CN115881983A - Hydrophobic modified carbon fiber paper and preparation method and application thereof - Google Patents
Hydrophobic modified carbon fiber paper and preparation method and application thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of gas diffusion layers of fuel cells, and provides hydrophobic modified carbon fiber paper and a preparation method thereof, wherein polyacrylonitrile-based chopped fiber precursors and a surfactant are mixed and then sequentially subjected to wet papermaking, pre-oxidation, resin solution impregnation and drying treatment to obtain polyacrylonitrile-based carbon fiber base paper; sequentially swelling, stirring and defoaming the acrylonitrile-N-vinyl formamide copolymer solution to obtain a precursor solution; and (3) electrospinning the precursor solution on polyacrylonitrile-based carbon fiber base paper through electrostatic spinning, and sequentially carrying out hot-pressing solidification, carbonization and graphitization to obtain the hydrophobic modified carbon fiber paper. The invention also provides application of the hydrophobic modified carbon fiber paper. The invention expands the preparation process of the carbon paper for the gas diffusion layer of the proton exchange membrane fuel cell, realizes the accurate control of the electrical conductivity, the hydrophobicity and the air permeability, has good effect in the PEMFC, and provides a new design idea for the practical industrial production of the carbon paper.
Description
Technical Field
The invention relates to the technical field of gas diffusion layers of fuel cells, in particular to hydrophobic modified carbon fiber paper and a preparation method and application thereof.
Background
A Proton Exchange Membrane Fuel Cell (PEMFC) is a power generation device that directly converts chemical energy into electrical energy, and has the advantages of high power density, high energy conversion rate, low-temperature start, no pollution, and the like. The gas diffusion layer, which is a key component in the PEMFC, generally consists of a substrate layer and a microporous layer, and the substrate layer is usually a carbon fiber paper, which mainly plays roles of supporting the microporous layer, catalyzing, draining, and exhausting, and thus the carbon paper for the PEMFC needs to have high porosity, conductivity, and hydrophobic properties.
The traditional method for hydrophobically modifying carbon paper is mainly an impregnation method, namely, the carbon paper is soaked in a hydrophobizing agent solution with a certain concentration and then is taken out, dried and calcined to obtain the carbon paper. However, the addition of the hydrophobic agent can affect the porosity of the carbon paper and seriously affect the transmission rate of gas and water vapor; in addition, due to the chemical inertness of the surface of the carbon paper, the affinity of the carbon paper and a hydrophobic agent is poor, the interface bonding strength is low, and the hydrophobic modification effect is greatly limited. At present, polymer materials such as polytetrafluoroethylene emulsion, polymethylsiloxane and the like are generally adopted as the hydrophobic agent, and the conductivity of the carbon paper can be seriously reduced in the using process due to the poor conductivity of the hydrophobic agent.
Therefore, the research on the method for obtaining the hydrophobic modified carbon paper which has excellent air permeability, conductivity and hydrophobic property and simple process has important significance for the development of fuel cells.
Disclosure of Invention
The invention aims to provide hydrophobic modified carbon fiber paper and a preparation method and application thereof in order to overcome the defects of the prior art.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a preparation method of hydrophobic modified carbon fiber paper, which comprises the following steps:
1) Preparing polyacrylonitrile-based precursor fibers from the acrylonitrile-N-vinylformamide copolymer by a dry-jet wet method, and carrying out short-cut treatment to obtain polyacrylonitrile-based short-cut fiber precursor fibers;
2) Mixing polyacrylonitrile-based chopped fiber precursor and a surfactant solution, and then sequentially carrying out wet papermaking, pre-oxidation, resin solution impregnation and drying treatment to obtain polyacrylonitrile-based carbon fiber base paper;
3) Mixing an acrylonitrile-N-vinyl formamide copolymer with a solvent to obtain a solution, and sequentially swelling, stirring and defoaming the solution to obtain a precursor solution;
4) And (3) electrospinning the precursor solution on polyacrylonitrile-based carbon fiber base paper through electrostatic spinning, and sequentially carrying out hot-pressing solidification, carbonization and graphitization to obtain the hydrophobic modified carbon fiber paper.
Preferably, the polyacrylonitrile-based chopped fiber strands in the step 1) have the length of 7-26 mm, the diameter of 4-10 microns and the orientation degree of more than or equal to 92%.
Preferably, the surfactant in the step 2) comprises one or more of polyethylene oxide, hydroxymethyl cellulose and polyacrylamide, and the mass concentration of the surfactant solution is 0.05-0.3%; the temperature of the drying treatment is 50-100 ℃, and the time of the drying treatment is 30-60 min.
Preferably, the specific process of the pre-oxidation in the step 2) is to pre-oxidize paper obtained by wet papermaking at 170-210 ℃ for 10-20 min, 240-280 ℃ for 20-80 min and 300-330 ℃ for 30-50 min in sequence;
the heating rate of heating from room temperature to 170-210 ℃ is 3-7 ℃/min, the heating rate of heating from 170-210 ℃ to 240-280 ℃ is 0.5-3 ℃/min, and the heating rate of heating from 240-280 ℃ to 300-330 ℃ is 5-10 ℃/min.
