Gas diffusion layer and preparation method and application thereof

Abstract

The invention provides a gas diffusion layer and a preparation method and application thereof. The gas diffusion layer comprises a substrate and a microporous layer arranged on one surface of the substrate, the preparation raw materials of the microporous layer comprise a combination of a conductive material, a binder and a first solvent; the binder includes a polymer having a hydrophobic backbone and hydrophilic pendant groups. The gas diffusion layer provided by the invention is simple in structure, adopts a polymer with a hydrophobic main chain and a hydrophilic side group as a binder and a hydrophilic-hydrophobic regulator of the microporous layer at the same time, simplifies the formula of the microporous layer, enables the microporous layer to have better bonding strength, enables the prepared microporous layer to be more compact and higher in peel strength, and is suitable for large-scale production. Meanwhile, the whole microporous layer contains hydrophilic components, so that a better water retention effect is achieved, and the water retention performance under low humidity is good.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells, and in particular relates to a gas diffusion layer and a preparation method and application thereof. Background Art

[0002] The membrane electrode assembly (MEA) is the core component of the proton exchange membrane fuel cell (PEMFC), crucially impacting the performance, cost, and lifespan of the entire fuel cell. Both the proton exchange membrane (Nafion membrane, a perfluorosulfonic acid polymer developed by DuPont that efficiently conducts protons while blocking the permeation of gases such as oxygen and hydrogen) in the membrane electrode structure and the Nafion resin in the catalyst layer require sufficient water to maintain their high proton conductivity. Traditional external humidification systems complicate the fuel cell system, leading to excessively high costs and reduced energy density. Furthermore, because fuel cells often encounter low-humidity environments in practical applications, the development and research of gas diffusion layers adapted to low-humidity conditions is of great significance.

[0003] As one of the components of the membrane electrode, the gas diffusion layer (GDL) has the main function of water vapor distribution and transmission, which is extremely important for the water management of PEMFC. In order to meet application requirements, the design and optimization of GDL need to consider the following factors: (1) It can improve the adaptability of PEMFC and make it more widely applicable, such as stable operation in cold or low humidity environments, thereby improving its market competitiveness; (2) Under low humidity conditions, it can reduce the dependence of PEMFC on complex humidity control systems, thereby simplifying system design and reducing costs; (3) Under low humidity conditions, GDL can prevent the proton exchange membrane from overdrying, reduce the physical stress and chemical degradation caused by this to the proton exchange membrane, and enhance the durability and reliability of PEMFC. Currently, chemical modification or doping methods, such as adding inorganic impurities (such as silica) to Nafion membrane, are used to improve the water retention of the membrane, but the introduction of impurities will have a significant impact on the performance of the cell.

[0004] CN116632272A discloses a gas diffusion layer with self-humidifying and water-retaining properties. Its microporous layer has hydrophilic pores, and the density of the hydrophilic pores in the direction perpendicular to the plane of the gas diffusion layer increases from the outside to the inside. This pore size distribution is beneficial to the water retention of the gas diffusion layer and optimizes its water management capabilities. However, the degree to which the water management capacity of the battery can be improved by optimizing the pore size distribution alone is very limited. Under low humidity conditions, the water retention effect of the gas diffusion layer is poor.

[0005] CN110148759A discloses a method for preparing a gas diffusion layer for a proton exchange membrane fuel cell. The method includes first subjecting a substrate layer to a hydrophobic and drying treatment, then preparing a slurry using carbon powder, a solvent, a hydrophobic agent, and a pore-forming agent. The slurry is then uniformly adhered to the substrate layer by a doctor blade coating method to a certain loading capacity, and finally drying and sintering to obtain the gas diffusion layer. However, the gas diffusion layer exhibits poor water retention under low-humidity conditions.

[0006] CN107123822A discloses a gas diffusion layer for a proton exchange membrane fuel cell and a preparation method thereof. The gas diffusion layer is composed of a support layer and a microporous layer. The microporous layer is composed of a hydrophilic carbon powder layer and a hydrophobic layer. The microporous layer of the gas diffusion layer has a multilayer structure, which makes the structure of the gas diffusion layer complex, the preparation process is complicated and tedious, the cost is high, and the consistency is poor. In addition, the multilayer structure increases the thickness of the gas diffusion layer, thereby increasing the mass transfer path of the gas diffusion layer, affecting mass transfer and damaging the performance of the battery.

