Gas diffusion layer and preparation method thereof

Abstract

The invention provides a gas diffusion layer and a preparation method thereof, and relates to the technical field of fuel cells, the surface of a substrate layer is coated with a microporous layer formed by microporous layer slurry, and the microporous layer slurry at least comprises a high-conductivity self-repairing material. The high-conductivity self-repairing material comprises one or more of an epoxy resin nano composite material, poly (3, 4-ethylenedioxythiophene)-polystyrolsulfon acid and a urea-urethane polymeric material. Based on the total weight of solids in the microporous layer slurry, the mass percent of the high-conductivity self-repairing material in the microporous layer slurry is 5%-55%. The high-conductivity self-repairing material introduced into the microporous layer of the gas diffusion layer can automatically repair microcracks and recover a conductive path, so that the automatic repairing function of the microcracks is realized, the service life of the gas diffusion layer is prolonged, and the performance and long-term durability of the fuel cell are enhanced.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a gas diffusion layer and its preparation method. Background Technology

[0002] Fuel cells have broad development prospects in transportation, backup power, and distributed power stations due to their advantages such as high energy conversion efficiency and low emissions. The core component of a fuel cell is the membrane electrode assembly (MEA), which typically consists of a gas diffusion layer (GDL), a catalyst layer, and a proton exchange membrane.

[0003] The gas diffusion layer (GDL) typically consists of a base layer and a microporous layer (MPL). Its main functions are to collect current, transfer gas, and remove water produced by electrochemical reactions, providing a channel for water-gas-heat transport in electrode reactions. The microporous layer is composed of carbon powder and hydrophobic fluoropolymers, and its main functions include drainage, gas permeability, and enhancing electron transport capabilities.

[0004] Currently, the main method for preparing the microporous layer is to uniformly mix conductive carbon black with a hydrophobic agent (PTFE), coat the mixture onto the surface of the substrate, and then calcine it at high temperature to obtain the microporous layer. However, the microporous layer of the gas diffusion layer often exhibits cracks due to process or preparation issues, making it impossible for fuel cells to meet the requirements for high durability.

[0005] To address this issue, existing technologies primarily employ material modification (such as rare earth oxide doping) and process optimization (such as hot pressing sintering). However, the microporous layers prepared still cannot achieve the ability to automatically repair cracks. After prolonged operation of the fuel cell, the GDL (Gas-Liquid Layer) will experience continuous crack propagation due to reduced mechanical stress and severe chemical corrosion, resulting in a significant decrease in gas-liquid transport efficiency. Furthermore, existing conductive agents are unable to restore the conductive path after cracks appear, leading to an increase in ohmic impedance and severely affecting the performance of the fuel cell.

[0006] Therefore, there is an urgent need to provide a gas diffusion layer with automatic crack repair function to meet the high durability requirements of fuel cells. Summary of the Invention

[0007] This invention provides a gas diffusion layer and its preparation method to solve the problems of unstable microporous layer structure and crack formation in gas diffusion layer after long-term operation in the prior art. The gas diffusion layer has a simple structure and is easy to prepare. The microporous layer it includes has the ability to self-repair cracks, which can effectively extend the service life of the gas diffusion layer and improve the durability and performance of the fuel cell.

[0008] This invention provides a gas diffusion layer comprising a base layer, the surface of which is coated with a microporous layer formed by a microporous layer slurry. The microporous layer slurry comprises at least one or more of a highly conductive self-healing material, including epoxy resin nanocomposite materials, poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS), and urea-urethane polymers. Based on the total weight of solids in the microporous layer slurry, the mass percentage of the highly conductive self-healing material in the microporous layer slurry is 5% to 55%. A mass percentage of the highly conductive self-healing material in the microporous layer slurry within the above range can achieve a better effect in repairing microporous layer cracks.

