Preparation method of modified toughened phenolic resin graphite fuel cell composite bipolar plate

Abstract

The invention belongs to the technical field of fuel cells, and particularly relates to a preparation method of a modified toughened phenolic resin graphite fuel cell composite bipolar plate, which comprises the following steps: (1) premixing: mixing toughening agent-containing phenolic resin, graphite powder, short carbon fibers, carbon nanotubes and conductive carbon black to obtain composite material powder; (2) primary mixing: weighing the composite material powder, heating, and cooling to obtain a mixture; and (3) mold pressing: loading the obtained mixture into a mold, pre-pressing, pressurizing, heating, decompressing and demolding to obtain the modified toughened phenolic resin graphite fuel cell composite bipolar plate. The fuel cell composite bipolar plate is prepared from conventional and bulk chemical raw materials, and has the characteristics of simplicity, convenience, high efficiency and low cost.

Description

Technical Field

[0001] The invention belongs to the technical field of fuel cells, and in particular relates to a method for preparing a modified toughened phenolic resin graphite fuel cell composite bipolar plate. Background Art

[0002] Fuel cells are efficient and clean energy sources that were initially used in the aerospace field. Currently, major countries have invested a lot of money and resources in the development of fuel cell technology to promote its application in transportation, energy production, industrial production and other fields, in order to provide an effective way to solve energy shortages and reduce environmental pollution (Shen Fuqiang, CN109599574).

[0003] Bipolar plates are an important component of fuel cells, accounting for a large proportion in terms of price and quality, and also have an important impact on key indicators of fuel cells such as current density, airtightness and life. Compared with traditional graphite and metal bipolar plates, composite bipolar plates have the advantages of easy processing, low cost and corrosion resistance, and are the only way for fuel cells to move towards practical application. Reducing the cost of composite bipolar plates, improving their performance, and overcoming the various obstacles they encounter in practical applications are also inevitable for the development of fuel cell technology (Song et al. Int J Hydrogen Energ 2020, 45, 29832).

[0004] The phenolic resin molecular chain is rich in active groups such as aldehyde and phenol groups. They cross-link with each other during the molding process to form a stable molecular structure. It has good thermal stability and corrosion resistance. It can form a reliable interface with carbon-based fillers such as graphite. It has high mechanical strength and allows for thinner molding thickness of the plate. It is one of the most promising and researched composite bipolar plate materials. However, the molding of phenolic composite plates will also encounter the problem of increased contact resistance due to the rich resin on the surface of the composite bipolar plate during the resin curing process. At the same time, the wettability of graphite and resin does not match, making it difficult to distribute evenly, resulting in the problem of particle / resin concentration and separation.

[0005] In addition, the fuel cell stack is a stacked series structure, and the electrochemical reaction will gradually increase the temperature inside the battery. Due to the different materials of the components, the thermal expansion coefficients are different, and the expansion amounts are also different. The plates need to face the coupling of heat and force, which leads to changes in contact pressure between the components inside the stack and uneven pressure distribution. However, the toughness and thermal conductivity of the composite bipolar plate are lower than those of graphite and metal plates, and the stress caused by uneven thermal expansion and contraction may lead to insufficient contact between the gas diffusion layer, catalyst and bipolar plate, resulting in uneven thermal expansion of the plate, causing risks such as warping of the composite bipolar plate.

[0006] Tetsuya Harada et al. (CN1409426) of Japan disclosed a technology for preparing composite bipolar plates by dispersing conductive materials in varnish-type phenolic resin and phenol dicyclopentadiene resin for addition crosslinking reaction. It is believed that the resulting plate is impermeable and has good mechanical strength, and does not warp, crack or expand. The mechanical properties can also be improved by toughening the phenolic resin and modifying the matrix by filling fillers such as carbon fiber and carbon nanotubes. Wang Hongfei et al. (CN 114188552 B) disclosed a carbon fiber toughened benzoxazine resin molded bipolar plate. Wang Liujun et al. (CN 116454307) disclosed a technology for preparing composite phenolic bipolar plates using two graphite particle sizes, and 60 to 70 parts of two graphites with particle sizes between 100 microns and submicrons were bonded with 40 to 60 parts of phenolic resin. Its bending strength reaches 55MPa and its conductivity reaches 120S / cm. Zheng Junsheng et al. of Tongji University (CN118248883) reduced the amount of graphite used. Through a five-stage treatment method, 10-30 parts of graphite powder and 30-90 parts of phenolic resin were used as raw materials, and pressed at 30MPa for 3-6 minutes. The conductivity of the resulting composite bipolar plate was ≥180S / cm and the bending strength was ≥50MPa. However, for these high-carbon systems with high content of graphite, carbon fiber, and carbon nanotubes, insufficient consideration of high thermal conductivity and high toughness has caused obstacles to the application of low-cost, high-thermal conductivity toughened phenolic resin-based bipolar plates.

