Microporous layer slurry, microporous layer and fuel cell

Abstract

The invention discloses microporous layer slurry, a microporous layer and a fuel cell, the microporous layer slurry comprises first carbon powder, second carbon powder and a mixed solvent, the mass ratio of the first carbon powder in the microporous layer slurry is 4-10%, the mass ratio of the second carbon powder in the microporous layer slurry is 2-6%, and the particle size of the first carbon powder is smaller than that of the second carbon powder; the microporous layer slurry is used for being coated on the surface of a substrate layer of the gas diffusion layer to form a microporous layer. Two kinds of carbon powder with different particle sizes are adopted, macropores can be effectively formed in the microporous layer in the process of coating the surface of the substrate layer, effective water and gas channels are established, water and gas transmission balance in the operation process of the fuel cell can be conveniently controlled, a large amount of water generated by the cathode under high power can be efficiently discharged out of the fuel cell, and the fuel cell efficiency is improved. The cathode flooding phenomenon and the anode antipole phenomenon caused by excessive water are avoided to a great extent, and the performance of the fuel cell under high current density can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a microporous layer slurry, a microporous layer and a fuel cell. Background Art

[0002] As an alternative energy technology, fuel cells have attracted widespread attention and continued research and development due to their easy start-up, high energy density, zero emissions, and high energy conversion efficiency. They have been widely used as power sources for automobiles, communication base stations, portable power tools, etc.; as a commercial power supply system, their outstanding advantages are a sufficiently long operating life and high energy density, and are suitable for backup power supplies, passenger cars, material transport vehicles, submarines, etc.

[0003] Proton exchange membrane fuel cells are the most mature and commercially available fuel cells. The gas diffusion layer (GDL) is a key component of a proton exchange membrane fuel cell, located between the flow field and the catalyst layer. The GDL plays the following five roles in the membrane electrode of a proton exchange membrane fuel cell:

[0004] First, support the proton exchange membrane and catalyst layer;

[0005] Second, the cathode and anode reaction gases in the flow field flow channel are transported to the surface of the catalyst layer through molecular diffusion and Knudsen transport;

[0006] Third, the electrons generated by the catalytic layer are transferred to the electrode plate;

[0007] Fourth, the water produced in the catalytic layer is transferred to the flow channel in the gas diffusion layer through capillary effect and concentration diffusion and is removed in time to avoid mass transfer polarization.

[0008] In proton exchange membrane fuel cells, the resistance of the gas diffusion layer is a characteristic parameter of the electron transmission ability. Increased resistance will cause serious ohmic polarization problems, which will not only reduce battery performance, but also cause the temperature of the catalyst layer to rise due to heat, resulting in water loss in the proton exchange membrane, thereby reducing proton conduction efficiency; at the same time, the pore structure of the existing gas diffusion layer is small, making it difficult to stably maintain the water-gas balance during the operation of the fuel cell. As the electrochemical reaction gradually proceeds, the reaction product water will accumulate near the cathode catalyst layer, and will not only diffuse through the proton exchange membrane to the anode, but more importantly, diffuse through the cathode diffusion layer to the cathode flow field. When liquid water cannot be transferred quickly, it will cause water accumulation in the diffusion layer, that is, water flooding, which will cause the reaction gas to fail to be transmitted to the catalyst layer surface in time, resulting in serious mass transfer polarization and resulting in a decrease in battery performance. Summary of the Invention

[0009] In response to the problems existing in the above-mentioned prior art, the present invention provides a microporous layer slurry, a microporous layer and a fuel cell. The technical solution is as follows:

[0010] The present invention provides a microporous layer slurry, comprising a first carbon powder, a second carbon powder and a mixed solvent, wherein the mass proportion of the first carbon powder in the microporous layer slurry is 4% to 10%, the mass proportion of the second carbon powder in the microporous layer slurry is 2% to 6%, and the particle size of the first carbon powder is smaller than that of the second carbon powder; the microporous layer slurry is used to coat the surface of the base layer of the gas diffusion layer to form a microporous layer.

[0011] Furthermore, the particle sizes of the first carbon powder and the second carbon powder satisfy at least one of the following characteristics:

[0012] The difference in particle size between the first carbon powder and the second carbon powder is 80 nm to 250 nm;

[0013] The particle size of the first carbon powder is 20nm to 100nm;

[0014] The particle size of the second carbon powder is 100 nm to 400 nm.

