KR102683379B1 - A microporous layer coating solution for fuel cell and gas diffusion layer using the same - Google Patents

Abstract

The present invention is formed by dispersing a mixture of distilled water, carbon black, and a dispersant using a 3-roll mill. In the 3-roll mill, the spacing between rollers is 40 to 80㎛, and the linear speed of the rollers is in the range of 800 to 2000 mm/s. Provides a fuel cell microporous layer coating solution that is set and disperses the mixture within a set range.

Description

Fuel cell microporous layer coating solution and gas diffusion layer using the same {A MICROPOROUS LAYER COATING SOLUTION FOR FUEL CELL 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. It has the advantage of being environmentally friendly and having very high power generation efficiency because it directly produces electricity without burning fuel.

Here, the unit cell of a 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, which are stacked in that order. 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 this fuel cell is that the hydrogen supplied to the anode passes through the gas diffusion layer and is separated into hydrogen ions (cations) and electrons by catalytic action in the catalyst layer, and the hydrogen ions (cations) pass through the electrolyte layer to the cathode. As the electrons move to the cathode through an external circuit, a current is generated.

Additionally, on the cathode side, the fuel cell operates on the principle that water is generated when hydrogen ions (cations) that have moved through the electrolyte layer, electrons that have moved through the external circuit, and supplied oxygen meet.

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

In other words, in order to improve the performance of a fuel cell, the gas diffusion layer needs to have the characteristics of discharging water well under high-humidity operating conditions and retaining water under low-humidity operating conditions. In the case of water discharging characteristics, technology for forming a micropore layer within the gas diffusion layer is required. It may vary depending on.

Conventionally, water discharge performance has been improved by adjusting the particle size of carbon black used to form the micropore layer in the gas diffusion layer. However, if the particle size of carbon black is small, water discharge characteristics deteriorate under high humidity operating conditions, and the particle size of carbon black decreases. If it is large, the water discharge characteristics are improved, but there is a problem that the electrical resistance of the gas diffusion layer increases.

“Microporous layer for fuel cell, gas diffusion layer containing same, and fuel cell containing same” of Publication Patent No. 2021-0087825 (publication date: 2021.07.13)

In the present invention, the dispersion degree of the microporous layer coating solution can be adjusted by controlling the fuel cell microporous layer coating solution and the gas diffusion layer using the same, specifically the spacing between rollers using a 3-roll mill and the linear speed of the rollers, and the dispersion degree is adjusted. A fuel cell microporous layer coating liquid and a gas diffusion layer using the same can be obtained by controlling the pore size of the microporous layer formed on carbon paper using a microporous layer coating liquid to obtain a gas diffusion layer with excellent low humidity characteristics and excellent water discharge characteristics. We would like to provide.

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 problems described above, the present invention is formed by dispersing a mixture of distilled water, carbon black, and a dispersant using a 3-roll mill. The 3-roll mill has a gap between rollers of 40 to 80㎛ and a line of rollers. The speed is set within the range of 800 to 2000 mm/s, and a fuel cell microporous layer coating solution that disperses the mixture within the set range is provided.

In addition, a fuel cell microporous layer coating solution formed by stirring a polytetrafluoroethylene dispersion into the dispersed mixture using a three-roll mill is provided.

Meanwhile, in another aspect of the present invention to solve the problems described above, a microporous layer coating solution is prepared by dispersing a mixture of distilled water, carbon black, and a dispersant using a three-roll mill, and hydrophobically treated carbon paper is prepared. A microporous layer coating solution is coated on the carbon paper to form a microporous layer. In the 3-roll mill, the spacing between rollers is set to 40 to 80㎛, the linear speed of the rollers is set to within the range of 800 to 2000mm/s, and within the set range. Provides a fuel cell gas diffusion layer that controls the pore size of the microporous layer formed on carbon paper by controlling the degree of dispersion of the microporous layer coating solution.

The fuel cell gas diffusion layer according to an embodiment of the present invention disperses the microporous layer coating liquid by controlling the spacing between rollers and the linear speed of the rollers using a 3-roll mill during the process of manufacturing the microporous layer coating liquid coated on carbon paper. By adjusting the degree, the pore size of the microporous layer formed on carbon paper by the microporous layer coating liquid can be easily controlled.

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

The effects that can be obtained from 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.

