Membrane electrode gas diffusion layer microporous layer, preparation method thereof and fuel cell

Abstract

The invention provides a membrane electrode gas diffusion layer microporous layer, a preparation method thereof and a fuel cell. Fluorine-containing organosilane and conductive polyaniline modified nano silicon dioxide microspheres are introduced into the surface of the gas diffusion layer, so that the conductivity of the microporous layer is improved; the microporous layer with good hydrophobicity and conductivity is obtained by fixing the microporous layer on a substrate layer by adopting methods of spraying, dip-coating and the like and carrying out drying and roasting treatment to generate a dense pore structure, optimize the mass point fitting property of the microporous layer and a membrane electrode catalyst and improve an interface electrochemical reaction. Compared with the prior art, the water management capability of the microporous layer is improved by adding the nano SiO2 modified by the organic fluorosilane, and meanwhile, the conductive performance of the microporous layer is improved by adding the components such as the conductive polymer and the carbon black; meanwhile, through coating, drying and roasting treatment, a micropore layer with a certain thickness and dense and uniform distribution of micropores is formed on the surface of the gas diffusion layer substrate layer, so that the interface electrochemical reaction can be improved, and the performance of the fuel cell is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of fuel cell gas diffusion layers, and in particular relates to a membrane electrode gas diffusion layer microporous layer and a preparation method thereof, and a fuel cell. Background Art

[0002] Proton exchange membrane fuel cell is a low-temperature fuel cell that uses proton exchange membrane as electrolyte, Pt / C as catalyst, hydrogen as fuel, and air or pure oxygen as oxidant. Proton exchange membrane fuel cell has the advantages of high power density and environmental friendliness, making it promising to replace automatic, fixed and portable equipment that uses fossil fuels as energy sources. Membrane electrode MEA is a crucial part of the proton exchange membrane fuel cell system, which includes proton exchange membrane, catalyst layer and gas diffusion layer.

[0003] The gas diffusion layer is a porous medium in which the reaction gas, water vapor and water generated by the reaction can transfer mass in the pores. The side of the gas diffusion layer in contact with the bipolar plate flow channel is the support layer, which is mainly made of carbon paper or carbon cloth, with a thickness of generally 100 to 300 μm, and its function is gas distribution and current collection; the side in contact with the catalyst layer is the microporous layer, which is generally 10 to 50 μm thick and includes carbon powder and hydrophobic components, mainly to reduce the contact resistance between the catalyst layer and the porous layer, and to carry out effective water management to prevent flooding.

[0004] The conventional gas diffusion layer microporous layer is prepared using polytetrafluoroethylene (PTFE) as the hydrophobic material, but as the PTFE content increases, the cumulative pore volume and average pore size of the gas diffusion layer decrease, resulting in obstruction of gas transmission and supply, thereby reducing the performance of the fuel cell; in addition, since PTFE is not conductive, a higher content of PTFE will increase the overall resistance of the electrode, which will have an adverse effect on the electrical performance of the membrane electrode.

[0005] The patent with publication number CN 106898791 A published on June 27, 2017 discloses a fuel cell gas diffusion layer surface modified by electrochemical method and its preparation method, and uses electrochemical method to modify polyaniline on the surface of carbon paper substrate layer to improve the water management ability and mass transfer ability of fuel cell under high current density and improve the output performance of fuel cell, but the conductivity of polyaniline is lower than that of carbon paper, and the surface modification is not enough to improve the conductivity. The patent with publication number CN 105576264 A published on May 11, 2016 discloses a gas diffusion electrode and its preparation, and fuel cell, and the preparation method of its microporous layer uses carbon powder mixed with PTFE or Nafion binder, which cannot solve the problem of reduced conductivity caused by PTFE giving hydrophobicity to the microporous layer. The patent with publication number CN 114551919 A ​​published on May 27, 2022 discloses a hydrogel, a microporous layer slurry and a gas diffusion layer and a preparation method thereof. The double-network hydrogel has good resilience, high conductivity and certain self-healing ability, which can improve the poor battery performance caused by damage or scratches on the microporous layer of the gas diffusion layer. However, the water absorption and expansion of the superabsorbent material therein may cause changes in the flow field extrusion, affecting the stable output of performance. Summary of the invention

[0006] The purpose of the present invention is to provide a membrane electrode gas diffusion layer microporous layer and a preparation method thereof, by introducing conductive polymer and fluorine-containing organic modified nano-silicon dioxide to replace PTFE in the gas diffusion layer, thereby improving the conductivity of the gas diffusion layer, reducing the contact resistance between the gas diffusion layer and the bipolar plate and CCM, improving the output performance of the fuel cell, and improving the stability.