[0015] Furthermore, the materials of the first carbon powder and the second carbon powder meet at least one of the following characteristics:

[0016] The first carbon powder comprises at least one of self-grinding carbon powder, superconductive carbon black, acetylene black, graphitized carbon black, carbon nanotubes, carbon whiskers, carbon nanofibers, graphene, and high surface area graphite;

[0017] The second carbon powder comprises at least one of self-grinding carbon powder, superconductive carbon black, acetylene black, graphitized carbon black, carbon nanotubes, carbon whiskers, carbon nanofibers, graphene, and high surface area graphite;

[0018] In the microporous layer slurry, the components of the first carbon powder are different from the components of the second carbon powder.

[0019] Furthermore, the microporous layer slurry further includes a dispersant, and the dispersant satisfies at least one of the following characteristics:

[0020] The dispersant is a nonionic surfactant, including at least one of vinyl alcohol, polyethylene glycol, polyethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, polyoxyethylene, polyoxyethylene sorbitol monooleate, polymethyl methacrylate microspheres, ammonium bicarbonate and polystyrene microspheres;

[0021] The mass proportion of the dispersant in the microporous layer slurry is 0.1% to 10%.

[0022] Furthermore, the mixed solvent includes deionized water and an alcohol solvent, and the alcohol solvent satisfies at least one of the following characteristics:

[0023] The alcohol solvent includes at least one of ethanol, n-propanol, isopropanol and ethylene glycol;

[0024] The alcohol solvent accounts for 5% to 30% by mass in the microporous layer slurry.

[0025] Furthermore, the microporous layer slurry further includes a hydrophobic agent, and the hydrophobic agent satisfies at least one of the following characteristics:

[0026] The hydrophobic agent includes any one of polyvinyl fluoride and silane;

[0027] The hydrophobic agent accounts for 1% to 10% by mass in the microporous layer slurry.

[0028] Furthermore, the microporous layer slurry further includes a stabilizer, and the stabilizer satisfies at least one of the following characteristics:

[0029] The stabilizer comprises at least one of polyvinyl pyrrolidone, polyvinyl alcohol, carboxymethyl cellulose, polyurethane, acrylic acid, polyurea and phenolic resin;

[0030] The stabilizer accounts for 0.1% to 5% by mass in the microporous layer slurry.

[0031] On the other hand, the present invention further provides a microporous layer, which is formed by coating the microporous layer slurry as described above on the surface of the base layer of the gas diffusion layer.

[0032] Furthermore, the microporous layer satisfies at least one of the following characteristics:

[0033] The porosity of the microporous layer is 50% to 80%;

[0034] The pores in the microporous layer have a pore diameter of 0.01 μm to 40 μm.

[0035] On the other hand, the present invention also provides a method for preparing a microporous layer, comprising:

[0036] The microporous layer slurry is coated on the surface of the base layer of the gas diffusion layer to form a microporous layer.

[0037] On the other hand, the present invention further provides a gas diffusion layer comprising a base layer and the microporous layer as described in any one of the above items, wherein the microporous layer is coated on the surface of the base layer.

[0038] On the other hand, the present invention further provides a fuel cell comprising a gas diffusion layer, wherein the gas diffusion layer comprises a substrate layer and a microporous layer as described above, wherein the microporous layer is coated on a surface of the substrate layer.

[0039] The implementation of the present invention has the following beneficial effects:

[0040] The microporous layer slurry of the present invention adopts a first carbon powder and a second carbon powder. The two carbon powders with different particle sizes can effectively form large pores during the process of coating the surface of the base layer of the gas diffusion layer, avoid pore closure, establish effective water and gas channels while reducing resistance, effectively improve the proton conductivity of the proton exchange membrane, facilitate water transmission in the microporous layer, the gas diffusion layer and the fuel cell, control the water and gas transmission balance during the operation of the fuel cell, so that a large amount of water generated by the cathode under high power can be efficiently discharged from the fuel cell, and to a great extent avoid the occurrence of cathode flooding and anode reverse polarity caused by excessive water, which is beneficial to improving the performance of the fuel cell under high current density and improving the durability of the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] To more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings used in the embodiments, wherein identical components are denoted by identical reference numerals. It is apparent that the drawings described below are merely some embodiments of the present invention, and those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0042] Figure 1 The figure is a comparison chart of the performance tests of the gas diffusion layers prepared in the embodiment of the present invention and the comparative example. DETAILED DESCRIPTION

[0043] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments, and therefore should not be understood as limiting the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0044] It should be noted that the terms "first", "second", etc. in the specification, claims, and drawings of the present invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way are interchangeable where appropriate so that the embodiments of the present invention can be implemented in an order other than the following diagrams or descriptions. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or server that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or inherent to these processes, methods, products, or devices.