[0007] Therefore, there is an urgent need to design a gas diffusion layer with adjustable hydrophilicity, simple preparation process, simple structure and wide application scenarios. Summary of the Invention

[0008] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide a gas diffusion layer and its preparation method and application. Through the screening of raw materials and structural design, the obtained gas diffusion layer has good consistency, adjustable hydrophilicity and hydrophobicity, and a wide range of application scenarios. It can be used in both high-humidity and low-humidity environments. In addition, the structure of the gas diffusion layer is simple, and the preparation process is simple and efficient.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a gas diffusion layer, which includes a substrate and a microporous layer arranged on one surface of the substrate; the raw materials for preparing the microporous layer include a combination of a conductive material, a binder and a first solvent; the binder includes a polymer having a hydrophobic main chain and hydrophilic side groups.

[0011] The gas diffusion layer (GDL) provided by the present invention has a simple structure and good performance. Among the raw materials for preparing the microporous layer, a polymer having both a hydrophobic main chain and a hydrophilic side group can be used as a binder for the microporous layer and can also adjust the hydrophilicity and hydrophobicity of the microporous layer. Compared with the traditional hydrophobic binder polytetrafluoroethylene, the amphiphilic polymer has higher bonding strength, and the prepared microporous layer is more compact, has higher peel strength, and has stronger water retention. In addition, the existing technology often adds hydrophilic substances as additives to the microporous layer to obtain a certain water retention, but this will lead to a decrease in battery performance and a complication of the microporous layer structure. The amphiphilic polymer used in the present invention can be used as both a binder and a hydrophilicity regulator for the microporous layer, which can simplify the formulation of the microporous layer.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the objectives and beneficial effects of the present invention can be better achieved and realized.

[0013] As a preferred technical solution, the conductive material includes any one of carbon black, hard carbon, soft carbon, graphite, graphene or acetylene black, or a combination of at least two of them.

[0014] In the present invention, the conductive materials can be purchased. For example, the carbon black can be purchased from but not limited to Cabot XC-72R, Cabot BP2000, Lion EC300J, Lion EC600JD, JVC FCX80, etc.

[0015] Preferably, the binder comprises any one of perfluorosulfonic acid ionomer, polyvinyl alcohol, polyvinyl pyrrolidone, epoxy resin, phenolic resin or polyacrylamide, or a combination of at least two thereof.

[0016] Preferably, the number average molecular weight of the perfluorosulfonic acid ionomer is 1000-2000, for example, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950, etc.

[0017] Preferably, the number average molecular weight of the polyvinyl alcohol is 1800-2700, for example, 1850, 1900, 1950, 2000, 2050, 2100, 2150, 2200, 2250, 2300, 2350, 2400, 2450, 2500, 2550, 2600, 2650, etc.

[0018] Preferably, the number average molecular weight of the polyvinyl pyrrolidone is 1000-2000, for example, it can be 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950, etc.

[0019] Preferably, the number average molecular weight of the epoxy resin is 1000-10000, for example, it can be 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000, 9500, etc.

[0020] Preferably, the number average molecular weight of the phenolic resin is 1200-1600, for example, 1250, 1300, 1350, 1400, 1450, 1500, 1550, etc.

[0021] Preferably, the number average molecular weight of the polyacrylamide is 1200-16000, for example, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000, 9500, 10000, 11000, 12000, 13000, 14000, 15000, etc.

[0022] Preferably, the binder is dissolved in a second solvent before use. When the binder is dissolved in a second solvent, the second solvent is also a raw material for preparing the microporous layer.

[0023] Preferably, the second solvent includes any one of n-propanol, isopropanol, ethanol, water, N,N-dimethylformamide or dimethyl sulfoxide, or a combination of at least two thereof.

[0024] Preferably, based on the total mass of the binder and the second solvent as 100%, the mass of the binder is 5-25%, for example, it can be 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 22%, 24%, etc.

[0025] Preferably, the first solvent includes any one of isopropyl alcohol, ethanol, n-propyl alcohol, n-butanol, water, 1,2-propylene glycol or ethylene glycol, or a combination of at least two thereof.

[0026] Preferably, the mass ratio of the conductive material to the binder is 1:(0.1-0.5), for example, it can be 1:0.2, 1:0.22, 1:0.25, 1:0.28, 1:0.3, 1:0.32, 1:0.35, 1:0.38, 1:0.4, 1:0.42, 1:0.45, 1:0.48, 1:0.5, etc.

[0027] Preferably, the total mass percentage of the conductive material and the binder in the raw materials for preparing the microporous layer is 0.5-10%, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, etc.

[0028] Preferably, the substrate comprises a carbon paper substrate or a carbon cloth.

[0029] Preferably, the thickness of the substrate is 140-220 μm, for example, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, 210 μm, etc.

