CN116525841A - Gas diffusion layer with gradient structure for fuel cell and preparation method thereof - Google Patents
Gas diffusion layer with gradient structure for fuel cell and preparation method thereof Download PDFInfo
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- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/8647—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites
- H01M4/8657—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites layered
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- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- 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
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- D—TEXTILES; PAPER
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- D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
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- D21H13/20—Organic non-cellulose fibres from macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
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- D21H13/36—Inorganic fibres or flakes
- D21H13/46—Non-siliceous fibres, e.g. from metal oxides
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- D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
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- H—ELECTRICITY
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- 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
- H01M4/8605—Porous electrodes
- H01M4/861—Porous electrodes with a gradient in the porosity
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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
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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
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Abstract
The invention relates to a gas diffusion layer with gradient structure for fuel cell and its preparation method, the gas diffusion layer is 2-4 composite layers, the pore diameter of each layer is gradient structure distribution, the average pore diameter of each layer is gradually reduced from bottom to top; the average pore diameter of the lowest layer in the gas diffusion layer is 20-80 mu m, and the average pore diameter of the uppermost layer is 50-1500 nm; each layer of the gas diffusion layer comprises chopped carbon fibers, carbon microfibers and resin carbon; the preparation method comprises the following steps: and sequentially stacking 2-4 pieces of carbon fiber base paper with different pore diameters from bottom to top according to the order of pore diameters from large to small, performing hot press molding, and sequentially performing impregnation curing, heat treatment and hydrophobic treatment to obtain the gas diffusion layer. The preparation method is simple, the matching property between the gas diffusion layer and the catalytic layer of the fuel cell is improved, and the prepared gas diffusion layer with the gradient structure for the fuel cell has better water guide performance, better mechanical performance and conductivity.
Description
Technical Field
The invention belongs to the technical field of fuel cells, and relates to a gas diffusion layer with a gradient structure for a fuel cell and a preparation method thereof.
Background
The Gas Diffusion Layer (GDL) is one of the important components of a Proton Exchange Membrane Fuel Cell (PEMFC), and as it supports a catalytic layer in the fuel cell, collects current, and provides multiple transport channels for fuel gas, protons, electrons, etc. Therefore, the gas diffusion layer needs to exhibit functional characteristics of high conductivity, high stability, high water management ability, high gas permeability, and the like. In early studies of gas diffusion layers, materials with a macro-porous matrix such as carbon fiber paper could be used directly as a gas diffusion layer.
Since carbon fiber paper pores are generally in the micrometer scale, and catalytic layer pores are in the nanometer scale, the direct contact of the two causes the transmission of electrons, gas and water between interfaces to be affected, and in order to realize smooth transition and better matching between the gas diffusion layer and the catalytic layer pores, a microporous layer (MPL) is successfully introduced between a macroporous matrix (MPS, i.e. carbon fiber paper) and a Catalytic Layer (CL). Generally, the gas diffusion layer is composed of a macroporous matrix and a microporous layer, wherein the macroporous matrix is served by carbon fiber paper, the microporous layer is mixed with polytetrafluoroethylene binder through nano carbon particles to prepare slurry, and the slurry is coated on the surface of the carbon fiber paper in a spraying or knife coating mode.
Chinese patent application No. 200610047931.2 discloses a method for preparing a gas diffusion layer for a fuel cell, wherein the gas diffusion layer is composed of a macroporous substrate and a microporous layer, the microporous layer slurry is formed by mixing a hydrophobic agent and a conductive carbon material, and is coated on one side of the macroporous substrate, so as to prepare the gas diffusion layer, and the assembled fuel cell has good output performance. Although good battery performance is obtained, the preparation process of the gas diffusion layer is complex, macroporous matrix materials are required to be prepared first, then the microporous layer is coated, and the whole preparation process is complex and has a plurality of control factors. Therefore, a gas diffusion layer was developed which omits the microporous layer coating step in the preparation, not only can simplify the preparation process, but also can improve the stability of the battery operation.
In order to better match the catalyst layer, high battery efficiency is obtained. The Chinese patent application 202211066247.4 provides a preparation method of a microporous layer with double gradients of hydrophobicity and air permeability, which comprises the steps of preparing two slurries containing different doses of hydrophobic agents, adding pore formers into the slurry with larger hydrophobic agent content to obtain a hydrophobic gradient structure with sequentially reduced hydrophobicity of a carbon paper substrate layer, an intermediate layer and an outer layer, sequentially reducing the pore diameters and the porosities of the hydrophobic carbon fiber paper substrate layer, the intermediate layer and the outer layer, and improving the water management and gas transmission capacity of a gas diffusion layer by adopting the microporous layer with double gradients of hydrophobicity and air permeability. However, although the porous layer is endowed with both hydrophobic and breathable properties, so that the water conductivity of the gas diffusion layer is improved, the span of the pore size gradient formed between the porous layer and the macroporous substrate is too large, and when water in the porous layer diffuses into the macroporous substrate layer, the water still stays and gathers in the porous layer, and likewise, flooding of the electrode is caused, and mass transfer of fuel gas and water is hindered. Therefore, the water management capability of the fuel cell needs to be further improved.
The requirements for the thickness, pore structure regulation and control, air permeability, normal resistance, mechanical strength and other functionalities of the gas diffusion layer are continuously improved in order to enable the fuel cell to have higher output performance. In the preparation process, the regulation and control of the thickness and pore structure of the gas diffusion layer are very difficult, the content of resin carbon in the carbon fiber paper is reduced in order to improve the air permeability, and the reduction of the content of the resin carbon can lead to the reduction of bonding points among chopped carbon fibers, so that the mechanical properties of the carbon fiber paper are reduced, and the problem of how to balance the relationship between the air permeability and the mechanical strength is challenging. In addition, the gas diffusion layer used by the current domestic fuel cell stack manufacturers is basically purchased from foreign production, for example, the preparation technology of carbon fiber paper with or without microporous layer structures produced by the SGL company in eastern and germany of japan is very mature, and is in monopoly in the market, so that the preparation cost of the domestic gas diffusion layer is increased.
Thus, it is of great importance to develop a gas diffusion layer for a fuel cell and a method for producing the same, in order to solve the above-mentioned problems.
Disclosure of Invention
The present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a gas diffusion layer having a gradient structure for a fuel cell and a method for manufacturing the same. Aiming at the problems, the invention mainly comprises the following conception: (1) The invention constructs a gas diffusion layer with a gradient structure, and the gas diffusion layer has the characteristic of functional structure integration. The gas diffusion layers with different pore diameter gradient structures can optimize the water management capacity of the battery, can drain water rapidly, do not influence the entry of gas, and enhance the performance and operation stability of the battery. (2) The constructed gradient structure is a multilayer gradient structure, wherein the uppermost layer in the gradient structure can be added with nano carbon particles as an intrinsic microporous layer, and the aperture structure is adjusted by utilizing the nano carbon particles, so that the aperture structure accords with the characteristics of the aperture structure of the microporous layer, the porous structure can be well matched with a catalytic layer, the integrated preparation of a macroporous substrate and the microporous layer is realized, the preparation process is simplified, the uniformity of a gas diffusion layer is improved, and the preparation cost is reduced. (3) In the construction of the gradient structure, the relationship between the air permeability and the mechanical strength is regulated by using the carbon microfibers, and the selection of materials generally selects carbon microfiber precursors with higher carbon residue rate. In addition, in the preparation process of the base paper, the carbon microfiber precursor has the effects of winding and bonding the chopped carbon fibers, so that the chopped carbon fibers are in better contact with each other, and the strength of the carbon fiber base paper is improved. After hot pressing, the carbon microfiber precursor structure is recombined, so that the carbon microfiber precursor structure can penetrate through the sheets mutually, and the normal bonding strength is improved. After heat treatment (carbonization and graphitization), the structure is kept through the morphology of the carbon microfibers, so that the in-plane and normal conductivity of the gas diffusion layer is improved; meanwhile, the use amount of the resin binder can be reduced in the impregnation process, the content of resin carbon in the final gas diffusion layer is reduced, and the air permeability is improved without losing mechanical strength; in addition, the carbon microfiber precursor is also beneficial to the dispersion of the chopped carbon fibers during the preparation of the slurry.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the gas diffusion layer with gradient structure for fuel cell is 2-4 composite layers, and the pore diameters of all layers are distributed in gradient structure;
the fuel cell is characterized in that the uppermost layer of the gas diffusion layer with the gradient structure is attached to a catalyst layer in the fuel cell, and the lowermost layer is attached to a bipolar plate of the fuel cell;
the average pore diameter of the lowest layer in the gas diffusion layer with the gradient structure for the fuel cell is 20-80 mu m, and the roughness is less than or equal to 15 mu m; the average pore diameter of each layer in the gas diffusion layer with the gradient structure for the fuel cell is gradually reduced from bottom to top, the average pore diameter of the uppermost layer is 50-1500 nm, and the roughness is less than or equal to 7 mu m;
each layer of the gas diffusion layer with the gradient structure for the fuel cell comprises chopped carbon fibers, carbon microfibers and resin carbon, wherein the carbon microfibers in each layer are wound around the chopped carbon fibers, and the carbon microfibers and the chopped carbon fibers are connected together by the resin carbon; the different layers are also penetrated by chopped carbon fibers in the vertical direction and are wound by carbon microfibers and connected by resin carbon.
