Composite filament for in-situ growth of carbon nanotubes as well as preparation method and application of composite filament

Abstract

The invention provides a composite filament for in-situ growth of carbon nanotubes as well as a preparation method and application of the composite filament. The method comprises the following steps: placing carbon fiber short shreds in a rotary furnace, and heating to 650-850 DEG C; introducing an absolute ethyl alcohol solution containing nickel acetylacetonate and tetraethoxysilane into the hearth by using inert gas, and keeping at a constant temperature; keeping the hearth rotating, and naturally cooling to obtain the composite filament of the in-situ growth carbon nano tube; and preparing the integrated gas diffusion layer from the composite filament with the carbon nanotube content less than 15% and the composite filament with the carbon nanotube content greater than or equal to 15%. The technical problem to be solved is to enable an integrated gas diffusion layer to effectively eliminate macroscopic interface difference so as to reduce electron conduction resistance and mass transfer impedance. A hydrophilic and hydrophobic gradient is formed by regulating and controlling the content of the carbon nanotubes of the composite filaments so as to solve the problem of water vapor management antagonism; meanwhile, the GDL thickness and the surface density are accurately controllable, the mechanical supporting performance and the cell performance under the high power density are considered, the process is stable and repeatable, and the industrial application requirement of the proton exchange membrane fuel cell is met.

Description

Technical Field

[0001] This invention relates to the field of proton exchange membrane fuel cell (PEMFC) core component preparation technology, and particularly to a composite filament for in-situ growth of carbon nanotubes, its preparation method and application. Background Technology

[0002] The gas diffusion layer (GDL) is a core component of a proton exchange membrane fuel cell, undertaking four core functions: electron conduction, gas transport, liquid water management, and mechanical support. Its structure and design directly determine the fuel cell's limiting current density, hydrothermal management efficiency, and durability. Currently, mainstream GDLs adopt a multi-layer composite structure consisting of a carbon paper substrate, a microporous layer, and a hydrophobic layer. As fuel cells develop towards higher power density and longer lifespan, the multi-layer composite structure of traditional GDLs is gradually showing performance bottlenecks: First, there is antagonism in electron-mass transport coupling. While increasing stacking pressure can reduce interlayer contact resistance, it leads to increased tortuosity of the mass transfer channels and a simultaneous increase in mass transfer impedance. Engineering design requires a compromise between ohmic impedance and mass transfer impedance. Second, there is antagonism in hydrophilic-hydrophobic requirements. GDLs need to balance the drainage and flood prevention requirements under high current density with the passive moisturizing requirements of the proton exchange membrane (PEM) under low humidity. However, the inherent differences in the wetting characteristics of the carbon paper substrate and the microporous layer result in poor consistency in water and gas management under variable load conditions.

[0003] In recent years, some studies have attempted to improve gas-deposit drainage (GDL) using nanomaterials such as carbon nanotubes (CNTs) and graphene to achieve integrated design. Examples include in-situ growth of carbon nanotubes on the surface of carbon paper using a flame-calcination method to create an integrated carbon paper-microporous layer GDL; direct growth of spun-type CNTs on the surface of carbon paper using organic small-molecule liquids and hydrogen; and inserting carbon nanotubes as independent functional layers between the carbon paper substrate and the microporous layer to improve interlayer interface differences. However, existing carbon nanotube-based GDL improvement technologies are limited to carbon paper surface modification / functional layer construction, exhibiting the following drawbacks: the carbon nanotubes grown / coated on the carbon paper surface are essentially still multilayer composite structures, making it difficult to significantly reduce the GDL thickness, resulting in relatively high mass transfer resistance. Furthermore, it is impossible to achieve differentiated hydrophilic functional region design on the same GDL, making it difficult to simultaneously meet the contradictory requirements of high current density drainage and low humidity humidification. Summary of the Invention

[0004] The main objective of this invention is to provide a composite filament for in-situ growth of carbon nanotubes, its preparation method, and its application. The technical problem to be solved is how to prepare an integrated gas diffusion layer by in-situ growing composite filaments of carbon nanotubes, so that the prepared integrated gas diffusion layer can effectively eliminate macroscopic interface differences to reduce electron conduction resistance and mass transfer impedance; differentiated design can be achieved by controlling the carbon nanotube content of the composite filaments, thereby forming a hydrophilic-hydrophobic gradient to solve the water-gas management antagonism problem; at the same time, the thickness and areal density of the gas diffusion layer can be precisely controlled, taking into account both mechanical support and battery performance under high power density, and the preparation process is stable and repeatable, ultimately adapting to the industrial application requirements of proton exchange membrane fuel cells.

