A microporous layer slurry, a gas diffusion layer with high porosity, and a preparation method thereof

Abstract

This application relates to the field of gas diffusion layer materials, and particularly to a microporous layer slurry, a gas diffusion layer with high porosity and a preparation method thereof; the raw materials of the microporous layer slurry include: polymethyl methacrylate microspheres, composite microspheres, carbon black slurry and polytetrafluoroethylene; among them, the polymethyl methacrylate microspheres include at least three kinds of polymethyl methacrylate microspheres with different particle sizes; the composite microspheres are composite microspheres of polymethyl methacrylate composite halloysite nanotube silicon aluminum tubes; the particle size of the polymethyl methacrylate microspheres is 20 μm to 100 μm; the particle size of the composite microspheres is 7 μm to 20 μm; by using polymethyl methacrylate microspheres and composite microspheres of polymethyl methacrylate composite halloysite nanotube silicon aluminum tubes as pore formers, and restricting the polymethyl methacrylate microspheres to include at least three different particle sizes, the pore size of the gas diffusion layer can be reasonably and uniformly distributed, and the pore size distribution of the gas diffusion layer can be effectively improved.

Description

Technical Field

[0001] The present application relates to the field of gas diffusion layer materials, and particularly relates to a microporous layer slurry, a gas diffusion layer with high porosity, and a preparation method thereof. Background Art

[0002] A fuel cell is a chemical device that directly converts the chemical energy of a fuel into electrical energy, also known as an electrochemical generator; it is the fourth power generation technology after hydraulic power generation, thermal power generation, and nuclear power generation. Since a fuel cell converts the Gibbs free energy part of the chemical energy of a fuel into electrical energy through an electrochemical reaction and is not restricted by the Carnot cycle effect, it has high efficiency; in addition, a fuel cell uses fuel and oxygen as raw materials, and at the same time has no mechanical transmission components, so the harmful gases emitted are extremely few and the service life is long. Thus, from the perspective of saving energy and protecting the ecological environment, a fuel cell is the most promising power generation technology.

[0003] The most important membrane electrode of a fuel cell consists of a catalytic layer and a gas diffusion layer. One of the functions of the gas diffusion layer in a fuel cell is to remove the water generated in the catalytic layer through its own pores. At the same time, the existence of pores also has the function of conducting gas, enabling the battery to have good performance. If the pore size distribution is unreasonable, there will be a certain risk of water blockage, seriously affecting the battery performance. And the gas diffusion layer is mainly prepared from a microporous layer slurry. Therefore, how to provide a microporous layer slurry for a gas diffusion layer with a reasonable pore size distribution and high porosity is a technical problem that needs to be solved urgently at present. Summary of the Invention

[0004] The present application provides a microporous layer slurry, a gas diffusion layer with high porosity, and a preparation method thereof, to solve the technical problem of unreasonable pore size distribution of the gas diffusion layer in the prior art and achieve the technical effect of uniform and reasonable pore size distribution of the gas diffusion layer.

[0005] In the first aspect, the present application provides a microporous layer slurry, and the raw materials of the slurry include: polymethyl methacrylate microspheres with at least three different particle sizes, composite microspheres, carbon black slurry, and polytetrafluoroethylene;

[0006] The composite microspheres are microspheres of polymethyl methacrylate composite halloysite nano-silicoaluminate tubes;

[0007] The particle sizes of the polymethyl methacrylate microspheres with at least three different particle sizes are 20 μm to 100 μm respectively;

[0008] The particle size of the composite microspheres is 7 μm to 20 μm.

[0009] Optionally, the ratio of the total mass of the polymethyl methacrylate microspheres and the composite microspheres to the total mass of the carbon black slurry and the polytetrafluoroethylene is 1:2.4 to 4.7.

[0010] Optionally, the carbon black slurry is a mixed slurry formed by conductive carbon black particles and an isopropanol solution;

[0011] The mass ratio of the conductive carbon black particles to the isopropanol solution is 3:1 to 10:1.

[0012] Optionally, the conductive carbon black particles include at least one of acetylene black, Vulcan XC-72, Black pearls, and carbon nanotubes.

