A freestanding microporous layer for fuel cells, its preparation method, membrane electrode assembly, and fuel cell.

Abstract

This invention provides a freestanding microporous layer for fuel cells, composed of carbon nanotubes, a base carbon material, and a hydrophobic treatment agent. The carbon nanotubes provide a supporting structure for the freestanding microporous layer, the base carbon material serves as the framework of the freestanding microporous layer and provides a porous structure, and the hydrophobic treatment agent provides hydrophobic support. The microstructure of the freestanding microporous layer allows it to exist independently of the substrate layer when used as a component of the membrane electrode assembly (MEA), supporting a detachable MEA structure. Furthermore, it does not need to be coated onto the substrate layer, preventing the freestanding microporous layer from penetrating into the substrate layer and not affecting the gas transport performance of the substrate layer.

Description

Technical Field

[0001] This invention relates to the field of energy-free and clean technologies, specifically to an independent microporous layer for fuel cells, a method for preparing the same, a membrane electrode assembly, and a fuel cell. Background Technology

[0002] Hydrogen energy is considered the "ultimate energy source" of the 21st century and is the most promising candidate energy source to address the traditional fossil fuel system that causes environmental pollution, energy crises, and the greenhouse effect. Hydrogen-based fuel cells are among the most promising energy conversion devices currently available, boasting advantages such as low pollution, high energy conversion efficiency, and low noise, and possessing immense development potential. The gas diffusion layer, a crucial component of fuel cells, connects the catalyst layer and the flow field, providing essential transport channels for reactant gases and product water. After decades of development, the current structure of the gas diffusion layer in fuel cells primarily consists of a macroporous substrate layer (pore size 10 nm). 5 nm) and a microporous layer (pore size 10 nm) coated on the substrate. 2 ~10 3 The fuel cell features a bilayer structure composed of microporous layers (nm). The microporous layer provides structural support for the catalytic layer and also enhances the fuel cell's water management capabilities.

[0003] However, current commercial microporous layers still have some drawbacks. First, most current microporous layers are applied using coating methods such as blade coating, spraying, or screen printing, to the surface of the gas diffusion layer substrate to form an integrated gas diffusion layer. Solution coating inevitably introduces numerous structural defects into commercial gas diffusion layers, such as high roughness and cracks on the microporous layer surface due to solvent evaporation. These structural defects can lead to problems during the operation of actual fuel cells: on the one hand, due to these structural defects, the proton exchange membrane may deform due to uneven stress, which accelerates the aging of the proton exchange membrane and shortens the battery's lifespan; on the other hand, these structural defects can create gaps between the catalyst layer and the gas diffusion layer, leading to water accumulation during battery operation, causing flooding and limited mass transfer, reducing not only the utilization rate of the catalyst layer but also significantly degrading the performance of the fuel cell; third, the size of the microporous layer slurry (10–100 nm) in solution-coated gas diffusion layers... The pore size is much smaller than that of the substrate (>10μm). Therefore, the microporous layer can penetrate into the substrate, causing loss of the substrate's pore structure and reducing the substrate's gas transport capacity. For some gas diffusion layers with larger pore structures, such as carbon cloth, carbon felt, metal mesh, and metal foam, it is difficult to coat the microporous layer due to its traditional characteristics. Finally, the integrated structure of commercial microporous layers makes it difficult to directly separate the entire membrane electrode assembly after the catalyst layer and microporous layer of the fuel cell have fused together at the end of their lifespan. Moreover, the catalyst will adhere to the gas diffusion layer after separation, which not only increases the difficulty of disassembling and recycling the catalyst of the membrane electrode, but also causes structural damage to the gas diffusion layer, which has a longer lifespan, during catalyst recycling.

[0004] To address the structural shortcomings of commercial microporous layers, Chinese invention patent CN113964330A discloses a carbonless paper self-supporting microporous layer obtained through dry molding. This microporous layer utilizes a dry method for vegetation formation, avoiding the surface cracks and roughness caused by solvent evaporation in wet molding, preventing water accumulation at defects, alleviating flooding issues, and enhancing mass transfer in fuel cells. However, the microporous layer prepared by this method lacks a macroporous substrate layer for enhanced gas distribution. Furthermore, the preparation process requires the addition of a large amount of pore-forming agent followed by acid washing to remove it, potentially introducing ions that could affect battery performance. In addition, it is unclear whether the structure of this microporous layer can enhance the recyclability of fuel cells; therefore, its application may be limited.

[0005] Chinese invention patent CN102694184A introduces a freestanding microporous layer structure. This microporous layer structure does not depend on a macroporous substrate, avoiding penetration into the macroporous substrate during coating and preserving the abundant porosity of the macroporous structure, thus ensuring a certain level of mass transfer performance. However, the microporous layer in this patent is a commercially available microporous layer with poor tunability. Furthermore, the membrane electrode fabricated using this microporous layer remains an integrated structure, making it difficult to utilize in the recovery of the microporous layer and the reuse of the gas diffusion layer.