Preferably, in the step 2), the mass concentration of the resin solution is 5-20%, and the impregnation time of the resin solution is 10-40 min; in the resin solution, the resin is boron phenolic resin, and the solvent is methanol and/or ethanol.
Preferably, in the solution in the step 3), the mass concentration of the acrylonitrile-N-vinyl formamide copolymer is 10-20%, and the swelling, stirring and defoaming time is independently 6-12 h; the temperature for swelling, stirring and defoaming is independently 50-90 ℃.
Preferably, the electrostatic spinning time in the step 4) is 2-5 h; in the electrostatic spinning process, the thickness of the sprayed precursor solution is 0.02-0.06 mm; the temperature of the hot-pressing curing is 130-170 ℃, the pressure of the hot-pressing curing is 5-15 MPa, and the time of the hot-pressing curing is 10-30 min.
Preferably, the carbonization temperature in the step 4) is 800-1300 ℃, and the carbonization time is 5-15 min; the graphitization temperature is 2200 to 2600 ℃, and the graphitization time is 10 to 20min;
the temperature rise rate from room temperature to carbonization temperature and the temperature rise rate from carbonization temperature to graphitization temperature are respectively 3-9 ℃/min; the carbonization and the graphitization are carried out under the protection of high-purity nitrogen.
The invention also provides the hydrophobic modified carbon fiber paper prepared by the preparation method, and the gram weight of the hydrophobic modified carbon fiber paper is 60-180 g/m 2 The contact angle is 125-135 degrees, and the air permeability is 75-100 m 3 ·(m 2 ·s·bar) -1 (ii) a The carbon fiber paper comprises a carbon fiber film, and the thickness of the carbon fiber film is 0.01-0.04 mm.
The invention also provides application of the hydrophobic modified carbon fiber paper in a gas diffusion layer of a proton exchange membrane fuel cell.
The beneficial effects of the invention include the following:
1) The invention adopts the electrostatic spinning technology to prepare the carbon fiber paper hydrophobic layer, avoids the problems of uneven impregnation and poor interface bonding force of traditional macromolecule hydrophobic agent polytetrafluoroethylene and the like, avoids the blockage of the porosity of the carbon fiber, has no influence on the electric conductivity, effectively constructs the carbon fiber paper hydrophobic layer by a one-step method, expands the preparation process of the carbon paper for the gas diffusion layer of the proton exchange membrane fuel cell, realizes the accurate control of the electric conductivity, the hydrophobicity and the porosity, and has good effect in the PEMFC.
2) The invention takes carbon fiber precursor as raw material, utilizes the synergistic effect of hydrogen bond of cyano-group, acylamino and water and surfactant to realize the uniform dispersion of precursor in water, ensures the uniformity of finished paper, simultaneously does not need secondary carbonization and graphitization in the whole preparation process, has simple process flow and low energy consumption, and is suitable for batch production.
Drawings
FIG. 1 is a scanning electron micrograph of hydrophobically modified carbon fiber paper of example 1;
FIG. 2 is a scanning electron micrograph of the hydrophobically modified carbon fiber paper of example 2;
FIG. 3 is the contact angle of the hydrophobically modified carbon fiber paper of example 2;
fig. 4 is a contact angle of the carbon fiber paper of comparative example 1.
Detailed Description
The invention provides a preparation method of hydrophobic modified carbon fiber paper, which comprises the following steps:
1) Preparing polyacrylonitrile-based precursor fibers from the acrylonitrile-N-vinylformamide copolymer by a dry spraying wet method, and carrying out short-cut treatment to obtain polyacrylonitrile-based short-cut fiber precursor fibers;
2) Mixing polyacrylonitrile-based chopped fiber protofilaments and a surfactant solution, and then sequentially carrying out wet papermaking, pre-oxidation, resin solution impregnation and drying treatment to obtain polyacrylonitrile-based carbon fiber base paper;
3) Mixing an acrylonitrile-N-vinyl formamide copolymer with a solvent to obtain a solution, and sequentially swelling, stirring and defoaming the solution to obtain a precursor solution;
4) And (3) electrospinning the precursor solution on polyacrylonitrile-based carbon fiber base paper through electrostatic spinning, and sequentially carrying out hot-pressing solidification, carbonization and graphitization to obtain the hydrophobic modified carbon fiber paper.
The invention takes acrylonitrile-N-vinylformamide copolymer as a raw material, and obtains fine denier and high orientation polyacrylonitrile-based protofilament through dry-jet wet spinning, multi-stage washing drafting, oiling and drying, two-stage steam drafting and heat setting.