Most of the chopped carbon fibers are stacked in the plane direction during the wet vacuum deposition, and a few of the chopped carbon fibers have a penetration phenomenon in the vertical direction. Meanwhile, in the hot pressing process, the carbon microfiber precursor can undergo structural recombination and also drive the chopped carbon fibers to be arranged in the vertical direction.
As a preferable technical scheme:
the gas diffusion layer for a fuel cell as described above, which has a gradient structure, has a thickness of 80 to 280 μm,porosity is 60-80%, air permeability is 1600-2200 (mL.mm)/(cm) 2 h.mmAq), in-plane resistivity of 3.5 to 7.0mΩ & cm, normal resistivity of 40 to 80mΩ & cm, and tensile strength of 15 to 50MPa; the tensile strength, normal resistivity, in-plane resistivity and air permeability of the invention are all tested according to the test method of the seventh part of carbon paper characteristic in the reference GB/T20042.7-2014.
The gas diffusion layer with gradient structure for the fuel cell has the advantages that the length of the chopped carbon fiber is 3-10 mm, and the average fiber diameter is 4-10 mu m; the average diameter of the carbon microfibers is 10-500 nm.
The gas diffusion layer with the gradient structure for the fuel cell is characterized in that the carbon microfiber precursor is one or more of plant pulp, chopped superfine organic fibers and chemical fiber pulp;
the plant pulp is cotton pulp, wood pulp, bamboo pulp or grass pulp; the chopped superfine organic fiber is superfine polyacrylonitrile fiber or superfine mesophase pitch-based fiber obtained through electrostatic spinning; the chemical fiber pulp is para-aramid pulp or meta-aramid pulp, polysulfonamide pulp or polyimide pulp.
The gas diffusion layer with the gradient structure for the fuel cell is a four-layer composite layer, and is sequentially a first fiber sheet layer, a second fiber sheet layer, a third fiber sheet layer and a fourth intrinsic microporous layer from bottom to top;
the average pore diameter of the first fiber sheet layer is 20-80 mu m, the average pore diameter of the second fiber sheet layer is 10-46 mu m, the average pore diameter of the third fiber sheet layer is 1-15 mu m, and the average pore diameter of the fourth intrinsic microporous layer is 50-1500 nm.
The gas diffusion layer with the aperture gradient structure constructed by the invention is preferably a gradient structure constructed by four layers of carbon fiber base papers with different aperture sizes. The pore size gradient structure with three layers or less has the disadvantages that the pore size gradient structure with four layers cannot generate enough capillary pressure difference, water is smoothly discharged out of the battery, and the supporting effect of one less fiber sheet layer on the catalytic layer is weakened. The five-layer and six-layer (i.e. more than four-layer) aperture gradient structure has the disadvantages that the gas diffusion layer is thickened as a whole, the transmission paths of protons, electrons, water and gas are increased, the mass transfer resistance is increased, and the performance of the fuel cell is influenced; in addition, the manufacturing cost is increased.
The gas diffusion layer with gradient structure for the fuel cell, wherein the fourth intrinsic microporous layer also contains nano carbon particles;
the nano carbon particles are more than one of carbon black, graphene and carbon nano tubes;
the particle size of the carbon black is 10-60 nm; the number of layers of the graphene is less than or equal to 10; the diameter of the carbon nano tube is 3-30 nm, and the length is 1-50 nm.
The invention also provides a preparation method of the gas diffusion layer with the gradient structure for the fuel cell, which comprises the steps of sequentially stacking 2-4 pieces of carbon fiber base paper with different pore diameters from bottom to top according to the order of the pore diameters from large to small, performing hot press molding, and sequentially performing impregnation curing, heat treatment and hydrophobic treatment to obtain the gas diffusion layer with the gradient structure for the fuel cell;
the carbon fiber base paper is prepared by preparing slurry by taking chopped carbon fibers and carbon microfiber precursors as main raw materials and carrying out wet papermaking.
As a preferable technical scheme:
the preparation method of the gas diffusion layer with the gradient structure for the fuel cell comprises the steps that the gas diffusion layer with the gradient structure for the fuel cell is a four-layer composite layer, the four-layer composite layer comprises a first fiber sheet layer, a second fiber sheet layer, a third fiber sheet layer and a fourth intrinsic microporous layer from bottom to top, the first fiber sheet layer, the second fiber sheet layer and the third fiber sheet layer do not contain nano carbon particles, and the fourth intrinsic microporous layer contains or does not contain nano carbon particles; the average pore diameter of the first fiber sheet layer is 20-80 mu m, the average pore diameter of the second fiber sheet layer is 10-46 mu m, the average pore diameter of the third fiber sheet layer is 1-15 mu m, and the average pore diameter of the fourth intrinsic microporous layer is 50-1500 nm; the preparation steps of the gas diffusion layer with the gradient structure for the fuel cell are specifically as follows:
(1) Preparation of carbon fiber base paper: the method comprises the steps of taking chopped carbon fibers and carbon microfiber precursors as main raw materials, and obtaining single-layer carbon fiber base papers with different aperture sizes, namely a first layer of carbon fiber base paper, a second layer of carbon fiber base paper, a third layer of carbon fiber base paper and a fourth layer of carbon fiber base paper by changing the mass ratio of the chopped carbon fibers and the carbon microfiber precursors and utilizing a wet papermaking process;
(2) Compounding four layers of carbon fiber base paper: sequentially stacking the first layer of carbon fiber base paper, the second layer of carbon fiber base paper, the third layer of carbon fiber base paper and the fourth layer of carbon fiber base paper from bottom to top;
in the preparation raw materials of the first layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers in the preparation raw materials of the carbon fiber base paper corresponding to the first layer of carbon fiber base paper is 80-95%, and the mass percentage of the carbon microfiber precursors is 5-20%;
in the preparation raw materials of the second layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers in the preparation raw materials of the carbon fiber base paper corresponding to the second layer of carbon fiber base paper is 55-75%, and the mass percentage of the carbon microfiber precursors is 25-45%;
in the preparation raw materials of the carbon fiber base paper of the third layer, the mass percentage of the chopped carbon fibers is 30-50% and the mass percentage of the carbon microfiber precursors is 50-70% in the preparation raw materials of the carbon fiber base paper corresponding to the carbon fiber base paper of the third layer;
In the preparation raw materials of the fourth layer of carbon fiber base paper, the mass percentage of the chopped carbon fiber is 10-30% and the mass percentage of the carbon microfiber precursor is 70-90% based on the total mass of the chopped carbon fiber and the carbon microfiber precursor; the nano carbon particles account for less than 35% of the total absolute dry mass of the four-layer carbon fiber composite base paper;
(3) Preparation of precursor paper with pore size gradient structure: carrying out hot pressing treatment (namely primary hot pressing) on the four layers of carbon fiber base paper compounded in the step (2) to obtain precursor paper with an aperture gradient structure;
(4) Preparation of a gas diffusion layer for a fuel cell with a gradient structure: dipping and drying the precursor paper with the pore diameter gradient structure obtained in the step (3) in a binder solution, and then performing hot press curing (namely secondary hot press), heat treatment and hydrophobic treatment to obtain a gas diffusion layer for the fuel cell;
the preparation method of the gas diffusion layer with the gradient structure for the fuel cell comprises the following steps of:
uniformly dispersing chopped carbon fibers and carbon microfiber precursors into a polyethylene oxide solution with the concentration of 0.1-0.2 wt.% according to different proportions to respectively obtain a slurry of a first layer of carbon fiber base paper, a slurry of a second layer of carbon fiber base paper and a slurry of a third layer of carbon fiber base paper; uniformly dispersing chopped carbon fibers, carbon microfiber precursors and nano carbon particles into a polyethylene oxide solution with the concentration of 0.1-0.2 wt.% to obtain a slurry of a fourth layer of carbon fiber base paper;
(1.2) respectively forming the slurry obtained in the step (1.1) through a wet paper machine to prepare a first layer of carbon fiber base paper, a second layer of carbon fiber base paper, a third layer of carbon fiber base paper and a fourth layer of carbon fiber base paper;
the aperture size in each layer can be regulated and controlled by regulating and controlling the proportion of the chopped carbon fiber, the carbon microfiber precursor and the nano carbon particles in each layer, so that the gas diffusion layer with the aperture gradient structure is constructed. Specifically, the invention provides an effective proportion regulation and control method for utilizing chopped carbon fibers and carbon microfiber precursors, which can be used for effectively regulating the pore size of a gas diffusion layer and constructing the gas diffusion layer with pore size gradient functionalization in the thickness direction.
