KR102531043B1 - A microporous layer coating solution for fuel cell and gas diffusion layer using the same - Google Patents

Abstract

The present invention provides a fuel cell microporous layer coating solution formed by dispersing an intermediate mixture of a solvent, carbon powder, a dispersant, and a foaming agent, and stirring a polytetrafluoroethylene dispersion solution in a dispersed intermediate mixture. The present invention controls the pore size of the microporous layer to suppress an increase in electrical resistance through a gas diffusion layer and to improve gas permeability.

Description

Fuel cell microporous layer coating solution and gas diffusion layer using the same

The present invention relates to a fuel cell microporous layer coating solution and a gas diffusion layer using the same.

In general, a fuel cell is a device that generates electrical energy by electrochemically reacting hydrogen and oxygen. Because it directly produces electricity without burning fuel, it is environmentally friendly and has a very high power generation efficiency.

Here, the unit cell of the fuel cell is usually composed of an anode, a gas diffusion layer, a catalyst layer, an electrolyte layer, a catalyst layer, a gas diffusion layer, and a cathode in the order of stacking, and hydrogen used as fuel is supplied to the anode, and oxygen is supplied to the cathode ( supplied to the cathode).

The power generation principle of such a fuel cell is that hydrogen supplied to the anode passes through a gas diffusion layer, is separated into hydrogen ions (cations) and electrons by catalytic action in the catalyst layer, and hydrogen ions (cations) pass through the electrolyte layer to the cathode. As the electrons move to the cathode through the external circuit, current is generated.

In addition, on the cathode side, the fuel cell operates on the principle that hydrogen ions (positive ions) that have moved through the electrolyte layer, electrons that have moved through an external circuit, and supplied oxygen meet to generate water.

Among the components of such a fuel cell, the gas diffusion layer needs to have the characteristics of uniformly diffusing and supplying oxygen or hydrogen to the catalyst layer and discharging water well.

That is, in order to improve the performance of the fuel cell, the gas diffusion layer needs to have a property of discharging water well under high-humidity operating conditions.

Conventionally, the water discharge performance is improved by adjusting the particle size of carbon black used to form the microporous layer in the gas diffusion layer. If it is large, the water discharge characteristics are improved, but there is a problem in that the electrical resistance of the gas diffusion layer increases.

Patent Publication No. 2021-0087825 (published date: 2021.07.13) "Microporous layer for fuel cell, gas diffusion layer including the same, and fuel cell including the same"

In the present invention, by effectively controlling the pore size of the microporous layer formed on carbon paper using a fuel cell microporous layer coating liquid and a gas diffusion layer using the same, specifically, a microporous layer coating liquid containing a foaming agent, excellent water discharge characteristics are obtained. It is intended to provide a fuel cell microporous layer coating solution capable of obtaining a gas diffusion layer having a gas diffusion layer and a gas diffusion layer using the same.

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below. You will be able to.

In order to solve the above problems, the present invention is a fuel cell microporous layer formed by dispersing an intermediate mixture in which a solvent, carbon powder, dispersant, and foaming agent are mixed, and stirring a polytetrafluoroethylene dispersion in the dispersed intermediate mixture. coating solution is provided.

In addition, the intermediate mixture is dispersed using a 3-roll mill, and the foaming agent provides a fuel cell microporous layer coating solution having a foaming temperature of 120 to 250°C.

In addition, the foaming agent provides a fuel cell microporous layer coating solution in which 10 to 20 parts by weight is added based on 100 parts by weight of the total of the solvent, carbon powder, dispersant and polytetrafluoroethylene dispersion.

In addition, the foaming agent is an azodicarbonamide-based, toluenesulfonylhydrazide-based, oxydibenzenesulfonylhydrazide-based, or dinitrosopentamethylenetetramine-based. Provided is a fuel cell microporous layer coating solution containing at least one of toluenesulfonyl semicarbazide-based, phenyl tetrazole-based, inorganic, capsular foaming agents, and spherical polymeric foaming agents.

On the other hand, in another aspect of the present invention for solving the above problems, a microporous layer coating solution is prepared by including a foaming agent, the microporous layer coating solution is coated on hydrophobic treated carbon paper, and heat treatment is performed to obtain microporous layer coating solution on the carbon paper. Provided is a fuel cell gas diffusion layer that increases the pore size of the microporous layer formed on the carbon paper by forming a porous layer and allowing the foaming agent to be foamed during the heat treatment process.