In the invention, the distance of the air section of the dry-jet wet spinning is 5mm, the content of DMSO in a coagulating bath is 60wt%, the temperature of the coagulating bath is 5 ℃, the coagulating time is 1.2min, the drafting multiple of the nascent fiber is 5 times, the hot water drafting temperature is 95 ℃, the hot water drafting multiple is 2.2 times, the drying temperature is 145 ℃, the steam drafting multiple is 2.8 times, and the heat setting temperature is 130 ℃.
In the present invention, the length of the polyacrylonitrile-based chopped strand fiber of step 1) is preferably 7 to 26mm, more preferably 8 to 22mm, and still more preferably 10 to 16mm; the diameter of the polyacrylonitrile-based chopped strand fibers is preferably 4 to 10 μm, more preferably 5 to 8 μm, and still more preferably 6 to 7 μm; the degree of orientation of the polyacrylonitrile-based chopped strand fibers is preferably not less than 92%, more preferably not less than 93%, and still more preferably not less than 94%.
In the present invention, the surfactant in step 2) preferably comprises one or more of polyethylene oxide, hydroxymethyl cellulose and polyacrylamide, and the mass concentration of the surfactant solution is preferably 0.05 to 0.3%, more preferably 0.1 to 0.25%, and even more preferably 0.15 to 0.2%.
The polyacrylonitrile-based chopped fiber precursor is used as a raw material, and the uniform dispersion of the precursor in water is easier to realize by utilizing the synergistic effect of hydrogen bonds of cyano groups, amide groups and water and a surfactant, so that the uniformity of finished paper is ensured.
In the present invention, the wet papermaking is preferably performed under vacuum, and the degree of vacuum is preferably 0.03 to 0.07MPa, more preferably 0.04 to 0.06MPa, and still more preferably 0.05MPa; the time for dehydration is preferably 80 to 120 seconds, more preferably 90 to 110 seconds, and still more preferably 100 seconds.
In the invention, the specific process of the pre-oxidation in the step 2) is preferably that the paper obtained by wet papermaking is sequentially subjected to primary pre-oxidation, secondary pre-oxidation and tertiary pre-oxidation, wherein the temperature of the primary pre-oxidation is preferably 170-210 ℃, more preferably 180-200 ℃, and more preferably 185-190 ℃; the time for the first pre-oxidation is preferably 10 to 20min, more preferably 12 to 18min, and even more preferably 14 to 16min; the temperature of the second pre-oxidation is preferably 240-280 ℃, more preferably 250-270 ℃, and more preferably 255-265 ℃; the time for the second pre-oxidation is preferably 20 to 80min, more preferably 30 to 70min, and even more preferably 40 to 60min; the temperature of the third pre-oxidation is preferably 300-330 ℃, more preferably 310-320 ℃, and more preferably 313-316 ℃; the time for the third pre-oxidation is preferably 30 to 50min, more preferably 35 to 45min, and still more preferably 40min.
In the invention, the heating rate of heating from room temperature to 170-210 ℃ is preferably 3-7 ℃/min, more preferably 4-6 ℃/min, and even more preferably 4.5-5.5 ℃/min; the heating rate from 170-210 ℃ to 240-280 ℃ is preferably 0.5-3 ℃/min, more preferably 1-2.5 ℃/min, and even more preferably 1.5-2 ℃/min; the heating rate from 240 to 280 ℃ to 300 to 330 ℃ is preferably 5 to 10 ℃/min, more preferably 6 to 9 ℃/min, and still more preferably 7 to 8 ℃/min.
In step 2) of the present invention, the mass concentration of the resin solution is preferably 5 to 20%, more preferably 8 to 16%, and still more preferably 10 to 13%; the time for impregnating the resin solution is preferably 10 to 40min, more preferably 15 to 30min, and still more preferably 20 to 25min; in the resin solution, the resin is preferably a boron phenolic resin, and the solvent is preferably methanol and/or ethanol.
In the present invention, the resin solution is impregnated in a vacuum or under atmospheric pressure, and the degree of vacuum in the vacuum impregnation is preferably 120 to 140Pa, more preferably 125 to 135Pa, and still more preferably 130Pa.
The boron phenolic resin is high in carbon residue rate, and the carbon residue rate at 800 ℃ is 70%; the preparation method of the boron phenolic resin is a method known in the field; the boron phenolic resin with high carbon residue rate can increase the connectivity among fibers, and the carbon fiber paper with good mechanical property and electrical conductivity is obtained.
In the invention, the temperature of the drying treatment in the step 2) is preferably 50-100 ℃, more preferably 60-90 ℃, and more preferably 70-80 ℃; the time for the drying treatment is preferably 30 to 60min, more preferably 40 to 50min, and still more preferably 43 to 45min.