[0013] Optionally, the mass of the conductive carbon black particles accounts for 4:1 to 20:1 of the total mass of the polymethyl methacrylate microspheres and the composite microspheres, and the mass ratio of the conductive carbon black particles to the polytetrafluoroethylene is 1:10 to 1:30.

[0014] In a second aspect, the present application provides a method for preparing the microporous layer slurry described in the first aspect. The method includes:

[0015] Preparing composite microspheres and polymethyl methacrylate microspheres with different particle sizes respectively;

[0016] Mixing the carbon black slurry and the polytetrafluoroethylene solution, and performing stirring and first ultrasonic treatment to obtain a mixed slurry;

[0017] Mixing the composite microspheres, the polymethyl methacrylate microspheres and the mixed slurry, and performing second ultrasonic treatment to obtain a microporous layer slurry.

[0018] Optionally, the time of the first ultrasonic treatment and the second ultrasonic treatment are 25 min to 35 min respectively; the frequencies of the first ultrasonic treatment and the second ultrasonic treatment are 25 kHz to 40 kHz respectively.

[0019] In a third aspect, the present application provides a gas diffusion layer with high porosity. The raw materials of the gas diffusion layer include the microporous layer slurry and a base layer, and the gas diffusion layer is prepared by spraying the microporous layer slurry on the base layer.

[0020] In a fourth aspect, the present application provides a method for preparing the gas diffusion layer described in the first aspect. The method includes:

[0021] Impregnating the base layer with an impregnating solution, and then performing first drying to obtain a pretreated base layer;

[0022] Spraying the microporous layer slurry described in the first aspect on the surface of the pretreated base layer, and performing roasting, and then naturally cooling to obtain a crude sample;

[0023] The crude sample is soaked in an organic solvent and subjected to a third ultrasonic treatment to remove the polymethyl methacrylate microspheres in the microporous layer, and then heat treatment is carried out to obtain a gas diffusion layer;

[0024] Among them, the impregnating solution is a water repellent solution; the time of the impregnation treatment is 20 min to 40 min.

[0025] Optionally, the weight content of the water repellent in the microporous layer is 15% to 30%.

[0026] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0027] A microporous layer slurry provided by an embodiment of the present application, by using polymethyl methacrylate microspheres as pore formers and restricting the polymethyl methacrylate microspheres to include at least three different particle sizes, can better control the pore size distribution on the final gas diffusion layer. In addition, composite microspheres of polymethyl methacrylate composite halloysite nano-silicoaluminate tubes are introduced. On the one hand, due to the large amount of hydroxyl groups at the tube ends and surfaces of the halloysite nano-silicoaluminate tubes in the composite microspheres, they have good surface effects. On the other hand, by modifying the halloysite nano-silicoaluminate tubes with polymethyl acrylate, the polymethyl methacrylate composite halloysite nano-silicoaluminate tubes can be used to modify the non-polar slurry containing polytetrafluoroethylene, ensuring the stable existence of the halloysite nano-silicoaluminate tubes in the microporous layer slurry. Finally, the polymethyl methacrylate microspheres in the polymethyl methacrylate microspheres and the composite microspheres are washed away by the solution, and the remaining halloysite nano-silicoaluminate tubes are hollow long tubes. Due to their positive charge, they will attract the negatively charged carbon black particles in the carbon black slurry, and the carbon particles can come to the vicinity of the orifice of the halloysite nano-silicoaluminate tubes through electrostatic interaction, so that the halloysite nano-silicoaluminate tubes and the carbon black particles form a through network, enhancing the interfacial bonding force and ensuring the stable distribution of the pore size on the gas diffusion layer. Therefore, the pore size of the gas diffusion layer can be reasonably and evenly distributed in the range of 7 μm to 100 μm, and thus the pore size distribution of the gas diffusion layer can be effectively improved. Description of the Drawings

[0028] The drawings here are incorporated into the specification and constitute a part of this specification, showing the embodiments consistent with the present application and used together with the specification to explain the principles of the present application.

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

[0030] Figure 1 Schematic flow chart of the method for preparing the microporous layer slurry provided by the embodiment of the present application;

[0031] Figure 2 Schematic flow chart of the method for preparing the gas diffusion layer provided by the embodiment of the present application;

[0032] Figure 3 Schematic diagram for comparing the polarization curves of each gas diffusion layer sample provided by the embodiment of the present application. Detailed implementation manners

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Apparently, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0034] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments, and equipment used in the present application can be obtained through market purchase or can be prepared by existing methods.

