Carbon paper and its preparation method and application

Abstract

The present invention discloses carbon paper, its preparation method, and application. The carbon paper preparation method comprises the following steps: uniformly mixing expanded polystyrene particles and vermicular graphite, and then pressing the mixture into a graphite block, wherein the volume ratio of expanded polystyrene particles to vermicular graphite is 0.2 to 0.8:1; heating the graphite block to 350°C ± 30°C to form a porous graphite block; and further pressing the porous graphite block into graphite paper. The graphite paper is then rinsed with hot water and dried to produce the carbon paper. Compared with existing carbon fiber-based carbon paper products, this carbon paper has the advantages of low manufacturing cost and simple production process.

Description

Technical Field

[0001] The present invention belongs to the field of fuel cells, and in particular relates to carbon paper and a preparation method and application thereof. Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) have the characteristics of high energy conversion efficiency, low vibration and noise, and no exhaust emissions. They are considered one of the most promising solutions to solving the energy crisis and environmental pollution in the 21st century, and have great application potential in areas such as ships, automobiles, and backup power supplies.

[0003] The membrane electrode is the core component of the proton exchange membrane fuel cell, and the gas diffusion layer is a core material for making the membrane electrode. The current process mainly uses carbon fiber to make carbon paper, which is then hydrophobic treated and coated with a gas microporous layer to form a gas diffusion layer.

[0004] Carbon paper for fuel cells primarily serves to transport reactant gases, manage generated water, and conduct electricity. Its primary characteristic is its porous structure. Graftech, a US company, has conducted research on producing fuel cell carbon paper using natural flake graphite as raw material. However, mechanical perforation is used to achieve this porous structure, resulting in low porosity and a monotonous pore structure.

[0005] Patent CN107681164A proposes a method for preparing a gas diffusion layer. The gas diffusion layer uses porous graphite paper as a substrate. The porous graphite paper is punched with holes using etching or ablation methods such as laser drilling or mechanical punching. However, this method has a complicated manufacturing process and low efficiency, and also suffers from problems such as low porosity and a single pore structure. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention aims to provide a carbon paper and its preparation method and application, so as to solve the problems of complex production process and high manufacturing cost in the prior art.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for preparing carbon paper comprises the following steps: uniformly mixing expanded polystyrene particles and vermicular graphite and pressing the mixture into a graphite block, wherein the volume ratio of the expanded polystyrene particles to the vermicular graphite is 0.2-0.8:1; heating the graphite block to 350°C±30°C to form a porous graphite block; and pressing the porous graphite block again to obtain graphite paper, and rinsing the graphite paper with hot water and then drying the graphite paper to obtain the carbon paper.

[0009] Preferably, the vermicular graphite is prepared according to the following steps:

[0010] (1) Mix 20 wt% hydrofluoric acid and natural graphite in a ratio of 1 to 1.5:1 and soak for at least 4 hours to remove inorganic salt impurities in the graphite and complete the purification process. The fixed carbon content in the purified graphite reaches 99.9 wt% or more;

[0011] (2) The graphite purified in step (1) is mixed with an intercalating agent and soaked for 4 to 12 hours. After washing and drying, the mixture is expanded at 900° C. to prepare the worm-shaped graphite; the intercalating agent is a mixture of nitric acid and hydrogen peroxide in a mass ratio of 1:2 to 5; and the mass ratio of the intercalating agent to the purified graphite is 1 to 1.5:1.

[0012] Preferably, the natural graphite is large flake graphite with a mesh size of 80 or 50.

[0013] Preferably, the particle size of the expanded polystyrene particles is ≤0.5 mm.

[0014] Preferably, the particle size of the expanded polystyrene particles is 0.1-0.3 mm.

[0015] Preferably, the thickness of the graphite block is ≤4 mm.

[0016] Preferably, the porous graphite block is pressed by vacuum molding, the graphite block is placed in a mold, and the mold is sealed and vacuumed to complete the pressing of the carbon paper.

[0017] Preferably, the thickness of the graphite paper is ≤0.3 mm.

[0018] Preferably, the graphite paper is washed with water at 90°C±5°C and then dried.

[0019] Preferably, the volume ratio of the expanded polystyrene particles to the vermicular graphite is 0.2-0.6:1.

[0020] The carbon paper is prepared by the above-mentioned method for preparing carbon paper.

