Dry preparation process for gas diffusion layer of fuel cell

Abstract

The preparation method comprises the following steps: directly mixing a conductive material and polytetrafluoroethylene (PTFE) powder, carrying out PTFE fibrillation in a high-speed shearing machine, an emulsifying machine, a ball mill or a jet mill to form a mixture, coating the mixture on a substrate through an extruding machine, a molding press, a coating machine or a spraying machine, carrying out hot pressing, and separating from a substrate layer to form an unsupported microporous layer (MPL); and hot-pressing the microporous layer on the carbon paper subjected to hydrophobic treatment again, and sintering to form a gas diffusion layer (GDL) with the microporous layer. The invention aims to simplify the mixing process of a microporous layer material, directly mix a conductive material and PTFE to carry out fibrillation, do not need to introduce a PTFE solution and a solvent, and reduce the process cost and solvent harm. The dry process does not need the evaporation and drying process of the solvent, so that the energy consumption in the preparation process can be saved; the dry process can accurately control the material ratio, and the preparation consistency is higher.

Description

Technical Field

[0001] The invention relates to a fuel cell, in particular to a method for preparing a gas diffusion layer of a fuel cell. Background Art

[0002] The gas diffusion layer is an important component of the fuel cell membrane. It is located between the catalyst layer and the electrode plate and plays a role in the transport of reactants, product discharge, heat and electricity conduction, etc. The gas diffusion layer is mainly composed of a large-pore substrate layer and a small-pore microporous layer (MPL). The microporous layer is used to improve the contact interface between the substrate layer and the catalyst layer. On the one hand, the small-pore microporous layer can prevent the loss of catalyst particles; on the other hand, it can increase the contact area with the catalyst layer and reduce the contact resistance; in addition, the microporous layer can form a pore size gradient with the substrate layer to improve the drainage capacity of the gas diffusion layer.

[0003] The microporous layer of the gas diffusion layer needs to have high hydrophobicity and high conductivity to ensure that the reaction gas reaches the catalyst layer smoothly, the product water is discharged in time, and the electrons are conducted. The preparation of the microporous layer mainly includes hydrophobic treatment and coating. The conductive material is impregnated with PTFE solution to form a hydrophobic channel, which is then coated on the base layer and dried and sintered to obtain.

[0004] Currently, MPL is mainly prepared through a wet process, that is, the conductive material and PTFE solution are mixed and impregnated in a certain proportion, and then coated on the treated carbon paper surface after ultrasonic dispersion. In this technical route, it is difficult to control the material ratio during the PTFE solution impregnation process; the process is complicated, and a drying process is required after coating, which consumes a lot of energy; organic solvents are required during the wet dispersion process, which is not environmentally friendly. Summary of the invention

[0005] The present invention directly mixes the conductive material and polytetrafluoroethylene (PTFE) powder, fibrillates the PTFE in a high-speed shearing machine, emulsifier, ball mill or air flow mill to form a mixture, and then applies the mixture to a substrate through an extruder, a molding machine, a coating machine or a sprayer and performs hot pressing, and then separates the mixture from the substrate layer to form an unsupported microporous layer (MPL); the microporous layer is once again hot pressed on a hydrophobic treated carbon paper, and sintered to form a gas diffusion layer (GDL) with a microporous layer. The purpose is to simplify the mixing process of the microporous layer material, directly mix the conductive material and PTFE for fibrillation, without the introduction of PTFE solution and solvent, reduce process costs and solvent hazards; the dry process does not require the evaporation and drying process of the solvent, which can save energy consumption in the preparation process; the dry process can accurately control the material ratio, and the preparation consistency is higher.