Figure 1 is a flowchart showing a method of manufacturing a fuel cell gas diffusion layer according to an embodiment of the present invention.
Figure 2 is a flowchart showing a method for producing a microporous layer coating solution according to an embodiment of the present invention.
Figures 3 and 4 are SEM images of the surface of the microporous layer of Example 1 and Comparative Example 2, respectively.
Figures 5 to 7 show pore size distributions as a result of mercury porosity measurements on the gas diffusion layers prepared according to Comparative Example 1, Example 1, and Example 6, respectively.
Figure 8 shows the results of unit cell evaluation in a current-voltage graph under low humidity operating conditions of the fuel cell to which the gas diffusion layer according to Example 1 and Comparative Example 1 was applied.
Figure 9 shows the results of unit cell evaluation in a current-voltage graph under high humidity operating conditions of the fuel cell to which the gas diffusion layer according to Example 1 and Comparative Example 1 was applied.

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

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

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

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

Additionally, in an embodiment of the present invention, the pore size of the microporous layer can be defined as naming the size of the most distributed pores among the pores formed in the microporous layer.

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

Referring to FIG. 1, the fuel cell gas diffusion layer according to an embodiment of the present invention includes a step of preparing a microporous layer coating solution (S100), a step of hydrophobically treating the carbon paper (S200), and a step of hydrophobically treating the carbon paper. It may include the step of coating the pore layer coating solution (S300).

The fuel cell gas diffusion layer according to this embodiment is manufactured by controlling the dispersion degree of the microporous layer coating liquid using a 3-roll mill method during the manufacturing process of the microporous layer coating liquid. Pore formation can be controlled, and by coating the microporous layer coating solution prepared in this way on carbon paper to manufacture a gas diffusion layer, it is possible to have excellent low humidity characteristics and excellent water discharge characteristics.

First, in the step of preparing a microporous layer coating solution (S100), a microporous layer coating solution can be prepared by stirring and dispersing carbon black, polytetrafluoroethylene (PTFE) dispersion, a dispersant, and a solvent.

Specifically, referring to FIG. 2, a primary mixture can be prepared by first stirring carbon black and a dispersant in distilled water (S110).

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

Additionally, in this example, Triton

As an example, the first mixture can be prepared by adding 20 parts by weight of carbon black and 10 parts by weight of Triton

In the first stirring process, carbon black and Triton

Next, the primary mixture can be dispersed using a three-roll mill including first to third rollers (S120).

As an example, the spacing between the first and second rollers is set to 40 to 80㎛, the spacing between the second and third rollers is set to 40 to 80㎛, and the linear speed of the first to third rollers is set to 800 to 2000mm/mm. By setting it to s, the primary mixture can be dispersed using a 3-roll mill set to the corresponding conditions.

At this time, the dispersion degree of the primary mixture can be easily adjusted according to the spacing between rollers and the linear speed setting of the rollers. By adjusting the dispersion degree of the primary mixture, the pore size of the microporous layer manufactured later can be adjusted.

As an example, when the dispersion process is performed using a three-roll mill under the above-mentioned conditions, the pore size of the microporous layer manufactured later can be adjusted at the level of 60 to 90 nm.

At this time, in the dispersion process of the above-mentioned example, if the gap between the rollers (the gap between the first and second rollers, and the gap between the second and third rollers) exceeds 80㎛, carbon agglomeration occurs on the surface of the microporous layer. If the gap between rollers is excessively narrowed to less than 40㎛, dispersibility increases and the pore size of the microporous layer decreases, which affects performance. Therefore, the gap between rollers is set in the range of 40 to 80㎛. It is important to do.

In addition, if the linear speed of the rollers exceeds 2000 mm/s even within the gap between the rollers, the dispersibility increases excessively and the pore size of the micropore layer decreases, which has a negative effect on performance and the linear speed of the rollers decreases. If set to less than 800 mm/s, there is a problem of carbon agglomeration occurring on the surface of the microporous layer, so it is desirable to set the linear speed of the roller within 800 to 2000 mm/s.

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

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

As described above, in the process of manufacturing the microporous layer coating liquid, the dispersion of the microporous layer coating liquid can be adjusted according to the linear speed of the rollers using a 3-roll mill and the spacing between rollers, and the degree of dispersion of the microporous layer can be adjusted by adjusting the dispersion. By utilizing the fact that the pore size changes, the pore size of the microporous layer formed on carbon paper by the microporous layer coating liquid can be easily controlled.