The preparation method of the gas diffusion layer with the gradient structure for the fuel cell comprises the following process parameters of hot-pressing treatment in the step (3): the temperature is 150-320 ℃ and the pressure is 5-40 MPa;
the binder solution in the step (4) is a solution prepared by dissolving phenolic resin in absolute ethyl alcohol and having a concentration of 3 to 30 wt.%;
the hot press curing process parameters in the step (4) are as follows: the temperature is 140-220 ℃ and the pressure is 5-30 MPa;
the heat treatment conditions of the step (4) are as follows: under the protection of inert gas, the heating rate is 5 ℃/min, and carbonization treatment is carried out for 1 to 1.5 hours at the temperature of 1050 to 1200 ℃; continuously heating to 1600-2800 ℃ to carry out graphitization treatment for 30-60 min;
After graphitization treatment, phenolic resin is changed into resin carbon, a carbon microfiber precursor is changed into carbon microfibers, carbon microfibers and resin carbon are connected at the crossing nodes of the chopped carbon fibers, the carbon microfibers are distributed at the overlapping positions, the lap joints and the crossing nodes of the chopped carbon fibers, the resin carbon is intensively distributed at the crossing nodes of the chopped carbon fibers, and the carbon microfibers and the resin carbon are entangled and bonded to form a carbon fiber sheet layer, so that the formed interconnected network structure can generate more electric conduction paths;
the hydrophobic treatment conditions in the step (4) are as follows: soaking in 5-20 wt.% PTFE solution for 5-45 min, drying at 60-80 deg.c for 15-60 min, and final treating at 250-350 deg.c for 30-60 min.
The beneficial effects are that:
(1) The invention constructs a gas diffusion layer with a gradient structure, which is a composite layer of 2-4 layers, and the pore diameters of all the layers are distributed in a gradient structure, so that capillary pressure gradient is generated, the gas diffusion layer is endowed with higher unidirectional moisture-conducting performance, the problem that the fuel cell is easy to be flooded in the prior art is effectively solved, the water can be quickly conducted, the gas transmission is not influenced, and the output performance of the fuel cell is improved;
(2) According to the invention, the carbon microfiber is introduced into the gas diffusion layer with the gradient structure, and the chopped carbon fiber can be effectively wound and bonded in the carbon fiber sheet layer, so that the mechanical strength of the gas diffusion layer can not be reduced, the pore diameter structure can be effectively regulated, the air permeability can be increased, and the air permeability can be improved while the mechanical strength of the gas diffusion layer is not lost;
(3) According to the invention, the nano carbon particles are doped in the fourth layer in the constructed gas diffusion layer with the gradient structure, and the nano carbon particles, the chopped carbon fibers and the carbon microfibers are effectively regulated and controlled in proportion, so that the gas diffusion layer with the intrinsic microporous layer is successfully obtained, the preparation method of the microporous layer greatly simplifies the preparation flow of the gas diffusion layer, improves the uniformity of the gas diffusion layer, and reduces the preparation cost.
Drawings
Fig. 1 is a schematic view of a gas diffusion layer having a multi-layered composite structure for a fuel cell, which is produced in example 2, along the thickness direction.
Detailed Description
The invention is further described below in conjunction with the detailed description. It is to be understood that these examples are illustrative of the present invention and are not intended to limit the scope of the present invention. Further, it is understood that various changes and modifications may be made by those skilled in the art after reading the teachings of the present invention, and such equivalents are intended to fall within the scope of the claims appended hereto.
The porosity test method is as follows:
(1) The gas diffusion layer with a multi-layered composite structure for a fuel cell prepared in example was prepared to have a size of 25cm 2 (5 cm. Times.5 cm) of a test sample;
(2) Immersing the sample in an acetone solution for 0.5h, removing oil and ash on the surface and inside of the sample, then drying the sample in an oven at 120 ℃ for at least 2h, and weighing the mass M of the sample by using a precision electronic balance;
(3) Preparing a mixed solution with a certain volume fraction from n-heptane and dibromoethane, and injecting the mixed solution into a measuring cylinder with a plug;
(4) Cutting the sample fiber, grinding the sample fiber with an agate mortar until the length is less than 2mm, placing the sample fiber into a mixed solution in a measuring cylinder with a plug, stirring the sample fiber with a glass rod to disperse the sample fiber in the mixed solution, covering a grinding plug, placing the sample fiber into a constant-temperature water bath at 25+/-1 ℃, and exposing the plug and the neck of the measuring cylinder with the plug to the water surface;
(5) Observing the mixed solution, and if the fiber floats or sinks in the mixed solution, correspondingly adding n-heptane or dibromoethane to adjust the density of the mixed solution until the fiber is uniformly suspended in the mixed solution;
(6) After the mixed solution is stood for 4 hours, if the fibers are still uniformly distributed in the mixed solution, the density of the mixed solution at the temperature is measured by a densimeter, namely the density value (ρ) of the fibers CF )；
(7) The porosity is calculated as follows:
epsilon-porosity of the sample,%;
m-mass of sample in grams (g);
ρ CF -density of carbon fibres in grams per cubic centimeter (g/cm) 3 )；
Lcp-the length of the sample in centimeters (cm);
wcp-width of sample in centimeters (cm);
d-thickness of the sample in centimeters (cm).
Example 1
A preparation method of a gas diffusion layer with a gradient structure for a fuel cell comprises the following specific steps:
(1) Preparation of raw materials:
cutting carbon fibers;
the carbon microfiber precursor is para-aramid pulp;
(2) Preparing carbon fiber base paper;
(2.1) uniformly dispersing chopped carbon fibers and carbon microfiber precursors into a polyethylene oxide aqueous solution with the concentration of 0.1wt.% according to different proportions to respectively obtain a slurry of a first layer of carbon fiber base paper, a slurry of a second layer of carbon fiber base paper and a slurry of a third layer of carbon fiber base paper; uniformly dispersing chopped carbon fibers and carbon microfiber precursors into a polyethylene oxide aqueous solution with the concentration of 0.1wt.% to obtain slurry of a fourth intrinsic microporous layer;
(2.2) respectively forming the slurry obtained in the step (2.1) through a wet paper machine to prepare a first layer of carbon fiber base paper, a second layer of carbon fiber base paper, a third layer of carbon fiber base paper and a fourth layer of carbon fiber base paper;
In the preparation raw materials of the first layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 95 percent, and the mass percentage of the carbon microfiber precursors is 5 percent;
in the preparation raw materials of the second layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 75%, and the mass percentage of the carbon microfiber precursors is 25%;
in the raw materials for preparing the carbon fiber base paper of the third layer, the mass percent of the chopped carbon fibers is 40 percent, and the mass percent of the carbon microfiber precursors is 60 percent;
in the preparation raw materials of the fourth layer of carbon fiber base paper, the mass percent of the chopped carbon fibers and the mass percent of the carbon microfiber precursors are taken as the reference, and the mass percent of the chopped carbon fibers and the mass percent of the carbon microfiber precursors are 75%;
(3) Compounding four layers of carbon fiber base paper: sequentially stacking the first layer of carbon fiber base paper, the second layer of carbon fiber base paper, the third layer of carbon fiber base paper and the fourth layer of carbon fiber base paper from bottom to top;
(4) Preparation of precursor paper with pore size gradient structure: carrying out hot pressing treatment on the four layers of carbon fiber base paper compounded in the step (3) at the temperature of 240 ℃ and the pressure of 40MPa to obtain precursor paper with an aperture gradient structure;
(5) Preparation of a gas diffusion layer for a fuel cell with a gradient structure: dipping and drying the precursor paper with the pore diameter gradient structure obtained in the step (4) in a binder solution, then carrying out hot press curing at the temperature of 140 ℃ and the pressure of 30MPa, then heating to 1050 ℃ at the speed of 5 ℃/min under the protection of argon, and carrying out carbonization treatment at the temperature of 1050 ℃ for 1.5 hours; continuously heating to 1600 ℃ to carry out graphitization treatment for 60min; immersing the graphitized product in a polytetrafluoroethylene hydrophobizing agent solution with the concentration of 5wt.% for 5min, drying at the temperature of 60 ℃ for 60min, and finally treating at the temperature of 350 ℃ for 30min to prepare a gas diffusion layer with a multilayer composite structure for a fuel cell; wherein the binder solution is a solution with a concentration of 3wt.% prepared by dissolving a phenolic resin in absolute ethanol, and the phenolic resin is composed of thermosetting phenolic resin and thermoplastic phenolic resin in a mass ratio of 1:1.