[0006] In view of this, the present invention provides an independent microporous layer that can exist independently of the base layer and can be directly assembled / disassembled, which ensures the good performance of the gas diffusion layer and can be reused repeatedly, thereby solving the technical problems of the prior art. Summary of the Invention

[0007] The purpose of this invention is to provide an independent microporous layer for fuel cells, a method for preparing the same, a membrane electrode assembly (MEA), and a fuel cell. The independent microporous layer in the MEA exists independently of the substrate layer and does not need to be coated onto the substrate layer during the preparation process. It has good removability, facilitates the recycling of waste catalyst coated with ion exchange membranes, and both the independent microporous layer and the substrate layer can be reused.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a freestanding microporous layer for fuel cells, comprising carbon nanotubes, a base carbon material, and a hydrophobic treatment agent; the carbon nanotubes provide a supporting structure for the freestanding microporous layer, the base carbon material serves as the framework of the freestanding microporous layer and provides a porous structure, and the hydrophobic treatment agent provides hydrophobic support for the freestanding microporous layer. The microstructure of the freestanding microporous layer allows it to exist independently of the substrate layer when used as a component of a membrane electrode assembly, without needing to be coated onto the substrate layer. Therefore, the freestanding microporous layer will not penetrate the substrate layer, and its porous structure can prevent it from affecting the gas transport performance of the substrate layer.

[0009] Preferably, by mass percentage, the freestanding microporous layer for fuel cells consists of 0-20% carbon nanotubes, 50-80% basic carbon material, and 5-30% hydrophobic treatment agent.

[0010] Preferably, the carbon nanotubes include single-walled carbon nanotubes (SWCNTs) and / or multi-walled carbon nanotubes (MWCNTs); the base carbon material is a linear carbon material, including any one or more of multi-walled carbon nanotubes, whisker carbon nanotubes, and carbon nanofibers; the hydrophobic treatment agent is a fluoropolymer, including any one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), and fluorinated ethylene-propylene copolymer (FEP).

[0011] To achieve another objective, the present invention provides a method for preparing the above-mentioned freestanding microporous layer, comprising the following steps:

[0012] S1. Preparation of dispersions: Carbon nanotubes and basic carbon materials are dispersed in water, and surfactants are added to form carbon nanotube dispersions and basic carbon material dispersions.

[0013] S2. Preparation of slurry: The carbon nanotube dispersion, the basic carbon material dispersion and the hydrophobic treatment agent are mixed and ultrasonically dispersed to obtain a slurry;

[0014] S3. Formation of the independent microporous layer: The slurry prepared in S2 is filtered to obtain a carbon film, which is then peeled off and dried to obtain the membrane-like independent microporous layer.

[0015] Preferably, the concentration of the carbon nanotube dispersion and the basic carbon material dispersion is 0.1–10 mg / mL; the concentration of the basic carbon material dispersion is 0.1–10 mg / mL; the concentration of the hydrophobic treatment agent is 6–30 wt%; and the surfactant is any one of alkyl glucoside, Tween, or polyethylene glycol octylphenyl ether.

[0016] The independent microporous layer provided by the above technical solution is used as a gas diffusion layer to assemble an independent microporous layer membrane electrode, forming an assembly structure of a membrane electrode with a detachable structure.

[0017] Preferably, the gas diffusion layer comprises the freestanding microporous layer and a substrate layer, disposed on both sides of the catalyst-coated ion exchange membrane; the freestanding microporous membrane electrode has a structure of freestanding microporous layer-substrate layer-catalyst-coated ion exchange membrane-substrate layer-freestanding microporous layer. Specifically, the substrate layer can be any one of carbon paper, carbon cloth, carbon felt, nickel foam, or copper mesh.

[0018] Preferably, the detachable assembly structure includes hot-pressing the independent microporous layer, the substrate layer, the catalyst-coated ion exchange membrane, the substrate layer, and the independent microporous layer into an integrated structure, or directly assembling and using it without hot-pressing.

[0019] Preferably, the disassembly method of the detachable assembly structure includes directly mechanically disassembling the components of the independent microporous membrane electrode or removing them after soaking in water.

[0020] The membrane electrode assembly obtained using the above technical solution can be used to assemble and prepare a fuel cell. After multiple aging and use, the independent microporous layer and the substrate layer in the membrane electrode assembly can be reused, and other components can be recycled.

[0021] The detachable membrane electrode provided in this invention uses an independent microporous layer that can be independent of the substrate layer without infiltrating, which greatly reduces the impact on the gas transport performance of the substrate layer, and the detachable structure can be recycled.