In the invention, the gram weight of the polyacrylonitrile-based carbon fiber base paper is preferably 120-360 g/m 2 More preferably 180 to 300g/m 2 More preferably 220 to 260g/m 2 。
In the solution in step 3) of the present invention, the mass concentration of the acrylonitrile-N-vinylformamide copolymer is preferably 10 to 20%, more preferably 12 to 18%, and even more preferably 14 to 16%; the swelling, stirring and defoaming time is preferably 6 to 12 hours, more preferably 7 to 11 hours, and even more preferably 9 to 10 hours; the swelling, stirring and defoaming preferably take the same time; the temperature for swelling, stirring and defoaming is preferably 50 to 90 ℃, more preferably 60 to 80 ℃, and still more preferably 65 to 75 ℃ independently.
In the invention, the time of electrostatic spinning in the step 4) is preferably 2 to 5 hours, and more preferably 3 to 4 hours; in the electrostatic spinning process, the thickness of the spraying of the precursor solution is preferably 0.02-0.06 mm, more preferably 0.03-0.05 mm, and more preferably 0.035-0.045 mm; the temperature of the hot-pressing curing is preferably 130-170 ℃, more preferably 140-160 ℃, and more preferably 145-155 ℃, and the pressure of the hot-pressing curing is preferably 5-15 MPa, more preferably 8-12 MPa, and more preferably 9-10 MPa; the time for hot-pressing curing is preferably 10 to 30min, more preferably 15 to 25min, and still more preferably 18 to 22min; the hot-pressing curing is preferably a flat vulcanizing agent.
In the invention, the carbonization temperature in the step 4) is preferably 800-1300 ℃, more preferably 900-1200 ℃, and more preferably 1000-1100 ℃; the carbonization time is preferably 5 to 15min, more preferably 7 to 13min, and still more preferably 9 to 11min; the graphitization temperature is preferably 2200 to 2600 ℃, more preferably 2300 to 2500 ℃, and more preferably 2350 to 2450 ℃; the graphitization time is preferably 10 to 20min, more preferably 12 to 18min, and still more preferably 14 to 16min.
In the invention, the temperature rising rate from room temperature to carbonization temperature and the temperature rising rate from carbonization temperature to graphitization temperature are independent, preferably 3-9 ℃/min, more preferably 4-8 ℃/min, and more preferably 5-7 ℃/min; the carbonization and graphitization are preferably performed under the protection of high-purity nitrogen.
In the step 4), the carbonization and graphitization is preferably carried out in one step in a multistage distribution program temperature control tube furnace.
The invention also provides the hydrophobic modified carbon fiber paper prepared by the preparation method, wherein the gram weight of the hydrophobic modified carbon fiber paper is 60-180 g/m 2 The contact angle is 125-135 degrees, and the air permeability is 75-100 m 3 ·(m 2 ·s·bar) -1 (ii) a The carbon fiber paper comprises a carbon fiber film, and the thickness of the carbon fiber film is 0.01-0.04 mm.
The gram weight of the hydrophobically modified carbon fiber paper of the invention is preferably 80 to 160g/m 2 More preferably 100 to 140g/m 2 (ii) a The contact angle is preferably 128 to 132 °, more preferably 129 to 130 °; the air permeability is preferably 80-95 m 3 ·(m 2 ·s·bar) -1 More preferably 85 to 90m 3 ·(m 2 ·s·bar) -1 (ii) a The resistivity is preferably 5 to 8 m.OMEGA.cm, more preferably 6 to 7 m.OMEGA.cm; the thickness of the carbon fiber film is preferably 0.02 to 0.03mm.
The invention also provides application of the hydrophobic modified carbon fiber paper in a gas diffusion layer of a proton exchange membrane fuel cell.
The technical solutions provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of the present invention.
The multi-stage step-wise temperature programmed tubular furnace used in the examples and comparative examples was of the type KSL-1700X-GS.
Example 1
Taking an acrylonitrile-N-vinylformamide copolymer as a raw material, carrying out dry-jet wet spinning, multistage water washing drafting, oiling and drying, two-section steam drafting and heat setting to obtain fine denier (with the diameter of 8 mu m) and high orientation (with the orientation degree of 92 percent) polyacrylonitrile-based precursor, and carrying out short cutting to obtain the polyacrylonitrile-based short-cut fiber precursor (with the length of 8 mm). Adding polyacrylonitrile-based chopped fiber precursors into a fiber dissociator, then adding an aqueous solution of surfactants of hydroxymethyl cellulose and polyethylene oxide 68441-17-8 (in the aqueous solution, the mass concentration of the hydroxymethyl cellulose and the polyethylene oxide 68441-17-8 is 0.1%), and dispersing for 3min at a stirring speed of 500r/min to obtain a uniform carbon fiber precursor dispersion liquid.