[0009] The microporous layer in the gas diffusion layer of this invention introduces a highly conductive self-healing material. This material can fill the cracks and restore the conductive path when microcracks occur, reducing performance degradation and forming a dynamic repair network. This achieves active repair and healing of cracks, extends the life of the gas diffusion layer, and improves the performance of the fuel cell.

[0010] Epoxy resin nanocomposites are novel materials composed of epoxy resin as the matrix and fiber reinforcement, exhibiting mechanical properties such as longitudinal tensile strength, transverse tensile strength, and longitudinal compressive strength. Preferably, they are carbon-based nano-epoxy resin composites, nano-silica-epoxy resin composites, or nano-cellulose-epoxy resin composites. Epoxy resin nanocomposites can be prepared by adding 1-3 wt% of nanomaterials to epoxy resin, or they can be purchased directly from reagent companies such as Aladdin.

[0011] Urea-urethane polymers exhibit self-healing properties due to the aggregation of urea bonds into microdomains or physical cross-linking points, dispersed within a matrix composed of urethane bonds. Urea bonds are among the strongest hydrogen bond donors and acceptors, and this dynamic hydrogen bond network allows the material to self-heal at heating or room temperature. After damage, the hydrogen bonds on the fracture surface can reform, healing the crack. Urea-urethane polymers are preferably made from one or both of ethyl ureaformate and ethyl 4-ureabenzoate, which can be purchased directly from reagent companies.

[0012] According to the present invention, a gas diffusion layer is provided in which the conductivity of the highly conductive self-healing material is greater than 1 S / m.

[0013] Preferably, the highly conductive self-healing material is provided in the form of a solution.

[0014] According to a gas diffusion layer provided by the present invention, the microporous layer slurry further includes a polymer, the content of which is 3% to 15% of the content of the highly conductive self-healing material. When the content of the polymer is less than 3%, the repair effect will be unsatisfactory; when the content is greater than 15%, the overall conductivity of the gas diffusion layer will decrease.

[0015] Preferably, the polymer is one or more of polyethylene glycol, polyethylene, polystyrene, and polyvinyl chloride.

[0016] Preferably, the polyethylene glycol is one or more of PEG-200, PEG-400, PEG-600, PEG-1000, PEG-3000, and PEG-6000, and more preferably PEG-400.

[0017] According to a gas diffusion layer provided by the present invention, based on the total weight of solids in the microporous layer slurry, the total content of polymer and highly conductive self-healing material in the microporous layer slurry is 5.5% to 70%; preferably, the mass percentage of the highly conductive self-healing material is 5% to 55%, and the mass percentage of the polymer is 0.5% to 15%.

[0018] According to a gas diffusion layer provided by the present invention, the microporous layer slurry further includes a conductive agent, a hydrophobic agent, and a dispersant; based on the total weight of solids in the microporous layer slurry, the mass percentage of the conductive agent is 2% to 70%, the mass percentage of the hydrophobic agent is 5% to 30%, and the mass percentage of the dispersant is 5% to 40%.

[0019] Preferably, the hydrophobic agent is provided in the form of an emulsion, and the dispersant is provided in the form of a solution.

[0020] Preferably, the dispersant is one or more of polyethylene oxide, polyvinyl alcohol, carboxymethyl cellulose, carboxyethyl cellulose, and polymethyl methacrylate.

[0021] Preferably, the microporous layer slurry further includes a solvent, which is one or more of isopropanol, n-propanol, ethanol, dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylformamide.

[0022] Preferably, the hydrophobic agent is one or two of polytetrafluoroethylene (PTFE) and polysiloxane.

[0023] The present invention also provides a method for preparing the gas diffusion layer as described above, wherein the microporous layer slurry is coated onto the surface of a substrate layer at a coating loading of 0.1~1.5 mg / cm³. 2 The microporous layer is then formed by at least drying and curing.

[0024] According to a method for preparing a gas diffusion layer provided by the present invention, the substrate layer comprises carbon paper that has undergone hydrophobic treatment.

