KR101228545B1 - A Catalyst Slurry Composition, a Method for Preparing a Membrane-Electrode Assembly For Fuel Cell Using the Same and the Membrane-Electrode Assembly For Fuel Cell Prepared Therefrom - Google Patents

Abstract

The present invention is a catalyst; Dispersing agent containing a modified alkoxylate compound as an active ingredient; Conductive ionomers; And a catalyst slurry composition for producing a membrane-electrode assembly for fuel cell (MEA) comprising a solvent, a method for producing a membrane-electrode assembly for a fuel cell using the same, and a membrane-electrode assembly for a fuel cell prepared therefrom.
It is possible to improve the dispersibility of the catalyst and the conductive ionomer particles contained in the catalyst slurry composition, and after the coating process of applying the catalyst slurry composition and the drying process of removing the solvent, the uniformity is excellent and the catalyst and ionomer particles are excellent. Since there is no continuous connection between them, it is possible to form a catalyst layer having a large crack-free structure arrangement called a dead space, and ultimately, the membrane-electrode assembly having a pore structure can exhibit improved performance.

Description

A catalyst slurry composition, a method for preparing a membrane-electrode assembly for fuel cell using the same and the membrane -Electrode Assembly For Fuel Cell Prepared Therefrom}

The present invention relates to a catalyst slurry composition for producing a fuel cell membrane-electrode assembly (MEA), a method for producing a fuel cell membrane-electrode assembly using the same, and a membrane-electrode assembly for a fuel cell manufactured therefrom, specifically, a catalyst Catalyst slurry composition comprising a dispersant capable of structurally stabilizing the catalyst and conductive ionomer particles dispersed in a solvent when coating the slurry composition, to achieve excellent dispersibility, a method for producing a membrane-electrode assembly for a fuel cell using the same and a fuel prepared therefrom A battery membrane electrode assembly.

A fuel cell is a power generation system that directly converts chemical energy of hydrogen and oxygen contained in hydrocarbon-based materials such as methanol, ethanol, and natural gas into electrical energy by an electrochemical reaction.

Fuel cells are considered to be the most suitable energy source for the trend of the popularization of portable mobile electronic products such as mobile phones, laptops and PDAs due to the rapid development of the electronic industry. Currently, portable electronic products have been popularized, but batteries used as power sources for these products have not yet provided satisfactory performance in terms of high performance, and are expensive and heavy.

Therefore, in order to meet these demands, recently, a small polymer electrolyte fuel cell (PEEMC) or a direct methanol fuel cell (DMFC) using methanol as a fuel is referred to as "DMFC". The development and research on fuel cells are being actively conducted.

It is the membrane-electrode assembly (MEA) that determines performance in PEMFC or DMFC. The MEA consists of a solid polymer electrolyte membrane, an ion conducting membrane (hereinafter referred to as "ICM"), and two catalyzed electrodes separated by it. The powder forms a gas diffusion layer, and the carbon powder carrying the catalyst is applied on the diffusion layer to form a catalyst layer.

In order to achieve good performance of the MEA, the dispersibility of the catalyst and conductive ionomer particles into the solvent is important. This is because it greatly affects the physical properties of the coating process.

The coating process is carried out while the substrate is fixed in a vacuum mold, and 3 ml of the catalyst slurry is added to give a shear stress and pushed out. If the viscosity of the slurry is too low during the coating process, the flowability is so good that the original particles are not subjected to the coagulation or leveling step of rearrangement after stressing, and the thickness cannot be maintained properly.

In this state, when the solution enters the drying process and removes the solution, the catalyst slurry, which has not undergone proper reagglomeration, may have a small or isolated connection site for the particles through the conductive ionomer, and may not have sufficient pore structure or crack during the cell performance test. This occurs and the fuel cell cannot obtain sufficient performance.

Conventionally, the process focused on lowering the viscosity for dispersing characteristics of the catalyst slurry, but after the coating process and drying process, the slurry particles are unevenly distributed or cracked due to evaporation of the solvent, resulting in thermocompression. Even when the MEA was manufactured, the pore structure became unstable, resulting in poor performance.

