Rapidly-prepared hot-pressed fuel cell composite bipolar plate

Abstract

The invention discloses a hot-pressing type fuel cell composite bipolar plate capable of being rapidly prepared, which is characterized in that the bipolar plate is formed by compounding graphite, carbon black, expanded graphite loaded with nano-copper, mixed resin, a curing agent and a curing accelerator, and the bipolar plate can be formed at one time by hot pressing at 120-180 DEG C for 200-300 seconds, and other treatments are not needed, but the high bending strength, the high conductivity and the good air tightness are still achieved. According to the invention, the hot press molding time of the composite bipolar plate is greatly shortened, the production efficiency is improved, and batch production of the composite bipolar plate is facilitated.

Description

Technical Field

[0001] The invention relates to the field of proton exchange membrane fuel cells, in particular to a rapidly prepared hot-pressed fuel cell composite bipolar plate. Background Art

[0002] Proton exchange membrane fuel cell is a highly efficient clean energy conversion technology, which consists of membrane electrode assembly, gas diffusion layer, catalyst layer and bipolar plate. Bipolar plate plays a vital role in providing strength support, distributing reaction gas and collecting conduction current. Bipolar plates of proton exchange membrane fuel cells can be classified according to different materials, mainly including metal bipolar plates, graphite bipolar plates and composite bipolar plates.

[0003] Metal bipolar plates have excellent electrical and thermal conductivity, high mechanical strength, good processing performance and relatively low cost. They generally have good mechanical properties and a small volume, which is conducive to reducing the cost of the battery stack and improving the overall performance. The main disadvantage is that a passivation film is easily formed in the PEMFC environment, which will increase the contact resistance and affect the battery performance. In addition, the corrosion products of metal ions may diffuse to other parts of the battery, resulting in performance degradation. Although coating technology has been used to improve the corrosion resistance and conductivity of metal bipolar plates, the coating process may increase manufacturing costs and process complexity, and improper coating may cause the coating to fall off or fail.

[0004] Graphite bipolar plates have good corrosion resistance, low density, high electrical and thermal conductivity, and good chemical stability. They are commonly used in traditional PEMFCs and are suitable for long-term stable operation due to their chemical corrosion resistance. However, graphite materials have low mechanical strength, high brittleness, high processing costs, and high porosity, which may cause gas permeation problems. In addition, the large volume and mass of graphite bipolar plates are not conducive to the compact design of battery stacks.

[0005] Composite bipolar plates combine the advantages of metal and graphite bipolar plates, such as corrosion resistance, easy forming, small size, and high strength. They can provide good mechanical strength and chemical stability, while having a lower density. However, the resistance of composite bipolar plates is higher than that of the other two bipolar plates, and it often takes more than 1 hour to manufacture a composite bipolar plate, which greatly limits the mass production of composite bipolar plates. Although there are a lot of studies on improving the conductivity of composite bipolar plates, the preparation efficiency has always been unsatisfactory.

[0006] Therefore, a new formula is urgently needed for proton exchange membrane fuel cell composite bipolar plates to improve their production efficiency, while also having high conductivity and flexural strength, good air tightness and low cost. Summary of the invention

[0007] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a rapidly prepared hot-pressed fuel cell composite bipolar plate, and the technical solution to the problem is: the present invention provides a rapidly prepared hot-pressed fuel cell composite bipolar plate, which is composited with components including graphite, carbon black, expanded graphite loaded with nano-copper (hereinafter replaced by EG-CuNPs), mixed resin, curing agent and curing accelerator.

[0008] Preferably, the fuel cell composite bipolar plate of the present invention uses graphite, carbon black and EG-CuNPs as conductive fillers, and the particle sizes of the three fillers are EG-CuNPs, graphite, and carbon black in descending order. The three conductive fillers of different particle sizes are combined with each other to form a more complete conductive network. However, the compatibility of carbon black with resin is not good, and excessive carbon black will lead to a decrease in the mechanical strength of the bipolar plate, so the amount of carbon black added should be controlled. Copper is the metal with the best conductivity except silver. By embedding nano copper into expanded graphite, the conductivity of expanded graphite itself can be improved. The mixed resin and curing agent provide mechanical strength and air tightness for the bipolar plate, and the curing accelerator is used to shorten the curing time of the resin and improve production efficiency. Through the compounding of the above raw materials, the bipolar plate after hot pressing has high conductivity and bending strength, good air tightness, and chemical stability such as acid and alkali resistance.

