A method for preparing a gas diffusion layer suitable for a forced air cooling membrane electrode

Abstract

The application belongs to the field of membrane electrode, and particularly relates to a preparation method of a gas diffusion layer suitable for air-cooled membrane electrode. The gas diffusion layer is composed of a substrate layer, a microporous layer and a filler layer, and a detailed preparation method is provided based on carbon material, hydrophobic agent and solvent as basic raw materials. The application solves the defect of high condition sensitivity of the existing air-cooled membrane electrode, reduces porosity by utilizing the porous characteristics of the microporous layer and the filler layer, prolongs the diffusion length of the gas, so as to achieve the effect of water retention and ensure the wetting property of the proton exchange membrane.

Description

Technical Field

[0001] This invention belongs to the field of membrane electrodes, and specifically relates to a method for preparing a gas diffusion layer suitable for air-cooled membrane electrodes. Background Technology

[0002] Open-cathode air-cooled fuel cell stacks simplify the cooling system, air compressor, and air pump components of traditional fuel cell stacks, making fuel cells more convenient for portable power applications. However, this simplification leads to significant differences in heat and mass transfer between air-cooled and traditional stacks, placing different demands on the core components of the fuel cell membrane electrode assembly (MEA). Open-cathode air-cooled stacks omit the cathode humidification system, relying on fan airflow for air supply and stack cooling. During operation, the increased stack temperature and fan airflow accelerate the evaporation and diffusion of water vapor at the cathode, causing the proton exchange membrane to dry out, reducing proton conductivity, and ultimately degrading stack performance. Therefore, a highly stable MEA that improves proton exchange membrane dehydration is urgently needed to address this deficiency. Summary of the Invention

[0003] To address the problems in the prior art, this invention provides a method for preparing a gas diffusion layer suitable for air-cooled membrane electrodes, which solves the defects of existing membrane electrodes. By utilizing the low porosity of the microporous layer and the filler layer, the diffusion length of the gas is extended, thereby achieving the effect of moisture retention and ensuring the wettability of the proton exchange membrane.

[0004] To achieve the above technical objectives, the technical solution of the present invention is as follows:

[0005] A method for preparing a gas diffusion layer suitable for air-cooled film electrodes, the gas diffusion layer being composed of a substrate layer, a microporous layer, and a filling layer.

[0006] The base layer is made of carbon paper or carbon cloth, and the carbon paper or carbon cloth is woven from carbon fibers.

[0007] The microporous layer is formed by coating a carbon slurry made by thoroughly mixing conductive carbon black, a hydrophobic agent, and a solvent, with a solid content of 8-12%. The mass of the hydrophobic agent is 25-35% of the mass of the conductive carbon black. The conductive carbon black is a mixed carbon powder composed of bulk graphite and carbon particles. The particle size of the bulk graphite is 10-30 μm, and the particle size of the carbon particles is 30-60 nm, with a mass ratio of bulk graphite to carbon particles of 3-0.5. The hydrophobic agent is one or more of polytetrafluoroethylene emulsion, a copolymer emulsion of tetrafluoroethylene and hexafluoropropylene, polyvinylidene fluoride emulsion, and polychlorotrifluoroethylene suspension. The solvent is one or more of ethanol, isopropanol, n-propanol, and ethylene glycol. The stirring method is one or more of ultrasonic dispersion, high-speed dispersion, and centrifugal dispersion. The viscosity of the carbon slurry is 1000-5000 cps. The conductive carbon black here forms a cross-filled structure of large and small particles. The porous structure of graphite is used to fix the cavity structure, thus achieving fixed cavity. The carbon particles of the small particle size system compress the space of the cavity to form a long channel structure. Secondly, the small particle size structure can form a stable surface covering effect. With the use of hydrophobic agents, the microporous layer can form a hydrophobic structure and achieve a water retention effect.

[0008] The filler layer is formed by coating a carbon slurry made from conductive carbon black, a hydrophobic agent, and a solvent after thorough mixing. The solid content is 5-10%, and the hydrophobic agent accounts for 10-30% of the carbon black mass. The carbon black consists of carbon particles with a particle size range of 30-60 nm. The hydrophobic agent is one or more of the following: polytetrafluoroethylene emulsion, a copolymer emulsion of tetrafluoroethylene and hexafluoropropylene, polyvinylidene fluoride emulsion, and polychlorotrifluoroethylene suspension. The solvent is one or more of the following: ethanol, isopropanol, n-propanol, and ethylene glycol. The mixing method is one or more of the following: ultrasonic dispersion, high-speed dispersion, and centrifugal dispersion. The viscosity of the filler layer slurry is <200 cps. Under this viscosity condition, the slurry has excellent downward penetration ability and can form a complex with the microporous layer. The filler layer forms a coating on the substrate surface, and combined with the permeability of the carbon particles and the fluidity of the hydrophobic agent solvent, achieves a penetrating and covering effect, thereby achieving overall uniform hydrophobicity and ensuring stable use in special environments.