[0007] Another object of the present invention is to provide a fuel cell, which comprises the membrane electrode gas diffusion layer microporous layer prepared as above.

[0008] The specific technical solutions of the present invention are as follows:

[0009] A method for preparing a microporous layer of a membrane electrode gas diffusion layer comprises the following steps:

[0010] 1) preparing a fluorinated organic silane-modified nano-silica microsphere solution;

[0011] 2) mixing the fluorinated organosilane-modified nano-silica microsphere solution and the conductive polymer organic solution uniformly;

[0012] 3) Add conductive agent and pore-forming agent and disperse by ultrasonic;

[0013] 4) coating the solution prepared in step 3) on the surface of the substrate layer, drying and calcining to obtain a membrane electrode gas diffusion layer microporous layer.

[0014] In step 1), the preparation method of the fluorinated organic silane modified nano-silica microsphere solution is:

[0015] Add nano-silica microspheres into an alcohol-water solvent, dropwise add acid under stirring conditions, adjust the pH value of the solution to 4-6, then add fluorinated organic silane, and continue stirring.

[0016] In step 1), the particle size of the nano-silica microspheres is 40 to 100 nm;

[0017] In step 1), the alcohol-water solvent is a mixed solvent of alcohol and water in a volume ratio of 0.5 to 1:1; the alcohol is selected from one or more of ethanol, n-propanol, isopropanol or n-butanol; the water is deionized water or distilled water;

[0018] In step 1), the acid added dropwise is acetic acid or sulfuric acid;

[0019] In step 1), after the acid is added dropwise, stirring is continued for 15 to 30 minutes;

[0020] In step 1), the continued stirring refers to continuous stirring for 90 to 120 minutes.

[0021] In step 1), the chemical formula of the fluorinated organosilane is R f -(CH2) m -Si(X) 3-n (R) n , where R f represents a straight carbon chain or branched carbon chain perfluoroalkyl or perfluoroalkoxy group, in which the number of carbon atoms is 3 to 8, m is 2 to 3, and the value of n is in the range of 0 to 3; X is a hydrolyzable group, such as a halide or an alkoxy group, preferably chlorine or ethoxy, methoxy, and R is an alkoxy group, preferably ethoxy or methoxy;

[0022] In step 1), the stirring condition refers to stirring at a stirring rate of 300 to 1500 rpm; the stirring reaction temperature in step 1) is 15 to 35° C., and the stirring method is magnetic stirring or paddle stirring; through stirring dispersion and adjusting the pH value of the solution, on the one hand, -OH hydrophilic functional groups are formed on the surface of the nano-silica microspheres; on the other hand, the fluorosilane X group is hydrolyzed to form a long-chain fluorinated silane with a hydroxyl group, and this hydroxyl group is condensed and cross-linked with part of the hydroxyl groups on the surface of the nano-silica microspheres, giving the silica microspheres a hydrophobic surface;

[0023] The addition ratio of the fluorinated organic silane is 0.5wt% to 5wt% of the total mass of the fluorinated organic silane, nano-silica microspheres and alcohol-water solvent;

[0024] In step 1), the mass fraction of the fluorinated organic silane modified nano-silica microspheres in the fluorinated organic silane modified nano-silica microsphere solution is 5% to 10%.

[0025] In step 2), the conductive polymer organic solution is prepared by adding the conductive polymer into an organic solvent and performing ultrasonic dispersion.

[0026] In step 2), the mass fraction of the conductive polymer organic solution is 1% to 10%.