The fuel cell gas diffusion layer according to an embodiment of the present invention is a heat treatment process by adding an appropriate amount of a foaming agent in the process of preparing a microporous layer coating solution, coating the prepared microporous layer coating solution on carbon paper, and performing heat treatment. The pore size of the microporous layer formed in the carbon paper can be effectively controlled through the foaming action generated in the carbon paper.

In addition, by increasing the pore size of the microporous layer formed on the carbon paper, it is possible to provide a gas diffusion layer having excellent water discharge characteristics, thereby improving the performance of the fuel cell.

The effects obtainable in the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by those skilled in the art from the description below. will be.

1 is a flowchart illustrating a method of manufacturing a gas diffusion layer for a fuel cell according to an embodiment of the present invention.
2 is a flow chart showing a method for preparing a microporous layer coating solution according to an embodiment of the present invention.
3 and 4 show pore size distribution as a result of measuring the mercury porosity of the gas diffusion layers prepared according to Comparative Example 1 and Example 3, respectively.
5 is a SEM photograph of the surface of the microporous layer of Comparative Example 1.
6 to 8 are SEM images of the surface of the microporous layer of Examples 1 to 3, respectively.
9 is a current-voltage graph illustrating unit cell evaluation results under high humidity operating conditions of fuel cells to which gas diffusion layers according to Examples 1, 3, and Comparative Example 1 are applied.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

The detailed description set forth below in conjunction with the accompanying drawings is intended to describe exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced.

In order to clearly describe the present invention in the drawings, parts irrelevant to the description may be omitted, and the same reference numerals may be used for the same or similar components throughout the specification.

In embodiments of the present invention, expressions such as “or” and “at least one” may represent one of the words listed together, or a combination of two or more.

1 is a flow chart showing a method for manufacturing a fuel cell gas diffusion layer according to an embodiment of the present invention, and FIG. 2 is a flow chart showing a method for manufacturing a coating liquid for a microporous layer according to an embodiment of the present invention.

Referring to FIG. 1, a method for manufacturing a fuel cell gas diffusion layer according to an embodiment of the present invention includes preparing a microporous layer coating solution containing a foaming agent (S100), hydrophobic treatment of carbon paper (S200), and A step of coating the microporous layer coating solution on the hydrophobic treated carbon paper (S300) may be included.

In the manufacturing process of the fuel cell gas diffusion layer according to this embodiment, a foaming agent is added to prepare a microporous layer coating solution, the prepared microporous layer coating solution is coated on carbon paper, and heat treatment is performed to prepare a gas diffusion layer, Water discharge characteristics can be improved by controlling the size of pores formed in the microporous layer by enabling foaming by a foaming agent during the heat treatment process.

First, in the step of preparing a microporous layer coating solution (S100), carbon powder (eg carbon black), a dispersing agent, a foaming agent, a solvent (eg propylene glycol, distilled water) and polytetrafluoroethylene (PTFE) dispersion are stirred. and dispersion to prepare a microporous layer coating solution.

Specifically, referring to FIG. 2, an intermediate mixture may be prepared by primary stirring of carbon black, a dispersant, and a foaming agent in propylene glycol (S110).

Here, carbon black, as a major component of the microporous layer, can play an important role in electrical conduction and formation of a contact area with the catalyst layer.

In addition, in this embodiment, Triton X-100 or the like may be used as a dispersant.

In addition, as the blowing agent, azodicarbonamide (ADCA)-based blowing agent, p-toluene sulfonyl hydrazide (TSH; p-Toluene sulfonyl hydrazide)-based blowing agent, 4,4'-oxydibenzenesulfonylhydra Zide (OBSH; 4,4'-Oxydibenzene sulfonyl hydrazide)-based blowing agent, N,N'-dinitroso pentamethylene tetramine (DPT; N,N'-Dinitroso pentamethylene tetramine)-based blowing agent, P-toluene sulfonyl semicarba Zide (PTSS; p-Toluene sulfonyl semicarbazide)-based foaming agent, 5-phenyl tetrazole (5-Phenyl tetrazole)-based foaming agent, inorganic foaming agent (sodium bicarbonate), capsule type foaming agent (e.g. thermally expandable capsule type foaming agent, hollow capsule type foaming agent) and spherical polymeric foaming agent, etc. may be applied.

