KR20210036068A - Preparing method of gas diffusion layer for full cell - Google Patents

Abstract

The present invention relates to a manufacturing method of a gas diffusion layer for a fuel cell comprising a pre-treatment step by humidification, and to a gas diffusion layer for a fuel cell manufactured therefrom. According to the present invention, it is possible to prevent a decrease in ion permeability of an electrolyte membrane even in a dry or low-humidity environment without additional components such as a humidifier or a catalyst to show excellent economic feasibility.

Description

Manufacturing method of gas diffusion layer for fuel cell {PREPARING METHOD OF GAS DIFFUSION LAYER FOR FULL CELL}

The present invention relates to a method of manufacturing a gas diffusion layer for a fuel cell including pretreatment by humidification, and a fuel cell having excellent output performance even in a dry or low-humidity environment including the gas diffusion layer produced therefrom.

The fuel cell is driven by the principle of generating electrons by using oxidation and reduction reactions of oxygen and hydrogen, and is a key component of a hydrogen electric vehicle. In addition, the fuel cell is typically composed of an electrolyte membrane-electrode assembly (MEA), a gas diffusion layer (GDL), a separator, a current collector plate, and the like. Specifically, a flow path exists in the separation plate to allow hydrogen and oxygen to flow into the conjugate, and the conjugate serves to generate electric power through an oxidation-reduction reaction. In addition, the gas diffusion layer serves to allow hydrogen and oxygen to spread into the conjugate to facilitate the reaction, and is usually composed of a substrate layer and a porous layer. At this time, the base layer serves to impart rigidity to the porous layer, and the porous layer serves to facilitate the oxidation/reduction reaction by diffusion of hydrogen and oxygen into the conjugate.

In this regard, Korean Patent Application Laid-Open No. 2007-0079424 (Patent Document 1) includes the steps of preparing a carbon slurry by mixing a dispersion containing a carbon powder, a solvent, a dispersant, and a water-based polymer resin, and a fluororesin suspension; Forming a primer layer by applying and drying the carbon slurry on a carbon substrate; And forming a microporous layer on the primer layer and performing heat treatment thereon.

On the other hand, the oxidation/reduction reaction in the fuel cell proceeds when ions permeate the electrolyte membrane, and the permeation characteristics of the ions are greatly influenced by humidity. In addition, a hydrogen electric vehicle including a fuel cell must be operated in various environments such as low humidity and high humidity, and the change in output performance according to the surrounding environment should be small. For example, a fuel cell under high humidity conditions is relatively advantageous in realizing output performance because moisture can be removed through pores or gaps on the surface of the gas diffusion layer. However, a fuel cell including a conventional gas diffusion layer manufactured by a conventionally known method as in Patent Document 1 lacks the electrolyte membrane permeation characteristics of ions in a dry or low-humidity environment, resulting in a problem that the output characteristics of the vehicle are deteriorated. I can.

As an alternative to this, a method of preventing deterioration of the output performance of the vehicle by introducing an additional device such as supplying water to the fuel cell under low humidity conditions or using a catalyst has been proposed. However, when a humidifier is installed on a hydrogen electric vehicle, there is a problem that negatively affects the overall fuel efficiency of the hydrogen electric vehicle due to the cost and weight of the humidifier. In addition, in the case of using a catalyst such as a cerium compound, the output performance of the fuel cell is excellent, but the manufacturing cost of the fuel cell is greatly increased, so that the application to hydrogen electric vehicles is limited.

Therefore, it is possible to maintain the output characteristics of the fuel cell by preventing deterioration of the ion permeability of the electrolyte membrane even in a dry or low-humidity environment without additional configuration of a humidifier or catalyst, and research and development on a gas diffusion layer for fuel cells with excellent economical efficiency and a manufacturing method thereof It is a necessary situation.

Korean Patent Application Publication No. 2007-0079424 (Publication date: 2007.8.7.)

Accordingly, the present invention provides a gas diffusion layer for a fuel cell with excellent economical efficiency and a gas diffusion layer for a fuel cell that can maintain the output characteristics of a fuel cell by preventing a decrease in the ion permeability of the electrolyte membrane even in a dry or low-humidity environment without additional configuration of a humidifier or catalyst, and the like. do.

The present invention comprises the steps of pre-treating the carbon-based powder by humidification;

Preparing a microporous layer composition by mixing the pretreated carbon-based powder and a binder;

It provides a method of manufacturing a gas diffusion layer for a fuel cell comprising; preparing a microporous layer by applying the microporous layer composition on a substrate.