[0006] The specific plan is as follows: A dry preparation process for a fuel cell gas diffusion layer, characterized in that it includes: configuring a conductive material powder and a polytetrafluoroethylene (PTFE) powder in a specific mass ratio; placing the configured conductive material powder and PTFE powder into a high-speed disperser, an emulsifier, a ball mill or a gas flow mill for mixing to form a mixture; applying the mixture on a substrate through an extruder, a mold temperature controller, a coater or a sprayer, and performing a first hot pressing, and then separating the mixture from the substrate to form an unsupported microporous layer; performing a hydrophobic treatment on carbon paper to form a base layer; hot pressing the unsupported microporous layer on the above-mentioned carbon paper base layer for a second time; and sintering the above-mentioned hot-pressed microporous layer and base layer to form a gas diffusion layer.

[0007] In some embodiments, the mass ratio of the conductive material powder to PTFE is 1:1 to 7:1.

[0008] In some embodiments, the conductive material is one or more mixtures of graphite, carbon fiber, expanded graphite, intercalated graphite, carbon black, carbon nanotubes, or graphene materials.

[0009] In some embodiments, the high-speed disperser, emulsifier, ball mill or air flow mill is used to perform high-speed shear mixing on the conductive material and PTFE powder, and the shear rate is 10000-80000 s -1 .

[0010] Furthermore, the high-speed shear mixing time is 10 to 50 minutes.

[0011] In some embodiments, the first hot pressing temperature is 200-600° C., and the hot pressing pressure is 1-8 MPa.

[0012] In some embodiments, the second hot pressing temperature is 200-300° C., and the hot pressing pressure is 1-3 MPa.

[0013] In some embodiments, the final sintering temperature is 320-380° C., and the sintering time is 20-40 min.

[0014] In some embodiments, the microporous layer loading in the gas diffusion layer is 0.8-10 mg / cm 2 .

[0015] Compared with the prior art, the present invention has the following advantages: the process is simple, no solvent solution is required, and it is environmentally friendly; no drying process is required, and the energy consumption of the preparation process is low; the precision control of the material ratio in MPL is simple and the consistency is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention is a flowchart showing a dry process for preparing a fuel cell gas diffusion layer according to an embodiment of the present invention.

[0017] Figure 2 The figure is a schematic diagram showing the structure of a fuel cell gas diffusion layer prepared by the process of the present invention. Example

[0018] The technical solution of the present invention is further described in detail below through embodiments and in combination with the accompanying drawings, but is not limited to the contents of the embodiments. Example 1

[0019] A dry preparation process for a fuel cell gas diffusion layer, characterized in that it includes: (1) preparing a mixture, weighing 25 g of carbon black powder and 10 g of polytetrafluoroethylene (PTFE) powder; putting the prepared carbon black powder and PTFE powder into a high-speed disperser for mixing, the high-speed disperser has a rotation speed of 7000 rpm and a shear rate of 10000 s -1 , the mixing time is 30min, and a mixture is formed; (2) an unsupported microporous layer. The mixture is coated on a substrate through an extruder or a sprayer, hot-pressed at 350°C and 3MPa, and then separated from the substrate to obtain an unsupported microporous layer. The density of the microporous layer is controlled at 2mg / cm 2 . (3) Hydrophobic treatment of carbon paper. The carbon paper was impregnated with a 5% PTFE solution so that the mass proportion of PTFE was about 5% to 10%. After drying at 80°C, the solution was heat treated at 350°C for about 30 minutes to obtain a hydrophobic treated substrate layer. (4) Preparation of a gas diffusion layer with a microporous layer. The unsupported microporous layer was hot pressed again onto the hydrophobic treated carbon paper at a temperature of 200°C and a pressure of 3 MPa. After hot pressing, the solution was sintered at 350°C for 30 minutes to form a gas diffusion layer. The microporous layer loading in the gas diffusion layer is 2 mg / cm 2 . Example 2

