Gas diffusion layer with water storage function and preparation method thereof

Abstract

The invention provides a gas diffusion layer with a water storage function and a preparation method thereof, the gas diffusion layer sequentially comprises a first carbon paper layer, a second carbon paper layer and a microporous layer, and one side, facing the second carbon paper layer, of the first carbon paper layer is provided with a plurality of water storage pits. The polarization performance of the fuel cell under the condition of no humidification and the stability of long-time operation under large current are remarkably improved, moisture is rapidly provided in the starting stage, the starting time is shortened, the reaction efficiency is improved, an external humidification system is not needed, the structure of the fuel cell is simplified, the cost and the weight are reduced, and the application range is wide. When the external humidity is insufficient, especially in high-temperature weather, the stored water can evaporate to wet the membrane electrode, and the damage of the proton membrane caused by dryness due to insufficient water is delayed, so that the service life is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of proton exchange membrane fuel cell technology, specifically relating to a gas diffusion layer with water storage function and its preparation method. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) have been widely used in new energy vehicles and distributed power generation in recent years due to their high efficiency and environmental friendliness. However, in low-humidity environments, severe moisture loss within the fuel cell leads to dry membrane electrode assembly (MEA) and decreased proton conductivity, consequently affecting battery performance and lifespan. Currently, the industry primarily addresses this issue through external humidification systems or optimized flow field design, but these methods suffer from drawbacks such as system complexity, high cost, and low efficiency. With the increasing demand for lightweight and miniaturized fuel cells, and the surge in applications for air-cooled fuel cells, ensuring fuel cell performance under low or even no humidification conditions while simplifying the system has become a pressing technical challenge.

[0003] In existing technologies, several solutions are commonly used to address the insufficient performance of fuel cells under low humidity conditions: First, an external humidification system is added to increase humidity by injecting water vapor into the reaction gas; however, this method increases system complexity and energy consumption. Second, hydrophilic materials are coated onto the surface of the gas diffusion layer to enhance moisture retention; however, these materials are prone to aging and failure after long-term operation. Third, the bipolar plate flow field design is optimized to improve water distribution uniformity; however, this approach is challenging to design and has limited effectiveness. Each of these solutions has its advantages and disadvantages, but none can fundamentally solve the problem of moisture supply under low humidity conditions.

[0004] External humidification systems increase the size and weight of fuel cell systems, reducing energy density; hydrophilic coatings are prone to performance degradation during long-term operation, affecting cell stability; flow field design optimization is limited by processing precision and cost, and its performance improvement is very limited. Furthermore, none of these methods can quickly provide sufficient moisture during the fuel cell startup phase, resulting in poor startup performance. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of the embodiments of the present invention and to briefly describe some preferred embodiments.

[0006] As one aspect of the present invention, the present invention provides a gas diffusion layer with water storage function, which comprises a first carbon paper layer, a second carbon paper layer and a microporous layer in sequence, wherein a plurality of water storage pits are provided on the side of the first carbon paper layer facing the second carbon paper layer.

[0007] As a preferred embodiment of the gas diffusion layer with water storage function described in this invention: the plurality of water storage pits are arranged in an array on the first carbon paper layer; the water storage pits are hemispherical concave structures.

[0008] As a preferred embodiment of the gas diffusion layer with water storage function described in this invention: the water storage pit is a hemispherical concave structure, wherein the depth of the hemispherical concave structure is 50μm-100μm, the diameter of the hemispherical concave structure is 1mm-3mm, and the spacing between the water storage pits is 5mm-30mm.

[0009] As a preferred embodiment of the gas diffusion layer with water storage function described in this invention, the lateral spacing between the water storage pits is 5mm-15mm, and the longitudinal spacing is 15-30mm.

[0010] This invention also provides a method for preparing the gas diffusion layer with water storage function, which includes the following steps:

[0011] (1) Impregnate the first fiber base paper with resin solution; cover one side of the first fiber base paper after impregnation with resin solution with a mold having a protrusion structure corresponding to the water storage pit structure, press and heat it on a hot press to obtain a first carbon paper layer with a water storage pit on one side surface, and then perform carbonization treatment to obtain a carbonized first carbon paper layer.

[0012] (2) A layer of resin solution is scraped onto the surface of the first carbon paper layer with the water storage pit after carbonization, and the second fiber base paper is impregnated with the resin solution to obtain the second carbon paper layer; the second carbon paper layer is laid on the surface of the first carbon paper layer with the water storage pit after carbonization and hot-pressed for curing, and then carbonized to obtain the carbonized composite carbon paper layer.

[0013] Wherein, the areal density of the first fiber base paper is greater than the areal density of the second fiber base paper;

[0014] (3) The composite carbon paper layer is subjected to hydrophobic impregnation heat treatment. A microporous layer slurry is coated on the side surface of the second carbon paper layer in the carbonized composite carbon paper layer, dried and heat-treated to obtain a gas diffusion layer.