[0009] The method for preparing the gas diffusion layer includes the following steps:

[0010] Step 1: The prepared microporous carbon paste is coated onto the surface of the substrate and dried at high temperature and sintered at high temperature to form a gas diffusion layer intermediate. The coating method is one of screen printing, scraping, or spraying. The coating thickness is 30-80μm. The high temperature drying temperature is 80-120℃ and the high temperature sintering temperature is 350-380℃.

[0011] Step 2: Place the gas diffusion layer intermediate on a coating platform with a vacuum adsorption panel, with the microporous layer facing down and the substrate layer facing up; coat the prepared filling layer carbon paste onto the substrate surface, dry at high temperature, and sinter at high temperature to form a gas diffusion layer with high water retention capacity; the coating loading is 0.2-2 mg / cm³. 2 The high-temperature drying temperature is 80-120℃, and the high-temperature sintering temperature is 350-380℃.

[0012] This technical solution utilizes the particulate nature of graphite to form a microporous layer on the substrate surface, combined with the low particle size of carbon materials to achieve surface coverage and pore size control, thereby increasing the gas particle size. Furthermore, by utilizing secondary coating on the reverse side in conjunction with the high-efficiency permeability of vacuum adsorption, the penetration and coverage effect of carbon paste is improved, resulting in overall surface coverage and enhanced moisture retention.

[0013] As can be seen from the above description, the present invention has the following advantages:

[0014] 1. This invention solves the defects of existing membrane electrodes by utilizing the low porosity of the microporous layer and the filler layer to extend the gas diffusion length, thereby achieving the effect of moisture retention and ensuring the wettability of the proton exchange membrane.

[0015] 2. The microporous layer in this invention, constructed with graphitized carbon and filled with carbon particles, reduces the porosity of the gas diffusion layer and extends the diffusion length of the gas in the microporous layer. This allows more water vapor generated at the cathode to remain near the catalyst layer, ensuring the wettability of the proton exchange membrane.

[0016] 3. The present invention performs secondary filling on the substrate, which further reduces the porosity of the gas diffusion layer, extends the diffusion length of gas in the microporous layer, and improves the water retention capacity of the gas diffusion layer. Attached Figure Description

[0017] Figure 1 This describes the performance of Embodiment 1 and the comparative example of the present invention in an air-cooled fuel cell stack. Detailed Implementation

[0018] Combination Figure 1 This invention provides a detailed description of specific embodiments of the invention, but does not limit the scope of the claims.

[0019] Example 1

[0020] A gas diffusion layer includes: a substrate layer, a microporous layer, and a filling layer.

[0021] Base layer: Carbon paper: TGP-H-060;

[0022] The microporous layer slurry is formed by coating a carbon slurry after thorough mixing of conductive carbon black, a hydrophobic agent, and a solvent. The conductive carbon black is a mixture of 20μm graphite and 50nm carbon black in a mass ratio of 3:1. The hydrophobic agent is selected from PTFE emulsion and added at 30% of the carbon black mass. The above materials are thoroughly mixed with ethanol, and the solid content is 10%. The microporous layer is screen-printed onto the substrate surface, with a controlled thickness of 60μm. After drying at 100℃ and sintering at 370℃, a gas diffusion layer intermediate is formed.

[0023] The filler layer is a mixture of 50nm carbon black, PTFE emulsion, and ethanol, with a solid content of 5% and PTFE accounting for 30% of the carbon black content. The filler layer is sprayed into the substrate layer, with the loading controlled at 0.5 mg / cm³. 2 A gas diffusion layer with high water retention capacity is formed by drying at 100℃ and sintering at 370℃.

[0024] Example 2

[0025] A gas diffusion layer includes: a substrate layer, a microporous layer, and a filling layer.

[0026] Base layer: Carbon paper: TGP-H-060;

[0027] The microporous layer slurry is formed by coating a carbon slurry after thorough mixing of conductive carbon black, a hydrophobic agent, and a solvent. The conductive carbon black is a mixture of 10μm graphite and 30nm carbon black in a mass ratio of 3:1. The hydrophobic agent is a copolymer emulsion of tetrafluoroethylene and hexafluoropropylene, added at 25% of the carbon black mass. Isopropanol is used to thoroughly mix the above materials, with a solid content of 8%. The microporous layer is screen-printed onto the substrate surface, with a controlled thickness of 30μm. After drying at 80℃ and sintering at 350℃, a gas diffusion layer intermediate is formed.

[0028] The filler layer is a mixture of 30nm carbon black, PTFE emulsion, and n-propanol, with a solid content of 5% and PTFE accounting for 20% of the carbon black content. The filler layer is sprayed into the substrate layer, with the loading controlled at 0.2 mg / cm³. 2 A gas diffusion layer with high water retention capacity is formed by drying at 80℃ and sintering at 350℃.