In addition, the present invention comprises the steps of preparing a microporous layer composition by mixing a carbon-based powder and a binder;

Pretreating the microporous layer composition by humidification;

It provides a method for producing a gas diffusion layer for a fuel cell comprising; coating the pretreated microporous layer composition on a substrate to prepare a microporous layer.

In addition, the present invention provides a gas diffusion layer for a fuel cell manufactured by the above method.

In addition, the present invention provides a fuel cell including the gas diffusion layer for the fuel cell.

The method of manufacturing a gas diffusion layer for a fuel cell according to the present invention can produce a gas diffusion layer including a large amount of micropores. Accordingly, the fuel cell including the gas diffusion layer for fuel cells manufactured by the method according to the present invention is prevented from lowering the ion permeability and ion conduction rate of the electrolyte membrane even in a dry or low-humidity environment without an additional configuration such as a humidifier or catalyst, and thus the output of the fuel cell It can maintain characteristics and has excellent economics.

1 is a cross-sectional view of a gas diffusion layer according to an embodiment of the present invention.
2 is a cross-sectional view of a fuel cell according to an embodiment of the present invention.
3 is a graph of changes in the pore distribution of the gas diffusion layer according to the pretreatment time measured in Example 1. FIG.
4 is a graph showing the change in the total volume of micropores in the gas diffusion layer according to the steam treatment time measured in Example 1. FIG.
5 is a graph of output voltage change according to steam treatment time of a fuel cell stack measured in Example 2. FIG.

Hereinafter, the present invention will be described in detail.

In the present specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

In the present specification, when a member is said to be positioned "on" another member, this includes not only the case where the member is in contact with the other member, but also the case where another member exists between the two members.

Method of manufacturing gas diffusion layer for fuel cell

A method of manufacturing a gas diffusion layer for a fuel cell according to an embodiment of the present invention includes the steps of: pre-treating; Preparing a microporous layer composition; And preparing a microporous layer.

In this case, the manufacturing method improves the generation of micropores in the carbon-based powder by reacting and vaporizing carbon and moisture in the carbon-based powder through a pretreatment step by humidification. For this reason, the gas diffusion layer manufactured by the above-described method has the effect of maintaining the output characteristics of the fuel cell by preventing the decrease in the ion permeability and the ion conduction rate of the electrolyte membrane even in a dry or low-humidity environment.

Pre-treatment steps

In this step, the carbon-based powder is pretreated by humidification.

The carbon-based powder is carbon black, active carbon powder, activated carbon fiber, carbon aero-sol, carbon nanotube, carbon nanofiber, carbon It may include at least one selected from the group consisting of a carbon nanohorn and graphite powder.

The carbon-based powder may have an average diameter of 10 nm to 1,000 μm, or 50 nm to 800 μm.

The pretreatment may be performed with water vapor at 300 to 1,000° C., or 450 to 900° C. for 1 to 40 minutes, or 3 to 30 minutes. When the temperature and treatment time of the water vapor during the pretreatment are within the above ranges, the porosity of the microporous layer increases, so that the output characteristics of the manufactured battery may be improved.

The pretreated carbon-based powder has an average porosity of 60 to 80%, 65 to 75%, or 67.5 to 73%, and may include micropores having a diameter of 100 nm or less, or 1 to 100 nm. As described above, the pretreated carbon-based powder has an appropriate average porosity and contains the water generated during the oxidation/reduction reaction, including micropores, in the micropores, and provides moisture to the supplied gas, so that the ion permeability and ion conduction rate of the electrolyte membrane. It is possible to prevent the deterioration of the output characteristics of the battery by properly maintaining.

Preparing a microporous layer composition

In this step, the pretreated carbon-based powder and a binder are mixed to prepare a microporous layer composition.

The binder is polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE), It may contain at least one selected from the group consisting of tetrafluoroethylene-ethylene copolymer (ETFE) and polyfluorovinylidene (PVDF).

The microporous layer composition may include 100 parts by weight of the pretreated carbon-based powder and 5 to 100 parts by weight, or 10 to 80 parts by weight of a binder.

In addition, the microporous layer composition may have a viscosity of 10 to 500,000 cps, or 100 to 100,000 cps at 25°C. When the viscosity of the microporous layer composition is within the above range, there is an effect of easy formation of the microporous layer.

The microporous layer composition may additionally include additives, for example, a dispersant, a solvent, etc. that may be included in the composition when the microporous layer is manufactured. In this case, the additives such as the dispersant and the solvent are not particularly limited as long as they can be used in the composition when preparing the gas diffusion layer.

Step of preparing a microporous layer

In this step, a microporous layer is prepared by applying the microporous layer composition on a substrate.

