CN112982023B

CN112982023B - High-strength thin carbon paper and preparation method thereof

Info

Publication number: CN112982023B
Application number: CN202110180825.6A
Authority: CN
Inventors: 汤秀秀; 宋佃凤; 郁国强; 何冬梅; 刘娜; 吴立群
Original assignee: Shandong Renfeng Speical Materials Co ltd
Current assignee: Shandong Renfeng Speical Materials Co ltd
Priority date: 2021-02-08
Filing date: 2021-02-08
Publication date: 2022-09-02
Anticipated expiration: 2041-02-08
Also published as: CN112982023A

Abstract

The application discloses a preparation method of high-strength thinned carbon paper, which comprises the steps of firstly preparing high-dispersity carbon fiber powder, and then preparing raw paper of the carbon paper by adopting a wet papermaking process; dipping and coating resin/carbon fiber powder mixed solution; then, coating a carbon fiber powder layer on the base material foam; subsequently, carrying out hot-pressing curing treatment on the base material; and finally, obtaining a carbon paper product through carbonization and graphitization treatment, wherein the carbon paper material has good air permeability and mechanical properties.

Description

High-strength thin carbon paper and preparation method thereof

Technical Field

The invention relates to novel carbon fiber paper for a hydrogen fuel cell, in particular to high-strength thin carbon paper for a proton exchange membrane fuel cell modified by carbon fiber powder and a preparation method thereof, belonging to the technical field of hydrogen fuel cell materials.

Background

As a high-efficiency and environment-friendly power generation device, a Proton Exchange Membrane Fuel Cell (PEMFC) has the advantages of high power density, high energy conversion efficiency, quick low-temperature start, no pollution and the like, and has wide application prospects. In a proton exchange membrane fuel cell, a Membrane Electrode Assembly (MEA), which is the most important component of a PEMFC, is mainly composed of a proton exchange membrane, a Catalyst Layer (CL), and a Gas Diffusion Layer (GDL), and its characteristics directly affect the performance of the PEMFC. The GDL plays an important role in the three-in-one assembly of the MEA, and plays a role in mechanical support on one hand and has key characteristics (water-electricity-gas-heat transfer) such as reaction gas diffusion, product water diffusion transmission, electric conduction and heat conduction on the other hand in the running process of the PEMFC.

The GDL is composed of two parts, a support layer and a microporous layer (MPL), wherein the MPL is supported on the support layer. The support layer is generally made of carbon fiber paper as a base material, and the carbon paper is a porous paper-like section formed by bonding uniformly dispersed carbon fibers together (by using a carbonizable binder). The carbon paper is used as a supporting layer material of the gas diffusion layer, not only plays a role in supporting the catalyst layer and stabilizing the electrode structure, but also can provide a gas channel, an electronic channel and a drainage channel for electrode reaction, and is one of key components influencing the performance of the membrane electrode.

The carbon paper used for the membrane electrode material of the fuel cell is required to have the following properties: 1) uniform porous structure and excellent air permeability; 2) the resistivity is low, and the conductivity is good; 3) the structure is compact and the surface is smooth so as to reduce the contact resistance and improve the conductivity; 4) the membrane has certain mechanical strength and toughness so as to be beneficial to the manufacture of a membrane electrode; 5) has chemical stability and thermal stability; 6) corrosion resistance; 7) high thermal conductivity. Currently, carbon paper is developing towards thinning, high stability and high reliability, including mastering of key technologies and improvement of conductivity, air permeability, strength, toughness and the like. The hydrogen fuel cell is turned from a commercial vehicle to a passenger vehicle, the volume of the galvanic pile is required to be reduced, and the carbon paper thickness is required to be reduced due to the improvement of the volume density. The development of a batch preparation technology with thinness, high reliability, high stability, long service life and low cost is a future development trend of the carbon paper.

The mechanical strength of the carbon paper is mainly dependent on the binding action of the resin among the carbon fibers, and is not greatly related to the strength and modulus of the carbon fibers. The process mainly occurs in the hot-pressing solidification link, the resin can be converted into a cross-linked net-shaped (or body-shaped) structure from linear (branch) molecules under proper hot-pressing solidification conditions, the density of a matrix is increased, the carbon fiber and the resin are tightly combined, and the strength of a carbon paper matrix is increased. The thinning of the carbon paper requires a reduction in the basis weight and thickness of the raw carbon paper, and the amount of resin used is limited, which inevitably results in a reduction in the mechanical strength of the carbon paper. Therefore, the carbon paper needs to be optimally designed, and the mechanical strength, the resistivity and the air permeability are ensured to meet the requirements of users while the carbon paper is low in thickness.