As an example, the intermediate mixture may be prepared by adding 20 parts by weight of carbon black, 10 parts by weight of Triton X-100, and 10 parts by weight of a foaming agent to 60 parts by weight of propylene glycol based on 100 parts by weight, followed by primary stirring.

In the first stirring process, while carbon black, Triton X-100, and a foaming agent are added to propylene glycol, stirring is performed with a paste mixer at 1200 RPM and 1000 RPM for 10 minutes to prepare an intermediate mixture.

Subsequently, the intermediate mixture may be dispersed using a 3-roll mill including first to third rollers (S120).

As an example, by setting the distance between the first and second rollers to 30 μm, the distance between the second and third rollers to 30 μm, and setting the linear speed of the first to third rollers to 800 mm / s, The intermediate mixture can be dispersed using a 3-roll mill set to the conditions.

Next, a microporous layer coating solution may be prepared by secondary stirring of the polytetrafluoroethylene dispersion in the dispersed intermediate mixture using a 3-roll mill (S130).

As an example, a microporous layer coating solution may be prepared by adding 10 parts by weight of the polytetrafluoroethylene dispersion to 100 parts by weight of the intermediate mixture, and stirring with a paste mixer for 2 minutes under conditions of revolution of 400 RPM and rotation of 100 RPM.

As the foaming agent used in the preparation of the microporous layer coating solution, a foaming agent having a foaming property of a foaming size of 10 to 20 μm and a foaming temperature of 120 to 250° C. may be applied. Preferably, the foaming size is 15 μm and the foaming temperature is 200 μm. A blowing agent having a foaming property of °C can be applied.

Since the foaming reaction by the blowing agent is preferably carried out before the solvent is removed and the polytetrafluoroethylene is sintered, the temperature of 120 to 250 ° C. is higher than the temperature at which the solvent can be removed and lower than the temperature at which the polytetrafluoroethylene is sintered. A foaming agent having a foaming temperature characteristic may be applied.

In addition, when preparing the microporous layer coating solution, the amount of the foaming agent may be added in an amount of 10 to 20 parts by weight based on 100 parts by weight of the total of propylene glycol, carbon black, dispersant and polytetrafluoroethylene dispersion.

When the microporous layer is formed by coating and heat-treating the microporous layer coating solution prepared as described above on carbon paper, foaming by a foaming agent is accompanied during the heat treatment process, thereby increasing the size of pores generated in the microporous layer. .

In particular, the size of pores generated in the microporous layer can be controlled according to the amount of the foaming agent added to the microporous layer coating solution. The amount of the added foaming agent is 100 When the amount exceeds 20 parts by weight, the viscosity of the microporous layer coating solution excessively increases, making it difficult to coat the coating solution on carbon paper, and the pores formed in the microporous layer become too large, resulting in a rapid increase in through electrical resistance. will do

In addition, when the content of the added foaming agent is less than 10 parts by weight relative to 100 parts by weight of the sum of the solvent, carbon powder, dispersant and polytetrafluoroethylene dispersion, the effect of forming pores and increasing the size by the foaming agent is insignificant, resulting in a microporous layer does not significantly contribute to the increase in gas permeability.

Accordingly, it is preferable to adjust the amount of the added foaming agent in the range of 10 to 20 parts by weight based on 100 parts by weight of the total of the solvent, carbon powder, dispersant and polytetrafluoroethylene dispersion.

As such, in this embodiment, the pore size of the microporous layer formed on the carbon paper can be controlled by using the microporous layer coating solution containing the foaming agent in an appropriate amount, thereby increasing the gas permeability to have excellent water discharge characteristics. A gas diffusion layer can be prepared.

On the other hand, in the step of hydrophobizing the carbon paper (S200), a polytetrafluoroethylene impregnation solution may be prepared by mixing the polytetrafluoroethylene dispersion with distilled water.

Here, polytetrafluoroethylene dispersion may be added to impart hydrophobicity.

Subsequently, the carbon paper may be immersed in a polytetrafluoroethylene impregnation solution and then dried to prepare a hydrophobic treated carbon paper.

Next, in the step of coating the microporous layer coating liquid on the hydrophobic treated carbon paper (S300), the microporous layer coating liquid is coated on the hydrophobic treated carbon paper using a bar coater, and drying and heat treatment are performed. A gas diffusion layer according to the

As described above, in this embodiment, a microporous layer coating solution containing an appropriate amount of a foaming agent is coated on hydrophobic treated carbon paper and heat-treated to prepare a gas diffusion layer. The number of large pores formed in the layer can be effectively increased, and through this, the water discharge characteristics of the gas diffusion layer can be improved.