[0045] In response to the problem that water flooding is prone to occur in existing fuel cells, the reaction gas cannot be transmitted to the surface of the catalytic layer in time, resulting in serious mass transfer polarization and a decrease in battery performance, an embodiment of the present invention provides a microporous layer slurry, a microporous layer and a fuel cell, wherein the microporous layer slurry is used to coat the surface of the base layer of the gas diffusion layer to form a microporous layer; wherein the microporous layer slurry includes a first carbon powder, a second carbon powder and a mixed solvent, wherein the particle size of the first carbon powder is smaller than that of the second carbon powder. By using two carbon powders with different particle sizes, large pores can be effectively established inside the microporous layer during the coating process, and it is easier to form connected through holes, which is conducive to water transmission, establishes effective water and gas channels during the operation of the fuel cell, maintains the water and gas transmission balance during the operation of the fuel cell, and thus is beneficial to the performance of the fuel cell, especially the performance under high electrical density, and is also beneficial to the improvement of the durability of the fuel cell.

[0046] Specifically, the mass proportion of the first carbon powder in the microporous layer slurry is 4% to 10%; it can be understood that the mass proportion of the first carbon powder in the microporous layer slurry can be any point value between 4% and 10%; illustratively, the mass proportion of the first carbon powder in the microporous layer slurry can be 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0047] Specifically, the mass proportion of the second carbon powder in the microporous layer slurry is 2% to 6%; it can be understood that the mass proportion of the second carbon powder in the microporous layer slurry can be any point value between 2% and 6%; illustratively, the mass proportion of the second carbon powder in the microporous layer slurry can be 2%, 3%, 3.5%, 4%, 5%, 6%, etc.

[0048] Within the mass ratio range of the first carbon powder and the second carbon powder, the formation of large-aperture through-holes can be effectively promoted during the coating process, which is convenient for the transmission of water and gas. During the operation of the fuel cell, liquid water can be quickly discharged from the fuel cell to prevent flooding. At the same time, the reaction gas can be transmitted to the surface of the catalytic layer in time to avoid the degradation of battery performance caused by mass transfer polarization, thereby effectively improving the performance and durability of the fuel cell under high electrical density.

[0049] Specifically, the particle size difference between the first carbon powder and the second carbon powder is 80nm to 250nm; it can be understood that the particle size difference between the first carbon powder and the second carbon powder can be any point value between 80nm and 250nm; illustratively, the particle size difference between the first carbon powder and the second carbon powder can be 80nm, 100nm, 150nm, 200nm, 225nm, 250nm, etc.; within this particle size difference range, the particle size difference between the first carbon powder and the second carbon powder is relatively large, which facilitates the effective formation of large pores during the coating process and is easier to form through holes, thereby facilitating the establishment of effective water and gas paths, improving the effectiveness of water and gas management of the fuel cell at high potential, and is beneficial to the performance and durability of the fuel cell.

[0050] Specifically, the particle size of the first carbon powder is 20nm~100nm; it can be understood that the particle size of the first carbon powder can be any point value between 20nm~100nm; illustratively, the particle size of the first carbon powder can be 20nm, 30nm, 50nm, 75nm, 80nm, 100nm, etc.

[0051] Specifically, the particle size of the second carbon powder is 100nm~400nm; it can be understood that the particle size of the second carbon powder can be any point value between 100nm~400nm; illustratively, the particle size of the second carbon powder can be 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, etc.

[0052] Within the particle size range of the first carbon powder and the second carbon powder, the first carbon powder is relatively small and the second carbon powder is relatively large. The two carbon powders with different particle sizes work together to effectively promote the formation of a large number of large-diameter through-holes in the microporous layer, thereby improving the proton conduction capacity of the proton exchange membrane, preventing water flooding, and improving the performance and durability of the fuel cell.