[0035] The creative concept of the present application is:

[0036] The main membrane electrode of a fuel cell consists of a catalyst layer and a gas diffusion layer (GDL). Among them, the diffusion layer can be further divided into a base layer and a microporous layer. The base layer is directly in contact with the catalyst layer and functions to support the microporous layer and the catalyst layer, collect current, conduct gas, and discharge water. The main materials used for it are carbon paper and carbon cloth.

[0037] The normal working process of a fuel cell is as follows: When the fuel cell is operating normally, the transfer of reactive gases mainly occurs through diffusion, and the driving force for diffusion is the concentration difference of the reactive gases. The gas concentration near the bipolar plate is relatively high, while the air or oxygen near the cathode catalyst layer side has a relatively low concentration due to continuous reactions, which promotes the diffusion of gas from the bipolar plate side to the catalyst layer side. During the diffusion process, the pore diameter for molecular diffusion is required to be greater than 7 μm. The water generated on the cathode catalyst layer side will first be transported in relatively large pores. When the relatively large pores are filled with water, the water will tend to transfer to the second-largest pores. When the fuel cell operates at a high current density, a large amount of water is generated. If the pore size distribution in the GDL is unreasonable, it will affect the gas transfer. In severe cases, flooding may occur and the fuel cell may not operate normally. Therefore, a reasonable pore size distribution in the GDL is extremely important for the transfer of water and gas. If the pore size distribution is unreasonable, there will be a certain risk of water blockage, seriously affecting the performance of the fuel cell. Since the gas diffusion layer is mainly prepared from a microporous layer slurry, how to provide a microporous layer slurry for a gas diffusion layer with a reasonable pore size distribution and a high porosity is a technical problem that urgently needs to be solved at present.

[0038] A microporous layer slurry provided by an embodiment of the present application, the raw materials of the microporous layer slurry include: polymethyl methacrylate microspheres of at least three different particle sizes, composite microspheres, carbon black slurry, and polytetrafluoroethylene;

[0039] The composite microspheres are microspheres of polymethyl methacrylate composite halloysite nanotube silicon aluminum tubes;

[0040] The particle sizes of the polymethyl methacrylate microspheres of at least three different particle sizes are 20 μm to 100 μm respectively;

[0041] The particle size of the composite microspheres is 7 μm to 20 μm.

[0042] In the embodiment of the present application, the positive effect of controlling the particle sizes of the polymethyl methacrylate microspheres of at least three different particle sizes to be 20 μm to 100 μm respectively is that within this particle size range, using polymethyl methacrylate (PMMA) microspheres as one of the pore-forming agents and limiting it to include at least three different particle sizes, different particle size distributions of the microporous layer slurry can be formed by different polymethyl methacrylate microspheres. After subsequent solution elution, gas diffusion layers with different pore sizes can be obtained.

[0043] The positive effect of controlling the particle size of the composite microspheres to be 7 μm to 20 μm is that within this particle size range, the poly(methyl methacrylate) composite halloysite nanotube (HNTs tube) can be tightly combined, while also ensuring the size of the HNTs tube. When the PMMA microspheres in the composite microspheres are removed later, the remaining hollow long HNTs tubes will attract carbon black particles with a negatively charged surface due to the positively charged inner surface, enabling the carbon black particles to be enriched near the orifice of the HNTs tube through electrostatic interaction, forming a through-network between the HNTs tube and the carbon particles, enhancing the interfacial bonding force, which can not only improve the mechanical strength of the gas diffusion layer but also ensure that the HNTs tube stably maintains the pore size of the gas diffusion layer and guarantees a reasonable pore size distribution of the gas diffusion layer.

[0044] In some alternative embodiments, the ratio of the total mass of the poly(methyl methacrylate) microspheres and the composite microspheres to the total mass of the carbon black slurry and the polytetrafluoroethylene is 1:2.4 to 4.7.

