WO2021068318A1 - Method for preparing fuel cell graphite bipolar plate - Google Patents

Abstract

Disclosed is a method for preparing a fuel cell graphite bipolar plate, the method involving adding natural flake graphite to a mixed solution of sulfuric acid and nitric acid and stirring same during the addition process, after the addition of the natural flake graphite is completed, further adding potassium permanganate and ferric trichloride, maintaining the temperature at 24-26ºC, stirring same for 30-40 min, then separating same by means of centrifugation, washing same with water until neutral and then dehydrating same to prepare an expandable graphite; mixing the prepared expandable graphite with carbon black and polyphenylene sulfide by means of a mixer with a mixing time of 20 min-25 min, and adding the resulting mixture to a solvent, i.e. anhydrous ethanol, mixing same until uniform by means of mechanical stirring and ultrasonic dispersion, and drying and crushing same into a powder, placing the prepared powder into a mold, and press molding same at 25-30ºC with a molding pressure of 10-11 MPa after the pressurization is continued for 3 minutes; and then subjecting a sample obtained after press molding to a curing treatment by means of stepped temperature-rising, and finally cooling same to obtain a finished product. The advantages of the present invention lie in that the prepared bipolar plate has a higher anti-bending strength and a better conductivity performance.

Description

Method for preparing fuel cell graphite bipolar plate Technical field

The invention relates to the field of fuel cells, in particular to a method for preparing a graphite bipolar plate of a fuel cell.

Background technique

Graphite bipolar plates, also known as graphite collector plates and graphite separators, are one of the important components of fuel cells. Graphite bipolar plates play a role in providing gas flow channels in fuel cells, preventing different gases from colluding, and establishing current paths.

Graphite material is a bipolar plate material that was developed and used earlier. The traditional bipolar plate mainly uses non-porous graphite plate, and the groove is processed by machining. The graphite bipolar plate has a low thermal expansion coefficient, good thermal conductivity, stable chemical properties, good corrosion resistance and strong electrical conductivity. However, the brittleness of graphite causes processing difficulties, and it is easy to produce pores during the manufacturing process, so that the fuel and the oxidant can penetrate each other, so other substances must be added to improve the battery performance.

Summary of the invention

The purpose of the present invention is to provide a method for preparing the graphite bipolar plate of a fuel cell.

The above-mentioned technical purpose of the present invention is achieved through the following technical solutions:

A method for preparing a graphite bipolar plate for a fuel cell is characterized in that it comprises the following steps:

(1) Take natural flake graphite and add it to the mixed solution of sulfuric acid and nitric acid. The mass ratio of the natural flake graphite, sulfuric acid and nitric acid is 1: (1.8-2.1): (1-1.1), stir during the adding process, the natural flake graphite After the addition is complete, add potassium permanganate and ferric chloride, keep the temperature at 24-26°C, stir for 30-40 minutes, centrifuge, and wash with water until it is neutral and dehydrated to obtain expandable graphite;

(2) Take the expandable graphite, carbon black and polyphenylene sulfide prepared in step (1) and mix them with a mixer, and the mixing time is 20min-25min. The expandable graphite, carbon black and polyphenylene sulfide The mass ratio is 15: (1-1.2): (3.8-4.2);

(3) The mixture obtained in step (2) is added to the solvent absolute ethanol, mixed with mechanical stirring and ultrasonic dispersion, and dried and broken into powder;

(4) Put the powder obtained in step (3) into a mold, and press it to form after a molding pressure of 10-11 MPa at 25-30°C and a pressure for 3 minutes;

(5) Solidify the sample press-formed in step (4) through stepped heating, and finally cool it to obtain a finished product.

Preferably, in the step (2), carbon black is first dispersed in polyphenylene sulfide, and then expandable graphite is added.

Preferably, the quality of the anhydrous ethanol in the step (3) is at least 3 times the quality of the mixture.

Preferably, in the step (5), the stepped temperature rise is to firstly increase to 80°C at a rate of 20°C/h, and then increase to 180°C at a rate of 15°C/h, and keep the temperature for 2-2.5h.

Preferably, the particle size of the natural flake graphite in the step (1) is less than 74 μm.

Preferably, the particle size of the carbon black in the step (2) is less than 20 μm.

Preferably, the masses of potassium permanganate and ferric chloride added in the step (1) are both 7%-9% of the mass of graphite.

Preferably, the dehydration in the step (1) is completed under an inert gas.

In summary, the present invention has the following beneficial effects:

1. In the present invention, natural flake graphite is added to the mixed solution of sulfuric acid and nitric acid and mixed uniformly, and then potassium permanganate and ferric chloride are added. The reaction at a fixed temperature can make the generated expandable graphite reduce the generation of edge compounds and disperse More uniform, dehydration under inert gas prevents reaction with air, thereby affecting the quality of expandable graphite.

