High-air-tightness flexible graphite polar plate and preparation method thereof

Abstract

The invention provides a high-air-tightness flexible graphite polar plate and a preparation method thereof. The preparation method comprises the following steps: (1) carrying out compression molding on an expanded graphite prefabricated plate to form a graphite blank polar plate; (2) punching a micro needle hole in the graphite blank pole plate by adopting a micro needle; (3) carrying out dipping treatment on the graphite blank polar plate with the micro pinholes obtained in the step (2) in dipping glue to obtain a dipped polar plate; and (4) cleaning, curing, drying and leveling the pole plate impregnated in the step (3) to obtain the high-air-tightness flexible graphite pole plate. According to the method disclosed by the invention, a method for punching the micro holes in the surface of the molded graphite blank polar plate is innovatively adopted, so that a part of pores in the molded graphite blank polar plate are broken. The punched micro holes enable gas in pores existing in the prefabricated plate to be extracted more easily, and the pole plate is filled with the impregnating adhesive more easily, so that the impregnating difficulty of the impregnating adhesive is reduced, and the air permeability is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of proton exchange membrane fuel cells, and particularly relates to a flexible graphite polar plate with high air tightness and a preparation method thereof. BACKGROUND

[0002] The proton exchange membrane fuel cell bipolar plate is one of the most important core structural components in a fuel cell, and the air tightness of the bipolar plate is a core index of the performance and safety of the proton exchange membrane fuel cell. Air tightness failure will directly lead to performance reduction and safety risk of the stack.

[0003] However, the raw material for producing the fuel cell polar plate is flexible graphite, and the material has a porous characteristic after being molded. It is often difficult to completely seal the pores thereof in production. With the accelerated development of ultra-thin molded polar plates, the improvement of the air tightness of the polar plate is more urgent. With the reduction of the thickness of the polar plate, the material tightness is further increased, and the difficulty of filling the internal pores is further increased.

[0004] Patent application with publication number CN111129537A discloses a composite graphite bipolar plate and a preparation method and application thereof. The composite graphite bipolar plate comprises a graphite bipolar plate and a sealing coating bonded to the cathode face and the anode face of the graphite bipolar plate. The sealing coating forms a dense protective structure on the cathode face and the anode face of the graphite bipolar plate, effectively plugs the surface defects on the graphite bipolar plate, improves the flatness of the fuel field channel on the graphite bipolar plate and the air tightness of the graphite bipolar plate, and realizes air tightness compensation of the graphite bipolar plate.

[0005] Patent application with publication number CN115472859A discloses a graphite bipolar plate material with high air tightness and high strength, a preparation method thereof and a graphite bipolar plate. The graphite bipolar plate material comprises an aluminum-magnesium alloy phase and a graphite matrix. The aluminum-magnesium alloy phase is embedded in the pores of the graphite matrix by high-pressure injection. Since the aluminum-magnesium alloy filling the pores of the graphite is a metal, the organization density is very high, and the plasticity is good, so that the porosity of the graphite bipolar plate material can be reduced to 0-0.5%.

[0006] It is still of great significance to develop a method for reducing the impregnation difficulty of the polar plate and improving the air tightness of the polar plate. SUMMARY

[0007] To solve the above technical problems in the prior art, the application provides a flexible graphite polar plate with high air tightness and a preparation method thereof.

[0008] The application provides a preparation method of a flexible graphite polar plate with high air tightness, comprising the following steps: (1) molding an expanded graphite preform plate into a graphite blank polar plate; (2) using a micro-needle to punch a micro-needle hole on the graphite blank plate; (3) immersing the graphite blank plate with the micro-needle hole obtained in step (2) in an impregnating glue to obtain an impregnated plate; (4) cleaning, curing, drying and flattening the impregnated plate in step (3) to obtain the high-air-tightness flexible graphite plate.

[0009] Preferably, in step (1), the surface density of the expanded graphite preformed plate is 50-70 mg / cm 2 , and the thickness of the graphite blank plate is 0.3-1.0 mm.

[0010] Further preferably, in step (1), the surface density of the expanded graphite preformed plate is 50 mg / cm 2 , and the thickness of the graphite blank plate is 0.8 mm.

[0011] Preferably, in step (1), the pressure of the mould pressing is 200-300 t.

[0012] Preferably, in step (2), the micro-needle is cylindrical with a diameter of 0.01-0.5 mm; the punched micro-needle hole is a through hole and is distributed at equal intervals with a hole spacing of 0.5-1 mm.

[0013] Preferably, in step (3), the impregnating device is an impregnating tank.

[0014] Preferably, in step (3), the impregnating glue is an acrylic resin.