[0030] Preferably, the thickness of the microporous layer is 10-100 μm, for example, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, etc.

[0031] Preferably, the carbon loading of the microporous layer is 1.0-2.8 mg / cm 2 , for example, it can be 1.0 mg / cm 2 , 1.1mg / cm 2 , 1.2mg / cm 2 , 1.3mg / cm 2 , 1.4mg / cm 2 , 1.5mg / cm 2 , 1.6mg / cm 2 , 1.7mg / cm 2 , 1.8mg / cm 2 , 1.9mg / cm 2 , 2mg / cm 2 , 2.1mg / cm 2 , 2.2mg / cm 2 , 2.3mg / cm 2 , 2.4mg / cm 2 , 2.5mg / cm 2 , 2.6mg / cm 2, 2.7mg / cm 2 wait.

[0032] In a second aspect, the present invention provides a method for preparing the gas diffusion layer according to the first aspect, the method comprising:

[0033] The raw materials for preparing the microporous layer are mixed and coated on a substrate, and then heat treated to obtain the gas diffusion layer.

[0034] The preparation method of the gas diffusion layer provided by the present invention is simple and efficient, reduces preparation costs, and improves product consistency.

[0035] Preferably, the mixing method comprises any one of cell pulverization, ultrasound, ultra-high speed stirrer mixing, ball milling or sand milling, or a combination of at least two thereof.

[0036] Preferably, the mixing temperature is 0-25°C, for example, it can be 2°C, 4°C, 6°C, 8°C, 10°C, 12°C, 14°C, 16°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, etc.

[0037] Preferably, the mixing time is 1-12 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, etc.

[0038] Preferably, the coating method includes any one of spraying, blade coating or electrospinning, or a combination of at least two of them.

[0039] Preferably, the coating has a thickness of 10-100 μm, for example, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, etc.

[0040] Preferably, the substrate is subjected to a hydrophobic treatment before the coating.

[0041] In the present invention, the hydrophobic treatment method comprises the following steps:

[0042] (S1) immersing the substrate in a PTFE solution having a concentration of 0.1-10 wt % for 1-10 min, and then drying at 60-100° C. for 10-120 min; repeating the above steps until the PTFE content of the substrate is 10-40 wt %;

[0043] The PTFE content of the substrate is calculated using the following formula: (m2-m1) / m1×100%; wherein m1 is the initial mass of the substrate, and m2 is the final mass of the substrate after being immersed in the PTFE solution and dried;

[0044] (S2) placing the substrate obtained in step (S1) horizontally in a tube furnace, heating it to 280-340°C at a heating rate of 3-15°C / min under a nitrogen atmosphere, and maintaining it for 20-60 minutes to remove the surfactant; then continuing to heat it to 350-400°C and maintaining it for 30-300 minutes to complete the hydrophobic treatment.

[0045] Preferably, the temperature of the heat treatment is 150-350°C, for example, 160°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, 320°C, 340°C, etc.

[0046] Preferably, the heat treatment time is 30-150 min, for example, it can be 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, etc.

[0047] Preferably, when the binder is the perfluorosulfonic acid ionomer, the temperature of the heat treatment is 280-340°C (for example, it can be 285°C, 290°C, 295°C, 300°C, 305°C, 310°C, 315°C, 320°C, 325°C, 330°C, 335°C, etc.), and the time of the heat treatment is 30-110min (for example, it can be 35min, 40min, 45min, 50min, 55min, 60min, 65min, 70min, 75min, 80min, 85min, 90min, 95min, 100min, 105min, etc.).

[0048] Preferably, when the binder is the polyacrylamide, the temperature of the heat treatment is 200-350°C (for example, it can be 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, etc.), and the time of the heat treatment is 60-120min (for example, it can be 65min, 70min, 75min, 80min, 85min, 90min, 95min, 100min, 105min, 110min, 115min, etc.).

[0049] Preferably, when the binder is the phenolic resin, the temperature of the heat treatment is 150-330°C (for example, it can be 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, etc.), and the time of the heat treatment is 60-150min (for example, it can be 65min, 70min, 75min, 80min, 85min, 90min, 95min, 100min, 105min, 110min, 115min, 120min, 125min, 130min, 135min, 140min, 145min, etc.).

[0050] The present invention controls the temperature and time of heat treatment within a certain range, combines a polymer with a hydrophobic main chain and a hydrophilic side group, and can precisely control the hydrophilicity and hydrophobicity of the microporous layer by regulating the temperature and time of heat treatment on the basis of ensuring good bonding strength and water management ability of the microporous layer, thereby optimizing the water management function of the GDL, maintaining appropriate humidity inside the battery, and ensuring the proton conductivity of the proton exchange membrane and Nafion resin. As a result, the membrane electrode equipped with the GDL has excellent performance not only under high humidification conditions, but also under low humidification conditions.