CN107127907A provides a preparation process of high-performance ultrathin carbon fiber paper, which comprises the steps of impregnating a carbon fiber blank in resin, carrying out die pressing solidification, then impregnating, carrying out die pressing solidification, repeatedly carrying out multiple times of impregnation-die pressing solidification, and carrying out heat treatment to obtain the ultrathin carbon fiber paper. The preparation process is repeated impregnation-die pressing solidification, in the last two impregnation-die pressing solidification processes, the resin solidified at the previous time can prevent the molten resin from flowing up and down, the actual solidification pressure of the resin is increased, the pores between the resin and the carbon fibers are reduced, the resin solidified at the previous time is subjected to post-solidification treatment, the strength of matrix carbon of the carbon fiber paper is improved, the interface combination between the carbon fibers and the matrix carbon is enhanced, the ultrathin carbon fiber paper can be produced in a large area and in batch, the operation is simple, and the ultrathin carbon fiber paper with the requirements on electric conductivity, mechanical property and air permeability can be prepared. However, the preparation of the ultrathin carbon fiber paper needs repeated impregnation-mould pressing solidification, so that the process is more, the energy consumption is higher, the production cost can be increased, and the large-scale industrial production of the carbon fiber paper is not facilitated. In addition, in the two last impregnation-die pressing curing processes, the effect of increasing the actual curing pressure of the resin on the cured carbon paper substrate is not as obvious as before, the influence on the resistivity is smaller, the phenolic resin is basically cured at the moment, the lap joint between the resin and the carbon fiber is formed, the hot pressing only plays a role in modifying the substrate such as the flatness, and the effect of the preparation method on improving the mechanical property of the carbon fiber paper substrate is not obvious.

CN 107012739A relates to an ultrathin carbon fiber paper modified by a conductive polymer film and a preparation method thereof, and mainly adopts an electrochemical deposition method to deposit the conductive polymer film in the high-flux unmodified ultrathin carbon fiber paper to prepare the conductive polymer film modified ultrathin carbon fiber paper. The conductive polymer film is coated on the carbon fiber and the matrix carbon-carbon fiber nodes to form a film network with uniform thickness in the carbon paper. The preparation method is simple, and the prepared conductive polymer film can obviously improve the mechanical property of the ultrathin carbon fiber paper and enable the ultrathin carbon fiber paper to have higher air permeability.

However, the patent adopts an electrochemical deposition method to deposit a conductive polymer film inside the ultrathin carbon fiber paper to prepare the conductive polymer film modified ultrathin carbon fiber paper. It is difficult to prepare a thin film material of an ideal and complicated composition by the electrodeposition method, the thickness variation is large due to the difference in polymerization current, and it is difficult to control the generation and growth rate of crystal nuclei on the surface of the substrate. The polythiophene film can increase the conductive channel between the carbon fiber and improve the conductivity of the carbon paper. However, the conductivity of the polythiophene film decreases with the increase in thickness, and when the thickness of the polythiophene film is increased to a certain range, the sheet resistivity of the carbon paper produced tends to increase, and the air permeability is also affected to a certain extent. In addition, the polythiophene film can form a three-dimensional network in the carbon paper, so that the rigidity of the carbon fiber paper is increased, the toughness of the carbon fiber paper is reduced, and the carbon fiber paper is not beneficial to continuous production of the carbon paper and processing and assembling of downstream users.

Disclosure of Invention

At present, the hydrogen fuel cell is turned from a commercial vehicle to a passenger vehicle, the volume of a galvanic pile is required to be reduced, and the thickness of carbon paper is required to be reduced due to the improvement of the volume density. The carbon paper mainly plays a role in supporting the microporous layer and the catalyst layer, the thickness of the carbon paper is reduced due to the thinning of the carbon paper, the mechanical property of the carbon paper is reduced, the processing and the assembly of a membrane electrode of a downstream user are not facilitated, and the service life of a fuel cell is indirectly influenced.

The existing thin carbon paper has few preparation technologies, is mostly in the research stage of colleges and universities, and has a certain distance from industrialization. In the prior art, the process is complicated, the operation cost and the labor cost are high, the energy consumption is high, and the continuous large-scale production of the carbon paper is not facilitated.

The existing thin carbon paper preparation technology improves the mechanical strength of the carbon paper, but other properties such as conductivity, air permeability and the like are adversely affected, and the water-electricity-gas-heat transmission of the product is not facilitated.

In order to solve the technical problems, the thin carbon paper capable of being continuously produced in large scale is provided, so that the mechanical property of the thin carbon paper meets the requirements of users, namely, the thin carbon paper has certain mechanical strength and toughness, and the technical parameters such as conductivity and air permeability are not lost.

Specifically, the present application provides a novel carbon fiber powder dispersion technique.

The carbon fiber powder can be polyacrylonitrile-based carbon fiber powder, pitch-based carbon fiber powder, viscose-based carbon fiber powder or phenolic-based carbon fiber powder and the like.

The preparation technology of the carbon fiber powder comprises the steps of firstly mixing sizing agent-free treated chopped carbon fibers with fluorine-containing polymers, then sintering at low temperature (200-.

The fluorine-containing polymer is selected from aqueous polytetrafluoroethylene, polyvinylidene fluoride, polychlorotrifluoroethylene and the like, and aqueous polytetrafluoroethylene emulsion is preferred.

The carbon fiber powder retains the excellent properties of the carbon fiber, has fine shape, pure surface and large specific surface area, and is easier to be wetted, uniformly dispersed, adsorbed and compounded by the resin material. The carbon fiber powder is filled in the resin, so that the tensile strength and toughness of the base material can be improved, and the brittleness of the resin can be weakened.

The surfactant in the PTFE emulsion is removed by primary low-temperature sintering, the bonding effect of PTFE is really exerted, the carbon fibers are tightly wrapped together, and the mixture is conveniently ground into carbon fiber powder; and finally, high-temperature treatment can decompose the PTFE and remove the PTFE and impurities.

