Construction method of gas diffusion layer microporous layer gradient straight-through hole structure

Abstract

The invention belongs to the field of fuel cells, and discloses a gas diffusion layer microporous layer gradient straight-through hole structure construction method, which comprises: weighing conductive carbon black powder, adding a solvent, carrying out ultrasonic stirring for A1 min, adding a water repellent agent, carrying out ultrasonic stirring for a certain time of B1 min so as to fully fuse, and controlling the viscosity to reach a controllable range to obtain a gas diffusion layer microporous layer gradient straight-through hole structure; slurry 1 is obtained; coating the surface of hydrophobic carbon paper with a layer of the slurry 1; repeatedly needling the coated carbon paper by using a manufactured micron needle plate to form a preformed product A with a gradient hole structure; the product A is soaked with deionized water and then frozen, and finally a shaped product B of a gradient hole structure is obtained; placing the product B in a drying oven for high-temperature heat treatment to obtain a finished product. The gas diffusion layer is needled by using a micron-sized needle plate to obtain gradient straight-through holes, so that the problem of single pore structure of a traditional microporous layer is solved, and the porosity of the gas diffusion layer is improved.

Description

Technical Field

[0001] The present invention relates to the field of fuel cells, and specifically to a method for constructing a microporous layer gradient straight-through hole structure of a gas diffusion layer. Background Art

[0002] Proton exchange membrane fuel cell (PEMFC) is an efficient energy conversion device that can directly convert the chemical energy contained in fuel into electrical energy, representing a new generation of power generation technology following hydraulic, thermal, and nuclear power generation. This type of battery efficiently utilizes the Gibbs free energy of fuel through electrochemical reactions for energy conversion, getting rid of the efficiency limitations of the traditional Carnot cycle. Using fuels such as hydrogen or natural gas to react with oxygen, PEMFC not only avoids the noise pollution caused by mechanical transmission, but also the harmful gases it emits are very limited, showing its great potential in energy conservation, emission reduction, and environmental protection. However, the performance and service life of PEMFC are greatly affected by water management. During the operation of the battery, if the water generated in the catalyst layer cannot be effectively removed, it may lead to water accumulation inside the electrode, and in severe cases, "flooding phenomenon" will occur, which will significantly reduce the working efficiency of the battery.

[0003] The gas diffusion layer (GDL), as a core component of the proton exchange membrane fuel cell (PEMFC), is composed of a base layer and a microporous layer (MPL), and is located between the catalyst layer and the bipolar plate. During the operation of PEMFC, liquid water is generated on the cathode side through electrochemical reactions, and these water molecules will gradually migrate to the surface of the gas diffusion layer. Especially under high-power operating conditions, the generation rate of water accelerates. If it cannot be effectively discharged, it may lead to the occurrence of "flooding phenomenon". This phenomenon will hinder the transmission of gas in the gas diffusion layer, thereby affecting the effective contact between the reaction gas and the catalyst layer, and ultimately weakening the performance and service life of the fuel cell. To address this problem, the single-hole structure of the traditional MPL is inadequate under high current density, and its gas-liquid transmission capacity is limited and difficult to meet the requirements. To solve this problem, this patent designs an innovative solution of a multi-stage gradient hole structure in the microporous layer. Through this structural optimization, the porosity of the gas diffusion layer is increased, thereby enhancing the gas-liquid transmission efficiency of PEMFC under high current density. This improvement is of great significance for improving the overall performance of the fuel cell and extending its service life.