At this time, in this embodiment, by controlling the pore size of the microporous layer formed on the carbon paper, a gas diffusion layer with excellent low humidity characteristics and excellent water discharge characteristics can be manufactured, which will be described in detail later.

Meanwhile, in the step of hydrophobic treatment of carbon paper (S200), a polytetrafluoroethylene impregnation solution can be prepared by mixing a polytetrafluoroethylene dispersion with distilled water.

Here, polytetrafluoroethylene dispersion may be added to impart hydrophobicity.

Next, hydrophobically treated carbon paper can be produced by immersing the carbon paper in a polytetrafluoroethylene impregnation solution and drying it.

Next, in the step (S300) of coating the microporous layer coating solution on the hydrophobically treated carbon paper, the microporous layer coating solution is coated on the hydrophobically treated carbon paper using a bar coater, followed by drying and heat treatment, according to the present embodiment. A gas diffusion layer can be manufactured.

In the process as described above, in this embodiment, the degree of dispersion of the microporous layer coating liquid is adjusted through a dispersion process using a three-roll mill, and the pore size of the microporous layer formed by coating the microporous layer coating liquid on carbon paper is 60. It can be selectively controlled in the range of 90 nm to 90 nm, and through this, a fuel cell gas diffusion layer with excellent low humidity characteristics and excellent water discharge characteristics can be manufactured.

Meanwhile, the carbon paper used in this example includes the steps of preparing a phenol impregnation solution mixed with an acrylic acid-based binder, impregnating a carbon veil in the phenol impregnation solution, drying and curing the impregnated carbon veil, and the hardened carbon paper. It can be manufactured through the steps of carbonizing the carbon veil and graphitizing the carbonized carbon veil.

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

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

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

In addition, the acrylic acid-based binder mixed with 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. This can contribute to increasing gas permeability.

Such acrylic acid-based binders include polyacrylic acid or styrene, methylmethacrylate, ethylmethacrylate, n-Butylmethacrylate, and isobutylmethacrylate. Crylate (iso-Butylmethacrylate), t-Butylmethacrylate, Vinylchloride, Vinylacetate, Acrylonitrile, 2-ethylhexyl methacrylate (2- Ethylhexylmethacrylate, Laurylmethacrylate, Methylacrylate, Ethylacrylate, n-Butylacrylate, iso-Butylacrylate, 2-ethyl Copolymerization of one or more selected raw materials that can form a copolymer with acrylic acid such as 2-Ethylhexylacrylate, Ethylene, Octadecylmethacrylate, and acrylamide A copolymer binder may be applied.

In addition, when carbon paper is manufactured by applying a binder with a high carboxylic acid ratio in an acrylic acid-based 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 can be increased. Because it is excellent, the effect of removing protruding fibers can be achieved with a smaller amount of binder input than before.

Accordingly, a phenol impregnation solution is prepared by adding an appropriate amount of an acrylic acid-based binder containing an appropriate ratio of carboxylic acid, and carbon paper is manufactured using the thus prepared phenol impregnation solution, thereby suppressing protruding fibers on the surface and maintaining impregnation uniformity. By increasing this, carbon paper with excellent gas permeability can be manufactured, and the compression rate of the carbon paper can be adjusted to appropriately lower, ensuring durability and easily applying to the gas diffusion layer of a fuel cell.

As a preferred example, in this embodiment, a phenol impregnation solution was prepared by adding an acrylic acid-based binder containing carboxylic acid at a ratio of 10 to 50% in an amount of 5 to 20 parts by weight based on 100 parts by weight of the phenol impregnation solution. Using this, carbon paper with excellent gas permeability and suitable for the gas diffusion layer can be manufactured.

Next, in the step of impregnating the carbon veil with the phenol impregnation solution, the carbon veil can be impregnated with the prepared phenol impregnation solution.

Carbon veil can be manufactured through a wet-laid manufacturing process by dispersing carbon fiber in water, and electrical properties can be improved only when the carbon fiber is well cultured two-dimensionally.

Recently, as the gas diffusion layer of fuel cells has become thinner, the thickness of the carbon veil has become thinner compared to the length of the carbon fibers that make up the carbon veil, resulting in a high frequency of carbon fibers protruding from the surface after manufacturing carbon paper. The carbon fibers protruding from the surface are removed. When a gas diffusion layer is manufactured after coating a microporous layer without coating and applying it to a fuel cell, the membrane electrode assembly (at least one of the catalyst layer, electrolyte layer, and gas diffusion layer) is penetrated by the protruding carbon fiber. This can cause physical damage and reduce the durability and performance of the fuel cell.

