阅读说明：本技术 一种导电性炭纸及其制备方法 (Conductive carbon paper and preparation method thereof ) 是由 吴刚平 刘玉婷 于 2020-05-09 设计创作，主要内容包括：本发明属于导电性材料制备方法技术领域,具体涉及一种导电性炭纸及其制备方法。本发明导电性炭纸由2～10层孔隙率为10～80％的单层碳纤维纸构成,其中最外侧一面的单层碳纤维纸的孔隙率记为A,另一面最外侧的单层碳纤维纸的孔隙率记为B,其中A、B单位为％,导电性炭纸的总厚度记为L,其中L单位为μm,三者须符合如下关系：0.2≤│A-B│/L≤0.8。本发明通过将含有分散剂、短切碳纤维、纳米碳纤维的混合物置于水中,打浆使得碳纤维和纳米碳纤维分散均匀,形成悬浮液；采用常规湿法抄纸技术将悬浮液进行制造,形成碳纤维原纸；浸渍粘结剂,并烘干,然后进行炭化,得到导电性炭纸。(The invention belongs to the technical field of preparation methods of conductive materials, and particularly relates to conductive carbon paper and a preparation method thereof. The conductive carbon paper is composed of 2-10 layers of single-layer carbon fiber paper with porosity of 10-80%, wherein the porosity of the single-layer carbon fiber paper on one outermost side is represented as A, the porosity of the single-layer carbon fiber paper on the other outermost side is represented as B, wherein A, B is unit, the total thickness of the conductive carbon paper is represented as L, wherein L is unit of mum, and the three layers meet the following relationship: L-A-B/L is not less than 0.2 and not more than 0.8. The method comprises the steps of putting a mixture containing a dispersing agent, chopped carbon fibers and nano carbon fibers into water, and pulping to uniformly disperse the carbon fibers and the nano carbon fibers to form a suspension; manufacturing the suspension by adopting a conventional wet papermaking technology to form carbon fiber base paper; and (3) impregnating the binder, drying, and carbonizing to obtain the conductive carbon paper.)

1. An electrically conductive carbon paper characterized by: the conductive carbon paper is composed of 2-10 layers of single-layer carbon fiber paper with porosity of 10-80%, wherein the porosity of the single-layer carbon fiber paper on one outermost side is recorded as A, the porosity of the single-layer carbon fiber paper on the other outermost side is recorded as B, the unit of A, B is% and the total thickness of the conductive carbon paper is recorded as L, the unit of L is mum, and the three layers meet the following relationship: L-A-B/L is not less than 0.2 and not more than 0.8.

2. The conductive carbon paper as set forth in claim 1, wherein: the conductive carbon paper is asymmetric porous carbon paper, one side of the conductive carbon paper with high porosity is used for contacting with the bipolar plate, the other side of the conductive carbon paper with low porosity is used for contacting with the catalyst layer, and the surface of the conductive carbon paper is provided with a microporous layer; the carbon papers are arranged in sequence from small porosity to large porosity or from large porosity to small porosity.

3. A preparation method of conductive carbon paper is characterized by comprising the following steps: the method comprises the following steps:

step 1, placing a mixture containing a dispersing agent, chopped carbon fibers and nano carbon fibers into water, and pulping to uniformly disperse the chopped carbon fibers and the nano carbon fibers to form a suspension;

step 2, preparing the suspension by adopting a conventional wet papermaking technology to form carbon fiber base paper;

step 3, impregnating the carbon fiber base paper with a binder, and drying;

and 4, carbonizing the carbon fiber base paper which is impregnated with the binder, dried and hot-pressed to obtain the conductive carbon paper.

4. The method for preparing conductive carbon paper according to claim 3, wherein the method comprises the following steps: the diameter of the short-cut carbon fiber in the step 1 is 2-15 mu m, and the length is 1-30 mm.

5. The method for preparing conductive carbon paper according to claim 3, wherein the method comprises the following steps: the diameter of the carbon nanofiber in the step 1 is 20 nm-200 nm, and the length of the carbon nanofiber is 0.5 mu m-500 mu m.

