CN112761025A - Carbon paper for gas diffusion layer, preparation method thereof and fuel cell - Google Patents
Carbon paper for gas diffusion layer, preparation method thereof and fuel cell Download PDFInfo
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- CN112761025A CN112761025A CN201911066598.3A CN201911066598A CN112761025A CN 112761025 A CN112761025 A CN 112761025A CN 201911066598 A CN201911066598 A CN 201911066598A CN 112761025 A CN112761025 A CN 112761025A
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/88—Processes of manufacture
- H01M4/8803—Supports for the deposition of the catalytic active composition
- H01M4/8807—Gas diffusion layers
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Abstract
In order to overcome the problems of low porosity and poor hydrophobicity of the existing carbon paper for the gas diffusion layer of the fuel cell, the invention provides the carbon paper for the gas diffusion layer, which comprises a three-dimensional cross-linked fiber membrane formed by a plurality of carbon fibers, wherein macropores are formed among the plurality of carbon fibers, a plurality of micropores are formed in the interior and on the surface of each carbon fiber, and the micropores are communicated with the macropores. Meanwhile, the invention also discloses a preparation method of the carbon paper for the gas diffusion layer and a fuel cell. The carbon paper for the gas diffusion layer provided by the invention has better air permeability and drainage performance, and effectively improves the battery performance in a high current density area.
Description
Technical Field
The invention belongs to the technical field of fuel cells, and particularly relates to carbon paper for a gas diffusion layer, a preparation method of the carbon paper and a fuel cell.
Background
As an important component in fuel cells, the gas diffusion layer can affect the transport of reactants and products and the electrical conductivity characteristics, which in turn affects the fuel cell performance. At present, the base material of the gas diffusion layer mainly comprises carbon fiber paper, carbon fiber woven cloth, non-woven fabric, carbon black paper and the like, and the high-performance carbon paper is widely adopted. Carbon paper is usually made by adding carbon fiber with a proper amount of adhesive by a paper making process, then impregnating carbonized resin, hot-pressing, curing and shaping, and high-temperature carbonization treatment, has a uniform porous structure, good strength and excellent conductivity, is a core component of a fuel cell, can play a role in supporting a catalyst layer and providing an electronic channel, a gas channel and a drainage channel for electrode reaction.
The ideal gas diffusion layer should have the following properties: (1) good hydrophobic property; (2) good air permeability; (3) good conductive performance. The hydrophobic property can be realized by adding a water repellent on the conductive net, and the air permeability and the electric conductivity are related to the porosity of the conductive net, and researches show that the air permeability of the carbon paper is increased along with the increase of the porosity, but the electric conductivity is reduced along with the increase of the porosity, however, the good air permeability is relatively more important for the carbon paper, so that the carbon paper with larger porosity is beneficial to be selected. The current common method is to add a microporous layer into the carbon paper, which can not only increase the air permeability of the gas diffusion layer, but also ensure the hydrophobicity and the electrical conductivity. Generally, the microporous layer is composed of conductive carbon black and hydrophobic Polytetrafluoroethylene (PTFE), however, such microporous layer still has the problems of low porosity, undesirable gas channels, decreased cell performance in case of large current discharge, and gradual oxidation of carbon black material under long-term operation environment of the fuel cell, making the microporous layer hydrophilic, increasing mass transfer polarization, shortening the service life and stability of the cell.
When the gas diffusion layer requires gradient porosity and hydrophobicity, the prior technical scheme is that coating materials consisting of different types of conductive agents and adhesives are added, the preparation is generally divided into two steps, a carbon paper substrate is prepared firstly, and then the microporous layer is prepared by adopting the coating materials, and the preparation methods need to use a hydrophobic agent, so that the conductive powder is bonded with each other while the hydrophobicity of the conductive powder is improved. The conventional water repellent such as polytetrafluoroethylene, monotetrafluoroethylene, polyvinylidene fluoride, polypropylene, etc. has no conductivity and poor stability, and more importantly, the gas diffusion layer prepared using the conductive powder has small porosity and average pore size, which is not favorable for the transmission of reaction gas and water vapor. The conductive agent and the water repellent have triple composite effects of changing the pore structure of the diffusion layer and the conductivity and the hydrophobicity, but the network structure consisting of the conductive agent and the water repellent is used for adjusting the micro-pore layer structure of the fuel cell, so that the structure with special functions is difficult to obtain.
