High-conductivity and low-ventilation-resistance gas diffusion layer and preparation method and application thereof

Abstract

The invention relates to a high-conductivity and low-ventilation-resistance gas diffusion layer and a preparation method and application thereof. The gas diffusion layer comprises a supporting body and a microporous layer located on the surface of the supporting body, the microporous layer is formed by microporous layer slurry, and the microporous layer slurry comprises conductive filler, a wetting agent, a water repellent agent and water; the conductive filler comprises conductive carbon black AC80; the hydrophobic agent is selected from polytetrafluoroethylene and / or FEP (fluorinated ethylene propylene). The gas diffusion layer has excellent surface appearance performance and comprehensive performance such as conductivity, compression ratio and ventilation resistance.

Description

Technical Field

[0001] The invention belongs to the field of proton exchange membrane fuel cells, and in particular relates to a gas diffusion layer with high conductivity and low air permeability resistance, and a preparation method and application thereof. Background Art

[0002] Proton exchange membrane fuel cells are recognized for their high energy conversion efficiency, high energy density and environmental friendliness. The traditional gas diffusion layer is mainly composed of carbon paper and a microporous layer. The carbon paper, as the skeleton of the gas diffusion layer, mainly plays the role of conducting electricity, dissipating heat, and supporting the microporous layer; while the microporous layer mainly plays the role of reducing contact resistance and water vapor management. The quality of water vapor management is one of the important indicators for evaluating the performance of the gas diffusion layer. Carbon paper itself is a porous material. Generally, its porosity is as high as 90% or more. Therefore, the preparation of a microporous layer with low air permeability resistance is crucial to improving the performance of proton exchange membrane fuel cells. In the prior art, it is usually necessary to add an aqueous resin, such as an acrylic resin, when preparing the microporous layer. When such an aqueous resin is not added, the film-forming performance of the microporous layer slurry is insufficient, and the obtained microporous layer is prone to surface cracks and other phenomena. In addition, the conductivity of the existing microporous layer is not high enough, the air permeability resistance is still not low enough, and the compression rate is not moderate enough, resulting in the comprehensive performance of the gas diffusion layer is not excellent enough, which limits its application in proton exchange membrane fuels. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide an improved gas diffusion layer in view of the shortcomings and deficiencies of the prior art, wherein the gas diffusion layer has excellent surface appearance performance and comprehensive properties such as electrical conductivity, compressibility and air permeability resistance.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0005] A gas diffusion layer comprises a support and a microporous layer located on the surface of the support, wherein the microporous layer is formed by a microporous layer slurry, wherein the microporous layer slurry comprises a conductive filler, a wetting agent, a hydrophobic agent and water; the conductive filler comprises conductive carbon black AC80; and the hydrophobic agent is selected from polytetrafluoroethylene and / or polyperfluoroethylene propylene (FEP).

[0006] In the prior art, it is usually necessary to add water-based resins, such as acrylic resins, when preparing the microporous layer. When such water-based resins are not added, the film-forming performance of the microporous layer slurry is insufficient, and the obtained microporous layer is prone to surface cracks and the like. In addition, the conductivity of the existing microporous layer is not high enough, the air permeability resistance is still not low enough, and the compression rate is not moderate enough, resulting in the comprehensive performance of the gas diffusion layer being not excellent enough, limiting its application in proton exchange membrane fuels. The inventors of the present application have discovered through research that by using specific polytetrafluoroethylene and / or polyperfluoroethylene propylene FEP as a hydrophobic agent, and the dispersion of the above hydrophobic agent in water can also act as a film-forming resin. After the microporous layer slurry is sintered, the above hydrophobic agent can form a film, which can ensure that no cracks or the like will appear on the surface of the microporous layer, and has excellent surface appearance performance; secondly, by selecting conductive carbon black AC80 as a component of the conductive filler, compared with other conventional conductive fillers, the conductivity of the gas diffusion layer can be further improved, and the air permeability resistance of the gas diffusion layer can be reduced; adding a wetting agent to the microporous layer slurry can improve the wetting properties of the conductive filler, so that the microporous layer slurry is dispersed more evenly, so that the microporous layer is not easy to fall off on the support body, and the conductivity and air permeability of the gas diffusion layer are further improved.