6. The method for preparing conductive carbon paper according to claim 3, wherein the method comprises the following steps: the dispersing agent in the step 1 is as follows: sodium dodecyl benzene sulfonate, sodium acyl isethionate, polyphosphate, sodium polyacrylate, N-alkyltrimethylammonium chloride, polyoxyethylene amine, polyethyleneimine, polyoxyethylene alkylphenol, polyoxyethylene ester, polyvinyl alcohol, polyethylene glycol, glycerol, polyoxyethylene, polyacrylamide, aliphatic polyoxyethylene ether, carboxymethyl cellulose, N-alkyl betaine, N-alkyl amino acid, imidazoline carboxylate, or a mixture of two or more thereof in any proportion.

7. The method for preparing conductive carbon paper according to claim 3, wherein the method comprises the following steps: the amount of the dispersing agent in the step 1 is 0.01-2 wt% of the amount of water, the chopped carbon fibers and the nano carbon fibers are mixed in any proportion, and the sum of the amounts of the chopped carbon fibers and the nano carbon fibers is 0.01-0.5 wt% of the amount of water.

8. The method for manufacturing conductive carbon paper according to claim 3, wherein: in the step 3, the binder is a solution of one or a mixture of more than two of phenolic resin, polyacrylonitrile resin with the hydrolysis degree of 10-90%, chitosan, furan resin, melamine, asphalt and benzoxazine resin in any proportion, and the solvent of the solution is water, methanol or ethanol.

9. The method for manufacturing conductive carbon paper according to claim 3, wherein: the concentration of the binder in the step 3 is 1-100 g/L.

10. The method for manufacturing conductive carbon paper according to claim 3, wherein: the drying temperature in the step 3 is 120 ℃, and the drying time is 10 min; the hot pressing temperature of the hot pressing in the step 4 is 120-200 ℃, and the hot pressing pressure is 0.5-5 Mpa; the carbonization temperature of the carbonization in the step 4 is 1400-2200 ℃, and the carbonization time is 5 s-20 min.

Technical Field

The invention belongs to the technical field of preparation methods of conductive materials, and particularly relates to conductive carbon paper and a preparation method thereof.

Background

The gas diffusion layer of the pem hydrogen fuel cell needs to have the functions of current collection, gas transmission, gas flow distribution, etc. Accordingly, the carbon fiber paper layer material constituting the gas diffusion layer is required to have performance such as high electrical conductivity, high gas diffusion property, and high gas distribution property at the same time.

As a carbon paper for a gas diffusion layer of a proton exchange membrane fuel cell, japanese patent laid-open No. 6-20710 discloses a carbon fiber paper material having a porous structure formed by randomly dispersing chopped carbon fibers to form a carbon fiber paper and then binding the carbon fiber paper with a carbon material. However, it is difficult for the carbon fiber paper material to significantly exhibit the ability to distribute airflow.

On the other hand, carbon paper for a gas diffusion layer of a proton exchange membrane fuel cell has one surface bonded to a bipolar plate having a gas transmission flow path and the other surface bonded to a catalyst layer. Therefore, as the conductive substrate of the fuel cell gas diffusion layer, in addition to the above-described required conductivity, gas permeability, gas distribution property, and the like, good bondability to the catalyst layer is required. However, in the conventional electrode substrate, in order to improve the gas transport performance, the porosity of the carbon paper is increased, so that the surface of the carbon paper becomes rough and the bonding with the catalyst layer is poor.

Disclosure of Invention

The invention provides conductive carbon paper and a preparation method thereof aiming at the problems.

In order to achieve the purpose, the invention adopts the following technical scheme:

the conductive carbon paper is composed of 2-10 layers of single-layer carbon fiber paper with the porosity of 10-80%, wherein the porosity of the single-layer carbon fiber paper on one outermost side is represented as A, the porosity of the single-layer carbon fiber paper on the other outermost side is represented as B, wherein A, B is unit, the total thickness of the conductive carbon paper is represented as L, wherein L is unit of mum, and the three layers meet the following relationship: L-A-B/L is not less than 0.2 and not more than 0.8. When the-A-B/L is more than 0.8, the flatness of at least one side of the carbon paper is reduced due to excessive difference of porosity of the two sides of the carbon paper; when the-A-B/L is less than 0.2, the difference in porosity between the two sides of the carbon paper is too small to perform the function of gradient distribution of the gas flow.

