A method for manufacturing a fuel cell composite bipolar plate

Abstract

The application discloses a preparation method of a fuel cell composite bipolar plate, which comprises the following steps: treating carbon black by using low-temperature plasma for 10-30 min, carbonizing melamine foam at 500-700 DEG C for 1-3 h, soaking the activated melamine foam in a carbon black water dispersion solution with a concentration of 1.2-3.6 g / l, and drying to obtain carbonized melamine foam / carbon black composite foam; uniformly laying graphite in a mold, then layering the graphite, the carbonized melamine foam / carbon black composite foam and the graphite, uniformly laying graphite on the upper layer again, cold-pressing into shape at one time, then placing into a vacuum impregnation tank, vacuumizing and keeping for 0.5-2 h, then sucking in thermosetting resin, impregnating for 10-30 h, and curing at 80-180 DEG C in an oven for 2-6 h to obtain the composite bipolar plate, which has an electric conductivity of more than 322 S / cm, a bending strength of 40 MPa and an air tightness of 1.65*10 ‑6 cm 3 cm 2 s ‑1 The composite bipolar plate is formed at one time, the synergistic effect of the conductive carbon black treated by plasma and the carbonized melamine foam improves the comprehensive performance by coordinating the relationship among the electric conductivity, the bending strength and the air tightness.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fuel cells, and particularly relates to a preparation method of a fuel cell composite bipolar plate. BACKGROUND

[0002] The bipolar plate is a key component directly affecting the output performance and service life of the fuel cell. The fuel cell prepared by using the metal bipolar plate has excellent volume energy density, but the metal fuel cell is prone to corrosion reaction with the electrolyte under high temperature conditions to form small holes or even penetrate the gas resistance failure, and the corrosion metal ions will diffuse to the membrane electrode to exchange ions with the protons, resulting in reduction of the proton exchange flux and electrical conductivity. The graphite bipolar plate has good electrical conductivity, thermal conductivity and corrosion resistance, but has large volume, complex production process and poor mechanical strength. The composite bipolar plate is formed by mixing the graphite material and the resin and then curing and molding, but the graphite material and the resin are difficult to be uniformly mixed due to the differences in density and particle size, thereby directly affecting the electrical conductivity, surface roughness, mechanical strength and service life of the bipolar plate after molding.

[0003] A patent with the title of a preparation method of a bipolar plate for a vanadium cell and the publication number of CN108023105A prepares a composite bipolar plate by first hot spraying a layer of carbon black on a heated glass plate or steel plate, then spraying a layer of resin on the carbon black layer, and spraying a layer of carbon black on the resin layer after curing. However, when the graphite material is sprayed by air pressure, the bottom plate needs to be placed in a temperature of 150-300℃ incubator throughout the process, which is complex and difficult to realize large-scale production. A patent with the title of a mixing method of raw materials of a composite bipolar plate and the publication number of CN115241481A mixes the curing agent and the accelerator after heating and softening, and then mixes the graphite powder after cooling to achieve a relatively stable mixing state by bonding on the surface of the graphite powder. After crushing, the hot-setting resin is mixed. The whole process needs multiple high-temperature mixing, crushing and screening processes, which is complex and time-consuming. The above two preparation methods cannot solve the problem of uniform dispersion of the conductive material and the resin from the source. SUMMARY

[0004] The application aims to solve the problems of the prior art, and provides a preparation method of a composite bipolar plate with a simple preparation process, carbonized melamine foam loaded plasma activated carbon black and one-time cold pressing.

[0005] In order to achieve the above application purposes, the application adopts the following technical solutions.

[0006] A preparation method of a fuel cell composite bipolar plate comprises the following steps:

[0007] (1) Put the melamine foam into a tube furnace, pass nitrogen gas, and keep at 500-700℃ for 1-3h to obtain carbonized melamine foam;

[0008] (2) Put the conductive carbon black into a low-temperature plasma generator, pass gas, and react at a voltage of 30-60V, a current of 1-3A, and room temperature for 5-30min to obtain surface-activated conductive carbon black, and prepare a conductive carbon black water dispersion liquid with a concentration of 1.6-3.2g / l by using deionized water;

[0009] (3) Soak the carbonized melamine foam in step (1) in the conductive carbon black water dispersion liquid in step (2) for 4-8h, and dry in a vacuum drying oven at 90-110℃ to obtain conductive carbon black composite foam;

[0010] (4) Uniformly lay a layer of graphite material on the bottom surface of a mold, uniformly lay the conductive carbon black composite foam in step (3) on the middle layer of the mold, and uniformly lay another layer of graphite material, and then cold-press once at 1-20MPa to obtain a bipolar plate with a runner;

[0011] (5) Put the bipolar plate with a runner in step (4) into a vacuum impregnation tank, vacuumize at a pressure of 0.1-0.5MPa for 0.5-2h to absorb thermosetting resin, and impregnate at a pressure of 0.01-0.5MPa for 1-20h, clean the surface after taking out, and cure in an oven at 90-180℃ for 1-5h to obtain a fuel cell composite bipolar plate.