[0029] Example 3

[0030] A gas diffusion layer includes: a substrate layer, a microporous layer, and a filling layer.

[0031] Base layer: Carbon paper: TGP-H-060;

[0032] The microporous layer slurry is formed by coating a carbon slurry after thorough mixing of conductive carbon black, a hydrophobic agent, and a solvent. The conductive carbon black is a mixture of 30μm graphite and 60nm carbon black in a mass ratio of 3:1. The hydrophobic agent is a copolymer emulsion of tetrafluoroethylene and hexafluoropropylene, added at 35% of the carbon black mass. Isopropanol is used to thoroughly mix the above materials, with a solid content of 12%. The microporous layer is screen-printed onto the substrate surface, with a controlled thickness of 80μm. After drying at 120℃ and sintering at 380℃, a gas diffusion layer intermediate is formed.

[0033] The filler layer is a mixture of 30nm carbon black, PTFE emulsion, and ethylene glycol, with a solid content of 10% and PTFE accounting for 30% of the carbon black content. The filler layer is sprayed into the substrate layer, with the loading controlled at 2 mg / cm³. 2 A gas diffusion layer with high water retention capacity is formed by drying at 120℃ and sintering at 380℃.

[0034] Comparative Example

[0035] The carbon paper TGP-H-060 undergoes hydrophobic treatment through PTFE emulsion soaking, drying, and sintering, with PTFE weight gain of 10%. The microporous layer slurry is made by mixing 50nm carbon black in a mass ratio of 3:1. The hydrophobic agent is selected from PTFE emulsion, with an addition amount of 30% of the carbon black mass. The above materials are thoroughly mixed with ethanol, with a solid content of 10%. The paper is then screen-printed onto the surface of the substrate layer and prepared through a drying and sintering process.

[0036] Performance testing

[0037] Using the gas diffusion layer prepared in Example 1 as a test example and the comparative example as an existing example, it was applied to an air-cooled fuel cell stack, such as... Figure 1 As shown, the gas diffusion layer provided by this technical solution is significantly better than the comparative example in terms of electrical density performance. By utilizing the combination of the microporous layer and the filling layer, the porosity is reduced, thereby extending the gas channel and ensuring the wettability of the proton exchange membrane.

[0038] It is understood that the above detailed description of the present invention is for illustrative purposes only and is not intended to limit the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention to achieve the same technical effects; as long as the usage requirements are met, they are all within the protection scope of the present invention.

Claims

1. A method for preparing a gas diffusion layer suitable for air-cooled film electrodes, characterized in that: The gas diffusion layer consists of a base layer, a microporous layer, and a filling layer; The microporous layer is formed by coating a carbon paste made by thoroughly mixing conductive carbon black, a hydrophobic agent, and a solvent, with a solid content of 8-12%, and the mass of the hydrophobic agent is 25-35% of the mass of the conductive carbon black. The conductive carbon black in the microporous layer is a mixed carbon powder composed of bulk graphite and carbon particles; the particle size of the bulk graphite in the microporous layer is 10-30 μm, the particle size of the carbon particles is 30-60 nm, and the mass ratio of bulk graphite to carbon particles is 3-0.

5. The filler layer is formed by coating a carbon paste made by thoroughly mixing conductive carbon black, a hydrophobic agent, and a solvent. The solid content is 5-10%, and the mass of the hydrophobic agent is 20-30% of the mass of the carbon black. The viscosity of the filler slurry is <200 cps; The method for preparing the gas diffusion layer includes the following steps: Step 1: The prepared microporous carbon paste is coated onto the surface of the substrate and dried at high temperature and sintered at high temperature to form a gas diffusion layer intermediate. The coating method is one of screen printing, scraping, or spraying. The coating thickness is 30-80μm. The high temperature drying temperature is 80-120℃ and the high temperature sintering temperature is 350-380℃. Step 2: Place the gas diffusion layer intermediate on a coating platform with a vacuum adsorption panel, with the microporous layer facing down and the substrate layer facing up; coat the prepared filling layer carbon paste onto the substrate surface, dry it at high temperature, and sinter it at high temperature to form a gas diffusion layer with high water retention capacity.

2. The method for preparing a gas diffusion layer suitable for an air-cooled film electrode according to claim 1, characterized in that: The base layer is made of carbon paper or carbon cloth, and the carbon paper or carbon cloth is woven from carbon fibers.

3. The method for preparing a gas diffusion layer suitable for an air-cooled film electrode according to claim 1, characterized in that: The viscosity of the carbon paste is 1000-5000 cps.

4. The method for preparing a gas diffusion layer suitable for an air-cooled film electrode according to claim 1, characterized in that: The filler loading in step 2 is 0.2-2 mg / cm³. 2 The high-temperature drying temperature is 80-120℃, and the high-temperature sintering temperature is 350-380℃.

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