CN110380061B - All-working-condition-matched fuel cell diffusion layer and preparation method thereof - Google Patents

All-working-condition-matched fuel cell diffusion layer and preparation method thereof Download PDF

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CN110380061B
CN110380061B CN201910594895.9A CN201910594895A CN110380061B CN 110380061 B CN110380061 B CN 110380061B CN 201910594895 A CN201910594895 A CN 201910594895A CN 110380061 B CN110380061 B CN 110380061B
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diffusion layer
gradient
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water repellent
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CN110380061A (en
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章俊良
闫晓晖
柯长春
夏国锋
程晓静
韩爱娣
朱凤鹃
陈俊任
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Shanghai Jiaotong University
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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
    • H01M4/8605—Porous electrodes
    • 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
    • H01M4/8636—Inert electrodes with catalytic activity, e.g. for fuel cells with a gradient in another property than porosity
    • H01M4/8642—Gradient in composition
    • 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
    • H01M4/8647—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
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/023—Porous and characterised by the material
    • H01M8/0234—Carbonaceous material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/023—Porous and characterised by the material
    • H01M8/0241—Composites
    • H01M8/0245—Composites in the form of layered or coated products
    • 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

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Abstract

The invention discloses a fuel cell diffusion layer matched with all working conditions and a preparation method thereof; the diffusion layer consists of a porous conductive carbon paper substrate layer and a conductive carbon powder microporous layer, the diffusion layer is positioned between a gas flow channel and a proton exchange membrane in the fuel cell structure, and the substrate layer is positioned on one side of the gas flow channel; the base layer has a hydrophobic gradient in a direction parallel to the diffusion layer, while the microporous layer has a hydrophobic gradient in a direction perpendicular to the diffusion layer. Under the working condition of high humidity, the microporous layer has hydrophobicity gradient which rises from the flow field plate to the membrane electrode, so that the drainage effect of the cathode can be effectively improved, and the gas transmission rate of the diffusion layer is improved; under the working condition of medium and low humidity, the microporous layer has hydrophobic gradient descending from the flow field plate to the membrane electrode, can play a certain role in moisturizing, can ensure that the proton exchange membrane is fully wetted, reduces the internal resistance of the cell, and improves the output performance of the cell.

Description

All-working-condition-matched fuel cell diffusion layer and preparation method thereof
Technical Field
The invention belongs to the technical field of fuel cells, and particularly relates to a fuel cell diffusion layer matched with all working conditions and a preparation method thereof.
Background
A Proton Exchange Membrane Fuel Cell (PEMFC) is a type of Fuel Cell, and corresponds in principle to an "inverter" device for water electrolysis. The single cell consists of anode, cathode and proton exchange membrane, the anode is the place where hydrogen fuel is oxidized, the cathode is the place where oxidant is reduced, and both electrodes contain catalyst for accelerating electrochemical reaction of the electrodes.
Gas Diffusion Layers (GDLs) are important components of proton exchange membrane fuel cells, in which a Gas Diffusion Layer is located between a flow field and a catalytic Layer. In the proton exchange membrane fuel cell, as the electrochemical reaction gradually proceeds, water generated by the reaction accumulates near the cathode catalyst layer, and the water not only diffuses to the anode through the proton exchange membrane, but also diffuses to the cathode flow field through the cathode diffusion layer, and if the liquid water cannot be rapidly transferred, the accumulation of the water in the diffusion layer, namely, the flooding phenomenon, can be caused. Since the oxygen transport rate in water is only in the order of one hundred thousandth of that in air, the "flooding" phenomenon greatly increases the gas transport resistance, thereby inhibiting the overall performance of the fuel cell (especially at higher current densities). Meanwhile, if the reaction gas is not properly wetted, the degree of dryness of the proton exchange membrane is increased along with the increase of the current density, so that the resistance is increased, the output performance of the battery is reduced, and when the proton exchange membrane loses water seriously, the membrane can be damaged, and the normal operation of the battery is influenced. Therefore, water management of fuel cells has been an important concern for researchers in the related art.