[0007] In some embodiments, the microporous layer slurry includes, by weight, 10 to 30 parts of a conductive filler, 0.3 to 1 part of a wetting agent, 10 to 20 parts of a hydrophobic agent, and 150 to 180 parts of water.

[0008] In some embodiments, the conductive filler further includes graphite powder.

[0009] Preferably, the graphite powder is high-purity graphite powder (purity ≥ 99.95%).

[0010] Preferably, the graphite powder is nano graphite powder.

[0011] The combination of conductive carbon black AC80 and graphite powder can further improve the conductivity of the gas diffusion layer, reduce the air permeability resistance, and provide a moderate compression rate.

[0012] In some embodiments, the mass ratio of the conductive carbon black AC80 to the graphite powder is 1: 0.25 to 2. When there is too much graphite powder, it tends to aggregate into large particles and is not easy to disperse evenly, resulting in increased air permeability resistance of the gas diffusion layer and poor compression performance.

[0013] In some embodiments, the particle size of the conductive carbon black AC80 is 30 to 500 μm.

[0014] In some embodiments, the graphite powder has a particle size of 30 to 70 nm.

[0015] In some embodiments, the wetting agent is selected from a combination of one or more of a polyether wetting agent, a sodium alkylbenzene sulfonate wetting agent, and a silicone wetting agent.

[0016] In some embodiments, the microporous layer slurry further includes a dispersant. There is a synergistic effect between the dispersant and the wetting agent. After adding the dispersant, the uniform dispersion of the conductive filler can be further ensured, and the comprehensive performance of the gas diffusion layer can be further improved.

[0017] In some embodiments, the microporous layer slurry includes 2.5 to 10 parts of a dispersant by weight.

[0018] In some embodiments, the dispersant is selected from a combination of one or more of polyethylene oxide, polyacrylamide, sodium carboxymethyl cellulose, and Triton X-100.

[0019] In some embodiments, the support is carbon paper.

[0020] In some embodiments, the carbon paper is treated with a hydrophobic agent, and the hydrophobic agent is selected from polytetrafluoroethylene and / or poly(perfluoroethylene propylene) FEP.

[0021] The present invention further provides a method for preparing the above-mentioned gas diffusion layer, which comprises the steps of mixing the raw materials of the microporous layer slurry into the microporous layer slurry, and coating the microporous layer slurry on the support body and drying and sintering to form the microporous layer.

[0022] In some embodiments, the step of mixing the raw materials of the microporous layer slurry into the microporous layer slurry comprises the following steps:

[0023] Dissolving the wetting agent in part of the water to obtain a wetting agent aqueous solution; dispersing the hydrophobic agent in the remaining water to obtain a hydrophobic agent dispersion; adding the conductive filler to the wetting agent aqueous solution, dispersing, and then adding the hydrophobic agent dispersion, dispersing, to obtain the microporous layer slurry;

[0024] Alternatively, the wetting agent is dissolved in part of the water to obtain a wetting agent aqueous solution; the conductive filler and the dispersant are mixed to obtain a mixed powder; the hydrophobic agent is dispersed in the remaining water to obtain a hydrophobic agent dispersion; the mixed powder is added to the wetting agent aqueous solution, dispersed, and then the hydrophobic agent dispersion is added and dispersed to obtain the microporous layer slurry.

[0025] In some embodiments, the portion of water is 9 to 12 parts, and the remaining portion of water is 141 to 168 parts.

[0026] In some embodiments, the drying temperature is 120-210° C. and the drying time is 5-10 min.

[0027] In some embodiments, the sintering temperature is 330-380° C. and the sintering time is 20-40 min.

[0028] The present invention further provides use of the gas diffusion layer in a proton exchange membrane fuel cell.