[0051] In the present invention, the hydrophilicity and hydrophobicity of the microporous layer are related to the time and temperature of the heat treatment. Within a certain range, as the time and temperature of the heat treatment increase, the hydrophilic side groups of the polymer having a hydrophobic main chain and hydrophilic side groups gradually decompose, the hydrophobicity of the microporous layer becomes stronger, and the hydrophilicity becomes worse. Therefore, it is only necessary to regulate the time and temperature of the heat treatment to regulate the hydrophilicity and hydrophobicity of the microporous layer. A gas diffusion layer that is more suitable for battery performance can be quickly and conveniently customized according to different usage scenarios and different needs of the membrane electrode.

[0052] Preferably, the heat treatment further includes a drying step before the heat treatment.

[0053] Preferably, the drying temperature is 85-100°C, for example, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C, etc.

[0054] Preferably, the drying time is 0.5-3 h, for example, 0.6 h, 0.8 h, 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h, 2 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h, etc.

[0055] Preferably, the preparation method specifically comprises the following steps:

[0056] The raw materials for preparing the microporous layer are mixed at 0-25°C for 1-12 hours, and then coated on a hydrophobically treated substrate with a thickness of 10-100 μm, followed by drying at 85-100°C for 0.5-3 hours, and finally heat-treated at 150-350°C for 30-150 minutes to obtain the gas diffusion layer.

[0057] In a third aspect, the present invention provides a use of the gas diffusion layer described in the first aspect in a proton exchange membrane fuel cell.

[0058] Preferably, the gas diffusion layer is used in the anode of the proton exchange membrane fuel cell.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] (1) The gas diffusion layer provided by the present invention uses a polymer having both a hydrophobic main chain and a hydrophilic side group, which can be used as both a binder and a hydrophilicity regulator for the microporous layer. The polymer has better bonding strength, and the prepared microporous layer is more compact and has higher peel strength. Moreover, since the entire microporous layer contains a hydrophilic component, the polymer has a better water retention effect and good water retention under low humidity conditions.

[0061] (2) The present invention uses the amphiphilic polymer as both the binder and the hydrophilicity and hydrophobicity regulator of the microporous layer, which can simplify the formulation of the microporous layer;

[0062] (3) The gas diffusion layer provided by the present invention contains only a single microporous layer, and the structure of the gas diffusion layer is simple. DETAILED DESCRIPTION

[0063] For the convenience of understanding the present invention, the present invention is given below with examples. It should be understood by those skilled in the art that the examples are only for the purpose of helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0064] The sources of some components in the following examples and comparative examples are as follows:

[0065] (1) XC-72R carbon powder: purchased from Cabot Corporation;

[0066] (2) Acetylene black: purchased from Cabot Corporation;

[0067] (3) Perfluorosulfonic acid ionomer: purchased from Sichuan Dongcai New Materials Co., Ltd., DFPSA-2079S, number average molecular weight of 1000-2000;

[0068] (4) Carbon paper substrate: purchased from Toray Industries, Inc., TGP-H-060, thickness 180 μm;

[0069] The hydrophobic treatment of the carbon paper substrate was carried out as follows:

[0070] (S1) A 0.6 g carbon paper substrate was placed in a 4 wt % PTFE solution (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., P111312, containing a surfactant) and immersed in an ultrasonic bath for 3 min. The carbon paper substrate was then removed and baked on a 95°C hot plate for 30 min. After complete drying, the above steps were repeated until the carbon paper substrate had a mass of 0.7 g.

[0071] (S2) placing the carbon paper substrate obtained in step (S1) horizontally in a tube furnace, heating the substrate to 300° C. at a heating rate of 5° C. / min under a nitrogen atmosphere, and maintaining the temperature for 30 min to remove the surfactant; then continuing to heat the substrate to 370° C. and maintaining the temperature for 180 min, and finally slowly cooling the substrate to room temperature to complete the hydrophobic treatment;

[0072] (5) Polyacrylamide: purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., P108471, number average molecular weight of 1200-16000;

[0073] (6) Phenolic resin: purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., P195710, number average molecular weight of 1200-1600;

[0074] (7) Polytetrafluoroethylene: purchased from McLean, 767293, number average molecular weight of 5000-20000.

[0075] In the following embodiments, the carbon loading of the microporous layer is tested by accurately weighing the mass before and after coating using an analytical balance and dividing the mass by the coating area to calculate the carbon loading.