In addition, in the gas diffusion layer manufacturing method of the above-described embodiment, after the step of preparing the microporous layer coating solution (S100), the step of hydrophobizing the carbon paper (S200) is performed, but the present invention is not necessarily limited thereto. , After the step of hydrophobizing the carbon paper (S200), the step of preparing the microporous layer coating solution (S100) may be performed, or each step may be performed simultaneously in parallel.

On the other hand, the carbon paper used in this embodiment is prepared by preparing a phenol impregnation solution in which an acrylic acid binder is mixed, impregnating the carbon veil in the phenol impregnation solution, drying and curing the impregnated carbon veil, and curing the impregnated carbon veil. It can be produced through the step of carbonizing the carbon bale and the step of graphitizing the carbonized carbon bale.

Specifically, in the process of manufacturing the carbon paper used in this embodiment, in the step of preparing a phenol impregnation solution in which an acrylic acid binder is mixed, a phenol resin, graphite powder, and an acrylic acid binder are mixed with ethanol, an alcohol solvent. It can be manufactured by

As an example, the phenol impregnation solution may include 55 to 90 wt% of ethanol, 2 to 10 wt% of a phenolic resin, 3 to 15 wt% of graphite powder, and 5 to 20 wt% of an acrylic acid-based binder.

Here, the phenolic resin is a thermosetting resin used to manufacture carbon paper, and has an advantage of high carbon yield after the carbonization process.

In addition, the acrylic acid-based binder mixed in the phenol impregnation solution binds the carbon fibers protruding from the surface of the carbon veil, so that the surface of the carbon veil can be formed flat, and a uniform impregnation film can be formed from the surface of the carbon veil to the inside. It can contribute to increase gas permeability by enabling

Such an acrylic acid-based binder is polyacrylic acid or styrene, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, Iso-Butylmethacrylate, t-Butylmethacrylate, Vinylchloride, Vinylacetate, Acrylonitrile, 2-Ethylhexylmethacrylate (2- Ethylhexylmethacrylate, Laurylmethacrylate, Methylacrylate, Ethylacrylate, n-Butylacrylate, Iso-Butylacrylate, 2-ethyl Copolymerization of at least one selected raw material capable of forming a copolymer with acrylic acid such as 2-Ethylhexylacrylate, Ethylene, Octadecylmethacrylate, and Acrylamide Copolymer binders designed for use may be applied.

In addition, when carbon paper is manufactured by applying a binder having a high carboxylic acid ratio in an acrylic acid binder, the gas permeability (vertical and horizontal gas permeability) of the carbon paper can be increased, and the effect of removing protruding fibers compared to the same binder input amount is increased. It is excellent, and it is possible to obtain the effect of removing protruding fibers with a smaller amount of binder than before.

Accordingly, a phenol impregnation solution is prepared by introducing an appropriate amount of an acrylic acid-based binder containing an appropriate ratio of carboxylic acid, and carbon paper is prepared using the phenol impregnation solution prepared in this way, thereby suppressing protruding fibers on the surface and improving impregnation uniformity. It is possible to manufacture carbon paper having excellent gas permeability by increasing the gas permeability, and the compression ratio of the carbon paper can be adjusted to appropriately lower, so that durability can be secured and it can be easily applied to the gas diffusion layer of the fuel cell.

As a preferred example, in this embodiment, a phenol impregnation solution is prepared by adding 5 to 20 parts by weight of an acrylic acid-based binder containing 10 to 50% of carboxylic acid relative to 100 parts by weight of the phenol impregnation solution. Carbon paper having excellent gas permeability and suitable for a gas diffusion layer can be manufactured by using the carbon paper.

Next, in the step of impregnating the carbon veil into the phenol impregnating liquid, the carbon veil may be impregnated into the prepared phenol impregnating liquid.

The carbon veil can be manufactured through a wet-laid manufacturing process by dispersing carbon fibers in water, and the electrical properties can be improved only when the carbon fibers are well cultured in two dimensions.

Recently, as the gas diffusion layer of a fuel cell has been thinned, the thickness of the carbon veil has become thinner compared to the length of the carbon fiber constituting the carbon veil, resulting in a high frequency of carbon fibers protruding from the surface after carbon paper is produced. The carbon fibers protruding from the surface have been removed. When the gas diffusion layer is prepared after coating the microporous layer without being coated and applied to the fuel cell, the membrane electrode assembly (at least one of the catalyst layer, the electrolyte layer and the gas diffusion layer) is penetrated by the protruding carbon fibers. It may cause physical damage to cause deterioration in durability and performance of the fuel cell.