[0005] The objective of this invention and the technical problem it solves are achieved through the following technical solution. A method for preparing composite filaments of in-situ grown carbon nanotubes according to this invention includes the following steps: Short carbon fiber filaments are placed in a rotary kiln, and the kiln rotates. Inert gas is introduced into the kiln, and the temperature is raised to 650~850℃ to maintain a constant temperature inside the kiln. Prepare an anhydrous ethanol solution of nickel acetylacetonate and tetraethyl orthosilicate; introduce the solution into the furnace using an inert gas as a carrier gas and maintain it at a constant temperature; Stop heating, keep the furnace rotating, and allow the furnace to cool naturally to obtain composite filaments of in-situ grown carbon nanotubes.

[0006] The objectives of this invention and the technical problems it addresses can be further achieved by the following technical measures.

[0007] Preferably, in the preparation method, the concentration of nickel acetylacetone is 0.005~0.02 mol / L and the concentration of tetraethyl orthosilicate is 0.002~0.005 mol / L.

[0008] Preferably, in the preparation method, the isothermal holding time is 2-8 hours; and the mass content of carbon nanotubes in the composite filament is 5-30%.

[0009] Preferably, in the preparation method, the rotation speed of the furnace is 10~20 rpm.

[0010] Preferably, in the preparation method, the inert gas is argon with a flow rate of 800-1000 ccm.

[0011] The objective of this invention and the technical problem it solves are achieved through the following technical solution. A composite filament for in-situ growth of carbon nanotubes, according to this invention, comprises: Short carbon fiber filaments; Carbon nanotubes are grown in situ on the surface and in the micropores of chopped carbon fibers, forming an integrated composite structure with no macroscopic interface; the mass content of carbon nanotubes in the composite filament is 5% to 30%.

[0012] The objective of this invention and the technical problem it solves are achieved through the following technical solution. A method for preparing an integrated gas diffusion layer according to this invention includes the following steps: S1 The aforementioned in-situ grown carbon nanotube composite filaments are prepared according to the aforementioned method; those with a carbon nanotube mass content of <15% are low-density composite filaments, and those with a carbon nanotube mass content of ≥15% are high-density composite filaments. S2 involves mixing low-density composite filaments with carboxymethyl cellulose and then hot-pressing the mixture to obtain membrane layer A; then mixing high-density composite filaments with carboxymethyl cellulose and then hot-pressing the mixture to obtain membrane layer B. S3 stacks membrane layer A and membrane layer B, aligns the edges, and then hot-presses them to obtain an integrated gas diffusion layer.

[0013] The objectives of this invention and the technical problems it addresses can be further achieved by the following technical measures.

[0014] Preferably, in the preparation method, the low-density composite filament content in film layer A is 85-90% by mass percentage, and the high-density composite filament content in film layer B is 80-85%; the hot pressing temperature of the first and second hot pressing is 50-80℃, and the hot pressing pressure is 5-10MPa; the hot pressing temperature of the third hot pressing is 110-130℃, and the hot pressing pressure is 15-30MPa.

[0015] The objective of this invention and the technical problem it solves are achieved by the following technical solution. According to this invention, an integrated gas diffusion layer comprises: The first gas diffusion layer is composed of the aforementioned in-situ grown carbon nanotube composite filaments and carboxymethyl cellulose; the mass content of carbon nanotubes in the composite filaments is <15%; and the composite filament content is 85-90% by mass percentage. A second gas diffusion layer is disposed on the first gas diffusion layer; the second gas diffusion layer is composed of the aforementioned in-situ grown carbon nanotube composite filaments and carboxymethyl cellulose; the mass content of carbon nanotubes in the composite filaments is ≥15%; and the composite filament content is 80~85% by mass percentage. The first gas diffusion layer and the second gas diffusion layer form an integral gas diffusion layer with a thickness of 100~160μm and an areal density of 0.15~0.24g / cm³. 2 The contact angle on the first gas diffusion layer side is 70~100°, and the contact angle on the second gas diffusion layer side is 90~130°.

[0016] The objective of this invention and the technical problem it solves are achieved by the following technical solution: An application of the aforementioned integrated gas diffusion layer in a proton exchange membrane fuel cell, according to this invention.

[0017] By employing the above technical solution, the composite filament for in-situ growth of carbon nanotubes proposed in this invention, its preparation method, and its application have at least the following beneficial effects: This invention proposes an in-situ grown carbon nanotube composite filament, its preparation method, and its application. It encompasses a complete technology chain, including composite filament preparation, composite filament products, GDL preparation, GDL products, and PEMFC applications. The beneficial effects of each technical solution are progressively enhanced. The absence of a macroscopic interface in the composite filament facilitates GDL's ability to overcome electro-mass transport antagonism. The hydrophilic-hydrophobic gradient design of GDL can directly solve the water and gas management problem under varying operating conditions in PEMFCs. The controllability of the entire process chain and the stability of product performance ultimately achieve the high power and long lifespan goals of PEMFCs, comprehensively overcoming existing technological bottlenecks.

