give it a loose, porous, and hydrophilic / hydrophobic gas reaction channel. However, this preparation method only uses a hydrophobic agent, which cannot improve low-humidity performance or mitigate the adverse effects of metal ions entering the catalyst layer on battery performance.

[0007] Existing microporous layers all have certain defects, including insufficient gas-water transport performance, poor low-humidity performance, risk of flooding, and metal ion contamination, which lead to insufficient electrochemical performance of fuel cells. Therefore, it is crucial to develop and design a novel bilayer microporous layer for fuel cells, its preparation method, a gas diffusion layer, and the fuel cell itself. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a bilayer microporous layer for fuel cells, its preparation method, a gas diffusion layer, and a fuel cell. On one hand, the gradient porosity and gradient pore size of the first and second microporous layers optimize water-gas transport. On the other hand, both the first and second microporous layers contain benzene polymers with tertiary amine or sulfonic acid groups, whose hydrophilic and hydrophobic properties effectively regulate the humidity of the membrane electrode assembly (MEA). Furthermore, the benzene polymers with sulfonic acid groups can adsorb metal ions through ionic interactions, reducing metal ion contamination of the MEA. Therefore, the fuel cell containing the bilayer microporous layer exhibits excellent electrochemical performance.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a double-layer microporous layer for fuel cells, the double-layer microporous layer comprising a first microporous layer and a second microporous layer stacked together, wherein the porosity and average pore size of the first microporous layer are both greater than those of the second microporous layer.

[0011] Both the first and second microporous layers contain a conductive agent and a benzene polymer, wherein the benzene polymer has tertiary amine groups or sulfonic acid groups.

[0012] In the bilayer microporous layer provided by this invention, the porosity and average pore size of the first microporous layer are both greater than those of the second microporous layer. The first microporous layer (near the flow field) has higher porosity and larger pore size, which can reduce gas transport resistance and accelerate the discharge of reaction water. The second microporous layer (near the catalyst layer) has lower porosity and smaller pore size, which can closely adhere to the catalyst layer, reduce interfacial contact resistance, and block impurities. The combination of the first and second microporous layers provides a continuous electron transport channel while improving the gas transport and water management capabilities of the bilayer microporous layer, thereby enhancing the electrochemical performance of the fuel cell.

[0013] In the bilayer microporous layer provided by this invention, both the first and second microporous layers contain benzene polymers with tertiary amine groups or sulfonic acid groups. Benzene polymers with tertiary amine groups or sulfonic acid groups are selected as polymers to regulate the water management capability of the microporous layer. Because the benzene polymers have high thermal stability and high mechanical strength, and the benzene backbone is hydrophobic while the tertiary amine groups or sulfonic acid groups are hydrophilic, the humidity inside the membrane electrode can be effectively regulated, avoiding the problems of water flooding and poor low-humidity performance, thereby improving the overall performance of the fuel cell.

[0014] In the bilayer microporous layer provided by this invention, both the first and second microporous layers contain benzene polymers with sulfonic acid groups. Sulfonate ions dissociate from these benzene polymers, and these sulfonate ions interact electrostatically or coordinate with metal ions, thereby attracting or forming coordinate bonds with positively charged metal ions. Therefore, this bilayer microporous layer can adsorb metal ions (such as Cu) introduced from the external air or generated during the operation of the fuel cell stack. 2+ Fe 3+ Ce 3+ (etc.) In the membrane electrode, it acts as a barrier to prevent metal ion contamination, reducing the extent to which these metal ions enter the catalyst layer and damage the three-phase reaction interface during stack operation, thereby improving the stability of the fuel cell.

[0015] In summary, this invention optimizes water vapor transport by setting gradient porosity and gradient pore size between the first and second microporous layers. Furthermore, both the first and second microporous layers contain benzene polymers with tertiary amine or sulfonic acid groups, whose hydrophilic and hydrophobic properties effectively regulate the humidity of the membrane electrode. Additionally, the benzene polymers with sulfonic acid groups can adsorb metal ions through ion interactions, reducing metal ion contamination of the membrane electrode. Therefore, the fuel cell containing the aforementioned bilayer microporous layers exhibits excellent electrochemical performance.

[0016] Preferably, the benzene polymer has the general structural formula -[Ar-C m H 2m-2 N(R)-] n -or-[-Ar(SO3H)-] n - where Ar is aryl, R is methyl or ethyl, m is 4 or 5, n is the degree of polymerization, and the relative molecular mass M W The value ranges from 1 kg / mol to 200 kg / mol.

[0017] In this invention, the relative molecular mass M of the benzene polymer is... W The value is 1 kg / mol to 200 kg / mol, for example, it can be 1 kg / mol, 5 kg / mol, 10 kg / mol, 50 kg / mol, 100 kg / mol, 150 kg / mol or 200 kg / mol, but it is not limited to the listed values. Other unlisted values ​​within this range also apply.

[0018] Preferably, the mass ratio of the conductive agent to the benzene polymer in the first microporous layer is 1:(0.02~2.5), for example, it can be 1:0.02, 1:0.05, 1:0.1, 1:0.2, 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2 or 1:2.5, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0019] Preferably, the mass ratio of the conductive agent to the benzene polymer in the second microporous layer is 1:(0.02~2.5), for example, it can be 1:0.02, 1:0.05, 1:0.1, 1:0.2, 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2 or 1:2.5, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0020] Preferably, the porosity of the first microporous layer is 50%~70%, and the average pore size is 300nm~10μm.

[0021] In this invention, the porosity of the first microporous layer is 50% to 70%, for example, it can be 50%, 52%, 53%, 55%, 58%, 60%, 64%, 67% or 70%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] In this invention, the average pore size of the first microporous layer is 300nm~10μm, for example, it can be 300nm, 500nm, 650nm, 700nm, 900nm, 1μm, 2μm, 3μm, 5μm, 8μm or 10μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, the thickness of the first microporous layer is 30μm to 50μm, for example, it can be 30μm, 33μm, 40μm, 44μm, 48μm or 50μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, the surface contact angle of the first microporous layer is 100°~120° or 140°~160°, for example, it can be 100°, 105°, 110°, 120°, 140°, 150°, 156° or 160°, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Preferably, the porosity of the second microporous layer is 40%~50%, and the average pore size is 30nm~200nm.

[0026] In this invention, the porosity of the second microporous layer is 40% to 50%, for example, it can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49% or 50%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] In this invention, the average pore size of the second microporous layer is 30nm~200nm, for example, it can be 30nm, 35nm, 54nm, 78nm, 100nm, 148nm or 200nm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, the thickness of the second microporous layer is 15μm to 40μm, for example, it can be 15μm, 18μm, 23μm, 27μm, 34μm or 40μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, the surface contact angle of the second microporous layer is 90°~100° or 130°~140°, for example, it can be 90°, 95°, 100°, 130°, 136° or 140°, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, the conductive agent comprises a carbon material, which includes any one or a combination of at least two of graphite, conductive carbon black, or carbon nanotubes. Typical but non-limiting combinations include a combination of graphite and conductive carbon black, a combination of conductive carbon black and carbon nanotubes, a combination of graphite and carbon nanotubes, or a combination of graphite, conductive carbon black, and carbon nanotubes.

