A fuel cell gas diffusion layer and its preparation method and application

Abstract

The present application relates to a kind of fuel cell gas diffusion layer and its preparation method and application, the gas diffusion layer with carbon material, hydrophobic binder as raw material, by dry method moulding, laser drilling preparation obtains the gas diffusion layer of carbon-free paper, ordered pore structure, with good hydrophobicity, gas permeability and conductivity, can reduce the resistance of water discharge, thereby relieving cathode waterlogging.Dry preparation avoids the drawbacks that surface crack is generated due to solvent volatilization in wet method, thereby avoiding water gathering at crack to cause waterlogging.The thickness, porosity of the carbon-free paper, ordered pore structure gas diffusion layer prepared can be controlled;Preparation process is simple, mild condition, low equipment requirement.The single layer, ordered gas diffusion layer prepared by the present application is used as the gas diffusion layer of fuel cell and has good electrochemical performance.The present application has wide application value in the field of fuel cell.

Description

Technical Field

[0001] This invention relates to a single-layer, ordered porous structure gas diffusion layer for fuel cells, its preparation method and application, belonging to the field of fuel cell technology. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are energy conversion devices that convert chemical energy into electrical energy. Their only byproduct is water, making them environmentally friendly. They also possess advantages such as high energy conversion efficiency and rapid low-temperature start-up, showing promising application prospects in transportation, household power supplies, and stationary power plants, making them a current research hotspot. However, their commercialization still faces significant challenges, with improvements needed in cost, lifespan, and specific power.

[0003] When a proton exchange membrane fuel cell (PEMFC) operates at high current density, if the produced water cannot be drained from the PEMFC in time, the membrane electrode assembly (MEA) will be flooded, hindering hydrogen and oxygen from reaching the active sites of the catalyst for reaction, thus causing a sharp decline in PEMFC performance. Conversely, when the water content in the cell is low, the membrane is prone to drying out, which is detrimental to proton conduction. Therefore, effective water management to maintain the water balance within the cell is crucial for improving the output performance of the fuel cell. As a core component of the MEA, the gas diffusion layer plays a vital role in the fuel cell, including drainage, gas conduction, electrical conduction, and catalyst support, and is of significant research importance.

[0004] Currently, commercially available gas diffusion layers (GDLs) consist of two layers: a hydrophobically treated carbon paper or cloth, also known as the substrate layer (GDB), and a microporous layer (MPL), typically composed of conductive carbon black and a hydrophobic binder. Because the carbon paper requires graphitization at 2000℃ and the microporous layer uses large amounts of organic solvents, traditional GDL preparation methods suffer from overly complex processes, high energy consumption, high equipment costs, and environmental pollution. Furthermore, applying traditional bilayer gas diffusion layers to fuel cells can easily lead to flooding at high current densities, resulting in unstable battery performance. To address these issues, there is an urgent need to develop new GDL technologies that are simple to implement, require low preparation temperatures, consume low energy, and have low equipment costs, in order to produce novel, low-cost, and high-performance GDLs. Summary of the Invention

[0005] To address the shortcomings of existing technologies and in order to reduce costs, improve performance, and adapt to large-scale production, the present invention aims to provide a single-layer, ordered porous gas diffusion layer for fuel cells, its preparation method, and its application. The gas diffusion layer can be applied under different humidity conditions.

[0006] The specific technical solution of this invention is as follows:

[0007] On one hand, the present invention provides a gas diffusion layer for a proton exchange membrane fuel cell. The gas diffusion layer is a single-layer structure, consisting only of a carbon-free paper and a self-supporting microporous layer. The microporous layer has a porous structure, which includes micropores and ordered macropores. The micropores are pores with a diameter of less than 1 μm, and the macropores have a diameter of 20-70 μm.

[0008] Furthermore, in the above technical solution, the pore size of the micropores is 100-1000 nm, the pore size of the macropores is 30-50 μm, the porosity of the microporous layer is greater than 70%, and the proportion of macropores is 30%-35%.

[0009] On the other hand, the present invention provides a method for preparing the above-mentioned gas diffusion layer, wherein the microporous layer is prepared by dry molding and laser perforation technology, and the method includes the following steps:

[0010] Step 1: After mechanically grinding and mixing the raw materials evenly, the mixture is then subjected to hot pressing and cooling to obtain the self-supporting layer; the raw materials include conductive carbon materials and hydrophobic polymer binders;

[0011] Step 2: Using laser perforation technology, ordered macropores are prepared on the self-supporting layer to obtain the microporous layer.