[0029] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0030] The gas diffusion layer provided by the present invention has high conductivity, moderate compression rate, low air permeability resistance, and low surface resistance, which ensures good conductivity of the gas diffusion layer. The moderate compression rate ensures that the gas diffusion layer will not have sudden changes in pore size during stacking, and the low air permeability resistance enables the gas diffusion layer to have good water vapor management capabilities. The gas diffusion layer of the present invention has excellent surface appearance performance and comprehensive performances such as conductivity, compression rate and air permeability resistance.

[0031] The present invention adopts specific polytetrafluoroethylene and / or polyperfluoroethylene propylene FEP as a hydrophobic agent, selects conductive carbon black AC80 as a component of the conductive filler, and adds a wetting agent to the microporous layer slurry, so as to obtain a gas diffusion layer with excellent surface appearance performance and comprehensive properties such as conductivity, compressibility and air permeability resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a microscopic morphology of the gas diffusion layer prepared in Example 1;

[0033] Figure 2 This is a microscopic morphology of the gas diffusion layer prepared in Example 2;

[0034] Figure 3 This is a microscopic morphology of the gas diffusion layer prepared in Example 3;

[0035] Figure 4 This is a microscopic morphology of the gas diffusion layer prepared in Comparative Example 1;

[0036] Figure 5 This is a microscopic morphology of the gas diffusion layer prepared in Comparative Example 2;

[0037] Figure 6 This is a microscopic morphology of the gas diffusion layer prepared in Comparative Example 3. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is described in detail below in conjunction with specific embodiments so that those skilled in the art can better understand and implement the technical solution of the present invention, but the present invention is not limited to the scope of the examples.

[0039] In the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art.

[0040] Example 1

[0041] This embodiment provides a gas diffusion layer, and the preparation method thereof is as follows:

[0042] 0.5 g of a wetting agent, fatty alcohol polyoxyethylene ether, was added to 164.5 g of deionized water to obtain an aqueous solution having a low surface energy;

[0043] 12.5 g AC80 (particle size 50-200 μm) and 2.5 g dispersant sodium carboxymethyl cellulose were mechanically mixed to obtain a mixed powder;

[0044] Add 10 g of PTFE solid to 10 g of deionized water, stir and disperse, to obtain a PTFE aqueous dispersion;

[0045] 165 g of low surface energy aqueous solution was added to the mixed powder, and mechanically dispersed for 1.5 h. Then, PTFE aqueous dispersion was added and mechanically dispersed for 4.5 h to obtain a microporous layer slurry with high conductivity and low air permeability resistance.

[0046] The microporous layer slurry was coated on a support (hydrophobic carbon paper treated with PTFE aqueous dispersion), dried, and sintered at 350°C for 0.5 h to obtain a gas diffusion layer (containing carbon paper and microporous layer). The microscopic morphology is shown in the figure below. Figure 1 shown.

[0047] Example 2

[0048] This embodiment provides a gas diffusion layer, and the preparation method thereof is as follows:

[0049] 0.5 g of a wetting agent, fatty alcohol polyoxyethylene ether, was added to 164.5 g of deionized water to obtain an aqueous solution having a low surface energy;

[0050] 10 g AC80 (particle size 50-200 μm), 2.5 g high-purity graphite powder (purity ≥ 99.95%, particle size 30-50 nm) and 2.5 g dispersant sodium carboxymethyl cellulose were mechanically mixed to obtain a mixed powder;

[0051] Add 10 g of PTFE solid to 10 g of deionized water, stir and disperse, to obtain a PTFE aqueous dispersion;

[0052] 165 g of low surface energy aqueous solution was added to the mixed powder, and mechanically dispersed for 1.5 h. Then, PTFE aqueous dispersion was added and mechanically dispersed for 4.5 h to obtain a microporous layer slurry with high conductivity and low air permeability resistance.

[0053] The microporous layer slurry was coated on a support (hydrophobic carbon paper treated with PTFE aqueous dispersion), dried, and sintered at 350°C for 0.5 h to obtain a gas diffusion layer (containing carbon paper and microporous layer). The microscopic morphology is shown in the figure below. Figure 2 shown.