[0022] The carbon nanotubes provide a supporting structure for the freestanding microporous layer, and the base carbon material serves as the framework for the freestanding microporous layer and provides it with a porous structure. The microstructure of the freestanding microporous layer allows it to exist independently of the substrate layer when used as a component of a membrane electrode, without needing to be coated onto the substrate layer. Therefore, the freestanding microporous layer does not penetrate the substrate layer, and its porous structure prevents it from affecting the gas transport performance of the substrate layer. It has a mesh framework and a polymer filled within the mesh framework. The carbon substrate layer can be any of carbon paper, carbon cloth, carbon felt, nickel foam, or copper mesh, offering a wider range of choices compared to existing technologies.

[0023] During the assembly of fuel cells, carbon nanotubes serve as the supporting structure, while the basic carbon material acts as the framework for the independent microporous layer. This structure possesses a certain degree of rigidity, ensuring the pore structure of the microporous layer remains intact and thus maintaining the porosity of the gas diffusion layer. It also prevents deformation of the gas diffusion layer under high assembly pressure, continuing to provide support. Macroscopically, the gas diffusion layer exhibits good strength and toughness under repeated loading pressure, maintaining its porosity and enabling good aeration and drainage capabilities. This ensures the smooth progress of the fuel cell's chemical reactions, resulting in higher voltage at the same current density and thus increasing the power density of the stack, leading to excellent fuel cell performance. Furthermore, this superior supporting structure provides technical support for its reusability.

[0024] Technical effects of the present invention:

[0025] 1. The independent microporous layer provided by the technical solution of the present invention has good detachability when applied to the membrane electrode of a fuel cell, which enables the membrane electrode to be disassembled and facilitates the recycling of waste catalyst-coated ion exchange membranes. At the same time, the independent microporous layer and the substrate layer can be assembled with new catalyst-coated ion exchange membranes to obtain new membrane electrode assemblies.

[0026] 2. The independent microporous layer provided by the technical solution of the present invention can exist independently of the substrate layer. It does not need to be coated onto the substrate layer during the preparation process. It can be used after direct assembly. Therefore, the independent microporous layer will not have the problem of penetrating into the substrate layer, thus not affecting the gas transport performance of the substrate layer.

[0027] 3. By adopting the technical solution of this invention, the independent microporous layer is independent of the substrate layer, which can be widely used in a variety of macroporous substrates such as carbon paper, carbon cloth, carbon felt, metal mesh, and metal foam, thus expanding the range of raw material options. At the same time, it can be reused multiple times, greatly reducing the cost of raw materials.

[0028] 4. By adopting the technical solution of the present invention, an independent microporous layer is prepared by wet method. It is free of cracks and has a uniform thickness, which reduces the contact resistance between the gas diffusion layer and the catalyst layer, increases the utilization efficiency of the catalyst layer, and eliminates the problem of water accumulation in the interface cracks. Attached Figure Description

[0029] Figure 1 A schematic diagram of the assembly structure of the freestanding microporous membrane electrode in Embodiment 1 of the present invention.

[0030] Figure 2 A diagram illustrating the disassembly process of the motor assembly of the independent microporous membrane electrode in Embodiment 1 of this invention.

[0031] Figure 3 Comparison of the effects of different components of the freestanding microporous layer in Examples 1-5 of this invention on battery performance.

[0032] Figure 4 A comparison of the effects of carbon nanotube concentration and basic carbon material concentration on battery performance in the freestanding microporous layers of Examples 1 and 6-7 of this invention.

[0033] Figure 5 A comparison diagram of the effect of the loading of the freestanding microporous layer on battery performance in Examples 1, 8 and Comparative Example 1 of the present invention.

[0034] Figure 6 Comparison of the effects of different substrate layers on battery performance in the independent microporous layers of Examples 9-13 of this invention.

[0035] Figure 7 Comparison of the effects of different reuse cycles of the independent microporous layer and substrate layer used in the independent microporous layer of Examples 14-16 of the present invention on battery performance.

[0036] Figure 8a This is a SEM image of the cross-section of the commercially available microporous layer and substrate layer used as the gas diffusion layer in Comparative Example 1 of this invention.

[0037] Figure 8b This is a SEM image of the cross-section of the discrete microporous layer and substrate layer selected as the gas diffusion layer in Embodiment 1 of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0039] This invention provides a freestanding microporous layer composed of carbon nanotubes, a base carbon material, and a hydrophobic treatment agent. The carbon nanotubes provide strength support for the freestanding microporous layer, the base carbon material forms the framework of the freestanding microporous layer and provides a porous structure, and the hydrophobic treatment agent provides hydrophobic support for the freestanding microporous layer, preventing its pores from being occupied by liquid water and flooding in the fuel cell.