[0009] Preferably, the mass percentage of the component raw materials is as follows: graphite 60%-70%; carbon black 1%-10%; EG-CuNPs 1%-10%; mixed resin 15%-25%; curing agent 1%-5%; curing accelerator 0.5%-5%.

[0010] Preferably, the graphite and carbon black should be dried in an oven at 70° C.-100° C. for 1-2 hours before use.

[0011] Preferably, the nano copper in the EG-CuNPs is prepared by an in-situ chemical reduction method and adsorbed on the surface of expanded graphite, and the specific steps are: 1. dissolving 6-8 parts of CuSO4•5H2O in deionized water to prepare a CuSO4 aqueous solution; 2. Then disperse 20-30 parts of expanded graphite (EG) in the prepared copper sulfate solution and mix with magnetic stirring for 0.5h; 3. Then weigh 10 parts of polyvinyl pyrrolidone (PVP) and dissolve it in deionized water, then weigh 20-30 parts of ascorbic acid (LAA) and dissolve it in the PVP solution, and stir it magnetically for 0.5h; 4. Place the CuSO4-EG solution on a heated magnetic stirrer, slowly drop the LAA-PVP solution into the CuSO4-EG solution at a temperature of 60°C-90°C, and simultaneously drop NaOH solution to control the pH value at about 8; 5. After the addition is complete, cool to room temperature and filter under vacuum, add deionized water for washing and filter again, repeat three times. Finally, dry in a vacuum oven at 50°C to obtain EG-CuNPs powder.

[0012] Preferably, the mixed resin includes one or more of bisphenol F epoxy resin, bisphenol A epoxy resin, novolac resin, and polyimide resin.

[0013] Preferably, the curing agent is one or more of m-phenylenediamine, dicyandiamide, diaminodiphenylmethane, o-methylphenylbiguanide, and diaminomaleonitrile.

[0014] Preferably, the curing accelerator includes one or more of zinc acetylacetonate, aluminum acetylacetonate, 2-phenylimidazoline, 2-phenylimidazole, titanate, 2-ethyl-4-methylimidazole, 2-methylimidazole, benzoyl peroxide, and triphenylphosphine.

[0015] Preferably, the method for preparing the hot-pressed fuel cell composite bipolar plate of the present invention specifically comprises the following steps: Step 1. Premix a curing accelerator and a curing agent in a mortar or other resin mixing container to obtain a curing agent / curing accelerator mixed powder; Step 2. Add resin (including one or more of bisphenol F epoxy resin, bisphenol A epoxy resin, linear phenolic resin, and polyimide resin) to the curing agent / curing accelerator mixed powder in step 1, and preliminarily mix them evenly to obtain a curing agent / curing accelerator / resin mixed powder; Step 3. Adding a conductive filler (including one or more of graphite, carbon black, and EG-CuNPs) to the mixed powder of the curing agent / curing accelerator / resin in step (2) and simply premixing to obtain a mixed powder of the curing agent / curing accelerator / resin / conductive filler; Step 4. Place the mixed powder in step (3) into a planetary ball mill and dry mix for 0.5 h to obtain a uniform mixed powder of curing agent / curing accelerator / resin / conductive filler; Step 5. Place the mixed powder in step (4) into a mold for hot pressing at a pressure of 5 MPa-35 MPa, a hot pressing temperature of 120°C-180°C, and a hot pressing time of 200s-300s to obtain a formed composite bipolar plate.

[0016] The beneficial effects of the present invention are: (1) Short pressing time and fast molding time. Compared with the molding and curing time of more than 1 hour for general composite bipolar plates, the present invention only needs 200s-300s of hot pressing to complete one-time molding, without the need for post-curing and other treatments, which greatly improves production efficiency and is suitable for large-scale batch production.