[0015] Preferably, in step (3), during the impregnating treatment, dry vacuum suction, wet vacuum suction and positive pressure impregnating treatment are performed in sequence.

[0016] Further preferably, in step (3), the dry vacuum suction is vacuum suction at the upper part of the impregnating tank for not less than 30 minutes, and the pressure of the dry vacuum is not less than 2 mbar; the wet vacuum suction is vacuum suction after the plate is completely immersed in the impregnating glue for not less than 60 minutes, and the pressure of the wet vacuum is not less than 5 mbar; the positive pressure impregnating treatment is positive pressure impregnating treatment for not less than 90 minutes, and the positive pressure is not less than 6 bar.

[0017] Preferably, in step (4), the curing time is not less than 100 minutes, and the curing temperature is 90-95℃.

[0018] Preferably, in step (4), the drying temperature is not higher than 120℃, and the drying time is not less than 60 minutes.

[0019] The present invention also provides a highly airtight flexible graphite electrode plate, which is prepared by the above-described method for preparing a highly airtight flexible graphite electrode plate.

[0020] Compared with the prior art, the present invention has the following beneficial effects: This invention innovatively employs a method of punching micro-holes on the surface of the molded graphite preform electrode plate. This breaks down some of the pores within the molded graphite preform electrode plate, significantly reducing the difficulty of impregnation. During the manufacturing process, the punched micro-holes facilitate the extraction of gas from the pores within the preform plate, allowing the impregnating resin to more easily fill the electrode plate. Furthermore, the presence of micro-holes increases the contact area between the impregnating resin and graphite. Combined with the processing method, this significantly improves the contact area between the impregnating resin and graphite, enhancing the bonding strength. This reduces the difficulty of impregnation and increases air permeability, helping to solve the problem of poor airtightness in the production of ultra-thin electrode plates. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of punching holes in a graphite blank electrode plate. Figure 2 The statistical results of the resin filling ratio tests in Examples 1-3 and Comparative Example 1 are as follows; Figure 3 The results are statistical results of the air permeability tests in Examples 1-3 and Comparative Example 1. Detailed Implementation

[0022] The acrylic resin used in the impregnation method of this invention was purchased from Hernandez Manufacturing Co., Ltd. in the United States, and the product name is Hernandez 994M.

[0023] Example 1 S100, with a thickness of 5mm and a surface density of 50mg / cm³ 2 The expanded graphite preform is placed in the mold of the press, the pressure of the press is set to 300t, and it is molded into a graphite blank electrode plate with a thickness of 0.8mm. A graphite blank electrode plate with a size of 100mm×100mm is then cut out. S200, using a micro-needle with a diameter of φ=0.1mm, micro-needle holes are punched into the cut graphite blank electrode plate, with a hole spacing L=1mm, such as Figure 1 As shown; then weigh the graphite blank electrode plate and take the weight as m1; S300. Place the punched graphite blank electrode plate into the impregnation basket, then place the impregnation basket into the impregnation tank containing the impregnation adhesive acrylic resin, and perform dry vacuum for 30 minutes (vacuuming at the top of the impregnation tank), with a dry vacuum pressure of 2 mbar and wet vacuum for 60 minutes (vacuuming after complete impregnation into the impregnation adhesive), with a wet vacuum pressure of 5 mbar, and perform positive pressure impregnation for 90 minutes, with a positive pressure of 6 bar. S400. Clean the impregnated electrode plates to remove excess acrylic resin from the surface of the electrode plates. The cleaning time is about 10 minutes. The cleaning agent used is HPS Surfactant 381001 from Herrenknecht, the same below. S500. After cleaning, the plates are cured and dried. The curing time is 120 minutes and the curing temperature is 95℃. The drying time is 60 minutes and the drying temperature is 120℃. S600, use a 10kg leveling block to press onto the surface of the electrode plate in the oven for leveling, the leveling time is 180min; after leveling, the electrode plate is polished to remove glue and burrs, and finally the required high airtightness electrode plate is obtained, and the weight of the high airtightness electrode plate is measured as m2.