[0004] The present invention provides a method for constructing a gradient pore structure in a gas diffusion layer of a proton exchange membrane fuel cell; by using a customized micron needle plate to repeatedly puncture the MPL layer (5 - 15 times) to preform the pore structure; then impregnating with deionized water and freezing to shape the pore structure; finally, consolidating the pore structure through high-temperature heat treatment, so as to achieve the purpose of constructing a multi-stage gradient pore structure in the MPL, enhancing the gas-liquid transport capacity of the gas diffusion layer, and further optimizing and improving the performance and lifespan of the fuel cell, providing a technical basis for the further development of fuel cells in daily applications. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for constructing a gradient straight-through pore structure in the microporous layer of a gas diffusion layer to solve the problems raised in the above background technology. A method for constructing a multi-stage gradient pore structure in the gas diffusion layer of a fuel cell. Its core feature is to use a micron-level needle plate to perform a fine needle-punching process on the MPL layer 5 to 15 times to preform the pore structure. Next, through the impregnation of deionized water and subsequent freezing process, precise shaping of the pore structure is achieved. Finally, in a precisely controlled high-temperature heat treatment process, the pore structure is consolidated, thus obtaining a microporous layer with a unique multi-stage gradient pore structure. Perform relevant tests on the GDL such as gas permeability and conductivity, and apply it to a fuel cell, and analyze its performance through I-V curve and ohmic impedance tests. The specific technical solutions are as follows: A method for constructing a gradient straight-through pore structure in the microporous layer of a gas diffusion layer, comprising: Step 1: Weigh a certain mass of conductive carbon black powder, then add a solvent, perform ultrasonic stirring, then add a hydrophobic agent, and perform ultrasonic stirring again to make it fully blend, and control its viscosity within a controllable range to obtain Slurry 1; Step 2: Coat the Slurry 1 obtained in Step 1 onto the surface of a hydrophobic carbon paper and control its thickness within a certain range; Step 3: Use the fabricated micron needle plate to repeatedly puncture the coated carbon paper to form a preformed product A with a gradient pore structure; Step 4: Immerse the product A obtained in Step 3 in deionized water for 3 - 10 hours, then perform freezing treatment for 3 - 10 hours, and finally obtain a shaped product B with a gradient pore structure; Step 5: Place the product B obtained in Step 4 in an oven for high-temperature heat treatment to obtain the finished product.

[0006] Further, the conductive carbon black powder in Step 1 includes carbon powder materials such as acetylene black, Ketjen black, BP2000, and XC-72. The mechanical stirring time is 10 - 30 min, the solvent is one of deionized water, ethanol, and isopropanol. The range of time A1 is 10 - 60 min, the range of time B1 is 10 - 60 min, and the viscosity range of Slurry 1 is 1000 - 3500 mpa.s.

[0007] Further, the coating thickness range of Slurry 1 in Step 2 is 50 - 55 µm.

[0008] Further, the density of the customized micro-needle plate needles is 15 needles / cm 2 to 25 needles / cm 2 .

[0009] Further, in Step 3, the micro-needle plate needles the carbon paper coated with Slurry 1 5 - 15 times.

[0010] Further, the high-temperature heat treatment temperature range in Step 5 is 200 - 500 °C.

[0011] Further, in Step 4, the product A obtained in Step 3 is impregnated with deionized water for 6 hours and then freeze-treated for 6 hours.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) The gas diffusion layer is an indispensable component in a proton exchange membrane fuel cell (PEMFC), is the main component responsible for water management tasks, and is the key to ensuring the high performance and stable operation of the fuel cell. The traditional microporous layer is usually composed of a composite of polytetrafluoroethylene (PTFE) and carbon black. Its function is to reduce the internal contact resistance in the membrane electrode, improve the redistribution of gas and water at the three-phase interface, make the diffusion layer surface hydrophobic while ensuring a high porosity, and prevent the occurrence of "flooding phenomenon". The present invention obtains gradient straight through-holes by using a micro-scale needle plate to needle it, solves the problem of the single pore structure of the traditional microporous layer, increases the porosity of the gas diffusion layer, and further optimizes the ability of the microporous layer to redistribute water and gas, enabling the fuel cell to maintain a good gas-liquid transport capacity while operating under high current conditions, thereby optimizing and enhancing the performance and lifespan of the fuel cell.

[0013] 2) This method is applicable to any gas diffusion layer composed of a base layer and a microporous layer, fills the blank of the method for constructing a gradient straight through-hole structure in the microporous layer, and has a simple method and high accuracy, providing important technical support for the research on the gradient pore structure of the gas diffusion layer and the water management research of fuel cells.