[0025] According to a method for preparing a gas diffusion layer provided by the present invention, the microporous layer slurry includes a first slurry and a second slurry, wherein the first slurry includes a conductive agent, a dispersant, a hydrophobic agent and a solvent, and the second slurry includes the highly conductive self-healing material, a polymer and a solvent; When preparing the gas diffusion layer using the first and second slurries, the first slurry is first applied to the surface of the substrate, then dried, cured, and calcined; then the second slurry is sprayed onto the coating surface formed using the first slurry, with a spray loading of 0.1~1.0 mg / cm³. 2 The microporous layer is formed by drying and curing.

[0026] Preferably, in the first slurry, the weight of the solvent is 50-70 times the weight of the conductive agent.

[0027] Preferably, in the second slurry, the weight of the solvent is 2.1-4.3 times the weight of the highly conductive self-healing material.

[0028] Preferably, the first slurry comprises acetylene black (conductive agent), polyethylene oxide solution (dispersant), PTFE emulsion (hydrophobic agent), and isopropanol (solvent).

[0029] Preferably, the polyethylene oxide solution has a mass fraction of 0.1-1%, and the PTFE emulsion has a mass fraction of 15-25%.

[0030] More preferably, the polyethylene oxide solution has a mass fraction of 0.1-0.5%, and the PTFE emulsion has a mass fraction of 20%.

[0031] More preferably, the second slurry comprises a PEDOT:PSS solution (a highly conductive self-healing material), polyethylene glycol (a polymer), and a solvent, wherein the solvent is isopropanol and dimethyl sulfoxide, and the PEDOT:PSS is provided in solution form.

[0032] Preferably, the mass fraction of the PEDOT:PSS solution is 1-10%.

[0033] More preferably, the mass fraction of the PEDOT:PSS solution is 5%.

[0034] More preferably, the weight of the isopropanol is 2 to 4 times the weight of the PEDOT:PSS solution, and the weight of the dimethyl sulfoxide is 10 to 30% of the weight of the PEDOT:PSS solution.

[0035] In the preparation of the gas diffusion layer of the present invention, poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS) is doped into the slurry of the microporous layer. PEDOT:PSS has good conductivity and environmental stability, making it suitable for use in the harsh environment of fuel cells. Furthermore, the sulfonic acid groups in its molecular chain can form a reversible cross-linked network with the hydrophobic agent (PTFE) through hydrogen bonding or electrostatic interaction, making the structure of the microporous layer more stable. When microcracks are generated, the PEDOT:PSS molecular chains rearrange under the stimulation of humidity or temperature, which can fill the cracks and restore the conductive path, reduce performance degradation, realize the automatic healing and repair of cracks, and significantly extend the service life of the gas diffusion layer.

[0036] Furthermore, the addition of PEDOT:PSS and polyethylene glycol (PEG) to the second slurry allows the PEG chains to form hydrogen bonds with PSS, shielding the ionic interactions between PEDOT (poly(3,4-ethylenedioxythiophene)) and PSS (poly(p-phenylene sulfonic acid)). This leads to phase separation between PEDOT and PSS and facilitates the formation of aggregated PEDOT domains, thereby improving electrical conductivity. In addition, the PEG chains provide a humid environment during the fuel cell reaction, acting as a soft matrix for the PEDOT:PSS particles and ensuring thorough mixing and strong entanglement between the hydrophilic PSS chains. This structure allows the material to quickly flow back to the damaged area after cutting, achieving self-healing.

[0037] According to a method for preparing a gas diffusion layer provided by the present invention, the drying and curing temperature is 60~150℃.