[0053] Specifically, the first carbon powder includes at least one of self-grinding carbon powder, superconductive carbon black, acetylene black, graphitized carbon black, carbon nanotubes, carbon whiskers, carbon nanofibers, graphene, and high surface area graphite.

[0054] Specifically, the second carbon powder includes at least one of self-grinding carbon powder, superconductive carbon black, acetylene black, graphitized carbon black, carbon nanotubes, carbon whiskers, carbon nanofibers, graphene, and high surface area graphite.

[0055] In some exemplary embodiments, the components of the first carbon powder and the components of the second carbon powder may be the same, but the particle sizes of the first carbon powder and the second carbon powder may be different.

[0056] In some preferred embodiments, in the microporous layer slurry, the components of the first carbon powder are different from those of the second carbon powder, or the first carbon powder and the second carbon powder belong to different types of carbon materials, so that the particle size difference between the first carbon powder and the second carbon powder is obvious, and they can cooperate with each other to promote the formation of a large number of large-aperture through-holes inside the microporous layer during the coating process, which is beneficial to maintaining the water-gas transmission balance during the operation of the fuel cell, effectively improving the proton conductivity of the proton exchange membrane, and can also efficiently discharge a large amount of water generated by the cathode from the fuel cell under high power, preventing the occurrence of cathode flooding and anode reverse polarity phenomenon, greatly improving the performance of the fuel cell under high electrical density, and is beneficial to the durability of the fuel cell; for example, in some exemplary specific embodiments, the first carbon powder includes superconducting carbon black and acetylene black, the second carbon powder is carbon nanofiber, and the first carbon powder and the second carbon powder are different types of carbon.

[0057] Specifically, the microporous layer slurry also includes a dispersant, which is a non-ionic surfactant composed of a hydrophilic group and a hydrophobic group. It can be adsorbed on the surface of the carbon powder to form a protective layer on the surface of the solid particles of the first carbon powder and the second carbon powder, thereby reducing the surface tension of the first carbon powder and the second carbon powder, preventing aggregation and precipitation within the first carbon powder and the second carbon powder and between the two, and having a good dispersion effect.

[0058] In some exemplary embodiments, the dispersant includes at least one of ethylene alcohol, polyethylene glycol, polyethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, polyethylene oxide, polyoxyethylene sorbitan monooleate, polymethyl methacrylate microspheres, ammonium bicarbonate and polystyrene microspheres, which can be obtained commercially and can effectively disperse the first carbon powder and the second carbon powder, and improve the dispersion uniformity of the first carbon powder and the second carbon powder in the microporous layer slurry.

[0059] Specifically, the mass proportion of the dispersant in the microporous layer slurry is 0.1% to 10%; it can be understood that the mass proportion of the dispersant in the microporous layer slurry can be any point value between 0.1% and 10%; illustratively, the mass proportion of the dispersant in the microporous layer slurry can be 0.1%, 0.5%, 1%, 3%, 5%, 7.5%, 10%, etc.; within this mass proportion range, the dispersant can effectively disperse the first carbon powder and the second carbon powder, which is beneficial to the uniformity of the distribution of the first carbon powder and the second carbon powder after the microporous layer slurry is coated on the surface of the base layer, and is also beneficial to improving the coating uniformity of the microporous layer, avoiding the local loss of the microporous layer in the prepared gas diffusion layer and resulting in unstable performance of the gas diffusion layer, which is beneficial to improving the uniformity of the performance of the fuel cell at high electrical density and the durability of the fuel cell.

[0060] Specifically, the mixed solvent includes deionized water and an alcohol solvent, wherein the alcohol solvent includes at least one of ethanol, n-propanol, isopropanol and ethylene glycol, and can be obtained commercially; on the one hand, the mixed solvent has good dispersibility for the first carbon powder and the second carbon powder, wherein the alcohol solvent can reduce the surface tension of the mixed solvent, making the first carbon powder and the second carbon powder easier to disperse in the mixed solvent, and the volatility of the alcohol solvent can take away part of the heat, preventing the first carbon powder and the second carbon powder from agglomerating during the dispersion process, which is beneficial to improving the mixing uniformity and dispersion uniformity of the first carbon powder and the second carbon powder in the microporous layer slurry; on the other hand, in the process of coating the surface of the base layer to form a microporous layer, the alcohol solvent is easy to volatilize, which is beneficial to accelerate the film formation speed and reduce the solvent residue in the microporous layer.