[0018] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0019] Figure 1 These are the single-cell test data from Examples 1-3; Figure 2 These are the single-cell test data from Examples 4-6; Figure 3 Single-cell test data from Examples 5, 7, and 8; Figure 4 Example 5: Single-cell test data of Comparative Examples 1 and 2. Detailed Implementation

[0020] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following, in conjunction with the appended tables and preferred embodiments, details the specific implementation methods and effects of an in-situ grown carbon nanotube composite filament, its preparation method, and its application according to the present invention. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, the results of one or more embodiments can be combined in any suitable manner. These embodiments are provided to make the invention thorough and complete, and to fully express the scope of the invention to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, material composition, numerical expressions, and values ​​described in these embodiments should be interpreted as merely exemplary and not as limiting.

[0021] This invention proposes a composite filament for in-situ growth of carbon nanotubes and its preparation method, which includes the following steps: placing short carbon fiber filaments in a rotary furnace and keeping the furnace rotating while simultaneously introducing an inert gas to form a dual reaction atmosphere of dynamic and inertness. This solves the problem of uneven contact of reactants caused by filament stacking in traditional static processes and provides an environment free from oxidation interference for catalyst activation and carbon source decomposition at high temperatures; using anhydrous ethanol as a solvent and carbon source, compounding nickel acetylacetonate (catalyst precursor) and tetraethyl orthosilicate (auxiliary agent), and uniformly introducing the mixed solution into the furnace through an inert gas carrier gas to achieve synchronous delivery of catalyst, carbon source and auxiliary agent, avoiding reaction imbalance caused by delivery of a single substance; setting a constant temperature range of 650~850℃ to precisely match the reaction requirements of nickel acetylacetonate decomposition to generate active Ni particles and ethanol catalytic decomposition to generate active carbon species, providing the necessary thermodynamic conditions for in-situ nucleation and growth of CNTs.

[0022] Furthermore, provided that the reaction conditions are met, the present invention preferably uses a constant temperature range, that is, a reaction temperature of 650~750℃, to avoid energy waste caused by excessively high temperatures.

[0023] The above technical solution breaks through the limitations of existing carbon paper surface modification, and constructs an in-situ growth reaction system from the source of carbon fiber filaments, which is conducive to eliminating the macroscopic interface of the composite structure and improving the uniformity of the product.

[0024] In some preferred embodiments of the present invention, the concentration of nickel acetylacetone is preferably 0.005~0.02 mol / L, and the concentration of tetraethyl orthosilicate is preferably 0.002~0.005 mol / L. The concentration range of the above catalyst and promoter directly matches the requirements of Ni particle generation efficiency and CNT growth control. Nickel acetylacetone ensures the generation of sufficient and uniformly sized Ni active centers, avoiding particle sintering or insufficient activity. Tetraethyl orthosilicate inhibits CNT agglomeration and regulates surface wettability by decomposing the generated SiO2 nanoparticles. The two work together to ensure the quantity and quality of CNT growth.

[0025] In some preferred embodiments of the present invention, the preferred isothermal time is 2 to 8 hours, which corresponds to a CNT mass content of 5 to 30%. A shorter time, such as 2 to 6 hours, is suitable for low-density composite yarns with a CNT content of 5 to 15 wt%. A longer time, such as 6 to 8 hours, is suitable for high-density composite yarns with a CNT content of 15 to 30 wt%. This allows the CNT content to be precisely controlled through process conditions, providing a quantifiable process control method for the subsequent hydrophilic-hydrophobic gradient design of GDL.

[0026] In some preferred embodiments of the present invention, the furnace rotation speed is preferably 10~20 rpm. This rotation speed range can balance the contradiction between filament dispersion and mechanical damage, ensuring that the chopped carbon fiber filaments continue to tumble in the furnace so that the reactants can evenly cover the filament surface and micropores, while avoiding filament breakage caused by high rotation speed, thus ensuring the integrity of the mechanical skeleton of the composite filament.

[0027] In some preferred embodiments of the present invention, the argon flow rate is preferably 800~1000ccm. This flow rate range can be precisely matched with the solution delivery rate of the rotary kiln injection pump, which is 0.1~0.5ml / min. This can not only achieve stable delivery of reactants, but also efficiently remove reaction by-products from the furnace, while maintaining an inert protective atmosphere to avoid high-temperature oxidation damage.

[0028] This invention prepares composite filaments with in-situ grown carbon nanotubes using the above-mentioned technical solution. Through in-situ growth and dynamic uniform contact, CNTs are directly grown on the surface and internal micropores of the carbon fiber filaments, forming an integrated composite structure without macroscopic interfaces. This completely eliminates the interface differences of traditional multilayer composite structures and reduces electronic conduction and mass transfer impedance. By synergistically controlling the concentration, time, rotation speed, and flow rate, the CNT content of the composite filaments can be precisely controlled to 5-30%, ensuring uniform distribution, morphology, and surface wettability, thus minimizing performance deviations between different batches and making it suitable for industrial-scale mass production. The composite filaments prepared by this invention can be flexibly divided into low-density and high-density categories based on their CNT content, respectively meeting the differentiated functional requirements of integrated GDL (Gas-Dependent Thermal) systems for low-humidity humidification and high-current drainage, providing core raw material support for subsequent GDL solutions to the antagonistic problem of water vapor management.

