Gas diffusion layer substrate, preparation method thereof, corresponding gas diffusion layer, membrane electrode assembly and fuel cell

Abstract

The present invention discloses a substrate for a gas diffusion layer. The substrate for the gas diffusion layer is a carbon paper with a multi-layer composite structure, wherein the carbon fibers of the support layer have a cross-support structure. Such a structure enables the gas diffusion layer to have a higher compressive elastic modulus and a lower resistivity, and can achieve a surface resistivity in the vertical direction of less than 5 mΩ·cm under a surface pressure of 0.3 MPa. 2 The present application also discloses a preparation method thereof, a gas diffusion layer formed by the substrate, a membrane electrode assembly including the gas diffusion layer, and a fuel cell.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and more particularly to a fuel cell gas diffusion layer substrate, a preparation method thereof, a gas diffusion layer, a membrane electrode assembly and a fuel cell. Background Art

[0002] Proton exchange membrane fuel cells are energy conversion devices that convert the Gibbs free energy of chemical reactions stored in fuel into electrical energy through an electrode-electrolyte system. At present, a series of energy and environmental problems caused by the use of fossil fuels need to be solved urgently, and the search for a sustainable green energy source is of great strategic significance. Proton exchange membrane fuel cells have become an important power source in the future in the fields of automobiles, power stations, etc. It has the advantages of high efficiency, environmental protection, and rapid response, and is an important driving force for reducing carbon dioxide emissions.

[0003] The gas diffusion layer is one of the core components of the proton exchange membrane fuel cell, which consists of a substrate and a microporous layer. In order to ensure the efficient operation of the proton exchange membrane fuel cell, the gas diffusion layer must not only provide a transmission path for reactants and products, but also provide an exchange path for electricity and heat. Therefore, the gas diffusion layer is required to have good electrical conductivity, thermal conductivity, mechanical strength, corrosion resistance, air permeability and drainage performance.

[0004] However, the current fuel cell gas diffusion layer substrate usually adopts the conventional wet papermaking method. Since there is no hydrogen bond between carbon fibers, when only carbon fibers are used, the preform has no bonding strength and cannot be made into paper. Generally, bonding fibers or bonding fibers are used as auxiliary materials to help the carbon fibers form a stable mesh structure, so that the preform has mechanical strength. Generally, the carbon yield of binder fibers and binders in preforming is low, and they cannot play a role after carbonization, resulting in low strength of carbon paper and no processing ability. Some researchers have also used resin impregnation preforms to improve the strength of carbon paper. Carbon paper with low resin content has poor conductivity and mechanical strength. Carbon paper with high resin content has low porosity, average pore size and permeability, which is not conducive to the mass transfer performance of the gas diffusion layer.

[0005] From the above description, it can be known that how to ensure that the gas diffusion layer in the fuel cell has a high elastic modulus or compression resistance and a low resistivity can achieve a reduction in the resistance value of the fuel cell at a lower compression rate, which will not cause a decrease in mass transfer capacity due to a decrease in the porosity of the carbon paper caused by a larger compression rate, thereby reducing the battery performance. Summary of the invention

[0006] The purpose of the present application is to solve at least one of the above technical problems and provide an improved gas diffusion layer substrate.

[0007] To this end, some embodiments of the present application provide a substrate for a gas diffusion layer, wherein the substrate is a composite structure including at least one supporting layer and at least one common layer, wherein the supporting layer and the common layer are formed of carbon fibers; wherein the supporting layer includes an irregular underlying structure and a regular cross-support structure, wherein the cross-support structure includes at least a plurality of supporting members, each of the supporting members including an angled portion facing a surface of the supporting layer.

[0008] In some embodiments, the substrate of the gas diffusion layer is a multilayer composite structure consisting of a middle layer and outer layers on both sides of the middle layer; wherein the middle layer is composed of the support layer, and the outer layers are composed of the common layers.

