Double-layer microporous layer for fuel cell, preparation method of double-layer microporous layer, gas diffusion layer and fuel cell

Abstract

The invention provides a double-layer microporous layer for a fuel cell, a preparation method of the double-layer microporous layer, a gas diffusion layer and the fuel cell, the double-layer microporous layer comprises a first microporous layer and a second microporous layer which are stacked, and the porosity and the average aperture of the first microporous layer are greater than those of the second microporous layer; each of the first microporous layer and the second microporous layer comprises a conductive agent and a benzene polymer, and the benzene polymer has a tertiary amine group or a sulfonic acid group. According to the invention, on one hand, through setting of gradient porosity and gradient aperture of the first microporous layer and the second microporous layer, water and gas transmission is optimized; on the other hand, the first microporous layer and the second microporous layer both contain benzene polymers with tertiary amine groups or sulfonic acid groups, and the hydrophilic and hydrophobic characteristics of the benzene polymers effectively adjust the humidity of the membrane electrode; in addition, the benzene polymer with the sulfonic acid group can adsorb metal ions through the ion action to reduce the pollution of the metal ions to the membrane electrode; therefore, the fuel cell comprising the double microporous layers shows excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of fuel cells, and relates to a double-layer microporous layer for a fuel cell, in particular to a double-layer microporous layer for a fuel cell, a preparation method thereof, a gas diffusion layer and a fuel cell. BACKGROUND

[0002] Fuel cells have a broad development prospect in the fields of transportation, standby power supply and distributed power station due to high energy conversion efficiency, low emission and no pollution. A membrane electrode assembly (MEA) is a core component of a fuel cell, is a place where an electrochemical reaction of the fuel cell occurs, and its performance directly determines whether the fuel cell is applied or not. The MEA is usually composed 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, and has a microporous layer (MPL) attached thereto. The microporous layer mainly functions to drain water, ventilate and enhance the electron transmission capacity, and therefore must have a suitable pore structure to ensure the transmission of gas and water and prevent water flooding.

[0003] At present, a mainstream preparation method of the microporous layer is to mix conductive carbon black and a hydrophobic agent (PTFE) uniformly, apply the mixture to the surface of a hydrophobic treated support layer (such as carbon paper, carbon cloth or carbon felt), and then obtain the microporous layer after high-temperature baking. The electron transmission channel of the microporous layer prepared in this way is discontinuous, and the porosity and pore size distribution are difficult to control, which affects the transmission of electrons, gas and water, and leads to the decline of the performance of the fuel cell.

[0004] CN101325259A discloses a preparation method of a gas diffusion layer for a proton exchange membrane fuel cell. The polytetrafluoroethylene (PTFE) in the gas diffusion layer is uniformly dispersed, and the diffusion layer has relatively low electronic resistance and gas mass transfer resistance. The preparation method is as follows: the microporous layer slurry is mixed with carbon powder by using a low-boiling point organic solvent which is easy to wet the carbon powder, and a fluorine surfactant is added into the PTFE water dispersion before the PTFE water dispersion is added; then the microporous layer slurry is uniformly dispersed on the support layer of the diffusion layer, and the gas diffusion layer is formed by heat treatment. The gas diffusion layer prepared by this method can be applied to cells, electrolytic cells and sensors with a gas diffusion electrode structure. However, the preparation method disclosed in the patent does not use a pore-forming agent, and is only a single-layer microporous layer, and therefore does not have high porosity and gradient pore size distribution; in addition, the hydrophobic polymer PTFE cannot improve the low humidity performance.

[0005] CN118057637A discloses a microporous layer and a preparation method thereof, the preparation method comprising: forming a slurry, the slurry comprising a conductive material, a binder, a pore-forming agent and a solvent; and after coating the slurry on the surface of a substrate, baking at 60-350 DEG C until the pore-forming agent is completely decomposed, and then continuing to bake to obtain the microporous layer. However, two binders are used in the disclosed preparation method, one is a hydrophilic polymer and the other is a hydrophobic polymer. The difference between the two types of polymers is large, and one of the binders cannot be completely dissolved in the solvent, which is difficult to disperse uniformly in the preparation of the microporous layer slurry. Therefore, the consistency of the prepared microporous layer is poor, which affects the hydrophilic and hydrophobic properties and water management capability of the microporous layer. In addition, neither of the two binders added in the preparation method can adsorb metal ions, cannot prevent metal ions from entering the catalyst layer, and cannot improve the adverse effects of metal ions entering the catalyst layer on the performance of the battery.