[0029] This invention also proposes a composite filament for in-situ growth of carbon nanotubes, comprising chopped carbon fiber filaments and carbon nanotubes. The chopped carbon fiber filaments serve as a carrier for the growth of carbon nanotubes, with carbon nanotubes growing in situ on their surface and within their internal micropores, forming an integrated composite structure with the chopped carbon fiber filaments without a macroscopic interface. This structural feature differs from existing technologies that involve coating / growing carbon nanotubes on carbon paper. In this invention, the carbon nanotubes in the composite filament are directly anchored to the carbon fiber substrate without interlayer gaps. Electrons can be conducted along a continuous carbon fiber-carbon nanotube path, significantly reducing contact resistance. Simultaneously, the gas-liquid transport channel is free of interfacial obstruction, resulting in a substantial decrease in mass transfer impedance and completely eliminating macroscopic interface differences.

[0030] In some preferred embodiments of the present invention, the mass content of carbon nanotubes in the composite filament is preferably 5% to 30%. This content range can be flexibly divided into low-density composite filaments and high-density composite filaments; the present invention defines carbon nanotube content of 5% to 15% (excluding) as low-density composite filaments, which have high porosity and can meet the moisture retention requirements of GDL; the present invention defines carbon nanotube content of 15% to 30% as high-density composite filaments, which, due to their high carbon nanotube content and abundant SiO2 decomposition products of tetraethyl orthosilicate, exhibit strong hydrophobicity and can meet the drainage requirements of GDL, providing core raw materials for the hydrophilic-hydrophobic gradient design of GDL.

[0031] This invention also proposes an integrated gas diffusion layer product and its preparation method. The product includes a first gas diffusion layer and a second gas diffusion layer. The first gas diffusion layer is composed of the aforementioned in-situ grown carbon nanotube composite filaments and carboxymethyl cellulose, wherein the mass content of carbon nanotubes in the composite filaments is <15%; the composite filament content of the first gas diffusion layer is 85-90% by mass percentage. The second gas diffusion layer is disposed on the first gas diffusion layer. The second gas diffusion layer is also composed of the aforementioned in-situ grown carbon nanotube composite filaments and carboxymethyl cellulose, but the mass content of carbon nanotubes in the composite filaments is ≥15%; the composite filament content of the second gas diffusion layer is 80-85% by mass percentage. The first and second gas diffusion layers of this invention form an integrated gas diffusion layer with a thickness of 100-160 μm and an areal density of 0.15-0.24 g / cm³. 2 The contact angle on the first gas diffusion layer side is 70~100°, and the contact angle on the second gas diffusion layer side is 90~130°.

[0032] This invention, through its differentiated double-layer structure, overcomes the contradiction of electron-mass transport antagonism. Specifically, while traditional GDLs can reduce contact resistance by increasing stacking pressure, they also increase mass transfer impedance. In this invention, the GDL lacks macroscopic interfaces, resulting in smooth electron conduction paths and low contact resistance. Its thickness of 100-160 μm is superior to or equivalent to traditional multilayer GDLs. The porosity can be controlled by adjusting the composite filament content, resulting in minimal tortuosity in the mass transfer channels and low mass transfer impedance, thus ensuring stable performance under high loads. Furthermore, the differentiated double-layer structure design of this invention features a first gas diffusion layer with a contact angle of 70-100° (hydrophilic) and a second gas diffusion layer with a contact angle of 90-130° (hydrophobic). This contact angle gradient design balances low-humidity moisture retention with high-current drainage. In practical applications, at low humidity, the hydrophilicity of the first gas diffusion layer in contact with the catalyst passively retains moisture, preventing PEM drying. At high current densities, the hydrophobicity of the second gas diffusion layer in contact with the electrode plate allows for rapid drainage of liquid water, preventing flooding.

[0033] Furthermore, the areal density of the integrated gas diffusion layer of the present invention is 0.15~0.24 g / cm², which, in conjunction with the carbon fiber skeleton of the composite filament, can ensure that the GDL has sufficient mechanical strength to withstand the pressure of fuel cell stacking. At the same time, the high conductivity and porous structure of carbon nanotubes can enable the GDL to stably transport electrons and gases at high power densities, avoiding performance degradation.

[0034] The preparation method of the above-mentioned integrated gas diffusion layer includes the following steps: First, composite filaments with different carbon nanotube contents are prepared respectively. In this invention, filaments with a carbon nanotube mass content of <15% are defined as low-density composite filaments, and filaments with a carbon nanotube mass content of ≥15% are defined as high-density composite filaments. Then, stepwise hot pressing is performed. First, the low-density composite filaments are mixed with carboxymethyl cellulose and then hot-pressed to obtain film layer A. Then, the high-density composite filaments are mixed with carboxymethyl cellulose and then hot-pressed to obtain film layer B. Finally, film layer A and film layer B are stacked, with the edges aligned, and then hot-pressed to obtain the integrated gas diffusion layer.