As shown in fig. 1, the gas diffusion layer with gradient structure for the fuel cell is a four-layer composite layer, which is sequentially a first fiber sheet layer, a second fiber sheet layer, a third fiber sheet layer and a fourth intrinsic microporous layer from bottom to top, wherein the average pore diameter of the first fiber sheet layer is 80 μm, the roughness is 15 μm, the average pore diameter of the second fiber sheet layer is 46 μm, the average pore diameter of the third fiber sheet layer is 11 μm, the average pore diameter of the fourth intrinsic microporous layer is 330nm, and the roughness is 5.3 μm; the fuel cell is bonded with the catalyst layer in the fuel cell by using the uppermost layer (namely the fourth intrinsic microporous layer) of the gas diffusion layer with the gradient structure, and the lowermost layer (namely the first fiber sheet layer) is bonded with the bipolar plate of the fuel cell; each layer of the gas diffusion layer with the gradient structure for the fuel cell comprises chopped carbon fibers, carbon microfibers and resin carbon, wherein the average diameter of the carbon microfibers is 12nm;
example 2
A preparation method of a gas diffusion layer with a gradient structure for a fuel cell comprises the following specific steps:
(1) Preparation of raw materials:
cutting carbon fibers;
the carbon microfiber precursor is meta-aramid pulp;
the nano carbon particles are graphene; the average layer number of the graphene is 5 layers;
(2) Preparing carbon fiber base paper;
(2.1) uniformly dispersing chopped carbon fibers and carbon microfiber precursors into a polyethylene oxide aqueous solution with the concentration of 0.15wt.% according to different proportions to respectively obtain a slurry of a first layer of carbon fiber base paper, a slurry of a second layer of carbon fiber base paper and a slurry of a third layer of carbon fiber base paper; uniformly dispersing chopped carbon fibers, a carbon microfiber precursor and nano carbon particles into a polyethylene oxide aqueous solution with the concentration of 0.15wt.% to obtain a slurry of a fourth intrinsic microporous layer;
(2.2) respectively forming the slurry obtained in the step (2.1) through a wet paper machine to prepare a first layer of carbon fiber base paper, a second layer of carbon fiber base paper, a third layer of carbon fiber base paper and a fourth layer of carbon fiber base paper;
in the raw materials for preparing the first layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 92 percent, and the mass percentage of the carbon microfiber precursors is 8 percent;
in the preparation raw materials of the second layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 75%, and the mass percentage of the carbon microfiber precursors is 25%;
in the raw materials for preparing the carbon fiber base paper of the third layer, the mass percentage of the chopped carbon fibers is 45 percent, and the mass percentage of the carbon microfiber precursors is 55 percent;
In the preparation raw materials of the fourth layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 20% and the mass percentage of the carbon microfiber precursors is 80% based on the total mass of the chopped carbon fibers and the carbon microfiber precursors; the nano carbon particles account for 25% of the total absolute dry mass of the four-layer carbon fiber composite base paper;
(3) Compounding four layers of carbon fiber base paper: sequentially stacking the first layer of carbon fiber base paper, the second layer of carbon fiber base paper, the third layer of carbon fiber base paper and the fourth layer of carbon fiber base paper from bottom to top;
(4) Preparation of precursor paper with pore size gradient structure: carrying out hot pressing treatment on the four layers of carbon fiber base paper compounded in the step (3) at the temperature of 250 ℃ and the pressure of 35MPa to obtain precursor paper with an aperture gradient structure;
(5) Preparation of a gas diffusion layer for a fuel cell with a gradient structure: soaking and drying the precursor paper with the pore size gradient structure obtained in the step (4) in a binder solution, then carrying out hot press curing at the temperature of 150 ℃ and the pressure of 25MPa, then raising the temperature to 1070 ℃ at the speed of 5 ℃/min under the protection of argon, and carrying out carbonization treatment for 1.4h at the temperature of 1070 ℃; continuously heating to 1750 ℃ to carry out graphitization treatment for 55min; immersing the graphitized product in a polytetrafluoroethylene hydrophobizing agent solution with the concentration of 5wt.% for 10min, drying at the temperature of 70 ℃ for 50min, and finally treating at the temperature of 320 ℃ for 35min to prepare a gas diffusion layer with a gradient structure for a fuel cell; wherein the binder solution is a solution with a concentration of 10wt.% prepared by dissolving a phenolic resin in absolute ethanol, and the phenolic resin is composed of a thermosetting phenolic resin and a thermoplastic phenolic resin in a mass ratio of 1:1.
The gas diffusion layer with gradient structure for the fuel cell is a four-layer composite layer, which comprises a first fiber sheet layer, a second fiber sheet layer, a third fiber sheet layer and a fourth intrinsic microporous layer from bottom to top in sequence, wherein the average pore diameter of the first fiber sheet layer is 75 mu m, the roughness is 13.6 mu m, the average pore diameter of the second fiber sheet layer is 46 mu m, the average pore diameter of the third fiber sheet layer is 9 mu m, the average pore diameter of the fourth intrinsic microporous layer is 132nm, and the roughness is 4.1 mu m; the fuel cell is bonded with the catalyst layer in the fuel cell by using the uppermost layer (namely the fourth intrinsic microporous layer) of the gas diffusion layer with the gradient structure, and the lowermost layer (namely the first fiber sheet layer) is bonded with the bipolar plate of the fuel cell; each layer of the gas diffusion layer with the gradient structure for the fuel cell comprises chopped carbon fibers, carbon microfibers and resin carbon, wherein the average diameter of the carbon microfibers is 10nm; the carbon microfibers in each layer are wound around the chopped carbon fibers, and the carbon microfibers and the chopped carbon fibers are connected together by the resin carbon; the different layers are penetrated by short carbon fibers in the vertical direction and are wound by carbon microfibers and connected by resin carbon; the gas diffusion layer having a gradient structure for a fuel cell had a thickness of 110 μm, a porosity of 78%, and a permeability of 2065 (mL. Multidot. Mm)/(cm) 2 h.mmAq), in-plane resistivity of 3.9mΩ·cm, normal resistivity of 47mΩ·cm, and tensile strength of 18MPa.