Accordingly, in the process of impregnating the carbon veil in the phenol impregnating liquid, the surface of the carbon veil can be coated by impregnating the carbon veil with the acrylic acid-based binder included in the phenol impregnating liquid, thereby protruding from the surface of the carbon veil. The carbon fibers may be arranged in a horizontal direction to form a flat surface, and the durability and performance of the fuel cell may be improved by solving problems caused by the carbon fibers protruding from the surface as described above.

Next, in the step of drying and curing the impregnated carbon veil, residual solvent may be dried in the impregnated carbon veil, and the dried carbon veil may be cured.

At this time, preferably, the impregnated carbon veil may be dried at 70 to 100° C. for several minutes, and then cured at 150 to 200° C. for several minutes.

Subsequently, in the step of carbonizing the hardened carbon bale, the hardened carbon bale may be carbonized in an inert gas atmosphere.

Specifically, carbonization may be performed using an inert gas such as nitrogen or argon gas to block combustion of the phenolic resin, preferably at 700 to 900° C. for several tens of minutes.

Subsequently, in the step of graphitizing the carbonized carbon bale, the carbonized carbon bale may be graphitized in an inert gas atmosphere.

At this time, the graphitization process may be performed using nitrogen gas or argon gas, and the temperature of the graphitization process may be formed at 2000° C. or higher.

As described above, in the carbon paper according to the present embodiment, carbon fibers protruding from the surface of the carbon veil are easily removed by impregnating the carbon veil in a phenol impregnation solution prepared by adding an acrylic acid-based binder containing carboxylic acid. It is possible to reduce the compressibility, and in particular, it is possible to contribute to increasing the gas permeability by allowing a uniform impregnated film to be formed on the carbon bale through the acrylic acid binder.

Furthermore, by adjusting the ratio of carboxylic acid contained in the acrylic acid binder and the content of the acrylic acid binder mixed in the phenol impregnated liquid, durability can be secured and the compression rate of the produced carbon paper can be adjusted to be suitable for the thin film gas diffusion layer. .

Hereinafter, a gas diffusion layer manufactured according to an embodiment of the present invention will be described.

However, this is presented as a preferred example of the present invention and cannot be construed as limiting the present invention by this in any sense.

[Examples 1 to 3]

20 g of carbon black, 10 g of Triton X-100, 10 g of ADCA-based foaming agent, and 60 g of propylene glycol were weighed and stirred in a paste mixer at 1200 RPM and 1000 RPM for 10 minutes to prepare an intermediate mixture.

Here, the applied ADCA-based blowing agent has the characteristics of a foaming size of 15 μm and a foaming temperature of 200° C.

Then, the intermediate mixture was dispersed using a 3-roll mill, the distance between the first and second rollers was set to 30 μm, the distance between the second and third rollers was set to 30 μm, and the linear speed of the rollers was set to 800 mm/s. By setting, the intermediate mixture was dispersed under the conditions.

Next, 10 g of the polytetrafluoroethylene dispersion was added to the intermediate mixture dispersed by a 3-roll mill, and stirred for 2 minutes at 400 RPM and 100 RPM using a paste mixer to prepare a microporous layer coating solution.

In the preparation process, 10 parts by weight, that is, 10 g of the ADCA-based blowing agent was added based on 100 parts by weight of the total of carbon black, Triton X-100, propylene glycol, and polytetrafluoroethylene dispersion.

Meanwhile, 3 g of the polytetrafluoroethylene dispersion and 97 g of distilled water were weighed and mixed for 1 minute at 200 RPM using a stirrer to prepare a polytetrafluoroethylene impregnation solution.

Subsequently, the carbon paper was immersed in a polytetrafluoroethylene impregnation solution, and then dried at 100° C. for 5 minutes to prepare hydrophobic treated carbon paper.

At this time, the thickness of the carbon paper was approximately 170 μm, and the amount of polytetrafluoroethylene impregnated into the carbon paper was formed to be about 10% of the weight of the carbon paper.

In addition, by using a bar coater, the prepared microporous layer coating solution is coated on hydrophobic treated carbon paper, dried at 100 ° C for 5 minutes, heated to 400 ° C at a heating rate of 10 ° C / min, maintained for 10 minutes, and gas A diffusion layer was prepared.