To improve the water management properties of the diffusion layer of a fuel cell, the diffusion layer is typically hydrophobized with a more hydrophobic material (e.g., polytetrafluoroethylene). Although the traditional integral modification of the diffusion layer enhances the drainage capacity of the diffusion layer and avoids the flooding phenomenon to a certain extent, the hydrophobic agent is usually accumulated on the surface of the diffusion layer, the hydrophobic agent permeating into the diffusion layer is less, the drainage performance is still unsatisfactory, meanwhile, the hydrophobicity of different positions of the integrally modified diffusion layer is usually basically the same, and the targeted treatment cannot be carried out by considering the water content of different positions under the actual working condition. In view of this, some researchers have proposed a diffusion layer structure having a hydrophobic gradient, and patent document CN107123822A discloses a diffusion layer structure having a hydrophobic gradient formed by dividing a microporous layer into two parts, i.e., a hydrophilic carbon powder layer and a hydrophobic layer, and patent document CN107507983A provides a diffusion layer having a gradient change in the hydrophobic property in a direction parallel to the diffusion layer, and a method for preparing the same. However, the above patent is only applicable to a single working condition, i.e. the problem of flooding or moisture retention of the cathode of the fuel cell can only be solved, for example, the optimized gradient diffusion layer improves the cell performance under the working condition of high humidity, and then the performance under low humidity is sacrificed; and vice versa. However, the actual operation condition of the fuel cell is not single and fluctuates with the ambient temperature, humidity and other conditions.
Disclosure of Invention
The invention aims to prepare a diffusion layer with better performance according to different working conditions of a fuel cell, and provides a fuel cell diffusion layer matched with all working conditions and a preparation method thereof.
The purpose of the invention is realized by the following technical scheme:
the invention relates to a fuel cell diffusion layer matched with all working conditions, which consists of a porous conductive carbon paper substrate layer and a conductive carbon powder microporous layer, wherein the diffusion layer is positioned between a gas flow channel and a proton exchange membrane in a fuel cell structure, and the substrate layer is positioned on one side of the gas flow channel; the base layer has a hydrophobicity gradient in a direction parallel to the diffusion layer, the content of the water repellent on the base layer is gradually changed from 12 wt% to 28 wt% from the gas inlet direction to the gas outlet direction, and the average content is 20 wt%; the microporous layer has a hydrophobic gradient in a direction perpendicular to the diffusion layer.
Preferably, the hydrophobicity gradient in the microporous layer is obtained by spraying conductive carbon powder slurry with hydrophobicity in gradient distribution on the substrate layer, wherein the conductive carbon powder slurry contains a water repellent; the hydrophobic property is distributed in a gradient mode, namely the content of the hydrophobic agent is changed layer by layer, namely 10 wt.%, 15 wt.% and 20 wt.%.
Preferably, the hydrophobic gradient in the substrate layer is obtained by treatment by capillary diffusion.
Preferably, the total content of the water repellent in the substrate layer is 15-25 wt%. More preferably 20 wt%.
Preferably, in the diffusion layer matched to the high humidity condition, the water repellency of the part of the microporous layer close to the proton exchange membrane is higher than that of the part close to the gas flow channel.
Preferably, in the diffusion layer matched with the high humidity working condition, the microporous layer is divided into at least three layers according to the hydrophobic gradient, and the range of the content of the water repellent is reduced by 4-6 wt% in each layer from the part close to the proton exchange membrane to the part close to the gas flow channel and is gradually reduced. More preferably, the water repellent content decreases in steps of 5 wt% reduction per layer.
Preferably, in the diffusion layer matched with the high humidity working condition, the microporous layer is divided into three layers according to the hydrophobic gradient, and the content of the hydrophobic agent is 20 wt%, 15 wt% and 10 wt% in sequence from the part close to the proton exchange membrane to the part close to the gas flow channel.
Preferably, in the diffusion layer matched with the working condition of medium and low humidity, the hydrophobicity of the part of the microporous layer close to the proton exchange membrane is lower than that of the part close to the gas flow channel.
Preferably, in the diffusion layer matched with the working condition of medium and low humidity, the microporous layer is divided into at least three layers according to the hydrophobic gradient, and the range of the hydrophobic agent content is increased by 4-6 wt% from the part close to the proton exchange membrane to the part close to the gas flow channel and is sequentially increased. More preferably, the water repellent content increases in order of magnitude by 5 wt% per layer.
Preferably, in the diffusion layer matched with the working condition of medium and low humidity, the microporous layer is divided into three layers according to the hydrophobic gradient, and the content of the hydrophobic agent is 10 wt%, 15 wt% and 20 wt% in sequence from the part close to the proton exchange membrane to the part close to the gas flow channel.