[0006] CN106299398A discloses a preparation method of a double-layer microporous layer for improving the performance of a fuel cell, comprising the following steps: preparing a first slurry with uniform composition by stirring high-conductivity material, pore-forming agent, hydrophobic agent and dispersing liquid; coating the prepared first slurry on a hydrophobic-treated carbon paper or carbon cloth by screen printing to form a first coating layer; spraying a second slurry composed of high-conductivity material, hydrophobic agent and dispersing liquid on the surface of the carbon paper or carbon cloth to form a second spraying layer by spraying; and making it have a loose and porous gas reaction channel with hydrophilic and hydrophobic properties by heat treatment. However, the preparation method only uses a hydrophobic agent and cannot improve the low humidity performance, nor can it improve the adverse effects of metal ions entering the catalyst layer on the performance of the battery.

[0007] The microporous layers disclosed in the prior art have certain defects, such as insufficient gas and water transport performance, poor low humidity performance, risk of water flooding, and metal ion pollution, which leads to insufficient electrochemical performance of the fuel cell. Therefore, it is crucial to develop a new type of double-layer microporous layer for fuel cells, a preparation method thereof, a gas diffusion layer and a fuel cell. SUMMARY

[0008] In view of the deficiencies in the prior art, the purpose of the present application is to provide a double-layer microporous layer for fuel cells, a preparation method thereof, a gas diffusion layer and a fuel cell. On the one hand, the gradient porosity and gradient pore size of the first microporous layer and the second microporous layer optimize the water and gas transport. On the other hand, the first microporous layer and the second microporous layer both contain benzene polymers with tertiary amine groups or sulfonic acid groups, which effectively adjust the humidity of the membrane electrode. In addition, the benzene polymers with sulfonic acid groups can also adsorb metal ions through ionic action to reduce the pollution of metal ions to the membrane electrode. Therefore, the fuel cell containing the double-layer microporous layer exhibits excellent electrochemical performance.

[0009] To achieve the above object, the present application adopts the following technical solutions:

[0010] In a first aspect, the present application provides a double-layer microporous layer for a fuel cell, which comprises a first microporous layer and a second microporous layer stacked together, the first microporous layer having a porosity and an average pore size both greater than those of the second microporous layer.

[0011] Both the first microporous layer and the second microporous layer comprise an electrically conductive agent and a benzene-based polymer having a tertiary amine group or a sulfonic acid group.

[0012] In the double-layer microporous layer provided by the present application, the first microporous layer has a higher porosity and a larger average pore size than the second microporous layer, which can reduce the gas transmission resistance and accelerate the removal of reaction water; the second microporous layer has a lower porosity and a smaller average pore size, which can closely adhere to the catalyst layer, reduce the interfacial contact resistance, and block impurities; the combination of the first microporous layer and the second microporous layer not only provides a continuous electron transmission channel, but also improves the gas transmission and water management capabilities of the double-layer microporous layer, thereby improving the electrochemical performance of the fuel cell.

[0013] In the double-layer microporous layer provided by the present application, both the first microporous layer and the second microporous layer comprise a benzene-based polymer having a tertiary amine group or a sulfonic acid group. The benzene-based polymer with a tertiary amine group or a sulfonic acid group is selected as the polymer for adjusting the water management capability of the microporous layer. Since the benzene-based polymer has high thermal stability and high mechanical strength, and the benzene backbone has hydrophobicity and the tertiary amine group or the sulfonic acid group has hydrophilicity, it can effectively adjust the humidity in the membrane electrode, avoid water flooding and poor performance under low humidity, and thereby improve the overall performance of the fuel cell.

[0014] In the double-layer microporous layer provided by the present application, both the first microporous layer and the second microporous layer comprise a benzene-based polymer having a sulfonic acid group. The benzene-based polymer with a sulfonic acid group can dissociate sulfonate ions, which can interact electrostatically or coordinately with metal ions, thereby attracting or forming coordination bonds with positively charged metal ions. Therefore, the double-layer microporous layer can adsorb metal ions (such as Cu 2+ , Fe 3+ , Ce 3+ , etc.) introduced from the outside air or generated during the operation of the fuel cell, thereby playing a barrier role in preventing metal ion pollution in the membrane electrode, reducing the extent of the entry of these metal ions into the catalyst layer during the operation of the fuel cell to destroy the three-phase reaction interface, and thereby improving the stability of the fuel cell.

[0015] In summary, in the present application, on one hand, the gradient porosity and the gradient pore size of the first microporous layer and the second microporous layer optimize the water vapor transmission; on the other hand, the first microporous layer and the second microporous layer both contain benzene polymers with tertiary amine groups or sulfonic acid groups, and the hydrophilic and hydrophobic properties of the benzene polymers effectively adjust the humidity of the membrane electrode; in addition, the benzene polymers with sulfonic acid groups can also adsorb metal ions through ionic action to reduce the pollution of metal ions to the membrane electrode; therefore, the fuel cell containing the double-layer microporous layer exhibits excellent electrochemical performance.