[0040] Its preparation method includes the following steps:

[0041] (1) Preparation of raw material dispersion

[0042] Preparation of carbon nanotube dispersion: Carbon nanotubes are dispersed in water, and a water-miscible surfactant is added. The carbon nanotubes can be single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or a mixture of both, with a concentration of 0.1–10 mg / mL. The surfactant used for dispersion is any one of alkyl glucoside, Tween, or polyethylene glycol octylphenyl ether. The steric hindrance of the surfactant promotes the dispersion of carbon nanotubes in water. The dispersion method is ultrasonic dispersion or mechanical stirring. Preferably, the mass of the surfactant added is 1–10 times the mass of the carbon nanotubes.

[0043] Dispersion of basic carbon materials: The basic carbon materials can be any of the linear carbon materials such as multi-walled carbon nanotubes, whisker carbon nanotubes, and carbon nanofibers. The basic carbon materials are dispersed in water, and a water-miscible surfactant is added at a concentration of 0.1–20 mg / mL. The surfactant used for dispersion is any of alkyl glucoside, Tween, or polyethylene glycol octylphenyl ether. The dispersion method is ultrasonic dispersion or mechanical stirring.

[0044] Selection of hydrophobic treatment agent: The hydrophobic treatment agent can be any of the fluoropolymers such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), and fluorinated ethylene-propylene copolymer (FEP), with a concentration of 6–30 wt%. Specifically, the hydrophobic treatment agent can be any of the following: Wokai PTFE concentrated dispersion D10362, Jingfu Technology perfluoroethylene propylene concentrated dispersion FC-D-1, and Solef PVDF concentrated dispersion XPH-838.

[0045] (2) Preparation of slurry

[0046] After mixing the carbon nanotube dispersion, basic carbon material dispersion and hydrophobic treatment agent prepared in step (1), the mixture is further mixed evenly by ultrasonic dispersion or mechanical stirring to obtain a slurry; wherein, by mass percentage, carbon nanotubes account for 0-20%, basic carbon materials account for 50-80%, and hydrophobic treatment agent accounts for 5-30%.

[0047] (3) Preparation of independent microporous layers for film formation

[0048] The above slurry was filtered to form a film, with an SMPL loading of 0.5–3.0 mg / cm³. 2 After drying the sheet-like carbon membrane obtained by vacuum filtration, peel it off from the filter membrane and place it in an oven or muffle furnace at 350°C for 10–60 minutes to remove the residual solvent and surfactant in the freestanding microporous layer after vacuum filtration and drying, so that the hydrophobic treatment agent is evenly distributed inside the freestanding microporous layer.

[0049] The above-mentioned technical solution is used to prepare a membrane-like independent microporous layer, and then the membrane electrode is assembled to prepare an independent microporous layer membrane electrode.

[0050] like Figure 1 The schematic diagram of the assembled structure of the freestanding microporous membrane electrode shows that a freestanding microporous layer 2 and a substrate layer 3 are sequentially added to both sides of the catalyst-coated ion exchange membrane 1, forming a membrane electrode with a structure of freestanding microporous layer-substrate layer-catalyst-coated ion exchange membrane-substrate layer-freestanding microporous layer. The freestanding microporous layer 2 and substrate layer 3 serve as gas diffusion layers. The membrane electrode can be integrated through hot pressing, or the fuel cell structure can be directly assembled without hot pressing. The directly assembled fuel cell structure can be disassembled to recycle or reuse its components. The hot-pressed membrane electrode can be disassembled by immersion in water, enabling the recycling or reuse of its components.

[0051] In a freestanding microporous membrane electrode, the substrate layer 3 can be made of various porous materials such as carbon cloth, carbon felt, metal foam, or metal mesh.

[0052] Catalyst-coated ion exchange membranes are general-purpose components that can be used to coat commercial catalysts such as SIN-1211-0.6 (Suzhou Shengernuo) and HPM-H151N (Suzhou Qingdong).

[0053] The independent microporous membrane electrode prepared by the above method is detachable after assembly, thus providing great convenience for the recycling and reuse of components.

[0054] See Figure 2The disassembly process of the stand-alone microporous membrane electrode assembly is provided in (a)-(h), where the catalyst-coated ion exchange membrane has an anode gas diffusion layer and a cathode gas diffusion layer on both sides, which are removed in sequence. Figure 2 In the diagram, (a) shows the assembled independent microporous membrane electrode; (b)-(c) shows the removal of the anode gas diffusion layer; (d) shows the separation of the anode independent microporous layer and the substrate layer; (e)-(f) shows the removal of the cathode gas diffusion layer; (g) shows the separation of the cathode independent microporous layer and the substrate layer; and (h) shows the membrane electrode in the disassembly completed state.