Therefore, the inventors of the present application simply improve the dispersibility by having a proper elasticity value of the catalyst slurry composition through the addition of a predetermined dispersant, unlike the prior art, in which the dispersion of the catalyst slurry composition is controlled by lowering the viscosity of the catalyst slurry composition. After the process of coating a catalyst solution on the substrate, i.e., applying a shear stress on the substrate to maintain a constant thickness of the catalyst, the structure of the molecules on the substrate is uniformly arranged even though the initial shear stress is removed. To keep. Such a catalyst slurry composition prevents cracking or damage to the catalyst coating layer even after a drying process, thereby securing stability of the pore structure of the final MEA, thereby ultimately improving fuel cell performance. To provide an electrode assembly.

One embodiment according to the invention is a catalyst; Dispersing agent containing a modified alkoxylate compound as an active ingredient; Conductive ionomers; And it relates to a catalyst slurry composition for the production of a fuel cell membrane-electrode assembly (MEA) comprising a solvent.

One embodiment according to the invention comprises the steps of: (a) sonicating and homogenizing the catalyst slurry composition; (b) applying and drying the catalyst slurry composition passed through step (a) onto a substrate; And (c) transferring the substrate having passed through step (b) to one or both surfaces of the electrolyte membrane to form a catalyst layer.

One embodiment according to the present invention relates to a membrane-electrode assembly for a fuel cell manufactured according to the manufacturing method.

The catalyst slurry composition according to the present invention can improve the dispersibility of the catalyst and the conductive ionomer particles included in the catalyst slurry composition through a dispersant containing a modified alkoxylate compound as an active ingredient, and by maintaining the slurry to have proper viscoelasticity, Even when the preparation process for preparing the resin, i.e., the coating / drying process, the distribution is stabilized and structural stability may be secured even when the solvent is removed. This makes it possible to form a catalyst layer having a large crack-free structural arrangement called dead space, because the catalyst and ionomer particles do not continuously connect, resulting in a very good uniformity as well as the final MEA pore structure. The membrane-electrode assembly can be formed to ensure stability, and ultimately, the fuel cell to which the membrane is applied can exhibit improved performance.

1 is a graph showing the viscosity measurement results of the catalyst slurry composition according to an embodiment of the present invention;
2 is a graph showing a frequency sweep test result of the catalyst slurry composition according to one embodiment of the present invention;
3 is a graph showing the results of experiments to examine the degree of deformation of the catalyst slurry composition according to an embodiment of the present invention; And
Figure 4 is a FE-SEM of the catalyst slurry composition according to an embodiment of the present invention after the drying process to remove the solvent and the coating, the catalyst and Nafion ionomer coating state and structural stability of the coating applied on the substrate to enlarge the observation (Picture of Field Emission-Scanning Electron Microscope)

Depending on the viscoelastic properties made through initial stabilization of the catalyst and the conductive ionomer included in the catalyst slurry composition, the physical properties of the coated catalyst layer are determined. In order to determine the desired viscoelasticity, it was intended to stabilize the dispersion of the catalyst and the conductive ionomer, and the catalyst slurry composition according to the present invention includes a dispersant containing a modified alkoxylate compound as an active ingredient, thereby preventing electrostatic repulsion. It was confirmed that the particle distribution can be stabilized after the coating process through the steric hindrance effect.

Even after the force of the shear stress in the coating was removed, a dispersant was added so that the particles had a property to return to their original state to have an appropriate elasticity to form an appropriate structure. The dispersant reduces the interfacial tension between the carbon catalyst particles and the conductive ionomer and the solvent, accelerates the wetting and facilitates the dispersion, strongly adsorbs on the surface of the particles, and then alkoxylate chains in the surrounding solution, causing steric hindrance on the surface of the catalyst. To effect, or to form an electric double layer through the counterion can have an electrostatic repulsive force.

This ensures stable dispersion of the particles and facilitates wetting and dispersing so that they can retain improved rheological and viscoelastic properties compared to conventional catalyst slurry compositions that do not contain a dispersant, thereby eliminating cracks. A catalyst layer having a structural arrangement and a MEA having a stable pore structure can be formed.