[0076] Example 1

[0077] A gas diffusion layer, comprising a substrate and a microporous layer (50 μm thick) disposed on one surface of the substrate; the microporous layer is prepared from raw materials including XC-72R carbon powder, isopropyl alcohol, and a 10 wt% perfluorosulfonic acid ionomer (Nafion) solution (the solvent is n-propyl alcohol and water, with a mass ratio of 1:1);

[0078] The method for preparing the gas diffusion layer comprises the following steps:

[0079] (1) 1 g of XC-72R carbon powder was mixed with 120 g of isopropyl alcohol and the mixture was crushed in an ice bath for 30 min to obtain a uniform suspension. The suspension was then mixed with 2.5 g of a 10 wt% Nafion solution and the mixture was crushed at 0°C for 100 min to obtain a microporous layer slurry.

[0080] (2) The microporous layer slurry was sprayed onto a hydrophobic treated carbon paper substrate with a coating thickness of 50 μm and a carbon loading of 2.3 mg / cm 2 ; The coated carbon paper substrate was baked at 95°C for 30 minutes to completely dry it, and then placed horizontally in a tubular furnace. The temperature was raised to 310°C at a heating rate of 5°C / min under a nitrogen atmosphere, maintained for 100 minutes for heat treatment, and then cooled to room temperature at a cooling rate of 5°C / min to obtain the gas diffusion layer.

[0081] Example 2

[0082] A gas diffusion layer, comprising a substrate and a microporous layer (40 μm thick) disposed on one surface of the substrate; the microporous layer is prepared from raw materials comprising acetylene black, n-propanol, deionized water, and a 10 wt% Nafion solution (the solvent is n-propanol and water, with a mass ratio of 1:1);

[0083] The method for preparing the gas diffusion layer comprises the following steps:

[0084] (1) 2 g of acetylene black, 25 g of a mixed solution of n-propanol and deionized water (the mass ratio of n-propanol to deionized water is 20:1), and 7.5 g of a 10 wt% Nafion solution were mixed and ball-milled at 25 °C for 12 h to obtain a microporous layer slurry;

[0085] (2) The microporous layer slurry was scraped onto a hydrophobic treated carbon paper substrate with a coating thickness of 40 μm and a carbon loading of 2 mg / cm 2 ; The coated carbon paper substrate was placed in an oven at 100°C and baked for 30 minutes to completely dry it, then placed horizontally in a tubular furnace, heated to 310°C at a heating rate of 5°C / min under a nitrogen atmosphere, maintained for 100 minutes for heat treatment, and then cooled to room temperature at a cooling rate of 5°C / min to obtain the gas diffusion layer.

[0086] Example 3

[0087] A gas diffusion layer comprising a substrate and a microporous layer (50 μm thick) disposed on one surface of the substrate; the microporous layer is prepared from raw materials comprising XC-72R carbon powder, isopropyl alcohol, and a 10 wt% polyacrylamide aqueous solution;

[0088] The method for preparing the gas diffusion layer comprises the following steps:

[0089] (1) 1 g of XC-72R carbon powder was mixed with 120 g of isopropyl alcohol and the mixture was crushed in an ice bath for 30 min to obtain a uniform suspension. The suspension was then mixed with 1 g of a 10 wt% aqueous polyacrylamide solution and the mixture was crushed at 0°C for 100 min to obtain a microporous layer slurry.

[0090] (2) The microporous layer slurry was sprayed onto a hydrophobic treated carbon paper substrate with a coating thickness of 50 μm and a carbon loading of 2.3 mg / cm 2 ; The coated carbon paper substrate was baked at 95°C for 30 minutes to completely dry it, then placed horizontally in a tubular furnace, heated to 200°C at a heating rate of 5°C / min under a nitrogen atmosphere, maintained for 120 minutes for heat treatment, and then cooled to room temperature at a cooling rate of 5°C / min to obtain the gas diffusion layer.