Disclosure of Invention
The invention provides carbon paper for a gas diffusion layer, a preparation method thereof and a fuel cell, aiming at the problems of low porosity and poor hydrophobicity of the existing carbon paper for the gas diffusion layer of the fuel cell.
The technical scheme adopted by the invention for solving the technical problems is as follows:
in one aspect, the present invention provides a carbon paper for a gas diffusion layer, including a three-dimensionally crosslinked fibrous membrane formed of a plurality of carbon fibers, the plurality of carbon fibers having macropores formed therebetween, each of the interior and the surface of a single carbon fiber having a plurality of micropores formed therein, the micropores communicating with the macropores.
Optionally, the carbon fiber is graphitized carbon fiber.
Optionally, the graphitized carbon fiber is obtained by heating and converting mixed fibers of a porous carbon material and mesophase pitch.
Optionally, the porous carbon material is selected from one or more of three-dimensional graphene, microporous carbon, or mesoporous carbon.
Optionally, the porous carbon material is granular, and the particle size is 0.1-1 um.
Optionally, the pore diameter range of the micropores is 5-50 nm.
Optionally, the diameter of the carbon fiber is 5-20 um, and the porosity of the fiber membrane is 80% -90%.
In another aspect, the present invention provides a method for preparing a carbon paper for a gas diffusion layer as described above, comprising the following steps:
mixing a porous carbon material into the mesophase pitch, fully stirring and swelling to prepare the mesophase pitch modified by the porous carbon material;
fusing and spinning the mesophase pitch modified by the porous carbon material to prepare a nascent fiber membrane;
pre-oxidizing the nascent fiber membrane to obtain a pre-oxidized fiber membrane;
and carrying out heat treatment on the pre-oxidized fiber membrane under a protective atmosphere to graphitize the fibers in the pre-oxidized fiber membrane to obtain a three-dimensional cross-linked fiber membrane formed by a plurality of carbon fibers.
Optionally, before mixing the porous carbon material, crushing the porous carbon material to obtain particles with a particle size of 0.1-1 um, wherein the pore size of the porous carbon material is 5-50 nm, adding the porous carbon material into the molten mesophase pitch, stirring and swelling for 15-30 min, shearing at a high speed for 90-120 min, and keeping the temperature at 300-350 ℃ to obtain the mesophase pitch modified by the porous carbon material.
Optionally, in the intermediate phase asphalt modified by the porous carbon material, the mass ratio of the porous carbon material to the intermediate phase asphalt is 3-6: 100.
optionally, the nascent fiber membrane is prepared by melt-jet spinning or electrostatic spinning.
Optionally, the nascent fiber membrane is prepared by adopting an electrostatic spinning mode, wherein the spinning temperature is 300-350 ℃, the spinning voltage is 10-20 kV, the injection speed is 0.3-0.8 mm/h, the distance between a receiving plate and a spinning nozzle is 10-20 cm, and the thickness of the nascent fiber membrane is 0.5-0.8 mm.
Optionally, in the pre-oxidation operation, the nascent fiber membrane is heated to 180-200 ℃ at a speed of 3-6 ℃/min, then heated to 270-300 ℃ at a speed of 0.5-2 ℃/min, and kept at a constant temperature for 30-60 min.
Optionally, the heat treatment of the pre-oxidized fiber film under a protective atmosphere includes a carbonization treatment and a graphitization treatment.