[0016] Preferably, the benzene polymer has a general structure of -[Ar-C m H 2m-2 N(R)-] n - or -[-Ar(SO3H)-] n - wherein Ar is an aryl group, R is a methyl group or an ethyl group, m is 4 or 5, n is a polymerization degree, the relative molecular mass M W is 1 kg / mol~200 kg / mol.

[0017] In the present application, the benzene polymer has a relative molecular mass M W of 1 kg / mol~200 kg / mol, for example, 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 is not limited to the listed values, and other values not listed in this range are also applicable.

[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, 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 is not limited to the listed values, and other values not listed in 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, 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 is not limited to the listed values, and other values not listed in this range are also applicable.

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

[0021] In the present application, 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 not limited to the listed values, other values not listed in the range are also applicable.

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

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

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

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

[0026] In the present application, 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 not limited to the listed values, other values not listed in the range are also applicable.

[0027] In the present application, the average pore size of the second microporous layer is 30 nm to 200 nm, for example, it can be 30 nm, 35 nm, 54 nm, 78 nm, 100 nm, 148 nm or 200 nm, but not limited to the listed values, other values not listed in the range are also applicable.

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

[0030] Preferably, 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 a typical but non-limiting combination includes 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 the form of a powder.

[0033] In a second aspect, the present application provides a method for preparing the double-layer microporous layer of the first aspect, the method comprising:

[0034] (1) using a non-solvent phase separation method to prepare a first microporous layer from a conductive agent and a benzene-based polymer as raw materials;

[0035] (2) using a non-solvent phase separation method to prepare a second microporous layer on the first microporous layer obtained in step (1) from a conductive agent and a benzene-based polymer as raw materials;

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

[0037] In steps (1) and (2), the benzene-based polymer independently has a tertiary amine group or a sulfonic acid group, respectively.

[0038] In the present application, a double-layer microporous layer is prepared by a non-solvent phase separation method, i.e., the polymer is dissolved in a main solvent, a non-solvent that cannot dissolve the polymer and is miscible with the main solvent is used as a pore-forming agent, and the process conditions or the content of raw materials of the non-solvent phase separation method are controlled; in the drying process, the main solvent is first volatilized to gradually solidify the polymer into a film, and the non-solvent is then volatilized to form a uniform pore size distribution of secondary pores, and finally a double-layer microporous layer with a gradient porosity and a pore size gradient 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 a higher porosity and a larger pore size, and the second microporous layer (near the catalyst layer) has a lower porosity and a smaller pore size, which improves the gas transmission and water management capability of the membrane electrode, and is conducive to ensuring the orderly transmission of gas and water.

[0039] Preferably, the method for preparing the benzene polymer with tertiary amine groups comprises:

[0040] The aromatic methane compound and / or the aromatic diphenyl compound are mixed with the ketone monomer containing tertiary amine groups, an organic solvent and an acid catalyst to obtain a first slurry through a reaction; the obtained first slurry is diluted to obtain a diluted solution; and the obtained diluted solution is mixed with an alkaline solution to obtain the benzene polymer with tertiary amine groups.

[0041] Preferably, the first mixing comprises: mixing the aromatic methane compound and / or the aromatic diphenyl compound with the ketone monomer containing tertiary amine groups to obtain a mixture; mixing the obtained mixture with the organic solvent to obtain a mixed solution; and mixing the obtained mixed solution with the acid catalyst to obtain the first slurry through an acid-catalyzed polymerization reaction.

[0042] Preferably, in the first mixing, the molar ratio of the aromatic methane compound and / or the aromatic diphenyl compound to the ketone monomer containing tertiary amine groups is 1:(1-2).

[0043] In the present application, in the first mixing, the molar ratio of the aromatic methane compound and / or the aromatic diphenyl compound to the ketone monomer containing tertiary amine groups 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, and other values not listed in the range are also applicable.

[0044] Preferably, the method for preparing the benzene polymer with sulfonic acid groups comprises:

[0045] The concentrated sulfuric acid is mixed with the polyaryletherketone polymer or the polysulfone polymer to obtain a first slurry through a post-sulfonation reaction; and the obtained first slurry is mixed with ice water to obtain the benzene polymer with sulfonic acid groups.

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

[0047] Preferably, the aromatic diphenyl compound comprises biphenyl and / or terphenyl.

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

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

[0050] Preferably, the component of the acid catalyst includes trifluoroacetic acid and triflic acid in a volume ratio of 1:(9~15), such as 1:9, 1:10, 1:11, 1:12, 1:13, 1:14 or 1:15, but not limited to the listed values, and other values not listed in the range are also applicable.

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

[0052] In the present application, the temperature of the final mixing is -5℃~5℃, such as -5℃, -4℃, -3℃, -2℃, -1℃, 0℃, 1℃, 2℃, 3℃, 4℃ or 5℃, but not limited to the listed values, and other values not listed in the range are also applicable.