The carbon fiber powder dispersing technology is used for ensuring the uniformity of the distribution of the carbon fiber powder in the thermosetting resin or on the surface of the base material, and has the functions of regulating the size and the distribution of a pore structure and enhancing and toughening the base material.

The application also provides high-strength thin carbon paper and a preparation method thereof, the preparation method comprises the steps of firstly preparing carbon fiber powder dispersion liquid, adding a foam coating device in the resin impregnation coating process, namely after the carbon paper base paper is impregnated and coated with resin, respectively coating a layer of carbon fiber powder dispersion liquid on the upper surface and the lower surface of a base material in a foam manner, wherein the thickness of the carbon fiber powder dispersion liquid is about 10-20 mu m, then carrying out drying treatment to obtain a carbon paper intermediate base material, and then carrying out hot-pressing curing, carbonization and graphitization to obtain a carbon paper product.

Specifically, the application provides high-strength thin carbon paper and a preparation method thereof, and the main process steps are as follows:

(1) preparation of carbon fiber powder

Firstly, mixing chopped carbon fiber without sizing agent treatment with fluoropolymer, then removing surfactant in the fluoropolymer through low-temperature sintering (200-. The fluorine-containing polymer can be aqueous polytetrafluoroethylene emulsion, polyvinylidene fluoride solution, polychlorotrifluoroethylene solution and the like, and the aqueous polytetrafluoroethylene emulsion is preferred.

The carbon fiber is used in an amount of 0.2 to 5 parts by weight, the fluorine-containing polymer is used in an amount of 0.5 to 10 parts by weight, and more preferably, the mass ratio of the carbon fiber to the fluorine-containing polymer is 1: 1.5-3.

When the content of the fluorine-containing polymer is too small, the bonding property is poor, and when the addition amount is too small, the carbon fibers are difficult to be completely wrapped together, so that the grinding and chopping at the later stage are difficult, and the uniform particle size of the carbon fiber powder is difficult to ensure. If the content is too much, the particle size distribution of the carbon fiber can be influenced, the particle size of the carbon fiber is not uniform, the dispersibility of the carbon fiber in resin and the thickness uniformity and the pore size distribution of a carbon fiber powder layer at the later stage are influenced, meanwhile, the utilization rate of the carbon fiber powder can be reduced, and the production and manufacturing cost is increased.

(2) Preparation of raw paper of carbon paper

The raw materials of the chopped carbon fiber, the binder and the dispersant are made into the raw carbon paper by a wet papermaking process, and the quantitative amount of the raw carbon paper is 10-30g/m ² The thickness is 50-150 μm.

(3) Dip coating of thermosetting resins

Preparing mixed liquid containing resin-carbon fiber powder, wherein the solid content is 10-60%. Soaking the carbon paper base paper in the mixed solution for 1-10min, taking out, and heating at 50-100 ℃ to make the paper in a semi-drying state.

The mixed solution containing resin and carbon fiber powder consists of resin, carbon fiber powder, surfactant and alcohol solvent.

The resin is liquid alcohol-soluble thermosetting resin and can be one or more of phenolic resin, epoxy resin and furan resin, the solid content is 60%, and the addition amount is 20-60% of the total amount.

The carbon fiber powder is the material prepared in the step (1), and the adding amount of the carbon fiber powder is 1-10% of the total amount.

Moreover, the thermosetting resin: the mass ratio of the carbon fiber powder is 3-9: 1.

the conductivity of the system can be influenced by the excessive addition of the resin, because the carbon residue rate of the resin is basically fixed, the content of the resin is increased, the reduction degree of the resistivity of the resin is not as obvious as the effect of reducing the resistance of carbon fiber, and the final conductivity of the system is influenced; too little resin will affect the dispersion effect of the carbon fiber and deteriorate the uniformity of the pore size distribution.

The alcohol solvent ethanol and methanol can be used, and the addition amount is 30-70% of the total amount.

The surfactant is selected from anionic surfactants, and specifically can be one or more of alkyl ether lactose type positive and negative ion fluorocarbon surfactants, perfluoroalkyl ether alkylol amine salt type anionic fluorocarbon surfactants, perfluoroalkyl ether quaternary ammonium salt cationic surfactants and perfluoroalkyl ether carboxylic acid potassium anionic surfactants.

Further, an alkyl ether lactose type positive/negative ion fluorocarbon surfactant (FC-16) is preferable, mainly because the surfactant in which a hydrocarbon chain and a fluorocarbon chain are hybridized (a linking group connects one end to the other end and has a hydrocarbon chain structure and one end to the other end has a fluorocarbon chain structure) has the characteristics of both (hydrocarbon surfactant and fluorocarbon surfactant) surfactants. The two have good synergistic effect, can form a double-layer film in aqueous solution, and can spontaneously form small bubbles. The fluorocarbon surfactant has a special structure and high surface activity, and can greatly reduce the surface tension of the liquid, the super-strong dispersing ability and the viscosity reduction. The addition amount of the surfactant is 0.1-2% of the total mass.