[0020] A dry preparation process for a fuel cell gas diffusion layer, characterized in that it includes: (1) preparation of a mixture. Weigh 25 g of carbon black powder and 10 g of polytetrafluoroethylene (PTFE) powder; put the prepared carbon black powder and PTFE powder into an emulsifier for mixing, the ultrasonic power of the emulsifier is 600 W, the mixing time is 10 min, to form a mixture; (2) preparation of an unsupported microporous layer. The mixture is molded on a substrate by a molding machine, hot-pressed at 350°C and 3 MPa, and then separated from the substrate to obtain an unsupported microporous layer. The microporous layer density is controlled at 2 mg / cm 2. (3) Hydrophobic treatment of carbon paper. The carbon paper was impregnated with a 5% PTFE solution so that the mass proportion of PTFE was about 5% to 10%. After drying at 80°C, the solution was heat treated at 350°C for about 30 minutes to obtain a hydrophobic treated substrate layer. (4) Preparation of a gas diffusion layer with a microporous layer. The unsupported microporous layer was hot pressed again onto the hydrophobic treated carbon paper at a temperature of 200°C and a pressure of 3 MPa. After hot pressing, the solution was sintered at 350°C for 30 minutes to form a gas diffusion layer. The microporous layer loading in the gas diffusion layer is 2 mg / cm 2 . Example 3

[0021] A dry preparation process for a fuel cell gas diffusion layer, characterized in that it includes: (1) preparation of a mixture. Weigh 10 g of graphite powder and 10 g of polytetrafluoroethylene (PTFE) powder; put the prepared graphite powder and PTFE powder into a ball mill for mixing, wherein the rotation / revolution ratio of the ball mill is about 2:1, the revolution speed is 200-300 rpm, and the mixing time is 50 min to form a mixture; (2) preparation of an unsupported microporous layer. The mixture is molded on a substrate by a molding machine, hot-pressed at 350°C and 3 MPa, and then separated from the substrate to obtain an unsupported microporous layer. The microporous layer density is controlled at 2 mg / cm 2 . (3) Hydrophobic treatment of carbon paper. The carbon paper was impregnated with a 5% PTFE solution so that the mass proportion of PTFE was about 5% to 10%. After drying at 80°C, the solution was heat treated at 350°C for about 30 minutes to obtain a hydrophobic treated substrate layer. (4) Preparation of a gas diffusion layer with a microporous layer. The unsupported microporous layer was hot pressed again onto the hydrophobic treated carbon paper at a temperature of 200°C and a pressure of 3 MPa. After hot pressing, the solution was sintered at 350°C for 30 minutes to form a gas diffusion layer. The microporous layer loading in the gas diffusion layer is 2 mg / cm 2 . Example 4

[0022] This embodiment is similar to the embodiment 1, except that: the conductive material is carbon fiber, the resin material is PTFE powder, the mass ratio is 7:1; after high-speed shear mixing in the air jet mill, the shear rate is 80000s -1 The first hot pressing temperature was 350℃ and the hot pressing pressure was 3MPa; the second hot pressing temperature was 200℃ and the hot pressing pressure was 3MPa. The sintering temperature was 350℃ and the time was 30min. The microporous layer loading in the gas diffusion layer was 0.8mg / cm 2 . Example 5

[0023] This embodiment is similar to embodiment 1, except that the conductive material is graphite and carbon fiber, and the resin material is PTFE powder, with a mass ratio of 4:4:2; after high-speed shear mixing, the first hot pressing temperature is 200°C and the hot pressing pressure is 1MPa; the second hot pressing temperature is 200°C and the hot pressing pressure is 3MPa. The sintering temperature is 350°C and the time is 30min. The microporous layer loading in the gas diffusion layer is 3.3mg / cm 2 . Example 6

[0024] This embodiment is similar to embodiment 1, except that the conductive material is graphite and carbon nanotubes, and the resin material is PTFE powder, with a mass ratio of 7:1:2; after high-speed shear mixing, the first hot pressing temperature is 350°C and the hot pressing pressure is 3MPa; the second hot pressing temperature is 200°C and the hot pressing pressure is 1MPa. The sintering temperature is 320°C and the time is 40min. The microporous layer loading in the gas diffusion layer is 4.8mg / cm 2 . Example 7