Accordingly, in the process of impregnating the carbon veil with the phenol impregnation solution, the acrylic acid-based binder contained in the phenol impregnation solution can be impregnated with the carbon veil to coat the surface of the carbon veil, thereby causing the surface of the carbon veil to protrude from the surface of the carbon veil. The carbon fibers can be arranged in a horizontal direction to form a flat surface, and the durability and performance of the fuel cell can be improved by solving the 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, the remaining solvent can first be dried in the impregnated carbon veil, and the dried carbon veil can be cured.

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

Next, in the step of carbonizing the hardened carbon veil, the hardened carbon veil can be carbonized in an inert gas atmosphere.

Specifically, carbonization can be performed using nitrogen or argon gas, which is an inert gas, to block combustion of the phenol resin, and preferably carbonization can be performed at 700 to 900°C for several tens of minutes.

Next, in the step of graphitizing the carbonized carbon veil, the carbonized carbon veil can be graphitized in an inert gas atmosphere.

At this time, the graphitization process can be performed using nitrogen gas or argon gas, and the temperature of the graphitization process can be set to 2000°C or higher.

As described above, the carbon paper according to this embodiment impregnates the carbon veil with a phenol impregnation solution prepared by adding an acrylic acid-based binder containing carboxylic acid, thereby easily removing the carbon fibers protruding from the surface of the carbon veil. It can reduce the compressibility, and in particular, it can contribute to increasing gas permeability by forming a uniform impregnation film on the carbon veil through an acrylic acid-based binder.

Furthermore, by adjusting the ratio of carboxylic acid contained in the acrylic acid-based binder and the content of the acrylic acid-based binder mixed in the phenol impregnation liquid, durability can be secured and the compression rate of the produced carbon paper can be adjusted to be suitable for the thin film-type 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 should not be construed as limiting the present invention in any way.

1) Evaluation of characteristics according to changes in roller spacing of 3-roll mill

[Examples 1 to 3]

20 g of carbon black, 10 g of Triton

Next, the first mixture is dispersed using a 3-roll mill, the spacing between the first and second rollers is set to 40㎛, the spacing between the second and third rollers is set to 40㎛, and the linear speed of the rollers is set to 800mm/s. was set to and the first mixture was dispersed under the corresponding conditions.

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

In addition, 3 g of 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.

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

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

In addition, the microporous layer coating solution was coated on hydrophobically treated carbon paper using a bar coater, dried at 100°C for 5 minutes, then raised to 400°C at a temperature increase rate of 10°C/min and maintained for 10 minutes to prepare a gas diffusion layer. did.

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

Meanwhile, Examples 2 and 3 were manufactured in the same manner as Example 1, except that in the dispersion process using a 3-roll mill, Example 2 had the first and second rollers spaced at 60㎛, and the second and third rollers were manufactured in the same manner as Example 1. The spacing of the rollers was set to 60㎛, and in Example 3, the spacing of the first and second rollers was set to 80㎛, and the spacing of the second and third rollers was set to 80㎛, and the micropores produced under the corresponding conditions were respectively set. A gas diffusion layer was prepared using a layer coating solution.

[Comparative Examples 1 and 2]

Manufactured in the same manner as Example 1, but in the dispersion process using a 3-roll mill, in Comparative Example 1, the spacing between the first and second rollers was set to 30㎛, and the spacing between the second and third rollers was set to 30㎛, In Comparative Example 2, the spacing between the first and second rollers was set to 90㎛, and the spacing between the second and third rollers was set to 90㎛, and a gas diffusion layer was manufactured using the microporous layer coating solution prepared under the corresponding conditions. .

Evaluation results of detecting the pore size and carbon agglomeration of the microporous layer for the gas diffusion layer manufactured by varying the process conditions (interval between rollers) of the three-roll mill according to Examples 1 to 3 and Comparative Examples 1 and 2, respectively. Table 1 shows the unit cell evaluation results of the fuel cell to which the gas diffusion layer according to Examples 1 to 3 and Comparative Examples 1 and 2 was applied.