(4) Foam coated carbon fiber powder layer

And (3) coating a layer of carbon fiber powder foam slurry on the upper surface and the lower surface of the base material obtained in the step (3) respectively by using a foam slurry distribution device, wherein the thickness of the carbon fiber powder foam slurry is about 10-20 mu m, and then carrying out drying treatment (50-100 ℃) to obtain the carbon paper intermediate base material.

The carbon fiber powder foam slurry is composed of carbon fiber powder, a surfactant, a dispersing agent, a foaming agent and water, and the concentration (solid content) of the foam slurry is 1-10%.

Wherein, the amount of the carbon fiber powder is 5 to 15 weight parts, the amount of the surface active agent is 0.5 to 3 weight parts, the amount of the dispersing agent is 0.5 to 3 weight parts, the amount of the foaming agent is 1 to 5 weight parts, and the amount of the water is 80 to 90 weight parts.

Preferably, the mass ratio of the raw materials is carbon fiber powder: surfactant (B): dispersing agent: foaming agent: 5-15 parts of water: 0.5-3: 0.5-3: 2: 80-90.

The carbon fiber powder and the surfactant are as described in the step (3); the dispersant can be a cellulose ether thickening agent, and specifically can be one or more of sodium carboxymethylcellulose, methylcellulose, hydroxypropyl methylcellulose and hydroxyethyl cellulose; the foaming agent is sulfonyl hydrazine foaming agents such as ammonium bicarbonate, sodium bicarbonate, azo foaming agents, benzene sulfonyl hydrazide and the like; the water may be tap water, preferably deionized water.

(5) Hot-pressing solidification of carbon paper

Heating and pressurizing the carbon paper intermediate base material by a flat plate hot press or a flat plate vulcanizing machine, wherein the hot pressing temperature is 100-; the hot pressing pressure is 1-10MPa, preferably 3-6MPa, and the hot pressing time is 1-10min, preferably 3-8 min.

(6) Carbonization and graphitization of carbon paper

And (3) carbonizing and graphitizing the base material obtained in the step (5) in a graphite furnace under the protection of inert gas (nitrogen or argon). The carbonization temperature is 800-; the graphitization temperature is 2000-2800 ℃, and the heat preservation time is 0.5-2.0 h.

The high-strength thin carbon paper is prepared by adopting the carbon paper preparation process of the technical scheme, and the quantitative content of the carbon paper is 40-60g/m ² The thickness is 100-150 μm.

The beneficial effects of the invention include:

since the carbon fiber powder sold in the market is easy to agglomerate and difficult to disperse uniformly when added into the resin, the thickness uniformity and the mechanical property of the carbon paper are adversely affected. The carbon fiber powder is prepared by adopting the special process, and the preparation method is simple and easy to implement. Firstly, removing a surfactant in the fluorine resin through high-temperature sintering so as to enable the resin to fully exert a bonding effect, fixing and binding carbon fibers together by virtue of the bonding effect of the fluorine resin, and then grinding or ball-milling the carbon fibers into powdery fine particles by virtue of a mechanical physical effect; the second high-temperature sintering is to remove the fluorine resin, decompose and remove the fluorine resin, and finally obtain the carbon fiber powder, wherein the obtained carbon fiber powder has relatively uniform granularity, retains the original excellent properties of the carbon fiber, and is easy to be wetted by resin materials, uniformly dispersed and adsorbed.

The carbon fiber powder is filled in the resin, so that the tensile strength and toughness of the base material can be improved, the brittleness of the resin is weakened due to the existence of the carbon fiber powder, the resin is subjected to stress relaxation, and the stress loss of a fracture point of the resin is buffered; meanwhile, the carbon fiber powder has excellent conductivity, and a uniform conductive network is formed in the matrix, so that the conductivity of the carbon paper substrate is effectively improved, and the electrode performance is optimized and improved.

The surface of the base material coated with the resin is coated with a layer of carbon fiber powder by adopting a foam coating process, the carbon fiber powder layer is of a small and dense porous structure, the pore diameter of the base material is modified, the air permeability of the base material is not influenced, the pore diameter distribution is narrower and relatively uniform, and the porosity is higher.

The existence of the carbon fiber powder layer and the mixing of the carbon fibers into the resin improve the mechanical strength of the carbon paper base material, and the base material has good air permeability, excellent conductivity, high porosity and concentrated pore size distribution.

The experimental result shows that the thickness of the prepared carbon paper is in the range of 100-150 mu m, the carbon paper meets the requirements of the current hydrogen fuel cell market, and the carbon paper has excellent mechanical property, uniform pore size distribution, large air permeability and high electrical conductivity. Wherein the tensile strength can reach 20.8MPa, the bending strength reaches 25.2MPa, and the bending modulus reaches 18.1 GPa; the porosity is 82.1%, the pore size distribution is relatively concentrated, the pore size distribution range is 20-23 mu m, the air permeability is large (8.15s/100cc), the resistivity is low (the resistivity in the plane direction is 4.3m omega cm), the thermal conductivity is high (2.125W (m K)), the water-electricity-gas-heat transmission is ensured, meanwhile, the ohmic loss is reduced, and the electrode performance is improved.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the application and together with the description serve to explain the principles of the application.

FIG. 1 is a process flow diagram of a high strength thin carbon paper

FIG. 2 is a microscopic image of the carbon fiber powder prepared in example 1

Detailed Description

The present application will be described in further detail with reference to the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are for purposes of illustration only and are not to be construed as limitations of the present application. It should be noted that, for convenience of description, only the portions related to the present application are shown in the drawings.