[0091] Example 4

[0092] A gas diffusion layer, comprising a substrate and a microporous layer (50 μm thick) disposed on one surface of the substrate; the microporous layer is prepared from raw materials including XC-72R carbon powder, isopropyl alcohol, and a 10 wt% phenolic resin solution (the solvent is dimethyl sulfoxide and N,N-dimethylformamide, with a mass ratio of 1:1);

[0093] The method for preparing the gas diffusion layer comprises the following steps:

[0094] (1) 1 g of XC-72R carbon powder was mixed with 120 g of isopropyl alcohol and pulverized in an ice bath for 30 min to obtain a uniform suspension; the suspension was mixed with 5 g of a 10 wt% phenolic resin solution and pulverized at 0°C for 100 min to obtain a microporous layer slurry;

[0095] (2) The microporous layer slurry was sprayed onto a hydrophobic treated carbon paper substrate with a coating thickness of 50 μm and a carbon loading of 2.3 mg / cm 2 ; The coated carbon paper substrate was baked at 95°C for 30 minutes to completely dry it, and then placed horizontally in a tubular furnace. The temperature was raised to 330°C at a heating rate of 5°C / min under a nitrogen atmosphere, maintained for 100 minutes for heat treatment, and then cooled to room temperature at a cooling rate of 5°C / min to obtain the gas diffusion layer.

[0096] Example 5

[0097] A gas diffusion layer and a preparation method thereof, which differ from Example 1 only in that the heat treatment time in step (2) is 70 minutes, and the remaining raw materials, process parameters and steps are the same as those in Example 1.

[0098] Example 6

[0099] A gas diffusion layer and a preparation method thereof, which differ from Example 1 only in that the heat treatment temperature in step (2) is 300°C, and the remaining raw materials, process parameters and steps are the same as those in Example 1.

[0100] Example 7

[0101] A gas diffusion layer and a preparation method thereof, which differ from Example 1 only in that the heat treatment temperature in step (2) is 350°C and the heat treatment time is 120 minutes, and the remaining raw materials, process parameters and steps are the same as those in Example 1.

[0102] Example 8

[0103] A gas diffusion layer and a preparation method thereof, which differ from Example 1 only in that the amount of 10wt% Nafion solution used in step (1) is 0.5g, and the remaining raw materials, process parameters and steps are the same as those in Example 1.

[0104] Example 9

[0105] A gas diffusion layer and a preparation method thereof, which differ from Example 1 only in that the amount of 10wt% Nafion solution used in step (1) is 8g, and the remaining raw materials, process parameters and steps are the same as those in Example 1.

[0106] Example 10

[0107] A gas diffusion layer and a preparation method thereof, which differ from Example 1 only in that the heat treatment temperature in step (2) is 145°C, and the remaining raw materials, process parameters and steps are the same as those in Example 1.

[0108] Example 11

[0109] A gas diffusion layer and a preparation method thereof, which differ from Example 1 only in that the heat treatment temperature in step (2) is 400°C, and the remaining raw materials, process parameters and steps are the same as those in Example 1.

[0110] Comparative Example 1

[0111] A gas diffusion layer and a preparation method thereof, the preparation method comprising the following steps:

[0112] (1) 1 g of XC-72R carbon powder was mixed with 120 g of isopropyl alcohol and the mixture was crushed in an ice bath for 30 min to obtain a uniform suspension. 0.417 g of a 60 wt% polytetrafluoroethylene (PTFE) suspension (solvent: deionized water) was mixed with the suspension and the mixture was crushed at 0°C for 100 min to obtain a microporous layer slurry.

[0113] (2) The microporous layer slurry was sprayed onto a hydrophobic treated carbon paper substrate with a coating thickness of 50 μm and a carbon loading of 2.3 mg / cm 2 ; The coated carbon paper substrate was baked at 95°C for 30 minutes to completely dry it, and then placed horizontally in a tubular furnace. The temperature was raised to 310°C at a heating rate of 5°C / min under a nitrogen atmosphere, maintained for 100 minutes for heat treatment, and then cooled to room temperature at a cooling rate of 5°C / min to obtain the gas diffusion layer. The thickness of the microporous layer in the gas diffusion layer is 50 μm.

[0114] Performance Testing

[0115] The gas diffusion layers provided in the above embodiments and comparative examples were used in a single cell to test their relevant performance. The single cell includes an anode terminal plate, an anode insulating plate, an anode current collecting plate, an anode flow field plate, an anode gas diffusion layer, an anode catalyst layer, a proton exchange membrane, a cathode catalyst layer, a cathode gas diffusion layer, a cathode flow field plate, a cathode current collecting plate, a cathode insulating plate and a cathode terminal plate stacked in sequence; wherein the anode terminal plate and the cathode terminal plate are both aluminum plates; the materials of the anode insulating plate and the cathode insulating plate are both phenolic resin; the anode current collecting plate and the cathode current collecting plate are both copper plates with gold plating on the surface; the anode flow field plate and the cathode flow field plate are both carbon plates; the anode gas diffusion layer is the gas diffusion layer provided in Examples 1-11 and Comparative Example 1; the cathode catalyst layer and the anode catalyst layer are both sprayed with a Pt / C catalyst with a conductive carbon black EC600J as a carrier, and the platinum loading thereof is 0.42 mg / cm 2 and 0.06 mg / cm 2 The proton exchange membrane is Gore's M788.12 proton exchange membrane; the cathode gas diffusion layer is Freudenberg's H14cx653; the anode frame is made of 145μm PEN material, and the cathode frame is made of 100μm PEN material;