In unit cell evaluation, the gas diffusion layer manufactured according to each example and comparative example was applied to the 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 measure the performance. was evaluated.

In addition, the fuel cell unit cell evaluation device is Cytech Korea's unit cell evaluation device, and the flow rate hydrogen Stoic. 1.5, Air Stoic. It was evaluated under 2.0 conditions, and FCT (Company) 3-channel 25㎠ unit cell hardware and Vinatec (Company) 25㎠ MEA were used as accessories.

In addition, the unit cell evaluation results shown in Tables 1 to 3 below show, as an example, the voltage value measurement results in a current density section of 2A/cm2 under high humidity operating conditions of a temperature of 65°C and a relative humidity of 100%.

In addition, the pore sizes listed in Tables 1 to 3 represent the sizes of the most distributed pores among the pores formed in the micropore layer for each Example and Comparative Example.

division Process conditions Evaluation results First and second roller spacing (㎛) Second and third roller spacing (㎛) linear speed
(mm/s) Pore size
(㎚) Carbon agglomeration on the surface of the microporous layer unit cell
Evaluation results
(V@2A/㎠) Example 1 40 40 800 71 - 0.443 Example 2 60 60 800 83 - 0.446 Example 3 80 80 800 88 - 0.449 Comparative Example 1 30 30 800 51 - 0.404 Comparative example 2 90 90 800 87 NG -

As shown in Table 1, looking at Examples 1 to 3 and Comparative Examples 1 and 2, in the dispersion process of the microporous layer coating solution using a 3-roll mill, the linear speed of the roller was 800 mm/s under the same conditions, In the order of Comparative Example 1, Example 1, Example 2, Example 3, and Comparative Example 2, as the gap between the rollers (the first and second roller gap, and the second and third roller gap) increases, the carbon paper increases. It can be seen that the pore size of the formed microporous layer increases, but as in Comparative Example 2, if the gap between rollers is excessively widened to 90㎛, carbon agglomeration occurs on the surface of the microporous layer, causing defects.

If carbon agglomeration occurs in the microporous layer, the performance of the gas diffusion layer is greatly reduced.

In addition, as the gap between rollers narrows, dispersibility increases and the pore size of the micropore layer formed on the carbon paper decreases. As in Comparative Example 1, when the gap between rollers is excessively narrow to 30㎛, It can be seen that the pore size of the microporous layer decreases significantly compared to Examples 1 to 3, and the performance of the fuel cell deteriorates.

Accordingly, as in Examples 1 to 3, if the dispersion of the microporous layer coating liquid is adjusted by setting the spacing between rollers in the range of 40 to 80㎛, the pores of the microporous layer formed on the carbon paper are reduced without carbon agglomeration. By adjusting the size to a level within the range of 60 to 90 nm, it can be confirmed that the performance is excellent in the unit cell evaluation results of the fuel cell.

2-1) Evaluation of characteristics according to changes in roller linear speed of 3-roll mill

[Example 4 and 5]

Manufactured in the same manner as Example 1, but in the dispersion process using a three-roll mill, Example 4 set the linear speed of the roller to 1400 mm/s, and Example 5 set the linear speed of the roller to 2000 mm/s, A gas diffusion layer was prepared using the microporous layer coating solution prepared under each corresponding condition.

[Comparative Examples 3 and 4]

Manufactured in the same manner as Example 1, but in the dispersion process using a three-roll mill, in Comparative Example 3, the linear speed of the roller was set to 600 mm/s, and in Comparative Example 4, the linear speed of the roller was set to 2200 mm/s, A gas diffusion layer was prepared using the microporous layer coating solution prepared under each corresponding condition.

Detecting the pore size and carbon agglomeration of the microporous layer for the gas diffusion layer manufactured by varying the process conditions (linear speed of the rollers) of the three-roll mill according to Examples 1, 4, and 5 and Comparative Examples 3 and 4, respectively. Table 2 shows the evaluation results and the unit cell evaluation results of the fuel cell to which the gas diffusion layer according to Examples 1, 4, and 5 and Comparative Examples 3 and 4 were applied.

division Process conditions Evaluation results First and second roller spacing (㎛) Second and third roller spacing (㎛) linear speed
(mm/s) Pore size
(㎚) Carbon agglomeration on the surface of the microporous layer unit cell
Evaluation results
(V@2A/㎠) Example 1 40 40 800 71 - 0.443 Example 4 40 40 1400 66 - 0.442 Example 5 40 40 2000 64 - 0.441 Comparative Example 3 40 40 600 72 NG - Comparative example 4 40 40 2200 54 - 0.405