[0027] In step 2), the conductive polymer is analytically pure or premium pure, preferably premium pure conductive polyaniline, polyphenylene vinylene or polypyrrole; the particle size of premium pure conductive polyaniline is less than 30 μm, and the molecular weight is 40,000-80,000; the particle size of premium pure conductive polypyrrole powder is less than 150 nm, and the molecular weight is 10,000-80,000; the particle size of premium pure conductive polyphenylene vinylene powder is less than 30 μm, and the molecular weight is 500-2000;

[0028] In step 2), the organic solvent is one or a mixture of N,N-dimethylformamide, N-methylpyrrolidone, butanol;

[0029] In step 2), the ultrasonic dispersion frequency is 20 to 40 kHz and the time is 10 to 40 minutes.

[0030] In step 2), the mass ratio of the fluorinated organic silane modified nano-silica microsphere solution to the conductive polymer organic solution is 1:0.33-5;

[0031] The mass proportion of the conductive agent in the solution prepared in step 3) is 1.94% to 8.75%;

[0032] The mass proportion of the pore-forming agent in the solution prepared in step 3) is 0.69% to 6.25%;

[0033] In step 3), the conductive agent is selected from one or a mixture of acetylene black, Vulcan XC-72, Black pearls, carbon nanotubes, graphene powder, and carbon fiber powder;

[0034] Preferably, the conductive agent has hydrophilic functional groups such as hydroxyl, carboxyl, and amine on its surface;

[0035] Furthermore, the conductive agent is oxidized by one or more of nitric acid, sulfuric acid, and hydrogen peroxide, filtered, and dried. The oxidation treatment conditions are 5 to 15 minutes at room temperature, and the drying conditions are 20 to 30 minutes at 80 to 120° C.; after the oxidation treatment, hydrophilic functional groups such as hydroxyl, carboxyl, and amine groups are given to the surface;

[0036] In step 3), the pore-forming agent is selected from one or a mixture of carbonates or oxalates; the carbonate is selected from one or both of ammonium carbonate and ammonium bicarbonate; the oxalate is selected from ammonium oxalate;

[0037] In step 3), the ultrasonic dispersion refers to ultrasonic dispersion at 20 to 40 kHz for 30 to 60 minutes.

[0038] In step 3), the fluorinated organic silane modified nano-silica microsphere solution and the conductive polymer organic solution are mixed and stirred at a mass ratio of 1:0.33-5, in order to allow the fluorinated silane modified nano-silica particles to be fully dispersed in the conductive polymer solution system. Due to the large number of hydrophilic groups such as hydroxyl groups on the surface of nano-silica, its surface energy is high, it is easy to agglomerate, and it cannot be well dispersed in the polymer matrix. At the same time, the excessively high polarity leads to poor compatibility between nano-silica and the polymer matrix, so that the nano properties of the particles cannot be fully reflected. Therefore, by modifying nano-silica with fluorinated silane, on the one hand, it can give its surface hydrophobic function, and on the other hand, due to the reduced surface energy, it is conducive to the uniform dispersion and mixing of the conductive polymer solution and the fluorinated silane modified nano-silica solution. At the same time, due to the presence of hydroxyl groups in different bonding states on the surface of nano-silica, the surface hydroxyl groups can form hydrogen with some groups in the polymer material. The presence of hydrogen bonds enhances the binding force between nano-particles and polymer matrix, and plays a certain role in improving the mechanical properties and antioxidant properties of the composite material.

[0039] In the present invention, the conductive agent carbon black used is pre-treated with sulfuric acid, nitric acid, and hydrogen peroxide to give it hydrophilic functional groups such as hydroxyl, carboxyl, and amine groups on its surface, thereby improving the dispersibility and environmental protection of the carbon black. The generation of hydrophilic functional groups can make the carbon black better dispersed in the solvent and reduce aggregation and agglomeration. After acidification and oxidation treatment, a certain amount of harmful substances such as polycyclic aromatic hydrocarbons that may exist on the surface of the carbon black are removed or degraded, reducing their harm to the environment and human body. In addition, the hydroxyl groups on the surface of the carbon black can establish hydrogen bonds with the hydroxyl groups on the surface of the nano-silicon dioxide, thereby improving the bonding strength between the carbon black and the silicon dioxide material.