[0015] As a preferred embodiment of the method for preparing the gas diffusion layer with water storage function according to the present invention: in step (1), the pressure of pressurization and heating curing is 0.3-0.6 MPa, the temperature is 170-180 ℃, and the time is 20-30 min.

[0016] As a preferred embodiment of the method for preparing a gas diffusion layer with water storage function according to the present invention: in step (2), a layer of resin solution is scraped onto the surface of the first carbon paper layer after carbonization with a water storage pit, and the scraping thickness is 20-50μm.

[0017] As a preferred embodiment of the method for preparing the gas diffusion layer with water storage function according to the present invention: in step (1), the carbonization treatment temperature is 1600-2200 ℃ and the time is 15-20 min.

[0018] As a preferred embodiment of the method for preparing the gas diffusion layer with water storage function according to the present invention: the thickness of the first fiber base paper is 150-400μm, the thickness of the second fiber base paper is 50-200μm, and the thickness of the first fiber base paper is greater than the thickness of the second fiber base paper.

[0019] The porosity of the first carbon paper layer after carbonization obtained in step (1) is 75%-83%; in the carbonized composite carbon paper layer obtained in step (2), the porosity of the second carbon paper layer is 78%-90%, and the porosity of the first carbon paper layer after carbonization is 3%-7% lower than that of the second carbon paper layer in the composite carbon paper layer.

[0020] As a preferred embodiment of the method for preparing the gas diffusion layer with water storage function according to the present invention: in the hydrophobic impregnation heat treatment, the hydrophobic material includes a fluorinated hydrophobic material; the resin solution includes a phenolic resin; the microporous layer slurry is composed of water, conductive carbon black, a fluorinated hydrophobic material, a thickener, and a pore-forming agent.

[0021] The beneficial effects of this invention are as follows: This invention significantly improves the polarization performance of fuel cells without humidification, as well as the stability of long-term operation under high current. It rapidly provides moisture during the start-up phase, shortens the start-up time, and improves reaction efficiency. This invention eliminates the need for an external humidification system, simplifies the fuel cell structure, and reduces cost and weight. When external humidity is insufficient, especially in hot weather, the stored moisture can evaporate and wet the membrane electrode assembly, delaying damage to the proton exchange membrane caused by insufficient moisture and thus extending its service life. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, wherein:

[0023] Figure 1 This is a schematic diagram of the gas diffusion layer structure with a water storage pit prepared in Example 1.

[0024] Figure 2 This is a schematic diagram of the gas diffusion layer structure prepared in Example 3.

[0025] Among them, 1 is the first carbon paper layer; 2 is the second carbon paper layer; 3 is the water storage pit; and 4 is the microporous layer. Detailed Implementation

[0026] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples.

[0027] Example 1:

[0028] like Figure 1 As shown, this embodiment provides a gas diffusion layer with water storage function, which includes a first carbon paper layer, a second carbon paper layer and a microporous layer in sequence. Several water storage pits are provided on the side of the first carbon paper layer facing the second carbon paper layer.

[0029] Preferably, the plurality of water storage pits are arranged in an array on the first carbon paper layer; the water storage pits are hemispherical concave structures.

[0030] The preparation method of the gas diffusion layer with water storage function is as follows:

[0031] A 200μm thick first fiber base paper (R207008) and a 50μm thick second fiber base paper (T276410) were selected as the raw materials for the first and second carbon paper layers, respectively. The areal densities of the first and second fiber base papers were measured to be 23 g / cm³. 2 and 8g / cm 2 .

[0032] The resin solution is a mixture of phenolic resin (Meisheng Resin PF01A) and ethanol, with a mass ratio of 9:1.

[0033] The surface of the micro-convex mold has several arrayed hemispherical protrusions. The protrusions are characterized as follows: the height of the hemispherical protrusions is 80μm, the diameter is 2mm, the horizontal spacing between the protrusions is 10mm, and the vertical spacing is 15mm (the top view of the micro-convex mold is rectangular, and the direction corresponding to the longer side of the rectangle is defined as the horizontal).

[0034] First, the first fiber base paper was impregnated in a resin solution at room temperature for 15 seconds. Then, the impregnated first fiber base paper was laid on a flat plate, and the raised surface of a micro-convex mold was placed on the surface of the carbon fiber base paper. The paper was then transferred to a flatbed hot press, with a pressure of 0.5 MPa and a temperature of 180°C. After hot pressing for 20 minutes, the material was removed, resulting in a first carbon paper layer with a water-retaining pit on one side of its surface. The areal density of the cured first carbon paper layer was tested, and the areal density was found to be 117 g / cm³. 2 The first carbon paper layer was carbonized in a nitrogen atmosphere furnace at a temperature increased to 1900℃ at a rate of 10℃ / min for 15 minutes to obtain the carbonized first carbon paper layer. The density of the carbonized first carbon paper layer was measured to be 59 g / cm³. 2 .