Optionally, in the carbonization treatment operation, the pre-oxidized fiber film is heated to 500-600 ℃ at a speed of 6-10 ℃/min under a protective atmosphere, the temperature is kept for 5-10 min, then the temperature is heated to 1200-1400 ℃ at a speed of 4-6 ℃/min, and the temperature is kept for 30-40 min.
Optionally, in the graphitization treatment operation, the temperature is raised to 2800-3000 ℃ at a rate of 20-40 ℃/min under a protective atmosphere, and the temperature is kept for 20-30 min.
In another aspect, the present invention provides a fuel cell comprising the carbon paper for a gas diffusion layer as described above.
According to the carbon paper for the gas diffusion layer, the fiber membrane is formed by three-dimensionally crosslinking the plurality of carbon fibers, a large number of micropores are formed in the single carbon fiber and on the surface of the single carbon fiber and are communicated with the macropores among the carbon fibers, so that the air permeability and the water drainage performance of the carbon paper for the gas diffusion layer are effectively improved, the porosity and the water management capacity of the carbon paper are improved, and on the other hand, the carbon fibers have better electric conductivity and hydrophobicity, and no water repellent is required to be additionally added, so that the battery performance in a high current density area is improved.
Drawings
Fig. 1 is a microscopic view of a carbon paper for a gas diffusion layer provided in example 1 of the present invention;
FIG. 2 is a microscopic view of a porous carbon material provided by an embodiment of the present invention.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The embodiment of the invention provides carbon paper for a gas diffusion layer, which comprises a three-dimensional cross-linked fiber membrane formed by a plurality of carbon fibers, wherein macropores are formed among the plurality of carbon fibers, a plurality of micropores are formed in the interior and on the surface of each carbon fiber, and the micropores are communicated with the macropores.
The carbon paper for the gas diffusion layer forms a fiber membrane through three-dimensional crosslinking of a plurality of carbon fibers, a large number of micropores are formed in the single carbon fiber and on the surface of the single carbon fiber and are communicated with macropores among the carbon fibers, so that the air permeability and the drainage performance of the carbon paper for the gas diffusion layer are effectively improved, the porosity and the water management capacity of the carbon paper are improved, and on the other hand, the carbon fibers have better electric conductivity and hydrophobicity, and no water repellent is required to be additionally added, so that the battery performance in a high current density area is improved.
In some embodiments, the carbon fibers are graphitized carbon fibers.
Compared with common carbon fibers, the carbon fibers are graphitized, so that the strength and tensile modulus of the carbon fibers can be effectively improved, and the mechanical strength of the carbon paper for the gas diffusion layer is improved.
In a more preferred embodiment, the graphitized carbon fibers are obtained by heating and converting mixed fibers of a porous carbon material and mesophase pitch.
The porous carbon material forms micropores in the graphitized carbon fiber, so that the porosity of the carbon paper for the gas diffusion layer is improved, the gas diffusion and water drainage capabilities are improved, and the porous carbon material can adapt to different functions with special requirements by adjusting the pore structure of the porous carbon material.
The mesophase pitch is a mixture composed of a plurality of flat disc-shaped fused ring aromatic hydrocarbons with the relative molecular mass of 370-2000, can form a melt at a lower temperature, such as 250-350 ℃, has strong infiltration and swelling capacity on porous carbon materials, ensures the mixing uniformity, is stable in form after cooling, is favorable for forming a fibrous structure, and can form non-woven fabrics through spinning, on the other hand, the mesophase pitch is adopted to prepare carbon fibers, the crystallinity is higher in the subsequent graphitization process, and the conductivity and mechanical properties required by carbon paper are not influenced under the condition of improving the microporous structure.
In some embodiments, the porous carbon material is selected from one or more of three-dimensional graphene, microporous carbon, or mesoporous carbon.
As shown in fig. 2, a microscopic view of the three-dimensional graphene provided by the present invention is shown.
The three-dimensional graphene has a graphitized structure, has good bonding strength with graphitized carbon fibers, can effectively ensure the fiber strength, and avoids falling off.