[0012] Further, the thickness of the carbonized melamine foam obtained in step (1) is 0.1-0.4mm.

[0013] Further, the particle size of the conductive carbon black in step (2) is 20-40nm, the ash content is 1.0-2.0%, and the iodine absorption value is 550-650g / kg.

[0014] Further, the gas in step (2) is one or a combination of oxygen, air, carbon dioxide, nitrogen, hydrogen, etc.

[0015] Further, the graphite material in step (4) is one or a combination of expanded graphite, flaky graphite powder, and graphite sheet.

[0016] Further, the thermosetting resin in step (5) is one or a combination of epoxy resin, polyester resin, cyanate ester, and phenolic resin.

[0017] The beneficial effects of the present application are as follows:

[0018] The carbonized melamine foam has rough surface, small foam volume and low density, has a compact internal skeleton structure and uniform voids, and has stronger and more uniform adsorption capacity for conductive carbon black. The conductive carbon black is prepared into a uniformly dispersed conductive carbon black dispersion liquid by using low-temperature plasma treatment, the carbonized melamine foam is uniformly adsorbed and loaded with the conductive carbon black, the conductive carbon black forms a multi-layer compact conductive path on the carbonized melamine foam, and the conductivity of the composite bipolar plate is improved. The resin is uniformly loaded in the voids of the carbonized melamine foam through vacuum impregnation, and the bending strength and air tightness of the composite bipolar plate are improved. The raw materials are widely available, the one-step forming and pressing process is simple, the conductivity of the prepared composite bipolar plate is more than 322 S / cm, the bending strength is 40 MP, the air tightness is 1.65*10 -6 cm 3 cm 2 s -1 , and the scale production can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a water dispersion liquid of the conductive carbon black without low-temperature plasma treatment;

[0020] Figure 2 is a water dispersion liquid of the conductive carbon black treated by plasma in the present application;

[0021] Figure 3 is an electron microscope image of the carbonized melamine foam loaded with the conductive carbon black treated by plasma in the present application;

[0022] Figure 4 is a real object image of the melamine foam without carbonization after soaking in the carbon black water dispersion liquid;

[0023] Figure 5 is a conductive carbon black composite foam prepared in Example 1 of the present application;

[0024] Figure 6 is a composite bipolar plate prepared in Example 1 of the present application;

[0025] Figure 7 is a water contact angle of the composite bipolar plate prepared in Example 1 of the present application;

[0026] Figure 8 is a surface roughness image of the composite bipolar plate prepared in Comparative Example 2 of the present application;

[0027] Figure 9 is a surface roughness image of the composite bipolar plate prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0028] The present application is described in more detail by listing examples and comparative examples, but the present application is not limited by these examples within the scope of the main idea.

[0029] Example 1

[0030] A method for preparing a fuel cell composite bipolar plate, comprising the following steps:

[0031] (1) cut the commercially available melamine foam with a thickness of 2 mm into 50x5 mm and put it into a tube furnace, introduce nitrogen, keep at 700℃ for 2 h to obtain carbonized melamine foam;

[0032] (2) put 2.4 g of conductive carbon black into a low-temperature plasma generator, introduce air, react at a voltage of 50 V, a current of 2 A and room temperature for 5 min to obtain surface-activated conductive carbon black, and prepare a conductive carbon black water dispersion liquid of 2.4 g / l with deionized water, as shown in Figure 2 , the conductive carbon black dispersion liquid treated by low-temperature plasma is uniformly dispersed.

[0033] (3) soak the carbonized melamine foam in step (1) in the conductive carbon black water dispersion liquid in step (2) for 5 h, and then put it into a vacuum drying oven and dry at 100℃ for 4 h to obtain a conductive carbon black composite foam, as shown in Figure 3 , Figure 5 .