[0035] This invention simplifies the process and avoids delamination through the above-described preparation method. Specifically, traditional GDL requires the separate preparation and composite of a carbon paper substrate, a microporous layer, and a hydrophobic layer, involving multiple steps and a high risk of delamination. In contrast, the method of this invention directly uses composite filaments as raw materials and achieves GDL molding through a two-step hot-pressing process of preliminary hot-pressing shaping and final hot-pressing integration. This reduces the number of steps, and since both film layers A and B contain carbon nanotubes and carbon fibers, they have good interlayer compatibility and no risk of delamination. This invention also enables differentiated and controllable preparation of two different surfaces of an integrated gas diffusion layer. By selecting composite filaments with different carbon nanotube contents to prepare film layers A and B separately, the hydrophilic and hydrophobic properties of both sides of the GDL can be precisely controlled, thereby solving the problem of inconsistent water and gas management under varying operating conditions in the prior art.

[0036] In some specific embodiments of the present invention, by mass percentage, the low-density composite filament content in film layer A is preferably 85-90%, and the high-density composite filament content in film layer B is preferably 80-85%. Simultaneously, the hot-pressing temperatures for the first and second hot-pressing processes are 50-80°C, and the hot-pressing pressures are 5-10 MPa; the hot-pressing temperature for the third hot-pressing process is 110-130°C, and the hot-pressing pressure is 15-30 MPa. Through the optimization of the above process parameters, the integrated gas diffusion layer prepared by the present invention exhibits strong process stability. Extensive experimental verification has shown that it can stably control the GDL thickness and density to 100-160 μm, and the performance deviation between different batches of products is small, making it suitable for industrial scale-up.

[0037] This invention also proposes an application of the aforementioned integrated gas diffusion layer in a proton exchange membrane fuel cell. The low impedance and excellent water vapor management characteristics of the GDL of this invention enable stable output of the PEMFC at high power densities, such as >1000mA·cm², without issues like stratification or flooding, reducing battery performance degradation. This demonstrates the superior performance of the GDL of this invention under high power density and harsh operating conditions. Furthermore, the fabrication process of the GDL of this invention is stable and cost-controllable, using chopped carbon fiber filaments and common chemicals as raw materials, without rare materials. It is also compatible with existing PEMFC assembly processes, requiring no modification to the battery structure, and can directly replace traditional GDLs. This facilitates the development of PEMFCs towards high power, long lifespan, and low cost, meeting the application requirements of vehicle-mounted and stationary power generation scenarios.

[0038] The present invention will be further described below with reference to specific embodiments, but this should not be construed as a limitation on the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description of the present invention still fall within the scope of protection of the present invention.

[0039] Unless otherwise specified, all materials and reagents mentioned below are commercially available products well known to those skilled in the art; unless otherwise specified, all methods described are methods known in the art. Unless otherwise defined, the technical or scientific terms used should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0040] Example 1 This embodiment proposes a material with a thickness of 100 μm and an areal density of 0.15 g / cm³. 2 The preparation method of an integral gas diffusion layer with a contact angle of 70° on surface A and 90° on surface B is as follows.

[0041] Preparation of composite filaments with carbon nanotubes: 1.1 Take 10g of 1mm chopped carbon fiber and place it in a rotary kiln; 1.2 Prepare a mixed solution of anhydrous ethanol with nickel acetylacetone concentration of 0.005 mol / L and tetraethyl orthosilicate concentration of 0.002 mol / L, and add it to the injection pump connected to the air inlet of the rotary kiln; 1.3 Turn on the rotary furnace and simultaneously introduce 800ccm of argon gas. The furnace rotation speed is 10rpm, and the furnace temperature is raised to 650℃ at a rate of 10℃ / min and maintained at a constant temperature. After reaching the constant temperature range, turn on the injection pump and introduce the solution prepared in step 1.2 into the furnace under the argon carrier gas at a rate of 0.1ml / min. Maintain the constant temperature for 2h, then turn off the injection pump and keep the furnace rotating. After the furnace cools down naturally, a low-density composite filament with a carbon nanotube content of 5wt% is obtained.

[0042] Repeat steps 1.1 to 1.3, except that the isothermal time in step 1.3 is changed to 6 hours, to obtain a high-density composite filament with a carbon nanotube content of 15 wt%.