The microporous carbon, the mesoporous carbon and the three-dimensional graphene have the characteristics of high porosity and thin pore wall, and have better air permeability and drainage performance.
In some embodiments, the porous carbon material is in the form of particles having a particle size of 0.1 to 1 um. The inventor finds through a large number of experiments that a porous carbon material with a particle size of 0.1-1 um can ensure more micropores and can also ensure the dispersion uniformity of the porous carbon material in the mesophase pitch, if the particle size of the porous carbon material is too small, sufficient micropores are difficult to form, and if the particle size of the porous carbon material is too large, the porous carbon material is difficult to completely disperse in the mesophase pitch, so that the formation of carbon fibers is influenced.
In some embodiments, the pores have a pore size in the range of 5 to 50 nm.
Since the micropores are derived from the porous carbon material, the pore diameter range of the micropores is the pore diameter range of the porous carbon material.
In some embodiments, the carbon fibers have a diameter of 5-20 um, and the porosity of the fiber membrane is 80-90%.
Another embodiment of the present invention provides a method for preparing a carbon paper for a gas diffusion layer as described above, comprising the following steps of:
mixing a porous carbon material into the mesophase pitch, fully stirring and swelling to prepare the mesophase pitch modified by the porous carbon material;
fusing and spinning the mesophase pitch modified by the porous carbon material to prepare a nascent fiber membrane;
pre-oxidizing the nascent fiber membrane to obtain a pre-oxidized fiber membrane;
and carrying out heat treatment on the pre-oxidized fiber membrane under a protective atmosphere to graphitize the fibers in the pre-oxidized fiber membrane to obtain a three-dimensional cross-linked fiber membrane formed by a plurality of carbon fibers.
According to the preparation method provided by the invention, the intermediate phase pitch modified by the porous carbon material is melted and spun to prepare the nascent fiber membrane, and then the nascent fiber membrane is further subjected to pre-oxidation and graphitization, so that the porous carbon material can be effectively embedded into the carbon fibers of the fiber membrane, and a structure with micropores communicated with macropores between the carbon fibers is further formed, and the purposes of improving the air permeability and the water permeability are realized.
Compared with the prior art, the method has the advantages that the porous carbon material is introduced in the process of preparing the carbon fiber raw material, so that a large number of microporous structures are formed on the nascent fiber membrane, the step-by-step operation of firstly preparing the carbon paper substrate and then preparing the microporous layer in the traditional method is avoided, the preparation efficiency is improved, and the air permeability and the water permeability of the prepared fiber membrane are greatly improved.
In some embodiments, in order to ensure sufficient mixing of a porous carbon material in mesophase pitch and avoid the influence of the porous carbon material on fiber forming, before the porous carbon material is mixed, the porous carbon material is crushed into particles with the particle size of 0.1-1 um, the pore size of the porous carbon material is 5-50 nm, the porous carbon material is added into molten mesophase pitch, stirred and swelled for 15-30 min, the temperature of the molten mesophase pitch is 250-300 ℃, and then sheared at a high speed for 90-120 min, the temperature is maintained at 300-350 ℃, and the rotating speed is 5000-6000 r/min, so that the mesophase pitch modified by the porous carbon material is obtained.
The crushing treatment mode can adopt ball milling or air flow crushing.
In some embodiments, in the porous carbon material modified mesophase pitch, the mass ratio of the porous carbon material to the mesophase pitch is 3-6: 100.
if the amount of the porous carbon material added is too small, the number of micropores formed inside the carbon fiber is likely to be small; if the amount of the porous carbon material added is too large, the mesophase pitch is likely to be difficult to spin into fibers.
In some embodiments, the nascent fiber membrane is prepared by melt-jet spinning or electrospinning.