Further, the conductive carbon paper is asymmetric porous structure carbon paper, one side of the conductive carbon paper with high porosity is used for contacting with the bipolar plate, the other side of the conductive carbon paper with low porosity is used for contacting with the catalyst layer, and a microporous layer is arranged on the surface of the conductive carbon paper; the carbon papers are arranged in sequence from small porosity to large porosity or from large porosity to small porosity. When in use, the side with the largest porosity is contacted with the bipolar plate, so that the gradual and uniform distribution of the airflow is ensured in the process of transition from big holes to small holes; the side with the smallest porosity is contacted with the catalyst layer to ensure that the catalyst layer is tightly combined. If the porosity is not arranged from large to small or from small to large, the gas flow will be disturbed.

Still further, the microporous layer is a mixture of polytetrafluoroethylene and carbon particles. The polytetrafluoroethylene enhances the overall hydrophobicity of the microporous layer, and is beneficial to discharging water generated by reaction; and the addition of the carbon particles improves the conductivity of the microporous layer, which is beneficial to electron transmission.

A preparation method of conductive carbon paper comprises the following steps:

step 1, placing a mixture containing a dispersing agent, chopped carbon fibers and nano carbon fibers into water, and pulping to uniformly disperse the chopped carbon fibers and the nano carbon fibers to form a suspension;

step 2, preparing the suspension by adopting a conventional wet papermaking technology to form carbon fiber base paper;

step 3, impregnating the carbon fiber base paper with a binder, and drying;

and 4, drying the impregnated binder and carbonizing the hot-pressed carbon fiber base paper to obtain the conductive carbon paper.

Further, the diameter of the chopped carbon fiber in the step 1 is 2-15 μm, and the length is 1-30 mm. If the diameter of the chopped carbon fiber is less than 2 μm, the process is complicated, and the production cost is increased; if the diameter of the chopped carbon fiber is larger than 15 μm, stable production will be difficult. If the length of the chopped carbon fibers is less than 1mm, it will cause an increase in the cost of the shredding process, while if the length of the chopped carbon fibers exceeds 30mm, it will cause difficulty in uniform dispersion of the chopped carbon fibers.

Further, the diameter of the carbon nanofiber in the step 1 is 20 nm-200 nm, and the length of the carbon nanofiber is 0.5 μm-500 μm. If the diameter of the carbon nanofibers is less than 20nm, the material loss in the papermaking process is serious; such as the diameter of the filamentous nanocarbon exceeding 200nm, will cause the production cost to be excessively high. If the length of the carbon nanofibers is less than 0.5 μm, the material loss in the papermaking process is serious; if the length of the carbon nanofibers exceeds 500 μm, dispersion during papermaking becomes difficult.

Further, the dispersing agent in the step 1 is: the paper is prepared from one or a mixture of more than two of sodium dodecyl benzene sulfonate, sodium acyl isethionate, polyphosphate, sodium polyacrylate, N-alkyl trimethyl ammonium chloride, polyoxyethylene amine, polyethyleneimine, polyoxyethylene alkylphenol, polyoxyethylene ester, polyvinyl alcohol, glycerol, polyoxyethylene, polyacrylamide, aliphatic polyoxyethylene ether, carboxymethyl cellulose, N-alkyl betaine, N-alkyl amino acid and imidazoline carboxylate in any proportion, and mainly has the function of uniformly dispersing short carbon fibers so that carbon fiber paper with uniform thickness can be prepared by a wet papermaking process.

Further, the using amount of the dispersing agent in the step 1 is 0.01-2 wt% of the using amount of water. The use amount of the dispersant exceeds the use amount of water by 2 wt%, so that the dispersant is excessively used, and the cost is increased; if the amount of the dispersant is 0.01% of the amount of water, the effect of the dispersant is not significant and the carbon fibers cannot be effectively dispersed.