Example 3
A preparation method of a gas diffusion layer with a gradient structure for a fuel cell comprises the following specific steps:
(1) Preparation of raw materials:
cutting carbon fibers;
the carbon microfiber precursor is superfine polyacrylonitrile fiber obtained through electrostatic spinning;
the nano carbon particles are carbon nanotubes; the average pipe diameter of the carbon nano-tube is 3nm, and the average length is 1nm;
(2) Preparing carbon fiber base paper;
(2.1) uniformly dispersing chopped carbon fibers and carbon microfiber precursors into a polyethylene oxide aqueous solution with the concentration of 0.2wt.% according to different proportions to respectively obtain a slurry of a first layer of carbon fiber base paper, a slurry of a second layer of carbon fiber base paper and a slurry of a third layer of carbon fiber base paper; uniformly dispersing chopped carbon fibers, a carbon microfiber precursor and nano carbon particles into a polyethylene oxide aqueous solution with the concentration of 0.2wt.% to obtain slurry of a fourth intrinsic microporous layer;
(2.2) respectively forming the slurry obtained in the step (2.1) through a wet paper machine to prepare a first layer of carbon fiber base paper, a second layer of carbon fiber base paper, a third layer of carbon fiber base paper and a fourth layer of carbon fiber base paper;
In the preparation raw materials of the first layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 90 percent, and the mass percentage of the carbon microfiber precursors is 10 percent;
in the preparation raw materials of the second layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 75%, and the mass percentage of the carbon microfiber precursors is 25%;
in the raw materials for preparing the carbon fiber base paper of the third layer, the mass percent of the chopped carbon fibers is 50 percent, and the mass percent of the carbon microfiber precursors is 50 percent;
in the preparation raw materials of the fourth layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 30% and the mass percentage of the carbon microfiber precursors is 70% based on the total mass of the chopped carbon fibers and the carbon microfiber precursors; the nano carbon particles account for 35% of the total absolute dry mass of the four-layer carbon fiber composite base paper;
(3) Compounding four layers of carbon fiber base paper: sequentially stacking the first layer of carbon fiber base paper, the second layer of carbon fiber base paper, the third layer of carbon fiber base paper and the fourth layer of carbon fiber base paper from bottom to top;
(4) Preparation of precursor paper with pore size gradient structure: carrying out hot pressing treatment on the four layers of carbon fiber base paper compounded in the step (3) at the temperature of 150 ℃ and the pressure of 30MPa to obtain precursor paper with an aperture gradient structure;
(5) Preparation of a gas diffusion layer for a fuel cell with a gradient structure: dipping and drying the precursor paper with the pore diameter gradient structure obtained in the step (4) in a binder solution, then carrying out hot press curing at 160 ℃ and 20MPa, then heating to 1100 ℃ at a speed of 5 ℃/min under the protection of argon, and carrying out carbonization treatment at 1100 ℃ for 1.3 hours; continuously heating to 1900 ℃ to carry out graphitization treatment for 50min; immersing the graphitized product in polytetrafluoroethylene hydrophobing agent solution with the concentration of 8wt.% for 15min, drying at 80 ℃ for 40min, and finally treating at 300 ℃ for 40min to obtain a gas diffusion layer with a gradient structure for a fuel cell; wherein the binder solution is a solution with a concentration of 15wt.% prepared by dissolving a phenolic resin in absolute ethyl alcohol, and the phenolic resin is composed of thermosetting phenolic resin and thermoplastic phenolic resin in a mass ratio of 1:1.
The gas diffusion layer with gradient structure for the fuel cell is a four-layer composite layer, which comprises a first fiber sheet layer, a second fiber sheet layer, a third fiber sheet layer and a fourth intrinsic microporous layer from bottom to top in sequence, wherein the average pore diameter of the first fiber sheet layer is 61 mu m, the roughness is 12.8 mu m, the average pore diameter of the second fiber sheet layer is 46 mu m, the average pore diameter of the third fiber sheet layer is 15 mu m, the average pore diameter of the fourth intrinsic microporous layer is 50nm, and the roughness is 4.6 mu m; the fuel cell is bonded with the catalyst layer in the fuel cell by using the uppermost layer (namely the fourth intrinsic microporous layer) of the gas diffusion layer with the gradient structure, and the lowermost layer (namely the first fiber sheet layer) is bonded with the bipolar plate of the fuel cell; each layer of the gas diffusion layer with the gradient structure for the fuel cell comprises chopped carbon fibers, carbon microfibers and resin carbon, wherein the average diameter of the carbon microfibers is 380nm; the carbon microfibers in each layer are wound around the chopped carbon fibers, and the carbon microfibers and the chopped carbon fibers are connected together by the resin carbon; the different layers are penetrated by short carbon fibers in the vertical direction and are wound by carbon microfibers and connected by resin carbon; the gas diffusion layer having a gradient structure for a fuel cell had a thickness of 150 μm, a porosity of 76%, and gas permeation The degree of refraction was 1990 (mL. Mm)/(cm) 2 h.mmAq), in-plane resistivity of 4.7mΩ·cm, normal resistivity of 56mΩ·cm, and tensile strength of 21MPa.
Example 4
A preparation method of a gas diffusion layer with a gradient structure for a fuel cell comprises the following specific steps:
(1) Preparation of raw materials:
cutting carbon fibers;
the carbon microfiber precursor is an ultrafine mesophase pitch-based fiber;
the nano carbon particles are carbon black; the average particle diameter of the carbon black is 40nm;
(2) Preparing carbon fiber base paper;
(2.1) uniformly dispersing chopped carbon fibers and carbon microfiber precursors into a polyethylene oxide aqueous solution with the concentration of 0.1wt.% according to different proportions to respectively obtain a slurry of a first layer of carbon fiber base paper, a slurry of a second layer of carbon fiber base paper and a slurry of a third layer of carbon fiber base paper; uniformly dispersing chopped carbon fibers, a carbon microfiber precursor and nano carbon particles into a polyethylene oxide aqueous solution with the concentration of 0.1wt.% to obtain slurry of a fourth intrinsic microporous layer;
(2.2) respectively forming the slurry obtained in the step (2.1) through a wet paper machine to prepare a first layer of carbon fiber base paper, a second layer of carbon fiber base paper, a third layer of carbon fiber base paper and a fourth layer of carbon fiber base paper;
in the raw materials for preparing the first layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 87 percent, and the mass percentage of the carbon microfiber precursors is 13 percent;
In the preparation raw materials of the second layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 70 percent, and the mass percentage of the carbon microfiber precursors is 30 percent;
in the raw materials for preparing the carbon fiber base paper of the third layer, the mass percentage of the chopped carbon fibers is 45 percent, and the mass percentage of the carbon microfiber precursors is 55 percent;
in the preparation raw materials of the fourth layer of carbon fiber base paper, the mass percent of the chopped carbon fibers and the mass percent of the carbon microfiber precursors are taken as the reference, and the mass percent of the chopped carbon fibers and the mass percent of the carbon microfiber precursors are 75%; the nano carbon particles account for 30% of the total absolute dry mass of the four-layer carbon fiber composite base paper;
(3) Compounding four layers of carbon fiber base paper: sequentially stacking the first layer of carbon fiber base paper, the second layer of carbon fiber base paper, the third layer of carbon fiber base paper and the fourth layer of carbon fiber base paper from bottom to top;
(4) Preparation of precursor paper with pore size gradient structure: carrying out hot pressing treatment on the four layers of carbon fiber base paper compounded in the step (3) at the temperature of 150 ℃ and the pressure of 25MPa to obtain precursor paper with an aperture gradient structure;
(5) Preparation of a gas diffusion layer for a fuel cell with a gradient structure: soaking and drying the precursor paper with the pore size gradient structure obtained in the step (4) in a binder solution, then carrying out hot press curing at the temperature of 170 ℃ and the pressure of 18MPa, then heating to 1120 ℃ at the speed of 5 ℃/min under the protection of argon, and carrying out carbonization treatment for 1.2h at the temperature of 1120 ℃; continuously heating to 2100 ℃ to carry out graphitization treatment for 45min; immersing the graphitized product in a polytetrafluoroethylene hydrophobizing agent solution with the concentration of 11wt.% for 25min, drying for 30min at the temperature of 80 ℃, and finally treating for 45min at the temperature of 290 ℃ to prepare a gas diffusion layer with a gradient structure for a fuel cell; wherein the binder solution is a solution with a concentration of 18wt.% prepared by dissolving a phenolic resin in absolute ethyl alcohol, and the phenolic resin is composed of thermosetting phenolic resin and thermoplastic phenolic resin in a mass ratio of 1:1.
The gas diffusion layer with gradient structure for the fuel cell is a four-layer composite layer, which comprises a first fiber sheet layer, a second fiber sheet layer, a third fiber sheet layer and a fourth intrinsic microporous layer from bottom to top in sequence, wherein the average pore diameter of the first fiber sheet layer is 52 mu m, the roughness is 11.6 mu m, the average pore diameter of the second fiber sheet layer is 39 mu m, the average pore diameter of the third fiber sheet layer is 12 mu m, the average pore diameter of the fourth intrinsic microporous layer is 960nm, and the roughness is 5.9 mu m; the uppermost layer (i.e., the fourth intrinsic microporous layer) of the gas diffusion layer with the gradient structure for the fuel cell is attached to the catalyst layer in the fuel cell, and the lowermost layer (i.e., the fourth intrinsic microporous layerA first fibrous sheet) is bonded to the bipolar plate of the fuel cell; each layer of the gas diffusion layer with the gradient structure for the fuel cell comprises chopped carbon fibers, carbon microfibers and resin carbon, wherein the average diameter of the carbon microfibers is 500nm; the carbon microfibers in each layer are wound around the chopped carbon fibers, and the carbon microfibers and the chopped carbon fibers are connected together by the resin carbon; the different layers are penetrated by short carbon fibers in the vertical direction and are wound by carbon microfibers and connected by resin carbon; the gas diffusion layer having a gradient structure for a fuel cell had a thickness of 190. Mu.m, a porosity of 73%, and a permeability of 1980 (mL. Mm)/(cm) 2 h.mmAq), in-plane resistivity of 5.1mΩ·cm, normal resistivity of 68mΩ·cm, and tensile strength of 23MPa.