At this time, the thickness coated on the carbon paper (thickness: 170 μm) was formed to be approximately 45 μm, so that the total thickness of the gas diffusion layer was formed to 215 μm.

On the other hand, Examples 2 and 3 are prepared in the same way as Example 1, but in the process of preparing the microporous layer coating solution, Example 2 changes the amount of the foaming agent added to carbon black, Triton X-100, and propylene glycol. and 15 parts by weight, that is, 15 g, based on 100 parts by weight of the sum of the polytetrafluoroethylene dispersion, and in Example 3, the amount of the added foaming agent is the sum of carbon black, Triton X-100, propylene glycol, and polytetrafluoroethylene dispersion. It was 20 parts by weight, that is, 20 g, with respect to 100 parts by weight, and a gas diffusion layer was prepared using the microporous layer coating solution prepared under the respective conditions.

[Comparative Examples 1 to 3]

It was prepared in the same manner as Example 1, but in the process of preparing the microporous layer coating solution, Comparative Example 1 did not add a foaming agent, and Comparative Example 2 adjusted the content of the foaming agent to carbon black, Triton X-100, propylene glycol and poly 5 parts by weight, that is, 5 g, based on 100 parts by weight of the total tetrafluoroethylene dispersion, and in Comparative Example 3, the amount of the foaming agent added was 100 parts by weight of the total of carbon black, Triton X-100, propylene glycol, and polytetrafluoroethylene dispersion It was 25 parts by weight, that is, 25 g, and a gas diffusion layer was prepared using the microporous layer coating solution prepared under the respective conditions.

Table 1 shows the results of detecting the through electrical resistance, gas permeability, and pore size of the microporous layer for the gas diffusion layers prepared by varying the content of the foaming agent according to Examples 1 to 3 and Comparative Examples 1 to 3, respectively. was

Here, the through electrical resistance and gas permeability of the gas diffusion layer were measured using CPRT-10, and the pore size of the microporous layer was measured using a mercury porosity analyzer (AutoPore V).

The pore size shown in Table 1 below shows the size of the most distributed pores among the pores formed in the microporous layer for each example and comparative example, and as shown in the pore size distribution chart of FIG. Accordingly, when the distribution of pores is concentrated in the two sections, the size of the most distributed pores in each section is shown.

division blowing agent
content penetration electrical resistance
(mΩ·cm²) gas permeability
(㎡) pore size One 2 Example 1 10% 9.8 1.9×10 ^-13 58 nm 195 nm Example 2 15% 9.5 5.8×10 ^-13 61 nm 199 nm Example 3 20% 9.7 7.3×10 ^-13 62 nm 201 nm Comparative Example 1 0% 9.5 3.2×10 ^-14 50 nm - Comparative Example 2 5% 9.6 5.2×10 ^-14 57 nm - Comparative Example 3 25% 16.8 9.1×10 ^-13 87 nm 203 nm

As shown in Table 1, in the case of Examples 1 to 3 and Comparative Examples 2 and 3 in which a foaming agent was added during the preparation of the gas diffusion layer, the gas permeability was improved compared to Comparative Example 1 in which no foaming agent was added and the pores of the microporous layer were improved. It can be seen that there is an effect of increasing the size.

At this time, even in the case of Comparative Example 2 in which the content of the foaming agent was 5%, some effects were confirmed in improving the gas permeability and increasing the pore size, but it was confirmed that the formation of pores by the foaming agent was insufficient, and the gas permeability was also insufficient. there is.

As in Examples 1 to 3, when the content of the foaming agent is added in the range of 10 to 20%, the gas permeability is remarkably improved, and it can be seen that a large number of pores of an increased size are formed by the foaming agent.

In particular, in the case of Comparative Example 1 in which no foaming agent was added and Comparative Example 2 in which the content of the foaming agent was 5%, the most distributed pore sizes in the microporous layer were 50 nm and 57 nm, respectively, and less than 60 nm While the pores are concentratedly distributed, in Examples 1, 2, and 3 in which the contents of the blowing agent are 10%, 15%, and 20%, respectively, the pore sizes most distributed in the microporous layer are 58 nm and 195 nm, respectively. , 61 nm and 199 nm, 62 nm and 201 nm, it can be seen that the pore size is increased compared to Comparative Examples 1 and 2, and pores of a relatively large size of 190 nm or more are concentrated together.