[0053] In the present application, the time of the final mixing is 1h~4h, such as 1h, 1.5h, 2h, 2.5h, 3h, 3.5h or 4h, but not limited to the listed values, and other values not listed in the range are also applicable.

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

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

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

[0057] In the present application, the time of the second mixing is 5h~24h, such as 5h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h, but not limited to the listed values, and other values not listed in the range are also applicable.

[0058] Preferably, the basic solution comprises any one of sodium hydroxide solution or potassium hydroxide solution.

[0059] Preferably, the basic solution comprises 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 not limited to the listed values, other values not listed in the range are also applicable.

[0060] Preferably, the second mixing solution is followed by filtration, washing and drying in sequence.

[0061] Preferably, the method for preparing the benzene-based polymer with sulfonic acid group further comprises filtration, washing and drying in sequence after the fourth mixing.

[0062] Preferably, the polyaryletherketone-based polymer comprises polyether ether ketone, polyaryletherketone, polyether ketone or polyether ketone ketone.

[0063] Preferably, the polysulfone-based polymer comprises polysulfone or polyether sulfone.

[0064] Preferably, the non-solvent induced phase separation method of step (1) and step (2) respectively independently comprises:

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

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

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

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

[0069] In the present application, in the non-solvent induced phase separation method of step (1), the mass ratio of the conductive agent and 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, and other values not listed in this range are also applicable.

[0070] In the present application, in the non-solvent induced phase separation method of step (1), the mass ratio of the conductive agent and 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, and other values not listed in this range are also applicable.

[0071] In the present application, in the non-solvent induced phase separation method of step (1), the mass ratio of the conductive agent and the benzene-based 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, and other values not listed in this range are also applicable.

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

[0073] In the present application, in the non-solvent induced phase separation method of step (2), the mass ratio of the conductive agent and 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, and other values not listed in this range are also applicable.

[0074] In the present application, the mass ratio of the conductive agent to the non-solvent in the non-solvent induced phase separation method of step (2) 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 not limited to the listed values, other values not listed in this range are also applicable.

[0075] In the present application, the mass ratio of the conductive agent to the benzene-based polymer in the non-solvent induced phase separation method of step (2) 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 not limited to the listed values, other values not listed in this range are also applicable.

[0076] Preferably, the high-boiling non-solvent used in the non-solvent induced phase separation method of step (1) and step (2) respectively independently includes N,N-dimethylformamide, diethyl phthalate or dibutyl phthalate.

[0077] Preferably, the low-boiling primary solvent used in the non-solvent induced phase separation method of step (1) and step (2) respectively independently includes dichloromethane or trichloromethane.

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

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

[0080] Preferably, the drying temperature used in the non-solvent induced phase separation method of step (1) and step (2) respectively independently is 20-45°C, for example, it can be 20°C, 25°C, 30°C, 35°C, 40°C or 45°C, but not limited to the listed values, other values not listed in this range are also applicable.

[0081] As a preferred technical solution of the preparation method of the present application, the preparation method comprises:

[0082] (I) mixing aromatic methane compound and / or aromatic biphenyl compound with tertiary amine group-containing ketone monomer in a molar ratio of 1:(1-2) to obtain a mixture; mixing the obtained mixture with an organic solvent to obtain a mixed solution; and then mixing the obtained mixed solution with an acid catalyst containing trifluoroacetic acid and triflic acid in a volume ratio of 1:(9-15) at -5-5°C for 1-4h to obtain a first slurry by acid catalytic polymerization;

[0083] After adding a diluent to the obtained first slurry, a diluted solution is obtained; mixing the obtained diluted solution with a sodium hydroxide solution with a concentration of 0.5-3 mol / L for 5-24h with stirring, and then sequentially performing filtration, washing and drying to obtain the benzene polymer with a tertiary amine group;

[0084] Or

[0085] The polyaryletherketone polymer or polysulfone polymer is dried in an oven at 60-90°C to obtain a dried polyaryletherketone polymer or polysulfone polymer; 20-40 mL of concentrated sulfuric acid is mixed with 1-10 g of the dried polyaryletherketone polymer or polysulfone polymer, and the mixture is reacted in an oil bath at 45-75°C for 2-10h to undergo post-sulfonation to obtain a first slurry; the obtained first slurry is mixed with ice water with stirring, and then sequentially performing filtration, washing and drying to obtain the benzene polymer with a sulfonic acid group;

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

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

[0088] (III) mixing the benzene polymer obtained in step (I) with a main solvent to obtain a first mixture; mixing the first mixture with a non-solvent to obtain a second mixture; mixing the second mixture with a conductive agent by stirring, grinding, shaking or ultrasonic to obtain a mixed slurry; and then coating the obtained mixed slurry on the first microporous layer obtained in step (II) by spraying, doctor blade coating, slot coating or screen printing, and then drying at 20-45°C to obtain a second microporous layer.

