KR20180052905A - Manufacturing method of catalyst ink for forming fuel cell electrode catalyst layer - Google Patents

Abstract

The present invention relates to a method for manufacturing a catalyst ink for forming an electrode catalyst layer for a fuel cell. An object of the present invention is to provide a method for a catalyst ink for forming the electrode catalyst layer for the fuel cell capable of forming a catalyst layer having a uniform structure.

Description

TECHNICAL FIELD [0001] The present invention relates to a catalyst ink for forming an electrode catalyst layer for a fuel cell,

The present invention relates to a method for producing a catalyst ink for forming an electrode catalyst layer for a fuel cell.

Fuel Cell is a power generation system that directly converts the 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 a clean energy source that can replace fossil energy. Recently, with the rapid development of the electronics industry, portable mobile electronic products are regarded as the most suitable energy sources for the trend of popularization. In addition, fuel cell is attracting attention as a power source for high performance portable electronic products because it exhibits a high energy density while outputting a wide range of power compared to a battery currently used as a power source for portable electronic products.

Typical examples of such a fuel cell include a polymer electrolyte membrane fuel cell (PEMFC) and a direct methanol fuel cell (DMFC) using methanol as a fuel. Development and research are actively being carried out.

Membrane Electrode Assembly (MEA) is the key to performance in PEMFC or DMFC. The MEA is composed of a solid polymer electrolyte membrane containing a proton conductive polymer and two catalyzed electrodes separated therefrom. The two electrodes are connected to an anode electrode (also called an "oxidizing electrode" or "fuel electrode") and a cathode electrode (Aka "reduction electrode" or "air electrode").

At the anode electrode, the oxidation reaction of the fuel occurs and hydrogen ions and electrons are generated. The hydrogen ions move to the cathode electrode through the electrolyte membrane, and the electrons are transferred to the external circuit through the conductor (or current collector). In the cathode electrode, hydrogen ions transferred through the electrolyte membrane and electrons transferred from the external circuit react with oxygen, which is an oxidizing agent, to generate water. At this time, the movement of electrons via the anode, the external circuit, and the cathode is power.

The anode is provided with a catalyst layer for promoting the oxidation of the fuel, and the cathode is provided with a catalyst layer for promoting the reduction of the oxidant.

In order to increase the reaction rate of the catalyst layer, the structure of the catalyst layer must be uniform. In order to accomplish this, the ionomer should be sufficiently adsorbed to the carbon support in the catalyst during the preparation of the catalyst ink for forming the catalyst layer. If the catalyst layer structure is not uniform using the catalyst ink having insufficient adsorption, the reactant transfer resistance to the three phase poundary where the electrochemical reaction occurs may be increased, and the electrode performance may be deteriorated.

Conventionally, in order to produce a uniform catalyst layer, after the ionomer and the catalyst are mixed, that is, after the ionomer is adsorbed on the carbon support, the ultrasonic treatment is performed to produce catalyst in which catalyst particles are uniformly dispersed. Since the particle size of the catalyst particles is very small, it is difficult to achieve high dispersion by only post-adsorption dispersion.

Korean Patent Laid-Open Publication No. 10-2011-0114992

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a catalyst ink for forming an electrode catalyst layer for a fuel cell, which can form a catalyst layer having a uniform structure, in order to solve the problems of the above-

One embodiment of the present disclosure

1) sonicating a mixture of ionomer and solvent; And

2) introducing the catalyst into the ultrasonic treated mixture

The present invention also provides a method for producing a catalyst ink for forming an electrode catalyst layer for a fuel cell.

The method for preparing a catalyst ink for forming an electrode catalyst layer for a fuel cell according to the present invention is characterized in that an ionomer and a mixture of a solvent are ultrasonically treated to reduce the particle size of the ionomer before injecting the catalyst, Thereby forming an electrode catalyst layer having a high uniformity.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a flow chart summarizing a process for producing a catalyst ink according to an embodiment of the present invention; Fig.
2 is a SEM photograph of an electrode catalyst layer formed using the catalyst ink according to Example 1 of the present invention.
3 is a SEM photograph of an electrode catalyst layer formed using the catalyst ink according to Comparative Example 1 of this specification.
4 schematically shows a fuel cell used in the art.

Whenever a component is referred to as "comprising ", it is to be understood that the component may include other components as well, without departing from the specification unless specifically stated otherwise.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

In one embodiment of the present disclosure,

1) sonicating a mixture of ionomer and solvent; And

2) introducing the catalyst into the ultrasonic treated mixture

The present invention also provides a method for producing a catalyst ink for forming an electrode catalyst layer for a fuel cell.

Specifically, prior to the introduction of the catalyst, the size of the ionomer particles is reduced through the ultrasonic treatment in the above step 1) to enhance the adsorption between the ionomer and the carbon support in the catalyst, and as a result, a uniform adsorption structure is formed in the electrode catalyst layer, A method for producing a catalyst ink for forming an electrode catalyst layer for a fuel cell capable of enhancing performance is provided.