[0031] Preferably, the carbon material comprises solid carbon and / or porous carbon.

[0032] Preferably, the carbon material is in powder form.

[0033] In a second aspect, the present invention provides a method for preparing the bilayer microporous layer described in the first aspect, the method comprising:

[0034] (1) The first microporous layer was prepared by using a non-solvent phase separation method with conductive agent and benzene polymer as raw materials;

[0035] (2) Using conductive agent and benzene polymer as raw materials, a second microporous layer is prepared on the first microporous layer obtained in step (1) by non-solvent phase separation method;

[0036] In steps (1) and (2), by controlling the process conditions or the content of raw materials in the non-solvent phase separation method, the porosity and average pore size of the first microporous layer are both greater than those of the second microporous layer.

[0037] In steps (1) and (2), the benzene polymers each independently have tertiary amine groups or sulfonic acid groups.

[0038] In this invention, a non-solvent phase separation method is used to prepare a bilayer microporous layer. The polymer is dissolved in a main solvent, and a non-solvent that cannot dissolve the polymer but is miscible with the main solvent is used as a pore-forming agent. The process conditions or raw material content of the non-solvent phase separation method are controlled. During the drying process, the main solvent evaporates first, causing the polymer to gradually solidify into a film. The non-solvent then evaporates, forming secondary pores with a uniform pore size distribution. Ultimately, a bilayer microporous layer with gradient porosity and pore size distribution is obtained (the porosity and average pore size of the first microporous layer are both greater than those of the second microporous layer; the first microporous layer (near the flow field) has higher porosity and larger pore size, while the second microporous layer (near the catalyst layer) has lower porosity and smaller pore size). This improves the gas transport and water management capabilities of the membrane electrode, and helps ensure the orderly transport of gas and water.

[0039] Preferably, the method for preparing the benzene polymer having tertiary amine groups includes:

[0040] Aromatic methane compounds and / or aromatic biphenyl compounds are first mixed with ketone monomers containing tertiary amine groups, organic solvents, and acid catalysts to produce a first slurry; the first slurry is then diluted to obtain a diluted solution; the diluted solution is then mixed with an alkaline solution to obtain the benzene polymer containing tertiary amine groups.

[0041] Preferably, the first mixture comprises: initially mixing aromatic methane compounds and / or aromatic biphenyl compounds with ketone monomers containing tertiary amine groups to obtain a mixture; further mixing the obtained mixture with an organic solvent to obtain a mixed liquid; and finally mixing the obtained mixed liquid with an acid catalyst to undergo an acid-catalyzed polymerization reaction to obtain a first slurry.

[0042] Preferably, in the first mixture, the molar ratio of aromatic methane compounds and / or aromatic biphenyl compounds to ketone monomers containing tertiary amine groups is 1:(1~2).

[0043] In this invention, the molar ratio of aromatic methane compounds and / or aromatic biphenyl compounds to ketone monomers containing tertiary amine groups in the first mixture is 1:(1~2), for example, it can be 1:1, 1:1.2, 1:1.3, 1:1.35, 1:1.4, 1:1.5, 1:1.65, 1:1.8 or 1:2, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0044] Preferably, the method for preparing the benzene polymer having sulfonic acid groups includes:

[0045] Concentrated sulfuric acid is mixed with polyarylether ketone polymers or polysulfone polymers in a third process, followed by a sulfonation reaction to obtain a first slurry; the first slurry is then mixed with ice water in a fourth process to obtain the benzene polymer having sulfonic acid groups.

[0046] Preferably, the aromatic methane compound includes triphenylmethane and / or diphenylmethane.

[0047] Preferably, the aromatic biphenyl compounds include biphenyl and / or terphenyl.

[0048] Preferably, the ketone monomer containing a tertiary amine group includes any one or a combination of at least two of N-methyl-4-piperidinone, N-ethyl-4-piperidinone, 1-methyl-3-pyrrolidone, or 1-ethyl-3-pyrrolidone. Typical but non-limiting combinations include combinations of N-methyl-4-piperidinone and N-ethyl-4-piperidinone, combinations of 1-methyl-3-pyrrolidone and N-methyl-4-piperidinone, or combinations of N-methyl-4-piperidinone, N-ethyl-4-piperidinone, and 1-methyl-3-pyrrolidone, or combinations of N-ethyl-4-piperidinone, 1-methyl-3-pyrrolidone, and 1-ethyl-3-pyrrolidone.

[0049] Preferably, the organic solvent includes dichloromethane or tetrahydrofuran.

[0050] Preferably, the acid catalyst comprises trifluoroacetic acid and trifluoromethanesulfonic acid in a volume ratio of 1:(9~15), for example, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14 or 1:15, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0051] Preferably, the final mixing temperature is -5℃ to 5℃, and the time is 1h to 4h.

[0052] In this invention, the final mixing temperature is -5℃ to 5℃, for example, it can be -5℃, -4℃, -3℃, -2℃, -1℃, 0℃, 1℃, 2℃, 3℃, 4℃ or 5℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0053] In this invention, the final mixing time is 1h to 4h, for example, it can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h or 4h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0054] Preferably, the dilution includes adding a diluent to the resulting first slurry.

[0055] Preferably, the diluent includes any one of dimethyl sulfoxide, N-methylpyrrolidone, or N,N-dimethylacetamide.

[0056] Preferably, the second mixing time is 5h to 24h, and the second mixing process is accompanied by stirring.

[0057] In this invention, the time for the second mixing is 5h to 24h, for example, it can be 5h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0058] Preferably, the alkaline solution includes either sodium hydroxide solution or potassium hydroxide solution.

[0059] Preferably, the alkaline solution comprises a sodium hydroxide solution with a concentration of 0.5 mol / L to 3 mol / L, for example, it can be 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, 2.2 mol / L, 2.5 mol / L, 2.8 mol / L or 3.0 mol / L, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0060] Preferably, the second mixture is followed by sequential filtration, washing, and drying.

[0061] Preferably, the method for preparing the benzene polymer having sulfonic acid groups further includes filtration, washing, and drying sequentially after the fourth mixing.

[0062] Preferably, the polyaryletherketone polymer includes polyetheretherketone, polyaryletherketone, polyetherketone, or polyetherketoneketone.

[0063] Preferably, the polysulfone polymer includes polysulfone or polyethersulfone.

[0064] Preferably, the non-solvent-induced phase separation method in step (1) and step (2) each independently includes:

[0065] A benzene-based polymer, a main solvent, a non-solvent, and a conductive agent are mixed to obtain a slurry. The slurry is then coated and dried to obtain either a first microporous layer or a second microporous layer.