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

[0090] By controlling the content of the benzene-based polymer and / or the non-solvent used in the non-solvent induced phase separation method in step (1) and step (2), the content of the benzene-based polymer in the raw material in step (1) is less than that in step (2), and / or the content of the non-solvent used in the non-solvent induced phase separation method in step (1) is greater than that in step (2), so that the porosity and the average pore size of the first microporous layer are both greater than those of the second microporous layer.

[0091] In a second aspect, the present application provides a gas diffusion layer, which comprises the double-layer microporous layer of the first aspect.

[0092] Preferably, the gas diffusion layer comprises a substrate layer, and the double-layer microporous layer is covered on one side of the substrate layer.

[0093] Preferably, the substrate layer comprises but is not limited to carbon paper, and 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 comprises preparing the double-layer microporous layer on the substrate layer by the preparation method provided by the present application.

[0095] In a third aspect, the present application provides a fuel cell, which comprises the double-layer microporous layer of the first aspect.

[0096] The numerical ranges of the present application include not only the point values recited above, but also any numerical values between the recited point values, which are not specifically recited. Due to the length and for the sake of simplicity, the present application does not list all the specific point values included in the ranges.

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

[0098] (1) The double-layer microporous layer provided by the present application, the porosity and average pore diameter of the first microporous layer are both larger than those of the second microporous layer, the first microporous layer (near the flow field) has a higher porosity and a larger pore diameter, which can reduce the 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 diameter, which can closely adhere to the catalyst layer, reduce the interface contact resistance, and also block impurities; the cooperation of the first microporous layer and the second microporous layer not only provides a continuous electron transmission channel, but also improves the gas transmission and water management capability of the double-layer microporous layer, thereby improving the electrochemical performance of the fuel cell;

[0099] (2) In the double-layer microporous layer provided by the present application, the first microporous layer and the second microporous layer both contain benzene polymers with tertiary amine groups or sulfonic acid groups, and the benzene polymers with tertiary amine groups or sulfonic acid groups are selected as the polymers for adjusting 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 has hydrophobicity and the tertiary amine groups or sulfonic acid groups have hydrophilicity, the humidity in the membrane electrode can be effectively adjusted to avoid water flooding and poor performance under low humidity, thereby improving the overall performance of the fuel cell.

[0100] (3) In the double-layer microporous layer provided by the present application, the first microporous layer and the second microporous layer both contain benzene polymers with sulfonic acid groups. The benzene polymers with sulfonic acid groups can dissociate sulfonic acid ions, which can interact with metal ions through electrostatic interaction or coordination, thereby attracting metal ions with positive charges or forming coordination bonds, so as to firmly bind the metal ions. Therefore, the double-layer microporous layer can adsorb metal ions (such as Cu 2+ , Fe 3+ , Ce 3+ , etc.) introduced from the outside air or generated during the operation of the stack, thereby playing a barrier role in preventing metal ion pollution in the membrane electrode, reducing the degree of damage to the three-phase reaction interface caused by these metal ions entering the catalyst layer during the operation of the stack, and thereby improving the stability of the fuel cell.

[0101] (4) In the present application, on the one hand, the gradient porosity and gradient pore diameter of the first microporous layer and the second microporous layer are set to optimize water and gas transmission; on the other hand, the first microporous layer and the second microporous layer both contain benzene polymers with tertiary amine groups or sulfonic acid groups, which have hydrophilic and hydrophobic properties, effectively adjusting the humidity of the membrane electrode; in addition, the benzene polymers with sulfonic acid groups can also adsorb metal ions through ionic interaction to reduce the pollution of metal ions to the membrane electrode; therefore, the fuel cell containing the double-layer microporous layer exhibits excellent electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS

[0102] Figure 1 is the polarization curve of the fuel cell containing the double-layer microporous layer in Example 1 in different humidity environments.

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

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

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

[0106] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0107] Example 1

[0108] The present embodiment provides a double-layer microporous layer for a fuel cell, which comprises a first microporous layer and a second microporous layer arranged in a stack, the porosity and average pore diameter of the first microporous layer are both greater than those of the second microporous layer.

[0109] The porosity of the first microporous layer is 55%, the average pore diameter is 1 μm, the thickness is 40 μm, and the surface contact angle is 150°.

[0110] The porosity of the second microporous layer is 45%, the average pore diameter is 100 nm, the thickness is 25 μm, and the surface contact angle is 135°.

[0111] Both the first microporous layer and the second microporous layer contain a conductive agent (carbon black, Vulcan XC-72, average particle size about 30 nm) and a benzene-based polymer.