[0055] The above-described membrane electrode is used for assembling fuel cells. In this invention, all other components except the membrane electrode use common battery modules, and this invention does not limit this part.

[0056] After a single use, the individual components of the membrane electrode assembly (MEA), which uses an independent microporous layer, can be disassembled sequentially. Disassembly can be performed mechanically or by immersion in water. For fuel cells, the removability of the MEA facilitates the recycling and reuse of its components.

[0057] After disassembly, the catalyst-coated ion exchange membrane of the membrane electrode assembly can be directly recycled, while the substrate layer and the freestanding microporous layer can be reused. According to the membrane electrode assembly method provided by this invention, a new membrane electrode can be assembled after replacing the catalyst-coated ion exchange membrane for continued use.

[0058] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0059] Example 1

[0060] The method for preparing a freestanding microporous layer includes the following steps:

[0061] (1) Preparation of raw material dispersion

[0062] Preparation of carbon nanotube dispersion: Carbon nanotubes were dispersed in water. The carbon nanotubes were single-walled carbon nanotubes (SWCNTs) with a concentration of 0.5 mg / mL. The surfactant used for dispersion was Tween-80. The dispersion was performed by ultrasonication. The mass of the surfactant was 2.5 times the mass of the carbon nanotubes.

[0063] Preparation of basic carbon material dispersion: The basic carbon materials include multi-walled carbon nanotubes and whisker carbon nanotubes. The basic carbon materials are dispersed in water at a concentration of 1 mg / mL. The surfactant used for dispersion is Tween-80, and the dispersion is performed by ultrasonication. The mass of the surfactant is 0.1 times the mass of the basic carbon materials.

[0064] The carbon nanotube dispersion and the basic carbon material dispersion have the same volume.

[0065] Selection of hydrophobic treatment agent: Polytetrafluoroethylene (Wokai polytetrafluoroethylene concentrated dispersion D10362 with a concentration of 60wt%) was selected as the hydrophobic treatment agent and diluted to a concentration of 6wt%.

[0066] (2) Preparation of slurry

[0067] The carbon nanotube solution, basic carbon material and hydrophobic treatment agent prepared in step (1) are mixed. After mixing, the mixture is further mixed evenly by ultrasonic dispersion or mechanical stirring to obtain a slurry. In this slurry, by mass percentage, single-walled carbon nanotubes account for 10%, MWCNTs account for 10% of the basic carbon material, whisker carbon nanotubes account for 60%, and hydrophobic treatment agent PTFE accounts for 20%.

[0068] (3) Preparation of independent microporous layers for film formation

[0069] The slurry prepared in step (2) was used to form a film by vacuum filtration, with an SMPL loading of 0.5–3.0 mg / cm³. 2 After drying the sheet-like carbon membrane obtained by vacuum filtration, it is peeled off from the filter membrane and placed in a muffle furnace at 350°C for 30 minutes to remove the solvent and surfactant in the freestanding microporous layer, so that the hydrophobic treatment agent is evenly distributed, and a membrane-like freestanding microporous layer is obtained.

[0070] This embodiment also provides an independent microporous layer membrane electrode, which uses the above-mentioned independent microporous layer and substrate layer as gas diffusion layers. Specifically, the membrane electrode is assembled by adding the independent microporous layer and substrate layer prepared in step (3) to both sides of the proton exchange membrane in sequence, and directly assembling the membrane electrode according to the stacked structure of independent microporous layer-substrate layer-catalyst coated ion exchange membrane-substrate layer-independent microporous layer, wherein the independent microporous layer and substrate layer serve as gas diffusion layers.

[0071] In this embodiment, the substrate layer is Toray TGP-H-060 carbon paper, and the catalyst is coated on the freestanding microporous layer. The catalyst is Johnson Matthey HiSPEC 13100 (70% Pt / C), and the anode and cathode loadings are both 0.5 mg. Pt / cm 2 .

[0072] The proton exchange membrane used is DuPont's Nafion XL (27.5 microns).

[0073] Membrane electrode assembly: The gas diffusion layer substrate is Toray TGP-H-060 carbon paper, coated with a freestanding microporous layer of catalyst; the anode and cathode loadings are both 0.5 mg. Pt / cm 2 Total loading of the independent microporous layer: 2 mg / cm³ 2 .

[0074] Test conditions: 25℃, hydrogen flow rate: 30mL / min, air flow rate: 100mL / min, humidity: 60%.

[0075] The fuel cell is assembled using common components and the membrane electrode assembly provided in this embodiment, and the performance of a single cell is tested.

[0076] Example 2

[0077] The difference between this embodiment and Embodiment 1 is that the composition of the independent microporous layer is as follows: by mass percentage, 5% SWCNT content, auxiliary carbon materials including 5% MWCNT and 70% whisker carbon nanotubes, and 20% hydrophobic treatment agent PTFE.