[0009] In some embodiments, the intermediate layer is a composite structure, which is formed by combining at least one supporting layer and at least one common layer.

[0010] In some embodiments, a plurality of the support members are arranged in rows and columns to form at least one bridge-type cross-support structure.

[0011] In some embodiments, the support member is an angle support member and / or a triangular support member, wherein the triangular support member is a support member having a stable structure; and the angle support member is a support member that does not constitute a triangular stable structure.

[0012] In some embodiments, the angle α of the angled portion of the support member is less than 90°.

[0013] In some embodiments, the surface resistivity of the substrate in the perpendicular direction under a surface pressure of 0.3 MPa is less than 5 mΩ·cm 2 .

[0014] In some embodiments, a method for preparing the substrate of the gas diffusion layer is provided, which is used to prepare the substrate of the gas diffusion layer according to claim 1, and the method comprises: preparing a support layer base paper and preparing a common layer base paper, and then compounding the support layer base paper and the common layer base paper; wherein, preparing the support layer base paper comprises chopping carbon fibers into short carbon fibers with a length of 3 mm to 110 mm; dissociating the short carbon fibers into loose single short carbon fibers in a hammer mill; conveying the single short carbon fibers to a web-forming machine by air flow to form a first fiber web on a forming net; then forming the cross-support structure on the first fiber web by a needle punching process; then spraying an adhesive on the first fiber web to shape it; and then drying to prepare the support layer base paper; wherein, preparing the common layer base paper comprises chopping carbon fibers into short carbon fibers with a length of 3 mm to 110 mm; dissociating the short carbon fibers into loose single short carbon fibers in a hammer mill; conveying the single short carbon fibers to a web-forming machine by air flow to form a second fiber web on a forming net; directly spraying an adhesive on the second fiber web to shape it; and then drying to prepare the common layer base paper.

[0015] In some embodiments, the compounding includes respectively impregnating the support layer base paper and the common layer base paper with a resin solution; drying; stacking them in a predetermined order; and then hot pressing, carbonizing, and graphitizing to prepare the substrate.

[0016] Other embodiments of the present application provide a gas diffusion layer, which is formed based on any one of the above-mentioned gas diffusion layer substrates.

[0017] Other embodiments of the present application provide a membrane electrode assembly, which includes: a cathode side gas diffusion layer, a cathode side catalyst layer, a proton exchange membrane, an anode side catalyst layer and an anode side gas diffusion layer stacked in sequence; wherein the cathode side gas diffusion layer and / or the anode side gas diffusion layer include the gas diffusion layer as described above.

[0018] Some other embodiments of the present application provide a fuel cell, which includes a fuel cell stack consisting of the membrane electrode assembly as claimed in claim 9, a polar plate, a current collecting plate, an insulating plate, a sealing structure and an end plate.

[0019] The beneficial effects of the technical solution proposed in the present application include: the substrate of the gas diffusion layer proposed in the present application has a bridge-type cross-support structure, so it has a lower surface resistivity at a lower surface pressure, so that the carbon paper does not need to be compressed too much, thereby reducing the surface resistivity to the expected value while ensuring that the mass transfer capacity is not reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0021] Figure 1 It is a schematic structural diagram of a substrate in a gas diffusion layer according to an embodiment of the present application.

[0022] Figure 2 It is a schematic structural diagram of a substrate in a gas diffusion layer according to another embodiment of the present application.

[0023] Figure 3 It is a schematic diagram showing the included angle of the cross-support structure of the substrate of the gas diffusion layer according to an embodiment of the present application.

[0024] Figure 4 It is a schematic diagram showing the included angle of the cross-support structure of the substrate of the gas diffusion layer according to another embodiment of the present application.