[0066] Preferably, the non-solvent-induced phase separation method in steps (1) and (2) independently includes: mixing a benzene polymer with a main solvent to obtain a first mixture; then mixing the first mixture with a non-solvent to obtain a second mixture; then mixing the second mixture with a conductive agent to obtain a mixed slurry; and then coating the obtained mixed slurry and drying it to obtain a first microporous layer or a second microporous layer, respectively.

[0067] Preferably, by controlling the content of benzene polymers and / or non-solvents used in the non-solvent phase separation method in steps (1) and (2), the content of benzene polymers in the raw materials in step (1) is less than the content of benzene polymers in the raw materials in step (2), and / or the content of non-solvents used in the non-solvent phase separation method in step (1) is greater than the content of non-solvents used in the non-solvent phase separation method in step (2), so that the porosity and average pore size of the obtained first microporous layer are both greater than those of the second microporous layer.

[0068] Preferably, in the non-solvent phase separation method described in step (1), the mass ratio of conductive agent, main solvent, non-solvent, and benzene polymer is 1:(25~150):(10~25):(0.02~2.5).

[0069] In this invention, in the non-solvent-induced phase separation method described in step (1), the mass ratio of the conductive agent to the main solvent is 1:(25~150), for example, it can be 1:25, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, 1:110, 1:120, 1:130, 1:140 or 1:150, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0070] In this invention, in the non-solvent phase separation method described in step (1), the mass ratio of the conductive agent to the non-solvent is 1:(10~25), for example, it can be 1:10, 1:12, 1:14, 1:16, 1:18, 1:20, 1:23 or 1:25, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0071] In this invention, in the non-solvent-induced phase separation method described in step (1), the mass ratio of the conductive agent to the benzene polymer is 1:(0.02~2.5), for example, it can be 1:0.02, 1:0.05, 1:0.1, 1:0.2, 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2 or 1:2.5, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0072] Preferably, in the non-solvent phase separation method described in step (2), the mass ratio of conductive agent, main solvent, non-solvent, and benzene polymer is 1:(25~150):(1~10):(0.02~2.5).

[0073] In this invention, in the non-solvent-induced phase separation method described in step (2), the mass ratio of the conductive agent to the main solvent is 1:(25~150), for example, it can be 1:25, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, 1:110, 1:120, 1:130, 1:140 or 1:150, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0074] In this invention, in the non-solvent phase separation method described in step (2), the mass ratio of the conductive agent to the non-solvent is 1:(1~10), for example, it can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0075] In this invention, in the non-solvent-induced phase separation method described in step (2), the mass ratio of the conductive agent to the benzene polymer is 1:(0.02~2.5), for example, it can be 1:0.02, 1:0.05, 1:0.1, 1:0.2, 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2 or 1:2.5, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0076] Preferably, in the non-solvent phase separation method described in steps (1) and (2), the high-boiling-point non-solvents used independently include N,N-dimethylformamide, diethyl phthalate, or dibutyl phthalate.

[0077] Preferably, in the non-solvent-induced phase separation method described in steps (1) and (2), the low-boiling-point main solvent used independently includes dichloromethane or trichloromethane.

[0078] Preferably, in the non-solvent phase separation method described in step (2), the obtained mixed slurry is coated onto the first microporous layer.

[0079] Preferably, in the non-solvent phase separation method described in steps (1) and (2), the coating method independently includes any one of spraying, blade coating, slot coating, or screen printing.

[0080] Preferably, in the non-solvent-induced phase separation method described in steps (1) and (2), the drying temperature is independently 20℃~45℃, for example, it can be 20℃, 25℃, 30℃, 35℃, 40℃ or 45℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0081] As a preferred embodiment of the preparation method of the present invention, the preparation method includes:

[0082] (I) Aromatic methane compounds and / or aromatic biphenyl compounds with a molar ratio of 1:(1~2) and ketone monomers containing tertiary amine groups are initially mixed to obtain a mixture; the obtained mixture is then mixed with an organic solvent to obtain a mixed liquid; the obtained mixed liquid is then subjected to a final mixing at -5℃~5℃ with an acid catalyst containing trifluoroacetic acid and trifluoromethanesulfonic acid in a volume ratio of 1:(9~15) for 1h~4h, and an acid-catalyzed polymerization reaction occurs to obtain the first slurry;

[0083] After adding a diluent to the first slurry, a diluted solution is obtained; the diluted solution is then mixed with a sodium hydroxide solution with a concentration of 0.5 mol / L to 3 mol / L for 5 h to 24 h, with stirring during the mixing process, and then filtered, washed and dried in sequence to obtain the benzene polymer with tertiary amine groups;

[0084] or

[0085] The polyarylether ketone polymer or polysulfone polymer is dried in an oven at 60℃~90℃ to obtain the dried polyarylether ketone polymer or polysulfone polymer; then 20mL~40mL of concentrated sulfuric acid is mixed with 1g~10g of the dried polyarylether ketone polymer or polysulfone polymer, and the mixture is reacted in an oil bath at 45~75℃ for 2h~10h to undergo a post-sulfonation reaction to obtain a first slurry; then the obtained first slurry is added to ice water with stirring for mixing, and then filtered, washed and dried in sequence to obtain the benzene polymer with sulfonic acid groups.

[0086] (II) The benzene polymer obtained in step (I) is mixed with the main solvent to obtain a first mixture; the first mixture is then mixed with a non-solvent to obtain a second mixture; the second mixture is then mixed with a conductive agent by stirring, grinding, shaking or ultrasonication to obtain a mixed slurry; the obtained mixed slurry is then coated by spraying, doctor blade coating, slot coating or screen printing, and then dried at 20℃~45℃ to obtain a first microporous layer;

[0087] In step (II), the benzene polymer has tertiary amine groups or sulfonic acid groups, and the mass ratio of the conductive agent, main solvent, non-solvent to benzene polymer is 1:(25~150):(10~25):(0.02~2.5).

[0088] (III) The benzene polymer obtained in step (I) is mixed with the main solvent to obtain a first mixture; the first mixture is then mixed with a non-solvent to obtain a second mixture; the second mixture is then mixed with a conductive agent by stirring, grinding, shaking or ultrasonication to obtain a mixed slurry; the obtained mixed slurry is then coated onto the first microporous layer obtained in step (II) by spraying, doctor blade coating, slot coating or screen printing, and then dried at 20℃~45℃ to obtain a second microporous layer;

[0089] In step (III), the benzene polymer has tertiary amine groups and sulfonic acid groups, and the mass ratio of conductive agent, main solvent, non-solvent, and benzene polymer is 1:(25~150):(1~10):(0.02~2.5).

[0090] By controlling the content of benzene polymers and / or non-solvents used in the non-solvent phase separation method in steps (1) and (2), the content of benzene polymers in the raw materials in step (1) is less than the content of benzene polymers in the raw materials in step (2), and / or the content of non-solvents used in the non-solvent phase separation method in step (1) is greater than the content of non-solvents used in the non-solvent phase separation method in step (2), the porosity and average pore size of the obtained first microporous layer are both greater than those of the second microporous layer.