[0007] In view of this, the present invention is proposed. Summary of the invention

[0008] The purpose of the present invention is to provide a method for preparing a high thermal conductivity and high electrical conductivity graphite composite bipolar plate by using a modified toughened phenolic resin. Specifically, a method is provided for compounding particles of various sizes to construct thermal and electrical conduction paths; a technology for obtaining high-performance bipolar plates by toughening phenolic resins with cardanol, cellulose modification, carbon fiber and carbon nanotubes. While enhancing the toughness of the plate, the thermal and electrical conduction capabilities of the plate are enhanced, and heat is transferred in a timely manner to avoid warping of the plate.

[0009] In order to achieve the above objectives, the present invention particularly adopts the following technical solutions:

[0010] The present invention provides a method for preparing a modified toughened phenolic resin graphite fuel cell composite bipolar plate, comprising the following steps:

[0011] (1) Premixing: mixing a phenolic resin containing a toughening agent, graphite powder, chopped carbon fibers, carbon nanotubes and conductive carbon black to obtain a composite powder;

[0012] (2) Preliminary mixing: weigh the above composite powder, heat it, and cool it to obtain a mixed material;

[0013] (3) Molding: The mixture obtained above is placed into a mold, pre-pressed, pressurized, heated, and decompressed to demould to obtain a modified toughened phenolic resin graphite fuel cell composite bipolar plate.

[0014] Preferably, in step (1), by weight, the phenolic resin containing the toughening modifier is 15-65 parts, the graphite powder is 12-63 parts, the short-cut carbon fibers are 0.1-10 parts, the carbon nanotubes are 0.1-2 parts, and the conductive carbon black is 5-15 parts, wherein the content of the toughening agent accounts for 0.5-15% of the phenolic resin.

[0015] Preferably, the length of the chopped carbon fibers is 2-5 mm; the carbon nanotubes have a diameter of 2-10 nm and a length of 0.5-20 μm.

[0016] Preferably, the graphite powder is a powder of three or more sizes, and its D50 size range is: 150-250: 30-80: 10-20: 1-3 microns, and the ratio is 1: A: B: C, wherein the numerical range of A, B, C is 0.1-2.

[0017] Preferably, the toughening agent includes one or more of cardanol, hydroxymethyl cellulose, and glyoxal.

[0018] Preferably, in step (1), the mixing step is: a. mixing chopped carbon fibers and phenolic resin containing a toughening modifier; b. uniformly mixing graphite powder, conductive carbon black and carbon nanotubes; and c. mixing step a and step b to obtain composite powder.

[0019] Preferably, in step (2), the temperature is raised to 60-100° C. at a rate of 0.1-5° C. / min, maintained at the temperature for 0.5-3 h, and then cooled.

[0020] Preferably, in step (3), pre-pressing is performed at a pressure of 6-10 MPa for 1-5 min, and then pressurized to 50-90 MPa, and the pressure is maintained at 140-230° C. for 5-30 min.

[0021] Beneficial effects of the present invention:

[0022] The present invention uses conventional, bulk material chemical raw materials to prepare fuel cell composite bipolar plates, which are simple, efficient and low-cost. The core lies in the modification of phenolic resin by toughening agent, carbon fiber and carbon nanotubes to improve the toughness of the composite bipolar plate, and the introduction of conductive modifier asphalt-based carbon fiber and carbon nanotube filler also constructs a heat conduction path and an electron transfer channel to improve thermal conductivity and electronic conductivity. It is simple, efficient and low-cost. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] First, the present invention is explained as a whole, as follows:

[0025] (1) Premixing: Weigh 15-65 parts of thermosetting phenolic resin containing toughening agent, 15-63 parts of graphite powder, 0.1-10 parts of 2-5 mm short carbon fiber, 0.1-2 parts of carbon nanotubes, and 5-15 parts of conductive carbon black by weight. Put them into a high-speed mixer and mix them evenly to obtain composite powder; (2) Preliminary mixing: Weigh the above composite powder, add it into an internal mixer or a kneader and mix it evenly, raise the temperature to 60-100°C at a rate of 0.1-5°C / min, maintain the temperature for 0.5-3h, and cool it to obtain a mixture; (3) Molding: Put the above obtained mixture into a mold, pre-press it at 6-10 MPa for 2-3 minutes, then increase the pressure to 50-90 MPa, maintain the pressure at 140-230°C for 5-30 minutes, and then decompress and demold to obtain a modified toughened phenolic resin graphite fuel cell composite bipolar plate.