The base material is not particularly limited as long as it can be used for a gas diffusion layer for a fuel cell in general, but it may be directly synthesized according to a known method, or a commercially available product may be used. For example, the substrate may be a porous material made of a carbon-based material.

For example, the substrate may include at least one selected from the group consisting of carbon paper, carbon fiber, carbon felt, and carbon sheet. Specifically, the substrate may include carbon fibers.

For example, as the substrate, a carbon fiber matrix manufactured according to a known method or a commercially available carbon fiber matrix may be used, or the carbon fiber matrix may be impregnated and dried in an impregnating solution. At this time, the impregnation liquid may include a carbon precursor and a resin, for example, the carbon precursor may include rayon-based, polyacrylonitrile (PAN)-based, pitch-based, and the like. . In addition, the resin may be, for example, the same as described in the binder. In addition, the impregnation may be repeated once to several times, and the drying may be performed at room temperature to 40°C.

E.g. The application may apply the microporous layer composition to one surface of the substrate. At this time, the application is not particularly limited as long as it is a method of coating the substrate in general, and for example, die coating, comma coating, bar coating, gravure coating, knife A method such as coating can be used.

In addition, the coating may be performed such that the average thickness of the prepared microporous layer is 10 to 200 µm, or 30 to 100 µm.

In addition, the manufacturing method may further include a step of heat-treating the substrate on which the microporous layer is formed.

Heat treatment step

In this step, the substrate on which the microporous layer is formed is heat-treated to prepare a gas diffusion layer. Through the heat treatment, there is an effect of improving the electrical conductivity and durability of the manufactured fuel cell by improving the crystallinity of the carbon-based powder in the microporous layer.

In this case, the heat treatment may be performed at 3,000° C. or less, 500 to 3,000° C., or 700 to 2,500° C. for 30 minutes or less, 5 to 30 minutes, or 10 to 20 minutes. When the temperature and treatment time during the heat treatment are within the above ranges, there is an effect of improving the electrical conductivity and durability of the manufactured fuel cell. If, during the heat treatment, the temperature is excessively high or sustained for an excessively long time, the electrical conductivity and durability of the fuel cell may be impaired.

Method of manufacturing gas diffusion layer for fuel cell

In addition, a method of manufacturing a gas diffusion layer for a fuel cell according to another embodiment of the present invention includes the steps of preparing a microporous layer composition; Pre-treating the microporous layer composition; And preparing a microporous layer.

Preparing a microporous layer composition

In this step, a microporous layer composition is prepared.

The microporous layer composition is as described in the method of manufacturing the gas diffusion layer. For example, the microporous layer composition may include 100 parts by weight of carbon-based powder and 5 to 100 parts by weight, or 10 to 80 parts by weight of a binder.

Pre-treatment steps

In this step, the microporous layer composition is pretreated by humidification. At this time, through the pretreatment, carbon and moisture in the carbon-based powder of the microporous layer composition react and vaporize, thereby improving the content of micropores in the microporous layer. For this reason, the gas diffusion layer manufactured by the above-described method is effective in maintaining the output performance of the fuel cell by preventing the decrease in the ion permeability and the ion conduction rate of the electrolyte membrane even in a dry or low-humidity environment.

As the pretreatment, water vapor at 300 to 1,000° C., or 450 to 900° C. may be treated for 1 to 40 minutes, or 3 to 30 minutes. In addition, the pretreatment is as described in the method of manufacturing the gas diffusion layer.

Step of preparing a microporous layer

In this step, a microporous layer is prepared by applying the pretreated microporous layer composition on a substrate. At this time, the coating is as described in the method for manufacturing the gas diffusion layer.

Heat treatment step

In addition, the manufacturing method may further include a step of heat-treating the substrate on which the microporous layer is formed.

In this step, the substrate on which the microporous layer is formed is heat-treated to prepare a gas diffusion layer. In this case, the heat treatment is as described in the method of manufacturing the gas diffusion layer.

The gas diffusion layer for a fuel cell prepared as described above contains a large amount of microporosity in the microporous layer, and by properly supplying moisture to the electrolyte membrane even in a low-humidity environment to maintain the ion permeability and ion conduction rate of the electrolyte membrane, the output characteristics of the fuel cell It can prevent deterioration.

On the other hand, if the carbon-based powder pretreated by humidification as described above is not used or the microporous layer composition is not pretreated by humidification, but a microporous layer is formed on the substrate and then humidified, even the substrate is subjected to humidification. As a result, micropores are formed in the substrate, and the electrical conductivity of the substrate decreases due to a decrease in the movement path of electrons, thereby deteriorating the output performance of the fuel cell. In addition, when the substrate is treated with high-temperature water vapor as described above, the substrate may be damaged or warped.