[0035] The porosity of the first carbonized paper layer was tested by mercury intrusion porosimetry, and the porosity was found to be 79.2%.

[0036] With the water-reservoir surface of the carbonized first carbon paper layer facing upwards, a resin solution was applied to the upper surface of the first carbon paper layer using a scraper with a scraper height of 50 μm. Then, the second fiber base paper was impregnated with the resin solution at room temperature for 10 seconds to obtain the second carbon paper layer. This second carbon paper layer was then laid on top of the first carbon paper layer to obtain a composite carbon paper layer. A separate second carbon paper layer was also prepared for parameter testing. Both the composite carbon paper layer and the separately prepared second carbon paper layer were placed in a flatbed hot press for hot pressing and curing at 180℃ and 0.6 MPa for 30 minutes. The materials were then removed. The areal density of the cured second carbon paper layer was measured to be 32 g / cm³. 2 The composite carbon paper layer and the second carbon paper layer were then carbonized in a nitrogen atmosphere furnace at a heating rate of 10℃ / min to 1900℃ for 15 minutes to obtain the carbonized composite carbon paper layer and the second carbon paper layer. The areal density of the carbonized second carbon paper layer was measured to be 14 g / cm³. 2 The porosity of the second carbon paper layer was tested using mercury intrusion porosimetry, and the porosity was found to be 84.5%.

[0037] The composite carbon paper layer was hydrophobically impregnated for 5 seconds at room temperature using a 3% PTFE aqueous solution prepared with PTFE emulsion (DuPont TE3970), followed by heat treatment at 340°C for 5 minutes. Then, water, conductive carbon black (VULCAN XC72), PTFE emulsion, polyethylene glycol (PVA2488), and sodium carbonate were mixed in a mass ratio of 90:6.5:4.2:2.7:0.4 and stirred at 1500 rpm for 120 minutes to obtain a microporous slurry. Using a doctor blade set to a height of 150 μm, the microporous slurry was applied to the second carbon paper layer side of the composite carbon paper layer. After drying, the carbon paper was heat-treated at 380°C for 10 minutes to obtain a gas diffusion layer.

[0038] A schematic diagram of the gas diffusion layer structure with a water storage pit prepared in this embodiment is shown below. Figure 1 As shown.

[0039] When the fuel cell is running, water is generated at the membrane electrode interface through an electrochemical reaction. During the transport of external reactant gas, water and gas interact internally and externally. Since the water storage pit is located inside the carbon paper, it forms an "underground cave" structure. This structure allows water to diffuse rapidly to the catalyst layer during the start-up phase, shortening the start-up time, improving reaction efficiency, avoiding flooding and water loss inside the fuel cell, and improving fuel cell performance.

[0040] Example 2:

[0041] Following the method of Example 1, the surface protrusion characteristics of the micro-convex mold were changed as follows: the protrusion height was 50 μm, the diameter was 1.5 mm, the lateral spacing between the hemispherical protrusions was 8 mm, and the longitudinal spacing was 25 mm. Other preparation processes were the same as in Example 1.

[0042] Example 3:

[0043] In this embodiment, the gas diffusion layer with the water storage pit structure is manufactured as a single carbon paper layer. A 300μm thick carbon fiber base paper, R207013, was selected as the raw material, and its areal density was measured to be 35 g / cm³. 2 .

[0044] The remaining manufacturing process and parameter settings are the same as those in Example 1 for manufacturing the first carbon paper layer. During the preparation process, the density of the cured carbon paper layer was measured to be 163 g / cm³. 2 The density of the carbonized paper layer is 81 g / cm³. 2 The test results showed a porosity of 82.3%.

[0045] After preparing the first carbon paper layer, a microporous layer was prepared according to the microporous layer preparation method in Example 1 to obtain a gas diffusion layer. A schematic diagram of the gas diffusion layer structure prepared in this example is shown below. Figure 2 As shown.

[0046] Comparative Example 1:

[0047] Based on Example 1, during the manufacturing process of the first carbon paper layer, the water storage pit is not constructed for the first carbon paper layer. Instead, the first carbon paper layer and the second carbon paper layer are directly combined to form a gas diffusion layer.

[0048] Comparative Example 2:

[0049] Based on Comparative Example 1, before heat treatment of the microporous layer, a water storage pit was created on the surface of the microporous layer using the micro-convex mold of Example 1.

[0050] Comparative Example 3:

[0051] According to the method of Example 1, the surface protrusion features of the micro-convex mold are set as follows: protrusion height 150μm, diameter 4mm, lateral spacing between protruding hemispheres 3mm, and longitudinal spacing 40mm. Other preparation processes are the same as in Example 1.