[0025] Figure 5 The present invention is a flow chart of a method for preparing a substrate of a gas diffusion layer in an embodiment of the present application. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Since the gas diffusion layer is a porous structure material, the porosity of the substrate carbon paper is above 70%, so it has a large body resistance and does not utilize electron transmission. Therefore, in the assembly of the battery stack, the resistance is reduced by compressing the thickness of the carbon paper. The compression rate is generally between 15% and 30%. This compression will directly reduce the volume of the gas diffusion layer while reducing the resistance, resulting in a significant reduction in porosity. The reduction in porosity or pore volume will cause the fuel cell's ability to transmit hydrogen, air, and water to decrease, thereby causing the fuel cell's performance to decrease.

[0028] In order to solve the above problems, the present invention provides a gas diffusion layer of a fuel cell. The gas diffusion layer adopts a substrate formed based on carbon paper. The substrate has a higher compressive elastic modulus and a lower surface resistivity.

[0029] The substrate of the gas diffusion layer in some embodiments of the present application is as follows Figure 1 As shown, such a substrate includes a middle layer of base paper A and outer layers of base paper B on both sides of the middle layer of base paper A. The outer layer of base paper B can be an ordinary layer formed based on traditional non-woven web technology, while the middle layer of base paper has a support layer with supporting structural characteristics, including irregularly distributed chopped carbon fibers represented by thick solid lines, i.e., bottom carbon fibers 200, and regular chopped carbon fibers represented by short dashed lines, i.e., the chopped carbon fibers form a cross-support structure 100 through a needle-punching or hydroentanglement process in the base paper preparation process.

[0030] The cross support structure 100 may be formed by a plurality of support members 101, each of which includes an angle portion 101A facing the outer base paper B. The angle portion has an angle α, which is less than 90°, preferably less than 60°, and more preferably less than 30°. For example, the angle α may be Figure 3 30° as shown, or Figure 4 60° shown.

[0031] The support member 101 is generally divided into two types, namely, an angle support member and / or a triangular support member, wherein the triangular support member is a support member with a stable structure; the angle support member is a support member that does not form a triangular stable structure. The angle support member is generally composed of two carbon fibers, while the triangular support member is composed of two carbon fibers and carbon fibers in the fiber web that are not raised by the needle punching process, and this triangular support member has the most stable mechanical support. After impregnation with resin and drying, a triangular support structure with stronger support can be obtained.

[0032] The support members 101 may be distributed uniformly or non-uniformly in the middle layer base paper A, and may be distributed throughout the entire middle layer base paper A, or only in a portion of the middle layer base paper A, such as the central portion.

[0033] A typical cross-support structure 100 may be a bridge-type cross-support structure, that is, it is composed of support members 100 arranged in continuous rows and columns. In addition, the bridge-type cross-support structure may be multiple, so as to cover the entire middle layer base paper A.

[0034] These support members 101 of the middle layer base paper A can be formed by needling a carbon fiber net (referred to as fiber net) made by a dry process through a needling process. After subsequent impregnation with resin and drying, the support member 101 can be shaped to further enhance the support effect. In the present invention, the chopped fibers of the base paper prepared by the dry process are fluffy and irregular, and the fiber distribution can be changed by needling, that is, the support member 101 is formed so that it becomes partially regular. The needling process is particularly suitable for base paper prepared by the dry process, while the base paper prepared by the wet process will directly cut the chopped carbon fibers due to the influence of dispersants, binders, etc. in the wet process.

[0035] The above different angles can be achieved by controlling the direction of the needle.

[0036] Furthermore, it should be understood that although Figure 1 , Figure 2 Only a cross-support structure facing one direction is given, but the embodiments of the present application can be easily expanded to form cross-support structures facing two different directions. For example, one or a group of first cross-support structures face the outer base paper of the upper layer, while another or another group of second cross-support structures face the outer base paper of the lower layer. Moreover, the physical properties of the substrate can be adjusted by controlling the first cross-support structure and the second cross-support structure. In addition, similarly, the first cross-support structure and the second cross-support structure can be bridge-type cross-support structures formed by continuous supporting members.