[0054] Example 3

[0055] This embodiment provides a gas diffusion layer, and the preparation method thereof is as follows:

[0056] 0.5 g of a wetting agent, fatty alcohol polyoxyethylene ether, was added to 164.5 g of deionized water to obtain an aqueous solution having a low surface energy;

[0057] 5 g AC80 (particle size 50-200 μm), 7.5 g high-purity graphite powder (purity ≥ 99.95%, particle size 30-50 nm) and 2.5 g dispersant sodium carboxymethyl cellulose were mechanically mixed to obtain a mixed powder;

[0058] Add 10 g of PTFE solid to 10 g of deionized water, stir and disperse, to obtain a PTFE aqueous dispersion;

[0059] 165 g of low surface energy aqueous solution was added to the mixed powder, and mechanically dispersed for 1.5 h. Then, PTFE aqueous dispersion was added and mechanically dispersed for 4.5 h to obtain a microporous layer slurry with high conductivity and low air permeability resistance.

[0060] The microporous layer slurry was coated on a support (hydrophobic carbon paper treated with PTFE aqueous dispersion), dried, and sintered at 350°C for 0.5 h to obtain a gas diffusion layer (containing carbon paper and microporous layer). The microscopic morphology is shown in the figure below. Figure 3 shown.

[0061] Comparative Example 1

[0062] This comparative example provides a gas diffusion layer, and its preparation method is as follows (refer to the graduation thesis "Preparation process and experimental research of new gas diffusion layer of proton exchange membrane fuel cell"):

[0063] A certain amount of conductive carbon black is added to a beaker containing anhydrous ethanol; the prepared mixed liquid beaker is placed in an ultrasonic cleaner and ultrasonically dispersed at 30°C for 0.5h, and then the beaker is placed on a magnetic stirrer and stirred again for 0.5h, and this process is repeated 5 times; after the above process is completed, a certain proportion of PTFE emulsion is weighed with a dropper and dripped into the mixed liquid, and the magnetic stirrer is continued to be dispersed for 0.5h; this part of the prepared slurry is sprayed onto the support layer as MPL1. At the same time, a certain proportion of PVP is weighed and added to anhydrous ethanol for magnetic stirring for 5h, mixed with the conductive carbon black and PTFE slurry and stirred for 2h, and this part of the slurry is sprayed onto the support layer as MPL2; the spraying process in the above experiment is carried out on an electric heating plate, the purpose is to quickly volatilize the anhydrous ethanol in the slurry. Finally, the prepared GDL is sintered in a tubular furnace.

[0064] The final microscopic morphology of the gas diffusion layer is shown in Figure 4 As shown, it can be seen that the surface of the GDL prepared by this method is smooth, but relatively dense, which is not conducive to water vapor transmission.

[0065] Comparative Example 2

[0066] This comparative example provides a gas diffusion layer, and its preparation method is basically the same as that of Example 1, except that the conductive carbon black AC80 is replaced by conductive carbon black XC-72. The microscopic morphology of the gas diffusion layer finally obtained is shown in FIG. Figure 5 As shown, it can be seen that the GDL prepared by XC-72 has a rough surface, more particles, and a denser structure, which poses a risk of piercing the CCM when assembled into a membrane electrode.

[0067] Comparative Example 3

[0068] This comparative example provides a gas diffusion layer, and its preparation method is basically the same as that of Example 1, except that the conductive carbon black AC80 is replaced by acetylene black. The microscopic morphology of the gas diffusion layer finally obtained is shown in FIG. Figure 6 As shown, it can be seen that the surface of the GDL prepared by acetylene black is good, but the microporous layer is not very loose.

[0069] According to the standard of "Proton Exchange Membrane Fuel Cell Part 7: Carbon Paper Property Test Method", the performance of the gas diffusion layer prepared in each embodiment and comparative example was tested, and the results are shown in Table 1 below.