[0034] (4) first uniformly lay 1 g of expanded graphite on the bottom surface of the mold, then uniformly lay the conductive carbon black composite foam in step (3) on the middle layer of the mold, and then uniformly lay 1 g of expanded graphite, and cold-pressing at 20 MPa once to obtain a bipolar plate with a runner;

[0035] (5) put the bipolar plate with a runner in step (4) into a vacuum impregnation tank, vacuumize at a pressure of 0.1 MPa for 1 h, absorb epoxy resin and impregnate at 0.1 MPa for 20 h, clean the surface after taking out, and then cure in an oven at 150℃ for 5 h to obtain a composite bipolar plate with a thickness of 1 mm, as shown in Figure 6 .

[0036] The composite bipolar plate has a conductivity of 322 S / cm, a bending strength of 40.2 MPa, and a gas tightness of 1.65x10 - 5 cm 3 cm 2 s -1 , as shown in Figure 7 , the water contact angle is 95.5°, as shown in Figure 9 , and the surface of the bipolar plate is smooth.

[0037] Example 2

[0038] A method for preparing a fuel cell composite bipolar plate, comprising the following steps:

[0039] (1), cut the commercially available melamine foam with a thickness of 2 mm into 50x5 mm and put it into a tube furnace, introduce nitrogen, keep at 500℃ for 3h to obtain carbonized melamine foam;

[0040] (2), put 1.6g conductive carbon black into a low temperature plasma generator, introduce carbon dioxide at a voltage of 30V, a current of 3A and room temperature for 20min to obtain surface-activated conductive carbon black, prepare a 1.6g / l conductive carbon black aqueous dispersion by mechanically stirring the surface-activated conductive carbon black with deionized water at a speed of 200rmp for 30min;

[0041] (3), immerse the carbonized melamine foam of step (1) in the conductive carbon black aqueous dispersion of step (2) for 5h, then put it into a vacuum drying oven and dry at 90℃ for 6h to obtain a conductive carbon black composite foam.

[0042] (4), first evenly spread 1g of flake graphite powder on the bottom surface of the mold, then evenly spread the conductive carbon black composite foam of step (3) on the middle layer of the mold, and then evenly spread 1g of flake graphite powder, and then cold-pressing at 10MPa to obtain a bipolar plate with a runner;

[0043] (5), put the bipolar plate with a runner of step (4) into the bottom of a vacuum impregnation tank, vacuumize at a pressure of 0.5MPa for 2h, absorb polyester resin and impregnate at a pressure of 0.5MPa for 15h, then take it out, clean the surface, and then cure it in an oven at 180℃ for 3h to obtain a composite bipolar plate with a thickness of 1mm.

[0044] The conductivity of the composite bipolar plate is 307S / cm, the bending strength is 42.3MPa, and the air tightness is 1.57x10 - 5 cm 3 cm 2 s -1 .

[0045] Example 3

[0046] A method for preparing a fuel cell composite bipolar plate, comprising the following steps:

[0047] (1), cut the commercially available melamine foam with a thickness of 2 mm into 50x5 mm and put it into a tube furnace, introduce nitrogen, keep at 600℃ for 3h to obtain carbonized melamine foam;

[0048] (2), 2.4 g conductive carbon black is put into a low temperature plasma generator, nitrogen is introduced, and the reaction is carried out at a voltage of 60 V, a current of 1 A and room temperature for 30 min to obtain surface-activated conductive carbon black; the surface-activated conductive carbon black is mechanically stirred with deionized water at a speed of 300 rmp for 250 min to prepare a conductive carbon black water dispersion solution of 3.2 g / l;

[0049] (3), the carbonized melamine foam in step (1) is immersed in the conductive carbon black water dispersion solution in step (2) for 5 h, and then is placed in a vacuum drying oven at 110°C for 8 h to obtain a conductive carbon black composite foam.

[0050] (4), 1 g of graphite sheet is uniformly laid on the bottom surface of the mold, the conductive carbon black composite foam in step (3) is uniformly laid on the middle layer of the mold, and 1 g of graphite sheet is uniformly laid, and a double pole plate with runner is obtained by one-time cold pressing at 5 MPa;

[0051] (5), the double pole plate with runner in step (4) is placed at the bottom of a vacuum impregnation tank, vacuumized at a pressure of 0.3 MPa for 2 h, absorbs polyester resin and is impregnated at a pressure of 0.01 MPa for 15 h, and after being taken out, the surface is cleaned and then cured in an oven at 90°C for 1 h to obtain a composite double pole plate with a thickness of 1 mm.