[0038] This invention provides a gas diffusion layer and its preparation method. The microporous layer of the gas diffusion layer introduces a highly conductive self-healing material. Under the action of the highly conductive self-healing material, the stability of the microporous layer can be improved, and it can also automatically repair microcracks and restore conductive pathways, thereby realizing the automatic repair function of microcracks, extending the service life of the gas diffusion layer, and enhancing the performance and long-term durability of fuel cells. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 Scanning electron microscope images showing the changes in surface morphology of the gas diffusion layers prepared in Examples 1-3 from the initial stage to after 1000 hours of operation; Figure 2Scanning electron microscope image showing the surface morphology changes of the gas diffusion layer prepared for Comparative Example 1 from the initial stage to after 1000 hours of operation; Figure 3 This is a comparison chart of the polarization curves of the gas diffusion layers in Example 1 and Comparative Example 1 after 1000 hours of operation. Figure 4 This is a comparison chart of the polarization curves of the gas diffusion layers in Example 2 and Comparative Example 1 after 1000 hours of operation. Figure 5 The graph shows a comparison of the polarization curves of the gas diffusion layers in Example 3 and Comparative Example 1 after 1000 hours of operation. Figure 6 This is a comparison chart of the polarization curves of the gas diffusion layers of Example 3 and Comparative Examples 1 and 2 after 1000 hours of operation. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0042] The following is combined with Figures 1-6 This invention describes a gas diffusion layer and its preparation method.

[0043] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0044] The raw materials used in the following examples are from the following sources: Acetylene black: Model: DENKA BLACK LI Li-250, Particle size D50: 37nm; Polyethylene oxide: manufactured by Aladdin, molecular weight 2 million; PTFE emulsion: Manufacturer is Daikin Japan, product number is D210C; PEDOT:PSS: Manufacturer is Aladdin, mass fraction is 5.0wt%.

[0045] Example 1 A gas diffusion layer includes a substrate layer, the surface of which is coated with a microporous layer formed by a microporous layer slurry, the microporous layer slurry including a first slurry and a second slurry; the first slurry includes a conductive agent (acetylene black), a dispersant (polyethylene oxide), a hydrophobic agent (PTFE emulsion), and a solvent (isopropanol); the second slurry includes a highly conductive self-healing material (PEDOT:PSS), a polymer (polyethylene glycol, PEG 400), and a solvent (isopropanol and dimethyl sulfoxide).

[0046] This embodiment also provides a method for preparing the gas diffusion layer as described above, specifically including the following steps: Step 1): Impregnate the hydrophilic carbon paper (Toray TGP-H-060 carbon) in a 5% polytetrafluoroethylene (PTFE) emulsion for 15 minutes. After impregnation, place it in an oven at 100°C for 10 minutes. After drying and curing, calcine it at 360°C for 1 hour to obtain the base layer. Step 2): Weigh 0.6g of acetylene black, 30g of 0.5% polyethylene oxide solution, 1.25g of 20% PTFE emulsion, and 40g of isopropanol, mix thoroughly to obtain the first slurry; the first slurry is then screen-printed onto one side of the substrate surface until the carbon loading reaches 1.0mg / cm³. 2 Place it in an oven at 100℃ for 10 minutes; after drying and curing, place it in a muffle furnace for calcination at 360℃ for 1 hour. Step 3): Weigh 1.05g of 5% poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS) solution, 3.15g of isopropanol, 0.005g of polyethylene glycol (PEG 400), and 0.21g of dimethyl sulfoxide. Stir the mixture using ultrasonic vibration to obtain the second slurry. Apply the second slurry to the coating surface formed with the first slurry using ultrasonic spraying, with a spray loading of 0.2mg / cm³. 2 After spraying, the coating is processed in an oven at 100°C for 10 minutes to obtain a microporous layer, which is the gas diffusion layer.

[0047] In this embodiment, the total weight of solids in the microporous layer slurry is 1.0575g. Based on the total weight of solids in the microporous layer slurry, the mass percentages of the conductive agent, hydrophobic agent, dispersant, highly conductive self-healing material, and polymer are 5% and 0.5% respectively. The content of the polymer is 9.5% of the content of the highly conductive self-healing material.