The ionomer may serve to provide a passage through which ions generated by the reaction between the fuel and the catalyst, such as hydrogen or methanol, move to the electrolyte membrane.

According to one embodiment of the present invention, the weight average molecular weight of the ionomer used in step 1) may be 240 g / mol to 200,000 g / mol, specifically 240 g / mol to 10,000 g / mol.

According to one embodiment of the present invention, the ionomer may be a perfluorosulfonic acid (PFSA) -based polymer or a perfluorocarboxylic acid (PFCA) -based polymer. Nafion (Dupont) can be used as the perfluorosulfonic acid-based polymer, and Flemion (Asahi Glass) can be used as the perfluorocarboxylic acid-based polymer.

According to one embodiment of the present invention, the ionomer may be contained in an amount of 0.01 to 0.1% by weight based on the total weight of the catalyst ink, preferably 0.01 to 0.05% by weight, more preferably 0.01 By weight to 0.03% by weight.

When the content of the ionomer is within the above range, the ionomer does not excessively cover the catalyst layer, so that the reaction of the catalyst and the fuel is facilitated, and the ion transfer path in the catalyst layer is properly formed, so that the ion can be most smoothly moved.

According to one embodiment of the present invention, the solvent used in step 1) is at least one selected from the group consisting of water, methanol, ethanol, butanol, n-propanol, isopropanol, n-butyl acetate, ethylene glycol, glycerol, N, N-dimethylacetamide (DMA), N, N-dimethylformamide (DMF), hexamethylphosphoramide (HMPA) and 1,3-dimethyl-2-imidazolidinone (DMI), and preferably one or more selected from the group consisting of water, methanol, ethanol , Butanol, n-propanol, isopropanol, n-butyl acetate, ethylene glycol and glycerol, and more preferably, Propanol, but is not limited thereto.

According to one embodiment of the present disclosure, the solvent may be included in an amount of 50 to 95 wt%, preferably 65 to 95 wt%, more preferably 75 to 95 wt%, based on the total weight of the catalyst ink, To 95% by weight.

When the content of the solvent in the catalyst ink is 50 wt% or more, the viscosity of the catalyst ink is prevented from becoming too high, so that the degradation of the catalytic particle and the uneven formation of the catalyst layer can be prevented. When the content of the solvent is 95% by weight or less, the viscosity of the catalyst ink is prevented from being too low, and thus the thickness of the catalyst layer is small, thereby preventing the problem that the coating is repeated several times.

According to an embodiment of the present invention, the ultrasonic processing in the step 1) may be a tip type or a bath type.

The term " ultrasonic wave treatment " refers to an action of applying energy having a frequency of 20 kHz or higher to particles to disperse the energy. The bath type uses relatively low and constant energy, It is possible to apply a high energy as high as about 50 times that of the mold.

In general, the ionomer is aggregated in a solvent by an electrostatic attraction force and exists as an aggregate having a particle diameter of 0.01 to 1 μm, and the unit particle formed by aggregating the ionomer in the solvent is called an ionomer cluster. When these are dispersed by ultrasonic treatment, specifically, by tip type or bath type ultrasonic treatment, most of the ionomer clusters have an average of 10 nm to 500 nm, preferably 10 nm to 300 nm And is uniformly dispersed so as to have a particle size.

The tip-type sonication may be performed for 10 minutes to 30 minutes, though not limited thereto. The bass type ultrasonic treatment may be performed for 20 minutes to 120 minutes, preferably 30 minutes to 60 minutes.

When the ultrasonic treatment is performed within the above-described time range, it is possible to prevent the occurrence of local ionomer bunching phenomenon. If the time range is exceeded, the effect of dispersion over time may not be significant and it may be inefficient.

In order to form a catalyst layer having a uniform structure, sufficient adsorption force between the ionomer and the carbon support in the catalyst is important. By controlling the particle size of the ionomer through the ultrasonic treatment, the ionomer can be uniformly adsorbed to the carbon support in the catalyst.

FIGS. 2 and 3 show SEM photographs of the electrode catalyst layer formed using the catalyst ink according to Example 1 and Comparative Example 1 of the present invention, respectively. It can be confirmed that the electrode catalyst layer using the catalyst ink of Example 1 subjected to the ultrasonic treatment has a much more uniform structure.

According to one embodiment of the present invention, the catalyst may be a catalyst in which a metal is supported on the surface of a carbon support.

The carbon support includes, but is not limited to, Carbon nanowires, carbon nanowires, fullerenes (C60), and superfine carbon blacks (graphite), carbon black, acetylene black, denka black, cacao black, activated carbon, mesoporous carbon, carbon nanotube, carbon nanofiber, P, may be used.