[0091] In a second aspect, the present invention provides a gas diffusion layer comprising the bilayer microporous layer described in the first aspect.

[0092] Preferably, the gas diffusion layer includes a base layer and a double-layer microporous layer covering one side of the base layer.

[0093] Preferably, the substrate layer includes, but is not limited to, carbon paper; any layered microporous layer carrier that can be used to form a gas diffusion layer is applicable.

[0094] Preferably, the method for preparing the gas diffusion layer includes: preparing a bilayer microporous layer on a substrate layer using the preparation method provided by the present invention.

[0095] Thirdly, the present invention provides a fuel cell comprising the bilayer microporous layer described in the first aspect.

[0096] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0097] Compared with the prior art, the present invention has the following beneficial effects:

[0098] (1) In the double microporous layer provided by the present invention, the porosity and average pore size of the first microporous layer are both greater than those of the second microporous layer. The first microporous layer (near the flow field) has a higher porosity and a larger pore size, which can reduce gas transmission resistance and accelerate the discharge of reaction water. The second microporous layer (near the catalyst layer) has a lower porosity and a smaller pore size, which can closely adhere to the catalyst layer, reduce interfacial contact resistance, and block impurities. The combination of the first microporous layer and the second microporous layer provides a continuous electron transmission channel and improves the gas transmission and water management capabilities of the double microporous layer, thereby improving the electrochemical performance of the fuel cell.

[0099] (2) In the double-layer microporous layer provided by the present invention, both the first microporous layer and the second microporous layer contain benzene polymers with tertiary amine groups or sulfonic acid groups. Benzene polymers with tertiary amine groups or sulfonic acid groups are selected as polymers to regulate the water management ability of the microporous layer. Since the benzene polymers have high thermal stability and high mechanical strength, and the benzene main chain is hydrophobic and the tertiary amine groups or sulfonic acid groups are hydrophilic, the humidity inside the membrane electrode can be effectively regulated to avoid the problems of water flooding and poor low humidity performance, thereby improving the overall performance of the fuel cell.

[0100] (3) In the double-layer microporous layer provided by the present invention, both the first microporous layer and the second microporous layer contain benzene polymers with sulfonic acid groups. Sulfonate ions will dissociate from the benzene polymers with sulfonic acid groups. The sulfonate ions will interact electrostatically or coordinate with metal ions, thereby attracting each other or forming coordinate bonds with positively charged metal ions, thus firmly binding the metal ions. Therefore, the double-layer microporous layer can adsorb metal ions (such as Cu) introduced from the outside air or generated during the operation of the fuel cell stack. 2+ Fe 3+ Ce 3+ (etc.) act as a barrier in the membrane electrode to prevent metal ion contamination, reducing the extent to which these metal ions enter the catalyst layer and damage the three-phase reaction interface during stack operation, thereby improving the stability of the fuel cell.

[0101] (4) In this invention, on the one hand, the water vapor transport is optimized by setting the gradient porosity and gradient pore size of the first microporous layer and the second microporous layer; on the other hand, both the first microporous layer and the second microporous layer contain benzene polymers with tertiary amine groups or sulfonic acid groups, whose hydrophilic and hydrophobic properties not only effectively regulate the humidity of the membrane electrode; in addition, benzene polymers with sulfonic acid groups can also adsorb metal ions through ion interaction to reduce the contamination of the membrane electrode by metal ions; therefore, the fuel cell containing the double microporous layer exhibits excellent electrochemical performance. Attached Figure Description

[0102] Figure 1 The polarization curves of the fuel cell containing the double microporous layer in Example 1 under different humidity environments are shown.

[0103] Figure 2 This is a comparison graph of the polarization curves of fuel cells containing the microporous layers in Example 1 and Comparative Example 3 at 100% RH.

[0104] Figure 3 This is a comparison graph of the polarization curves of fuel cells containing the microporous layers in Example 1 and Comparative Example 3 at 50% RH.

[0105] Figure 4 This is a comparison graph of the polarization curves of fuel cells containing the microporous layers in Example 1 and Comparative Example 3 at 20% RH. Detailed Implementation

[0106] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0107] Example 1

[0108] This embodiment provides a double-layer microporous layer for fuel cells, the double-layer microporous layer comprising a first microporous layer and a second microporous layer stacked together, wherein the porosity and average pore size of the first microporous layer are both greater than those of the second microporous layer.

[0109] The first microporous layer has a porosity of 55%, an average pore size of 1 μm, a thickness of 40 μm, and a surface contact angle of 150°.

[0110] The second microporous layer has a porosity of 45%, an average pore size of 100 nm, a thickness of 25 μm, and a surface contact angle of 135°.

[0111] Both the first and second microporous layers contain a conductive agent (carbon black, Vulcan XC-72, with an average particle size of approximately 30 nm) and a benzene polymer.

[0112] The benzene polymer has a tertiary amine group; the structural formula of the benzene polymer is -[Ar-C m H 2m-2 N(R)-] n - where Ar is aryl, R is methyl, m is 5, n is the degree of polymerization, and the relative molecular mass M W The value is 10 kg / mol to 30 kg / mol.

[0113] The mass ratio of the conductive agent to the benzene polymer in the first microporous layer is 1:1; the mass ratio of the conductive agent to the benzene polymer in the second microporous layer is 1:1.

[0114] The method for preparing the bilayer microporous layer is as follows:

[0115] (I) The mass ratio of aromatic methane compound (triphenylmethane) and aromatic biphenyl compound (biphenyl) is controlled at 0.2:2.5, and the molar ratio of the total molar amount of triphenylmethane and biphenyl to the molar amount of ketone monomer (N-methyl-4-piperidinone) containing tertiary amine group is controlled at 1:1.5. The aromatic methane compound (triphenylmethane), aromatic biphenyl compound (biphenyl), and ketone monomer (N-methyl-4-piperidinone) containing tertiary amine group are initially mixed to obtain a mixture. The obtained mixture is then mixed with an organic solvent (dichloromethane) to obtain a mixed liquid. The obtained mixed liquid is then subjected to a final mixing at 0°C with an acid catalyst containing trifluoroacetic acid and trifluoromethanesulfonic acid in a volume ratio of 1:10 for 2 hours to undergo an acid-catalyzed polymerization reaction to obtain the first slurry.

[0116] Diluent (dimethyl sulfoxide) was added to the first slurry to obtain a diluted solution. The diluted solution was then mixed with a 2 mol / L sodium hydroxide solution for 20 h with stirring during the mixing process. The mixture was then filtered, washed and dried in sequence to obtain the benzene polymer with tertiary amine groups.