[0024] Example 2 S100, with a thickness of 5mm and a surface density of 50mg / cm³ 2 The expanded graphite preform is placed in the mold of the press, the press pressure is set to 300t, and it is molded into a graphite blank electrode plate with a thickness of 0.8mm. A graphite blank electrode plate with a size of 100mm×100mm is then cut out. S200. Using a φ=0.5mm micro needle, micro holes are punched into the cut graphite blank electrode plate, with a hole spacing L=1mm. Then, the weight of the graphite blank electrode plate is weighed as m1. S300. Place the punched graphite blank electrode plate into the impregnation basket, then place the impregnation basket into the impregnation tank containing the impregnation adhesive acrylic resin, and perform dry vacuum for 30 minutes (vacuuming at the top of the impregnation tank), with a dry vacuum pressure of 2 mbar and wet vacuum for 60 minutes (vacuuming after complete impregnation into the impregnation adhesive), with a wet vacuum pressure of 5 mbar, and perform positive pressure impregnation for 90 minutes, with a positive pressure of 6 bar. S400. Clean the impregnated plates to remove excess acrylic resin from the surface of the plates. The cleaning time is approximately 10 minutes. S500. After cleaning, the plates are cured and dried. The curing time is 120 minutes and the curing temperature is 95℃. The drying time is 60 minutes and the drying temperature is 120℃. S600, use a 10kg leveling block to press onto the surface of the electrode plate in the oven for leveling, the leveling time is 180min; after leveling, the electrode plate is polished to remove glue and burrs, and finally the required high airtightness electrode plate is obtained, and the weight of the high airtightness electrode plate is measured as m2.

[0025] Example 3 S100, with a thickness of 5mm and a surface density of 50mg / cm³ 2The expanded graphite preform is placed in the mold of the press, the press pressure is set to 300t, and it is molded into a graphite blank electrode plate with a thickness of 0.8mm. A graphite blank electrode plate with a size of 100mm×100mm is then cut out. S200. Using a φ=0.1mm micro needle, micro holes are punched into the cut graphite blank electrode plate, with a hole spacing L=10mm. Then, the weight of the graphite blank electrode plate is weighed as m1. S300. Place the punched graphite blank electrode plate into the impregnation basket, then place the impregnation basket into the impregnation tank containing the impregnation adhesive acrylic resin, and perform dry vacuum for 30 minutes (vacuuming at the top of the impregnation tank), with a dry vacuum pressure of 2 mbar and wet vacuum for 60 minutes (vacuuming after complete impregnation into the impregnation adhesive), with a wet vacuum pressure of 5 mbar, and perform positive pressure impregnation for 90 minutes, with a positive pressure of 6 bar. S400. Clean the impregnated plates to remove excess acrylic resin from the surface of the plates. The cleaning time is approximately 10 minutes. S500. After cleaning, the plates are cured and dried. The curing time is 120 minutes and the curing temperature is 95℃. The drying time is 60 minutes and the drying temperature is 120℃. S600, use a 10kg leveling block to press onto the surface of the electrode plate in the oven for leveling, the leveling time is 180min; after leveling, the electrode plate is polished to remove glue and burrs, and finally the required high airtightness electrode plate is obtained, and the weight of the high airtightness electrode plate is measured as m2.

[0026] Comparative Example 1 S100, with a thickness of 5mm and a surface density of 50mg / cm³ 2 The expanded graphite preform is placed in the mold of the press, the press pressure is set to 300t, and it is molded into a graphite blank electrode plate, and a graphite blank electrode plate of size 100mm×100mm is cut out. S200, Weigh the graphite blank electrode plate as m1; S300. Place the punched graphite blank electrode plate into the impregnation basket, then place the impregnation basket into the impregnation tank containing the impregnation adhesive acrylic resin, and perform dry vacuum for 30 minutes (vacuuming at the top of the impregnation tank), with a dry vacuum pressure of 2 mbar and wet vacuum for 60 minutes (vacuuming after complete impregnation into the impregnation adhesive), with a wet vacuum pressure of 5 mbar, and perform positive pressure impregnation for 90 minutes, with a positive pressure of 6 bar. S400. Clean the impregnated plates to remove excess acrylic resin from the surface of the plates. The cleaning time is approximately 10 minutes. S500. After cleaning, the plates are cured and dried. The curing time is 120 minutes and the curing temperature is 95℃. The drying time is 60 minutes and the drying temperature is 120℃. S600. After curing and drying, the electrode plate is leveled in an oven for 180 minutes. The leveled electrode plate is then polished to remove adhesive and burrs, and the final electrode plate product is obtained. The weight of the finished electrode plate product is measured as m2.

[0027] Test Example 1 The acrylic resin in step S400 of Examples 1-3 and the acrylic resin in step S400 of Comparative Examples 1-2 were tested for resin filling ratio. The formula for calculating the resin filling ratio is as follows: Resin filling ratio = (m2-m1) / m2 × 100%; In the formula; m1 resin is the weight of the electrode plate before impregnation, in grams; m2 resin is the weight of the electrode plate after impregnation, in grams; (m2-m1) represents the weight of the resin filling the electrode plate.