[0061] Specifically, the mass proportion of alcohol solvent in the microporous layer slurry is 5% to 30%; it can be understood that the mass proportion of alcohol solvent in the microporous layer slurry can be any point value between 5% and 30%; illustratively, the mass proportion of alcohol solvent in the microporous layer slurry can be 5%, 7.5%, 10%, 15%, 20%, 25%, 30%, etc.; within this mass proportion range, the first carbon powder and the second carbon powder can be effectively dispersed, thereby facilitating the effective establishment of large-diameter through-holes in the microporous layer during the coating process, thereby improving the water and gas transmission balance of the fuel cell during operation.

[0062] Specifically, the microporous layer slurry also includes a hydrophobic agent, which includes any one of polyvinyl fluoride and silane, which can be obtained commercially. It can greatly improve the hydrophobicity of the microporous layer formed by coating the microporous layer slurry on the surface of the base layer, which is beneficial to efficient drainage during the operation of the fuel cell, avoiding flooding, and facilitating the effective entry of air to maintain the stability of the fuel cell output power. At the same time, the improvement of hydrophobicity can also slow down the life attenuation of the fuel cell and improve the durability of the fuel cell.

[0063] Specifically, the mass proportion of the hydrophobic agent in the microporous layer slurry is 1% to 10%; it can be understood that the mass proportion of the hydrophobic agent in the microporous layer slurry can be any point value between 1% and 10%; illustratively, the mass proportion of the hydrophobic agent in the microporous layer slurry can be 1%, 3%, 5%, 7%, 9%, 10%, etc.; within this mass proportion range, the hydrophobicity of the microporous layer formed based on the microporous layer slurry can be effectively improved, the efficiency of drainage of the microporous layer can be improved, and flooding can be prevented, which is beneficial to improving the proton conductivity of the proton exchange membrane, avoiding severe mass transfer polarization, improving the performance of the fuel cell at high current density, and can also greatly reduce the risk of battery performance degradation, which is beneficial to improving the durability of the fuel cell.

[0064] Specifically, the microporous layer slurry also includes a stabilizer, which includes at least one of polyvinyl pyrrolidone, polyvinyl alcohol, carboxymethyl cellulose, polyurethane, acrylic acid, polyurea and phenolic resin, which can be obtained commercially and can effectively maintain the stability of the electrochemical reaction environment.

[0065] Specifically, the mass proportion of the stabilizer in the microporous layer slurry is 0.1% to 5%; it can be understood that the mass proportion of the stabilizer in the microporous layer slurry can be any point value between 0.1% and 5%; illustratively, the mass proportion of the stabilizer in the microporous layer slurry can be 0.1%, 0.5%, 1%, 2%, 3%, 5%, etc.; within this mass proportion range, the stability of the microporous layer and the environment in which it is located can be effectively improved, the damage that may be caused by moisture intrusion into the microporous layer structure can be reduced, and the stability of the microporous layer structure can be improved; in addition, it can also reduce the interface resistance to a certain extent and improve the output power of the fuel cell.

[0066] On the other hand, the present invention provides a microporous layer, which is formed by coating the microporous layer slurry as described above on the surface of the base layer of the gas diffusion layer. A large number of large-diameter through holes are formed in the microporous layer, which can facilitate the transmission of water. Effective water and gas channels are established in the gas diffusion layer having the microporous layer, which is beneficial to the performance of the fuel cell. It can not only efficiently discharge liquid water and prevent cathode flooding, but also facilitate the timely transmission of the reaction gas to the catalyst layer surface of the fuel cell, avoiding the occurrence of anode reversal phenomenon caused by mass transfer polarization, thereby greatly improving the performance of the fuel cell under high current density and improving the durability of the fuel cell.