Through this, it can be seen that when a certain or more foaming agent is added during the manufacturing of the gas diffusion layer, the pore size of the microporous layer increases due to the foaming action.

In addition, it can be seen that the pore size increases as the content of the added foaming agent increases, and correspondingly, the gas permeability is also excellent.

However, when the content of the foaming agent exceeds 20% as in Comparative Example 3, the through electrical resistance due to the excessive number of large pores rapidly increases. do.

Accordingly, as in Examples 1 to 3, when the gas diffusion layer is prepared by adding a foaming agent of 10 to 20% content, the size of pores formed in the microporous layer can be increased by the foaming action of the foaming agent, and penetration It is possible to improve gas permeability while suppressing an increase in electrical resistance, and through this, a fuel cell gas diffusion layer having excellent water discharge characteristics can be obtained.

Meanwhile, FIGS. 3 and 4 show pore size distribution as a result of measuring the mercury porosity of the gas diffusion layers prepared according to Comparative Example 1 and Example 3, respectively.

Looking at the pore size distribution charts shown in FIGS. 3 and 4, the X axis represents the pore size and the Y axis represents the pore volume. The larger the Y axis, the more pores, and the left region represents the pore size of carbon paper. Regardless of the examples, the right area shows the pore size of the microporous layer.

At this time, the peak value displayed on the right side of the pore size distribution chart indicates the size of the most distributed pores among pores formed in the microporous layer.

Specifically, in Comparative Example 1, in which no foaming agent was added, the pore size most distributed in the microporous layer was 50 nm, and in Example 3, in which the content of the foaming agent was 20%, the pore size most distributed in the microporous layer was 50 nm. is shown as 62 nm and 201 nm in the two sections, respectively, and through this, it can be seen that when a gas diffusion layer is prepared by adding a foaming agent, a large number of pores with a large size are formed in the microporous layer.

5 is an SEM image of the microporous layer surface of Comparative Example 1, and FIGS. 6 to 8 are SEM images of the microporous layer surface of Examples 1 to 3, respectively.

5 to 8, it can be seen that a large number of large pores are formed in the microporous layers of Examples 1 to 3 to which a foaming agent is added, compared to the microporous layer of Comparative Example 1 to which no foaming agent is added. there is.

In particular, looking at Examples 1 to 3, it can be seen that the frequency of pores formed in the microporous layer increases according to the amount of the added foaming agent.

That is, it can be confirmed that the frequency of pores formed in the microporous layer is gradually increasing in the order of Example 1 in which the foaming agent content is 10%, Example 2 in which the foaming agent content is 15%, and Example 3 in which the foaming agent content is 20%. can

As such, it can be confirmed that when the microporous layer is formed by adding a foaming agent, pores having a large size can be formed in the microporous layer, and the frequency of pores formed in the microporous layer can be increased as the content of the foaming agent is increased. there is.

9 is a current-voltage graph illustrating unit cell evaluation results under high humidity operating conditions of fuel cells to which gas diffusion layers according to Examples 1, 3, and Comparative Example 1 are applied.

In the unit cell evaluation, the gas diffusion layer manufactured according to Examples and Comparative Examples was applied to fuel cell unit cell components (membrane electrode assembly, separator, etc.) under the same conditions, and the voltage according to the current density was measured to determine the performance. evaluated.

In addition, as unit cell evaluation equipment for fuel cells, the flow rate hydrogen Stoic. 1.5, Air Stoic. 2.0 conditions were evaluated, and FCT (company) 3-channel 25 cm 2 unit cell hardware and Vinatech (company) 25 cm 2 MEA were used as accessories.

Referring to the current-voltage graph of FIG. 9, examining the unit cell evaluation results of the fuel cells to which the gas diffusion layer according to Examples 1, 3, and Comparative Example 1 was applied, compared to Comparative Example 1 to which the foaming agent was not applied, It is shown that the voltage value in the current density 2A / cm 2 section of Examples 1 and 3 to which was applied increased, and it can be seen that Examples 1 and 3 are superior in water discharge characteristics compared to Comparative Example 1.

Here, it can be said that the water discharge characteristics of the gas diffusion layer are excellent as the voltage value increases in the current density 2A/cm 2 section.

In addition, Example 1 and Example 3 exhibited almost similar performance, but Example 3 to which 20% of the foaming agent was applied compared to Example 1 to which 10% of the foaming agent was applied, the voltage value in the 2A / cm 2 section. It can be seen that the water discharge characteristics are improved as the content of the foaming agent is increased.