[0040] In step 3), the role of the nano-silica microspheres is to use the hydroxyl functional groups rich on their surfaces to establish a firm connection with fluorosilane, carbon black, etc.; in addition, after the conductive polymer and the long-chain fluorosilane are combined with the hydroxyl groups on the surface of the nano-silica, the polymer chain forms a cross-linked structure, which, on the one hand, increases the distance between the nano-silica particles, and on the other hand, due to the rich pore structure possessed by the cross-linked structure itself, the modified microporous layer is given a higher porosity; carbonates or oxalates help to improve the uniformity of pore distribution of the carbon black, conductive polymer and fluorosilane modified nano-silica composite coating. During the drying and calcining process of the coating, the carbonates or oxalates release inert gases by decomposition to form uniform micropores on the surface. The carbonate (ammonium carbonate, ammonium bicarbonate) or oxalate (ammonium oxalate) selected in the present invention has the characteristic of low-temperature decomposition. The carbonate releases CO2 and NH3 gases, as well as water vapor during heating, forming a positive pressure in the coating layer, impacting the outer region of the organic fluorosilane cross-linked polymer skeleton, and forming uniform micropores after rupture; for the oxalate, it is necessary to heat to about 190°C, and the thermal decomposition products NH3, CO2 and H2O also form a positive pressure impact on the coating layer to produce uniform micropores.

[0041] In step 4), the solution prepared in step 3) is applied to the surface of the gas diffusion layer substrate by spraying or dipping, and then dried at a temperature of 80 to 130°C for 25 to 45 minutes; and then calcined at a high temperature of 160 to 300°C for 20 to 35 minutes.

[0042] The drying and calcining in step 4 can be carried out in air or inert gas atmosphere, and the inert gas includes argon or nitrogen.

[0043] The invention provides a membrane electrode gas diffusion layer microporous layer, which is prepared by the above method. The membrane electrode gas diffusion layer microporous layer has a thickness of 30-100 μm, a pore diameter of 10-45 nm, and a porosity of not less than 60%.

[0044] The present invention provides a fuel cell, which comprises the above-mentioned membrane electrode gas diffusion layer microporous layer. That is, the above-prepared membrane electrode gas diffusion layer microporous layer is used to prepare a membrane electrode, and the prepared membrane electrode is further used to prepare a fuel cell.

[0045] At present, the mainstream method for preparing the microporous layer is to mix conductive carbon black and hydrophobic agent (PTFE) evenly and then apply it to the surface of the hydrophobic treated support layer (such as carbon paper, carbon cloth or carbon felt), and then obtain the microporous layer after high temperature calcination. The electron transmission channel of the microporous layer prepared in this way is usually discontinuous, and because the microporous layer is mixed with non-conductive hydrophobic agent or PTFE, the electron transmission impedance of the microporous layer is increased, resulting in a decrease in the performance of the fuel cell. The present invention introduces fluorinated organic silane, conductive polyaniline-modified nano-silica microspheres, and conductive carbon black on the surface of the gas diffusion layer to replace PTFE and improve the conductivity of the microporous layer; then it is fixed to the base layer by spraying, dipping and other methods, and through drying and calcination, a dense pore structure is generated, the microporous layer and the membrane electrode catalyst particle adhesion are optimized, the interfacial electrochemical reaction is improved, and a gas diffusion layer microporous layer with good hydrophobicity and conductivity is obtained.

[0046] Compared with the prior art, the present invention, on the one hand, improves the water management capacity of the microporous layer by adding nano-SiO2 modified with organic fluorosilane, and at the same time, improves the conductivity of the microporous layer due to the addition of conductive polymers, carbon black and other ingredients; on the other hand, through coating, drying and calcining treatment, a microporous layer with a certain thickness and densely and evenly distributed micropores is formed on the surface of the gas diffusion layer base layer, thereby improving the interfacial electrochemical reaction in fuel cell applications and improving the performance of the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 Schematic diagram of microporous layer, 1-microporous layer; 2-base layer;

[0048] Figure 2 Polarization curve tests for Examples 1-4 and commercially available GDL products.