In one embodiment, the dispersing agent may include any type of modified alkoxylate compound as long as it can achieve the electrostatic repulsive force and steric hindrance effect for improving the dispersibility of the catalyst particles, for example MgSO ₄ or its Hydrate (MgSO ₄ · 7H ₂ O) may be included as an active ingredient.

The dispersant may, for example, exhibit a pH of 5-6. Generally, the catalyst slurry composition exhibits a strong acidity of 2 to 3 in a state of being mixed with a catalyst and alcohol solvents such as conductive ionomer, water, and IPA. In the case where a small amount of additive is added in such an environment, it is important to achieve a desired effect without large changes in the pH of the catalyst slurry composition and the internal environment of the fuel cell. Thus, in the present invention, through the dispersant containing a modified alkoxylate compound as an active ingredient that does not significantly affect the pH of the other components, the desired catalyst and conductive ionomer particles without significantly affecting the internal pH of the entire slurry An acidic improvement effect can be achieved.

The content of the dispersant may be included, for example, 1 to 5% by weight, specifically 2 to 4% by weight, based on the total weight of the composition. When the content of the dispersant is too small compared with the defined range, it is difficult to expect the desired dispersibility improvement effect, and when too much, the impurities and other than the catalyst and the conductive ionomer are present in excess, resulting in deterioration of conductivity and problems such as contamination. Its content is important because it can fall.

The content of the catalyst, conductive ionomer and dispersion solvent included in the catalyst slurry composition may be, for example, 2 to 4 wt% of dispersant and 4 to 5 wt%, based on the total weight of the catalyst slurry composition, in consideration of the amount of the added dispersant. Of catalyst, 9 to 11% by weight of conductive ionomer and 80 to 85% by weight of solvent.

In one embodiment, the catalyst may be, for example, a platinum supported carbon (Pt / C), the amount of platinum in the catalyst may be 40 to 50% by weight of the total catalyst, but is not limited thereto. .

The conductive ionomer may be a Nafion (dupont) product or a hydrocarbon-based polymer electrolyte ionomer of perfluorosulfonic acid (PFSA) type, which is commonly used in the preparation of a membrane-electrode assembly, but is not limited thereto. It doesn't happen.

The solvent may be, for example, one or two or more selected from the group consisting of isopropanol, normal propanol, ethanol, methanol, water, and normal butyl acetate, but is not limited thereto.

In some cases, due to the large activity of the platinum catalyst contained in the catalyst slurry composition, water may be essentially included as a solvent to prevent combustion from occurring due to an abnormal reaction with the dispersion solvent, As a result, the catalyst slurry composition can secure initial stability.

The invention also comprises the steps of (a) sonication and homogenizing the catalyst slurry composition; (b) applying and drying the catalyst slurry composition passed through step (a) onto a substrate; And (c) transferring the substrate having passed through step (b) to one or both surfaces of the electrolyte membrane to form a catalyst layer.

In some cases, the catalyst slurry composition itself in the form of the catalyst and the conductive ionomer dispersed in the solution maintains the settling state, and thus it is difficult to maintain a stable dispersion state, and thus, the step of stirring the catalyst slurry composition before step (a) is further performed. It may include.

When manufacturing the membrane-electrode assembly for a fuel cell through the catalyst slurry composition, it did not achieve the desired dispersibility improvement when only including the step of sonication and homogenizing (homogenizing).

If the catalyst slurry composition is not settled to achieve a stable dispersion state, the distribution of the catalyst is different due to the settling state during the subsequent transfer to the coating or electrolyte membrane, and thus the amount and distribution of the catalyst in each portion are different. In addition, the viscosity increased inconsistently due to the aggregation of the particles settled in the lower part was difficult to obtain a constant physical properties.

However, by including the step of stirring the catalyst slurry, the distribution of the catalyst particles is relatively narrowed to prevent the aggregation of the particles, and the viscosity of the slurry is prevented from increasing inconsistently by the agglomeration of the catalyst particles, resulting in a uniform dispersion state. Preparation of the catalyst slurry was maintained, through which it was confirmed that the catalyst layer can be produced without cracks.