Preferably, the conductive carbon powder slurry with hydrophobicity in gradient distribution comprises at least three conductive carbon powder slurries with different hydrophobicity, and the loading capacity of the conductive carbon powder on the basal layer in unit area is equal.
Preferably, the diffusion layer is square with the side length of 15-25 mm. More preferably 20mm square.
The invention also relates to a preparation method of the fuel cell diffusion layer matched with the all working conditions, which comprises the following steps:
s1, vertically placing the porous conductive carbon paper, contacting the porous conductive carbon paper with the liquid surface of a water repellent emulsion for 5-30S, and diffusing the water repellent emulsion in the plane of the carbon paper through capillary action to form a water repellent gradient; drying at 75-85 ℃ for 1-2 min;
s2, repeating the step S1 until the mass fraction of the water repellent in the substrate layer reaches a set value; heating the hydrophobic carbon paper to 350-360 ℃ at the speed of 4-6 ℃/min, and roasting to obtain carbon paper with a hydrophobicity gradient parallel to the diffusion layer direction;
s3, mixing conductive carbon powder, water repellent emulsion and alcohol solvent according to the set hydrophobicity gradient of the microporous layer, and respectively preparing at least three conductive carbon powder slurries with different water repellent concentrations;
s4, sequentially spraying conductive carbon powder slurry with the same loading amount and different water repellent concentrations on the surface of the carbon paper with the water repellent gradient parallel to the direction of the diffusion layer according to the set water repellent gradient of the microporous layer, drying at 75-85 ℃ for 1-2min, and then heating to 350-360 ℃ at the speed of 4-6 ℃/min for roasting to obtain the microporous layer with the water repellent gradient perpendicular to the direction of the diffusion layer.
Preferably, the conductive carbon powder is one or a mixture of acetylene Black, Vulcan XC-72, Black pearls, carbon nanotubes and graphene powder.
Preferably, the water repellent emulsion is one or a mixture of more of Polytetrafluoroethylene (PTFE) emulsion, tetrafluoroethylene and hexafluoropropylene copolymer (FEP) emulsion, polyvinylidene fluoride (PVDF) emulsion, Polychlorotrifluoroethylene (PCTFE) suspension and other fluorine-containing polymers.
This patent design has the hydrophobicity gradient that is on a parallel with the diffusion layer direction simultaneously concurrently and the hydrophobicity gradient of perpendicular to diffusion layer direction, realizes by low humidity to the performance promotion under the full operating mode of high humidity. The hydrophobicity in the parallel direction is gradually increased from the gas inlet to the gas outlet, so that the discharge of liquid water to the flow channel outlet is accelerated, and the local flooding under high humidity is avoided; the hydrophobic gradient in the vertical direction is designed to be gradually increased from the proton membrane side to the flow channel side, the high hydrophobicity of the outermost layer can relieve high-humidity flooding to a certain extent, and meanwhile, the capillary pressure can promote liquid water under low humidity to be retained in the membrane, so that the moisturizing effect is realized; the synergistic effect of the two can ensure the improvement of the performance of the battery in the full working condition range from low humidity to high humidity. Simultaneously, the gradient method designed by the patent is realized by a capillary adsorption method, is simple to operate, and can be further adjusted according to a single working condition in a special environment: for example, aiming at a high-humidity environment, the enhancement of the hydrophobic gradient from the inlet to the outlet in the parallel direction and the enhancement of the hydrophobic gradient from the flow field to the membrane in the vertical direction can be combined, so that the efficient drainage effect is realized, the performance of the battery is greatly improved, and the method has the characteristics of simplicity, flexibility and easiness in operation.