Transferring the carbon fiber precursor dispersion to a paper sheet former by wet forming technology, dehydrating for 100s under vacuum condition with vacuum degree of 0.05MPa to make the carbon fiber precursor dispersion pass through a stainless steel filter screen, and forming 20 × 20cm with uniform thickness (thickness of 0.9 mm) on the surface of the filter screen 2 The paper of (1); putting the paper into a multi-stage step-by-step program temperature control tube furnace, introducing air with the flow of 0.5L/min, heating to 190 ℃ from room temperature at the heating rate of 5 ℃/min, and preserving heat for 15min; then heating from 190 ℃ to 260 ℃ at the heating rate of 1 ℃/min, and preserving heat for 50min; then the temperature is increased from 260 ℃ to 315 ℃ at the heating rate of 8 ℃/min, and the temperature is kept for 40min. Then, the mixture is put into a methanol solution of boron phenolic resin (the mass fraction is 10 percent) and is soaked in vacuum for 20min under the vacuum degree of 130Pa, and the mixture is taken out and dried in a forced air drying oven for 40min under the temperature of 60 ℃ to obtain polyacrylonitrile-based carbon fiber base paper (the gram weight of the polyacrylonitrile-based carbon fiber base paper is 240 g/m) 2 )。
Dissolving an acrylonitrile-N-vinylformamide copolymer in N, N-dimethylformamide to prepare a solution with the mass fraction of 15%, standing and swelling the solution in a water bath at 60 ℃, performing magnetic stirring (the rotating speed is 800 r/min) and standing and defoaming at 60 ℃, wherein the standing and swelling, magnetic stirring and standing and defoaming time are 10h, and thus obtaining the electrostatic spinning precursor solution.
The polyacrylonitrile-based carbon fiber base paper is used as a receiver, an electrostatic spinning precursor solution is uniformly sprayed on the receiver through electrostatic spinning (the positive pressure is 12kV, the negative pressure is-2.5 kV, the receiving distance is 15 cm), the sprayed thickness is 0.04mm, and the spinning time is 3h. And then hot-pressing and curing the polyacrylonitrile-based carbon fiber base paper by a flat vulcanizing machine at the temperature of 155 ℃ for 20min under the pressure of 10MPa to obtain the hot-pressed and cured polyacrylonitrile-based carbon fiber base paper. Putting the polyacrylonitrile-based carbon fiber base paper subjected to hot pressing curing into a grading multi-step program temperature control tubular furnace for one-step carbonization and graphitization treatment: in high-purity nitrogen, raising the temperature from room temperature to 1000 ℃ at the heating rate of 5 ℃/min, and preserving the temperature for 10min to carry out carbonization treatment; and then heating from 1000 ℃ to 2400 ℃ at the heating rate of 5 ℃/min, and preserving heat for 15min for graphitization treatment to obtain the hydrophobic modified carbon fiber paper.
The gram weight of the hydrophobically modified carbon fiber paper of the embodiment is 120g/m 2 Contact angle of 129.7 °; the air permeability is 90m 3 ·(m 2 ·s·bar) -1 。
As shown in fig. 1, it can be seen from fig. 1 that a thin electrospun carbon fiber membrane is disposed on the surface of the carbon paper, the thickness of the electrospun carbon fiber membrane is 0.018mm, and the fibers are connected in a staggered manner.
Example 2
The vacuum impregnation resin in example 1 was changed to atmospheric impregnation, and the other conditions were the same as in example 1.
As shown in fig. 2, as can be seen from fig. 2, the surface of the hydrophobically modified carbon fiber is a layer of electrospun polyacrylonitrile carbon fiber, and the fibers are formed by connecting a small amount of resin carbon, which is obtained by carbonizing and graphitizing a part of resin permeated in the curing process.
As shown in fig. 3, the contact angle of the hydrophobically modified carbon fiber paper of the present example is 125.4 ° which is much higher than that of the carbon fiber paper without any treatment, as can be seen from fig. 3.
The grammage of the hydrophobically modified carbon fiber paper of the embodiment is 130g/m 2 Air permeability of 100m 3 ·(m 2 ·s·bar) -1 。
Example 3
The length of the polyacrylonitrile-based chopped strand fiber of example 1 was changed from 8mm to 16mm, and the temperature for the hot press curing was changed from 155 ℃ to 170 ℃, under the same conditions as in example 1.
The gram weight of the hydrophobically modified carbon fiber paper of the embodiment is 140g/m 2 Contact angle of 129.5 degrees and air permeability of 85m 3 ·(m 2 ·s·bar) -1 。
Example 4
The length of the polyacrylonitrile-based chopped strand fiber of example 1 was changed from 8mm to 26mm, and the graphitization temperature was changed from 2400 ℃ to 2600 ℃, under the same conditions as in example 1.
The grammage of the hydrophobically modified carbon fiber paper of the present example was 152g/m 2 Contact angle of 129.9 degrees and air permeability of 80m 3 ·(m 2 ·s·bar) -1 。
Example 5
The degree of orientation of the polyacrylonitrile-based carbon fiber precursor in example 1 was changed from 92% to 92.5%, and the mass concentrations of hydroxymethylcellulose and polyethylene oxide 68441-17-8 in the surfactant aqueous solution were both 0.15%, but the other conditions were the same as in example 1.