[0026] Among them, the initial mixing reaction before molding will initially cross-link the phenolic resin, increase its molecular weight, make it lose fluidity, and inhibit the resin from enriching at the edge during the molding process and the escape of phenolic polymerization by-product water to form interconnecting pores.

[0027] The toughening agent in the phenolic resin includes one or more of cardanol, hydroxymethyl cellulose, and glyoxal, and the content thereof accounts for 0.5-15% of the phenolic resin; the carbon fiber is pitch-based carbon fiber; the carbon nanotube has a diameter of 2-10nm and a length of 0.5-20μm. The purpose is to utilize its good electrical and thermal conductivity to connect adjacent graphite powders and construct a thermal conduction path.

[0028] The preferred graphite powder is a powder of two or more sizes, and its D50 size range is: 150-250: 30-80: 10-20: 1-3 microns, and its ratio is 1: A: B: C, wherein the preferred value range of A, B, C is 0.1-2;

[0029] Three or more different sizes of graphite are used in the present invention. The commercially available, easily accessible submillimeter graphite has good crystallization and low defect density, which is conducive to electronic conduction and heat transfer, and a heat-conducting and conductive skeleton is built. However, based on the large size of the large particles of 100 microns and the accumulation of layers, pores are easily generated, resulting in a significant decrease in mechanical properties, a high hydrogen permeability, and it is difficult to effectively overlap between large particles, and there are few effective electronic and heat channels. The present invention introduces medium-sized graphite with a D50 of 30-80 microns and 10-20 microns to fill the gaps in the conductive skeleton, to improve the combination between the graphite and resin interfaces, and improve its mechanical properties, thermal conductivity, electrical conductivity, and gas permeability; and the small-sized graphite (D50: 1-3 microns) is used. The orientation degree is low, and the large-particle graphite edge is overlapped, and the characteristics of connecting adjacent large-sized particles are reduced, and the interface resistance and thermal resistance between graphite sheets are reduced. According to the above principle, in view of the characteristics of three or more sizes of graphite fillers used in the present invention, cardanol, hydroxymethyl cellulose, and glyoxal-modified phenolic resin are preferably selected, which can improve the wetting ability and interface bonding of the composite graphite, enhance its mechanical properties and reduce its gas permeability, and finally obtain a phenolic resin-based bipolar plate with significantly improved electrical conductivity, thermal conductivity, gas permeability and mechanical properties.

[0030] The preferred mixing grouping sequence of the present invention is: a. uniformly mixing chopped carbon fibers and phenolic resin, b. uniformly mixing graphite powder, conductive carbon black and carbon nanotubes; c. mixing the mixtures obtained in step a and step b. The probability of direct contact between chopped carbon fibers, carbon nanotubes and graphite raw materials is increased, and their physical connection is enhanced, thereby increasing the conductivity of the plate.

[0031] The present invention uses a variety of matching graphites with different particle sizes, takes advantage of the characteristics of large particle structures with complete thermal and electrical conductivity, uses medium particles to fill the gaps of large particles, reduces the porosity of the pole plate, and simultaneously uses small particles that are not easy to orient, and the interface overlap makes the connection of the conductive phase tighter. And for the composite system of graphite particles with different particle sizes, the preferred phenolic resin tougheners of cardanol, hydroxymethyl cellulose and glyoxal improve the combination of resin and interface, so that each particle size graphite particle, carbon nanotube and carbon fiber are evenly dispersed in the phenolic resin matrix, significantly improving the toughness of the pole plate. The addition of carbon nanotubes and asphalt-based carbon fibers also enhances the electrical and thermal conductivity of the pole plate, and also effectively improves electrical conductivity, thermal conductivity and mechanical strength.

[0032] Example 1

[0033] (1) Premixing: Weigh graphite powders with D50 of 250, 80, 20, and 2 μm, respectively, and prepare them into 63 parts, 2 parts of carbon nanotubes, and 10 parts of conductive carbon black in a ratio of 1:1:1:2, and put them into a high-speed mixer, and mix them evenly to obtain composite powder 1#; take 15 parts of thermosetting phenolic resin containing 10% cardanol, put them into a kneader, add 10 parts of 2mm short-cut asphalt-based carbon fibers, and mix them evenly to obtain composite powder 2#. (2) Preliminary mixing: Weigh the above composite powders 1# and 2#, add them into a kneader and mix them evenly, raise the temperature to 60°C at a rate of 5°C / min, maintain the temperature for 3h, and cool to obtain a mixture; (3) Molding: Put the above mixture into a mold, pre-press at 10MPa for 3min, then pressurize to 90MPa, maintain the pressure at 210°C for 30min, and then decompress and demold to obtain a modified toughened phenolic resin graphite fuel cell composite bipolar plate.