[0048] Example 2 The difference from Example 1 is that in step 3): 8.67g of a 5% poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS) solution, 26.01g of isopropanol, 0.013g of polyethylene glycol (PEG 400), and 1.734g of dimethyl sulfoxide are weighed and ultrasonically stirred to obtain the second slurry. The second slurry is then ultrasonically sprayed onto the coating surface formed by the first slurry, with a spray loading of 0.2mg / cm³. 2 After spraying, the coating is processed in an oven at 100°C for 10 minutes to obtain a microporous layer, which is the gas diffusion layer.

[0049] In this embodiment, the total weight of solids in the microporous layer slurry is 1.4465g. Based on the total weight of solids in the microporous layer slurry, the mass percentages of the conductive agent, hydrophobic agent, dispersant, highly conductive self-healing material, and polymer are 41.5%, 17.3%, 10.4%, 30%, and 0.9%, respectively. The content of the polymer is 3% of the content of the highly conductive self-healing material.

[0050] Example 3 The difference from Example 1 is that in step 3): 26.9g of a 5% poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS) solution, 80.7g of isopropanol, 0.1g of polyethylene glycol (PEG 400), and 5.38g of dimethyl sulfoxide are weighed and ultrasonically stirred to obtain the second slurry. The second slurry is then ultrasonically sprayed onto the coating surface formed by the first slurry, with a spray loading of 0.2mg / cm³. 2 After spraying, the coating is processed in an oven at 100°C for 10 minutes to obtain a microporous layer, which is the gas diffusion layer.

[0051] In this embodiment, the total weight of solids in the microporous layer slurry is 2.445g. Based on the total weight of solids in the microporous layer slurry, the mass percentages of the conductive agent are 24.5%, the hydrophobic agent is 10.2%, the dispersant is 6.1%, the highly conductive self-healing material is 55%, and the polymer is 4.1%. The content of the polymer is 7.4% of the content of the highly conductive self-healing material.

[0052] Comparative Example 1 A method for preparing a gas diffusion layer, the steps of which are basically the same as those in Example 1, except that step 3 is not included.

[0053] Comparative Example 2 The difference from Example 3 is that in step 3): 33g of a 5% poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS) solution, 99g of isopropanol, 0.1g of polyethylene glycol (PEG 400), and 6.6g of dimethyl sulfoxide are weighed and ultrasonically stirred to obtain the second slurry. The second slurry is then ultrasonically sprayed onto the coating surface formed by the first slurry, with a spray loading of 0.2mg / cm³. 2 After spraying, the mixture is treated in an oven at 100°C for 10 minutes to obtain a microporous layer, which is the gas diffusion layer. The isopropanol and dimethyl sulfoxide function the same as in Example 3, acting only as solvents, and the mass ratio of both to the poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid solution is the same as in Example 3.

[0054] In this embodiment, the total weight of solids in the microporous layer slurry is 2.75g. Based on the total weight of solids in the microporous layer slurry, the mass percentage of the highly conductive self-healing material in the microporous layer slurry is 60%.

[0055] Test Example 1 The gas diffusion layers prepared in Examples 1-3 and Comparative Example 1 were used to assemble a film electrode assembly. SEM scanning electron microscopy observations were performed before and after 1000 hours of operation. Figure 1 and 2 As shown, through comparison Figure 1 and Figure 2 Cracks were found in the gas diffusion layer prepared using the present invention (Examples 1-3), which developed cracks after 1000 hours of operation. Figure 1 The gas diffusion layer is significantly smaller than that of Comparative Example 1 ( ). Figure 2 ).

[0056] Test Example 2 The gas diffusion layers prepared in Examples 1-3 and Comparative Examples 1-2 were used to assemble film electrode assemblies. Polarization curves were tested before and after 1000 hours of operation. The results of Examples 1-3 and Comparative Example 1 are shown in the figure below. Figure 3-5 As shown, the performance degradation of the single cell assembled using the gas diffusion layer prepared according to the present invention is less than that of the membrane electrode assembled using the conventional gas diffusion layer in Comparative Example 1. A comparison of the results of Example 3 with Comparative Examples 1 and 2 is shown in the figure below. Figure 6 As shown, the performance of the material containing a high content of highly conductive self-healing material (Comparative Example 2) is lower than that of Example 3 and Comparative Example 1.