Compared with the prior art, the invention has the following beneficial effects:
1. the hydrophobic gradient which rises along the gas flow direction is arranged in the direction parallel to the diffusion layer, so that the liquid water accumulation phenomenon (namely the water flooding phenomenon) generated along with the reaction can be effectively relieved; in addition, the invention forms hydrophobic gradient parallel to the direction of the diffusion layer in the substrate layer by utilizing the capillary action and the gravity action, the operation is simple, and the realization is easy;
2. the hydrophobic gradient matched based on the working condition is arranged in the direction vertical to the diffusion layer, and the structure with the hydrophobic gradient ascending along the direction from the flow field plate to the membrane electrode is adopted under the working condition of high humidity, so that the drainage effect of the cathode can be effectively improved, and the gas transmission rate of the diffusion layer is improved; under the working condition of medium and low humidity, a structure with hydrophobic gradient descending from the flow field plate to the membrane electrode is adopted, so that a certain moisture preservation effect can be achieved, the proton exchange membrane is ensured to be fully wetted, the internal resistance of the cell is reduced, and the output performance of the cell is improved.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a schematic illustration of the hydrophobization gradient of the diffusion layer of example 1;
FIG. 2 is a schematic illustration of the hydrophobization gradient of the diffusion layer of example 2;
FIG. 3 is a graph comparing the performance of three diffusion layers of examples 1, 2 and comparative example at 100% relative humidity;
fig. 4 is a graph comparing the performance of three diffusion layers of examples 1, 2 and comparative example at 80% relative humidity.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
Example 1
Aiming at the working characteristics of the diffusion layer of the proton exchange membrane fuel cell under the working condition of high humidity, the embodiment performs gradient hydrophobic modification on the substrate layer and the microporous layer of the traditional diffusion layer, thereby improving the transmission efficiency of gas, improving the drainage effect of a cathode and realizing the uniformity and stability of the performance of the cell.
The fuel cell diffusion layer structure based on the high humidity condition of the present embodiment is shown in fig. 1. The hydrophobicity of the part of the substrate layer close to the reaction gas inlet is lower than that of the part close to the reaction gas outlet (the total content of the hydrophobic agent PTFE in the substrate layer is 20 wt%); the hydrophobicity of the part of the microporous layer close to the proton exchange membrane is higher than that of the part close to the gas flow channel, the microporous layer is divided into three layers according to hydrophobicity gradient, the PTFE content is 10 wt%, 15 wt% and 20 wt% from low to high, wherein the unit area loading of each layer is 0.7mg/cm2。
The preparation method of the fuel cell diffusion layer based on the high humidity working condition of the embodiment is as follows:
1. preparation of the base layer: weighing carbon paper, vertically placing, contacting with PTFE emulsion liquid surface for 5-30s, diffusing carbon paper in a plane by capillary action to form hydrophobicity gradient (hydrophobicity is gradually reduced from bottom to top), drying at 80 deg.C for 1-2min, and weighing. Repeating the operation until the mass fraction of PTFE in the sample reaches 20 wt%, then placing the hydrophobic carbon paper in a muffle furnace, heating to 350 ℃ at the speed of 5 ℃/min, and roasting at the temperature for 60min to obtain the carbon paper with the hydrophobicity gradient parallel to the direction of the diffusion layer.
2. Preparing carbon powder slurry: according to the hydrophobicity gradient of a target microporous layer, Vulcan XC-72 carbon powder and PTFE emulsion with the concentration of 5% are mixed according to a certain proportion, ground and stirred for 24 hours on a ball mill, and then ultrasonically stirred for 30min to prepare carbon powder slurry with the PTFE contents of 10 wt%, 15 wt% and 20 wt%, respectively.
3. Preparation of microporous layer: sequentially spraying the carbon paper surface prepared in the step 1 by using an electrostatic spraying machine according to the gradient sequence of 10-15-20 wt% to obtain a loading amount of 0.7mg/cm2After drying the carbon powder slurry at the temperature of 80 ℃ for 1-2min, putting the sprayed carbon paper in a muffle furnace, heating to 350 ℃ at the speed of 5 ℃/min, and roasting at the temperature for 60min to obtain the microporous layer with the hydrophobicity gradient in the direction vertical to the diffusion layer.
Example 2
Aiming at the working characteristics of the diffusion layer of the proton exchange membrane fuel cell under the working condition of medium and low humidity, the embodiment performs gradient hydrophobic modification on the substrate layer and the microporous layer of the traditional diffusion layer, thereby ensuring that the proton exchange membrane is fully wetted during working, reducing the internal resistance of the cell and improving the output performance of the cell.