Gas diffusion layer for fuel cells

In addition, the gas diffusion layer for a fuel cell according to the present invention is manufactured by the above-described method. Referring to FIG. 1, the gas diffusion layer 100 for a fuel cell includes a substrate 20 and a microporous layer 10 formed on one surface of the substrate. For example, the substrate 20 and the microporous layer 10 are as described in the manufacturing method.

Compared with the conventional gas diffusion layer, the gas diffusion layer according to the present invention contains a large amount of micropores in the microporous layer, stores moisture in the micropores, and provides moisture to the electrolyte membrane under low humidity conditions, so that the ion permeability and ion conduction of the electrolyte membrane. By preventing a decrease in speed, there is an effect of preventing a decrease in output characteristics of the fuel cell according to the surrounding environment.

Fuel cell

The fuel cell according to the present invention includes a gas diffusion layer for a fuel cell as described above. In addition, the fuel cell may include a fuel cell that can be included in a conventional fuel cell in addition to the gas diffusion layer. For example, the fuel cell may further include an electrolyte membrane-electrode assembly (MEA), a separator, and a current collector plate.

Referring to FIG. 2, the fuel cell A according to the present invention includes an electrolyte membrane-electrode assembly 200 including an electrolyte membrane 210, a first electrode 221, and a second electrode 222; Gas diffusion layers (101, 102) formed on both sides of the assembly; Separation plates 301 and 302 formed on both sides of the gas diffusion layer; And a gasket 400 supporting side surfaces of the gas diffusion layers 101 and 102.

The fuel cell may have an output voltage of 0.6 to 0.8 V, 0.63 to 0.75 V, or 0.66 to 0.70 V.

The fuel cell according to the present invention as described above has high output voltage even in a dry or low-humidity environment, and thus has excellent output performance.

Hereinafter, the present invention will be described in more detail through examples. However, these examples are only intended to aid understanding of the present invention, and the scope of the present invention is not limited to these examples in any sense.

[Example]

Example 1. Preparation of gas diffusion layer

A microporous layer composition was prepared by mixing 100 parts by weight of carbon black and 60 parts by weight of a binder (polytetrafluoroethylene (PTFE)). Thereafter, the microporous layer composition was pretreated with water vapor at 750° C. for 3 to 30 minutes. Thereafter, the pretreated microporous layer composition was applied to one side of a substrate (consisting of carbon fibers) and heat-treated at 2,200° C. for 15 minutes to prepare a gas diffusion layer including a microporous layer having a thickness of 80 μm.

Test Example 1.

The pore distribution of the gas diffusion layer according to the pretreatment time with water vapor of Example 1 and the amount of pores of micropores having a diameter of 100 nm or less were measured and shown in FIGS. 3 and 4.

Specifically, the pore distribution of the gas diffusion layer and the amount of micropores were measured by the method described in the mercury porosity measurement method (ISO 15901-1), and in this case, the evaluation condition was a penetrometer (solid, bulb 3 cc) , The water vapor volume was supplied at 1.19cc, and the pressure was about 60,000psi.

As shown in FIGS. 3 and 4, the pore distribution and the amount of micropores were changed according to the time exposed to water vapor, and when the time to be exposed to water vapor was excessive, the carbon bonds in the carbon-based powder itself collapsed. It was found that the amount of pores decreased.

Example 2. Manufacture of fuel cell stack

After configuring a fuel cell stack using the gas diffusion layer of Example 1, electrochemical performance evaluation was performed. Specifically, the gas diffusion layer of Example 1 was bonded to the surfaces of the anode and cathode catalyst layers that are both sides of the electrolyte membrane-electrode assembly, the separation plate was bonded to the other side of the gas diffusion layer, and the current collector plate was bonded to the other side of the separation plate. Thus, a fuel cell stack was manufactured (see FIG. 2).

Test Example 2. Evaluation of output performance of fuel cell stack

As the electrochemical performance of the fuel cell stack of Example 2 ^{, the output voltage was measured based on a single cell of 25 cm 2} of the fuel cell, and in this case, the electrochemical performance was an electrochemical performance meter (manufacturer: Won-A Tech. Co., Korea) was used, and the measured results are shown in FIG. 5.

At this time, the conditions used to measure the electrochemical performance of the fuel cell stack of Example 2 are as follows.