[0012] Furthermore, in the above technical solution, the mass ratio of conductive carbon material to hydrophobic polymer binder is 1:0.075-0.2, preferably 9:1.

[0013] Furthermore, in the above technical solution, the conductive material is one or a mixture of more than one of conductive carbon powder, carbon fiber, and carbon nanotubes.

[0014] Furthermore, in the above technical solution, the hydrophobic polymer binder is one or a mixture of more than one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and perfluoroethylene propylene copolymer (FEP).

[0015] Furthermore, in the above technical solution, step one, dry molding, specifically includes the following steps:

[0016] 1) A certain proportion of carbon materials and hydrophobic agents are mechanically ground to form a uniformly mixed microporous layer mixture;

[0017] 2) Spread the well-mixed mixture evenly in the homemade mold, keeping the surface smooth;

[0018] 3) Place the mold in a hot press, apply a certain pressure at room temperature to make the raw material into sheet form, then release the pressure and heat treat it. After the temperature reaches the target temperature, maintain it for a certain time to make the binder evenly dispersed. Finally, turn off the heating and let it cool naturally to room temperature. Demold to obtain carbon-free paper and self-supporting layer.

[0019] Furthermore, in the above technical solution, the mechanical grinding time is 5-60 minutes, preferably 30 minutes.

[0020] Furthermore, in the above technical solution, the pressure is 0.1-1.0 MPa, preferably 0.5 MPa, and the pressure application time is 1-60 min, preferably 30 min.

[0021] Furthermore, in the above technical solution, the heat treatment temperature is 150-350℃, preferably 150℃, and the heat treatment time is 20-60min, preferably 20min.

[0022] The present invention also provides an application of a single-layer, ordered porous structure gas diffusion layer for proton exchange membrane fuel cells.

[0023] Furthermore, in the above technical solution, the cathode and anode fuels of the proton exchange membrane fuel cell are air and hydrogen, respectively, which undergo the same humidification treatment, namely 40%-100% RH.

[0024] Beneficial effects:

[0025] 1. The single-layer gas diffusion layer provided by this invention has no cracks on its surface and possesses an ordered porous structure with a porosity of over 70%. The ordered macropores within a certain range are beneficial for gas-liquid mass transfer, thereby reducing water flooding and mass transfer polarization in batteries with high electrical density.

[0026] 2. The method for preparing a single-layer gas diffusion layer provided by the present invention prepares ordered macropores on a microporous layer by laser perforation technology. The ordered pore structure forms a continuous mass transfer channel, reduces the mass transfer path, facilitates the discharge of liquid water, and reduces mass transfer resistance.

[0027] 3. This invention prepares the microporous layer by a dry method. No organic solvents are introduced in the preparation process, and no high-temperature treatment is required. The preparation method is healthy, green, inexpensive, simple, and easy to industrialize. At the same time, it avoids the drawback of surface cracks caused by solvent evaporation in wet methods, thereby avoiding water flooding caused by water accumulation at the cracks.

[0028] 4. Compared with traditional double-layer gas diffusion layers, the single-layer, ordered porous gas diffusion layer provided by this invention has better mass transfer capacity and electrochemical performance. This is because the pores of traditional gas diffusion layers are randomly distributed, mostly discontinuous, resulting in tortuous and lengthy mass transfer paths, and are prone to flooding in dead-pore regions. Under 40% humidification conditions, the mass transfer resistance of the single-layer, ordered porous gas diffusion layer sGDL is lower than that of the traditional gas diffusion layer C-GDL, indicating that sGDL has superior gas-liquid mass transfer capacity. Under 100% humidification conditions, the battery performance assembled using the single-layer, ordered porous gas diffusion layer as the cathode gas diffusion layer is better than that of traditional gas diffusion layers, with the battery performance of sGDL-2 being 60 mW / cm² higher than that of C-GDL. -2 . Attached Figure Description

[0029] Figure 1 This is a simplified schematic diagram of a single cell. sGDL is a single-layer, ordered porous gas diffusion layer prepared by the method of this application; CCM is a catalyst coating film; C-GDL is a traditional bilayer gas diffusion layer, composed of a microporous layer MPL and a substrate layer GDB.

[0030] Figure 2 (A) is a SEM image of the conventional gas diffusion layer in Comparative Example 1 of the present invention; Figure 2 (B) and (C) are SEM images of the single-layer, ordered porous gas diffusion layer obtained in Example 3.