[0045] In the embodiments of the present application, by controlling the ratio of the total mass of the poly(methyl methacrylate) microspheres and the composite microspheres to the total mass of the carbon black slurry and the polytetrafluoroethylene, on the one hand, the content of the poly(methyl methacrylate) microspheres in the poly(methyl methacrylate) microspheres and the composite microspheres can be controlled to ensure that there is a sufficient pore size distribution range in the gas diffusion layer when the poly(methyl methacrylate) microspheres are washed away later. On the other hand, the polytetrafluoroethylene can be modified by the composite microspheres, so that the HNTs tube can be stably present in the microporous layer slurry, ensuring that the HNTs tube can be enriched with sufficient carbon black particles through electrostatic interaction later to form a through-network and enhance the interfacial bonding force, thereby improving the mechanical strength of the gas diffusion layer and ensuring the stability of the pore size of the gas diffusion layer.

[0046] In some alternative embodiments, the carbon black slurry is a mixed slurry formed by conductive carbon black particles and isopropyl alcohol solution;

[0047] The mass ratio of the conductive carbon black particles to the isopropyl alcohol solution is 3:1 to 10:1.

[0048] In the embodiments of the present application, by controlling the mass ratio of the conductive carbon black particles to the isopropyl alcohol solution, the uniform dispersion of the conductive carbon black particles can be ensured, which is convenient for the HNTs tube to be enriched with sufficient carbon black particles through electrostatic interaction later, so as to obtain a uniformly dispersed and stable through-network and increase the strength of the gas diffusion layer.

[0049] In some alternative embodiments, the conductive carbon black particles include at least one of acetylene black, Vulcan XC-72, Blackpearls, and carbon nanotubes.

[0050] In the embodiments of the present application, by defining the specific material of the conductive carbon black particles, most of the carbon black particles with good conductivity can be included, and at the same time, it is ensured that they can be evenly dispersed in the isopropanol solution. Further, it is ensured that the HNTs tubes can enrich enough carbon black particles through electrostatic interaction and form a through-network, enhancing the interfacial bonding force, thereby improving the mechanical strength of the gas diffusion layer and ensuring the stability of the pore size of the gas diffusion layer.

[0051] In some alternative embodiments, the mass of the conductive carbon black particles accounts for 4:1 to 20:1 of the total mass of the polymethyl methacrylate microspheres and the composite microspheres, and the mass ratio of the conductive carbon black particles to the polytetrafluoroethylene is 1:10 to 1:30.

[0052] In the embodiments of the present application, by defining the proportion of the mass of the conductive carbon black particles in the total mass of the polymethyl methacrylate microspheres and the composite microspheres and the mass ratio of the conductive carbon black particles to the polytetrafluoroethylene, it can be ensured that the conductive carbon black particles can be fully mixed with the polymethyl methacrylate microspheres and the composite microspheres serving as pore-forming agents, and it is ensured that the HNTs tubes can enrich enough carbon black particles through electrostatic interaction and form a through-network, enhancing the interfacial bonding force, thereby improving the mechanical strength of the gas diffusion layer and ensuring the stability of the pore size of the gas diffusion layer.

[0053] As Figure 1 shown, based on a general inventive concept, the embodiments of the present application provide a method for preparing the microporous layer slurry, and the method includes:

[0054] S1. Prepare composite microspheres and polymethyl methacrylate microspheres with different particle sizes respectively;

[0055] S2. Mix the carbon black slurry and the polytetrafluoroethylene solution, and perform stirring and the first ultrasonic treatment to obtain a mixed slurry;

[0056] S3. Mix the composite microspheres, the polymethyl methacrylate microspheres and the mixed slurry, and perform the second ultrasonic treatment to obtain the microporous layer slurry.

[0057] In the embodiments of the present application, the specific process for preparing the polymethyl methacrylate microspheres with different particle sizes is as follows:

[0058] Dissolve the dispersant PVP, the monomer MMA, and the initiator AIBN in a mixed solvent composed of ethanol and water, and put them into a 250 mL three-necked flask equipped with a stirrer and a reflux condenser. React at a certain temperature for 6 h. After the reaction is completed, cool down. After the obtained dispersion polymerization sample is centrifuged and settled, wash the PMMA microspheres with absolute ethanol multiple times to remove unreacted monomers and oligomers, and finally dry them in vacuum at 60 °C for 24 h to obtain the PMMA microspheres.