[0025] This embodiment is similar to embodiment 1, except that the conductive material is graphite and carbon fiber, and the resin material is PTFE powder, with a mass ratio of 4:4:2; after high-speed shear mixing, the first hot pressing temperature is 450°C and the hot pressing pressure is 8MPa; the second hot pressing temperature is 300°C and the hot pressing pressure is 3MPa. The sintering temperature is 350°C and the time is 30min. The microporous layer loading in the gas diffusion layer is 2mg / cm 2 . Example 8

[0026] This embodiment is similar to embodiment 1, except that: the conductive material is graphite and carbon fiber, and the resin material is PTFE powder, with a mass ratio of 4:4:2; after high-speed shear mixing, the first hot pressing temperature is 600°C and the hot pressing pressure is 5MPa; the second hot pressing temperature is 300°C and the hot pressing pressure is 3MPa. The sintering temperature is 350°C and the time is 30min. The microporous layer loading in the gas diffusion layer is 2mg / cm 2 . Example 9

[0027] This embodiment is similar to embodiment 1, except that the conductive material is graphite and carbon fiber, and the resin material is PTFE powder, with a mass ratio of 4:4:2; after shear mixing, the first hot pressing temperature is 600°C and the hot pressing pressure is 5MPa; the second hot pressing temperature is 300°C and the hot pressing pressure is 3MPa. The sintering temperature is 380°C and the time is 20min. The microporous layer loading in the gas diffusion layer is 6mg / cm 2 . Example 10

[0028] This embodiment is similar to embodiment 1, except that: the conductive material is graphite, carbon fiber, and the mass ratio of the conductive material to the PTFE powder is 4:4:2; after high-speed shear mixing, the first hot pressing temperature is 600°C and the hot pressing pressure is 6MPa; the second hot pressing temperature is 300°C and the hot pressing pressure is 3MPa. The sintering temperature is 380°C and the time is 40min. The microporous layer loading in the gas diffusion layer is 10mg / cm 2 .

Claims

1. A dry method for preparing a fuel cell gas diffusion layer, characterized in that: The method comprises the following steps: configuring conductive material powder and polytetrafluoroethylene (PTFE) powder in a specific mass ratio, placing the configured conductive material powder and PTFE powder into a high-speed disperser, an emulsifier, a ball mill or a jet mill for mixing to form a mixture; applying the mixture onto a substrate through an extruder, a molding machine, a coater or a sprayer, and performing a first hot pressing, and separating the mixture from the substrate to form an unsupported microporous layer; hot pressing the microporous layer onto hydrophobically treated carbon paper for a second time, and then sintering to form a gas diffusion layer.

2. A dry method for preparing a fuel cell gas diffusion layer according to claim 1, characterized in that: The mass ratio of the conductive material powder to PTFE is 1:1 to 7:

1.

3. A dry method for preparing a fuel cell gas diffusion layer according to claim 1, characterized in that: The conductive material is one or more mixtures of graphite, carbon fiber, expanded graphite, intercalated graphite, carbon black, carbon nanotubes or graphene materials.

4. A dry method for preparing a fuel cell gas diffusion layer according to claim 1, characterized in that: The conductive material and the resin powder are mixed by high-speed shearing using the high-speed disperser, emulsifier, ball mill or air flow mill, and the shear rate is 10000~80000s -1 , the high-speed shear mixing time is 10~50min.

5. The dry method preparation process of a fuel cell gas diffusion layer according to claim 1, characterized in that: The first hot pressing temperature is 200-600° C., and the hot pressing pressure is 1-8 MPa.

6. A dry method for preparing a fuel cell gas diffusion layer according to claim 1, characterized in that: The second hot pressing temperature is 200-300° C., and the hot pressing pressure is 1-3 MPa.

7. A dry method for preparing a fuel cell gas diffusion layer according to claim 1, characterized in that: The sintering temperature is 320-380° C., and the sintering time is 20-40 minutes.

8. The dry method preparation process of a fuel cell gas diffusion layer according to claim 1, characterized in that: The microporous layer loading in the gas diffusion layer is 0.8-10 mg / cm 2 .

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