As shown in Table 2, looking at Examples 1, 4, and 5, and Comparative Examples 3 and 4, in the dispersion process of the microporous layer coating liquid using a 3-roll mill, the spacing between rollers (the spacing between first and second rollers and , second and third roller spacing) is 40㎛, and under the same conditions, in the order of Comparative Example 3, Example 1, Example 4, Example 5, and Comparative Example 4, the faster the linear speed of the roller, the better the dispersibility. It can be seen that the pore size of the micropore layer formed in the carbon paper decreases as the pore size increases.

At this time, when the linear speed of the roller is set in the range of 800 to 2000 mm/s, as in Examples 1, 4, and 5, the pore size of the microporous layer formed on the carbon paper is shown to be 60 nm or more, and the fuel The battery unit cell evaluation results also show excellent performance.

On the other hand, as in Comparative Example 4, when the linear speed of the roller is excessively fast at 2200 mm/s, the pore size of the micropore layer decreases significantly compared to Examples 1, 4, and 5, and the performance of the fuel cell deteriorates. can confirm.

In addition, as in Comparative Example 3, when the linear speed of the roller is reduced to 600 mm/s, it can be confirmed that carbon agglomeration occurs on the surface of the micropore layer due to the slow roller linear speed, resulting in defects.

2-2) Evaluation of characteristics according to changes in roller linear speed of 3-roll mill

[Examples 6 and 7]

Manufactured in the same manner as Example 3, but in the dispersion process using a three-roll mill, Example 6 set the linear speed of the roller to 1400 mm/s, and Example 7 set the linear speed of the roller to 2000 mm/s, A gas diffusion layer was prepared using the microporous layer coating solution prepared under each corresponding condition.

[Comparative Examples 5 and 6]

Manufactured in the same manner as Example 3, but in the dispersion process using a three-roll mill, in Comparative Example 5, the linear speed of the roller was set to 600 mm/s, and in Comparative Example 6, the linear speed of the roller was set to 2200 mm/s, A gas diffusion layer was prepared using the microporous layer coating solution prepared under each corresponding condition.

Detecting the pore size and carbon agglomeration of the microporous layer for the gas diffusion layer manufactured by varying the process conditions (linear speed of the rollers) of the three-roll mill according to Examples 3, 6, and 7 and Comparative Examples 5 and 6, respectively. Table 3 shows the evaluation results and the unit cell evaluation results of the fuel cell to which the gas diffusion layer according to Examples 3, 6, and 7 and Comparative Examples 5 and 6 were applied.

division Process conditions Evaluation results First and second roller spacing (㎛) Second and third roller spacing (㎛) linear speed
(mm/s) Pore size
(㎚) Carbon agglomeration on the surface of the microporous layer unit cell
Evaluation results
(V@2A/㎠) Example 3 80 80 800 88 - 0.449 Example 6 80 80 1400 82 - 0.446 Example 7 80 80 2000 67 - 0.442 Comparative Example 5 80 80 600 88 NG - Comparative Example 6 80 80 2200 58 - 0.408

As shown in Table 3, looking at Examples 3, 6, and 7, and Comparative Examples 5 and 6, in the dispersion process of the microporous layer coating solution using a 3-roll mill, the spacing between rollers (the spacing between first and second rollers) , second and third roller spacing) of 80 ㎛, it can be seen that the pore size of the microporous layer formed on the carbon paper decreases as the linear speed of the roller increases.

At this time, when the linear speed of the roller is set in the range of 800 to 2000 mm/s, as in Examples 3, 6, and 7, the pore size of the microporous layer formed on the carbon paper is shown to be 60 nm or more, and the fuel The battery unit cell evaluation results also show excellent performance.

In particular, in Example 3, where the linear speed of the roller was set to 800 mm/s, the pore size was the largest at 88 nm, but in the evaluation results of the unit cell of the fuel cell, Example 6 and Example 6, where the linear speed of the roller was set to 1400 mm/s, , There was only a slight performance improvement and no significant difference compared to Example 7, where the linear speed of the roller was set to 2000 mm/s.

On the other hand, as in Comparative Example 6, when the linear speed of the roller is excessively fast at 2200 mm/s, the pore size of the micropore layer decreases significantly compared to Examples 3, 6, and 7, thereby deteriorating the performance of the fuel cell. can confirm.