[0059] The specific process of the preparation method of the composite microspheres is as follows:

[0060] Mix MMA with 1.0 wt% of unmodified HNTs, and ultrasonically disperse them with an ultrasonic crusher. Add the suspension obtained after ultrasonic dispersion and deionized water into a three-necked flask at the same time, stir well, protect it in a nitrogen environment for 30 min, then heat it to 75 °C, add initiator BPO to initiate in-situ suspension polymerization. After reacting for 6 h, cool the reaction system, wash and filter the product with deionized water repeatedly, and dry it at 60 °C until a constant weight is obtained to obtain composite microspheres, denoted as PMMA / HNTs.

[0061] The specific preparation process of the mixed slurry is as follows:

[0062] Put carbon black particles into a beaker containing isopropanol, then place it on a magnetic stirrer and stir for 30 min, then perform ultrasonic treatment on the solution for 30 min. After repeating the steps 4 times, add PTFE solution and stir for 30 min and perform the first ultrasonic treatment respectively.

[0063] This method is for the preparation method of the above-mentioned microporous layer slurry. The specific components of the microporous layer slurry can refer to the above-mentioned embodiments. Since this method adopts some or all of the technical solutions of the above-mentioned embodiments, it has at least all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be elaborated one by one here.

[0064] In some alternative embodiments, the times of the first ultrasonic and the second ultrasonic are 25 min to 35 min respectively;

[0065] In the embodiments of the present application, controlling the specific time of the first ultrasonic can ensure that the carbon black slurry is evenly distributed in polytetrafluoroethylene, ensure that HNTs tubes can be enriched with enough carbon black particles through electrostatic action, and form a through network to enhance the interfacial bonding force, thereby improving the mechanical strength of the gas diffusion layer and ensuring the stability of the pore size of the gas diffusion layer.

[0066] Controlling the specific time of the second ultrasonic can ensure that PMMA microspheres and composite microspheres with different particle sizes in polytetrafluoroethylene are mixed evenly, thereby ensuring the uniform distribution of the pore size of the subsequent gas diffusion layer.

[0067] Based on a general inventive concept, the present application provides a gas diffusion layer with high porosity. The raw materials of the gas diffusion layer include the microporous layer slurry and the base layer, and the gas diffusion layer is prepared by spraying the microporous layer slurry on the base layer.

[0068] In the embodiments of the present application, the reason for adopting the spraying method is as follows: Since a large number of hydroxyl groups are contained at the tube ends and on the surface of HNTs, the surface action of HNTs is enhanced, resulting in easy agglomeration. It is difficult to be well dispersed and infiltrated in a non-polar organic polymer matrix, and the interfacial bonding force is weak, seriously affecting its use effect. If the conventional screen printing method is selected, during the scraping process, the slurry will be poured on the screen and needs to be scraped repeatedly with a squeegee. In this process, it is impossible to ensure that the HNTs tubes are always in a uniformly dispersed state, and the HNTs tubes are extremely easy to agglomerate. However, during the spraying process, the equipment itself is equipped with a stirring device to ensure that the slurry is always in a better dispersed state during the spraying process.

[0069] The gas diffusion layer is realized based on the above-mentioned microporous layer slurry. The specific composition of the microporous layer slurry can refer to the above embodiments. Since the gas diffusion layer adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated one by one here.

[0070] As Figure 2 shown, based on a general inventive concept, the present application provides a method for preparing the gas diffusion layer, and the method includes:

[0071] S1. Impregnate the base layer with an impregnating solution, and then perform the first drying to obtain a pretreated base layer;

[0072] S2. Spray the microporous layer slurry on the surface of the pretreated base layer, perform calcination, and then naturally cool to obtain a crude sample;

[0073] S3. Immerse the crude sample in an organic solvent and perform the third ultrasonic treatment to remove the polymethyl methacrylate microspheres in the microporous layer, and then perform heat treatment to obtain the gas diffusion layer;

[0074] Wherein, the impregnating solution is a water repellent solution; the time of the impregnation treatment is 20 min to 40 min.

[0075] In the embodiments of the present application, defining the specific time of the specific impregnation treatment can ensure that the base layer absorbs sufficient water repellent solution, ensure the adhesion effect of the subsequent microporous layer slurry sprayed on the surface of the base layer, and ensure the stability of the microporous layer.

[0076] The organic solvent can be acetone or N,N-dimethylformamide.