The gram weight of the hydrophobically modified carbon fiber paper of the embodiment is 70g/m 2 Contact angle of 131.5 degrees and air permeability of 100m 3 ·(m 2 ·s·bar) -1 。
Example 6
Taking an acrylonitrile-N-vinylformamide copolymer as a raw material, carrying out dry-jet wet spinning, multistage water washing drafting, oiling and drying, two-section steam drafting and heat setting to obtain fine denier (with the diameter of 6 mu m) and high orientation (with the orientation degree of 93.5%) polyacrylonitrile-based protofilaments, and carrying out short cutting to obtain the polyacrylonitrile-based short-cut fiber protofilaments (with the length of 10 mm).
Adding polyacrylonitrile-based chopped fiber precursors into a fiber dissociator, then adding a water solution of surfactant anionic polyacrylamide (the mass concentration of the polyacrylamide is 0.1%), and dispersing for 3min at a stirring speed of 500r/min to obtain a uniform carbon fiber precursor dispersion liquid.
Transferring the carbon fiber precursor dispersion to a paper sheet former by wet forming technology, dehydrating for 110s under the vacuum condition of 0.04MPa to make the carbon fiber precursor dispersion pass through a stainless steel filter screen, and forming 20 × 20cm with uniform thickness (0.85 mm) on the surface of the filter screen 2 The paper of (1); putting the paper into a multi-stage step-by-step program temperature control tubular furnace, introducing air with the flow rate of 0.5L/min, heating to 180 ℃ from room temperature at the heating rate of 4.5 ℃/min, and preserving heat for 18min; then raising the temperature from 180 ℃ to 245 ℃ at the heating rate of 1.5 ℃/min, and preserving the temperature for 70min; then the temperature is increased from 245 ℃ to 305 ℃ at the heating rate of 6 ℃/min, and the temperature is kept for 45min. Then, the obtained product is placed into an absolute ethyl alcohol solution of boron phenolic resin (the mass fraction of the boron phenolic resin is 7%) to be soaked for 30min at normal pressure, and the obtained product is taken out and dried for 35min in a forced air drying oven at the temperature of 80 ℃ to obtain polyacrylonitrile-based carbon fiber base paper (the gram weight of the polyacrylonitrile-based carbon fiber base paper is 300 g/m) 2 )。
Dissolving an acrylonitrile-N-vinyl formamide copolymer in N, N-dimethylformamide to prepare a solution with the mass fraction of 12%, standing and swelling the solution in a water bath at 50 ℃, performing magnetic stirring (rotating speed is 780 r/min) and standing and defoaming at 50 ℃, wherein the standing and swelling, magnetic stirring and standing and defoaming time are all 12h to obtain the electrostatic spinning precursor solution.
The polyacrylonitrile-based carbon fiber base paper is used as a receiver, an electrostatic spinning precursor solution is uniformly sprayed on the receiver through electrostatic spinning (the positive pressure is 12kV, the negative pressure is-2.5 kV, the receiving distance is 15 cm), the sprayed thickness is 0.03mm, and the spinning time is 2.5h. And then, carrying out hot-pressing curing on the polyacrylonitrile-based carbon fiber base paper by a flat vulcanizing machine at the temperature of 140 ℃ for 30min under the pressure of 7MPa to obtain the polyacrylonitrile-based carbon fiber base paper after hot-pressing curing. Putting the polyacrylonitrile-based carbon fiber base paper subjected to hot pressing curing into a grading multi-step program temperature control tubular furnace for one-step carbonization and graphitization treatment: in high-purity nitrogen, raising the temperature from room temperature to 900 ℃ at the heating rate of 4 ℃/min, and preserving the temperature for 13min to carry out carbonization treatment; and then heating to 2350 ℃ from 900 ℃ at the heating rate of 6 ℃/min, and preserving the temperature for 18min for graphitization treatment to obtain the hydrophobic modified carbon fiber paper.
The gram weight of the hydrophobically modified carbon fiber paper of the embodiment is 160g/m 2 Contact angle of 133.5 DEG and air permeability of 92m 3 ·(m 2 ·s·bar) -1 。
Example 7
Taking acrylonitrile-N-vinylformamide copolymer as a raw material, carrying out dry-jet wet spinning, multi-stage water washing drafting, oiling and drying, two-stage steam drafting and heat setting to obtain fine-denier (the diameter is 6 mu m) and high-orientation (the orientation degree is 93%) polyacrylonitrile-based precursor fibers, and carrying out short cutting to obtain the polyacrylonitrile-based short-cut precursor fibers (the length is 18 mm).
Adding polyacrylonitrile-based chopped fiber precursors into a fiber dissociator, adding a surfactant hydroxymethyl cellulose aqueous solution (the mass concentration of the hydroxymethyl cellulose is 0.15%), and dispersing at a stirring speed of 500r/min for 3min to obtain a uniform carbon fiber precursor dispersion liquid.