[0028] Table 1

[0029] The test results are shown in Table 1 and Figure 2 As shown in the results analysis, compared with Comparative Example 1, Examples 1-3 have added microporous plates, resulting in a higher resin filling ratio. Compared with Example 2 (φ=0.5mm), the resin filling ratio is higher in the electrode plate with microporous holes of φ=0.1mm in Example 1; compared with Example 3 (L=10mm), the resin filling ratio is higher in the electrode plate with L=1mm in Example 1. This indicates that as the hole spacing L increases, the number of holes decreases, and the difficulty of resin filling increases.

[0030] Test Example 2 Two pipettes were prepared into a U-shaped communicating vessel, each filled with liquid water. Using a fixture, helium gas was introduced into one side of the electrode plate, and the other side was connected to the upper end of the pipette. The volume V of liquid water discharged from the pipette was recorded, and the gas leakage on the other side was calculated. The detection time was specified as 180 minutes, and the detection pressure was 200 kPa. The amount of gas leakage during this period was investigated, and the permeability was calculated. A lower permeability indicates better airtightness of the impregnated electrode plate. The formula for calculating the permeability is as follows: Air permeability = gas leakage / (time × area) = V / (t × A). Air permeability unit: cm 3 × (cm) 2 ×s) -1 , The area A of the test fixture is generally 100 mm². 2 (10mm×10mm).

[0031] Table 2

[0032] The test results are shown in Table 2 and Figure 3 As shown in the results analysis, the air permeability of the electrode plate in Example 1 is significantly reduced compared to Comparative Example 3. This is mainly due to the introduction of micropores, which breaks down some of the pores inside the precast plate after molding, significantly reducing the difficulty of impregnation and thus significantly reducing the air permeability of the electrode plate and improving air tightness. Moreover, compared to Examples 2 and 3, the micropores in Example 1 are finer and have smaller spacing, making impregnation easier, resulting in lower air permeability and better air tightness.

Claims

1. A method for preparing a highly airtight flexible graphite electrode, characterized in that, Includes the following steps: (1) The expanded graphite preform is molded into a graphite blank electrode plate; (2) Micro-needles are punched out on the graphite blank electrode plate using micro-needles; (3) The graphite blank electrode plate with micro-pinholes obtained in step (2) is impregnated in impregnation adhesive to obtain the impregnated electrode plate; (4) The electrode plate impregnated in step (3) is cleaned, cured, dried and leveled to obtain the high airtightness flexible graphite electrode plate.

2. The method for preparing a highly airtight flexible graphite electrode plate according to claim 1, characterized in that, In step (2), the micro needle is cylindrical with a diameter of 0.1~0.5mm; the punched micro needle holes are through holes and are evenly distributed with a hole spacing of 1~10mm.

3. The method for preparing a highly airtight flexible graphite electrode plate according to claim 1, characterized in that, In step (1), the areal density of the expanded graphite precast plate is 50~70 mg / cm³. 2 The thickness of the graphite blank electrode plate is 0.3~1.0mm.

4. The method for preparing a highly airtight flexible graphite electrode plate according to claim 1, characterized in that, In step (1), the molding pressure is 200~300t.

5. The method for preparing a highly airtight flexible graphite electrode plate according to claim 1, characterized in that, In step (3), the impregnating adhesive is an acrylic resin.

6. The method for preparing a highly airtight flexible graphite electrode plate according to claim 1, characterized in that, In step (3), during the impregnation process, dry vacuum suction, wet vacuum suction and positive pressure impregnation are performed in sequence.

7. The method for preparing a highly airtight flexible graphite electrode plate according to claim 6, characterized in that, In step (3), the dry vacuum suction is to draw a vacuum in the upper part of the impregnation tank for a time of not less than 30 minutes and the pressure of the dry vacuum is not less than 2 mbar; the wet vacuum suction is to draw a vacuum after the electrode plate is completely immersed in the impregnation resin for a time of not less than 60 minutes and the pressure of the wet vacuum is not less than 5 mbar; the positive pressure impregnation is to draw a vacuum for a time of not less than 90 minutes and the positive pressure is not less than 6 bar.

8. The method for preparing a highly airtight flexible graphite electrode plate according to claim 1, characterized in that, In step (4), the curing time is not less than 100 minutes and the curing temperature is 90~95℃.

9. The method for preparing a highly airtight flexible graphite electrode plate according to claim 1, characterized in that, In step (4), the drying temperature is not higher than 120°C and the drying time is not less than 60 minutes.

10. A flexible graphite electrode with high airtightness, characterized in that, It is prepared by the method for preparing a high-airtightness flexible graphite electrode plate according to any one of claims 1 to 9.

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