Further, in the step 1, the chopped carbon fibers and the nano carbon fibers are mixed in any proportion, and the sum of the usage of the chopped carbon fibers and the nano carbon fibers is 0.01-0.5 wt% of the usage of water. If the sum of the amounts of the chopped carbon fibers and the nano carbon fibers exceeds 0.5 wt% of the amount of water, the chopped carbon fibers and the nano carbon fibers are difficult to be effectively dispersed; if the sum of the usage of the short carbon fiber and the nano carbon fiber is less than 0.01 wt% of the usage of water, the operation cost of paper making is obviously increased.

Further, in the step 3, the binder is a solution of one or a mixture of more than two of phenolic resin, polyacrylonitrile resin with a hydrolysis degree of 10-90%, chitosan, furan resin, melamine, asphalt and benzoxazine resin in any proportion, and the solvent of the solution is water, methanol or ethanol. The adhesive is selected to play a role in adhering adjacent short carbon fibers on one hand, and on the other hand, the resin is converted into a carbon structure in the later carbonization process, so that the conductivity of the carbon fiber paper is improved.

Further, the concentration of the binder in the step 3 is 1-100 g/L. If the concentration of the binder exceeds 100g/L, the hollow pore structure of the carbon fiber paper is blocked; if less than 1g/L, it does not function to effectively bind the short carbon fibers.

Further, the drying temperature in the step 3 is 120 ℃, and the drying time is 10 min; the hot pressing temperature of the step 4 is 120-200 ℃, and the pressure is 0.5-5 Mpa; the highest carbonization temperature of carbonization in the step 4 is 1400-2200 ℃, and the carbonization time is 5 s-20 min. If the highest carbonization temperature exceeds 2200 ℃, the energy is wasted and the cost is increased, and if the highest carbonization temperature is lower than 1400 ℃, the carbonization is insufficient, and the binder resin can not be fully converted into a carbon structure; if the carbonization time exceeds 20min, the production efficiency is lowered, and if it is less than 5s, the binder resin cannot be effectively carbonized.

An application of conductive carbon paper is applied to an electrode substrate of a proton exchange membrane hydrogen fuel gas diffusion layer. The carbon paper can be used as an electrode material of the gas diffusion layer after being subjected to hydrophobic modification and provided with the microporous layer, so that the carbon paper is an electrode substrate of the gas diffusion layer.

Compared with the prior art, the invention has the following advantages:

the invention meets the requirements of high conductivity, high gas diffusivity and high gas flow distribution as the gas diffusion layer material in the hydrogen fuel cell on one hand, and meets the requirement of good combination with the catalyst layer on the other hand.

The porosity of the traditional carbon paper is basically the same, if the porosity is too low, the gas transmitted from the gas flow path of the bipolar plate is difficult to effectively enter the carbon paper, and the side leakage risk exists; if the porosity is too high, the surface flatness of the carbon paper is integrally reduced, the carbon paper and the catalyst layer are not tightly combined, the possibility of gas side leakage exists, the uniform distribution of gas flow is not favorable for the catalyst layer, and the effective transmission of electrons generated by reaction is not favorable. The material structure of the invention can ensure that the surface with high porosity of the carbon paper is contacted with the bipolar plate, can ensure that gas is effectively transmitted into the carbon paper, and reduces the inlet pressure of the gas; on the other side, the carbon paper has low porosity and high surface flatness, so that the carbon paper can be fully contacted with the catalyst layer, airflow is uniformly distributed to the catalyst layer, and electrons generated by reaction are effectively transmitted.

Detailed Description

[ method for measuring hydrolysis degree of Polyacrylonitrile ]

The hydrolysis Degree (DH) of polyacrylonitrile can be determined by using the change of nitrogen content before and after hydrolysis of polyacrylonitrile, and N is set₀Nitrogen content of polyacrylonitrile before hydrolysis, N_tIs the nitrogen content of hydrolyzed polyacrylonitrile, the hydrolysis degree DH of polyacrylonitrile can be calculated by the following formula:

wherein the change of the nitrogen content is obtained by an element analysis method.