[0043] Fabrication of an integral gas diffusion layer: The low-density composite filaments obtained in step 1 and carboxymethyl cellulose are mixed in a ratio of 90:10, placed in a mold, and preliminarily hot-pressed at 10 MPa and 80°C to obtain film layer A. The high-density composite filaments obtained in step 1 and carboxymethyl cellulose are mixed in a ratio of 80:20, placed in a mold, and the remaining conditions are the same as in 2.1. The mixture is then hot-pressed to obtain film layer B. The membrane layers A and B obtained in 2.1 and 2.2 are stacked together and finally hot-pressed at 30MPa and 130℃ to obtain an integral gas diffusion layer. The original membrane layers A and B become the A and B surfaces of the gas diffusion layer.

[0044] Example 2 This embodiment proposes a material with a thickness of 100 μm and an areal density of 0.15 g / cm³. 2 A method for preparing an integral gas diffusion layer with a contact angle of 70° on surface A and 118° on surface B.

[0045] The difference between this embodiment and Example 1 is that when preparing high-density composite filaments with a carbon nanotube content of 15 wt%, the concentration of tetraethyl orthosilicate introduced is 0.0025 mol / L.

[0046] Example 3 This embodiment proposes a material with a thickness of 100 μm and an areal density of 0.15 g / cm³. 2 A method for preparing an integral gas diffusion layer with a contact angle of 70° on surface A and 130° on surface B.

[0047] The difference between this embodiment and Example 1 is that when preparing high-density composite filaments with a carbon nanotube content of 15 wt%, the concentration of tetraethyl orthosilicate introduced is 0.005 mol / L.

[0048] Examples 1-3 show that the hydrophobicity of the final gas diffusion layer can be changed by adjusting the concentration of tetraethyl orthosilicate introduced during the growth of carbon nanotubes; the higher the concentration of tetraethyl orthosilicate, the stronger the hydrophobicity.

[0049] Example 4 This embodiment proposes a material with a thickness of 120 μm and an areal density of 0.18 g / cm³. 2 The preparation method of an integral gas diffusion layer with a contact angle of 100° on surface A and 110° on surface B is as follows.

[0050] 1. Preparation of composite filaments with carbon nanotubes: 1.1 Take 10g of 1mm chopped carbon fiber and place it in a rotary kiln; 1.2 Prepare a mixed solution of anhydrous ethanol with nickel acetylacetone concentration of 0.01 mol / L and tetraethyl orthosilicate concentration of 0.002 mol / L, and add it to the injection pump connected to the gas inlet of the rotary kiln; 1.3 Turn on the rotary furnace and simultaneously introduce 800ccm of argon gas. The furnace rotation speed is 20rpm, and the furnace temperature is raised to 750℃ at a rate of 10℃ / min and maintained at a constant temperature. After reaching the constant temperature range, turn on the injection pump and introduce the solution prepared in step 1.2 into the furnace under the argon carrier gas at a rate of 0.25ml / min. Maintain the constant temperature for 2h, then turn off the injection pump and keep the furnace rotating. After the furnace cools down naturally, a low-density composite filament with a carbon nanotube content of 8wt% is obtained.

[0051] Repeat steps 1.1 to 1.3, except that the isothermal time in step 1.3 is changed to 4.5 h, to obtain a high-density composite filament with a carbon nanotube content of 24 wt%.

[0052] 2. Fabrication of an integrated gas diffusion layer: 2.1 The low-density composite filaments obtained in step 1 and carboxymethyl cellulose are mixed in a ratio of 85:15, placed in a mold, and preliminarily hot-pressed at 6MPa and 75℃ to obtain film layer A; 2.2 The high-density composite filaments obtained in step 1 and carboxymethyl cellulose are mixed in a ratio of 85:15, placed in a mold, and the remaining conditions are the same as in 2.1. The mixture is then hot-pressed to obtain film layer B. 2.3 The films A and B obtained in 2.1 and 2.2 are stacked together and finally hot-pressed at 24 MPa and 110 °C to obtain an integral gas diffusion layer. The original films A and B become the A and B surfaces of the gas diffusion layer.

[0053] Example 5 This embodiment proposes a material with a thickness of 140 μm and an areal density of 0.18 g / cm³. 2 A method for preparing an integral gas diffusion layer with a contact angle of 70° on surface A and 118° on surface B.

[0054] The difference between this embodiment and Embodiment 4 is that, in the gas diffusion layer preparation step, the final hot-pressing conditions are 20 MPa and 110°C.

[0055] Example 6 This embodiment proposes a material with a thickness of 160 μm and an areal density of 0.18 g / cm³. 2 A method for preparing an integral gas diffusion layer with a contact angle of 70° on surface A and 118° on surface B.

[0056] The difference between this embodiment and Embodiment 4 is that, in the gas diffusion layer preparation step, the final hot-pressing conditions are 15 MPa and 110°C.

[0057] Examples 4-6 show that the thickness of the gas diffusion layer can be changed by adjusting the final hot-pressing pressure; the higher the hot-pressing pressure, the smaller the thickness.

[0058] Example 7 This embodiment proposes a material with a thickness of 140 μm and an areal density of 0.22 g / cm³. 2 A method for preparing an integral gas diffusion layer with a contact angle of 70° on surface A and 118° on surface B.