[0049] Figure 3 For test conditions. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0052] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0053] Example 1

[0054] A method for preparing a microporous layer of a membrane electrode gas diffusion layer comprises the following steps:

[0055] 1) Add nano-silica microspheres with a particle size of 40 nm to an alcohol-water mixture with a volume ratio of anhydrous ethanol to deionized water of 1:1, then drop acetic acid at a stirring speed of 300 rpm, adjust the solution pH to 6, continue magnetic stirring for 30 min, and then add 0.5 wt%

[0056] (CF3)2-CFO(CH2)3Si(OCH3)3 (CAS No. 19116-61-1), and then continued magnetic stirring for 90 minutes to obtain a solution with a fluorine-containing organic silane-modified nano-silica microsphere content of 5wt%.

[0057] 2) Slowly adding high-grade pure conductive polyaniline powder (particle size 5-30 μm, molecular weight 50000-60000) into N,N-dimethylformamide solvent, the mass ratio of conductive polyaniline is 1%, and ultrasonically dispersed at 20 kHz for 10 minutes to obtain solution 2; mixing solution 1 and solution 2 at a mass ratio of 1:0.33, and stirring evenly;

[0058] 3) Add 1.94% by mass of Guosen high-purity graphitized 800-mesh carbon fiber powder that has been oxidized with nitric acid at room temperature for 5 minutes and dried to the solution prepared in step 2), and then add 0.69% by mass of analytically pure ammonium bicarbonate, and ultrasonically disperse at 20 kHz for 30 minutes to obtain solution three.

[0059] 4) The solution is applied to the surface of the gas diffusion layer substrate by spraying, and then the coated gas diffusion layer is dried under an argon atmosphere at a drying temperature of 80° C. for 25 min; then the drying temperature is 160° C. for 20 min to obtain a microporous layer with a thickness of 30 μm, a pore size of 45 nm, and a porosity of 66%.

[0060] Example 2

[0061] A method for preparing a microporous layer of a membrane electrode gas diffusion layer comprises the following steps:

[0062] 1) Add nano-silica microspheres with a particle size of 60 nm to an alcohol-water solvent with a volume ratio of anhydrous ethanol to deionized water of 0.5:1, then drop sulfuric acid at a stirring speed of 800 rpm, adjust the pH value of the solution to 4, continue magnetic stirring for 15 minutes, then add 5wt% CF3(CF2)7-(CH2)2-SiCl3 (CAS No. 78560-44-8) at 35°C, and then continue magnetic stirring for 120 minutes to obtain a solution with a mass fraction of 10wt% of fluorinated organic silane-modified nano-silica microspheres.

[0063] 2) Slowly add high-grade pure conductive polyaniline powder (particle size 5-30 μm, molecular weight 50000-60000) into N-methylpyrrolidone solvent, the conductive polyaniline mass ratio is 10%, and ultrasonically disperse at 40 kHz for 40 minutes to obtain solution 2. Mix solution 1 and solution 2 at a mass ratio of 1:5 and stir evenly;

[0064] 3) Then, 8.75% of Vulcan XC-72 dried after oxidation with nitric acid at room temperature for 15 minutes was added to the solution obtained in step 2), and then 6.25% of analytically pure ammonium carbonate was added, and ultrasonic dispersion was performed at 40 kHz for 60 minutes to obtain solution three.

[0065] 4) The solution was applied to the surface of the gas diffusion layer substrate by dipping, and then the coated gas diffusion layer was dried under a nitrogen atmosphere at a drying temperature of 130° C. for 45 min; and then dried at 300° C. for 35 min to obtain a microporous layer with a thickness of 100 μm, a pore size of 45 nm, and a porosity of 65%.

[0066] Example 3

[0067] A method for preparing a microporous layer of a membrane electrode gas diffusion layer comprises the following steps:

[0068] 1) Add nano-silica microspheres with a particle size of 100 nm to an alcohol-water solvent with a volume ratio of isopropanol to deionized water of 1:1, then drop acetic acid at a stirring speed of 1500 rpm, adjust the pH value of the solution to 5, continue magnetic stirring for 30 minutes, then add 2wt% CF3(CF2)5-(CH2)2-SiCl3 (CAS No. 78560-45-9) at 15°C, and then continue magnetic stirring for 120 minutes to obtain a solution with a mass fraction of 8wt% of fluorinated organic silane-modified nano-silica microspheres.