[0077] This method is for the preparation method of the above gas diffusion layer. The specific structure and composition of the gas diffusion layer can refer to the above embodiments. Since this method adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated one by one here.

[0078] In some alternative embodiments, the weight content of the water repellent in the microporous layer is 15% to 30%.

[0079] In the embodiments of the present application, the positive effect of controlling the weight content of the water repellent in the microporous layer to be 15% to 30% is that within this content range, sufficient water repellent in the microporous layer is ensured, the flooding of the gas diffusion layer is avoided, and the stability during the normal operation of the fuel cell composed of the subsequent gas diffusion layer is ensured.

[0080] The following further elaborates on the present application in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. For the experimental methods without specific conditions noted in the following embodiments, they are usually determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0081] Example 1

[0082] The process for preparing the gas diffusion layer is as follows:

[0083] 1. Preparation process of PMMA microspheres in the pore former: Dissolve the dispersant PVP, monomer MMA, and initiator AIBN in a mixed solvent composed of ethanol and water. Add the amount of PVP into a 250 mL three-necked flask equipped with a stirrer and a reflux condenser, and react at a certain temperature for 6 h. The temperatures are 60 °C, 65 °C, and 70 °C respectively. After the reaction, cool down by natural cooling. After centrifugal sedimentation of the obtained dispersion polymerization sample, wash the PMMA microspheres with absolute ethanol multiple times to remove unreacted monomers and oligomers, and finally dry them in vacuum at 60 °C for 24 h to obtain PMMA microspheres with different particle sizes; among them, the PMMA microspheres with different particle sizes are three kinds of microspheres with different particle sizes, namely 5 μm - 10 μm, 10 μm - 20 μm, and 20 μm - 100 μm. The mass ratio of these three kinds of PMMA microspheres from small to large particle size distribution is 1:26:4.

[0084] 2. Preparation process of composite microspheres in the pore former: Ultrasonically disperse MMA and 1.0 wt% of unmodified HNTs with an ultrasonic pulverizer. Add the suspension obtained after ultrasonic dispersion and deionized water into a three-necked flask at the same time, stir well, protect it in a nitrogen environment for 30 min, then raise the temperature to 75 °C, add the initiator BPO to initiate in-situ suspension polymerization. After reacting for 6 h, cool down the reaction system, wash and filter the product with deionized water repeatedly, and dry it at 60 °C until a constant weight is obtained to obtain composite microspheres, denoted as PMMA / HNTs.

[0085] 3. Pretreatment of the substrate layer: Immerse the substrate layer material (carbon paper) in a PTFE solution with a mass fraction of 15%, immerse it for 30 minutes and then put it into an oven to dry at 60°C for 1 hour. Repeat this step 4 times until the content of PETF in the pretreated carbon paper reaches 5.5%.

[0086] 4. Preparation of the microporous layer slurry: Mix the solvent isopropanol with Vulcan XC-72 carbon powder at a mass ratio of 3:1, and then perform magnetic stirring to obtain slurry A. Add pore-forming agents PMMA microspheres with a particle size of 20 μm - 100 μm and PMMA / HNTs composite microspheres with a particle size of 7 μm - 20 μm and a PTFE emulsion with a solid content of 60% to the slurry A that has been dispersed to a certain extent, and continue magnetic stirring to obtain a uniformly dispersed microporous layer slurry. Finally, the pore volume content is 1.03 mL / g for 100 μm, 26.53 mL / g for 20 μm - 100 μm, and 3.58 mL / g for 7 μm - 20 μm.

[0087] 5. Preparation of the gas diffusion layer: Coat the obtained microporous layer slurry on the surface of the pretreated carbon paper by spraying. After spraying, take it out and place it in an oven to dry at 60°C for 1 hour, then put it into a box-type resistance furnace and heat it up to 300°C for roasting for 3 hours, and then roast for 2 hours. After taking it out and naturally cooling, soak the sample in a beaker containing N,N-dimethylformamide for 24 hours. At the same time, ultrasonically treat the beaker containing N,N-dimethylformamide and the rough gas diffusion layer sample for 10 minutes every 6 hours. The purpose is to better remove the PMMA microspheres in the microporous layer. After soaking, wash the sample repeatedly with deionized water, and then put the washed sample into an oven for heat treatment at a temperature of 50°C for 1 hour to obtain the final gas diffusion layer sample.