[0067] Specifically, the porosity of the microporous layer is 50% to 80%; it can be understood that the porosity of the microporous layer can be any point value between 50% and 80%; illustratively, the porosity of the microporous layer can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc.; within this porosity range, it can effectively promote the rapid diffusion of gas in the gas diffusion layer and inside the fuel cell, so that the surface of the catalytic layer in the fuel cell can have a moderate supply of reactants, thereby improving the mass transfer efficiency and power density of the fuel cell; it can also effectively promote the discharge of reaction product water, maintain the water vapor transfer balance during the operation of the fuel cell, and effectively reduce the risk of cathode flooding and anode reverse polarity phenomenon under high power, which is beneficial to improving the performance and durability of the fuel cell under high current density.

[0068] Specifically, the pore size of the pores in the microporous layer is 0.01μm to 40μm; it can be understood that the pore size of the pores in the microporous layer can be any point value between 0.01μm and 40μm; illustratively, the pore size of the pores in the microporous layer can be 0.01μm, 0.1μm, 1μm, 5μm, 10μm, 20μm, 40μm, etc.; within this pore size range, it means that a large number of macropores are effectively formed in the microporous layer formed by the microporous layer slurry, which can effectively improve the proton conductivity, and is beneficial to the water-gas transport balance, avoiding the occurrence of cathode flooding and anode reverse polarity caused by excessive water residue, which is beneficial to improving the performance of the fuel cell under high electrical density.

[0069] Specifically, the thickness of the microporous layer is 40μm to 60μm; it can be understood that the thickness of the microporous layer can be any point value between 40μm and 60μm; illustratively, the thickness of the microporous layer can be 40μm, 42μm, 45μm, 50μm, 52.5μm, 55μm, 60μm, etc.; within this thickness range, the thickness of the microporous layer is relatively small, which can reduce resistance and thus reduce power output loss, especially when applied to automotive fuel cells. The acceleration of automotive fuel cells requires instantaneous output of large power, and the microporous layer in this thickness range enables the fuel cell to meet the instantaneous large power output required for vehicle acceleration.

[0070] On the other hand, the present invention also provides a method for preparing a microporous layer, comprising:

[0071] The microporous layer slurry is coated on the surface of the base layer of the gas diffusion layer to form a microporous layer.

[0072] Furthermore, the present invention also provides a method for preparing a microporous layer slurry, comprising:

[0073] mixing the dispersant and the mixed solvent to obtain a mixed solution;

[0074] mixing the mixed solution, the first carbon powder and the second carbon powder to obtain a carbon powder dispersion;

[0075] Based on the carbon powder dispersion, a microporous layer slurry is obtained.

[0076] Among them, the dispersant and the mixed solvent can be mixed by emulsification, so that the dispersant, deionized water and alcohol solvent can be mixed evenly; in some exemplary embodiments, the dispersant and the mixed solvent are emulsified in an emulsifier, and the emulsification speed is 2000rpm~3500rpm, and the time is 2min~7min; it can be understood that the emulsification speed can be any point value between 2000rpm~3500rpm, and the time can be any point value between 2min~7min, which will not be repeated here, and can effectively improve the dispersion uniformity.

[0077] Next, in the process of obtaining the carbon powder dispersion, the first carbon powder can be first added to the mixed solution and emulsified at 4000rpm~6000rpm for 8min~15min to make the first carbon powder completely dispersed in the mixed solution; then the second carbon powder is added to the mixed solution, and the emulsification is continued at 4500rpm~6500rpm for 8min~15min to make the second carbon powder completely dispersed in the mixed solution; in addition, in some optional embodiments, the second carbon powder can be first added to the mixed solution for emulsification and dispersion, and then the first carbon powder can be added to the mixed solution for emulsification and dispersion; in this way, the dispersion uniformity of the first carbon powder and the second carbon powder in the carbon powder dispersion can be effectively improved.

[0078] Next, a hydrophobic agent and a stabilizer are added to the obtained carbon powder dispersion, and the mixture is stirred at 100 rpm to 400 rpm for 15 min to 30 min to uniformly disperse the hydrophobic agent and the stabilizer, thereby obtaining a microporous layer slurry.

[0079] Finally, the microporous layer slurry is coated on the surface of the base layer, and is dried and sintered at 350° C. to 380° C. for 20 min to 50 min to obtain a microporous layer with a large number of large-diameter through-holes.

[0080] In addition, during the drying and sintering process, the base layer is treated with infiltration and sintering of a hydrophobic agent, so that the mass proportion of the hydrophobic agent in the final microporous layer decreases to a certain extent. The mass proportion of the hydrophobic agent in the microporous layer is 0.1% to 9%. It can be understood that the mass proportion of the hydrophobic agent in the microporous layer can be any point value between 0.1% and 9%, which will not be repeated here.