2. In the present invention, expandable graphite, carbon black, and polyphenylene sulfide are first mixed with a mixer, and the solvent is added, and then mixed by mechanical stirring and ultrasonic dispersion to reduce the porosity of the finished product and improve the quality of the product.

3. In the present invention, the sample is cured by a stepped heating method, so that the sheet is more compact, and both the electrical conductivity and the flexural strength are improved.

Detailed ways

The present invention will be further illustrated by the following examples, and this example does not constitute a limitation to the present invention.

Example 1

(1) Take natural flake graphite and add the mixed solution of sulfuric acid and nitric acid. The particle size of natural flake graphite is less than 74 μm, and the mass ratio of natural flake graphite, sulfuric acid and nitric acid is 1:1.8:1. Stir during the adding process, natural flake graphite After the addition is complete, add potassium permanganate and ferric chloride. The masses of the potassium permanganate and ferric chloride are 7% of the graphite mass. Keep the temperature at 24°C, stir for 30 minutes, centrifuge, and wash with water until neutral. Expandable graphite is prepared by dehydration under inert gas;

(2) Take the expandable graphite and carbon black obtained in step (1) and mix them for 5 minutes with a mixer, and then add polyphenylene sulfide for 20 minutes. The expandable graphite, carbon black and polyphenylene sulfide The mass ratio of ether is 15:1:3.8, and the particle size of carbon black is less than 20μm;

(3) The mixture obtained in step (2) is added to the solvent absolute ethanol, the quality of the absolute ethanol is 4 times that of the mixture, and then mechanical stirring and ultrasonic dispersion are used for mixing, and the mixture is dried and broken into powder;

(4) Put the powder prepared in step (3) into a mold, and press it into a mold at a molding pressure of 10 MPa at 26°C, and press for 3 minutes;

(5) Then, the sample formed in step (4) is cured by stepped heating. The stepped heating is specifically increased to 80°C at a rate of 20°C/h, and then to 180°C at a rate of 15°C/h. Keep the temperature for 2h, and finally cool down to obtain the finished product.

Example 2

(1) Take natural flake graphite and add it to the mixed solution of sulfuric acid and nitric acid. The particle size of natural flake graphite is less than 74 μm, and the mass ratio of natural flake graphite, sulfuric acid and nitric acid is 1:2:1. Stir during the adding process, natural flake graphite After the addition is complete, add potassium permanganate and ferric chloride. The masses of the potassium permanganate and ferric trichloride are 8% of the graphite mass. Keep the temperature at 26°C, stir for 35 minutes and centrifuge, and wash with water until neutral. Expandable graphite is prepared by dehydration under inert gas;

(2) Take the expandable graphite and carbon black obtained in step (1) and mix them for 5 minutes with a blender, and then add polyphenylene sulfide, the mixing time is 25 minutes, the expandable graphite, carbon black and polyphenylene sulfide The mass ratio of ether is 15:1.1:4, and the particle size of carbon black is less than 20μm;

(3) The mixture obtained in step (2) is added to the solvent absolute ethanol, the quality of the absolute ethanol is 4.5 times that of the mixture, and then mechanical stirring and ultrasonic dispersion are used for mixing, and the mixture is dried and broken into powder;

(4) Put the powder obtained in step (3) into a mold, and press it into a mold at a molding pressure of 10 MPa at 27°C, and press for 3 minutes;

(5) Then, the sample formed in step (4) is cured by stepped heating. The stepped heating is specifically increased to 80°C at a rate of 20°C/h, and then to 180°C at a rate of 15°C/h. Keep the temperature for 2h, and finally cool down to obtain the finished product.

Example 3

(1) Take natural flake graphite and add the mixed solution of sulfuric acid and nitric acid. The particle size of the natural flake graphite is less than 74 μm, and the mass ratio of the natural flake graphite, sulfuric acid and nitric acid is 1:2.1:1.1. Stir during the adding process, the natural flake graphite After the addition is complete, add potassium permanganate and ferric chloride. The masses of the potassium permanganate and ferric chloride are 9% of the graphite mass. Keep the temperature at 25° C., stir for 40 minutes, and centrifuge, and wash with water until neutral. Expandable graphite is prepared by dehydration under inert gas;

(2) Take the expandable graphite and carbon black obtained in step (1) and mix them for 5 minutes with a mixer, and then add polyphenylene sulfide for 30 minutes. The expandable graphite, carbon black and polyphenylene sulfide The mass ratio of ether is 15:1.2:4.1, and the particle size of carbon black is less than 20μm;