The stirring may be used in any device if it can achieve the desired effect, it can be stirred through a stirring (Magnetic Stirrer; Model name: MS-300) apparatus, wherein the stirring speed is 500 to 1000 rpm, specifically May be 800 rpm.

After the stirring, the sonication and homogenization process can be used without limitation in any method commonly used, for example, sonicating the catalyst slurry for 25 to 30 minutes, homogenizing for 110 to 120 minutes through a homogenizer (homogenizer) can do.

Step (a) is a step of applying and drying the catalyst slurry composition on a substrate, the substrate may be, for example, a support such as carbon cloth or carbon paper, but is not limited thereto.

The method for applying the catalyst slurry composition on a substrate is, for example, spray coating, screen printing, tape casting, brushing and slot die casting ( slot die casting), but is not limited thereto.

Drying of the applied catalyst slurry composition may be dried under vacuum conditions of drying conditions commonly used, for example, 20 to 60 ℃.

Subsequently, the substrate passed through step (a) is transferred to one or both surfaces of the electrolyte membrane to form a catalyst layer (b). The transfer may be performed, for example, by laminating and hot pressing a substrate having passed through step (c) onto an electrolyte membrane, and the heating temperature of the hot pressing machine is applied from a hot pressing machine at 100 to 140 ° C. The pressure is preferably 100 to 200 kgf / cm ² .

The electrolyte membrane is not particularly limited, but for example, perfluorosulfonic acid polymer, perfluorocarbon sulfonic acid polymer, hydrocarbon-based polymer, polyimide, polyvinylidene fluoride, polyethersulfone, polyphenylene sulfide, polyphenylene oxide, Polyphosphazide, polyethylene naphthalate, polyester, doped polybenzimidazole, polyetherketone, polysulfone, acid or base thereof, and may be composed of one or more selected from about 20 to 200 in thickness. Μm, preferably 40 to 60 μm.

The present invention also relates to a fuel cell membrane-electrode assembly manufactured according to the manufacturing method and a fuel cell including the same. The membrane-electrode assembly according to the present invention has excellent dispersibility and is manufactured by using a catalyst slurry composition which can maintain a constant shape even after many deformations, and thus there is no crack in the catalyst layer and the particle distribution of the catalyst is increased. Excellent, the MEA including the same may have a stable pore structure, and the fuel cell including the MEA may exhibit improved performance.

Hereinafter, the present invention will be described in more detail based on the following Examples and Experimental Examples, but the scope of the present invention is not limited thereto.

Example 1

Dispersant containing MgSO ₄ · 7H ₂ O as active ingredient (content of MgSO ₄ · 7H ₂ O in the total weight of the dispersant is 2 wt%), 1 g of Pt / C catalyst (or 5 wt% of the total dispersion solution) and Nafion A 2 g of ionomer (or 10 wt% of the total dispersion solution) was dispersed in IPA (isopropanol) and water. After stirring at a speed of 800rpm at a temperature of 25 ℃, ultrasonic treatment was performed for 30 minutes at room temperature, a catalyst slurry was prepared by mixing at a speed of 12000rpm for 120 minutes using a homogenizer (homogenizer).

Comparative Example 1

A catalyst slurry was prepared in the same manner as in Example 1, except that no dispersant was included in the course of Example 1.

[Experimental Example 1]

For rheological analysis on the viscoelastic properties of the catalyst slurries of Example 1 and Comparative Example 1, strain sweep test analysis of the slurry itself was performed with a rheometer of 0.1 to 1000 [1 / s] of Rheometer (Rheoplus, Model: MCR500). ] Was carried out at 25 ° C., a dynamic mode for measuring viscoelasticity while varying the shear rate, and the results are shown in FIG. 1.

Referring to FIG. 1, although the slurry of Example 1 and the slurry of Comparative Example 1 have similar regions near the low strain rate, the shear-thinning behavior in which the viscosity decreases gradually due to the arrangement of particles when deforming at high shear rate In addition, it was confirmed that the slurry of Example 1 exhibited a high viscosity at a relatively high shear rate, so that the slurry into which the dispersant was added does not have too much flowability in the coating process and was elastic. By adding a small amount of the dispersant it can be seen that the more stable in the shear zone to give a lot of deformation than the comparative example.