[0081] On the other hand, the present invention further provides a gas diffusion layer comprising a substrate layer and the microporous layer as described above, wherein the microporous layer is coated on the surface of the substrate layer.

[0082] On the other hand, the present invention provides a fuel cell, including a gas diffusion layer, which includes a base layer and a microporous layer as described above. The microporous layer is coated on the surface of the base layer. The microporous layer has a large number of large pores, which can improve the proton conductivity of the proton exchange membrane and facilitate the maintenance of water and gas transmission balance. At high power, it can also greatly avoid the occurrence of cathode flooding and anode reverse polarity phenomenon, thereby improving the performance and durability of the fuel cell under high current density.

[0083] Specifically, the fuel cell is a proton exchange membrane fuel cell for automobiles. Compared with ordinary fuel cells, such as self-breathing fuel cells, which are prone to large power loss, insufficient power output, difficulty in application in low-pressure environments, and short service life, the proton exchange membrane fuel cell for automobiles can not only be used for power sources under normal pressure such as backup batteries, but also for scenarios with pressure lower than normal pressure. For example, the proton exchange membrane fuel cell for automobiles can be used in high-altitude areas. In addition, under the condition of large power output when the vehicle accelerates, the fuel cell will produce a large amount of water, and the microporous layer has high hydrophobicity, so that the fuel cell with the microporous layer can effectively drain water through a large number of large pores, avoiding affecting the effective entry of air, and thereby avoiding the decline in battery output power. The improvement in the hydrophobicity of the microporous layer can also reduce the life decline of the fuel cell and improve the durability of the fuel cell.

[0084] The following describes specific embodiments of the present invention in conjunction with the above-mentioned microporous layer slurry and microporous layer.

[0085] Example 1

[0086] The microporous layer of this embodiment is prepared by the following steps:

[0087] According to the mass proportion of dispersant polyethylene glycol in the microporous layer slurry being 5%, the mass proportion of alcohol solvent ethanol in the microporous layer slurry being 20%, the dispersant, deionized water and alcohol solvent were mixed and emulsified at 3000 rpm for 5 minutes to obtain a mixed solution.

[0088] According to the mass proportion of the first carbon powder conductive carbon black with a particle size of 30 nm in the microporous layer slurry being 7%, the first carbon powder is added to the mixed solution and emulsified at 5000 rpm for 10 minutes; then according to the mass proportion of the second carbon powder carbon nanotube with a particle size of 240 nm in the microporous layer slurry being 4%, the second carbon powder is added to the mixed solution and emulsified at 5500 rpm for 10 minutes to obtain a carbon powder dispersion.

[0089] According to the mass proportion of hydrophobic agent polyvinyl fluoride in the microporous layer slurry being 7%, the mass proportion of stabilizer polyvinyl pyrrolidone in the microporous layer slurry being 2%, the hydrophobic agent and stabilizer were added to the carbon powder dispersion and stirred at 200 rpm for 20 minutes to obtain the microporous layer slurry.

[0090] The microporous layer slurry is coated on the surface of the base layer of the gas diffusion layer, and is dried and sintered at 350° C. for 30 minutes to form a microporous layer, thereby obtaining a gas diffusion layer.

[0091] Comparative Example 1

[0092] The difference between this embodiment and embodiment 1 is that the mass proportion of the second carbon powder in the microporous layer slurry is 7%; the rest is the same as embodiment 1.

[0093] Comparative Example 2

[0094] The difference between this comparative example and Example 1 is that the first carbon powder is not added; the rest is the same as Example 1.

[0095] Comparative Example 3

[0096] The difference between this comparative example and Example 1 is that the second carbon powder is not added; the rest is the same as Example 1.

[0097] The gas diffusion layers in the above examples and comparative examples were made into membrane electrodes and performance tests were conducted. The test results are shown in the figure below. Figure 1 As shown; it can be seen that at higher current density, the membrane electrode of Example 1 shows the best performance, which is about 100mV higher than that of Comparative Example 1, and is better than the performance of the membrane electrode with a single particle size carbon powder in Comparative Examples 2 and 3; at the same time, in the mass transfer area, the membrane electrode in Example 1 is less affected by mass transfer, indicating that the embodiment of the present invention cooperates with the first carbon powder and the second carbon powder with different particle sizes. The microporous layer slurry can effectively establish a large number of through holes in the process of forming the microporous layer, thereby improving the water vapor transmission efficiency and balance, and greatly improving the performance and durability of the fuel cell at high current density.