[0116] The method for preparing the single cell includes:

[0117] Use 50cm 2 The 10 flow channels (direct flow channels) fixture is assembled in sequence according to the positions of the positioning holes, and the anode end plate, anode insulating plate, anode current collecting plate, anode flow field plate, anode gas diffusion layer, anode catalyst layer, proton exchange membrane, cathode catalyst layer, cathode gas diffusion layer, cathode flow field plate, cathode current collecting plate, cathode insulating plate, and cathode end plate are assembled in sequence. The end plates on both sides are fastened with screws and bolts with an assembly torque of 4.5 Nm. The bolts are tightened diagonally to obtain the single cell.

[0118] (1) Water contact angle test: The static water contact angle of the microporous layer in the gas diffusion layer provided in the embodiment and the comparative example was tested using a static contact angle tester SZ-CAMB1 by the sitting drop method. The specific operation was as follows: the volume of the water droplet was controlled to 4 μL, and then the droplet was dropped on the sample. After waiting for 1-3 seconds, the image was captured after the droplet shape stabilized. The contact angle was automatically calculated by the software provided by the instrument. The static water contact angle of the anode catalyst layer in the single cell was measured to be 123°.

[0119] (2) Single cell polarization performance test: The test conditions are: humidity 20%, anode and cathode pressures are both 70 kPa, battery test temperature is 75 ° C, anode and cathode dew point temperatures are both 40 ° C, anode stoichiometric flow rate is 1.5, cathode stoichiometric flow rate is 2.5; select the current corresponding to 0.4 V as the starting point, and perform load reduction test at 5 A intervals, with a dwell time of 2 min at each point until the current drops to 0 A, and record 1 A / cm 2 The corresponding voltage (V) and 2A / cm 2 The corresponding voltage (V) is shown in Table 1.

[0120] Table 1

[0121]

[0122]

[0123] It can be seen from the test data in Table 1 that the water contact angle of the gas diffusion layer provided by the present invention is 142-158°, and the single cell using the gas diffusion layer provided by the present invention is 1A / cm 2 The corresponding voltage is 0.648-0.697V, 2A / cm 2 The corresponding voltage is 0.54-0.581V.

[0124] It can be seen from Examples 5-6 that shortening the heat treatment time or lowering the heat treatment temperature will result in less loss of hydrophilic groups of the binder, resulting in a stronger hydrophilicity of the microporous layer and a smaller contact angle, which can easily cause water flooding and air shortage, affecting mass transfer and reducing battery performance. This further proves the influence of heat treatment time and heat treatment temperature on the hydrophilicity and hydrophobicity of the microporous layer and battery performance.

[0125] After increasing the heat treatment time and temperature, the contact angle of Example 7 is 157°, which is 154° compared to Example 1, and its hydrophobicity is improved; at the same time, Example 7 has a contact angle of 157° at 1A / cm 2 and 2A / cm 2The performance of the above-mentioned embodiments is lower than that of Example 1. This is because increasing the temperature and time of heat treatment will lead to excessive loss of hydrophilic groups of the polymer having a hydrophobic main chain and hydrophilic side groups, the hydrophilicity of the microporous layer decreases, the hydrophobicity increases, the water retention capacity of the gas diffusion layer is insufficient under low humidity, and the battery performance decreases. This further proves that the heat treatment temperature and heat treatment time both affect the hydrophilicity and hydrophobicity of the microporous layer and have an impact on the battery performance.

[0126] In Example 8, the amount of Nafion solution used was too small, the hydrophobicity of the microporous layer increased, and the hydrophilicity of the gas diffusion layer was insufficient under low humidity, resulting in a decrease in battery performance.

[0127] In Example 9, the amount of Nafion solution used was too much, which increased the hydrophilicity of the microporous layer and easily caused water flooding and gas shortage, thereby reducing the performance of the battery.

[0128] In Example 10, the heat treatment temperature was too low, and the water retention of the gas diffusion layer was too good, resulting in serious water flooding and gas shortage, and the performance of the battery deteriorated.

[0129] The heat treatment temperature in Example 11 is too high, and the hydrophilic side groups of the binder decompose rapidly in large quantities, resulting in excessive loss of hydrophilic groups of the binder. The hydrophilicity of the microporous layer decreases, while the hydrophobicity increases. The water retention capacity of the gas diffusion layer is insufficient under low humidity, and the battery performance decreases.