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

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

[0114] The preparation method of the double-layer microporous layer is as follows:

[0115] (I) Controlling the mass ratio of aromatic methane compound (triphenylmethane) and aromatic biphenyl compound (biphenyl) to be 0.2:2.5, and making the ratio of the total mole of triphenylmethane and biphenyl to the mole of ketone monomer containing tertiary amine group (N-methyl-4-piperidone) to be 1:1.5, initially mixing aromatic methane compound (triphenylmethane), aromatic biphenyl compound (biphenyl) and ketone monomer containing tertiary amine group (N-methyl-4-piperidone) to obtain a mixture; re-mixing the obtained mixture with organic solvent (dichloromethane) to obtain a mixed solution; and finally mixing the obtained mixed solution with acid catalyst containing trifluoroacetic acid and triflic acid in a volume ratio of 1:10 at 0℃ for 2h to carry out acid catalytic polymerization to obtain a first slurry;

[0116] After adding diluent (dimethyl sulfoxide) into the obtained first slurry to obtain a diluted solution, mixing the obtained diluted solution with sodium hydroxide solution with a concentration of 2mol / L for 20h, and carrying out filtration, washing and drying in sequence, the benzene polymer with tertiary amine group is obtained.

[0117] (II) Mixing the benzene polymer with tertiary amine group obtained in step (I) with main solvent (dichloromethane) to obtain a first mixture; mixing the first mixture with non-solvent (N,N-dimethylformamide) to obtain a second mixture; mixing the second mixture with conductive agent (carbon black, Vulcan XC-72, with an average particle size of about 30nm) by stirring to obtain a mixed slurry; coating the obtained mixed slurry by doctor blade coating, and drying at 25℃ to obtain a first microporous layer.

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

[0119] (III) Mixing the benzene polymer with tertiary amine group obtained in step (I) with main solvent (dichloromethane) to obtain a first mixture; mixing the first mixture with non-solvent (N,N-dimethylformamide) to obtain a second mixture; mixing the second mixture with conductive agent (carbon black, Vulcan XC-72, with an average particle size of about 30nm) by ultrasonic to obtain a mixed slurry; coating the obtained mixed slurry on the first microporous layer obtained in step (II) by silk screen printing, and drying at 25℃ to obtain a second microporous layer.

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

[0121] The content of the non-solvent used in the non-solvent induced phase separation method of step (II) is greater than the content of the non-solvent used in the non-solvent induced phase separation method of step (III), so that the porosity and average pore size of the first microporous layer are both greater than those of the second microporous layer.

[0122] Embodiment 2

[0123] The embodiment provides a double-layer microporous layer for a fuel cell, which comprises a first microporous layer and a second microporous layer arranged in a stack, and the porosity and average pore size of the first microporous layer are both greater than those of the second microporous layer.

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

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

[0126] The first microporous layer and the second microporous layer both comprise an electrically conductive agent (powdery electrically conductive carbon black) and a benzene-based polymer.

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

[0128] The mass ratio of the electrically conductive agent to the benzene-based polymer in the first microporous layer is 1:2, and the mass ratio of the electrically conductive agent to the benzene-based polymer in the second microporous layer is 1:2.

[0129] The preparation method of the double-layer microporous layer is as follows:

[0130] (I) mixing an aromatic biphenyl compound (biphenyl) and a ketone monomer containing a tertiary amine group (N-ethyl-4-piperidone) in a molar ratio of 1:1 to obtain a mixture; mixing the obtained mixture with an organic solvent (chloroform) to obtain a mixed solution; and finally mixing the obtained mixed solution with an acid catalyst containing trifluoroacetic acid and triflic acid in a volume ratio of 1:15 at -5 ℃ for 4 h to cause an acid-catalyzed polymerization reaction, thereby obtaining a first slurry;

[0131] After adding diluent (N-methyl pyrrolidone) into the obtained first slurry, a diluted solution is obtained; after mixing the obtained diluted solution with 0.5 mol / L sodium hydroxide solution for 24 hours, the mixing process is accompanied by stirring, and then filtering, washing and drying are sequentially performed, the benzene-based polymer with tertiary amine groups is obtained;

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

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

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

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

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

[0137] Example 3

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

[0139] The porosity of the first microporous layer is 60%, the average pore size is 2 μm, the thickness is 30 μm, and the surface contact angle is 160°;

[0140] The porosity of the second microporous layer is 50%, the average pore size is 200 nm, the thickness is 20 μm, and the surface contact angle is 140°;

[0141] The first microporous layer and the second microporous layer both comprise a conductive agent (carbon black, Vulcan XC-72, with an average particle size of about 30 nm) and a benzene-based polymer;

[0142] The benzene-based polymer has a sulfonic acid group; the benzene-based polymer has a general structure of -[-Ar(SO3H)-] n , wherein Ar is an aryl group, n is a polymerization degree, and the relative molecular mass M W is 100 kg / mol to 150 kg / mol;