[0069] 2) Slowly add high-grade pure conductive polypyrrole powder (particle size 86-135nm, molecular weight 10000-58000) into N,N-dimethylformamide solvent, the conductive polypyrrole mass ratio is 3%, and ultrasonically disperse at 30kHz for 20min to obtain solution 2. Mix solution 1 and solution 2 at a mass ratio of 1:1 and stir evenly;

[0070] 3) Then, 5.83% of acetylene black dried after oxidation with nitric acid at room temperature for 10 min was added to the solution prepared in step 2), and then 2.08% of analytically pure ammonium bicarbonate was added, and ultrasonic dispersion was performed at 30 kHz for 45 min to obtain solution three.

[0071] 4) The solution is applied to the surface of the gas diffusion layer substrate by dipping three times, and then the coated gas diffusion layer is dried in an air atmosphere at a drying temperature of 100°C for 35 minutes; then the drying temperature is then 180°C for 35 minutes to obtain a microporous layer with a thickness of 60 μm, a pore size of 22 nm, and a porosity of 61%.

[0072] Example 4

[0073] A method for preparing a microporous layer of a membrane electrode gas diffusion layer comprises the following steps:

[0074] 1) Add nano-silica microspheres with a particle size of 60 nm to a mixed solvent of isopropanol and deionized water in a volume ratio of 1:1, then drop acetic acid at a stirring speed of 1200 rpm, adjust the pH value of the solution to 4, continue magnetic stirring for 25 minutes, then add 3wt% CF3(CF2)5-(CH2)2-Si(OCH2CH3)3 (CAS No. 51851-37-7) at 25°C, and then continue magnetic stirring for 90 minutes to obtain a solution with a mass fraction of 5wt% of fluorinated organic silane-modified nano-silica microspheres.

[0075] 2) Slowly add high-grade pure conductive polyphenylene vinylene powder (specifically, particle size 5-20 μm and molecular weight 600-1830) into N,N-dimethylformamide solvent, with a conductive polyphenylene vinylene mass ratio of 8%, and ultrasonically disperse at 40 kHz for 40 minutes to obtain solution 2. Mix solution 1 and solution 2 at a mass ratio of 1:3 and stir evenly;

[0076] 3) Then, 5.83% of acetylene black dried after oxidation with nitric acid at room temperature for 10 min was added to the solution prepared in step 2), and then 4.17% of analytically pure ammonium oxalate was added, and ultrasonic dispersion was performed at 40 kHz for 60 min to obtain solution three.

[0077] 4) The solution is applied to the surface of the gas diffusion layer substrate by spraying, and then the coated gas diffusion layer is dried under an argon atmosphere at a drying temperature of 130° C. for 45 min; then the drying is carried out at 300° C. for 35 min to obtain a microporous layer with a thickness of 60 μm, a pore size of 25 nm, and a porosity of 65%.

[0078] The commercially available GDL products and the GDL prepared in Examples 1 to 4 were respectively packaged into MEAs with the same batch of CCMs, and then assembled into single cells for polarization curve testing to compare the potentials at the same current density. The results are as follows: Figure 2 . Before conducting the polarization test, the fuel cell needs to be activated first. Under high current density, the anode hydrogen fuel and the cathode oxidant quickly undergo electrochemical reactions to generate water, accelerate the wetting of the proton membrane, open up the proton transmission channel, clean the active surface of the catalyst, form the best water vapor transmission channel, and enable the fuel cell to quickly establish the best performance state. The present invention adopts a constant voltage activation method. After the activation test starts, hydrogen and air are passed through the anode and cathode, and the dew point temperature, the intake temperature and the fuel cell temperature are waited for to rise. The anode and cathode outlet pressures are waited for to rise. After the anode and cathode outlet pressures reach the set value, the fuel cell voltage is pulled to 0.9V for 30s, and then the voltage is reduced to 0.5V in steps of -0.1V, and each voltage point lasts for 30s. Run at 0.4V for 20min. Then the voltage is increased to 0.9V in steps of 0.1V, and each voltage point lasts for 30s. When the current tends to be stable, the activation is completed.