[0014] 3) The present invention obtains gradient straight through-holes by needling it with a micron-level needle plate. The formation of gradient straight through-holes by needling provides an additional penetration path for liquid water, enabling water to be discharged from deeper within the GDL, reducing the residence time of water within the GDL. At the same time, the presence of the formed gradient straight through-holes enhances the lateral diffusion ability of liquid water within the GDL, contributing to the uniform distribution and discharge of water laterally within the GDL. Description of the Drawings

[0015] Figure 1 Schematic diagram of the structure of Product B with a shaped gradient hole structure in Example 1 Figure 2 Graph comparing the gas permeability of the comparative sample and Example 1; Figure 3 Graph comparing the electrical conductivity of the comparative sample and Example 1; Figure 4 Graph comparing the fuel cell polarization curve (I-V) and constant frequency (HFR) impedance test results of the comparative sample and Example 1; Figure 5 Graph comparing the gas permeability of the comparative sample and Examples 1, 2, and 3; Figure 6 Graph comparing the electrical conductivity of the comparative sample and Examples 1, 2, and 3.

[0016] In the figure, 1 is the microporous layer and 2 is the carbon paper. Detailed Description of the Invention

[0017] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention. Example 1

[0018] Using the present invention, a multi-level gradient hole structure is constructed in the microporous layer by performing 5 fine needling processes on the MPL layer using a micron-level needle plate. The specific steps are as follows: Step 1: Weigh 5 g of acetylene black, then add an appropriate amount of deionized water, stir and sonicate for 30 min, then add polytetrafluoroethylene (PTFE), and stir and sonicate for another 30 min to make it fully blend, and control its viscosity to be 2500 mpa.s to obtain Slurry 1.

[0019] Step 2: Coat one layer of the Slurry 1 obtained in Step 1 onto the surface of the hydrophobic carbon paper and control its thickness to be 50 µm.

[0020] Step 3: Use the fabricated micron needle plate to puncture the coated carbon paper 5 times to form a preformed product A with a gradient pore structure. Step 4: Immerse the product A obtained in Step 3 in deionized water for 6 hours, and then perform a freezing treatment for 6 hours to finally obtain a shaped product B with a gradient pore structure.

[0021] Step 5: Place the product B obtained in Step 4 in an oven and perform high-temperature heat treatment at 300 °C for 3 h to obtain the finished product.

[0022] Step 6: Conduct relevant tests on the GDL for gas permeability, conductivity, etc., and apply it to a fuel cell, and analyze its performance through I-V curve and ohmic impedance tests, etc.

[0023] Figure 2 Compare the gas permeability of Toray GDL and SGL GDL with the sample obtained in Example 1. Figure 3 Compare the resistivity of Toray GDL and SGL GDL with the sample obtained in Example 1. Furthermore, it is verified that by puncturing the coated carbon paper with a micron needle plate different numbers of times, after impregnation and freezing treatment, and finally after high-temperature heat treatment, a microporous layer with a multi-stage gradient pore structure is obtained. This method can effectively improve the gas permeability and conductivity of the GDL. From the fuel cell test results of the tissue, the voltage of the GDL prepared in Example 1 at medium and high current density points is significantly higher than that of the cells assembled with Toray-GDL and SGL-GDL, further verifying that the multi-stage pore structure design of the MPL optimizes the gas-liquid transport state of the fuel cell at high current density points and improves the mass transfer ability. From the comparison of the HFR test results, it can be seen that the GDL prepared in Example 1 also reduces the overall ohmic polarization loss of the fuel cell and improves the electron transport ability. The GDL prepared in Example 1 has a significant effect on improving the overall performance of the fuel cell. Example 2

[0024] The difference between Example 2 and Example 1 is that the number of punctures with the micron needle plate is changed, and the coated carbon paper in Step 3 is punctured 10 times with the fabricated micron needle plate. Example 3

[0025] The difference between Example 3 and Examples 1 and 2 is that the different numbers of punctures with the micron needle plate are changed, and the coated carbon paper in Step 3 is punctured 15 times with the fabricated micron needle plate.