[0088] Comparative Example 1

[0089] Compare Comparative Example 1 with Example 1. The differences between Comparative Example 1 and Example 1 are as follows:

[0090] Do not use PMMA microspheres and composite microspheres as pore-forming agents. The specific preparation process is as follows:

[0091] 1. Preparation of the microporous layer slurry: Mix the solvent isopropanol with Vulcan XC-72 carbon powder at a mass ratio of 3:1, and then perform magnetic stirring to obtain slurry A. Add the pore-forming agent ethylene glycol and a PTFE emulsion with a solid content of 60% to the slurry A that has been dispersed to a certain extent, and continue magnetic stirring, and then perform ball milling to obtain a uniformly dispersed microporous layer slurry.

[0092] 2. Preparation of gas diffusion layer: The obtained microporous layer slurry was coated on the surface of the substrate layer by spraying. After spraying, it was taken out and placed in an oven to be dried at 60 °C for 1 h, and then put into a box-type resistance furnace to be heated to 300 °C and calcined for 3 h to obtain the final gas diffusion layer.

[0093] Comparative Example 2

[0094] Comparing Comparative Example 2 with Example 1, the differences between Comparative Example 2 and Example 1 are as follows:

[0095] The gas diffusion layer was prepared using PMMA microspheres of a single particle size. The specific preparation process is as follows:

[0096] 1. Preparation of pore-forming agent: The dispersant PVP, monomer MMA, and initiator AIBN were dissolved in a mixed solvent composed of ethanol and water. The amount of PVP was put into a 250 mL three-necked flask equipped with a stirrer and a reflux condenser, and reacted at 75 °C for 6 h. After the reaction, the temperature was lowered. The obtained dispersion polymerization sample was centrifuged and settled, and the PMMA microspheres were washed with anhydrous ethanol multiple times to remove unreacted monomers and oligomers. Finally, it was vacuum-dried at 60 °C for 24 h to obtain PMMA microspheres of a certain particle size.

[0097] 2. Pretreatment of the substrate layer: The substrate layer material was immersed in a 15% PTFE solution by mass, and after being immersed for 30 minutes, it was put into an oven and dried at 60 °C for 1 h. This step was repeated 4 times until the content of PETF in the pretreated carbon paper reached 5.5%.

[0098] 3. Preparation of microporous layer slurry: The solvent isopropanol was mixed with Vulcan XC-72 carbon powder at a mass ratio of 3:1, and then magnetic stirring was carried out to obtain slurry A. The pore-forming agent PMMA microspheres and a PTFE emulsion with a solid content of 60% were added to slurry A that had been dispersed to a certain extent, and magnetic stirring was continued, followed by ball milling to obtain a uniformly dispersed microporous layer slurry;

[0099] 4. Preparation of gas diffusion layer: The obtained microporous layer slurry was coated on the surface of the substrate layer by spraying. After spraying, it was taken out and placed in an oven to be dried at 60 °C for 1 h, and then put into a box-type resistance furnace to be heated to 300 °C and calcined for 3 h to obtain the final gas diffusion layer.

[0100] Related experiments and effect data:

[0101] The pore size distribution and porosity data of the gas diffusion layers obtained from each example and comparative example were statistically analyzed. The results are shown in Table 1, and mechanical strength tests were carried out. The results are shown in Table 2. Then, performance tests were carried out at a current density of 2500, and the results are as Figure 3 shown.

[0102] Table 1 Aperture Distribution and Porosity Data of Each Gas Diffusion Layer Sample

[0103]

[0104] Table 2 Mechanical Strength Data of Each Gas Diffusion Layer Sample

[0105]

[0106]

[0107] It can be seen from Figure 3 that: at a current density of 2500, the voltage of Example 1 is 0.542, which is higher than 0.532 of Comparative Example 1 and 0.539 of Comparative Example 2. This shows that the gas diffusion layer of Example 1 has better performance.

[0108] From Table 1, Table 2 and Figure 3 the data, it can be known that: through the microporous layer slurry of the present application, the prepared gas diffusion layer has a reasonable pore size distribution, and the porosity can also be controlled within an optimal range. At the same time, the mechanical strength of the gas diffusion layer can be improved, and it shows good performance at high current density. When using the same CCM to prepare MEA, compared with the commercial GDL, the performance of this GDL is improved.