In a preferred embodiment, the nascent fiber membrane is prepared by adopting an electrostatic spinning mode, the spinning temperature is 300-350 ℃, the spinning voltage is 10-20 kV, the injection speed is 0.3-0.8 mm/h, the distance between a receiving plate and a spinning nozzle is 10-20 cm, and the thickness of the nascent fiber membrane is 0.5-0.8 mm.
The method for preparing the nascent fiber membrane by adopting electrostatic spinning is beneficial to obtaining the fiber membrane with a smoother surface, and the thickness of the nascent fiber membrane is controlled by controlling the spinning time.
In some embodiments, in the pre-oxidation operation, the nascent fiber membrane is heated to 180-200 ℃ at a speed of 3-6 ℃/min, then heated to 270-300 ℃ at a speed of 0.5-2 ℃/min, and kept at a constant temperature for 30-60 min. Then naturally cooling to room temperature.
The purpose of the pre-oxidation operation is to prevent the melting of the precursor during carbonization, and the fiber molecules contain hydroxyl and carbonyl groups through oxidation reaction, so that hydrogen bonds can be formed between molecules and in molecules, thereby improving the thermal stability of the fiber
In the pre-oxidation operation of the invention, low-speed slow temperature rise oxidation is adopted, the heat utilization efficiency of the operation is higher, the skin-core structure of the fiber can be weakened, and the fiber strength is improved.
In some embodiments, the heat treatment of the pre-oxidized fiber film under a protective atmosphere includes a carbonization treatment and a graphitization treatment.
The protective atmosphere may be selected from nitrogen or an inert gas.
In some embodiments, in the carbonization treatment operation, the pre-oxidized fiber film is heated to 500-600 ℃ at a speed of 6-10 ℃/min under a protective atmosphere, and is subjected to heat preservation for 5-10 min, and then heated to 1200-1400 ℃ at a speed of 4-6 ℃/min, and is subjected to heat preservation for 30-40 min. Then naturally cooling to room temperature.
The non-carbon atoms of the fibers in the pre-oxidized fiber film can be thermally decomposed and removed by carbonization treatment, so that the pitch-based fibers form carbon fibers.
In some embodiments, in the graphitization treatment operation, the temperature is raised to 2800-3000 ℃ at a rate of 20-40 ℃/min under a protective atmosphere, and the temperature is maintained for 20-30 min. Then naturally cooling to room temperature.
Residual heteroatoms in the carbon fibers can be further removed through graphitization treatment, and simultaneously, carbon-carbon rearrangement is carried out, so that the size of a layer sheet is increased, the proportion of crystalline carbon is increased, and the mechanical strength and the conductivity are improved.
The invention provides a fuel cell comprising the carbon paper for a gas diffusion layer as described above.
Specifically, in some embodiments, the fuel cell includes a proton exchange membrane, an anode catalyst layer, a cathode catalyst layer, and two carbon papers for gas diffusion layers, where the anode catalyst layer and the cathode catalyst layer are respectively located on two sides of the proton exchange membrane, one of the carbon papers for gas diffusion layers is located on a side of the anode catalyst layer facing away from the proton exchange membrane, and the other carbon paper for gas diffusion layers is located on a side of the cathode catalyst layer facing away from the proton exchange membrane.
The present invention will be further illustrated by the following examples.
Example 1
This example is used to illustrate the carbon paper for a gas diffusion layer and the preparation method thereof disclosed in the present invention, and includes the following steps:
crushing three-dimensional graphene microporous carbon by using a jet mill, controlling the average size of particles to be about 0.5um, controlling the aperture range of the three-dimensional graphene microporous carbon to be 5-15 nm, adding 50g of three-dimensional graphene microporous carbon powder into 1kg of mesophase pitch (AR pitch), fully stirring in a melting stirrer, stirring at 280 ℃ for 30min, standing for swelling, taking out modified pitch after 30min, putting the modified pitch into a high-speed shearing machine, and shearing at a high speed of 100min, wherein the temperature is kept at 320 ℃ and the rotating speed is 5000r/min in the shearing process to obtain the active mesophase pitch modified by the three-dimensional graphene microporous carbon.