(3) The mixture obtained in step (2) is added to the solvent absolute ethanol, the quality of the absolute ethanol is 5 times that of the mixture, and then mechanical stirring and ultrasonic dispersion are used for mixing, and the mixture is dried and broken into powder;

(4) The powder prepared in step (3) is put into a mold, the molding pressure is 10 MPa at 30°C, and the pressure is continued for 3 minutes, and then it is pressed into shape;

(5) Curing the sample formed by step (4) through stepped heating. The stepped temperature rise is first to increase to 80°C at a rate of 20°C/h, and then to 180°C at a rate of 15°C/h. , Heat preservation for 3h, and finally cool to make the finished product.

Comparative example 1

The natural flake graphite, carbon black and phenolic resin are mixed uniformly according to the mass ratio of 10:6:2, and then the mixture is put into the mold at room temperature and 10 MPa pressure for 3 minutes to press the molding, and then solidify and increase the temperature for solidification treatment. After cooling The prepared sample is obtained.

The samples prepared in the above examples were processed into samples of 60mm×5mm×2mm, and the bending strength of each sample was measured by the LWK-250 micro-control electronic tensile testing machine and the three-point bending method. The span was 40mm and the impact The moving speed of the head is 1.0 mm/min. The morphology of the sample was observed with JSM-6700F scanning electron microscope. The SX1934 digital four-probe tester was used to measure the volume resistivity ρ of each sample, and the electrical conductivity σ=1/ρ.

It can be obtained that the flexural strength of the samples of Examples 1-3 are all greater than 60Mpa, the electrical conductivity is greater than 80S/cm, the flexural strength of the comparative example is 15.5MPa, and the electrical conductivity is 18.3S/cm, it can be seen that the method of the present invention is used to prepare The resulting bipolar plate material has better performance, higher strength and better performance.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within the essence and protection scope of the present invention. Such modifications Or equivalent replacements should also be regarded as falling within the protection scope of the technical solution of the present invention.

Claims (8)

1. A method for preparing a graphite bipolar plate for a fuel cell is characterized in that it comprises the following steps:

   (1) Take natural flake graphite and add it to the mixed solution of sulfuric acid and nitric acid. The mass ratio of the natural flake graphite, sulfuric acid and nitric acid is 1: (1.8-2.1): (1-1.1), stir during the adding process, the natural flake graphite After the addition is complete, add potassium permanganate and ferric chloride, keep the temperature at 24-26°C, stir for 30-40 minutes, centrifuge, and wash with water until it is neutral and dehydrated to obtain expandable graphite;

   (2) Take the expandable graphite, carbon black and polyphenylene sulfide prepared in step (1) and mix them with a mixer, and the mixing time is 20min-25min. The expandable graphite, carbon black and polyphenylene sulfide The mass ratio is 15: (1-1.2): (3.8-4.2);

   (3) The mixture obtained in step (2) is added to the solvent absolute ethanol, mixed with mechanical stirring and ultrasonic dispersion, and dried and broken into powder;

   (4) Put the powder obtained in step (3) into a mold, and press it to form after a molding pressure of 10-11 MPa at 25-30°C and a pressure for 3 minutes;

   (5) Solidify the sample press-formed in step (4) through stepped heating, and finally cool it to obtain a finished product.
2. The method for preparing a graphite bipolar plate for a fuel cell according to claim 1, wherein in the step (2), carbon black is first dispersed in polyphenylene sulfide, and then expandable graphite is added.
3. A method for preparing a graphite bipolar plate for a fuel cell according to claim 1, wherein the quality of the absolute ethanol in the step (3) is at least three times the quality of the mixture.
4. The method for preparing a graphite bipolar plate for a fuel cell according to claim 1, characterized in that: in the step (5), the stepped temperature rise is first to increase to 80°C at a rate of 20°C/h, and then to 15°C/h. The rate of h is increased to 180°C and the temperature is kept for 2-2.5h.
5. The method for preparing a graphite bipolar plate for a fuel cell according to claim 1, wherein the particle size of the natural flake graphite in the step (1) is less than 74 μm.
6. A method for preparing a graphite bipolar plate for a fuel cell according to claim 1, wherein the particle size of the carbon black in the step (2) is less than 20 μm.
7. The method for preparing a graphite bipolar plate for a fuel cell according to claim 1, wherein the masses of potassium permanganate and ferric chloride added in the step (1) are 7%-9% of the mass of graphite. %.
8. The method for preparing a graphite bipolar plate for a fuel cell according to claim 1, wherein the dehydration in the step (1) is completed under an inert gas.