[0037] The present invention also provides a method for preparing the above-mentioned carbon paper as a substrate for the gas diffusion layer of a fuel cell, the method comprising the following steps: preparing the support layer base paper and the common layer base paper of the substrate by a dry method. The preparation of the support layer base paper comprises the following steps: chopping the carbon fibers into short carbon fibers with a length of 3 mm to 110 mm, dissociating them into loose single fibers in a hammer mill, and then conveying them to a web forming machine by air flow, forming a first fiber web on a forming net, and then forming a bridge-type cross-support structure by a needle punching or hydroentanglement process, and drying to prepare the support layer base paper A.

[0038] The preparation of the common layer base paper B includes the following steps: cutting the carbon fiber into short carbon fibers with a length of 3 mm to 110 mm, dissociating them into loose single fibers in a hammer mill, and then conveying them to a web forming machine by air flow to form a second fiber web on a forming net, and then directly spraying an adhesive and drying them to prepare the common layer base paper B.

[0039] Further, the prepared support layer base paper A and the common layer base paper B are respectively impregnated with a numerical solution, such as a phenolic resin, an epoxy resin, or a resin solution prepared by mixing a phenolic resin, an epoxy resin and polyetheretherketone, and then dried according to the following steps: Figure 1 BAB as shown, or Figure 2The BABAB, or BAAB and other common base paper B are stacked with the support layer base paper A, and then subjected to hot pressing, carbonization and graphitization treatment to prepare carbon paper that can be used as a substrate for a gas diffusion layer.

[0040] It can be seen that the middle layer of the substrate in the present application can be understood in a broad sense, that is, the middle layer can be made of only support layer base paper, or a composite structure formed by support layer base paper and ordinary layer base paper, for example, a composite structure with a support layer in the middle and ordinary layers on the upper and lower sides.

[0041] Example 1: Figure 5 As shown, a typical substrate according to the present application can be prepared at least by the following method, using T700-48K carbon fiber as the carbon fiber raw material.

[0042] Step S11: chopping into short fibers of about 5 mm, using air as a dispersion medium and a high-speed roller with a rotation speed of 3000 rpm to disperse the carbon fiber raw materials into a single fiber state;

[0043] Step S12: The chopped carbon fiber is then brought into a web laying machine through an air flow fiber conveyor with a flow rate of 300 m / s, and the chopped carbon fiber is settled by gravity. After the settling is completed, a needling process is used to form a bridge-type cross-supported carbon fiber structure. After the settling, a 0.8 mm thick non-woven support layer base paper A can be formed; after the settling is completed, a non-woven ordinary layer base paper B can be prepared by direct molding;

[0044] Step S13: After being outputted by the conveyor belt of the web laying machine, the non-woven support layer base paper A and the non-woven common layer base paper B are sprayed with an adhesive and dried at 95° C., and rolled up to obtain the support layer base paper A and the common layer base paper B of the gas diffusion layer substrate;

[0045] Step S14: Immerse the support layer base paper A and the common layer base paper B prepared in step 13 in the prepared phenolic resin solution, and then dry them. Then stack them in a BAB manner, and heat press them to prepare composite paper;

[0046] Step S15: heat-treating the composite paper prepared in step 14 in a carbonization and graphitization furnace to obtain a substrate of carbon paper material.

[0047] The thickness of the gas diffusion layer substrate is 200um, the volume density is 0.33g / cm3, and the vertical surface resistivity is 4.0mΩ·cm under a surface pressure of 0.3MPa. 2 .

[0048] It should be understood that under the principles of the present application, the above embodiments can be modified as needed. For example, the length and diameter of the short fibers can be changed according to different property requirements.

[0049] It should be understood that, in addition to T700-48K carbon fiber, other embodiments of the present application may use carbon fiber with other carbon filament quantities. In order to obtain substantially the same carbon fiber directional distribution effect, ie, directional effect, the blowing speed of the airflow may be adjusted.