[0078] Example 3

[0079] The difference between this embodiment and Embodiment 1 is that the composition of the independent microporous layer is as follows: by mass percentage, SWCNT content is 8.75%, auxiliary carbon materials include MWCNT 8.75% and whisker carbon nanotubes 52.5%, and hydrophobic treatment agent PTFE 30%.

[0080] Example 4

[0081] The difference between this embodiment and Embodiment 1 is that the composition of the independent microporous layer is as follows: by mass percentage, SWCNT content is 20%, auxiliary carbon materials include MWCNT 20% and whisker carbon nanotubes 40%, and hydrophobic treatment agent PTFE 20%.

[0082] Example 5

[0083] The difference between this embodiment and Embodiment 1 is that the composition of the independent microporous layer is as follows: by mass percentage, SWCNT content is 7.5%, auxiliary carbon materials include MWCNT 7.5% and whisker carbon nanotubes 45%, and hydrophobic treatment agent PTFE 40%.

[0084] Example 6

[0085] The composition of the freestanding microporous layer used in this embodiment is the same as that in Example 1. The difference is that the concentration of single-walled carbon nanotubes is 2.0 mg / mL, the concentration of the base carbon material is 10 mg / mL, and the surfactant is Tween 80. In step (1), the mass of the surfactant is 2.5 times the mass of the carbon nanotubes, and in step (2), the mass of the surfactant is 0.1 times the mass of the base carbon material. The hydrophobic treatment agent is the same as in Example 1.

[0086] Example 7

[0087] The composition of the freestanding microporous layer used in this embodiment is the same as that used in Example 1. The difference is that the concentration of single-walled carbon nanotubes is 2.0 mg / mL and the concentration of the basic carbon material is 20 mg / mL.

[0088] Example 8

[0089] The composition of the freestanding microporous layer used in this embodiment is the same as that used in Example 1. The difference is that the concentration of single-walled carbon nanotubes is 5.0 mg / mL and the concentration of the basic carbon material is 10 mg / mL.

[0090] Example 9

[0091] The composition of the freestanding microporous layer used in this embodiment is the same as that in Example 1. The difference is that the concentration of single-walled carbon nanotubes is 5.0 mg / mL, the concentration of the base carbon material is 20 mg / mL, and the surfactant is Tween 80. In step (1), the mass of the surfactant is 2.5 times the mass of the carbon nanotubes, and in step (2), the mass of the surfactant is 0.1 times the mass of the base carbon material. The hydrophobic treatment agent is the same as in Example 1.

[0092] Example 10

[0093] The difference between this embodiment and Embodiment 1 is that the loading capacity of the independent microporous layer is different.

[0094] Specifically, by mass percentage, the composition of the freestanding microporous layer includes 10% SWCNT, 10% MWCNT and 60% whisker carbon nanotubes as auxiliary carbon materials, and 20% PTFE as a hydrophobic treatment agent.

[0095] Membrane electrode assembly: The gas diffusion layer substrate is Toray TGP-H-060 carbon paper, and the catalyst is coated on an independent microporous layer. The anode and cathode loadings are both 0.5 mg. Pt / cm 2 .

[0096] Test conditions: 25℃, hydrogen flow rate: 30mL / min, air flow rate: 100mL / min

[0097] Total loading of the freestanding microporous layer: 3 mg cm -2 .

[0098] Example 11

[0099] The difference between this embodiment and Embodiment 1 is that the loading capacity of the independent microporous layer is different.

[0100] Specifically, by mass percentage, the composition of the freestanding microporous layer includes 10% SWCNT, 10% MWCNT, 60% whisker carbon nanotubes, and 20% PTFE.

[0101] Total loading of freestanding microporous layer: 2 mg cm -2

[0102] Membrane electrode assembly: A proton exchange membrane was coated with a commercial catalyst. The gas diffusion layer substrate was Toray TGP-H-060 carbon paper. The catalyst loading was 0.24 mg at the anode. Pt / cm 2 Cathode 0.48mg Pt / cm 2 .

[0103] Test conditions: 25℃, hydrogen flow rate: 30mL / min, air flow rate: 100mL / min.

[0104] Example 12

[0105] The difference between this embodiment and Embodiment 11 is that the base layer of the gas diffusion layer is carbon cloth (Shanghai Hesen Electric Co., Ltd., HCP330P hydrophobic carbon cloth).

[0106] Example 13

[0107] The difference between this embodiment and Embodiment 11 is that the base layer of the gas diffusion layer is carbon felt (Taiwan Carbon Energy GF020).

[0108] Example 14

[0109] The difference between this embodiment and Embodiment 11 is that the base layer of the gas diffusion layer is nickel foam (Suzhou Taili Foam Metal Factory, 0.3mm nickel foam).