[0026] The method for constructing the multi-stage gradient pore structure in Example 3 is the same as that in Examples 1 and 2. The microporous layer with a small pore diameter is beneficial to gas transmission, and the microporous layer with a large pore diameter is beneficial to the discharge of liquid water on the cathode side.

[0027] Analysis and comparison Figure 5 、Figure 6 As can be seen from the data, in Examples 2 and 3, by changing the number of needle punching times of the micro-needle plate, the air permeability and conductivity of GDL in Example 2 and Example 3 are improved compared with GDL in Example 1, and the air permeability and conductivity of GDL in Example 3 are further improved compared with GDL in Example 2. This further illustrates the technical feasibility of constructing a multi-level gradient pore structure on the microporous layer by controlling different needle punching times with a micro-scale needle plate, providing a guarantee for the wide application of fuel cells in the future.

[0028] Using the multi-level gradient pore structure construction method proposed in the present invention can effectively improve the gas-liquid transport capacity of fuel cells when operating under high current conditions. Through further performance testing and I-V curve analysis of fuel cells, the purpose of analyzing the performance improvement of fuel cells can be achieved, providing an important technical basis for the construction of gradient pore structures in gas diffusion layers and the research on fuel cell water management.

[0029] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for constructing a gradient through-hole structure of a gas diffusion layer microporous layer, characterized in that: include: Step 1, weighing a certain mass of conductive carbon black powder, then adding a solvent, performing ultrasonic stirring, then adding a hydrophobic agent, and then performing ultrasonic stirring to fully blend the powder, and controlling the viscosity thereof to reach a controllable range, to obtain slurry 1; Step 2, coating a layer of the slurry 1 obtained in step 1 on the surface of the hydrophobic carbon paper, and controlling the thickness thereof within a certain range; Step 3, repeatedly needle-punching the coated carbon paper with a prepared micron needle plate to form a preformed product A with a gradient pore structure; Step 4, immersing the product A obtained in step 3 in deionized water for 3 to 10 hours, and then freezing it for 3 to 10 hours, to finally obtain a product B with a fixed gradient pore structure; Step 5, placing the product B obtained in step 4 in an oven for high-temperature heat treatment to obtain a finished product.

2. The method for constructing a gradient through-hole structure of a gas diffusion layer microporous layer according to claim 1, characterized in that: The conductive carbon black powder in step 1 includes carbon powder materials of acetylene black, Ketjen black, BP2000, and XC-72, the mechanical stirring time is 10-30 min, the solvent is one of deionized water, ethanol, and isopropanol, the time A1 ranges from 10-60 min, the time B1 ranges from 10-60 min, and the viscosity range of slurry 1 is 1000-3500 mpa.s.

3. The method for constructing a gradient through-hole structure of a gas diffusion layer microporous layer according to claim 1, characterized in that: The thickness of the slurry 1 coated in step 2 is in the range of 50-55 μm.

4. The method for constructing a gradient through-hole structure of a gas diffusion layer microporous layer according to claim 1, characterized in that: The density of the customized micron needle board needle is 15 / CM 2 Up to 25 pieces / CM 2 .

5. The method for constructing a gradient through-hole structure of a gas diffusion layer microporous layer according to claim 1, characterized in that: In the step 3, the carbon paper coated with the slurry 1 is needle-punched 5-15 times by the micron needle board.

6. The method for constructing a gradient through-hole structure of a gas diffusion layer microporous layer according to claim 1, characterized in that: The high temperature heat treatment temperature in step 5 is in the range of 200-500°C.

7. The method for constructing a gradient through-hole structure of a gas diffusion layer microporous layer according to claim 1, characterized in that: In the step 4, the product A obtained in the step 3 is immersed in deionized water for 6 hours and then frozen for 6 hours.

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