[0034] Example 2

[0035] (1) Premixing: Weigh graphite powders with D50 of 150, 80, 10, and 1 μm, respectively, and prepare them into 20 parts, 0.1 parts of carbon nanotubes, and 9.9 parts of conductive carbon black according to the ratio of 2:1:1:0.1, and put them into a high-speed mixer, and mix them evenly to obtain composite powder 1#; take 65 parts of phenolic resin containing 2% hydroxymethyl cellulose, put them into a kneader, add 5 parts of 3mm short-cut asphalt-based carbon fibers, and mix them evenly to obtain composite powder 2#. (2) Preliminary mixing: Weigh the above composite powders 1# and 2#, add them into a kneader and mix them evenly, heat them to 100°C at a rate of 1°C / min, maintain the temperature for 3h, and cool them to obtain a mixture; (3) Molding: Put the above mixture into a mold, pre-press it at 6MPa for 5min, then pressurize it to 50MPa, maintain the pressure at 170°C for 30min, and then decompress and demold it to obtain a modified toughened phenolic resin graphite fuel cell composite bipolar plate.

[0036] Example 3

[0037] (1) Premixing: Weigh graphite powders with D50 of 200, 50, 15, and 1 μm respectively, and prepare them into 25 parts, 1 part carbon nanotubes, and 14 parts conductive carbon black according to the ratio of 2:1:1:0.1, and put them into a high-speed mixer, and mix them evenly to obtain composite powder 1#; 59.9 parts of phenolic resin containing 2% hydroxymethyl cellulose and 0.1 part of 3mm short-cut asphalt-based carbon fiber are added into a kneader, and mixed evenly to obtain composite powder 2#. (2) Preliminary mixing: Weigh the above composite powders 1# and 2#, add them into a kneader and mix them evenly, raise the temperature to 100°C at a rate of 1°C / min, maintain the temperature for 3h, and cool to obtain a mixture; (3) Molding: Put the above mixture into a mold, pre-press at 6MPa for 5min, then pressurize to 50MPa, maintain the pressure at 170°C for 30min, and then decompress and demould to obtain a modified toughened phenolic resin graphite fuel cell composite bipolar plate.

[0038] Example 4

[0039] (1) Premixing: Weigh graphite powders with D50 of 160, 80, 30, and 1 μm respectively, and prepare them into 30 parts, 1 part carbon nanotubes, and 10 parts conductive carbon black according to the ratio of 1:1:2:0.1, and put them into a high-speed mixer, and mix them evenly to obtain composite powder 1#; take 5 parts of 5mm short-cut asphalt-based carbon fibers and 54 parts of phenolic resin containing 5% glyoxal, and put them into a kneader, and mix them evenly to obtain composite powder 2#. (2) Preliminary mixing: Weigh the above composite powders 1# and 2#, add them into a kneader and mix them evenly, raise the temperature to 100°C at a rate of 1°C / min, maintain the temperature for 3h, and cool to obtain a mixture; (3) Molding: Put the above mixture into a mold, pre-press at 6MPa for 5min, then pressurize to 50MPa, maintain the pressure at 170°C for 30min, and then decompress and demold to obtain a modified toughened phenolic resin graphite fuel cell composite bipolar plate.

[0040] Comparative Example 1

[0041] (1) Premixing: Weigh graphite powder with D50 of 250 and 1μm respectively, prepare 63 parts, 2 parts carbon nanotubes and 10 parts conductive carbon black in a ratio of 1:1, put them into a high-speed mixer, mix them evenly to obtain composite powder 1#; take 15 parts of phenolic resin and put them into a kneader, add 10 parts of 2mm short-cut asphalt-based carbon fibers, and mix them evenly to obtain composite powder 2#. (2) Preliminary mixing: Weigh the above composite powders 1# and 2#, add them into a kneader and mix them evenly, raise the temperature to 60℃ at a rate of 5℃ / min, maintain the temperature for 3h, and cool to obtain a mixture; (3) Molding: Put the above mixture into a mold, pre-press at 10MPa for 3min, then press to 90MPa, maintain the pressure at 210℃ for 30min, and then decompress and demold to obtain a composite bipolar plate.