[0109] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0110] In this application, unless otherwise stated, the orientation terms such as "upper" and "lower" specifically refer to the drawing directions in the attached drawings. Additionally, in the description of the specification of this application, the terms "comprising", "including", etc. mean "including but not limited to". In this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this text, "and / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural. In this text, "at least one" means one or more, and "multiple" means two or more. "At least one kind", "at least one item (individual) below", or similar expressions refer to any combination of these items, including any combination of single item (individual) or plural items (individuals). For example, "at least one item (individual) among a, b, or c", or, "at least one item (individual) among a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0111] The above are only specific embodiments of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A microporous layer slurry, characterized in that, The raw materials of the slurry include: polymethyl methacrylate microspheres with three different particle sizes, composite microspheres, carbon black slurry, and polytetrafluoroethylene; The composite microspheres are microspheres of polymethyl methacrylate composite halloysite nano-silicoaluminate tubes; The particle sizes of the three different particle size polymethyl methacrylate microspheres are 5μm - 10μm, 10μm - 20μm, and 20μm - 100μm respectively; the mass ratio of the three different particle size polymethyl methacrylate microspheres from small to large particle size distribution is 1:26:4; the particle size of the composite microspheres is 7μm - 20μm.

2. The microporous layer slurry according to claim 1, characterized in that, The ratio of the total mass of the polymethyl methacrylate microspheres and the composite microspheres to the total mass of the carbon black slurry and the polytetrafluoroethylene is 1:2.4 - 4.

7.

3. The microporous layer slurry according to claim 1, characterized in that, The carbon black slurry is a mixed slurry formed by conductive carbon black particles and isopropanol solution; The mass ratio of the conductive carbon black particles to the isopropanol solution is 3:1 - 10:

1.

4. The microporous layer slurry according to claim 3, characterized in that, The conductive carbon black particles include at least one of acetylene black, Vulcan XC-72, Black pearls, and carbon nanotubes.

5. The microporous layer slurry according to claim 3, characterized in that, The mass of the conductive carbon black particles accounts for 4:1 - 20:1 of the total mass of the polymethyl methacrylate microspheres and the composite microspheres, and the mass ratio of the conductive carbon black particles to the polytetrafluoroethylene is 1:10 - 1:

30.

6. A method for preparing the microporous layer slurry according to any one of claims 1 - 5, characterized in that, The method includes: Preparing composite microspheres and polymethyl methacrylate microspheres with different particle sizes respectively; Mixing the carbon black slurry and the polytetrafluoroethylene solution, and performing stirring and the first ultrasonic treatment to obtain a mixed slurry; Mixing the composite microspheres, the polymethyl methacrylate microspheres, and the mixed slurry, and performing the second ultrasonic treatment to obtain a microporous layer slurry.

7. The method according to claim 6, characterized in that, The time of the first ultrasonic treatment and the second ultrasonic treatment are 25min - 35min respectively; the frequencies of the first ultrasonic treatment and the second ultrasonic treatment are 25kHz - 40 kHz respectively.

8. A gas diffusion layer with high porosity, characterized in that, The raw materials of the gas diffusion layer include the microporous layer slurry as described in any one of claims 1 - 5 and a base layer, and the gas diffusion layer is prepared by spraying the microporous layer slurry on the base layer.

9. A method for preparing the gas diffusion layer according to claim 8, characterized in that, The method includes: Impregnating the base layer with an impregnating solution, and then performing the first drying to obtain a pretreated base layer; Spraying the microporous layer slurry as described in any one of claims 1 - 5 on the surface of the pretreated base layer, and performing roasting, and then natural cooling to obtain a crude sample; Soaking the crude sample with an organic solvent, and performing the third ultrasonic treatment to remove the polymethyl methacrylate microspheres in the microporous layer, and then performing a heat treatment to obtain a gas diffusion layer; Among them, the impregnating solution is a water repellent solution; the time of the impregnating treatment is 20min - 40min.

10. The method according to claim 9, characterized in that, The weight content of the water repellent in the microporous layer is 15% - 30%.

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