[0052] The conductivity of the composite double pole plate is 252 S / cm, the bending strength is 56.2 MPa, and the air tightness is 2.57 x 10 - 6 cm 3 cm 2 s -1 .

[0053] Comparative example 1

[0054] (1) 2 g of expanded graphite is filled in the mold cavity, and then one-time cold pressing is carried out at a pressure of 20 MPa to obtain an expanded graphite plate with runner;

[0055] (2) the expanded graphite plate is fixed at the bottom of the impregnation tank, vacuum is extracted at a pressure of 0.2 MPa and kept for 1 h, then epoxy resin is absorbed, impregnated at a pressure of 0.1 MPa for 20 h, taken out, the surface of the impregnated plate is washed clean with anhydrous ethanol, and then placed in an oven at 120°C for 5 h to obtain a fuel cell composite graphite double pole plate.

[0056] Comparative example 2

[0057] (1) 0.012 g of carbon black is mechanically stirred with 2 g of expanded graphite at a speed of 150 rmp for 10 min, and then filled into a mold, and one-time cold pressing is carried out at a pressure of 20 MPa to obtain a carbon black / expanded graphite plate with runner;

[0058] (2) The carbon black / expanded graphite plate is fixed to the bottom of a vacuum impregnation tank, vacuum extraction is performed at a pressure of 0.1 MPa and maintained for 2 h, then the epoxy resin is sucked in, impregnation is performed at a pressure of 0.1 MPa for 20 h, the surface of the impregnated plate is washed clean using anhydrous ethanol, and is placed in an oven for curing at 120°C for 4 h, to obtain a fuel cell composite graphite bipolar plate.

[0059] Comparative Example 3

[0060] The preparation steps of the bipolar plate are as follows:

[0061] (1) The commercially available melamine foam with a thickness of 2 mm is cut into 50x5 mm, and is placed in a tube furnace, carbonization treatment is performed at 700°C for 2 h under nitrogen, to obtain carbonized melamine foam;

[0062] (2) The conductive carbon black is directly prepared into a dispersion liquid with a concentration of 2.4 g / l, the carbonized melamine foam is soaked in the conductive carbon black liquid for 5 h, and is then placed in a vacuum drying box for drying at 90°C for 6 h to obtain a composite foam. Figure 1

[0063] (2) 1 g of expanded graphite powder is uniformly laid on the bottom of the mold cavity, then the carbonized melamine foam and the expanded graphite are sequentially layered and filled into the middle part of the cavity, and then 1 g of expanded graphite powder is added to the upper part of the mold cavity, cold pressing is performed once at a pressure of 20 MPa, to obtain a bipolar plate with a runner;

[0064] (3) The composite plate of step (2) is placed at the bottom of a vacuum impregnation tank, vacuum extraction is performed at a pressure of 0.1 MPa and maintained for 1 h, then the epoxy resin is sucked in, impregnation is performed at a pressure of 0.1 MPa for 25 h, after taking out, the surface of the impregnated plate is washed clean using anhydrous ethanol, and is placed in an oven for curing at 120°C for 5 h, to obtain a fuel cell composite graphite bipolar plate, as shown in Figure 8 The rough surface will cause the surface contact area to become smaller, the pressure to become larger, and the wear to accelerate; the roughness causes the gap between objects to become larger, affecting the effective bonding strength during assembly, and damaging the stability and corrosion resistance of the part properties.

[0065] Comparative Example 4

[0066] The preparation steps of the bipolar plate are as follows:

[0067] ​(1) Put 2.4 g of conductive carbon black into a low-temperature plasma generator, and pass nitrogen gas at a voltage of 60 V, a current of 1 A, and room temperature for 30 min to obtain surface-activated conductive carbon black. The surface-activated conductive carbon black is mechanically stirred with deionized water at a speed of 300 rpm for 250 min to prepare a conductive carbon black water dispersion of 2.4 g / l;

[0068] (2) Soak the melamine foam in the conductive carbon black water dispersion of step (1) for 5 h, and then place it in a vacuum drying oven at 110°C for 8 h to obtain a composite foam as shown in Figure 4 .

[0069] (3) First, evenly lay 1 g of expanded graphite material on the bottom surface of the mold, then evenly lay the conductive carbon black composite foam of step (3) on the middle layer of the mold, and then evenly lay 1 g of expanded graphite material. After 20 MPa cold pressing, a bipolar plate with a runner is obtained;

[0070] (4) Place the bipolar plate with a runner of step (4) at the bottom of a vacuum impregnation tank, and vacuumize at a pressure of 0.3 MPa for 2 h. Absorb polyester resin and impregnate at a pressure of 0.01 MPa for 15 h. After cleaning the surface, solidify in an oven at 90°C for 1 h to obtain a composite bipolar plate with a thickness of ~1 mm as shown in Figure 4 .