In addition, the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present disclosure will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.

Example 1

(1) Preparation of carbon fiber powder

Firstly, mixing pulp-free chopped polyacrylonitrile-based carbon fibers with aqueous polytetrafluoroethylene emulsion (solid content is 20%), wherein the mass ratio of the carbon fibers to the polytetrafluoroethylene resin is 2: 3, sintering at 350 ℃ for 30min, ball milling at high speed to grind the mixture, and sintering at 500 ℃ for 30min to obtain the carbon fiber powder filler.

(2) Preparation of raw paper of carbon paper

Mixing the short-cut polyacrylonitrile-based carbon fiber, the binder and the dispersant raw materials, and preparing the carbon paper base paper by wet papermaking with the quantitative of 25 +/-5 g/m ² 。

(3) Dip coating of thermosetting resins

Preparing a thermosetting resin-carbon fiber powder mixed solution with the solid content of 40 percent, wherein the thermosetting resin: carbon fiber powder: alcohol: the surfactant is 35: 5: 59: 1, after the resin is weighed, adding methanol and uniformly stirring, adding carbon fiber powder while stirring, adding alkyl ether lactose type positive and negative ion fluorocarbon surfactant, then adjusting the speed of an ultrasonic dispersion device, and slowing at first and then speeding at a high speed until the carbon fiber powder is uniformly dispersed in a resin matrix. And (3) finally, placing the base paper of the carbon paper obtained in the step (2) in a thermosetting resin-carbon fiber powder mixed solution for dipping treatment for 5min, taking out the base material, and heating at 60 ℃ to enable the base material to be in a semi-dried state.

(4) Foam coated carbon fiber powder layer

Preparing carbon fiber powder foam slurry, wherein the concentration of the foam slurry is 8%, and the polyacrylonitrile-based carbon fiber powder: alkyl ether lactose type positive and negative ion fluorocarbon surfactant: sodium carboxymethylcellulose: azodiisobutyronitrile foaming agent: the deionized water is 8: 1: 1: 2: 88. and (4) coating a layer of carbon fiber powder slurry on the upper surface and the lower surface of the base material obtained in the step (3) by using a foam slurry distribution device in a foam manner, wherein the thickness of the carbon fiber powder slurry is 10 micrometers, and then drying at 80 ℃ to obtain the carbon paper intermediate base material.

(5) Hot-pressing solidification of carbon paper

Setting the temperature of a vulcanizing press to 160 ℃, putting the carbon paper intermediate base material in the step (4) when the standby device reaches the set temperature, preserving the heat for 5min under the pressure of 4MPa, and then demoulding and taking out the base material.

(6) Carbonization and graphitization of carbon paper

Carbonizing and graphitizing the base material prepared in the step (5) in a graphite furnace, wherein the inert gas is argon, the carbonization temperature is 1000 ℃, and the heat preservation time is 1.0 h; the graphitization temperature is 2500 ℃, and the heat preservation time is 1.0 h. The performance parameters of the final carbon paper product are shown in table 1.

Example 2

(1) Preparation of carbon fiber powder

Firstly, mixing pulp-free chopped polyacrylonitrile-based carbon fibers with aqueous polytetrafluoroethylene emulsion, wherein the mass ratio of the carbon fibers to the polytetrafluoroethylene resin is 3: 7, sintering at 350 ℃ for 30min, grinding the mixture at high speed, and sintering at 500 ℃ for 30min to obtain the carbon fiber powder filler.

The other steps are the same as in example 1, and the performance parameters of the final carbon paper product are shown in Table 1.

Example 3

(3) Dip coating of thermosetting resins

Preparing a thermosetting resin-carbon fiber powder mixed solution with the solid content of 40 percent, wherein the thermosetting resin: carbon fiber powder: alcohol: the surfactant is 30: 10: 59: firstly, after weighing the resin, adding ethanol, stirring uniformly, adding carbon fiber powder while stirring, adding alkyl ether lactose type positive and negative ion fluorocarbon surfactant, and then using an ultrasonic dispersion device to slowly disperse the carbon fiber in a resin matrix at a high speed. And (3) finally, placing the base material of the carbon paper obtained in the step (2) in a mixed solution of thermosetting resin and carbon fiber powder for dipping treatment for 5min, taking out the base material, and heating at 60 ℃ to enable the base material to be in a semi-drying state.

The other steps were the same as in example 1, and the performance parameters of the final carbon paper product are shown in Table 1.

Example 4

(4) Foam coated carbon fiber powder layer

Preparing carbon fiber powder foam slurry, wherein the concentration of the foam slurry is 8%, and the polyacrylonitrile-based carbon fiber powder: alkyl ether lactose type positive and negative ion fluorocarbon surfactant: sodium carboxymethylcellulose: 4,4' -oxybis-benzenesulfonyl hydrazide (OBSH) foaming agent: the deionized water is 8: 1: 1: 2: 88. and (3) coating a layer of carbon fiber powder slurry on each of the upper and lower surfaces of the base material obtained in the step (3) by using a foam slurry distribution device, wherein the thickness of the carbon fiber powder slurry is 10 micrometers, and then drying at 100 ℃ to obtain the carbon paper intermediate base material.