Transferring the carbon fiber precursor dispersion liquid into a paper sheet former by adopting a wet forming technology, and dehydrating for 90s under the vacuum condition that the vacuum degree is 0.06MPa to ensure that the carbon fibersThe precursor dispersion was passed through a stainless steel screen to form a uniform thickness (0.95 mm) of 20X 20cm on the surface of the screen 2 The paper of (1); putting the paper into a multi-stage step-by-step program temperature control tube furnace, introducing air with the flow of 0.5L/min, heating the paper to 200 ℃ from room temperature at the heating rate of 5.5 ℃/min, and keeping the temperature for 12min; then heating to 270 ℃ from 200 ℃ at the heating rate of 2.5 ℃/min, and preserving heat for 50min; then the temperature is increased from 270 ℃ to 325 ℃ at the heating rate of 9 ℃/min, and the temperature is kept for 45min. Then, the obtained product is put into a methanol solution of boron phenolic resin (the mass fraction of the boron phenolic resin is 16%) and dipped for 35min at normal pressure, and the obtained product is taken out and dried for 30min in a forced air drying oven at the temperature of 85 ℃ to obtain polyacrylonitrile-based carbon fiber base paper (the gram weight of the polyacrylonitrile-based carbon fiber base paper is 150 g/m) 2 )。
Dissolving an acrylonitrile-N-vinylformamide copolymer in N, N-dimethylformamide, preparing a solution with the mass fraction of 18%, standing and swelling the solution in a water bath at 75 ℃, performing magnetic stirring (the rotating speed is 820 r/min) and standing and defoaming at 75 ℃, wherein the standing and swelling, magnetic stirring and standing and defoaming time are 8h, and thus obtaining the electrostatic spinning precursor solution.
The polyacrylonitrile-based carbon fiber base paper is used as a receiver, an electrostatic spinning precursor solution is uniformly sprayed on the receiver through electrostatic spinning (the positive pressure is 12kV, the negative pressure is-2.5 kV, the receiving distance is 15 cm), the sprayed thickness is 0.05mm, and the spinning time is 5 hours. And then hot-pressing and curing the polyacrylonitrile-based carbon fiber base paper by a flat vulcanizing machine at the temperature of 165 ℃ for 15min under the pressure of 12MPa to obtain the hot-pressed and cured polyacrylonitrile-based carbon fiber base paper. Putting the polyacrylonitrile-based carbon fiber base paper subjected to hot pressing curing into a grading multi-step program temperature control tubular furnace for one-step carbonization and graphitization treatment: in high-purity nitrogen, raising the temperature from room temperature to 1200 ℃ at the heating rate of 7 ℃/min, and preserving the temperature for 7min for carbonization treatment; and then heating from 1200 ℃ to 2400 ℃ at the heating rate of 6 ℃/min, and preserving heat for 12min for graphitization treatment to obtain the hydrophobic modified carbon fiber paper.
The gram weight of the hydrophobically modified carbon fiber paper of the embodiment is 100g/m 2 Contact angle of 128.5 degrees and air permeability of 83m 3 ·(m 2 ·s·bar) -1 。
Comparative example 1
The preparation method comprises the steps of preparing carbon fiber paper by adopting a traditional wet forming technology, adding commercial chopped polyacrylonitrile-based carbon fibers (the model is T-700, the length is 9 mm) into a fiber dissociator, then adding surfactant hydroxymethyl cellulose and polyoxyethylene 68441-17-8 aqueous solutions (the mass concentrations of the hydroxymethyl cellulose and the polyoxyethylene 68441-17-8 in the aqueous solutions are both 0.1%), and dispersing for 3min at a stirring speed of 500r/min to obtain a carbon fiber dispersion liquid.
Transferring the carbon fiber dispersion to a paper sheet former by wet forming technology, dehydrating for 100s under the vacuum condition of 0.05MPa to make the carbon fiber dispersion pass through a stainless steel filter screen, and forming 20 × 20cm with uniform thickness on the surface of the filter screen 2 The paper of (1); soaking the boron phenolic resin in a methanol solution of the boron phenolic resin (the mass fraction of the boron phenolic resin is 10%), taking out the boron phenolic resin, drying the boron phenolic resin in a forced air drying oven for 30min at 100 ℃, then carrying out hot-pressing curing by a flat vulcanizing machine at 160 ℃, the time of the hot-pressing curing is 30min, the pressure is 10MPa, and finally, in high-purity nitrogen, heating the boron phenolic resin from room temperature to 1000 ℃ at the heating rate of 5 ℃/min, and carrying out heat preservation for 10min for carbonization treatment; and then heating from 1000 ℃ to 2400 ℃ at the heating rate of 5 ℃/min, and preserving the temperature for 15min for graphitization treatment to obtain the carbon fiber paper.