Example 5
A preparation method of a gas diffusion layer with a gradient structure for a fuel cell comprises the following specific steps:
(1) Preparation of raw materials:
cutting carbon fibers;
the carbon microfiber precursor is a mixture of polysulfonamide pulp and polyimide pulp with the mass ratio of 1:1;
the nano carbon particles are graphene; the average number of layers of graphene is 10;
(2) Preparing carbon fiber base paper;
(2.1) uniformly dispersing chopped carbon fibers and carbon microfiber precursors into a polyethylene oxide aqueous solution with the concentration of 0.15wt.% according to different proportions to respectively obtain a slurry of a first layer of carbon fiber base paper, a slurry of a second layer of carbon fiber base paper and a slurry of a third layer of carbon fiber base paper; uniformly dispersing chopped carbon fibers, a carbon microfiber precursor and nano carbon particles into a polyethylene oxide aqueous solution with the concentration of 0.15wt.% to obtain a slurry of a fourth intrinsic microporous layer;
(2.2) respectively forming the slurry obtained in the step (2.1) through a wet paper machine to prepare a first layer of carbon fiber base paper, a second layer of carbon fiber base paper, a third layer of carbon fiber base paper and a fourth layer of carbon fiber base paper;
In the raw materials for preparing the first layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 85 percent, and the mass percentage of the carbon microfiber precursors is 15 percent;
in the preparation raw materials of the second layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 65 percent, and the mass percentage of the carbon microfiber precursors is 35 percent;
in the raw materials for preparing the carbon fiber base paper of the third layer, the mass percent of the chopped carbon fibers is 40 percent, and the mass percent of the carbon microfiber precursors is 60 percent;
in the preparation raw materials of the fourth layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 20% and the mass percentage of the carbon microfiber precursors is 80% based on the total mass of the chopped carbon fibers and the carbon microfiber precursors; the nano carbon particles account for 15% of the total absolute dry mass of the four-layer carbon fiber composite base paper;
(3) Compounding four layers of carbon fiber base paper: sequentially stacking the first layer of carbon fiber base paper, the second layer of carbon fiber base paper, the third layer of carbon fiber base paper and the fourth layer of carbon fiber base paper from bottom to top;
(4) Preparation of precursor paper with pore size gradient structure: carrying out hot pressing treatment on the four layers of carbon fiber base paper compounded in the step (3) at the temperature of 290 ℃ and the pressure of 20MPa to obtain precursor paper with an aperture gradient structure;
(5) Preparation of a gas diffusion layer for a fuel cell with a gradient structure: soaking and drying the precursor paper with the pore size gradient structure obtained in the step (4) in a binder solution, then carrying out hot press curing at the temperature of 180 ℃ and the pressure of 14MPa, then heating to 1140 ℃ at the speed of 5 ℃/min under the protection of argon, and carrying out carbonization treatment for 1.1h at the temperature of 1140 ℃; continuously heating to 2300 ℃ to carry out graphitization treatment for 40min; immersing the graphitized product in a polytetrafluoroethylene hydrophobizing agent solution with the concentration of 14wt.% for 30min, drying for 25min at the temperature of 60 ℃, and finally treating for 50min at the temperature of 280 ℃ to prepare a gas diffusion layer with a gradient structure for a fuel cell; wherein the binder solution is a solution with a concentration of 22wt.% prepared by dissolving a phenolic resin in absolute ethyl alcohol, and the phenolic resin is composed of thermosetting phenolic resin and thermoplastic phenolic resin in a mass ratio of 1:1.
The fuel electricity producedThe cell is characterized in that the gas diffusion layer with a gradient structure is a four-layer composite layer, a first fiber sheet layer, a second fiber sheet layer, a third fiber sheet layer and a fourth intrinsic microporous layer are sequentially arranged from bottom to top, wherein the average pore diameter of the first fiber sheet layer is 48 mu m, the roughness is 10.7 mu m, the average pore diameter of the second fiber sheet layer is 33 mu m, the average pore diameter of the third fiber sheet layer is 13 mu m, the average pore diameter of the fourth intrinsic microporous layer is 865nm, and the roughness is 6.2 mu m; the fuel cell is bonded with the catalyst layer in the fuel cell by using the uppermost layer (namely the fourth intrinsic microporous layer) of the gas diffusion layer with the gradient structure, and the lowermost layer (namely the first fiber sheet layer) is bonded with the bipolar plate of the fuel cell; each layer of the gas diffusion layer with the gradient structure for the fuel cell comprises chopped carbon fibers, carbon microfibers and resin carbon, wherein the average diameter of the carbon microfibers is 410nm; the carbon microfibers in each layer are wound around the chopped carbon fibers, and the carbon microfibers and the chopped carbon fibers are connected together by the resin carbon; the different layers are penetrated by short carbon fibers in the vertical direction and are wound by carbon microfibers and connected by resin carbon; the gas diffusion layer for a fuel cell having a gradient structure had a thickness of 220 μm, a porosity of 71%, and a permeability of 1860 (mL. Mm)/(cm) 2 h.mmAq), in-plane resistivity of 5.8mΩ·cm, normal resistivity of 71mΩ·cm, and tensile strength of 37MPa.
Example 6
A preparation method of a gas diffusion layer with a gradient structure for a fuel cell comprises the following specific steps:
(1) Preparation of raw materials:
cutting carbon fibers;
the carbon microfiber precursor is bamboo pulp;
the nano carbon particles are carbon nanotubes; the average pipe diameter of the carbon nano-tube is 10nm, and the average length is 20nm;
(2) Preparing carbon fiber base paper;
(2.1) uniformly dispersing chopped carbon fibers and carbon microfiber precursors into a polyethylene oxide aqueous solution with the concentration of 0.2wt.% according to different proportions to respectively obtain a slurry of a first layer of carbon fiber base paper, a slurry of a second layer of carbon fiber base paper and a slurry of a third layer of carbon fiber base paper; uniformly dispersing chopped carbon fibers, a carbon microfiber precursor and nano carbon particles into a polyethylene oxide aqueous solution with the concentration of 0.2wt.% to obtain slurry of a fourth intrinsic microporous layer;
(2.2) respectively forming the slurry obtained in the step (2.1) through a wet paper machine to prepare a first layer of carbon fiber base paper, a second layer of carbon fiber base paper, a third layer of carbon fiber base paper and a fourth layer of carbon fiber base paper;
in the preparation raw materials of the first layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 82 percent, and the mass percentage of the carbon microfiber precursors is 18 percent;
In the preparation raw materials of the second layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 60 percent, and the mass percentage of the carbon microfiber precursors is 40 percent;
in the raw materials for preparing the carbon fiber base paper of the third layer, the mass percent of the chopped carbon fibers is 35 percent, and the mass percent of the carbon microfiber precursors is 65 percent;
in the preparation raw materials of the fourth layer of carbon fiber base paper, the mass percentage of the chopped carbon fiber is 15% and the mass percentage of the carbon microfiber precursor is 85% based on the total mass of the chopped carbon fiber and the carbon microfiber precursor; the nano carbon particles account for 10% of the total absolute dry mass of the four-layer carbon fiber composite base paper;
(3) Compounding four layers of carbon fiber base paper: sequentially stacking the first layer of carbon fiber base paper, the second layer of carbon fiber base paper, the third layer of carbon fiber base paper and the fourth layer of carbon fiber base paper from bottom to top;
(4) Preparation of precursor paper with pore size gradient structure: carrying out hot pressing treatment on the four layers of carbon fiber base paper compounded in the step (3) at the temperature of 300 ℃ and the pressure of 10MPa to obtain precursor paper with an aperture gradient structure;
(5) Preparation of a gas diffusion layer for a fuel cell with a gradient structure: soaking and drying the precursor paper with the pore size gradient structure obtained in the step (4) in a binder solution, then carrying out hot press curing at the temperature of 200 ℃ and the pressure of 10MPa, then heating to 1180 ℃ at the speed of 5 ℃/min under the protection of argon, and carrying out carbonization treatment for 1h at the temperature of 1180 ℃; continuously heating to 2500 ℃ to carry out graphitization treatment for 35min; immersing the graphitized product in a polytetrafluoroethylene hydrophobizing agent solution with the concentration of 17wt.% for 35min, drying at the temperature of 70 ℃ for 20min, and finally treating at the temperature of 270 ℃ for 55min to prepare a gas diffusion layer with a gradient structure for a fuel cell; wherein the binder solution is a 26wt.% solution prepared by dissolving a phenolic resin in absolute ethanol, and the phenolic resin is composed of a thermosetting phenolic resin and a thermoplastic phenolic resin in a mass ratio of 1:1.