[0117] (II) The benzene polymer obtained in step (I) is mixed with the main solvent (dichloromethane) to obtain a first mixture; the first mixture is then mixed with a non-solvent (N,N-dimethylformamide) to obtain a second mixture; the second mixture is then mixed with a conductive agent (carbon black, Vulcan XC-72, with an average particle size of approximately 30 nm) by stirring to obtain a mixed slurry; the obtained mixed slurry is then coated by a doctor blade and dried at 25°C to obtain a first microporous layer;

[0118] In step (II), the benzene polymer has tertiary amine groups, and the mass ratio of the conductive agent, main solvent, non-solvent to benzene polymer is 1:70:15:1;

[0119] (III) The benzene polymer obtained in step (I) is mixed with the main solvent (dichloromethane) to obtain a first mixture; the first mixture is then mixed with a non-solvent (N,N-dimethylformamide) to obtain a second mixture; the second mixture is then mixed with a conductive agent (carbon black, Vulcan XC-72, with an average particle size of about 30 nm) by ultrasonication to obtain a mixed slurry; the obtained mixed slurry is then coated onto the first microporous layer obtained in step (II) by screen printing, and then dried at 25°C to obtain a second microporous layer;

[0120] In step (III), the benzene polymer has tertiary amine groups, and the mass ratio of the conductive agent, main solvent, non-solvent, and benzene polymer is 1:70:5:1.

[0121] By controlling the content of the non-solvent used in the non-solvent phase separation method in step (II) to be greater than the content of the non-solvent used in the non-solvent phase separation method in step (III), the porosity and average pore size of the obtained first microporous layer are both greater than those of the second microporous layer.

[0122] Example 2

[0123] This embodiment provides a double-layer microporous layer for fuel cells, the double-layer microporous layer comprising a first microporous layer and a second microporous layer stacked together, wherein the porosity and average pore size of the first microporous layer are both greater than those of the second microporous layer.

[0124] The first microporous layer has a porosity of 50%, an average pore size of 500 nm, a thickness of 50 μm, and a surface contact angle of 120°.

[0125] The second microporous layer has a porosity of 40%, an average pore size of 30 nm, a thickness of 15 μm, and a surface contact angle of 100°.

[0126] Both the first and second microporous layers contain a conductive agent (powdered conductive carbon black) and a benzene polymer;

[0127] The benzene polymer has a tertiary amine group; the general structural formula of the benzene polymer is -[Ar-C]. m H 2m-2 N(R)-] n - where Ar is aryl, R is ethyl, m is 5, n is the degree of polymerization, and the relative molecular mass M W The value is 100 kg / mol to 120 kg / mol.

[0128] The mass ratio of the conductive agent to the benzene polymer in the first microporous layer is 1:2; the mass ratio of the conductive agent to the benzene polymer in the second microporous layer is 1:2.

[0129] The method for preparing the bilayer microporous layer is as follows:

[0130] (I) An aromatic biphenyl compound (biphenyl) and a ketone monomer (N-ethyl-4-piperidinone) with a tertiary amine group were initially mixed in a molar ratio of 1:1 to obtain a mixture; the obtained mixture was then mixed with an organic solvent (chloroform) to obtain a mixed liquid; the obtained mixed liquid was then subjected to a final mixing at -5°C with an acid catalyst containing trifluoroacetic acid and trifluoromethanesulfonic acid in a volume ratio of 1:15 for 4 hours to undergo an acid-catalyzed polymerization reaction to obtain the first slurry;

[0131] After adding a diluent (N-methylpyrrolidone) to the first slurry, a diluted solution is obtained. The diluted solution is then mixed with a 0.5 mol / L sodium hydroxide solution for 24 hours with stirring during the mixing process. The mixture is then filtered, washed, and dried sequentially to obtain the benzene polymer with tertiary amine groups.

[0132] (II) The benzene polymer obtained in step (I) is mixed with the main solvent (dichloromethane) to obtain a first mixture; the first mixture is then mixed with a non-solvent (N,N-dimethylformamide) to obtain a second mixture; the second mixture is then mixed with a conductive agent (powdered conductive carbon black) by stirring to obtain a mixed slurry; the obtained mixed slurry is then coated by a doctor blade and dried at 25°C to obtain a first microporous layer;

[0133] In step (II), the benzene polymer has tertiary amine groups, and the mass ratio of the conductive agent, main solvent, non-solvent to benzene polymer is 1:25:10:2;

[0134] (III) The benzene polymer obtained in step (I) is mixed with the main solvent (dichloromethane) to obtain a first mixture; the first mixture is then mixed with a non-solvent (N,N-dimethylformamide) to obtain a second mixture; the second mixture is then mixed with a conductive agent (powdered conductive carbon black) by stirring to obtain a mixed slurry; the obtained mixed slurry is then coated onto the first microporous layer obtained in step (II) by a doctor blade coating, and then dried at 25°C to obtain a second microporous layer;

[0135] In step (III), the benzene polymer has tertiary amine groups, and the mass ratio of the conductive agent, main solvent, non-solvent, and benzene polymer is 1:25:1:2;

[0136] By controlling the content of the non-solvent used in the non-solvent phase separation method in step (II) to be greater than the content of the non-solvent used in the non-solvent phase separation method in step (III), the porosity and average pore size of the obtained first microporous layer are both greater than those of the second microporous layer.

[0137] Example 3

[0138] This embodiment provides a double-layer microporous layer for fuel cells, the double-layer microporous layer comprising a first microporous layer and a second microporous layer stacked together, wherein the porosity and average pore size of the first microporous layer are both greater than those of the second microporous layer.

[0139] The first microporous layer has a porosity of 60%, an average pore size of 2 μm, a thickness of 30 μm, and a surface contact angle of 160°.

[0140] The second microporous layer has a porosity of 50%, an average pore size of 200 nm, a thickness of 20 μm, and a surface contact angle of 140°.

[0141] Both the first and second microporous layers contain a conductive agent (carbon black, Vulcan XC-72, with an average particle size of approximately 30 nm) and a benzene polymer.

[0142] The benzene-based polymer has sulfonic acid groups; the general structural formula of the benzene-based polymer is -[-Ar(SO3H)-]. n - where Ar is aryl, n is the degree of polymerization, and the relative molecular mass M W The value is 100 kg / mol to 150 kg / mol.

[0143] The mass ratio of conductive agent to benzene polymer in the first microporous layer is 1:0.2; the mass ratio of conductive agent to benzene polymer in the second microporous layer is 1:0.8.