[0057] Based on the above tests and analyses, this invention, by incorporating highly conductive self-healing materials into the microporous layer, enables automatic crack repair, resulting in significantly smaller cracks compared to conventional gas diffusion layers composed of microporous layers without the incorporation of highly conductive self-healing materials, thus effectively improving fuel cell performance.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A gas diffusion layer comprising a substrate layer, characterized by, The surface of the base layer is coated with a microporous layer formed by a microporous layer slurry, the microporous layer slurry at least including a high-conductivity self-repairing material, the high-conductivity self-repairing material including one or more of an epoxy resin nanocomposite, poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid, and a urea-urethane polymer; the mass percentage of the high-conductivity self-repairing material in the microporous layer slurry being 5% to 55% based on the total weight of solids in the microporous layer slurry.

2. The gas diffusion layer of claim 1, wherein The high-conductivity self-repairing material has a conductivity greater than 1 S / m.

3. The gas diffusion layer of claim 1, wherein The microporous layer slurry further includes a high-molecular polymer, the content of the high-molecular polymer being 3% to 15% of the content of the high-conductivity self-repairing material, the high-molecular polymer being one or more of polyethylene glycol, polyethylene, polystyrene, and polyvinyl chloride.

4. The gas diffusion layer of claim 3, wherein The total content of the high-molecular polymer and the high-conductivity self-repairing material in the microporous layer slurry is 5.5% to 70% based on the total weight of solids in the microporous layer slurry, and the mass percentage of the high-molecular polymer is 0.5% to 15%.

5. The gas diffusion layer according to any one of claims 1 to 4, wherein The microporous layer slurry further includes a conductive agent, a hydrophobic agent, and a dispersant; the mass percentage of the conductive agent is 2% to 70%, the mass percentage of the hydrophobic agent is 5% to 30%, and the mass percentage of the dispersant is 5% to 40% based on the total weight of solids in the microporous layer slurry.

6. The gas diffusion layer of claim 5, wherein The dispersant is one or more of polyethylene oxide, polyvinyl alcohol, carboxymethyl cellulose, carboxyethyl cellulose, and polymethyl methacrylate, and / or the hydrophobic agent is one or both of polytetrafluoroethylene and polysiloxane.

7. The gas diffusion layer according to any one of claims 1 to 4, wherein The microporous layer slurry further includes a solvent, the solvent being one or more of isopropyl alcohol, n-propanol, ethanol, dimethyl sulfoxide, N-methyl pyrrolidone, and N,N-dimethylformamide.

8. A method for producing the gas diffusion layer according to any one of claims 1 to 7, characterized by, The microporous layer slurry is coated on the surface of the substrate layer, the spray loading is 0.1-1.5 mg / cm 2 After at least drying and curing treatment, the microporous layer is formed.

9. The method for producing a gas diffusion layer according to claim 8, wherein The microporous layer slurry includes a first slurry and a second slurry, the first slurry including a conductive agent, a dispersant, a hydrophobic agent, and a solvent, and the second slurry including the high-conductivity self-repairing material, a high-molecular polymer, and a solvent. In the preparation of the gas diffusion layer using the first slurry and the second slurry, the first slurry is first coated on the surface of the substrate layer, and then dried, solidified and baked; then the second slurry is sprayed on the surface of the coating layer formed by the first slurry, and the spraying load is 0.1-1.0 mg / cm 2 , and then dried and solidified to form the microporous layer.

10. The method for producing a gas diffusion layer according to claim 8 or 9, wherein The temperature during drying and curing is 60 to 150°C.

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