[0079] Depend on Figure 2 It can be seen that the use of the product of the present invention can significantly increase the polarization current density at the same potential level, that is, reduce the contact resistance and improve the performance of the fuel cell.

[0080] Commercially available GDL Wei SGL 22BB;

[0081] The polarization curve test was performed using a constant current test method. Before the polarization curve test, nitrogen was first passed through for preheating. After the dew point temperature, intake temperature, and fuel cell temperature reached the set values, the nitrogen was switched to hydrogen and air. During the polarization curve test, the first test point was OCV for a total of 20 seconds, and then the current was increased from 0.1A / cm 2 Start with 0.1A / cm 2 The current density is stepped up to 2.0 A / cm 2 Each current density point is run for 90s. Figure 3 shown.

[0082] The membrane electrode gas diffusion layer microporous layer prepared by the invention improves the performance of the fuel cell and improves the stability of the fuel cell.

[0083] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a microporous layer of a membrane electrode gas diffusion layer, characterized in that: The preparation method comprises the following steps: 1) preparing a fluorinated organic silane-modified nano-silica microsphere solution; 2) mixing the fluorinated organosilane-modified nano-silica microsphere solution and the conductive polymer organic solution uniformly; 3) Add conductive agent and pore-forming agent and disperse by ultrasonic; 4) coating the solution prepared in step 3) on the surface of the substrate layer, drying and calcining to obtain a membrane electrode gas diffusion layer microporous layer.

2. The preparation method according to claim 1, characterized in that: In step 1), the preparation method of the fluorinated organic silane modified nano-silica microsphere solution is: Add nano-silica microspheres to an alcohol-water solvent, add acid dropwise under stirring, adjust the pH value of the solution to 4-6, then add fluorinated organic silane, and continue stirring; The addition ratio of the fluorine-containing organic silane is 0.5wt% to 5wt% of the total mass of the fluorine-containing organic silane, nano-silica microspheres and alcohol-water solvent.

3. The preparation method according to claim 2, characterized in that: In step 1), the chemical formula of the fluorinated organosilane is R f -(CH2) m -Si(X) 3-n (R) n , where R f It represents a straight carbon chain or branched carbon chain perfluoroalkyl or perfluoroalkoxy group, in which the number of carbon atoms is 3 to 8, m is 2 to 3, and the value of n is in the range of 0 to 3; X is a hydrolyzable group, and R is an alkoxy group.

4. The preparation method according to claim 1, characterized in that: In step 2), the mass fraction of the conductive polymer organic solution is 1% to 10%.

5. The preparation method according to claim 1 or 4, characterized in that: In step 2), the mass ratio of the fluorinated organic silane modified nano-silica microsphere solution to the conductive polymer organic solution is 1:0.33-5.

6. The preparation method according to claim 1, characterized in that: In step 3), the mass proportion of the conductive agent in the solution prepared in step 3) is 1.94% to 8.75%; the mass proportion of the pore-forming agent in the solution prepared in step 3) is 0.69% to 6.25%.

7. The preparation method according to claim 1 or 6, characterized in that: In step 3), the conductive agent is selected from one or a mixture of acetylene black, Vulcan XC-72, Black pearls, carbon nanotubes, graphene powder, carbon fiber powder; and the pore-forming agent is selected from one or a mixture of carbonates or oxalates.

8. The preparation method according to claim 1, characterized in that: In step 4), the calcination process is performed at a temperature of 160 to 300° C. and a time of 20 to 35 minutes.

9. A microporous layer of a membrane electrode gas diffusion layer prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The microporous layer of the membrane electrode gas diffusion layer has a thickness of 30-100 μm, a pore diameter of 10-45 nm, and a porosity of not less than 60%.

10. A fuel cell, characterized in that: The fuel cell comprises the membrane electrode gas diffusion layer microporous layer according to claim 9.

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