[0144] The method for preparing the bilayer microporous layer is as follows:

[0145] (I) The polyaryletherketone polymer (polyetheretherketone) was dried in an oven at 75°C to obtain the dried polyaryletherketone polymer (polyetheretherketone); 30 mL of concentrated sulfuric acid was mixed with 6 g of the dried polyaryletherketone polymer (polyetheretherketone) and reacted in an oil bath at 60°C for 6 h to undergo a post-sulfonation reaction to obtain the first slurry; the first slurry was then added to ice water with stirring for mixing, and then filtered, washed and dried in sequence to obtain the benzene polymer with sulfonic acid groups;

[0146] (II) The benzene polymer obtained in step (I) is mixed with the main solvent (chloroform) to obtain a first mixture; the first mixture is then mixed with a non-solvent (diethyl phthalate) to obtain a second mixture; the second mixture is then mixed with a conductive agent (carbon black, Vulcan XC-72, with an average particle size of approximately 30 nm) by stirring to obtain a mixed slurry; the obtained mixed slurry is then coated by a doctor blade and dried at 40°C to obtain a first microporous layer;

[0147] In step (II), the benzene polymer has sulfonic acid groups, and the mass ratio of the conductive agent, main solvent, non-solvent to benzene polymer is 1:150:20:0.2;

[0148] (III) The benzene polymer obtained in step (I) is mixed with the main solvent (trichloromethane) to obtain a first mixture; the first mixture is then mixed with a non-solvent (diethyl phthalate) to obtain a second mixture; the second mixture is then mixed with a conductive agent (carbon black, Vulcan XC-72, with an average particle size of about 30 nm) by stirring to obtain a mixed slurry; the obtained mixed slurry is then coated onto the first microporous layer obtained in step (II) by a doctor blade coating, and then dried at 40°C to obtain a second microporous layer;

[0149] In step (III), the benzene polymer has sulfonic acid groups, and the mass ratio of the conductive agent, main solvent, non-solvent, and benzene polymer is 1:150:10:0.8.

[0150] By controlling the content of benzene polymers used in the non-solvent phase separation method in step (II) to be less than the content of benzene polymers used in the non-solvent phase separation method in step (III); and controlling the content of non-solvents used in the non-solvent phase separation method in step (II) to be greater than the content of non-solvents used in the non-solvent phase separation method in step (III), the porosity and average pore size of the obtained first microporous layer are both greater than those of the second microporous layer.

[0151] Example 4

[0152] This embodiment provides a double-layer microporous layer for fuel cells, except that the mass ratio of conductive agent to benzene polymer in the first microporous layer is 1:0.01;

[0153] In step (II) of the method for preparing the double-layer microporous layer, the mass ratio of the conductive agent to the benzene polymer is 1:0.01, and all other steps are the same as in Example 1.

[0154] Example 5

[0155] This embodiment provides a bilayer microporous layer for fuel cells, except that the mass ratio of conductive agent to benzene polymer in the first microporous layer is 1:3;

[0156] In step (II) of the method for preparing the double-layer microporous layer, the mass ratio of the conductive agent to the benzene polymer is 1:3, and all other steps are the same as in Example 1.

[0157] Example 6

[0158] This embodiment provides a double-layer microporous layer for fuel cells, except that the mass ratio of conductive agent to benzene polymer in the second microporous layer is 1:0.01;

[0159] In step (III) of the method for preparing the double-layer microporous layer, the mass ratio of the conductive agent to the benzene polymer is 1:0.01, and all other steps are the same as in Example 1.

[0160] Example 7

[0161] This embodiment provides a bilayer microporous layer for fuel cells, except that the mass ratio of conductive agent to benzene polymer in the second microporous layer is 1:3;

[0162] In step (III) of the method for preparing the double-layer microporous layer, the mass ratio of the conductive agent to the benzene polymer is 1:3, and all other steps are the same as in Example 1.

[0163] Example 8

[0164] This embodiment provides a bilayer microporous layer for fuel cells, wherein the first microporous layer has a porosity of 47% and an average pore size of 200 nm.

[0165] That is, except for the mass ratio of conductive agent to non-solvent in step (II) of the method for preparing the double-layer microporous layer, which is 1:7, all other steps are the same as in Example 1.

[0166] Example 9

[0167] This embodiment provides a double-layer microporous layer for fuel cells, wherein the first microporous layer has a porosity of 80% and an average pore size of 18 μm.

[0168] Except for the mass ratio of conductive agent to non-solvent of 1:33 in step (II) of the method for preparing the double-layer microporous layer, all other steps are the same as in Example 1.

[0169] Example 10

[0170] This embodiment provides a bilayer microporous layer for fuel cells, wherein the second microporous layer has a porosity of 35% and an average pore size of 10 nm.

[0171] Except for the mass ratio of conductive agent to non-solvent of 1:0.2 in step (III) of the method for preparing the double-layer microporous layer, all other steps are the same as in Example 1.

[0172] Example 11

[0173] This embodiment provides a bilayer microporous layer for fuel cells, wherein the second microporous layer has a porosity of 53% and an average pore size of 800 nm.

[0174] Except for the mass ratio of conductive agent to non-solvent of 1:13 in step (III) of the method for preparing the double-layer microporous layer, all other steps are the same as in Example 1.

[0175] Comparative Example 1

[0176] This comparative example provides a microporous layer for a fuel cell, except that the second microporous layer is omitted and the thickness of the first microporous layer is the same as the total thickness of the double-layer microporous layer in Example 1.

[0177] That is, the amount of raw materials used in step (II) of the method for preparing the double-layer microporous layer is increased proportionally, and step (III) of the method for preparing the double-layer microporous layer is omitted, except that the rest are the same as in Example 1.

[0178] Comparative Example 2

[0179] This comparative example provides a bilayer microporous layer for fuel cells, except that the benzene polymer does not contain tertiary amine groups or sulfonic acid groups; the benzene polymer is polystyrene with the structural formula -[-CH2-CH(C6H5)-]. n -;

[0180] That is, step (I) of the method for preparing the double-layer microporous layer is omitted, and except for replacing the benzene polymer with tertiary amine groups or sulfonic acid groups in steps (II) and (III) of the method for preparing the double-layer microporous layer with benzene polymers without tertiary amine groups or sulfonic acid groups, the rest is the same as in Example 1.

[0181] Comparative Example 3

[0182] This comparative example provides a single-layer microporous layer for fuel cells. Except that the benzene polymer is replaced with a polytetrafluoroethylene dispersion, the single-layer microporous layer is prepared using conventional methods and not using a non-solvent phase separation method.

[0183] Specific experimental steps: Weigh a certain amount of XC-72R toner, add 1 wt% PTFE dispersion (prepared by dilution with water and isopropanol) at 350 times the mass of the toner to it to prepare a uniformly dispersed microporous layer slurry; scrape the microporous layer slurry onto the surface of the substrate layer, dry it at 70℃ for 15 min, and then calcine it at 370℃ for 3 h in a nitrogen protective atmosphere. After cooling, the microporous layer is obtained.

[0184] Comparative Example 4

[0185] This comparative example provides a bilayer microporous layer for fuel cells. Except that the benzene polymer is replaced with polytetrafluoroethylene, the bilayer microporous layer is prepared by conventional methods and is not prepared by non-solvent phase separation. The first microporous layer (near the flow field) is loaded on the substrate layer, and the second microporous layer (near the catalyst layer) is loaded on the first microporous layer.

[0186] That is, the mass of the PTFE dispersion in the first microporous layer is 300 times the mass of the toner, the mass of the PTFE dispersion in the second microporous layer is 400 times the mass of the toner, and the rest are the same as in Comparative Example 3.