[0017] (2) Due to the rapid curing time, the resin in the composite bipolar plate does not have time to accumulate on the surface during the pressing process, so it has a higher surface conductivity and can effectively reduce the contact resistance between the bipolar plate and the gas diffusion layer.

[0018] (3) The composite bipolar plate of the present invention is prepared by hot pressing of resin, curing agent, curing accelerator and conductive filler, and thus has high bending strength, good air tightness and chemical stability such as acid and alkali resistance.

[0019] (4) The nano copper in the EG-CuNPs of the present invention is prepared by an in-situ chemical reduction method and attached to the surface of expanded graphite, and is not easy to agglomerate. Compared with the composite bipolar plate directly adding nano copper, the method used in the present invention greatly reduces the cost, and the nano copper has better dispersibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Shown is the XRD of EG-CuNPs and the comparison with the standard card.

[0021] Figure 2 The figure shows the Lorentz peak fitting of Cu in the EG-CuNPs sample. The average size of the Cu grains calculated by the Debye-Scherrer formula is 12.77 nm.

[0022] Figure 3 A-C show the SEM images of EG-CuNPs, and D-F show the EDS-mapping in EG-CuNPs.

[0023] Figure 4 The curing curve of the sample of the present invention is shown. Curing starts at about 400 seconds and is completed at about 550 seconds, with a total time of 150 seconds to 200 seconds. DETAILED DESCRIPTION

[0024] Example 1 (1) Premix 3% 2-phenylimidazoline, 2.5% diaminodiphenylmethane and 2.5% m-phenylenediamine in a mortar or other resin mixing container to obtain a curing agent / curing accelerator mixed powder; (2) Add 20% bisphenol A epoxy resin to the mixed powder in step (1) and mix them evenly to obtain a mixed powder of curing agent / curing accelerator / resin; (3) Add 72% conductive filler (graphite: carbon black: EG-CuNPs = 6:2:2) to the curing agent / curing accelerator / resin mixed powder in step (2), and simply premix to obtain a curing agent / curing accelerator / resin / conductive filler mixed powder; (4) Place the mixed powder in step (3) into a planetary ball mill and dry mix for 0.5 h to obtain a uniform mixed powder of curing agent / curing accelerator / resin / conductive filler; (5) The mixed powder in step (4) is placed in a mold and hot-pressed at a pressure of 5 MPa, a temperature of 150°C, and a time of 200 s to obtain a formed composite bipolar plate.

[0025] The conductivity of the fuel cell bipolar plate was measured to be 180S / cm, the flexural strength was 53MPa, the hydrogen permeability was 1.42×10-6cm3(cm•s)-1, the tensile strength was 62MPa, and the contact resistivity was 6.82mΩ•cm2.

[0026] Example 2 (1) Premix 3% triphenylphosphine and 4% m-phenylenediamine in a mortar or other resin mixing container to obtain a curing agent / curing accelerator mixed powder; (2) Add 17% bisphenol A epoxy resin to the mixed powder in step (1) and mix them evenly to obtain a mixed powder of curing agent / curing accelerator / resin; (3) Add 76% conductive filler (graphite: carbon black = 8:2) to the curing agent / curing accelerator / resin mixed powder in step (2), and simply premix to obtain a curing agent / curing accelerator / resin / conductive filler mixed powder; (4) Place the mixed powder in step (3) into a planetary ball mill and dry mix for 0.5 h to obtain a uniform mixed powder of curing agent / curing accelerator / resin / conductive filler; (5) The mixed powder in step (4) is placed in a mold and hot-pressed at a pressure of 10 MPa, a temperature of 140°C, and a time of 250 seconds to obtain a formed composite bipolar plate.

[0027] The conductivity of the fuel cell bipolar plate was measured to be 206S / cm, the flexural strength was 49MPa, the hydrogen permeability was 1.55×10-6cm3(cm•s)-1, the tensile strength was 58MPa, and the contact resistivity was 5.41mΩ•cm2.