[0071] The performance tests of the composite bipolar plates obtained in the above examples 1-3 and comparative examples 1-4 are shown in Table 1:

[0072] Bending strength test of bipolar plate: (1) The bending strength of the bipolar plate was tested by a electronic universal testing machine (Shimadzu, 33012) using a three-point bending method. The length of the test sample was 20 times the thickness to improve accuracy. The sample for bending strength test had a uniform length of 80 mm, a width of 10 mm, and a thickness of 1 mm. The test speed was 2 mm / s, and the lower span was 30 mm;

[0073] (2) The area specific resistance was tested according to GB / T20042.6. The support layer was carbon paper used for fuel cell diffusion layer. The electrode was a metal-plated electrode, usually a gold-plated electrode;

[0074] (3) The conductivity was tested by a four-probe bulk resistivity tester (Keithley, 2400);

[0075] (4) The gas permeability was tested by a gas leak detector (AIRTEK, N50);

[0076] (5) The surface roughness was tested by an optical 3D surface profiler (WX-S100).

[0077] Table 1: Performance test of composite bipolar plates of Examples 1-3 and Comparative Examples 1-4

[0078] As shown in Table 1, Comparative Example 1 did not add carbonized foam and carbon black, and the bending strength and gas permeability after impregnation could not meet the application requirements (bending strength greater than 25 MPa, gas permeability less than 2.0*10 -6 cm 3 cm -2 s -1 ); Comparative Example 2 used the currently commonly used stirring mixing method, which improved the conductivity to a certain extent, but the bending strength and gas permeability still could not meet the requirements; the bending strength of Comparative Example 3 was greatly improved, but the area specific resistance could not meet the requirements (area specific resistance less than 10 mΩ*cm 2 The synergistic effect of the plasma-treated conductive carbon black and carbonized melamine foam improved the conductivity, bending strength and gas tightness of the bipolar plate.

[0079] The above-described examples only describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those of ordinary skill in the art should fall within the protection scope determined by the claims of the present application.

Claims

1. A method of making a fuel cell composite bipolar plate, characterized by, The method comprises the following steps: (1) placing melamine foam into a tube furnace, passing nitrogen gas, and keeping at 500-700℃ for 1-3 h to obtain carbonized melamine foam; (2) placing conductive carbon black into a low-temperature plasma generator, passing gas at a voltage of 30-60 V, a current of 1-3 A, and room temperature for 5-30 min to obtain surface-activated conductive carbon black, and preparing a conductive carbon black water dispersion liquid with a concentration of 1.6-3.2 g / L by using deionized water, wherein the gas is oxygen or carbon dioxide; (3) immersing the carbonized melamine foam in step (1) into the conductive carbon black water dispersion liquid in step (2) for 4-8 h, and drying at 90-110℃ in a vacuum drying box to obtain conductive carbon black composite foam; (4) uniformly laying a layer of graphite material on the bottom surface of a mold, uniformly laying the conductive carbon black composite foam in step (3) on the middle layer of the mold, and uniformly laying a layer of graphite material, and then cold pressing at 1-20 MPa to obtain a bipolar plate with a runner; (5) placing the bipolar plate with a runner in step (4) into a vacuum impregnation tank, vacuumizing at a pressure of 0.1-0.5 MPa for 0.5-2 h to absorb thermosetting resin, and impregnating at a pressure of 0.01-0.5 MPa for 1-20 h, cleaning the surface after taking out, and curing at 90-180℃ in an oven for 1-5 h to obtain a fuel cell composite bipolar plate.

2. The method of claim 1, wherein the method further comprises: The carbonized melamine foam obtained in step (1) has a thickness of 0.1-0.4 mm.

3. The method of claim 1, wherein the method further comprises the step of: The conductive carbon black in step (2) has a particle size of 20-40 nm, an ash content of 1.0-2.0%, and an iodine absorption value of 550-650 g / kg.

4. The method of claim 1, wherein the method further comprises: The graphite material in step (4) is one or a combination of expanded graphite and flake graphite powder.

5. The method of claim 1, wherein the method further comprises the step of:

5. coating the surface of the metal plate with a coating material. The thermosetting resin in step (5) is one or more of epoxy resin, polyester resin, cyanate ester, and phenolic resin.

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