[0031] Figure 3 The graph shows a comparison of the full cell performance under 40% humidification conditions between the single-layer, ordered porous structure gas diffusion layer obtained in Examples 1-3 of the present invention and the conventional gas diffusion layer in Comparative Example 1.

[0032] Figure 4 The graph shows a comparison of the full cell performance under 100% humidification conditions between the single-layer, ordered porous structure gas diffusion layer obtained in Examples 1-3 of the present invention and the conventional gas diffusion layer in Comparative Example 1. Detailed Implementation

[0033] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0034] Example 1

[0035] 0.72g of carbon fiber and 0.08g of hydrophobic binder PVDF were weighed and mechanically mixed in a pulverizer for 30 minutes. After thorough grinding and mixing, the uniformly mixed material was spread evenly in a self-made stainless steel mold, ensuring a smooth surface. The mold was then placed in a hot press and pressed at 0.5MPa at room temperature for 30 minutes to form a sheet. The pressure was then released and the temperature was raised to 150℃, where it was heat-treated for 20 minutes to ensure uniform distribution of PVDF within the carbon-free, self-supporting microporous layer. The heating was then turned off, and the mold was allowed to cool naturally to room temperature before demolding to obtain the carbon-free, self-supporting microporous layer. Holes with a diameter of 20μm were machined into the microporous layer using laser drilling technology, named sGDL-1, with a carbon powder loading of 28mg / cm³. -2 .

[0036] Example 2

[0037] 0.72g of carbon fiber and 0.08g of hydrophobic binder PVDF were weighed and mechanically mixed in a pulverizer for 30 minutes. After thorough grinding and mixing, the uniformly mixed material was spread evenly in a self-made stainless steel mold, ensuring a smooth surface. The mold was then placed in a hot press and pressed at 0.5MPa at room temperature for 30 minutes to form a sheet. The pressure was then released and the temperature was raised to 150℃, where it was heat-treated for 20 minutes to ensure uniform distribution of PVDF within the carbon-free, self-supporting microporous layer. The heating was then turned off, and the mold was allowed to cool naturally to room temperature. The carbon-free, self-supporting microporous layer was then demolded. Holes with a diameter of 50μm were machined into the microporous layer using laser drilling technology, named sGDL-2, with a carbon powder loading of 28mg / cm³. -2 .

[0038] Example 3

[0039] Weigh 0.72g of carbon fiber and 0.08g of hydrophobic binder PVDF, and mechanically mix them in a grinder for 30 minutes. After thorough grinding and mixing, spread the uniformly mixed material evenly in a self-made stainless steel mold, ensuring a smooth surface. Then, place the mold in a hot press and apply a pressure of 0.5MPa at room temperature for 30 minutes to form the mixture into sheets. Then, release the pressure and heat the material to 150℃, and heat-treat it at 150℃ for 20 minutes to ensure uniform distribution of PVDF within the carbon-free paper, self-supporting microporous layer. Turn off the heat and allow the mold to cool naturally to room temperature. Demold the material to obtain the carbon-free paper, self-supporting microporous layer. Use laser drilling technology to process 70μm diameter pores on the microporous layer, naming it sGDL-3, in which the carbon powder loading is 28mg / cm³. -2 .

[0040] Comparative Example 1

[0041] The traditional double-layer gas diffusion layer uses PTFE-treated carbon paper as the base layer and carbon powder and PTFE as the microporous layer. The specific preparation steps involve dispersing carbon powder and PTFE in isopropanol solvent using ultrasound and stirring. The uniformly dispersed microporous layer slurry is then coated onto the surface of the hydrophobically treated carbon paper, followed by heat treatment at 350℃ for 1 hour to remove the organic solvent from the diffusion layer. The carbon powder loading in the microporous layer is 1.0 mg / cm³. -2 The PTFE mass fraction was 40 wt.%, and the traditional double-layer gas diffusion layer was named C-GDL. A comparative sample of carbon-free paper and self-supporting microporous layer prepared using the traditional double-layer gas diffusion layer as the preparation method of this invention is presented.

[0042] The above embodiments, comparative examples, characterization, and experimental results are as follows:

[0043] Figure 2 (A) is the SEM image of C-GDL obtained from Comparative Example 1. Figure 2 (B) and (C) are SEM images of sGDL-3 obtained in Example 3. It can be seen that, compared with the gas diffusion layer prepared by the conventional wet method in Comparative Example 1, the single-layer, ordered porous gas diffusion layer prepared by the method of this application has a relatively smooth surface, no cracks caused by solvent evaporation, and the macropores are arranged in an orderly manner.