-Fuel cell inlet temperature= 65℃

-Hydrogen anode/air cathode relative humidity (RH) = 100%/100%

-Hydrogen anode/air cathode stoichiometric ratio (S.R.) = 1.5/2.0

4 and 5, as the amount of micropores increased, the output performance of the fuel cell stack was also improved. However, in the gas diffusion layer prepared using the composition treated with water vapor for 30 minutes, the amount of micropores decreased, and the output of the fuel cell was also reduced. This is judged to be a result of adversely affecting the output of the fuel cell due to excessive exposure to water vapor, breakdown of bonds between carbons in the carbon-based powder, disruption of the conduction path of ions, or decrease in micropores.

Example 3.

A gas diffusion layer was prepared in the same manner as in Example 1, except that the temperature and pretreatment time of water vapor were adjusted as shown in Table 1 below.

Thereafter, a fuel cell stack was manufactured in the same manner as in Example 2 using the gas diffusion layer.

Test Example 3.

The porosity of the gas diffusion layer of Example 3 and the output performance of the fuel cell stack of Example 3 were measured, and the results are shown in Table 1. At this time, the porosity of the gas diffusion layer was measured by the method described in the mercury porosity measurement method (ISO 15901-1) as in Test Example 1, and the output performance of the fuel cell stack was measured by the same method as in Test Example 2.

Water vapor temperature (℃) Pre-treatment time (minutes) Porosity of gas diffusion layer (%) Output voltage of fuel cell (V) - - 67 0.66 450 3 67.1 0.66 450 5 67.9 0.66 450 10 68.7 0.66 450 15 69.2 0.662 450 30 68.1 0.661 600 3 67.2 0.661 600 5 68.4 0.662 600 10 69.9 0.662 600 15 71.4 0.665 600 30 70.7 0.663 750 3 67.8 0.662 750 5 68.1 0.665 750 10 69.7 0.665 750 15 72.8 0.667 750 30 71.6 0.666 900 3 68.1 0.661 900 5 68.4 0.662 900 10 68.6 0.661 900 15 69.9 0.661 900 30 68.7 0.661

As shown in Table 1, when pre-treatment with water vapor at 450 to 900°C for 3 to 30 minutes, the porosity of the gas diffusion layer is appropriate to 67 to 75%, and thus the output voltage of the fuel cell stack including the same is 0.66V It was excellent above.

As described above, the gas diffusion layer according to the present invention includes a large amount of micropores and has an appropriate porosity, so that the decrease in the ion permeability and the ion conduction rate of the electrolyte membrane of the fuel cell including the same is prevented even in dry or low humidity conditions It was found that the deterioration of the output characteristics of the fuel cell was prevented.

Claims (12)

Pre-treating the carbon-based powder by humidification;
Preparing a microporous layer composition by mixing the pretreated carbon-based powder and a binder; And
A method for producing a gas diffusion layer for a fuel cell comprising; preparing a microporous layer by coating the microporous layer composition on a substrate. The method according to claim 1,
The carbon-based powder comprises at least one selected from the group consisting of carbon black, activated carbon powder, activated carbon fiber, carbon aerosol, carbon nanotube, carbon nanofiber, carbon nanohorn, and graphite powder. Manufacturing method. The method according to claim 1,
In the pretreatment step, a method of manufacturing a gas diffusion layer for a fuel cell, in which water vapor of 300 to 1,000° C. is treated for 1 to 40 minutes. The method according to claim 1,
The pretreated carbon-based powder has an average porosity of 60 to 80% and includes micropores having a diameter of 100 nm or less. The method according to claim 1,
The binder is polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE), A method for producing a gas diffusion layer for a fuel cell, comprising at least one selected from the group consisting of tetrafluoroethylene-ethylene copolymer (ETFE) and polyfluorovinylidene (PVDF). The method according to claim 1,
The microporous layer composition comprises 100 parts by weight of pretreated carbon-based powder and 5 to 100 parts by weight of a binder. Mixing a carbon-based powder and a binder to prepare a microporous layer composition;
Pretreating the microporous layer composition by humidification; And
A method of manufacturing a gas diffusion layer for a fuel cell comprising; applying the pretreated microporous layer composition on a substrate to prepare a microporous layer. The method of claim 7,
The microporous layer composition comprises 100 parts by weight of carbon-based powder and 5 to 100 parts by weight of a binder. The method of claim 7,
In the pretreatment step, a method of manufacturing a gas diffusion layer for a fuel cell, in which water vapor of 300 to 1,000° C. is treated for 1 to 40 minutes. A gas diffusion layer for a fuel cell manufactured by the method according to any one of claims 1 to 9. A fuel cell comprising a gas diffusion layer for a fuel cell of claim 10. The method of claim 11,
The fuel cell has an output voltage of 0.6 to 0.8 V.

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