[0042] Comparative Example 2

[0043] (1) Premixing: Weigh 20 parts of graphite powder with a D50 of 150 μm, 0.1 parts of carbon nanotubes, and 9.9 parts of conductive carbon black into a high-speed mixer and mix them evenly to obtain composite powder 1#; take 65 parts of phenolic resin and put them into a kneader, add 5 parts of 3 mm short-cut asphalt-based carbon fibers, and mix them evenly to obtain composite powder 2#. (2) Initial mixing: Weigh the above composite powders 1# and 2#, add them into a kneader and mix them evenly, raise the temperature to 100°C at a rate of 1°C / min, maintain the temperature for 3 hours, and cool to obtain a mixture; (3) Molding: Put the above mixture into a mold, pre-press at 6 MPa for 5 minutes, then pressurize to 50 MPa, maintain the pressure at 170°C for 30 minutes, and then decompress and demold to obtain a composite bipolar plate.

[0044] Table 1 Performance results of composite phenolic resin-based bipolar plates prepared in Examples and Comparative Examples

[0045]

[0046] The main difference between Example 1 and Comparative Example 1, and Example 2 and Comparative Example 2 is that Example 1 and Example 2 are compounded with four kinds of graphite with D50, and the phenolic resin is modified by cardanol or hydroxymethyl cellulose, while Comparative Example 1 is only compounded with two kinds of graphite powder with D50 of 250 and 1 μm, and Comparative Example 2 only uses one kind of graphite with D50 of 150 μm. As can be seen from Table 1, the bending strength, electrical conductivity and hydrogen permeability of Examples 1 and 2 are significantly improved compared with Comparative Examples 1 and 2. It can be seen that there are two reasons for the formation of such excellent technical effects: a. Medium-sized graphite can fill the pores formed by large-sized graphite, and small-sized graphite can overlap adjacent graphite sheets, which can give full play to the characteristics of large-sized graphite with good thermal and electrical conductivity. b. For the composite system of graphite with multiple particle sizes, the modification of phenolic resin by cardanol and hydroxymethyl cellulose can significantly improve the interface between graphite and resin. Finally, a composite bipolar plate with low hydrogen permeability, high electrical conductivity and thermal conductivity was prepared.

[0047] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all belong to the scope of protection of the present application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. A method for preparing a modified toughened phenolic resin graphite fuel cell composite bipolar plate, comprising the following steps: (1) Premixing: mixing a phenolic resin containing a toughening agent, graphite powder, chopped carbon fibers, carbon nanotubes and conductive carbon black to obtain a composite powder; (2) Preliminary mixing: weigh the above composite powder, heat it, and cool it to obtain a mixed material; (3) Molding: The mixture obtained above is placed into a mold, pre-pressed, pressurized, heated, and decompressed to demould to obtain a modified toughened phenolic resin graphite fuel cell composite bipolar plate.

2. The preparation method according to claim 1, characterized in that: In step (1), by weight, the phenolic resin containing a toughening modifier is 15-65 parts, the graphite powder is 12-63 parts, the short-cut carbon fibers are 0.1-10 parts, the carbon nanotubes are 0.1-2 parts, and the conductive carbon black is 5-15 parts, wherein the content of the toughening agent accounts for 0.5-15% of the phenolic resin.

3. The preparation method according to claim 1, characterized in that: The length specification of the chopped carbon fiber is 2-5 mm; the diameter of the carbon nanotube is 2-10 nm and the length is 0.5-20 μm.

4. The preparation method according to claim 1, characterized in that: The graphite powder is a powder compounded with three or more sizes, and its D50 size range is: 150-250: 30-80: 10-20: 1-3 microns, and its ratio is 1: A: B: C, wherein the numerical range of A, B, and C is 0.1-2.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The toughening agent includes one or more of cardanol, hydroxymethyl cellulose and glyoxal.

6. The preparation method according to claim 1, characterized in that: In step (1), the mixing steps are: a. mixing chopped carbon fibers and phenolic resin containing a toughening modifier; b. mixing graphite powder, conductive carbon black and carbon nanotubes evenly; and c. mixing step a and step b to obtain composite powder.

7. The preparation method according to claim 1, characterized in that: In step (2), the temperature is raised to 60-100°C at a rate of 0.1-5°C / min, maintained at the temperature for 0.5-3h, and cooled.

8. The preparation method according to claim 1, characterized in that: In step (3), pre-pressing is performed at a pressure of 6-10 MPa for 1-5 min, and then pressurized to 50-90 MPa, and the pressure is maintained at 140-230° C. for 5-30 min.

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