The gas diffusion layer with gradient structure for the fuel cell is a four-layer composite layer, which comprises a first fiber sheet layer, a second fiber sheet layer, a third fiber sheet layer and a fourth intrinsic microporous layer from bottom to top in sequence, wherein the average pore diameter of the first fiber sheet layer is 37 mu m, the roughness is 15 mu m, the average pore diameter of the second fiber sheet layer is 27 mu m, the average pore diameter of the third fiber sheet layer is 4 mu m, the average pore diameter of the fourth intrinsic microporous layer is 1210nm, and the roughness is 6.5 mu m; the fuel cell is bonded with the catalyst layer in the fuel cell by using the uppermost layer (namely the fourth intrinsic microporous layer) of the gas diffusion layer with the gradient structure, and the lowermost layer (namely the first fiber sheet layer) is bonded with the bipolar plate of the fuel cell; each layer of the gas diffusion layer with the gradient structure for the fuel cell comprises chopped carbon fibers, carbon microfibers and resin carbon, wherein the average diameter of the carbon microfibers is 20nm; the carbon microfibers in each layer are wound around the chopped carbon fibers, and the carbon microfibers and the chopped carbon fibers are connected together by the resin carbon; the different layers are penetrated by short carbon fibers in the vertical direction and are wound by carbon microfibers and connected by resin carbon; the gas diffusion layer having a gradient structure for a fuel cell had a thickness of 260 μm, a porosity of 68%, and a permeability of 1720 (mL. Mm)/(cm) 2 h.mmAq), in-plane resistivity of 6.8mΩ·cm, normal resistivity of 73mΩ·cm, and tensile strength of 43MPa.
Example 7
A preparation method of a gas diffusion layer with a gradient structure for a fuel cell comprises the following specific steps:
(1) Preparation of raw materials:
cutting carbon fibers;
the carbon microfiber precursor is cotton pulp;
the nano carbon particles are a mixture of carbon black and graphene in a mass ratio of 1:1; the average particle diameter of the carbon black is 60nm, and the average layer number of the graphene is 7;
(2) Preparing carbon fiber base paper;
(2.1) uniformly dispersing chopped carbon fibers and carbon microfiber precursors into a polyethylene oxide aqueous solution with the concentration of 0.1wt.% according to different proportions to respectively obtain a slurry of a first layer of carbon fiber base paper, a slurry of a second layer of carbon fiber base paper and a slurry of a third layer of carbon fiber base paper; uniformly dispersing chopped carbon fibers, a carbon microfiber precursor and nano carbon particles into a polyethylene oxide aqueous solution with the concentration of 0.1wt.% to obtain slurry of a fourth intrinsic microporous layer;
(2.2) respectively forming the slurry obtained in the step (2.1) through a wet paper machine to prepare a first layer of carbon fiber base paper, a second layer of carbon fiber base paper, a third layer of carbon fiber base paper and a fourth layer of carbon fiber base paper;
In the preparation raw materials of the first layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 80 percent, and the mass percentage of the carbon microfiber precursors is 20 percent;
in the preparation raw materials of the second layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 55 percent, and the mass percentage of the carbon microfiber precursors is 45 percent;
in the raw materials for preparing the third layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 30 percent, and the mass percentage of the carbon microfiber precursors is 70 percent;
in the preparation raw materials of the fourth layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 10% and the mass percentage of the carbon microfiber precursors is 90% based on the total mass of the chopped carbon fibers and the carbon microfiber precursors; the nano carbon particles account for 5% of the total absolute dry mass of the four-layer carbon fiber composite base paper;
(3) Compounding four layers of carbon fiber base paper: sequentially stacking the first layer of carbon fiber base paper, the second layer of carbon fiber base paper, the third layer of carbon fiber base paper and the fourth layer of carbon fiber base paper from bottom to top;
(4) Preparation of precursor paper with pore size gradient structure: carrying out hot pressing treatment on the four layers of carbon fiber base paper compounded in the step (3) at the temperature of 320 ℃ and the pressure of 5MPa to obtain precursor paper with an aperture gradient structure;
(5) Preparation of a gas diffusion layer for a fuel cell with a gradient structure: soaking and drying the precursor paper with the pore size gradient structure obtained in the step (4) in a binder solution, then carrying out hot press curing at the temperature of 220 ℃ and the pressure of 5MPa, then heating to 1200 ℃ at the speed of 5 ℃/min under the protection of argon, and carrying out carbonization treatment for 1h at the temperature of 1200 ℃; continuously heating to 2800 ℃ to carry out graphitization treatment for 30min; immersing the graphitized product in a polytetrafluoroethylene hydrophobizing agent solution with the concentration of 20wt.% for 45min, drying at 80 ℃ for 15min, and finally treating at 250 ℃ for 60min to obtain a gas diffusion layer with a gradient structure for a fuel cell; wherein the binder solution is a solution with a concentration of 30wt.% prepared by dissolving a phenolic resin in absolute ethanol, and the phenolic resin is composed of a thermosetting phenolic resin and a thermoplastic phenolic resin in a mass ratio of 1:1.
The gas diffusion layer with gradient structure for the fuel cell is a four-layer composite layer, which comprises a first fiber sheet layer, a second fiber sheet layer, a third fiber sheet layer and a fourth intrinsic microporous layer from bottom to top in sequence, wherein the average pore diameter of the first fiber sheet layer is 20 mu m, the roughness is 15 mu m, the average pore diameter of the second fiber sheet layer is 10 mu m, the average pore diameter of the third fiber sheet layer is 1 mu m, the average pore diameter of the fourth intrinsic microporous layer is 1500nm, and the roughness is 7 mu m; the fuel cell is bonded with the catalyst layer in the fuel cell by using the uppermost layer (namely the fourth intrinsic microporous layer) of the gas diffusion layer with the gradient structure, and the lowermost layer (namely the first fiber sheet layer) is bonded with the bipolar plate of the fuel cell; each layer of the gas diffusion layer with the gradient structure for the fuel cell comprises chopped carbon fibers, carbon microfibers and resin carbon, wherein the average diameter of the carbon microfibers is 60nm; the carbon microfibers in each layer are wound around the chopped carbon fibers, and the carbon microfibers and the chopped carbon fibers are connected together by the resin carbon; the different layers are penetrated by short carbon fiber in the vertical direction and are formed by carbon microfiber Winding and resin carbon connection; the gas diffusion layer having a gradient structure for a fuel cell had a thickness of 280 μm, a porosity of 65%, and a permeability of 1640 (mL. Mm)/(cm) 2 h.mmAq), in-plane resistivity of 7mΩ·cm, normal resistivity of 80mΩ·cm, and tensile strength of 50MPa.
Example 8
A method for producing a gas diffusion layer having a gradient structure for a fuel cell, which is substantially the same as in example 2, except that step (2) in example 8 does not produce a second layer of carbon fiber base paper.
The gas diffusion layer with gradient structure for the fuel cell is a three-layer composite layer, which is a first fiber sheet layer with an average pore diameter of 75 μm and a roughness of 13.6 μm from bottom to top, a second fiber sheet layer (original third fiber sheet layer) with an average pore diameter of 9 μm and a third intrinsic microporous layer (original fourth intrinsic microporous layer) with an average pore diameter of 132nm and a roughness of 4.1 μm; the uppermost layer of the gas diffusion layer for the fuel cell is bonded with the catalyst layer in the fuel cell, and the lowermost layer is bonded with the bipolar plate of the fuel cell; each of the gas diffusion layers for the fuel cell comprises chopped carbon fibers, carbon microfibers and resin carbon, wherein the average diameter of the carbon microfibers is 10nm; the carbon microfibers in each layer are wound around the chopped carbon fibers, and the carbon microfibers and the chopped carbon fibers are connected together by the resin carbon; the different layers are penetrated by short carbon fibers in the vertical direction and are wound by carbon microfibers and connected by resin carbon; the gas diffusion layer for a fuel cell had a thickness of 105 μm, a porosity of 69%, and a permeability of 2045 (mL. Mm)/(cm) 2 h.mmAq), in-plane resistivity of 3.8mΩ·cm, normal resistivity of 52mΩ·cm, and tensile strength of 16MPa.