[0187] On the substrate layer, using the preparation methods provided in the above embodiments and comparative examples, a double-layer microporous layer and a microporous layer provided in the above embodiments and comparative examples are prepared. Then, a three-in-one CCM composed of a cathode catalyst layer and an anode catalyst layer coated on both sides of the PEM is sandwiched between the double-layer microporous layer or the microporous layer on both sides of the cathode and anode to obtain a membrane electrode assembly. The assembled membrane electrode assembly is aligned with a graphite bipolar plate with flow channels and a sealing gasket. Subsequently, a current collector, an insulating plate, and an end plate are stacked and uniformly tightened with bolts to ensure sealing, thus obtaining a fuel cell single cell.

[0188] The electrochemical performance of the single cell was then tested in environments of 100%RH, 50%RH and 20%RH respectively.

[0189] The single-cell performance test conditions are as follows: The single-cell operating temperature is set to 70℃, the gas pressure to 70KPa, and H2 (2.4L / min) and air (9.6L / min) are introduced. The polarization curve of the single cell is tested while maintaining inlet air humidity at 100%RH, 50%RH, and 20%RH, respectively, with a current density of 1.0A / cm². 2 The corresponding polarization voltages are shown in Table 1; the voltage decay values ​​at 50% RH and 20% RH are calculated and shown in Table 2; among them, the polarization curves of the single cell including the double-layer microporous layer in Example 1 under different humidity environments are shown in Table 2. Figure 1 As shown; the polarization curves of a single cell containing the microporous layer of Example 1 and a single cell containing the microporous layer of Comparative Example 3 in environments of 100%RH, 50%RH, and 20%RH are compared as shown in the figures. Figure 2 , Figure 3 and Figure 4 As shown.

[0190] Table 1

[0191]

[0192] Table 2

[0193]

[0194] From Table 1 and Table 2, we can obtain:

[0195] (1) The fuel cell containing the double-layer microporous layer provided by the present invention has an efficiency of 1.0 A / cm in environments of 100%RH, 50%RH, and 20%RH. 2 The corresponding polarization voltage is higher, and the voltage decay value is lower.

[0196] (3) By comparing Examples 1 with Examples 4-7, it can be seen that in this invention, the mass ratio of the conductive agent to the benzene polymer in the first and second microporous layers affects the electrochemical performance of the fuel cell. When the mass ratio of the conductive agent to the benzene polymer in the first and second microporous layers is 1:(0.02~2.5), the fuel cell has better electrochemical performance. This is because, within this mass ratio range, the conductive agent ensures efficient electron conduction, while the benzene polymer provides suitable hydrophilic and hydrophobic properties, effectively regulating the water-air balance and avoiding excessive moisture or dryness of the membrane electrode. At the same time, the functional groups in the polymer (such as sulfonic acid groups) can fully adsorb metal ions, reducing pollution. When the mass ratio of the conductive agent to the benzene polymer is too high, the polymer content is insufficient, and the water management and ion adsorption effects are weak. When the mass ratio of the conductive agent to the benzene polymer is too low, the conductivity decreases, affecting electron transport.

[0197] (4) By comparing Example 1 with Examples 8 and 9, it can be seen that the porosity and average pore size of the first microporous layer will affect the electrochemical performance of the fuel cell. That is, the content of non-solvent during the preparation of the first microporous layer will affect the electrochemical performance of the fuel cell. When the mass ratio of conductive agent to non-solvent is 1:(10~25) in step (II), the fuel cell has better electrochemical performance. This is because the porosity of the first microporous layer can reach 50%~70%, and the average pore size can reach 300nm~10μm. The higher porosity and larger average pore size can collect and discharge the liquid water in the second microporous layer smoothly, and at the same time reduce the transmission resistance of the reaction gas.

[0198] (4) By comparing Example 1 with Examples 10 and 11, it can be seen that the porosity and average pore size of the second microporous layer will affect the electrochemical performance of the fuel cell. That is, the content of non-solvent during the preparation of the second microporous layer will affect the electrochemical performance of the fuel cell. When the mass ratio of conductive agent to non-solvent is 1:(1~10) in step (III), the fuel cell has better electrochemical performance. This is because the porosity of the second microporous layer can reach 40%~50%, and the average pore size can reach 30nm~200nm. The lower porosity and smaller average pore size have more uniform water distribution and stronger capillary suction, which can efficiently discharge water in the catalyst layer to the first microporous layer. At the same time, it has a smoother surface, reduces the contact resistance with the catalyst layer, and improves conductivity.

[0199] (5) As can be seen from the comparison between Example 1 and Comparative Examples 1 to 4, in the bilayer microporous layer prepared by the non-solvent phase separation method provided by the present invention, the porosity and average pore size of the first microporous layer are both greater than those of the second microporous layer. The first microporous layer (near the flow field) has higher porosity and larger pore size, which can reduce gas transmission resistance and accelerate the discharge of reaction water. The second microporous layer (near the catalyst layer) has lower porosity and smaller pore size, which can closely adhere to the catalyst layer, reduce interfacial contact resistance, and block impurities. The combination of the first microporous layer and the second microporous layer provides a continuous electron transmission channel and improves the gas transmission and water management capabilities of the bilayer microporous layer, thereby improving the electrochemical performance of the fuel cell.

[0200] In the bilayer microporous layer provided by the present invention, both the first microporous layer and the second microporous layer contain benzene polymers with tertiary amine groups or sulfonic acid groups. Benzene polymers with tertiary amine groups or sulfonic acid groups are selected as polymers to regulate the water management capability of the microporous layer. Since the benzene polymers have high thermal stability and high mechanical strength, and the benzene main chain is hydrophobic while the tertiary amine groups or sulfonic acid groups are hydrophilic, the humidity inside the membrane electrode can be effectively regulated, avoiding the problems of water flooding and poor low-humidity performance, thereby improving the overall performance of the fuel cell.

[0201] In the bilayer microporous layer provided by this invention, both the first and second microporous layers contain benzene polymers with tertiary amine groups or sulfonic acid groups. Sulfonate ions dissociate from the benzene polymers with sulfonic acid groups. These sulfonate ions interact electrostatically or coordinate with metal ions, attracting or forming coordinate bonds with the positively charged metal ions, thus firmly binding them. Therefore, this bilayer microporous layer can adsorb metal ions (such as Cu) introduced from the external air or generated during the operation of the fuel cell stack. 2+ Fe 3+ Ce 3+ (etc.) act as a barrier in the membrane electrode to prevent metal ion contamination, reducing the extent to which these metal ions enter the catalyst layer and damage the three-phase reaction interface during stack operation, thereby improving the stability of the fuel cell.

[0202] In this invention, on the one hand, the gradient porosity and gradient pore size of the first and second microporous layers optimize water vapor transport; on the other hand, both the first and second microporous layers contain benzene polymers with tertiary amine groups or sulfonic acid groups, whose hydrophilic and hydrophobic properties not only effectively regulate the humidity of the membrane electrode; in addition, the benzene polymers with sulfonic acid groups can also adsorb metal ions through ion interaction to reduce the contamination of the membrane electrode by metal ions; therefore, the fuel cell containing the double microporous layers exhibits excellent electrochemical performance.