[0059] The difference between this embodiment and Example 4 is that the concentration of nickel acetylacetone is 0.015 mol / L in the preparation step of the composite filament with carbon nanotubes.

[0060] Example 8 This embodiment proposes a material with a thickness of 140 μm and an areal density of 0.24 g / cm³. 2 A method for preparing an integral gas diffusion layer with a contact angle of 70° on surface A and 118° on surface B.

[0061] The difference between this embodiment and Example 4 is that the concentration of nickel acetylacetone is 0.02 mol / L in the preparation step of the composite filament with carbon nanotubes.

[0062] Examples 5, 7, and 8 show that by controlling the concentration of nickel acetylacetone introduced during the growth of carbon nanotubes, the density of the gas diffusion surface can be changed; the higher the concentration of nickel acetylacetone, the greater the surface density.

[0063] Comparative Example 1 This comparative example presents a method for directly generating carbon nanotubes on carbon paper and preparing an integrated gas diffusion layer.

[0064] A Toray TGP-H-030 carbon paper was cut into 5cm x 5cm pieces and placed on an alumina plate to ensure that carbon nanotubes only grow on the surface of the carbon paper that does not contact the alumina plate. The alumina plate was then placed in a tube furnace, and the carrier gas, catalyst solution, and temperature program were the same as in Example 1, ultimately resulting in a gas diffusion layer in which carbon nanotubes are grown directly on the carbon paper.

[0065] Comparative Example 2 This comparative example presents a method for generating composite filaments using impregnation-chemical vapor deposition and then hot-pressing to prepare an integral gas diffusion layer.

[0066] Prepare a 0.05 mol / L nickel nitrate aqueous solution and completely immerse 10 g of 1 mm chopped carbon fiber filaments for 2 min. Then filter and dry at 60 °C. Place the impregnated chopped carbon fiber filaments into a rotary kiln and introduce a mixed gas of 800 cC argon, 100 cC acetylene, and 20 cC tetraethyl orthosilicate vapor. The heating procedure is the same as in Example 1, to obtain composite filaments generated by impregnation-chemical vapor deposition.

[0067] The obtained composite filament was hot-pressed under the same conditions as in Example 1 to obtain an integral gas diffusion layer.

[0068] Testing and Analysis: The performance of the above embodiments and comparative examples was characterized and tested: The gas diffusion layers are assembled into a single cell, with side A (the first gas diffusion layer) facing inward and in contact with the cell catalyst, and side B (the second gas diffusion layer) facing outward and in contact with the electrode plate. The membrane electrode assembly (MEA) cathode has a platinum loading of 0.4 mg / cm³. 2 The platinum loading at the anode is 0.2 mg / cm³. 2 MEA effective area 6.25cm 2 .

[0069] Comparative tests were conducted on Examples 1, 2, and 3. The module temperature was 80°C, the humidity was 100%RH, and the back pressure was 1 bar. The test results are as follows: Figure 1 As shown, as the contact angle of surface B gradually increases, the hydrophobicity of the gas diffusion layer also gradually improves. This is beneficial for improving the battery's drainage performance under high humidity conditions. Figure 1 The results show that the gas diffusion layer obtained in Example 3 has the largest B-side contact angle, peak power density, and high load (>1000 mA•cm). -2 The power density at the above-mentioned levels is superior to the results of Examples 1 and 2.

[0070] Comparative tests were conducted on Examples 4, 5, and 6. The module temperature was 80°C, the humidity was 100%RH, and the back pressure was 1 bar. The test results are as follows: Figure 2 As shown in Examples 4-6, the thickness of the gas diffusion layer increases sequentially. This has two effects: first, as the thickness increases, the porosity increases and the mass transfer resistance decreases because the areal density remains unchanged; second, the increased thickness makes electron transport more difficult and the ohmic impedance increases. Figure 2 Test results show that after the gas diffusion layers obtained in Examples 4-6 are used to form single cells, the battery performance exhibits a trend of first increasing and then decreasing. Among them, Example 5 has the highest peak power density, reaching 994 mW•cm. -2This indicates that at lower thicknesses, the decrease in mass transfer resistance resulting from increased thickness initially dominates, while ohmic resistance becomes dominant as the thickness increases further.

[0071] Comparative tests were conducted on Examples 5, 7, and 8. The module temperature was 80°C, the humidity was 60%RH, and the back pressure was 1 bar. The test results are as follows: Figure 3 As shown. Test results indicate that Example 7 has a moderate areal density and the highest peak power density, reaching 1033 mW•cm. -2 This is because the areal density of Examples 5, 7, and 8 increases sequentially while the thickness remains the same, indicating that their porosity decreases sequentially. Decreasing porosity increases mass transfer tortuosity and mass transfer impedance, but it also generates more cross-linked three-dimensional conductive structures, increasing conductivity. Under low humidity conditions, the battery's mass transfer requirements are relatively low; therefore, the decrease in ohmic impedance due to reduced porosity initially dominates, followed by a dominance of mass transfer impedance.