[0110] Example 15

[0111] The difference between this embodiment and Embodiment 11 is that the base layer of the gas diffusion layer is a copper mesh (Taizhou Daoguan Rubber & Plastic Products Co., Ltd., 200 mesh copper mesh).

[0112] Example 16

[0113] This embodiment uses the composition of the freestanding microporous layer in Example 1, including 10wt% SWCNT, 10wt% MWCNT, 60wt% whisker carbon nanotubes, and 20wt% PTFE.

[0114] Total loading of freestanding microporous layer: 2 mg cm -2 .

[0115] Membrane electrode assembly: A proton exchange membrane was coated with a commercial catalyst, with a catalyst loading of 0.24 mg at the anode. Pt / cm 2 Cathode 0.48mg Pt / cm 2 .

[0116] Test conditions: 80℃, hydrogen flow rate: 125mL / min, air flow rate: 500mL / min.

[0117] This embodiment uses an unaged fuel cell.

[0118] Example 17

[0119] The only difference between this embodiment and Example 12 is the aging of the battery after one catalyst coating proton exchange membrane aging (equivalent time: 500 hours at 1.2V). The independent microporous layer and the substrate layer are reused for the first time. Assembly is performed according to the method of Example 1.

[0120] Example 18

[0121] The only difference between this embodiment and Example 12 is that the battery has undergone four aging cycles of the catalyst-coated proton exchange membrane (equivalent time: 500 hours at 1.2V). The independent microporous layer and the substrate layer are reused for the fourth time. Assembly is performed according to the method of Example 1.

[0122] Comparative Example 1

[0123] The difference between this comparative example and Example 6 is that a commercially available microporous layer was used instead of the freestanding microporous layer provided in Example 6. The commercially available microporous layer was TGP-H-060+ screen-printed microporous layer (purchased from Shanghai Hesen Electric Co., Ltd.), and the total loading of the microporous layer was 2 mg / cm³. 2 .

[0124] Table 1. Composition of the freestanding microporous layers in Examples 1-5

[0125]

[0126] Examples 1-5 illustrate battery performance under different composition ratios of the independent microporous layer (see Table 1). Figure 3 Examples 4 and 5, with their high PTFE and SWCNT content, showed a significant decrease in current density. Clearly, excessively high SWCNT or PTFE content leads to an overly dense, unconfined microporous layer, resulting in poor battery performance. It is reasonable to infer that unconfined microporous layer-assembled membrane electrodes prepared with SWCNT content greater than 20 wt% or PTFE content greater than 40 wt% will exhibit poor battery performance when used in batteries.

[0127] Examples 1 and 6-9 illustrate the effects of different carbon nanotube concentrations and base carbon material concentrations on battery performance. (See attached examples.) Figure 4 Increasing the concentrations of both the carbon nanotube dispersion and the basic carbon material dispersion can improve the mass transfer performance of their bulk diffusion layers; and increasing the total concentration of the carbon nanotube dispersion and the basic carbon material dispersion can improve the mass transfer performance of the gas diffusion layer.

[0128] Examples 1, 10, and Comparative Example 1 illustrate the effect of different freestanding microporous layer loadings on battery performance. (See attached documentation.) Figure 5 It is evident that the battery performance of Example 1 and Example 10 is significantly better than that of Comparative Example 1 (commercial microporous layer), with the battery performance of Example 1 being superior to that of Example 10.

[0129] Examples 11-15 illustrate battery performance testing using different substrates. (See attached document.) Figure 6 Carbon felt is the best, followed by carbon cloth and copper mesh.

[0130] Examples 16-18 illustrate the effect of different numbers of reuses of the freestanding microporous layer and substrate layer on battery performance. (See attached examples.) Figure 7 Reusing the material once has almost no impact on battery performance, while reusing it four times results in a slight decrease. Therefore, the independent microporous layer and substrate layer can be reused using the technical solution of this invention.

[0131] See Figure 8a The commercially available microporous layer used in Comparative Example 1 is deeply embedded in the substrate layer and firmly bonded to it, making separation between the microporous layer and the substrate layer extremely difficult. Furthermore, the surface of the commercial microporous layer exhibits certain defects, as shown in the figure, with significant high roughness and cracks. Therefore, the commercial microporous layer requires hot pressing to achieve good contact with the catalyst layer. This hot pressing process leads to fusion between the microporous layer and the substrate layer, requiring repeated boiling and washing to weaken the bond between the microporous layer, catalyst layer, and proton exchange membrane before separation can be achieved. Even after separation, it cannot be recycled. Therefore, the microporous layer in this comparative example is extremely difficult to reuse by direct disassembly after aging.