In addition, as in Comparative Example 5, when the linear speed of the roller is reduced to 600 mm/s, it can be confirmed that carbon agglomeration occurs on the surface of the micropore layer due to the slow roller linear speed, resulting in defects.

Accordingly, as shown in the results of Tables 1 to 3 above, the roller spacing (first and second roller spacing, second and third roller spacing) is set to 40 to 80㎛, and the linear speed of the roller is set to 40 to 80㎛. When a microporous layer coating solution with controlled dispersion degree is manufactured using the process conditions of a 3-roll mill set at 800 to 2000 mm/s, and a gas diffusion layer is manufactured using this, there is no carbon agglomeration and the thickness is reduced to 60 to 90 nm. A micropore layer with controlled pore size can be obtained, which can greatly improve the performance of the fuel cell.

Here, if the pore size of the microporous layer is less than 60 nm, the performance of the high current region deteriorates due to a decrease in water discharge characteristics in the high humidity environment of the fuel cell, and if the pore size of the microporous layer exceeds 90 nm, the catalyst layer and the gas diffusion layer deteriorate. As contact resistance increases, performance in the mid-current region deteriorates, resulting in a decrease in overall fuel cell characteristics.

Meanwhile, Figures 3 and 4 are SEM images of the surface of the microporous layer of Example 1 and Comparative Example 2, respectively.

Referring to Figures 3 and 4, there is no carbon agglomeration in the surface image of the microporous layer according to Example 1 shown in Figure 3, and there is carbon agglomeration in the surface image of the microporous layer according to Comparative Example 2 shown in Figure 4. You can confirm that this has occurred.

Figures 5 to 7 show pore size distributions as a result of mercury porosity measurements on the gas diffusion layers prepared according to Comparative Example 1, Example 1, and Example 6, respectively.

As shown in Tables 1 to 3 above, in manufacturing the fuel cell gas diffusion layer, during the microporous layer coating solution manufacturing process, the gap between the first and second rollers, the gap between the second and third rollers, and the line of the rollers By varying the process conditions using a three-roll mill, such as speed, and controlling the dispersion of the microporous layer coating liquid, the pore size of the microporous layer formed on the carbon paper can be adjusted.

Looking at the pore size distribution diagram shown in Figures 5 to 7, the The pore size of the microporous layer is shown.

At this time, the peak value displayed in the right area of the pore size distribution chart represents the size of the most distributed pores among the pores formed in the micropore layer.

Specifically, Comparative Example 1 had the most distributed pore size in the microporous layer at 51 nm, Example 1 had the most distributed pore size in the microporous layer at 71 nm, and Example 6 had the most distributed pore size in the microporous layer. It can be seen that the widely distributed pore size is 82 nm, and it can be confirmed that the pore size of the micropore layer can be controlled according to the process conditions using the 3-roll mill.

In addition, as shown in Tables 1 to 3, looking at the unit cell evaluation results of Examples 1 to 7 without carbon agglomeration in the microporous layer, Example 3 had the largest pore size of 88 nm in the microporous layer. The fuel cell unit cell shows the best performance, but when the pore size of the microporous layer is formed at the level of 60 to 90 nm, the unit cell evaluation results of the fuel cell all show excellent performance without much difference.

At this time, if the pore size of the microporous layer is large, the water discharge characteristics of the gas diffusion layer are excellent, but if the pore size of the microporous layer is too large, the contact resistance with the catalyst layer increases and performance may be reduced, which may reduce the microporous layer's performance. It is recommended that the pore size of the pore layer be around 60 to 90 nm.

The gas diffusion layer is important in its ability to store water in low-humidity operating conditions, and its water discharge properties are important in high-humidity operating conditions. The water discharge characteristics may vary depending on the pore size of the microporous layer provided in the gas diffusion layer. When the pore size of the microporous layer is adjusted to a level of 60 to 90 nm, the water discharge characteristics of the gas diffusion layer can be effectively improved.

As shown in the above-mentioned Tables 1 to 3, it can be seen that in the case of Examples 1 to 7, the voltage value in the current density section of 2A/cm2 is superior to Comparative Example 1, Comparative Example 4, and Comparative Example 6, This is the result of smooth discharge of residual water in the pores created by the fuel cell reaction in a high-humidity environment, making it easy for the fuel (e.g. hydrogen, oxygen) supplied to the fuel cell separator to diffuse into the catalyst layer.