The active mesophase pitch-based carbon fiber membrane, namely the nascent fiber membrane, is prepared by adopting an electrostatic spinning process, wherein the spinning temperature is 320 ℃, the spinning voltage is 15kV, the injection speed is 0.5mm/h, the distance between a receiving plate and a spinning nozzle is 15cm, the thickness of the carbon fiber membrane is controlled by controlling the spinning time, the spinning time is 2h, and the thickness of the nascent fiber membrane is about 0.6 mm.
And pre-oxidizing the obtained nascent fiber membrane, heating the nascent fiber membrane to 180 ℃ from room temperature (about 30 ℃) at the speed of 5 ℃/min in a low-speed slow heating mode, then heating the nascent fiber membrane to 300 ℃ at the speed of 1 ℃/min, keeping the temperature for 50min, and naturally cooling the nascent fiber membrane to the room temperature to obtain the pre-oxidized fiber membrane.
Taking out the pre-oxidized fiber membrane to carry out carbonization in a carbonization furnace in nitrogen atmosphere, heating to 600 ℃ from room temperature (about 30 ℃) at the speed of 10 ℃/min, preserving heat for 10min, then heating to 1400 ℃ at the speed of 5 ℃/min, keeping the temperature for 30min, and then naturally cooling to room temperature. And (2) placing the carbonized fiber membrane into a graphitization furnace, introducing high-purity nitrogen to replace the residual air in the furnace chamber until the oxygen content in an oxygen analyzer is lower than 2ppm and the temperature in a dew point instrument is lower than-72 ℃, starting to heat up for graphitization treatment, heating from room temperature (about 30 ℃) to 2800 ℃ at the speed of 30 ℃/min, standing at the final temperature for 30min, and naturally cooling to the room temperature after the graphitization is finished to obtain the carbon paper for the gas diffusion layer.
Example 2
This example is used to illustrate the carbon paper for a gas diffusion layer and the preparation method thereof disclosed in the present invention, and includes most of the operation steps in example 1, except that:
crushing three-dimensional graphene microporous carbon by using a jet mill, controlling the average size of particles to be about 0.1um, controlling the aperture range of the three-dimensional graphene microporous carbon to be 15-25 nm, adding 60g of three-dimensional graphene microporous carbon powder into 1kg of mesophase pitch (AR pitch), fully stirring in a melting stirrer, stirring at 280 ℃ for 30min, standing for swelling, taking out modified pitch after 30min, putting the modified pitch into a high-speed shearing machine, and shearing at a high speed of 100min, wherein the temperature is kept at 320 ℃ and the rotating speed is 5000r/min in the shearing process to obtain the active mesophase pitch modified by the three-dimensional graphene microporous carbon.
Example 3
This example is used to illustrate the carbon paper for a gas diffusion layer and the preparation method thereof disclosed in the present invention, and includes most of the operation steps in example 1, except that:
the preparation method comprises the following steps of crushing three-dimensional graphene microporous carbon by using a jet mill, controlling the average size of particles to be about 2um, controlling the aperture range of the three-dimensional graphene microporous carbon to be 25-40 nm, adding 30g of three-dimensional graphene microporous carbon powder into 1kg of mesophase pitch (AR pitch), fully stirring in a melting stirrer, stirring at 280 ℃ for 30min, standing for swelling, taking out modified pitch after 30min, putting the modified pitch into a high-speed shearing machine, and shearing at a high speed of 320 ℃ and a rotating speed of 5000r/min in the shearing process to obtain the active mesophase pitch modified by the three-dimensional graphene microporous carbon.
Example 4
This example is used to illustrate the carbon paper for a gas diffusion layer and the preparation method thereof disclosed in the present invention, and includes most of the operation steps in example 1, except that:
and pre-oxidizing the obtained nascent fiber membrane, heating the nascent fiber membrane to 300 ℃ from room temperature (about 30 ℃) at the speed of 10 ℃/min by adopting a rapid heating mode, keeping the temperature for 50min, and naturally cooling the nascent fiber membrane to the room temperature to obtain the pre-oxidized fiber membrane.