[0021] Application of the above carbon paper in preparing carbon paper for fuel cells.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention currently uses natural graphite to make carbon paper, and its indicators such as porosity and pore size are comparable to those of existing carbon paper. Compared with the existing process of making carbon paper using carbon fiber, its cost is extremely low.

[0024] The mainstream carbon paper on the market is currently made of carbon fiber with a porosity of over 70%, but the manufacturing cost of carbon fiber is extremely high. Natural graphite is cheap. Geaftech, a US company, uses a mechanical puncture method to prepare carbon paper, but its porosity is less than 50%, which does not allow the gas to diffuse well into the catalyst layer. Fuel cells prepared with this type of carbon paper have poor performance. Therefore, how to prepare high porosity and a reasonable pore size structure to allow the reaction gas to diffuse more efficiently into the catalyst layer is a problem that needs to be considered. When using natural graphite to prepare carbon paper, in addition to understanding the properties of graphite materials, one should also understand the characteristics of fuel cell carbon paper and the evaluation standards of carbon paper.

[0025] (2) The use of pore-forming technology is a feasible method. The pore-forming agent is cheap and needs to have a low density like the graphite worms so that it can be mixed evenly. At the same time, graphite will oxidize and decompose at 400℃-800℃, so the pore-forming agent needs to complete most of the decomposition below 400℃. These two conditions limit the use of pore-forming agents, so polystyrene particles are selected.

[0026] (3) The focus of the present invention is to ensure that the polystyrene particles and graphite worms are evenly mixed. At the same time, in order to ensure a reasonable porosity, it is necessary to add an appropriate amount of polystyrene particles through theoretical calculation. However, too many polystyrene particles cannot be formed into a thin plate. Therefore, the graphite original plate is first made to have a certain thickness to ensure the amount of polystyrene particles added. After thermal decomposition, vacuum pressing is performed to avoid the bulging problem that occurs when pressing into a thin plate below 0.3 mm. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] Example 1

[0029] A method for preparing carbon paper comprises the following steps: 50-mesh large-scale flake graphite is mixed with hydrofluoric acid in a mass ratio of 1:1.2 and immersed for at least 4 hours to purify the purified graphite; the graphite is then intercalated with an intercalating agent (a mixture of nitric acid and hydrogen peroxide in a mass ratio of 1:3) at a ratio of 1.2:1 to the purified graphite, and the intercalation time is 4 hours. After washing and drying, the graphite is expanded at 900°C to obtain vermicular graphite. The vermicular graphite is then mixed with expanded polystyrene particles with a particle size of 0.5 mm, at a volume ratio of 0.6:1 to the expanded polystyrene particles, and the mixed vermicular graphite is pressed using a roller press to a thickness of 4 mm, with a bulk density of 0.06 mg / cm. 3After heating at 380℃ for 2h, the product was put into vacuum mold for pressing. The pressing pressure was 0.7MPa, the vacuum degree was 5000Pa, and the pressing thickness was 0.25mm. The product was then rinsed with deionized water at 90℃ to remove impurities. The final surface density was 16mg / cm 2 , the volume density is 0.6g / cm 3 , graphite carbon paper with a porosity of 73% and an average pore size of 12um.

[0030] Example 2

[0031] A method for preparing carbon paper comprises the following steps: 50-mesh large-scale flake graphite is mixed with hydrofluoric acid in a mass ratio of 1:1.2 and immersed for at least 4 hours to purify the purified graphite; the graphite is then intercalated with an intercalating agent (a mixture of nitric acid and hydrogen peroxide in a mass ratio of 1:4) at a ratio of 1.2:1 to the purified graphite, and the intercalation time is 10 hours. After washing and drying, the graphite is expanded at 900°C to obtain vermicular graphite. The vermicular graphite is then mixed with expanded polystyrene particles with a particle size of 0.3 mm, at a volume ratio of 0.4:1 to the expanded polystyrene particles. The mixed vermicular graphite is then rolled onto a roller press to form a 3 mm thick sheet with a bulk density of 0.08 mg / cm. 3 After heating at 380℃ for 2h, the product was put into vacuum mold for pressing. The pressing pressure was 0.7MPa, the vacuum degree was 4000Pa, and the pressing thickness was 0.27mm. The product was then rinsed with deionized water at 90℃ to remove impurities. The final surface density was 17mg / cm 2 , the volume density is 0.63g / cm 3 , graphite carbon paper with a porosity of 72% and an average pore size of 9um.