[0098] What is described above are only some embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art should understand that the present invention may be subject to various changes and improvements, and any modifications, equivalent substitutions and improvements made in accordance with the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A microporous layer slurry, characterized in that: The invention comprises a first carbon powder, a second carbon powder and a mixed solvent, wherein the mass proportion of the first carbon powder in the microporous layer slurry is 4% to 10%, the mass proportion of the second carbon powder in the microporous layer slurry is 2% to 6%, and the particle size of the first carbon powder is smaller than that of the second carbon powder; the microporous layer slurry is used to coat the surface of the base layer of the gas diffusion layer to form a microporous layer.

2. The microporous layer slurry according to claim 1, characterized in that The particle sizes of the first carbon powder and the second carbon powder satisfy at least one of the following characteristics: The difference in particle size between the first carbon powder and the second carbon powder is 80 nm to 250 nm; The particle size of the first carbon powder is 20nm to 100nm; The particle size of the second carbon powder is 100 nm to 400 nm.

3. The microporous layer slurry according to claim 1, characterized in that The materials of the first carbon powder and the second carbon powder meet at least one of the following characteristics: The first carbon powder comprises at least one of self-grinding carbon powder, superconductive carbon black, acetylene black, graphitized carbon black, carbon nanotubes, carbon whiskers, carbon nanofibers, graphene, and high surface area graphite; The second carbon powder comprises at least one of self-grinding carbon powder, superconductive carbon black, acetylene black, graphitized carbon black, carbon nanotubes, carbon whiskers, carbon nanofibers, graphene, and high surface area graphite; In the microporous layer slurry, the components of the first carbon powder are different from the components of the second carbon powder.

4. The microporous layer slurry according to any one of claims 1 to 3, characterized in that: The microporous layer slurry further includes a dispersant, which satisfies at least one of the following characteristics: The dispersant is a nonionic surfactant, including at least one of vinyl alcohol, polyethylene glycol, polyethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, polyoxyethylene, polyoxyethylene sorbitol monooleate, polymethyl methacrylate microspheres, ammonium bicarbonate and polystyrene microspheres; The mass proportion of the dispersant in the microporous layer slurry is 0.1% to 10%.

5. The microporous layer slurry according to any one of claims 1 to 3, characterized in that: The mixed solvent includes deionized water and an alcohol solvent, and the alcohol solvent meets at least one of the following characteristics: The alcohol solvent includes at least one of ethanol, n-propanol, isopropanol and ethylene glycol; The alcohol solvent accounts for 5% to 30% by mass in the microporous layer slurry.

6. The microporous layer slurry according to any one of claims 1 to 3, characterized in that: The microporous layer slurry further includes a hydrophobic agent, which satisfies at least one of the following characteristics: The hydrophobic agent includes any one of polyvinyl fluoride and silane; The hydrophobic agent accounts for 1% to 10% by mass in the microporous layer slurry.

7. The microporous layer slurry according to any one of claims 1 to 3, characterized in that: The microporous layer slurry further includes a stabilizer, and the stabilizer satisfies at least one of the following characteristics: The stabilizer comprises at least one of polyvinyl pyrrolidone, polyvinyl alcohol, carboxymethyl cellulose, polyurethane, acrylic acid, polyurea and phenolic resin; The stabilizer accounts for 0.1% to 5% by mass in the microporous layer slurry.

8. A microporous layer, characterized in that The microporous layer is formed by coating the microporous layer slurry according to any one of claims 1 to 7 on the surface of a base layer of a gas diffusion layer.

9. The microporous layer according to claim 8, characterized in that The microporous layer satisfies at least one of the following characteristics: The porosity of the microporous layer is 50% to 80%; The pores in the microporous layer have a pore diameter of 0.01 μm to 40 μm.

10. A fuel cell, characterized in that: The gas diffusion layer comprises a base layer and the microporous layer according to any one of claims 8 to 9, wherein the microporous layer is coated on the surface of the base layer.

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