[0072] Comparative tests were conducted on Example 5, Comparative Examples 1 and 2. The module temperature was 80°C, the humidity was 100%RH, and the back pressure was 1 bar. The test results are as follows: Figure 4 As shown. Test results show that, because the gas diffusion layer proposed in this invention completely eliminates macroscopic interface differences and has a double-sided structure with different properties, it has better adaptability to working conditions, and its performance is far superior to the gas diffusion layer prepared by directly growing carbon nanotubes on carbon paper (Comparative Example 1).

[0073] Furthermore, since the present invention uses a rotary kiln to grow carbon nanotubes, the resulting composite filaments are more uniform than those obtained by static chemical vapor deposition in Comparative Example 2, thus resulting in a gas diffusion layer with better performance.

[0074] The technical features in the claims and / or specification of this invention can be combined, and the combination is not limited to the combinations obtained through reference in the claims. Technical solutions obtained by combining the technical features in the claims and / or specification are also within the scope of protection of this invention.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing composite filaments of in-situ grown carbon nanotubes, characterized in that, It includes the following steps: Short carbon fiber filaments are placed in a rotary kiln, and the kiln rotates. Inert gas is introduced into the kiln, and the temperature is raised to 650~850℃ to maintain a constant temperature inside the kiln. Prepare an anhydrous ethanol solution of nickel acetylacetonate and tetraethyl orthosilicate; introduce the solution into the furnace using an inert gas as a carrier gas and maintain it at a constant temperature; Stop heating, keep the furnace rotating, and allow the furnace to cool naturally to obtain composite filaments of in-situ grown carbon nanotubes.

2. The preparation method according to claim 1, characterized in that, The concentration of nickel acetylacetone is 0.005~0.02 mol / L, and the concentration of tetraethyl orthosilicate is 0.002~0.005 mol / L.

3. The preparation method according to claim 1, characterized in that, The constant temperature holding time is 2-8 hours; the mass content of carbon nanotubes in the composite filament is 5-30%.

4. The preparation method according to claim 1, characterized in that, The furnace rotates at a speed of 10-20 rpm.

5. The preparation method according to claim 1, characterized in that, The inert gas is argon, with a flow rate of 800~1000ccm.

6. A composite filament for in-situ growth of carbon nanotubes, characterized in that, It includes: Short carbon fiber filaments; Carbon nanotubes are grown in situ on the surface and in the micropores of chopped carbon fibers, forming an integrated composite structure with no macroscopic interface; the mass content of carbon nanotubes in the composite filament is 5% to 30%.

7. A method for preparing an integrated gas diffusion layer, characterized in that, It includes the following steps: S1. The composite filament of in-situ grown carbon nanotubes as described in claim 6 is prepared by the method according to any one of claims 1 to 5; the composite filament with a carbon nanotube mass content of <15% is a low-density composite filament, and the composite filament with a carbon nanotube mass content of ≥15% is a high-density composite filament. S2 involves mixing low-density composite filaments with carboxymethyl cellulose and then hot-pressing the mixture to obtain membrane layer A; then mixing high-density composite filaments with carboxymethyl cellulose and then hot-pressing the mixture to obtain membrane layer B. S3 stacks membrane layer A and membrane layer B, aligns the edges, and then hot-presses them to obtain an integrated gas diffusion layer.

8. The preparation method according to claim 7, characterized in that, By mass percentage, the low-density composite filament content in film layer A is 85-90%, and the high-density composite filament content in film layer B is 80-85%; the hot pressing temperature of the first and second hot pressing is 50-80℃, and the hot pressing pressure is 5-10MPa; the hot pressing temperature of the third hot pressing is 110-130℃, and the hot pressing pressure is 15-30MPa.

9. An integrated gas diffusion layer, characterized in that, It includes: The first gas diffusion layer is composed of composite filaments of in-situ grown carbon nanotubes as described in claim 6 and carboxymethyl cellulose; the mass content of carbon nanotubes in the composite filaments is <15%; and the composite filament content is 85-90% by mass percentage. A second gas diffusion layer is disposed on the first gas diffusion layer; the second gas diffusion layer is composed of composite filaments of in-situ grown carbon nanotubes as described in claim 6 and carboxymethyl cellulose; the mass content of carbon nanotubes in the composite filaments is ≥15%; and the content of composite filaments is 80~85% by mass percentage. The first gas diffusion layer and the second gas diffusion layer form an integral gas diffusion layer with a thickness of 100~160μm and an areal density of 0.15~0.24g / cm2; the contact angle on the first gas diffusion layer side is 70~100° and the contact angle on the second gas diffusion layer side is 90~130°.

10. The application of the integrated gas diffusion layer according to claim 9 in a proton exchange membrane fuel cell.

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