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

[0144] The preparation method of the double-layer microporous layer is as follows:

[0145] (I) Dry the polyaryletherketone polymer (polyether ether ketone) in an oven at 75°C to obtain a dried polyaryletherketone polymer (polyether ether ketone); then mix 30 mL of concentrated sulfuric acid with 6 g of the dried polyaryletherketone polymer (polyether ether ketone), and react in an oil bath at 60°C for 6 h to undergo a post-sulfonation reaction, thereby obtaining a first slurry; then mix the obtained first slurry with ice water with stirring, and then sequentially perform filtration, washing, and drying to obtain the benzene-based polymer with a sulfonic acid group;

[0146] (II) Mix the benzene-based polymer obtained in step (I) with a main solvent (trichloromethane) to obtain a first mixture; then mix the first mixture with a non-solvent (diethyl phthalate) to obtain a second mixture; then mix the second mixture 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; then coat the obtained mixed slurry by doctor blade coating, and then dry at 40°C to obtain the first microporous layer;

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

[0148] (III) mixing the benzene polymer obtained in step (I) with a main solvent (chloroform) to obtain a first mixture; mixing the first mixture with a non-solvent (diethyl phthalate) to obtain a second mixture; mixing the second mixture with a conductive agent (carbon black, Vulcan XC-72, average particle size about 30 nm) by stirring to obtain a mixed slurry; coating the obtained mixed slurry on the first microporous layer obtained in step (II) by doctor blade coating, and drying 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, the main solvent, the non-solvent, and the benzene polymer is 1:150:10:0.8.

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

[0151] Example 4

[0152] The present embodiment provides a double-layer microporous layer for a fuel cell, wherein the mass ratio of the conductive agent to the benzene polymer in the first microporous layer is 1:0.01.

[0153] That is, in step (II) of the preparation method of the double-layer microporous layer, the mass ratio of the conductive agent to the benzene polymer is 1:0.01, and the rest are the same as in Example 1.

[0154] Example 5

[0155] The present embodiment provides a double-layer microporous layer for a fuel cell, wherein the mass ratio of the conductive agent to the benzene polymer in the first microporous layer is 1:3.

[0156] That is, in step (II) of the preparation method of the double-layer microporous layer, the mass ratio of the conductive agent to the benzene polymer is 1:3, and the rest are the same as in Example 1.

[0157] Example 6

[0158] The present embodiment provides a double-layer microporous layer for a fuel cell, wherein the mass ratio of the conductive agent to the benzene polymer in the second microporous layer is 1:0.01.

[0159] That is, in step (III) of the preparation method of the double-layer microporous layer, the mass ratio of the conductive agent to the benzene polymer is 1:0.01, and the rest are the same as in Example 1.

[0160] Example 7

[0161] The present example provides a double-layer microporous layer for a fuel cell, wherein the mass ratio of the conductive agent to the benzene-based polymer in the second microporous layer is 1:3;

[0162] That is, in step (III) of the preparation method of the double-layer microporous layer, the mass ratio of the conductive agent to the benzene-based polymer is 1:3, and the rest is the same as in Example 1.

[0163] Example 8

[0164] The present example provides a double-layer microporous layer for a fuel cell, wherein the porosity of the first microporous layer is 47%, and the average pore size is 200 nm;

[0165] That is, in step (II) of the preparation method of the double-layer microporous layer, the mass ratio of the conductive agent to the non-solvent is 1:7, and the rest is the same as in Example 1.

[0166] Example 9

[0167] The present example provides a double-layer microporous layer for a fuel cell, wherein the porosity of the first microporous layer is 80%, and the average pore size is 18 μm;

[0168] That is, in step (II) of the preparation method of the double-layer microporous layer, the mass ratio of the conductive agent to the non-solvent is 1:33, and the rest is the same as in Example 1.

[0169] Example 10

[0170] The present example provides a double-layer microporous layer for a fuel cell, wherein the porosity of the second microporous layer is 35%, and the average pore size is 10 nm;

[0171] That is, in step (III) of the preparation method of the double-layer microporous layer, the mass ratio of the conductive agent to the non-solvent is 1:0.2, and the rest is the same as in Example 1.

[0172] Example 11

[0173] The present example provides a double-layer microporous layer for a fuel cell, wherein the porosity of the second microporous layer is 53%, and the average pore size is 800 nm;

[0174] That is, in step (III) of the preparation method of the double-layer microporous layer, the mass ratio of the conductive agent to the non-solvent is 1:13, and the rest is the same as in Example 1.

[0175] Comparative Example 1

[0176] The present comparative example provides a microporous layer for a fuel cell, wherein 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] The present comparative example provides a microporous layer for a fuel cell, wherein the amount of raw material in step (II) of the preparation method of the double-layer microporous layer is increased, and step (III) of the preparation method of the double-layer microporous layer is omitted, and the rest is the same as Example 1.