[0044] Figure 3 The graph shows a comparison of the full-cell performance of sGDL-1 obtained in Example 1, sGDL-2 obtained in Example 2, sGDL-3 obtained in Example 3, and C-GDL obtained in Comparative Example 1 under 40% humidification conditions. Comparing the mass transfer polarization regions of the four gas diffusion layer assembled cells, it can be seen that the mass transfer polarization of the monolayer, ordered porous structure gas diffusion layer sGDL is lower than that of the traditional gas diffusion layer C-GDL, indicating that sGDL has superior gas-liquid mass transfer capability.

[0045] Figure 4 This chart compares the full-cell performance of sGDL-1 obtained in Example 1, sGDL-2 obtained in Example 2, sGDL-3 obtained in Example 3, and C-GDL obtained in Comparative Example 1 under 100% humidification conditions. Comparing the maximum power density of the batteries assembled with the four gas diffusion layers shows that the single-cell performance of the monolayer and ordered porous structure gas diffusion layer sGDL is superior to that of the commercial gas diffusion layer (C-GDL). Specifically, the battery performance of sGDL-2 is improved by 60 mW / cm² compared to C-GDL. -2 .

Claims

1. A gas diffusion layer for a proton exchange membrane fuel cell, characterized by, The gas diffusion layer is a single-layer structure, consisting only of carbon-free paper and a self-supporting microporous layer. The microporous layer has a porous structure, which includes micropores and ordered macropores. The pore size of the micropores is less than 1 μm, and the pore size of the macropores is 20-70 μm. The porosity of the microporous layer is greater than 70%, of which the proportion of macropores is 30%-35%; The microporous layer is prepared by dry molding and laser perforation technology. The method includes the following steps: Step 1: After mechanically grinding and mixing the raw materials evenly, they are sequentially hot-pressed and cooled to obtain a self-supporting layer; the raw materials include conductive carbon materials and hydrophobic polymer binders; Step 2: Ordered macropores are prepared on the self-supporting layer using laser perforation technology to obtain the microporous layer.

2. The gas diffusion layer according to claim 1, characterized in that, The micropores have a diameter of 100-1000 nm, and the macropores have a diameter of 30-50 μm.

3. A method for preparing a gas diffusion layer according to any one of claims 1-2, characterized in that, The microporous layer is prepared by dry molding and laser perforation technology. The method includes the following steps: Step 1: After mechanically grinding and mixing the raw materials evenly, they are sequentially hot-pressed and cooled to obtain a self-supporting layer; the raw materials include conductive carbon materials and hydrophobic polymer binders; Step 2: Ordered macropores are prepared on the self-supporting layer using laser perforation technology to obtain the microporous layer.

4. The preparation method according to claim 3, characterized in that, The mass ratio of the conductive carbon material to the hydrophobic polymer binder is 1:0.075-0.

2.

5. The preparation method according to claim 3, characterized in that, The conductive carbon material is one or a mixture of more than one of conductive carbon powder, carbon fiber, and carbon nanotubes; the hydrophobic polymer binder is one or a mixture of more than one of polytetrafluoroethylene, polyvinylidene fluoride, and perfluoroethylene-propylene copolymer.

6. The preparation method according to claim 3, characterized in that, Step one specifically includes the following steps: 1) mechanically grinding carbon materials and hydrophobic agents to form a uniformly mixed microporous layer mixture; 2) spreading the uniformly mixed mixture evenly in a mold, keeping the surface flat; 3) placing the mold in a hot press, first applying pressure at room temperature to make the raw material into a sheet, then releasing the pressure and heat treating it. After the temperature reaches the target temperature, it is held for a period of time to allow the binder to be evenly dispersed. Finally, the heating is turned off, and the material is allowed to cool naturally to room temperature before demolding to obtain the self-supporting layer.

7. The preparation method according to claim 6, characterized in that, In step (1), the mechanical grinding time is 5-60 min. In step (3), the applied pressure is 0.1-1.0 MPa, the pressure application time is 1-60 min, the heat treatment temperature is 150-350℃, and the heat treatment time is 20-60 min.

8. The application of the gas diffusion layer according to any one of claims 1-2 in a proton exchange membrane fuel cell.

9. In the application according to claim 8, the cathode and anode fuels of the proton exchange membrane fuel cell are air and hydrogen, respectively, which undergo the same humidification treatment, wherein the humidification treatment is 40%-100% relative humidity.

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