Claims (10)
1. A gas diffusion layer having a gradient structure for a fuel cell, characterized in that: the pore diameter of each layer is distributed in a gradient structure and is a composite layer of 2-4 layers;
the fuel cell is characterized in that the uppermost layer of the gas diffusion layer with the gradient structure is attached to a catalyst layer in the fuel cell, and the lowermost layer is attached to a bipolar plate of the fuel cell;
the average pore diameter of the lowest layer in the gas diffusion layer with the gradient structure for the fuel cell is 20-80 mu m, and the roughness is less than or equal to 15 mu m; the average pore diameter of each layer in the gas diffusion layer with the gradient structure for the fuel cell is gradually reduced from bottom to top, the average pore diameter of the uppermost layer is 50-1500 nm, and the roughness is less than or equal to 7 mu m;
each layer of the gas diffusion layer with the gradient structure for the fuel cell comprises chopped carbon fibers, carbon microfibers and resin carbon, wherein the carbon microfibers in each layer are wound around the chopped carbon fibers, and the carbon microfibers and the chopped carbon fibers are connected together by the resin carbon; the different layers are also penetrated by chopped carbon fibers in the vertical direction and are wound by carbon microfibers and connected by resin carbon.
2. The gas diffusion layer having a gradient structure for a fuel cell according to claim 1, wherein the gas diffusion layer having a gradient structure for a fuel cell has a thickness of 80 to 280 μm, a porosity of 60 to 80%, and a permeability of 1600 to 2200 (mL. Mm)/(cm) 2 h.mmAq), in-plane resistivity of 3.5 to 7.0mΩ cm, normal resistivity of 40 to 80mΩ cm, and tensile strength of 15 to 50MPa.
3. A gas diffusion layer for a fuel cell having a gradient structure according to claim 1, wherein the length of the chopped carbon fibers is 3 to 10mm and the average fiber diameter is 4 to 10 μm; the average diameter of the carbon microfibers is 10-500 nm.
4. The gas diffusion layer with gradient structure for fuel cell of claim 1, wherein the carbon microfiber precursor is one or more of plant pulp, chopped superfine organic fiber and chemical fiber pulp;
the plant pulp is cotton pulp, wood pulp, bamboo pulp or grass pulp; the chopped superfine organic fiber is superfine polyacrylonitrile fiber or superfine mesophase pitch-based fiber obtained by electrostatic spinning; the chemical fiber pulp is para-aramid pulp, meta-aramid pulp, polysulfonamide pulp or polyimide pulp.
5. The gas diffusion layer with gradient structure for the fuel cell according to claim 1, wherein the gas diffusion layer with gradient structure for the fuel cell is a four-layer composite layer, which is a first fiber sheet layer, a second fiber sheet layer, a third fiber sheet layer and a fourth intrinsic microporous layer in sequence from bottom to top;
the average pore diameter of the first fiber sheet layer is 20-80 mu m, the average pore diameter of the second fiber sheet layer is 10-46 mu m, the average pore diameter of the third fiber sheet layer is 1-15 mu m, and the average pore diameter of the fourth intrinsic microporous layer is 50-1500 nm.
6. The gas diffusion layer with gradient structure for fuel cell of claim 5, wherein the fourth intrinsic microporous layer further contains nano carbon particles;
the nano carbon particles are more than one of carbon black, graphene and carbon nano tubes;
the particle size of the carbon black is 10-60 nm; the number of layers of the graphene is less than or equal to 10; the diameter of the carbon nano tube is 3-30 nm, and the length is 1-50 nm.
7. A method for producing a gas diffusion layer for a fuel cell having a gradient structure according to any one of claims 1 to 6, characterized in that: 2-4 pieces of carbon fiber base paper with different pore diameters are sequentially stacked from bottom to top according to the order of pore diameters from large to small, and are subjected to impregnation curing, heat treatment and hydrophobic treatment sequentially after hot press molding to prepare a gas diffusion layer with a gradient structure for a fuel cell;
The carbon fiber base paper is prepared by preparing slurry from chopped carbon fibers and carbon microfiber precursors serving as main raw materials and carrying out wet papermaking.
8. The method for preparing a gas diffusion layer with a gradient structure for a fuel cell according to claim 7, wherein the gas diffusion layer with a gradient structure for a fuel cell is a four-layer composite layer, and the preparation steps are as follows:
(1) Preparation of carbon fiber base paper: preparing single-layer carbon fiber base paper with different pore sizes, namely a first layer of carbon fiber base paper, a second layer of carbon fiber base paper, a third layer of carbon fiber base paper and a fourth layer of carbon fiber base paper by taking chopped carbon fibers and carbon microfiber precursors as main raw materials through wet papermaking;
(2) Compounding four layers of carbon fiber base paper: sequentially stacking the first layer of carbon fiber base paper, the second layer of carbon fiber base paper, the third layer of carbon fiber base paper and the fourth layer of carbon fiber base paper from bottom to top;
in the raw materials for preparing the first layer of carbon fiber base paper, the mass percent of the chopped carbon fibers is 80-95%, and the mass percent of the carbon microfiber precursors is 5-20%;
in the preparation raw materials of the second layer of carbon fiber base paper, the mass percentage of the chopped carbon fibers is 55-75%, and the mass percentage of the carbon microfiber precursors is 25-45%;
In the preparation raw materials of the third layer carbon fiber base paper, the mass percentage of the chopped carbon fibers is 30-50%, and the mass percentage of the carbon microfiber precursors is 50-70%;
in the preparation raw materials of the fourth layer of carbon fiber base paper, the mass percentage of the chopped carbon fiber is 10-30% and the mass percentage of the carbon microfiber precursor is 70-90% based on the total mass of the chopped carbon fiber and the carbon microfiber precursor; the nano carbon particles account for less than 35% of the total absolute dry mass of the four-layer carbon fiber composite base paper;
(3) Preparation of precursor paper with pore size gradient structure: carrying out hot pressing treatment on the four layers of carbon fiber composite base paper compounded in the step (2) to obtain precursor paper with an aperture gradient structure;
(4) Preparation of a gas diffusion layer for a fuel cell with a gradient structure: and (3) dipping the precursor paper with the pore diameter gradient structure obtained in the step (3) in a binder solution, drying, and then performing hot press curing, heat treatment and hydrophobic treatment to obtain the gas diffusion layer with the gradient structure for the fuel cell.
9. The method for producing a gas diffusion layer having a gradient structure for a fuel cell according to claim 8, wherein the step (1) is specifically:
Uniformly dispersing chopped carbon fibers and carbon microfiber precursors into a polyethylene oxide aqueous solution with the concentration of 0.1-0.2 wt.% according to different proportions to respectively obtain a slurry of a first layer of carbon fiber base paper, a slurry of a second layer of carbon fiber base paper and a slurry of a third layer of carbon fiber base paper; uniformly dispersing chopped carbon fibers, a carbon microfiber precursor and nano carbon particles into a polyethylene oxide aqueous solution with the concentration of 0.1-0.2 wt.% to obtain a slurry of a fourth layer of carbon fiber base paper;
and (1.2) respectively forming the slurry obtained in the step (1.1) through a wet paper machine to prepare a first layer of carbon fiber base paper, a second layer of carbon fiber base paper, a third layer of carbon fiber base paper and a fourth layer of carbon fiber base paper.
10. The method for producing a gas diffusion layer having a gradient structure for a fuel cell according to claim 8, wherein the process parameters of the hot press treatment in step (3) are: the temperature is 150-320 ℃ and the pressure is 5-40 MPa;
the binder solution in the step (4) is a solution prepared by dissolving phenolic resin in absolute ethyl alcohol and having a concentration of 3 to 30 wt.%;
the hot press curing process parameters in the step (4) are as follows: the temperature is 140-220 ℃ and the pressure is 5-30 MPa;
the heat treatment conditions of the step (4) are as follows: under the protection of inert gas, the heating rate is 5 ℃/min, and carbonization treatment is carried out for 1 to 1.5 hours at the temperature of 1050 to 1200 ℃; continuously heating to 1600-2800 ℃ to carry out graphitization treatment for 30-60 min;
The hydrophobic treatment conditions in the step (4) are as follows: soaking in 5-20 wt.% PTFE solution for 5-45 min, drying at 60-80 deg.c for 15-60 min, and final treating at 250-350 deg.c for 30-60 min.
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