[0028] Example 3 (1) Premix 1% benzoyl peroxide and 2% m-phenylenediamine in a mortar or other resin mixing container to obtain a curing agent / curing accelerator mixed powder; (2) Add 7% bisphenol A epoxy resin and 5% bisphenol F epoxy resin to the mixed powder in step (1) and mix them evenly to obtain a curing agent / curing accelerator / resin mixed powder; (3) Add 85% conductive filler (graphite: carbon black: EG-CuNPs = 7:1:2) to the curing agent / curing accelerator / resin mixed powder in step (2), and simply premix to obtain a curing agent / curing accelerator / resin / conductive filler mixed powder; (4) Place the mixed powder in step (3) into a planetary ball mill and dry mix for 0.5 h to obtain a uniform mixed powder of curing agent / curing accelerator / resin / conductive filler; (5) The mixed powder in step (4) is placed in a mold and hot-pressed at a pressure of 10 MPa, a temperature of 160°C, and a time of 250 seconds to obtain a formed composite bipolar plate.

[0029] The conductivity of the fuel cell bipolar plate was measured to be 266S / cm, the flexural strength was 57MPa, the hydrogen permeability was 1.32×10-6cm3(cm•s)-1, the tensile strength was 63MPa, and the contact resistivity was 4.36mΩ•cm2.

Claims

1. A rapidly prepared hot-pressed fuel cell composite bipolar plate, characterized in that: The composite bipolar plate is composed of graphite, carbon black, expanded graphite loaded with nano-copper (hereinafter replaced by EG-CuNPs), mixed resin, curing agent and curing accelerator. The mass percentage of the component raw materials is as follows: graphite 60%-70%; carbon black 1%-10%; EG-CuNPs 1%-10%; mixed resin 15%-25%; curing agent 1%-5%; curing accelerator 0.5%-5%; The graphite and carbon black should be dried in an oven at a temperature of 70°C-100°C for 1-2 hours before use; The nano copper in the EG-CuNPs is prepared by an in-situ chemical reduction method and adsorbed on the surface of expanded graphite, comprising the following steps: Step 1, dissolve 6-8 parts of CuSO4•5H2O in deionized water to prepare a CuSO4 aqueous solution; Step 2, then disperse 20-30 parts of expanded graphite (EG) in the prepared copper sulfate solution, and mix with magnetic stirring for 0.5h; Step 3, then weigh 10 parts of polyvinyl pyrrolidone (PVP) and dissolve it in deionized water, then weigh 20-30 parts of ascorbic acid (LAA) and dissolve it in the PVP solution, and stir it magnetically for 0.5h; Step 4, place the CuSO4-EG solution on a heated magnetic stirrer, slowly drop the LAA-PVP solution into the CuSO4-EG solution at a temperature of 60°C-90°C, and simultaneously drop NaOH solution to control the pH value to about 8; Step 5: After the addition is complete, cool to room temperature and filter under vacuum, add deionized water to wash and filter again, repeat three times.

2. Finally, the CuNPs-EG powder is obtained by drying in a vacuum drying oven at 50°C; the mixed resin includes one or more of bisphenol F epoxy resin, bisphenol A epoxy resin, linear phenolic resin, and polyimide resin; the curing agent is one or more of m-phenylenediamine, dicyandiamide, diaminodiphenylmethane, o-methylphenylbiguanide, and diaminomaleonitrile; the curing accelerator includes one or more of zinc acetylacetonate, aluminum acetylacetonate, 2-phenylimidazoline, 2-phenylimidazole, titanate, 2-ethyl-4-methylimidazole, 2-methylimidazole, benzoyl peroxide, and triphenylphosphine.

3. A rapidly prepared hot-pressed fuel cell composite bipolar plate, characterized in that: First, the mixed resin, curing agent, and curing accelerator are evenly mixed, and then one or more of graphite, carbon black, and EG-CuNPs are added, and then put into a planetary ball mill for dry mixing for 0.5 hours, and finally put into a mold for hot pressing.

4. The fast-prepared hot-pressed fuel cell composite bipolar plate according to claim 2, characterized in that: The molding pressure is 5MPa-35MPa, the hot pressing temperature is 120°C-180°C, and the hot pressing time is 200s-300s.

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