[0070] Table 1 Performance of gas diffusion layers of various embodiments and comparative examples

[0071]

[0072] It can be seen that the present invention uses specific polytetrafluoroethylene and / or polyperfluoroethylene propylene FEP as a hydrophobic agent, selects conductive carbon black AC80 as a component of the conductive filler, and adds a wetting agent to the microporous layer slurry to obtain a gas diffusion layer with excellent surface appearance performance and comprehensive properties such as conductivity, compressibility and air permeability resistance. The combination of conductive carbon black AC80 and graphite powder can further improve the conductivity of the gas diffusion layer, reduce the air permeability resistance, and provide a moderate compressibility.

[0073] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

[0074] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

Claims

1. A gas diffusion layer, comprising a support and a microporous layer located on the surface of the support, characterized in that: The microporous layer is formed by microporous layer slurry, and the microporous layer slurry includes conductive filler, wetting agent, hydrophobic agent and water; the conductive filler includes conductive carbon black AC80; the hydrophobic agent is selected from polytetrafluoroethylene and / or polyperfluoroethylene propylene.

2. The gas diffusion layer according to claim 1, characterized in that: In parts by weight, the microporous layer slurry includes 10 to 30 parts of conductive filler, 0.3 to 1 part of wetting agent, 10 to 20 parts of hydrophobic agent and 150 to 180 parts of water.

3. The gas diffusion layer according to claim 1, characterized in that: The conductive filler also includes graphite powder.

4. The gas diffusion layer according to claim 3, characterized in that: The mass ratio of the conductive carbon black AC80 to the graphite powder is 1:0.25-2; and / or the particle size of the conductive carbon black AC80 is 30-500 μm; and / or the particle size of the graphite powder is 30-70 nm.

5. The gas diffusion layer according to claim 1, characterized in that: The wetting agent is selected from a combination of one or more of a polyether wetting agent, a sodium alkylbenzene sulfonate wetting agent, and a silicone wetting agent.

6. The gas diffusion layer according to claim 1, characterized in that: The microporous layer slurry also includes a dispersant.

7. The gas diffusion layer according to claim 6, characterized in that: In parts by weight, the microporous layer slurry includes 2.5 to 10 parts of a dispersant; and / or the dispersant is selected from a combination of one or more of polyethylene oxide, polyacrylamide, sodium carboxymethyl cellulose, and Triton X-100.

8. The gas diffusion layer according to claim 1, characterized in that: The support is carbon paper.

9. The gas diffusion layer according to claim 8, characterized in that: The carbon paper is treated with a hydrophobic agent, and the hydrophobic agent is selected from polytetrafluoroethylene and / or polyperfluoroethylene propylene.

10. A method for preparing a gas diffusion layer according to any one of claims 1 to 9, characterized in that: The preparation method comprises the steps of mixing raw materials of the microporous layer slurry to form the microporous layer slurry, and coating the microporous layer slurry on the support body and drying and sintering to form the microporous layer.

11. The preparation method according to claim 10, characterized in that: The step of mixing the raw materials of the microporous layer slurry into the microporous layer slurry comprises the following steps: Dissolving the wetting agent in part of the water to obtain a wetting agent aqueous solution; dispersing the hydrophobic agent in the remaining water to obtain a hydrophobic agent dispersion; adding the conductive filler to the wetting agent aqueous solution, dispersing, and then adding the hydrophobic agent dispersion, dispersing, to obtain the microporous layer slurry; Alternatively, the wetting agent is dissolved in part of the water to obtain a wetting agent aqueous solution; the conductive filler and the dispersant are mixed to obtain a mixed powder; the hydrophobic agent is dispersed in the remaining water to obtain a hydrophobic agent dispersion; the mixed powder is added to the wetting agent aqueous solution, dispersed, and then the hydrophobic agent dispersion is added and dispersed to obtain the microporous layer slurry.

12. The preparation method according to claim 11, characterized in that: Part of the water is 9 to 12 parts, and the remaining water is 141 to 168 parts.

13. Use of the gas diffusion layer according to any one of claims 1 to 9 in a proton exchange membrane fuel cell.

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