Example 5

(4) Foam coated carbon fiber powder layer

Preparing carbon fiber powder foam slurry, wherein the concentration of the foam slurry is 12%, and the polyacrylonitrile-based carbon fiber powder: alkyl ether lactose type positive and negative ion fluorocarbon surfactant: sodium carboxymethylcellulose: azodiisobutyronitrile foaming agent: the deionized water was 12:1.5:1.5:2: 83. And (3) coating a layer of carbon fiber powder slurry on each of the upper and lower surfaces of the base material obtained in the step (3) by using a foam slurry distribution device, wherein the thickness of the carbon fiber powder slurry is 10 micrometers, and then drying at 100 ℃ to obtain the carbon paper intermediate base material.

Example 6

(4) Foam coated carbon fiber powder layer

Preparing carbon fiber powder foam slurry, wherein the concentration of the foam slurry is 8%, and the polyacrylonitrile-based carbon fiber powder: alkyl ether lactose type positive and negative ion fluorocarbon surfactant: sodium carboxymethylcellulose: azodiisobutyronitrile foaming agent: deionized water is 8: 1: 1: 2: 88. and (3) coating a layer of carbon fiber powder slurry on each of the upper surface and the lower surface of the base material obtained in the step (3) by using a foam slurry distribution device, wherein the thickness of the carbon fiber powder slurry is 15 micrometers, and then drying at 100 ℃ to obtain the carbon paper intermediate base material.

Example 7

(1) Preparation of carbon fiber powder

Firstly, mixing pulp-free chopped polyacrylonitrile-based carbon fibers with a water-based polytetrafluoroethylene emulsion, wherein the mass ratio of the pulp-free chopped polyacrylonitrile-based carbon fibers to the water-based polytetrafluoroethylene emulsion is 3: 7, sintering at 350 ℃ for 30min, ball-milling at high speed and grinding the mixture, and finally treating at 500 ℃ for 30min to obtain the carbon fiber powder filler.

(2) Preparation of raw paper of carbon paper

(3) Dip coating of thermosetting resins

Preparing a thermosetting resin-carbon fiber powder mixed solution, wherein the solid content is 40%, and the thermosetting resin: carbon fiber powder: alcohol: the surface active agent is 30: 10: 59: 1, after the resin is weighed, adding methanol and uniformly stirring, adding carbon fiber powder while stirring, adding alkyl ether lactose type positive and negative ion fluorocarbon surfactant, then adjusting the speed of an ultrasonic dispersion device, and slowing at first and then speeding at a high speed until the carbon fiber powder is uniformly dispersed in a resin matrix. And finally, placing the carbon paper base paper in the thermosetting resin-carbon fiber powder mixed solution for dipping treatment for 5min, taking out the base material, and heating at 60 ℃ to enable the base material to be in a semi-drying state.

(4) Foam coated carbon fiber powder layer

Preparing carbon fiber powder foam slurry, wherein the concentration of the foam slurry is 8%, and the polyacrylonitrile-based carbon fiber powder: alkyl ether lactose type positive and negative ion fluorocarbon surfactant: sodium carboxymethylcellulose: azodiisobutyronitrile foaming agent: the deionized water was 12:1.5:1.5:2: 83. And (3) coating a layer of carbon fiber powder slurry on each of the upper and lower surfaces of the base material obtained in the step (3) by using a foam slurry distribution device, wherein the thickness of the carbon fiber powder slurry is 10 micrometers, and then drying at 80 ℃ to obtain the carbon paper intermediate base material.

Example 8

(1) Preparation of carbon fiber powder

Firstly, mixing pulp-free chopped polyacrylonitrile-based carbon fibers with a polyvinylidene fluoride solution (the solvent is N-methyl pyrrolidone, and the solid content is 20%), wherein the mass ratio of the carbon fibers to the polyvinylidene fluoride resin is 2: 3, sintering at 350 ℃ for 30min, ball milling at high speed to grind the mixture, and sintering at 500 ℃ for 30min to obtain the carbon fiber powder filler.

Example 9

(3) Dip coating of thermosetting resins

Preparing a thermosetting resin-carbon fiber powder mixed solution with the solid content of 40 percent, wherein the thermosetting resin: carbon fiber powder: alcohol: the surfactant is 37: 3: 59: 1, after the resin is weighed, adding methanol and uniformly stirring, adding carbon fiber powder while stirring, adding alkyl ether lactose type positive and negative ion fluorocarbon surfactant, then adjusting the speed of an ultrasonic dispersion device, and slowing at first and then speeding at a high speed until the carbon fiber powder is uniformly dispersed in a resin matrix. And (3) finally, placing the base paper of the carbon paper obtained in the step (2) in a mixed solution of thermosetting resin and carbon fiber powder for dipping treatment for 5min, taking out the base material, and heating at 60 ℃ to enable the base material to be in a semi-drying state.