The structure of the diffusion layer of the fuel cell based on the working condition of medium and low humidity in the embodiment is shown in fig. 2. The hydrophobicity of the part of the substrate layer close to the reaction gas inlet is lower than that of the part close to the reaction gas outlet (the total content of the hydrophobic agent PTFE in the substrate layer is 20 wt%); the hydrophobicity of the part of the microporous layer close to the proton exchange membrane is lower than that of the part close to the gas flow channel, the microporous layer is divided into three layers according to hydrophobicity gradient, the PTFE content is 10 wt%, 15 wt% and 20 wt% from low to high, wherein the unit area loading of each layer is 0.7mg/cm2。
The preparation method of the fuel cell diffusion layer based on the high humidity working condition of the embodiment is as follows:
1. preparation of the base layer: weighing carbon paper, vertically placing, contacting with PTFE emulsion liquid surface for 5-30s, diffusing carbon paper in a plane by capillary action to form hydrophobicity gradient (hydrophobicity is gradually reduced from bottom to top), drying at 80 deg.C for 1-2min, and weighing. Repeating the operation until the mass fraction of PTFE in the sample reaches 20 wt%, then placing the hydrophobic carbon paper in a muffle furnace, heating to 350 ℃ at the speed of 5 ℃/min, and roasting at the temperature for 60min to obtain the carbon paper with the hydrophobicity gradient parallel to the direction of the diffusion layer.
2. Preparing carbon powder slurry: according to the hydrophobicity gradient of a target microporous layer, Vulcan XC-72 carbon powder and PTFE emulsion with the concentration of 5% are mixed according to a certain proportion, ground and stirred for 24 hours on a ball mill, and then ultrasonically stirred for 30min to prepare carbon powder slurry with the PTFE contents of 10 wt%, 15 wt% and 20 wt%, respectively.
3. Preparation of microporous layer: sequentially spraying the carbon paper surface prepared in the step 1 by using an electrostatic spraying machine according to the gradient sequence of 20-15-10 wt% to obtain a loading amount of 0.7mg/cm2After drying the carbon powder slurry at the temperature of 80 ℃ for 1-2min, putting the sprayed carbon paper in a muffle furnace, heating to 350 ℃ at the speed of 5 ℃/min, and roasting at the temperature for 60min to obtain the microporous layer with the hydrophobicity gradient in the direction vertical to the diffusion layer.
Comparative example 1
The comparative example used a more conventional fuel cell diffusion layer structure, and the carbon paper used for the base layer and the carbon powder used for the microporous layer were all the same as those used in examples 1 and 2. Both the substrate layer and the microporous layer in comparative example 1 were subjected to uniform hydrophobization treatment. The content of the water repellent PTFE in the substrate layer is 20 wt%; the content of PTFE in the microporous layer is 15 percent, and the unit area loading is 2.1mg/cm2。
The preparation method of the fuel cell diffusion layer of this comparative example is as follows:
1. preparation of the base layer: weighing the carbon paper, soaking the carbon paper in the PTFE emulsion for 5-30s, taking out, drying at 80 ℃ for 1-2min, and weighing. And repeating the operation until the mass fraction of the PTFE in the sample reaches 20 wt%, then placing the hydrophobic carbon paper in a muffle furnace, heating to 350 ℃ at the speed of 5 ℃/min, and roasting at the temperature for 60min to obtain the substrate layer carbon paper.
2. Preparing carbon powder slurry: mixing a certain proportion of Vulcan XC-72 carbon powder and 5% PTFE emulsion, grinding and stirring for 24h on a ball mill, and then ultrasonically stirring for 30min to obtain carbon powder slurry with the PTFE content of 15 wt%.
3. Preparation of microporous layer: carbon paper surface prepared in step 1 using electrostatic spray coaterThe spraying loading capacity is 2.1mg/cm2Drying the carbon powder slurry at 80 ℃ for 1-2min, putting the sprayed carbon paper in a muffle furnace, heating to 350 ℃ at the speed of 5 ℃/min, and roasting at the temperature for 60min to obtain the microporous layer.
The examples 1, 2 were compared to the conventional diffusion layer of the comparative example under the same operating conditions, and the experimental conditions were: relative humidity RH 100%, 80%, stoichiometric ratio H2：O22:9.5, operating pressure 1.5bar, operating temperature 80 ℃. The results of the performance comparison are shown in fig. 3 and 4.