[0130] The static water contact angle of the microporous layer in the gas diffusion layer provided in Example 1 is 154°, which is a hydrophobic surface, and its contact angle is greater than the static water contact angle of the anode catalyst layer (123°) and less than the static water contact angle of the microporous layer in the gas diffusion layer provided in Comparative Example 1 (160°). The gas diffusion layer provided by the present invention meets the water management requirements of the battery, and can achieve water retention while also realizing the water management requirements of liquid water being transferred from the anode catalyst layer to the gas diffusion layer.

[0131] The applicant states that while the present invention uses the aforementioned embodiments to illustrate the gas diffusion layer, its preparation method, and its application, the present invention is not limited to these embodiments. This does not necessarily mean that the present invention must rely on these embodiments in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for raw materials in the present invention, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A gas diffusion layer, characterized in that: The gas diffusion layer includes a substrate and a microporous layer disposed on one surface of the substrate; The raw materials for preparing the microporous layer include a combination of a conductive material, a binder and a first solvent; the binder includes a polymer having a hydrophobic main chain and a hydrophilic side group.

2. The gas diffusion layer according to claim 1, characterized in that The conductive material includes any one of carbon black, hard carbon, soft carbon, graphite, graphene or acetylene black, or a combination of at least two thereof.

3. The gas diffusion layer according to claim 1 or 2, characterized in that The binder includes any one or a combination of at least two of perfluorosulfonic acid ionomer, polyvinyl alcohol, polyvinyl pyrrolidone, epoxy resin, phenolic resin or polyacrylamide; Preferably, the number average molecular weight of the perfluorosulfonic acid ionomer is 1000-2000; Preferably, the number average molecular weight of the polyvinyl alcohol is 1800-2700; Preferably, the number average molecular weight of the polyvinyl pyrrolidone is 1000-2000; Preferably, the number average molecular weight of the epoxy resin is 1000-10000; Preferably, the number average molecular weight of the phenolic resin is 1200-1600; Preferably, the number average molecular weight of the polyacrylamide is 1200-16000; Preferably, the binder is dissolved in a second solvent before use; Preferably, the second solvent comprises any one of n-propanol, isopropanol, ethanol, water, N,N-dimethylformamide or dimethyl sulfoxide, or a combination of at least two thereof; Preferably, based on the total mass of the binder and the second solvent being 100%, the mass of the binder is 5-25%.

4. The gas diffusion layer according to any one of claims 1 to 3, characterized in that: The first solvent includes any one of isopropyl alcohol, ethanol, n-propyl alcohol, n-butanol, water, 1,2-propylene glycol or ethylene glycol, or a combination of at least two thereof.

5. The gas diffusion layer according to any one of claims 1 to 4, characterized in that: The mass ratio of the conductive material to the binder is 1:(0.1-0.5); Preferably, the total mass percentage of the conductive material and the binder in the raw materials for preparing the microporous layer is 0.5-10%.

6. The gas diffusion layer according to any one of claims 1 to 5, characterized in that: The substrate comprises a carbon paper substrate or a carbon cloth; Preferably, the thickness of the substrate is 140-220 μm; Preferably, the thickness of the microporous layer is 10-100 μm; Preferably, the carbon loading of the microporous layer is 1.0-2.8 mg / cm 2 .

7. A method for preparing a gas diffusion layer according to any one of claims 1 to 6, characterized in that: The preparation method comprises: The raw materials for preparing the microporous layer are mixed and coated on a substrate, and then heat treated to obtain the gas diffusion layer.

8. The preparation method according to claim 7, characterized in that The mixing method includes any one or a combination of at least two of cell crushing, ultrasound, ultra-high-speed stirrer mixing, ball milling or sand milling; Preferably, the mixing temperature is 0-25°C; Preferably, the mixing time is 1-12h; Preferably, the coating method comprises any one or a combination of at least two of spraying, blade coating or electrospinning; Preferably, the coating has a thickness of 10-100 μm; Preferably, the substrate is subjected to a hydrophobic treatment before the coating.

9. The preparation method according to claim 7 or 8, characterized in that The heat treatment temperature is 150-350°C; Preferably, the heat treatment time is 30-150 min; Preferably, the heat treatment further includes a drying step before the heat treatment; Preferably, the drying temperature is 85-100°C; Preferably, the drying time is 0.5-3 hours.

10. Use of the gas diffusion layer according to any one of claims 1 to 6 in a proton exchange membrane fuel cell.

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