Example 10

(1) Preparation of carbon fiber powder

(2) Preparation of raw paper of carbon paper

(3) Dip coating of thermosetting resins

Preparing a thermosetting resin-carbon fiber powder mixed solution with the solid content of 40 percent, wherein the thermosetting resin: carbon fiber powder: alcohol: the surfactant is 34: 6: 59: 1, after the resin is weighed, adding methanol and uniformly stirring, adding carbon fiber powder while stirring, adding alkyl ether lactose type positive and negative ion fluorocarbon surfactant, then adjusting the speed of an ultrasonic dispersion device, and slowing at first and then speeding at a high speed until the carbon fiber powder is uniformly dispersed in a resin matrix. And (3) finally, placing the base paper of the carbon paper obtained in the step (2) in a mixed solution of thermosetting resin and carbon fiber powder for dipping treatment for 5min, taking out the base material, and heating at 60 ℃ to enable the base material to be in a semi-drying state.

(4) Foam coated carbon fiber powder layer

Preparing carbon fiber powder foam slurry, wherein the concentration of the foam slurry is 8%, and the polyacrylonitrile-based carbon fiber powder: alkyl ether lactose type positive and negative ion fluorocarbon surfactant: sodium carboxymethylcellulose: azodiisobutyronitrile foaming agent: deionized water is 10: 1: 1: 2: and 86, coating a layer of carbon fiber powder slurry on each of the upper surface and the lower surface of the base material obtained in the step (3) in a foam mode through a foam slurry distribution device, wherein the thickness of the carbon fiber powder slurry is 10 micrometers, and then drying at 80 ℃ to obtain the carbon paper intermediate base material.

(5) Hot-pressing solidification of carbon paper

(6) Carbonization and graphitization of carbon paper

Comparative example 1

Different from the step (1) of the embodiment 1, the carbon fiber powder is obtained by outsourcing, and is non-pulp polyacrylonitrile-based carbon fiber powder with the particle size of 400 meshes.

Comparative example 2

And (4) coating the carbon fiber powder layer without foam (step (4)).

Comparative example 3

(1) Preparation of raw paper of carbon paper

Mixing the raw materials of the short-cut polyacrylonitrile-based carbon fiber, the binder, the dispersant and the like, and preparing the raw carbon paper by wet papermaking, wherein the quantitative ratio is 25 +/-5 g/m ² 。

(2) Dip coating of thermosetting resins

Preparing a thermosetting resin-alcohol mixed solution with the solid content of 40 percent, wherein the thermosetting resin: the alcohol is 40: and 60, after the resin is weighed, adding a methanol solvent and uniformly stirring. Soaking the carbon paper base paper in the mixed solution for 5min, taking out, and heating at 80 deg.C to obtain semi-dried carbon paper.

(3) Hot-pressing solidification of carbon paper

Setting the temperature of a vulcanizing press to 160 ℃, putting the base material into the vulcanizing press when the standby device reaches the set temperature, keeping the temperature for 5min under the pressure of 4MPa, and then demoulding and taking out the base material.

(4) Carbonization and graphitization of carbon paper

Carbonizing and graphitizing the base material prepared in the step (3) in a graphite furnace, wherein the inert gas is argon, the carbonizing temperature is 1000 ℃, and the heat preservation time is 1.0 h; the graphitization temperature is 2500 ℃, and the heat preservation time is 1.0 h. The performance parameters of the final carbon paper product are shown in table 1.

The test method comprises the following steps:

at present, no unified method for representing the performance of the carbon paper exists at home and abroad, and the technical performance parameters of the carbon paper are tested by adopting the following method by referring to the national standard GB/T20042.7-2014 (part 7 of a proton exchange membrane fuel cell: a carbon paper characteristic test method) and combining a self test platform.

Thickness: adopting a thickness tester to test the thickness of the carbon paper, the unit is as follows: mm.

Quantification: sampling by adopting a sampler, weighing by an electronic balance, calculating a result, and obtaining a unit: g/m ² 。

Resistivity: adopting a four-probe measuring method, and using a four-probe resistivity tester to test the resistivity of the carbon paper in the plane direction, wherein the unit is as follows: m omega cm.

Tensile strength: the tensile strength of the carbon paper is tested by using a universal tester according to GB/T12914-2018, the unit is as follows: MPa.

Bending strength: the bending strength of the carbon paper is tested by a three-point bending method and a universal testing machine, wherein the unit is as follows: MPa.

Flexural modulus: the bending modulus of the carbon paper is tested by a three-point bending method and a universal testing machine, and the unit is as follows: GPa.

Air permeability: the permeability of the carbon paper was tested using a Gurley permeability tester, units: s/100 cc.

Porosity: the porosity of the carbon paper was measured using a mercury porosimeter, unit: % of the total weight of the composition.

Coefficient of thermal conductivity: testing the heat conductivity coefficient of the carbon paper in the vertical direction by using an instant plane heat source method, wherein the unit is as follows: w (m.K).

Pore size distribution: adopting a capillary flow method, and using a pore size distributor to test the pore size distribution range of the carbon paper, wherein the unit is as follows: and mu m.