Figure 3 shows a comparison of the performance of the three diffusion layers at 100% relative humidity. It can be seen that under the working condition that the relative humidity RH is 100%, the performance of the high current region of the embodiments 1 and 2 is obviously better than that of the comparative example 1, and it can be seen that the gradient hydrophobization structure in the embodiments 1 and 2 has better drainage effect under the working condition of high humidity. From the viewpoint of battery power, the maximum power density of example 1 reached 1980mW/cm2Compared with the comparative ratio, the ratio is improved by nearly 200mW/cm2。
Figure 4 shows a comparison of the performance of the three diffusion layers at 80% relative humidity. It can be seen that under the working condition that the relative humidity RH is 80%, the performance of the high current region in example 2 is better than that of the comparative example and example 1, and meanwhile, the performance of the medium and low current region in example 2 is also better than that of example 1, so that the gradient hydrophobization structure in example 2 has a better moisturizing effect under the working condition of medium and low humidity, and the performance reduction of the battery in the medium and low current region due to insufficient film wetting can be avoided. From the viewpoint of battery power, the maximum power density of example 2 reached 1800mW/cm2Compared with the comparative ratio, the ratio is improved by nearly 50mW/cm2。
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

Claims (5)

1. The fuel cell diffusion layer matched with all working conditions is characterized by comprising a porous conductive carbon paper substrate layer and a conductive carbon powder microporous layer, wherein the diffusion layer is positioned between a gas flow channel and a proton exchange membrane in a fuel cell structure, and the substrate layer is positioned on one side of the gas flow channel; the base layer has a hydrophobicity gradient in a direction parallel to the diffusion layer, the content of the water repellent on the base layer is gradually changed from 12 wt% to 28 wt% from the gas inlet direction to the gas outlet direction, and the average content is 20 wt%; the microporous layer has a hydrophobicity gradient in a direction perpendicular to the diffusion layer; the hydrophobicity gradient in the microporous layer is obtained by spraying conductive carbon powder slurry with hydrophobicity in gradient distribution on the substrate layer, and the conductive carbon powder slurry contains a hydrophobic agent; the hydrophobic property is distributed in a gradient way, namely the content of the hydrophobic agent is changed layer by layer, namely 10 wt.%, 15 wt.% and 20 wt.%; the hydrophobic gradient in the substrate layer is obtained by processing through a capillary diffusion method;
the hydrophobicity of the portion of the microporous layer adjacent to the proton exchange membrane is lower than the hydrophobicity of the portion adjacent to the gas flow channel.
2. The all-condition-matched fuel cell diffusion layer according to claim 1, wherein the hydrophobic gradient-distributed conductive carbon powder slurry comprises at least three different hydrophobic conductive carbon powder slurries, and the conductive carbon powder loading on the substrate layer per unit area is equal.
3. A method of making an all-condition-matched fuel cell diffusion layer as claimed in claim 1 or claim 2, comprising the steps of:
s1, vertically placing the porous conductive carbon paper, contacting the porous conductive carbon paper with the liquid surface of a water repellent emulsion for 5-30S, and diffusing the water repellent emulsion in the plane of the carbon paper through capillary action to form a water repellent gradient; drying at 75-85 ℃ for 1-2 min;
s2, repeating the step S1 until the mass fraction of the water repellent in the substrate layer reaches a set value; heating the hydrophobic carbon paper to 350-360 ℃ at the speed of 4-6 ℃/min, and roasting to obtain carbon paper with a hydrophobicity gradient parallel to the diffusion layer direction;
s3, mixing conductive carbon powder, water repellent emulsion and alcohol solvent according to the set hydrophobicity gradient of the microporous layer, and respectively preparing at least three conductive carbon powder slurries with different water repellent concentrations;
s4, sequentially spraying conductive carbon powder slurry with the same loading amount and different water repellent concentrations on the surface of the carbon paper with the water repellent gradient parallel to the direction of the diffusion layer according to the set water repellent gradient of the microporous layer, drying at 75-85 ℃ for 1-2min, and then heating to 350-360 ℃ at the speed of 4-6 ℃/min for roasting to obtain the microporous layer with the water repellent gradient perpendicular to the direction of the diffusion layer.
4. The method for preparing the fuel cell diffusion layer matched with the all-working condition according to claim 3, wherein the conductive carbon powder is one or a mixture of acetylene Black, Vulcan XC-72, Black pearls, carbon nano tubes and graphene powder.
5. The method for preparing the diffusion layer of the fuel cell matched with the all-condition as claimed in claim 3, wherein the water repellent emulsion is one or a mixture of polytetrafluoroethylene emulsion, copolymer emulsion of tetrafluoroethylene and hexafluoropropylene, polyvinylidene fluoride emulsion and polychlorotrifluoroethylene suspension.
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