[0052] The gas diffusion layers prepared in each embodiment and comparative example were used to test the polarization performance of the air-cooled fuel cell. No external humidification was used during the test. The ambient temperature and humidity were 24.2℃ and 63%RH. The tail exhaust cycle was set to 30s.

[0053] The performance was judged by comparing the maximum current density reached at an average voltage of 0.6V, the decrease in current density after maintaining the maximum current density for 10 minutes, and the time it took to reach the maximum current density when the average voltage was set to 0.6V during the startup phase. The test results are shown in Table 1.

[0054] Table 1

[0055] index unit Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Maximum current density <![CDATA[mA / cm 2 ]]> 782 742 734 750 638 624 fuel cell stack temperature ℃ 58.1 59.5 57.9 58.4 54.5 53.8 The decrease in current density after maintaining the position for 10 minutes <![CDATA[mA / cm 2 ]]> 109 115 127 168 195 190 Time to reach maximum current S 43 49 51 64 68 77

[0056] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A gas diffusion layer with water storage function, characterized in that: It consists of a first carbon paper layer, a second carbon paper layer, and a microporous layer, with several water storage pits arranged on the side of the first carbon paper layer facing the second carbon paper layer.

2. The gas diffusion layer with water storage function according to claim 1, characterized in that: The plurality of water storage pits are arranged in an array on the first carbon paper layer; the water storage pits are hemispherical concave structures.

3. The gas diffusion layer with water storage function according to claim 2, characterized in that: The water storage pit is a hemispherical concave structure, wherein the depth of the hemispherical concave structure is 50μm-100μm, the diameter of the hemispherical concave structure is 1mm-3mm, and the spacing between the water storage pits is 5mm-30mm.

4. The gas diffusion layer with water storage function according to claim 3, characterized in that: The horizontal spacing between water storage pits is 5mm-15mm, and the vertical spacing is 15-30mm.

5. The method for preparing a gas diffusion layer with water storage function according to claim 1, characterized in that: Includes the following steps, (1) Impregnate the first fiber base paper with resin solution; A mold with a protrusion structure corresponding to the water storage pit structure is placed on one side of the first fiber base paper after it is impregnated with resin solution. The paper is then pressed and heated on a hot press to cure it, resulting in a first carbon paper layer with a water storage pit on one side. After carbonization, the first carbon paper layer is obtained. (2) A layer of resin solution is scraped onto the surface of the first carbon paper layer with the water storage pit after carbonization, and the second fiber base paper is impregnated with the resin solution to obtain the second carbon paper layer; the second carbon paper layer is laid on the surface of the first carbon paper layer with the water storage pit after carbonization and hot-pressed for curing, and then carbonized to obtain the carbonized composite carbon paper layer. Wherein, the areal density of the first fiber base paper is greater than the areal density of the second fiber base paper; (3) The composite carbon paper layer is subjected to hydrophobic impregnation heat treatment. A microporous layer slurry is coated on the side surface of the second carbon paper layer in the carbonized composite carbon paper layer, dried and heat-treated to obtain a gas diffusion layer.

6. The method for preparing a gas diffusion layer with water storage function according to claim 5, characterized in that: In step (1), the pressure for pressurization and heating curing is 0.3-0.6 MPa, the temperature is 170-180 ℃, and the time is 20-30 min.

7. The method for preparing a gas diffusion layer with water storage function according to claim 5, characterized in that: In step (2), a layer of resin solution is scraped onto the surface of the first carbonized carbon paper layer with the water storage pit, and the thickness of the scraping is 20-50μm.

8. The method for preparing a gas diffusion layer with water storage function according to claim 5, characterized in that: In step (1), the carbonization treatment is carried out at a temperature of 1600-2200 ℃ for 15-20 min.

9. The method for preparing a gas diffusion layer with water storage function according to any one of claims 5-8, characterized in that: The thickness of the first fiber base paper is 150-400μm, the thickness of the second fiber base paper is 50-200μm, and the thickness of the first fiber base paper is greater than the thickness of the second fiber base paper. The porosity of the first carbon paper layer after carbonization obtained in step (1) is 75%-83%; in the carbonized composite carbon paper layer obtained in step (2), the porosity of the second carbon paper layer is 78%-90%, and the porosity of the first carbon paper layer after carbonization is 3%-7% lower than that of the second carbon paper layer in the composite carbon paper layer.

10. The method for preparing a gas diffusion layer with water storage function according to any one of claims 5-8, characterized in that: In the hydrophobic impregnation heat treatment, the hydrophobic material includes a fluorinated hydrophobic material; the resin solution includes a phenolic resin; and the microporous layer slurry is composed of water, conductive carbon black, a fluorinated hydrophobic material, a thickener, and a pore-forming agent.

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