[0132] See Figure 8b The figure shows the freestanding microporous layer prepared in Example 1. As can be seen from the figure, the surface of the freestanding microporous layer is smooth and crack-free, and the boundary between the microporous layer and the substrate layer is clear. After the membrane electrode assembly, the microporous layer and the substrate layer can make good contact. Therefore, hot pressing is not required. The freestanding microporous layer and the substrate layer can make independent and good contact, and there is no interlayer fusion problem as in Comparative Example 1. Therefore, it has good mechanical disassembly. After disassembly, the microporous layer and the substrate layer can be reused.

[0133] In summary, this invention provides a freestanding microporous layer prepared via a wet process. This layer is crack-free and has a uniform thickness, reducing the contact resistance between the gas diffusion layer and the catalyst layer, increasing the utilization efficiency of the catalyst layer, and eliminating the problem of water accumulation in interfacial cracks. Furthermore, the freestanding microporous layer exists independently of the substrate layer and does not need to be coated onto the substrate layer during preparation. Therefore, the freestanding microporous layer does not penetrate into the substrate layer, meaning it does not affect the gas transport performance of the substrate layer.

[0134] The above are merely preferred embodiments of the present invention and do not limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any changes, modifications, substitutions, integrations, and parameter alterations to these embodiments within the spirit and principles of the present invention, achieved through conventional substitutions or by achieving the same function without departing from the principles and spirit of the present invention, fall within the scope of protection of the present invention.

Claims

1. A freestanding microporous layer for a fuel cell, characterized in that, It is composed of carbon nanotubes, basic carbon materials, and hydrophobic treatment agents; The carbon nanotubes provide a supporting structure for the freestanding microporous layer, the base carbon material serves as the framework of the freestanding microporous layer and provides a porous structure for the freestanding microporous layer, and the hydrophobic treatment agent provides hydrophobic support for the freestanding microporous layer. By mass percentage, the freestanding microporous layer consists of 5-10% carbon nanotubes, 61.25-75% basic carbon material, and 20-30% hydrophobic treatment agent; The carbon nanotubes are single-walled carbon nanotubes; The basic carbon materials are multi-walled carbon nanotubes and whisker carbon nanotubes.

2. The freestanding microporous layer for fuel cells according to claim 1, characterized in that, The hydrophobic treatment agent is a fluoropolymer, including any one of polytetrafluoroethylene, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, and fluorinated ethylene-propylene copolymer.

3. A method for preparing an independent microporous layer for a fuel cell as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. Preparation of dispersion: Carbon nanotubes are dispersed in water and a surfactant is added to form a carbon nanotube dispersion; Basic carbon materials are dispersed in water, and surfactants are added to form a basic carbon material dispersion. S2. Preparation of slurry: The carbon nanotube dispersion, the basic carbon material dispersion and the hydrophobic treatment agent are mixed and ultrasonically dispersed to obtain a slurry; S3. Formation of the independent microporous layer: The slurry prepared in S2 is filtered to obtain a carbon film, which is then peeled off and dried to obtain the membrane-like independent microporous layer.

4. The method for preparing a freestanding microporous layer for a fuel cell according to claim 3, characterized in that, In S1, the concentrations of the carbon nanotube dispersion and the basic carbon material dispersion are both 0.1–10 mg / mL; the concentration of the hydrophobic treatment agent is 6–30 wt%. The surfactant is any one of alkyl glucoside, Tween, or polyethylene glycol octylphenyl ether.

5. A freestanding microporous layer membrane electrode having a detachable assembly structure; comprising a freestanding microporous layer as described in any one of claims 1-2 or a freestanding microporous layer prepared by the preparation method described in any one of claims 3-4.

6. The freestanding microporous film electrode as described in claim 5, characterized in that, The gas diffusion layer of the freestanding microporous membrane electrode includes the freestanding microporous layer and the substrate layer, and the gas diffusion layer is disposed on both sides of the catalyst-coated ion exchange membrane; the freestanding microporous membrane electrode has a structure of freestanding microporous layer-substrate layer-catalyst-coated ion exchange membrane-substrate layer-freestanding microporous layer.

7. The freestanding microporous film electrode as described in claim 6, characterized in that, The detachable assembly structure includes hot-pressing the independent microporous layer, the substrate layer, the catalyst-coated ion exchange membrane, the substrate layer, and the independent microporous layer into an integrated structure, or assembling and using it directly without hot-pressing.

8. The freestanding microporous film electrode as described in claim 7, characterized in that, The disassembly method of the detachable assembly structure includes directly mechanically disassembling the components of the independent microporous membrane electrode or removing them after soaking in water.

9. A fuel cell comprising an independent microporous layer as described in any one of claims 1-2 or an independent microporous layer prepared by the preparation method described in any one of claims 3-4; or comprising an independent microporous membrane electrode as described in any one of claims 5-7; wherein the independent microporous layer can be reused multiple times after the fuel cell has been aged and used.

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