[0032] Example 3

[0033] A method for preparing carbon paper comprises the following steps: 50-mesh large-scale flake graphite is mixed with hydrofluoric acid in a mass ratio of 1:1.2 and immersed for at least 4 hours to purify the purified graphite; the graphite is then intercalated with an intercalating agent (a mixture of nitric acid and hydrogen peroxide in a mass ratio of 1:5) at a ratio of 1.2:1 to the purified graphite, and the intercalation time is 12 hours. After washing and drying, the graphite is expanded at 900°C to obtain vermicular graphite. The vermicular graphite is then mixed with expanded polystyrene particles with a particle size of 0.3 mm, at a volume ratio of 0.3:1 to the expanded polystyrene particles, and the mixed vermicular graphite is pressed using a roller press to a thickness of 2.5 mm and a bulk density of 0.1 mg / cm. 3After heating at 380℃ for 2h, the product was put into vacuum mold for pressing. The pressing pressure was 0.7MPa, the vacuum degree was 4000Pa, and the pressing thickness was 0.3mm. The product was then rinsed with deionized water at 90℃ to remove impurities. The final surface density was 17mg / cm 2 , the volume density is 0.64g / cm 3 , graphite carbon paper with a porosity of 71% and an average pore size of 8um.

[0034] Comparative Example 1

[0035] Referring to Example 1, the volume ratio of expanded polystyrene particles to vermicular graphite was adjusted to 1:1, and the other steps remained unchanged.

[0036] The test results show that the entire graphite original plate cannot be formed and is brittle when pressed to 4mm.

[0037] Comparative Example 2

[0038] Referring to Example 2, except that the vacuum pressing process was adjusted to normal pressing, the other steps remained unchanged. It was found that the pressed carbon paper bulged.

[0039] Comparative Example 3

[0040] Referring to Example 3, the volume ratio of expanded polystyrene particles to worm-shaped graphite was adjusted to 0.15:1, the thickness of the pressed carbon paper was adjusted to 0.25 mm, and the other steps remained unchanged.

[0041] The statistics of various properties of the carbon papers prepared in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0042] Table 1 List of properties of carbon papers prepared in Examples 1 to 3 and Comparative Examples 1 to 3

[0043]

[0044] Referring to Table 1, from Comparative Example 1, when the volume ratio of expanded polystyrene particles to vermicular graphite is too high, the initial graphite raw plate cannot be formed, resulting in the inability to carry out subsequent processes.

[0045] From Comparative Example 2, if the normal molding process is used, air is easily introduced into the carbon paper, causing the carbon paper to bulge. Air pockets are formed inside the bulging carbon paper, which is easy to break and is not conducive to gas transmission in the carbon paper use environment.

[0046] From Comparative Example 3, when the volume ratio of expanded polystyrene particles to worm-like graphite is 0.15:1, the porosity of the carbon paper is likely to decrease, affecting the gas transmission efficiency.

[0047] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing carbon paper, characterized in that: The method comprises the following steps: uniformly mixing expanded polystyrene particles and vermicular graphite and pressing the mixture into a graphite block, wherein the thickness of the graphite block is ≤4 mm and the volume ratio of the expanded polystyrene particles to the vermicular graphite is 0.2-0.8:1; heating the graphite block to 350° C.±30° C. to form a porous graphite block; pressing the porous graphite block again to obtain graphite paper, wherein the thickness of the graphite paper is ≤0.3 mm; rinsing the graphite paper with hot water and then drying the graphite paper to obtain the carbon paper; The particle size of the expanded polystyrene particles is ≤0.5 mm; The porous graphite block is pressed by vacuum molding, the graphite block is placed in a mold, and the mold is closed and vacuumed to complete the pressing of the carbon paper.

2. The method for preparing carbon paper according to claim 1, wherein: The volume ratio of the expanded polystyrene particles to the vermicular graphite is 0.2-0.6:

1.

3. The method for preparing carbon paper according to claim 1, wherein: The particle size of the expanded polystyrene particles is 0.1-0.3 mm.

4. The method for preparing carbon paper according to any one of claims 1 to 3, characterized in that: The graphite paper was washed with water at 90° C.±5° C. and then dried.

5. Carbon paper prepared by the method for preparing carbon paper according to any one of claims 1 to 4.

6. Use of the carbon paper according to claim 5 in preparing carbon paper for fuel cells.

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