However, when the content of the foaming agent exceeds 20%, as shown in [Table 1] above, since the through electrical resistance increases rapidly, it is preferable to adjust the amount of the foaming agent added in the range of 10 to 20%. .

Accordingly, as in Examples 1 to 3, the microporous layer coating solution was prepared by adding a foaming agent of 10 to 20% content, and the microporous layer coating solution was coated on carbon paper and heat treated to prepare a gas diffusion layer. A fuel cell gas diffusion layer having excellent water discharge characteristics can be obtained by forming a microporous layer having an increased pore size by the foaming agent on the gas diffusion layer.

As described above, in the fuel cell gas diffusion layer according to an embodiment of the present invention, an appropriate amount of a foaming agent is added in the process of preparing a microporous layer coating solution, the prepared microporous layer coating solution is coated on carbon paper, and heat treatment is performed. By performing, it is possible to effectively increase the pore size of the microporous layer formed in the carbon paper through the foaming action generated in the heat treatment process.

In addition, by forming a large number of large pores in the microporous layer formed in the carbon paper, a gas diffusion layer having excellent water discharge characteristics can be provided, and through this, the performance of the fuel cell can be improved.

Embodiments of the present invention disclosed in this specification and drawings are only presented as specific examples to easily explain the technical content of the present invention and help understanding of the present invention, and are not intended to limit the scope of the present invention.

Therefore, the scope of the present invention should be construed as including all changes or modifications derived based on the technical idea of the present invention in addition to the embodiments disclosed herein.

Claims (7)

In the fuel cell microporous layer coating liquid forming the microporous layer in the gas diffusion layer,
Formed by dispersing an intermediate mixture in which a solvent, carbon powder, dispersant, and ADCA-based blowing agent are mixed, and stirring a polytetrafluoroethylene dispersion in the dispersed intermediate mixture,
The ADCA-based blowing agent,
During the heat treatment process, it has the property of foaming at 120 to 250 ° C., which is higher than the temperature at which the solvent is removed and lower than the temperature at which polytetrafluoroethylene is sintered,
Based on 100 parts by weight of the sum of the solvent, carbon powder, dispersant and polytetrafluoroethylene dispersion, 10 to 20 parts by weight are added,
A fuel cell microporous layer coating solution that improves gas permeability while suppressing an increase in through electrical resistance of the gas diffusion layer by controlling the pore size of the microporous layer in the process of manufacturing the gas diffusion layer.
According to claim 1,
The intermediate mixture is a fuel cell microporous layer coating liquid that is dispersed using a 3-roll mill.
delete According to claim 1,
The foaming agent,
Azodicarbonamide-based, toluenesulfonylhydrazide-based, oxydibenzenesulfonylhydrazide-based, dinitrosopentamethylenetetramine-based. A fuel cell microporous layer coating solution comprising at least one of toluenesulfonyl semicarbazide-based, phenyl tetrazole-based, inorganic, capsular foaming agents, and spherical polymeric foaming agents.
A microporous layer coating solution including an ADCA-based foaming agent is prepared, the microporous layer coating solution is coated on hydrophobic treated carbon paper, and heat treatment is performed to form a microporous layer on the carbon paper. to increase the pore size of the microporous layer formed on the carbon paper,
The microporous layer coating solution includes a solvent, carbon powder, a dispersant, an ADCA-based blowing agent, and a polytetrafluoroethylene dispersion,
The ADCA-based blowing agent,
During the heat treatment process, it has the property of foaming at 120 to 250 ° C., which is higher than the temperature at which the solvent is removed and lower than the temperature at which polytetrafluoroethylene is sintered,
10 to 20 parts by weight is added to 100 parts by weight of the sum of the solvent, carbon powder, dispersant, and polytetrafluoroethylene dispersion to control the pore size of the microporous layer, thereby suppressing an increase in through electrical resistance and suppressing an increase in gas resistance. A fuel cell gas diffusion layer that improves permeability.
delete According to claim 5,
The carbon paper,
carbon veil; and
Including a carbon structure bound on the carbon veil,
The carbon veil is a fuel cell gas diffusion layer in which protrusion of carbon fibers from the surface is suppressed by using an acrylic acid-based binder containing carboxylic acid and a phenol impregnation solution in which a phenol resin is dissolved.

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