[Experimental Example 2]

The frequency sweep test was performed by a process [25 ° C.] of the dynamic mode of changing the frequency of the rheometer (Rheoplus, Model: MCR500) from 0.08 to 10 Hz, and the results are shown in FIG. 2.

Referring to Figure 2, it was confirmed that exhibiting a low viscosity in the relatively low Hertz range, which means that the dispersion of particles does not aggregate and spread well in the solvent. In addition, it can be seen that it has a high storage modulus in the low Hertz range, which means that it has an elastic ability to maintain a distributed structure well. In this case, Example 1 compared to Comparative Example 1, but at the same time at the same time, even if a lot of deformation, the width of the falling down compared to the comparative example was confirmed that it can have an improved composition that can maintain a certain form Can be.

[Experimental Example 3]

After the stress sweep test was carried out by the method of Experimental Example 2, a loop test for applying a constant strain and then removing the force was carried out five times to confirm the degree of deformation of the slurry itself, and the results are shown in FIG. 3. It was.

Referring to FIG. 3, it was found that during the five loop tests to increase the deformation rate and then remove the force, the slurry of Comparative Example 1 was more deformed than the slurry of Example 1, and thus, Example 1 was conventionally used. Relative comparison was confirmed to have more dispersion stability than the catalyst slurry composition of.

[Experimental Example 4]

The catalyst slurry of Example 1 and Comparative Example 1 was prepared by pushing a blade having a thickness of 150 to 200 μm on the substrate of the imide film by using a decal to give a shear stress, and then coating the same, and then performing this at a room temperature in a vacuum oven at 24hr. After removing the solvent by drying, the particle distribution and the structural stability of the remaining catalyst layer was magnified 1000 times with FE-SEM (Field Emission Scanning Electron Microscope).

Referring to FIG. 4, the embodiment in which a small amount of the dispersant is added is compared with the comparative example, in which the characteristic of the slurry having an appropriate elastic value after passing a constant shear stress in the coating process is characterized by rearrangement of the catalyst and ionomer particles. It was well distributed, and even after passing through the drying process, there were almost no scratches such as cracks on the surface, and it was confirmed that the structure was maintained. In addition, as a result of applying Example 1 to the coating process (a), it can be seen that a much improved particle distribution can be obtained compared to the coating (b) of the conventional slurry of Comparative Example 1.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (12)

delete delete delete delete delete (a) sonicating and homogenizing the catalyst slurry composition;
(b) applying and drying the catalyst slurry composition passed through step (a) onto a substrate; And
(c) a method of manufacturing a fuel cell membrane-electrode assembly (MEA) comprising the step of transferring the substrate passed through step (b) to one or both surfaces of an electrolyte membrane to form a catalyst layer,
The catalyst slurry composition is a catalyst; Dispersing agent containing a modified alkoxylate compound as an active ingredient; Conductive ionomers; And a solvent,
The dispersant is included in 1 to 5% by weight based on the total weight of the composition,
The dispersant is a method for producing a fuel cell membrane-electrode assembly (MEA), characterized in that the pH of 4 to 7 in the solvent. The method according to claim 6,
The production method further comprises the step of stirring the catalyst slurry composition before step (a). The method of claim 7, wherein
The manufacturing method is a method of manufacturing a membrane-electrode assembly for a fuel cell, characterized in that for stirring the catalyst slurry composition at 500 to 1000 rpm. The method according to claim 6,
Step (b) is selected from the group consisting of spray coating, screen printing, tape casting, brushing and slot die casting. Method of producing a membrane-electrode assembly for a fuel cell, characterized in that the coating of the catalyst slurry composition on a substrate by one method. The method according to claim 6,
The step (c) is a fuel characterized in that the laminated substrate on the electrolyte membrane through step (b), and hot pressing by applying a pressure of 100 to 200kgf / cm ² at a temperature of 100 to 140 ℃ Method for producing a membrane-electrode assembly for batteries. A membrane-electrode assembly for a fuel cell prepared according to the method of claim 6. A fuel cell comprising the membrane-electrode assembly of claim 11.

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