The contact angle of the carbon fiber paper of this comparative example is shown in fig. 4, and it can be seen from fig. 4 that the contact angle of the carbon fiber paper is only 101.7 °.
The grammage of the carbon fiber paper of this comparative example was 120g/m 2 Air permeability of 85m 3 ·(m 2 ·s·bar) -1 。
According to the embodiment and the comparative example, the hydrophobic modified carbon fiber paper prepared by the method has the advantages that the hydrophobicity is obviously improved, the air permeability is not obviously changed, the precise control of the hydrophobicity and the air permeability is realized, a new design idea is provided for the hydrophobic modification of the carbon fiber paper for the PEMFC, the whole process flow only needs one-time carbonization and graphitization, the process is simple, the energy consumption is low, and the foundation is laid for the actual industrial production.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. The preparation method of the hydrophobic modified carbon fiber paper is characterized by comprising the following steps:
1) Preparing polyacrylonitrile-based precursor fibers from the acrylonitrile-N-vinylformamide copolymer by a dry spraying wet method, and carrying out short-cut treatment to obtain polyacrylonitrile-based short-cut fiber precursor fibers;
2) Mixing polyacrylonitrile-based chopped fiber protofilaments and a surfactant solution, and then sequentially carrying out wet papermaking, pre-oxidation, resin solution impregnation and drying treatment to obtain polyacrylonitrile-based carbon fiber base paper;
3) Mixing an acrylonitrile-N-vinyl formamide copolymer with a solvent to obtain a solution, and sequentially swelling, stirring and defoaming the solution to obtain a precursor solution;
4) And (3) electrospinning the precursor solution on polyacrylonitrile-based carbon fiber base paper through electrostatic spinning, and sequentially performing hot-pressing solidification, carbonization and graphitization to obtain the hydrophobic modified carbon fiber paper.
2. The preparation method of claim 1, wherein the polyacrylonitrile-based chopped strand fibers of step 1) have a length of 7-26 mm, a diameter of 4-10 μm, and an orientation degree of not less than 92%.
3. The preparation method according to claim 1 or 2, characterized in that the surfactant in step 2) comprises one or more of polyethylene oxide, hydroxymethyl cellulose and polyacrylamide, and the mass concentration of the surfactant solution is 0.05-0.3%; the temperature of the drying treatment is 50-100 ℃, and the time of the drying treatment is 30-60 min.
4. The preparation method according to claim 3, wherein the pre-oxidation in step 2) is carried out by pre-oxidizing paper obtained by wet papermaking at 170-210 ℃ for 10-20 min, 240-280 ℃ for 20-80 min and 300-330 ℃ for 30-50 min in sequence;
the heating rate from room temperature to 170-210 ℃ is 3-7 ℃/min, the heating rate from 170-210 ℃ to 240-280 ℃ is 0.5-3 ℃/min, and the heating rate from 240-280 ℃ to 300-330 ℃ is 5-10 ℃/min.
5. The preparation method according to claim 3, wherein in the step 2), the mass concentration of the resin solution is 5 to 20%, and the impregnation time of the resin solution is 10 to 40min; in the resin solution, the resin is boron phenolic resin, and the solvent is methanol and/or ethanol.
6. The preparation method according to claim 4 or 5, characterized in that, in the solution in the step 3), the mass concentration of the acrylonitrile-N-vinylformamide copolymer is 10-20%, and the swelling, stirring and defoaming time is independently 6-12 h; the swelling, stirring and defoaming temperatures are independently 50-90 ℃.
7. The preparation method according to claim 6, wherein the time of the electrostatic spinning in the step 4) is 2 to 5 hours; in the electrostatic spinning process, the thickness of the sprayed precursor solution is 0.02-0.06 mm; the temperature of the hot-pressing curing is 130-170 ℃, the pressure of the hot-pressing curing is 5-15 MPa, and the time of the hot-pressing curing is 10-30 min.
8. The method according to claim 7, wherein the temperature of the carbonization in the step 4) is 800-1300 ℃, and the carbonization time is 5-15 min; the graphitization temperature is 2200 to 2600 ℃, and the graphitization time is 10 to 20min;
the temperature rising rate from room temperature to carbonization temperature and the temperature rising rate from carbonization temperature to graphitization temperature are independently 3-9 ℃/min; the carbonization and the graphitization are carried out under the protection of high-purity nitrogen.
9. The method of any one of claims 1 to 8The hydrophobic modified carbon fiber paper prepared by the preparation method is characterized in that the gram weight of the hydrophobic modified carbon fiber paper is 60-180 g/m 2 The contact angle is 125-135 degrees, and the air permeability is 75-100 m 3 ·(m 2 ·s·bar) -1 (ii) a The carbon fiber paper comprises a carbon fiber film, and the thickness of the carbon fiber film is 0.01-0.04 mm.
10. Use of the hydrophobically modified carbon fiber paper of claim 9 in a gas diffusion layer of a proton exchange membrane fuel cell.
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