[0203] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A bi-layer microporous layer for a fuel cell, characterized by, The double-layer microporous layer includes a first microporous layer and a second microporous layer stacked together, wherein the porosity and average pore size of the first microporous layer are both greater than those of the second microporous layer. The porosity of the first microporous layer is 50%~70%, and the average pore size is 300nm~10μm; The porosity of the second microporous layer is 40%~50%, and the average pore size is 30nm~200nm; Both the first and second microporous layers contain a conductive agent and a benzene polymer, wherein the benzene polymer has tertiary amine groups or sulfonic acid groups.

2. The dual-layer microporous layer of claim 1, wherein The general structure of the benzene polymer is -[Ar-C m H 2m-2 N(R)-] n - or -[-Ar(SO3H)-] n - wherein Ar is an aromatic group, R is a methyl or ethyl group, m is 4 or 5, n is the degree of polymerization, the relative molecular mass M W is 1 kg / mol ~ 200 kg / mol; And / or, the mass ratio of the conductive agent to the benzene polymer in the first microporous layer is 1:(0.02~2.5); And / or, the mass ratio of the conductive agent to the benzene polymer in the second microporous layer is 1:(0.02~2.5).

3. The dual-layer microporous layer of claim 1, wherein The thickness of the first microporous layer is 30μm~50μm; And / or, the surface contact angle of the first microporous layer is 100°~120° or 140°~160°; And / or, the thickness of the second microporous layer is 15 μm to 40 μm; And / or, the surface contact angle of the second microporous layer is 90°~100° or 130°~140°; And / or, the conductive agent comprises a carbon material, which comprises any one or a combination of at least two of graphite, conductive carbon black, or carbon nanotubes, and the carbon material comprises solid carbon and / or porous carbon.

4. A method for producing the double-layer microporous layer according to any one of claims 1 to 3, characterized by The preparation method includes: (1) The first microporous layer was prepared by using a non-solvent phase separation method with conductive agent and benzene polymer as raw materials; (2) Using conductive agent and benzene polymer as raw materials, a second microporous layer is prepared on the first microporous layer obtained in step (1) by non-solvent phase separation method; In steps (1) and (2), by controlling the process conditions or the content of raw materials in the non-solvent phase separation method, the porosity and average pore size of the first microporous layer are both greater than those of the second microporous layer. In steps (1) and (2), the benzene polymers each independently have tertiary amine groups or sulfonic acid groups.

5. The preparation method according to claim 4, characterized in that, The method for preparing the benzene polymer having tertiary amine groups includes: Aromatic methane compounds and / or aromatic biphenyl compounds are first mixed with ketone monomers containing tertiary amine groups, organic solvents, and acid catalysts to produce a first slurry; the first slurry is then diluted to obtain a diluted solution; the diluted solution is then mixed with an alkaline solution to obtain the benzene polymer containing tertiary amine groups. The first mixture comprises: initially mixing aromatic methane compounds and / or aromatic biphenyl compounds with ketone monomers containing tertiary amine groups to obtain a mixture; further mixing the obtained mixture with an organic solvent to obtain a liquid mixture; and finally mixing the obtained liquid mixture with an acid catalyst to undergo an acid-catalyzed polymerization reaction to obtain a first slurry. In the first mixture, the molar ratio of aromatic methane compounds and / or aromatic biphenyl compounds to ketone monomers containing tertiary amine groups is 1:(1~2); And / or, a method for preparing the benzene polymer having sulfonic acid groups includes: Concentrated sulfuric acid is mixed with polyarylether ketone polymers or polysulfone polymers in a third process, followed by a sulfonation reaction to obtain a first slurry; the first slurry is then mixed with ice water in a fourth process to obtain the benzene polymer having sulfonic acid groups.

6. The preparation method according to claim 5, characterized in that, The aromatic methane compounds include triphenylmethane and / or diphenylmethane; And / or, the aromatic biphenyl compounds include biphenyls and / or terphenyls; And / or, the ketone monomers containing tertiary amine groups include any one or a combination of at least two of N-methyl-4-piperidinone, N-ethyl-4-piperidinone, 1-methyl-3-pyrrolidone or 1-ethyl-3-pyrrolidone; And / or, the method for preparing the benzene polymer having sulfonic acid groups further includes sequential filtration, washing and drying after the fourth mixing; And / or, the polyaryletherketone polymers include polyetheretherketone, polyaryletherketone, polyetherketone, or polyetherketoneketone; And / or, the polysulfone polymer includes polysulfone or polyethersulfone.

7. The preparation method according to claim 4, characterized in that, The non-solvent-induced phase separation method described in steps (1) and (2) each independently includes: A benzene-based polymer, a main solvent, a non-solvent, and a conductive agent are mixed to obtain a slurry. The slurry is then coated and dried to obtain either a first microporous layer or a second microporous layer. And / or, by controlling the content of benzene polymers and / or non-solvents used in the non-solvent phase separation method in steps (1) and (2), the content of benzene polymers in the raw materials in step (1) is less than the content of benzene polymers in the raw materials in step (2), and / or the content of non-solvents used in the non-solvent phase separation method in step (1) is greater than the content of non-solvents used in the non-solvent phase separation method in step (2), so that the porosity and average pore size of the obtained first microporous layer are both greater than those of the second microporous layer.

8. The preparation method according to claim 7, characterized in that, In the non-solvent phase separation method described in step (1), the mass ratio of the conductive agent to the non-solvent is 1:(10~25); And / or, in the non-solvent phase separation method described in step (2), the mass ratio of the conductive agent to the non-solvent is 1:(1~10); And / or, in the non-solvent phase separation method described in step (1), the mass ratio of conductive agent, main solvent, non-solvent, and benzene polymer is 1:(25~150):(10~25):(0.02~2.5); And / or, in the non-solvent phase separation method described in step (2), the mass ratio of conductive agent, main solvent, non-solvent, and benzene polymer is 1:(25~150):(1~10):(0.02~2.5); And / or, in the non-solvent phase separation method described in steps (1) and (2), the non-solvents used independently include N,N-dimethylformamide, diethyl phthalate or dibutyl phthalate; And / or, in the non-solvent phase separation method described in steps (1) and (2), the main solvent used independently includes dichloromethane or trichloromethane; And / or, in the non-solvent phase separation method described in steps (1) and (2), the coating method independently includes any one of spraying, blade coating, slot coating or screen printing; And / or, in the non-solvent phase separation method described in steps (1) and (2), the drying temperature is independently 20℃~45℃.

9. A gas diffusion layer, characterized by, The gas diffusion layer comprises the bilayer microporous layer as described in any one of claims 1 to 3.

10. A fuel cell characterized by comprising: The fuel cell includes the gas diffusion layer as described in claim 9.

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