Figure 8 shows a current-voltage graph showing the results of unit cell evaluation under low humidity operating conditions of the fuel cell to which the gas diffusion layer according to Example 1 and Comparative Example 1 was applied, and Figure 9 shows the results of unit cell evaluation according to Example 1 and Comparative Example 1. The results of unit cell evaluation under high humidity operating conditions of a fuel cell with a gas diffusion layer are shown in a current-voltage graph.

Looking at the unit cell evaluation results of the fuel cell to which the gas diffusion layer according to Example 1 and Comparative Example 1 shown in FIGS. 8 and 9 is applied, the Examples were obtained under low humidity operating conditions of a temperature of 65° C. and a relative humidity of 50% as shown in FIG. 8. 1 and Comparative Example 1 show almost similar performance, and since the humidity is low, water clogging does not occur even in the current density range of 2A/cm2, so there is no difference in voltage reduction.

On the other hand, in the high-humidity operating conditions of 65°C and 100% relative humidity in FIG. 9, the voltage value at the current density of 2A/cm2 was increased in Example 1 compared to Comparative Example 1, and compared to Comparative Example 1, It can be seen that Example 1 has greatly improved water discharge performance.

In other words, by adjusting the pore size of the microporous layer to a level of 60 to 90 nm, a fuel cell can be produced that has excellent performance under high humidity operating conditions while maintaining the same performance under low humidity operating conditions.

In addition, as shown in the above-mentioned Tables 1 to 3, in the case of Examples 2 to 7, the voltage value in the current density 2A/cm2 section appears similar to Example 1, and compared to Comparative Example 1, water discharge It can be seen that performance has been greatly improved.

Accordingly, as in Examples 1 to 7, the spacing of the rollers is set in the range of 40 to 80㎛, and the linear speed of the rollers within the spacing is set to 800 to 2000 mm/s, so that the process conditions of the three-roll mill are set to When manufacturing a microporous layer coating solution with controlled dispersion and using it to manufacture a gas diffusion layer with a microporous layer with a pore size of 60 to 90 nm without carbon agglomeration, excellent low humidity characteristics and excellent water discharge characteristics are obtained. A fuel cell gas diffusion layer having a can be obtained.

As described above, the fuel cell gas diffusion layer according to an embodiment of the present invention controls the spacing between rollers and the linear speed of the rollers using a three-roll mill during the process of manufacturing a microporous layer coating solution coated on carbon paper. By adjusting the degree of dispersion of the microporous layer coating liquid, the pore size of the microporous layer formed on carbon paper by the microporous layer coating liquid can be easily controlled.

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

The embodiments of the present invention disclosed in this specification and drawings are merely provided as specific examples to easily explain the technical content of the present invention and to facilitate 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 modified forms derived based on the technical idea of the present invention in addition to the embodiments disclosed herein.

Claims (4)

A mixture of distilled water, carbon black, and dispersant is dispersed using a 3-roll mill to prepare a microporous layer coating solution, and the microporous layer coating solution is coated on hydrophobically treated carbon paper to form a microporous layer on the carbon paper. ,
The spacing between rollers is 40 to 80㎛, and the linear speed of the rollers is set in the range of 800 to 2000mm/s to control the dispersion of the microporous layer coating solution, so that the carbon paper has a range of 60 to 90㎚. A fuel cell gas diffusion layer that can improve water discharge performance and suppress contact resistance with the catalyst layer by forming a micropore layer with a pore size of .
According to clause 1,
The microporous layer coating solution is,
A fuel cell gas diffusion layer formed by adding polytetrafluoroethylene dispersion to the dispersed mixture using the three-roll mill and stirring it, and applied and coated on the carbon paper.
Preparing a primary mixture by stirring distilled water, carbon black, and a dispersant;
Dispersing the primary mixture using a three-roll mill where the spacing between rollers is set to 40 to 80㎛ and the linear speed of the rollers is set to within the range of 800 to 2000 mm/s;
Adding polytetrafluoroethylene dispersion to the dispersed primary mixture and secondary stirring to prepare a microporous layer coating solution; and
A fuel cell gas diffusion layer manufacturing method comprising the step of coating the microporous layer coating solution on hydrophobically treated carbon paper. delete

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