[0050] In addition, it should be understood that, in addition to being chopped into 5 mm short carbon fibers, in other embodiments, it can also be chopped into 3 mm, 7 mm, 10 mm, 20 mm, 50 mm, 100 mm or any length of carbon fibers in between. In addition, in addition to forming non-woven base paper based on short carbon fibers of the same length, other embodiments of the present application can form non-woven base paper based on carbon fibers of different lengths. For example, carbon fibers of different lengths can be input into the high-speed roller 10, such as 3 mm, 5 mm, 10 mm, 20 mm, 50 mm, 100 mm or any length in between, or short carbon fibers of different lengths less than 10 mm and long carbon fibers greater than 10 mm.

[0051] It should be understood that in addition to the nonwoven support layer base paper and the nonwoven common layer base paper having a thickness of 0.8 mm, nonwoven support layer base paper and nonwoven common layer base paper having other reasonable thicknesses may also be formed.

[0052] It should be appreciated that in addition to graphitizing the carbon fiber tows, in other embodiments they may also be rinsed in a cleaning solvent to remove the protective layer of epoxy or other resin.

[0053] Table 1 is a comparison of physical performance indicators of the substrates according to Examples 2 to 6 of the present application and the existing single-layer carbon paper as a substrate. Compared with the examples, these examples only adjust the angle of the support member in the cross support structure by changing the angle of the needle punching.

[0054] Combination Carbon paper thickness (μm) Area density (kg / m²) Angle of base paper A Thickness reduction rate at 1MPa <![CDATA[Surface resistivity at 0.3 MPa (mΩ·cm 2 )]]> Existing products 1 Single layer 150 0.33 —— 23.0% 12 Existing products 2 Single layer 200 0.40 —— 17.0% 12 Example 2 BAB 150 0.33 10° 5.0% 4.5 Example 3 BAB 150 0.33 30° 7.1% 3.46 Example 4 BAB 150 0.33 60° 5.0% 4.9 Example 5 BABAB 200 0.37 10° 5.9% 4.2 Example 6 BABAB 200 0.37 60° 6.2% 4.5

[0055] As can be seen from Table 1, the carbon paper material substrate provided in the present application can achieve a vertical surface resistivity of less than 5 mΩ·cm under a surface pressure of 0.3 MPa. 2 , it can achieve lower resistivity at low compression rate, thus ensuring that the gas diffusion layer has good mass transfer capacity.

[0056] Existing products can only reduce the surface resistivity to 5mΩ·cm under a higher surface pressure (>1MPa). 2, and this pressure will cause the carbon paper to compress by about 20% (median value), reduce the porosity of the carbon paper, and cause the mass transfer capacity to decrease. However, since the substrate of the present invention has a cross-support structure, especially a bridge-type cross-support structure, it has a lower surface resistivity at a lower surface pressure, so that the carbon paper does not need to be compressed too much, thereby reducing the surface resistivity to the desired value while ensuring that the mass transfer capacity is not reduced.

[0057] Based on this principle, the substrate of other embodiments of the present application may also be a structure including only a support layer and a common layer, and the common layer may be located above or below the support layer. The support layer and the common layer both have the structure of the aforementioned embodiment, and / or are both prepared by the aforementioned preparation method.

[0058] After the substrate is prepared, the present application may further include preparing a microporous layer slurry, wherein the microporous layer slurry includes a mixture of a conductive material, a pore-forming agent, a hydrophobic agent, and a dispersion liquid; mixing and dispersing the microporous layer slurry uniformly; applying the microporous layer slurry on the surface of the substrate after the hydrophobic treatment by direct coating or screen printing; and calcining the substrate coated with the microporous layer slurry.

[0059] Some other embodiments of the present application also disclose a membrane electrode assembly, which includes: a cathode side gas diffusion layer, a cathode side catalyst layer, a proton exchange membrane, an anode side catalyst layer and an anode side gas diffusion layer stacked in sequence; wherein the cathode side gas diffusion layer includes the gas diffusion layer of any one of the above-mentioned fuel cells; and the anode side gas diffusion layer includes the gas diffusion layer of any one of the above-mentioned fuel cells.