Comparative example 1
This comparative example is for comparative illustration of the carbon paper for a gas diffusion layer and the preparation method thereof disclosed in the present invention, including most of the operation steps in example 1, except that:
crushing graphite by using a jet mill to control the average size of particles to be about 0.5um, adding 50g of graphite powder into 1kg of intermediate phase asphalt (AR asphalt), fully stirring in a melting stirrer, stirring at 280 ℃ for 30min, standing for swelling, taking out the modified asphalt after 30min, putting the modified asphalt into a high-speed shearing machine, and shearing at a high speed for 100min, wherein the temperature is kept at 320 ℃ and the rotating speed is 5000r/min in the shearing process to prepare the graphite powder modified active intermediate phase asphalt.
Comparative example 2
This comparative example is for comparative illustration of the carbon paper for a gas diffusion layer and the preparation method thereof disclosed in the present invention, including most of the operation steps in example 1, except that:
1kg of mesophase pitch was taken in place of the three-dimensional graphene microporous carbon modified active mesophase pitch of example 1.
Performance testing
The microstructure of the carbon paper for a gas diffusion layer prepared in example 1 was observed by a scanning electron microscope, as shown in fig. 1, a three-dimensional cross-linked network skeleton was formed between fibers, and as can be seen from the fiber surface and the fiber cross-sectional view, a large number of micropores were formed both inside and on the surface of a single fiber, and these micropores were interconnected and communicated with macropores between the fiber skeleton, so that the air permeability of the carbon paper was greatly enhanced.
The carbon paper for the gas diffusion layer prepared in examples 1 to 4 was subjected to the test of mechanical strength and resistivity, the test method was as follows:
testing the tensile strength of the carbon paper by using a ZLL30 paper tension tester (Yibin paper mill, Sichuan); the volume resistance is measured by adopting a ZC-36 high-impedance instrument and a QJ23 direct-current bridge, and then the volume resistance is converted into the volume resistivity. The test results obtained are filled in Table 1.
TABLE 1
From the test results in table 1, it can be seen that the carbon paper for the gas diffusion layer provided by the invention has good mechanical strength and electrical properties, and can meet the use requirements of a fuel cell, and meanwhile, as can be seen from comparison of examples 1 to 3 and example 4, the skin-core structure of the fiber can be weakened and the fiber strength can be improved by adopting a slow temperature rise manner for pre-oxidation.
Porosity tests were performed on the carbon papers for gas diffusion layers prepared in examples 1 to 4 and comparative examples 1 and 2, and the test methods were as follows:
the porosity of the carbon paper was tested using an american microphone AutoPore IV 9500 mercury porosimeter. The test results obtained are filled in table 2.
TABLE 2
As can be seen from the test results in table 2, compared with the method in which no porous carbon material is added or solid graphite powder is added, the carbon paper for the gas diffusion layer prepared by the method provided by the present invention has higher porosity.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (17)
1. The carbon paper for the gas diffusion layer is characterized by comprising a three-dimensional cross-linked fiber membrane formed by a plurality of carbon fibers, wherein macropores are formed among the plurality of carbon fibers, a plurality of micropores are formed in the interior and the surface of each carbon fiber, and the micropores are communicated with the macropores.
2. The carbon paper for a gas diffusion layer according to claim 1, wherein the carbon fiber is graphitized carbon fiber.
3. The carbon paper for a gas diffusion layer according to claim 2, wherein the graphitized carbon fiber is obtained by heat conversion of a mixed fiber of a porous carbon material and a mesophase pitch.
4. The carbon paper for a gas diffusion layer according to claim 3, wherein the porous carbon material is selected from one or more of three-dimensional graphene, microporous carbon, or mesoporous carbon.