[0178] Comparative Example 2

[0179] The present comparative example provides a double-layer microporous layer for a fuel cell, wherein the benzene-based polymer does not contain a tertiary amine group or a sulfonic acid group; the benzene-based polymer is polystyrene, and the structural formula is -[-CH2-CH(C6H5)-] n -;

[0180] The present comparative example provides a double-layer microporous layer for a fuel cell, wherein step (I) of the preparation method of the double-layer microporous layer is omitted, and the benzene-based polymer with a tertiary amine group or a sulfonic acid group in steps (II) and (III) of the preparation method of the double-layer microporous layer is replaced by a benzene-based polymer that does not contain a tertiary amine group or a sulfonic acid group, and the rest is the same as Example 1.

[0181] Comparative Example 3

[0182] The present comparative example provides a single-layer microporous layer for a fuel cell, wherein the benzene-based polymer is replaced by a polytetrafluoroethylene dispersion, and the single-layer microporous layer is prepared by a conventional preparation method, not by a non-solvent phase separation method.

[0183] Specific experimental steps: a certain amount of XC-72R carbon powder is weighed, and a PTFE dispersion with a mass fraction of 1wt% (diluted with water and isopropyl alcohol) is added to the carbon powder at 350 times the mass of the carbon powder to prepare a uniformly dispersed microporous layer slurry; the microporous layer slurry is coated on the surface of the substrate layer, dried at 70°C for 15min, and then calcined at 370°C for 3h in a nitrogen protective atmosphere, and the microporous layer is obtained after cooling.

[0184] Comparative Example 4

[0185] The present comparative example provides a double-layer microporous layer for a fuel cell, wherein the benzene-based polymer is replaced by polytetrafluoroethylene, and the double-layer microporous layer is prepared by a conventional preparation method, not by a non-solvent phase separation method, and 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 of the first microporous layer is 300 times the mass of the carbon powder, and the mass of the PTFE dispersion of the second microporous layer is 400 times the mass of the carbon powder, and the rest is the same as Comparative Example 3.

[0187] The three-in-one CCM composed of the cathode catalytic layer and the anode catalytic 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 the anode to obtain a membrane electrode; the assembled membrane electrode assembly is aligned with a graphite bipolar plate with a flow channel and a sealing gasket; then, a current collector plate, an insulating plate and an end plate are stacked, and are uniformly fastened by bolts to ensure the sealing property, thereby obtaining a fuel cell single cell.

[0188] The single cell is subjected to electrochemical performance test in an environment with 100% RH, 50% RH and 20% RH, respectively.

[0189] The single cell performance test conditions are as follows: the single cell working temperature is set to 70 ℃, the gas pressure is set to 70 KPa, H2 (2.4 L / min) and air (9.6 L / min) are introduced, the inlet gas humidity is maintained at 100% RH, 50% RH and 20% RH, respectively, the polarization curve of the single cell is tested, and the current density is 1.0 A / cm 2 The corresponding polarization voltage under 1.0 A / cm Figure 1 is shown in Table 1; the voltage decay value at 50% RH and the voltage decay value at 20% RH are obtained by calculation and are shown in Table 2; the polarization curve of the single cell containing the double-layer microporous layer in Example 1 in different humidity environments is shown in Figure 2 , Figure 3 and Figure 4 .

[0190] Table 1

[0191]

[0192] Table 2

[0193]

[0194] From Table 1 and Table 2, it can be obtained that:

[0195] (1) The fuel cell containing the double-layer microporous layer provided by the application has higher corresponding polarization voltage under 1.0 A / cm 2 and lower voltage decay value in the environment with 100% RH, 50% RH and 20% RH;

[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 bilayer microporous layer for fuel cells, characterized in that, 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. 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 double-layer microporous layer according to claim 1, characterized in that, The general structural formula of the benzene polymer is -[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. 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 double-layer microporous layer according to claim 1, characterized in that, The porosity of the first microporous layer is 50%~70%, and the average pore size is 300nm~10μm; And / or, the thickness of the first microporous layer is 30 μm to 50 μm; And / or, the surface contact angle of the first microporous layer is 100°~120° or 140°~160°; And / or, the porosity of the second microporous layer is 40%~50%, and the average pore size is 30nm~200nm; 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 preparing a bilayer microporous layer according to any one of claims 1 to 3, characterized in that, 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 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. 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 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; 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, Step (1) and step (2) of the non-solvent-induced phase separation method each independently include: 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 in that, The gas diffusion layer comprises the bilayer microporous layer as described in any one of claims 1 to 3.

10. A fuel cell, characterized in that, The fuel cell includes the gas diffusion layer as described in claim 9.

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