[0060] Some other embodiments of the present application further disclose a fuel cell, which includes a fuel cell stack composed of the membrane electrode assembly, polar plates, current collecting plates, insulating plates, sealing structures, and end plates as described above.

[0061] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A substrate for a gas diffusion layer, characterized in that: The substrate is a composite structure including at least one support layer and at least one common layer, wherein the support layer and the common layer are formed of carbon fibers; wherein the support layer includes an irregular bottom layer structure and a regular cross support structure, wherein the cross support structure includes at least a plurality of support members, each of the support members includes an angle portion facing a surface of the support layer; wherein the substrate of the gas diffusion layer is prepared by the following method: Prepare a support layer base paper and a common layer base paper, and then composite the support layer base paper and the common layer base paper; wherein the preparation of the support layer base paper includes chopping carbon fibers into short carbon fibers with a length of 3 mm to 110 mm; dissociating the short carbon fibers into loose single short carbon fibers; Forming the single short carbon fiber into a first fiber web; Then forming the cross support structure on the first fiber web by a needle punching process; Then, the first fiber web is sprayed with adhesive to set the shape; and then the support layer base paper is prepared after drying; wherein, the preparation of the common layer base paper includes chopping the carbon fibers into short carbon fibers with a length of 3 mm to 110 mm; dissociating the short carbon fibers into loose single short carbon fibers; Forming the single short carbon fiber into a second fiber web; directly spraying adhesive onto the second fiber web to set the shape; Then drying to prepare a common layer base paper; The compounding comprises respectively impregnating the support layer base paper and the common layer base paper with a resin solution; After drying, the materials are stacked in a predetermined order; Then, the substrate is prepared through hot pressing, carbonization and graphitization treatment.

2. The gas diffusion layer substrate according to claim 1, characterized in that: The substrate of the gas diffusion layer is a multi-layer composite structure consisting of an intermediate layer and outer layers on both sides of the intermediate layer; wherein the intermediate layer is composed of the support layer, and the outer layers are composed of the common layers.

3. The substrate for the gas diffusion layer according to claim 2, characterized in that: Furthermore, the middle layer is a composite structure, and the composite structure is formed by combining at least one supporting layer and at least one common layer.

4. The substrate for the gas diffusion layer according to claim 1, characterized in that: in, A plurality of the support members are arranged in rows and columns to form at least one bridge-type cross-support structure.

5. The substrate for the gas diffusion layer according to claim 1, characterized in that: in, The support member is an angle support member and / or a triangular support member, wherein the triangular support member is a support member having a stable structure; and the angle support member is a support member that does not form a triangular stable structure.

6. The substrate for the gas diffusion layer according to claim 1, characterized in that: The angle α of the angle portion of the support member is less than 90°; the surface resistivity of the substrate in the vertical direction under a surface pressure of 0.3 MPa is less than 5 mΩ·cm 2 .

7. The substrate for the gas diffusion layer according to claim 1, characterized in that: The short carbon fibers are dissociated in a hammer mill to form the first fiber web and the second fiber web on a forming net of a web forming machine.

8. A gas diffusion layer, characterized in that: A substrate for a gas diffusion layer according to any one of claims 1 to 7 is formed.

9. A membrane electrode assembly, characterized in that: The membrane electrode assembly comprises: a cathode side gas diffusion layer, a cathode side catalyst layer, a proton exchange membrane, an anode side catalyst layer and an anode side gas diffusion layer stacked in sequence; wherein the cathode side gas diffusion layer and / or the anode side gas diffusion layer comprises the gas diffusion layer as claimed in claim 8.

10. A fuel cell, characterized in that A fuel cell stack comprising the membrane electrode assembly as claimed in claim 9, a polar plate, a current collecting plate, an insulating plate, a sealing structure and an end plate.

Images