Table 1 performance testing of carbon paper products prepared in examples and comparative examples

The experimental result shows that the thickness of the prepared carbon paper is within the range of 100-150 mu m, the carbon paper meets the requirements of the current hydrogen fuel cell market, and the carbon paper has excellent mechanical property, uniform pore size distribution, large air permeability and high conductivity. Wherein, the tensile strength can reach 20.8MPa, the bending strength reaches 25.2MPa, and the bending modulus reaches 18.1 GPa; the porosity is 82.1%, the pore size distribution is relatively concentrated, the pore size distribution range is 20-23 mu m, the air permeability is large (8.15s/100cc), the thermal conductivity is high (2.125W (m.K)), and the transmission of water, gas and heat is ensured; meanwhile, the resistivity of the electrode is low (the resistivity in the plane direction is 4.3m omega cm), so that the ohmic loss is reduced, and the electrode performance is improved.

In the description herein, reference to the description of the terms "one embodiment/mode," "some embodiments/modes," "example," "specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment/mode or example is included in at least one embodiment/mode or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment/mode or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments/modes or examples. Furthermore, the various embodiments/modes or examples and features of the various embodiments/modes or examples described in this specification can be combined and combined by one skilled in the art without being mutually inconsistent.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present application, "plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

It will be understood by those skilled in the art that the foregoing embodiments are provided merely for clarity of disclosure and are not intended to limit the scope of the invention. It will be apparent to those skilled in the art that other variations or modifications may be made on the above invention and still be within the scope of the invention. The above description is only for the best mode of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Those skilled in the art will appreciate that the invention may be practiced without these specific details.

Claims

1. The preparation method of the carbon fiber powder is characterized by firstly mixing the sizing agent-free treated chopped carbon fiber with polytetrafluoroethylene emulsion, wherein the polytetrafluoroethylene emulsion contains a surfactant; then sintering at low temperature, cutting and grinding the carbon fiber by high-speed ball milling, and finally removing the polytetrafluoroethylene by high-temperature sintering to obtain carbon fiber powder with relatively uniform particle size distribution; the mass ratio of the chopped fibers to the polytetrafluoroethylene emulsion is 1: 1.5-3, the low-temperature sintering temperature is 200-400 ℃, and the high-temperature sintering temperature is 500-600 ℃.

2. A preparation method of high-strength thin carbon paper is characterized by comprising the following main process steps:

(1) preparing carbon fiber powder: the carbon fiber powder is prepared by the method of claim 1;

(2) preparing raw paper of the carbon paper: uniformly mixing raw materials of short carbon fibers, a binder and a dispersant, and making the raw materials into raw paper of the carbon paper by a wet method;

(3) dip coating of thermosetting resin: preparing a mixed solution containing resin-carbon fiber powder, soaking the base paper of the carbon paper prepared in the step (2) in the mixed solution, taking out the base paper, and heating the base paper to enable the base paper to be in a semi-dried state, wherein the carbon fiber powder in the resin-carbon fiber powder adopts the carbon fiber powder prepared in the step (1);

(4) foam coating of carbon fiber powder layer: respectively coating a layer of foam slurry of the carbon fiber powder prepared in the step (1) on the upper surface and the lower surface of the base material obtained in the step (3), and drying to obtain a carbon paper intermediate base material;

(5) hot-pressing and curing the carbon paper: heating and pressurizing the carbon paper intermediate base material obtained in the step (4) by a flat hot press or a flat vulcanizing machine;

(6) carbonizing and graphitizing the carbon paper: and (5) sequentially carrying out carbonization and graphitization treatment on the hot-pressed base material obtained in the step (5) by means of a graphitization furnace.

3. The method for preparing carbon paper as claimed in claim 2, wherein the mixed solution containing resin-carbon fiber powder in step (3) is composed of resin, carbon fiber powder, surfactant and alcohol solvent; the resin is liquid alcohol-soluble thermosetting resin, and is selected from one or more of phenolic resin, epoxy resin and furan resin; the mass ratio of the thermosetting resin to the carbon fiber powder is 3-9: 1.

4. the preparation method of carbon paper as claimed in claim 2, wherein the carbon fiber powder foam slurry obtained in step (4) is composed of the carbon fiber powder obtained in step (1), a surfactant, a dispersant, a foaming agent and water, and the concentration of the carbon fiber powder foam slurry is 1% -10%.

5. The method of making a carbon paper as in claim 3, wherein the surfactant is selected from anionic surfactants.

6. The method for preparing carbon paper as claimed in claim 4, wherein the carbon fiber powder is used in an amount of 5 to 15 parts by weight, the surfactant is used in an amount of 0.5 to 3 parts by weight, the dispersant is used in an amount of 0.5 to 3 parts by weight, the foaming agent is used in an amount of 1 to 5 parts by weight, and the water is used in an amount of 80 to 90 parts by weight.

7. The method for preparing carbon paper as claimed in claim 2, wherein the hot pressing temperature for hot pressing and curing of the carbon paper in the step (5) is 100-200 ℃; the hot pressing pressure is 1-10MPa, and the hot pressing time is 1-10 min; the step (6) is to carry out carbonization and graphitization treatment on the base material obtained in the step (5) in a graphite furnace under the protection of inert gas; the carbonization temperature is 800-1500 ℃, and the heat preservation time is 0.5-2.0 h; the graphitization temperature is 2000-2800 ℃, and the heat preservation time is 0.5-2.0 h.

8. The carbon paper with high strength and thinness prepared by the preparation method of the carbon paper as claimed in claim 2.

9. Use of the carbon paper according to claim 8, wherein the high strength thin carbon paper is used for a gas diffusion layer of a hydrogen fuel cell.