5. The carbon paper for a gas diffusion layer according to claim 3, wherein the porous carbon material is in the form of particles having a particle size of 0.1 to 1 um.
6. The carbon paper for a gas diffusion layer according to claim 1, wherein the pores have a pore size ranging from 5 to 50 nm.
7. The carbon paper for a gas diffusion layer according to claim 1, wherein the carbon fiber has a diameter of 5 to 20um, and the porosity of the fiber membrane is 80 to 90%.
8. The method for preparing a carbon paper for a gas diffusion layer according to any one of claims 1 to 7, comprising the steps of:
mixing a porous carbon material into the mesophase pitch, fully stirring and swelling to prepare the mesophase pitch modified by the porous carbon material;
fusing and spinning the mesophase pitch modified by the porous carbon material to prepare a nascent fiber membrane;
pre-oxidizing the nascent fiber membrane to obtain a pre-oxidized fiber membrane;
and carrying out heat treatment on the pre-oxidized fiber membrane under a protective atmosphere to graphitize the fibers in the pre-oxidized fiber membrane to obtain a three-dimensional cross-linked fiber membrane formed by a plurality of carbon fibers.
9. The method for preparing the carbon paper for the gas diffusion layer according to claim 8, wherein the porous carbon material is pulverized before being mixed, the porous carbon material is pulverized into particles with a particle size of 0.1-1 um, the pore size of the porous carbon material is in a range of 5-50 nm, the porous carbon material is added into the molten mesophase pitch, stirred and swelled for 15-30 min, and then sheared at a high speed for 90-120 min, and the temperature is maintained at 300-350 ℃, so that the mesophase pitch modified by the porous carbon material is obtained.
10. The method for preparing the carbon paper for the gas diffusion layer according to claim 8, wherein the mass ratio of the porous carbon material to the mesophase pitch in the mesophase pitch modified with the porous carbon material is 3 to 6: 100.
11. the method of preparing a carbon paper for a gas diffusion layer according to claim 8, wherein the as-spun fiber membrane is prepared by melt-jet spinning or electrospinning.
12. The method for preparing the carbon paper for the gas diffusion layer according to claim 9, wherein the nascent fiber membrane is prepared by electrospinning at a spinning temperature of 300 ℃ to 350 ℃, a spinning voltage of 10 kV to 20kV, an injection speed of 0.3 mm/h to 0.8mm/h, a distance between a receiving plate and a spinneret of 10 cm to 20cm, and a thickness of the nascent fiber membrane of 0.5mm to 0.8 mm.
13. The method for preparing the carbon paper for the gas diffusion layer according to claim 8, wherein in the pre-oxidation operation, the nascent fiber membrane is heated to 180-200 ℃ at a rate of 3-6 ℃/min, then heated to 270-300 ℃ at a rate of 0.5-2 ℃/min, and kept at a constant temperature for 30-60 min.
14. The method of manufacturing a carbon paper for a gas diffusion layer according to claim 8, wherein the heat treatment of the pre-oxidized fiber membrane under a protective atmosphere includes a carbonization treatment and a graphitization treatment.
15. The method for preparing the carbon paper for the gas diffusion layer according to claim 14, wherein in the carbonization treatment, the pre-oxidized fiber membrane is heated to 500-600 ℃ at a rate of 6-10 ℃/min under a protective atmosphere, and is subjected to heat preservation for 5-10 min, and then heated to 1200-1400 ℃ at a rate of 4-6 ℃/min, and is subjected to heat preservation for 30-40 min.
16. The method for preparing the carbon paper for the gas diffusion layer according to claim 14, wherein in the graphitization treatment, the temperature is raised to 2800-3000 ℃ at a rate of 20-40 ℃/min under a protective atmosphere, and the temperature is maintained for 20-30 min.
17. A fuel cell comprising the carbon paper for a gas diffusion layer according to any one of claims 1 to 7.
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