The metals include, but are not limited to, platinum, ruthenium, osmium, platinum / ruthenium alloys, platinum / osmium alloys, platinum / , Co, Ni, Cu, Zn, Sn, Mo, W, Rh, Ru, or combinations thereof), or combinations thereof. As a specific example of the catalyst, Pt, Pt / Ru, Pt / W, Pt / Ni, Pt / Sn, Pt / Mo, Pt / Pd, Pt / Fe, Pt / , Pt / Ru / Mo, Pt / Ru / V, Pt / Fe / Co, Pt / Ru / Rh / Ni, Pt / Ru / Sn / W or combinations thereof.

According to one embodiment of the present invention, the catalyst may be platinum-supported carbon (Pt / C) or platinum-ruthenium alloy supported carbon (PtRu / C), preferably platinum- .

Here, the insertion of a slash (/) means an alloy of the metals described. For example, Pt / Ru means an alloy of platinum (Pt) and ruthenium (Ru).

According to one embodiment of the present disclosure, The catalyst may be included in an amount of 1 wt% to 20 wt%, preferably 1 wt% to 15 wt%, and more preferably 5 wt% to 15 wt% based on the total weight of the catalyst ink have.

If the content of the catalyst in the catalyst ink is 1 wt% or more, the viscosity of the catalyst ink is prevented from becoming too low, and thus the thickness of the catalyst layer is small, thereby preventing the coating from being repeated several times. When the content of the catalyst is 20 wt% or less, the viscosity of the catalyst ink is prevented from becoming too high, so that the degradation of the catalytic particle and the uneven formation of the catalyst layer can be prevented.

According to an embodiment of the present invention, the method for preparing the catalyst ink for forming the electrode catalyst layer for a fuel cell may further include dispersing the catalyst ink by ultrasonic treatment and a high-shear mixer. FIG. 1 schematically shows a production process flow chart of the catalyst ink including the dispersion step of the catalyst ink.

The tip-type sonication of the catalyst ink is not limited thereto, but may be performed for 10 minutes to 30 minutes. The bath-type ultrasonic treatment of the catalyst ink may be performed for 20 minutes to 120 minutes, preferably 30 minutes to 60 minutes.

When the ultrasonic treatment is performed within the time range described above, it is possible to prevent the occurrence of localized accumulation of catalyst particles. When the reaction time exceeds the above-mentioned time range, the catalytic particles carried on the support are desorbed and the electrochemically active area of the catalyst layer may be reduced.

The high-shear mixer method is preferably, but not limited to, performed at a speed of 10 m / s to 40 m / s for 15 minutes to 35 minutes.

The catalyst ink prepared according to the method for producing the catalyst ink can be used for forming an electrode catalyst layer for a fuel cell.

The electrode catalyst layer may be formed by a conventional method known in the art, for example, by coating the catalyst ink on a gas diffusion layer and drying the catalyst ink. At this time, a plurality of catalyst layers may be formed by sequentially coating and drying the catalyst ink having different ionomer contents.

At this time, the method of applying the catalyst ink on the gas diffusion layer may include printing, tape casting, slot die casting, spraying, rolling, blade coating coating, spin coating, inkjet coating, or brushing, but the present invention is not limited thereto.

The gas diffusion layer is not particularly limited as long as the substrate is generally conductive and has a porosity of 80% or more, and may include a conductive substrate selected from the group consisting of carbon paper, carbon cloth, and carbon felt. The thickness of the substrate may be 30 to 500 mu m. If the value is within the above range, the balance between the mechanical strength and the diffusion property of gas and water can be appropriately controlled. The gas diffusion layer may further include a microporous layer formed on one surface of the conductive substrate, and the microporous layer may include a carbon-based material and a fluororesin. The microporous layer promotes the discharge of excess water present in the catalyst layer, thereby suppressing the occurrence of flooding.

Examples of the carbon-based material include graphite, carbon black, acetylene black, denka black, cacao black, activated carbon, mesoporous carbon, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon nano ring, Fullerene (C60), and super P may be used, but are not limited thereto.

Examples of the fluororesin include polytetrafluoroethylene, polyvinylidene fluoride (PVdF), polyvinyl alcohol, cellulose acetate, copolymers of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) and styrene-butadiene rubber (SBR) may be used, but the present invention is not limited thereto.

The fuel cell including the electrode catalyst layer for a fuel cell may be formed using materials and methods known in the art, except that the electrode catalyst layer for a fuel cell is included. Referring to FIG. 4, the fuel cell includes a stack 60, a fuel supply unit 80, and an oxidant supply unit 70.

The stack 60 includes one or more membrane-electrode assemblies (MEAs) and, when two or more membrane-electrode assemblies are included, a separator interposed therebetween. The separators are electrically connected to the membrane- And to transfer the fuel and the oxidant supplied from the outside to the membrane electrode assembly.

The fuel supply unit 80 serves to supply fuel to the stack and includes a fuel tank 81 for storing the fuel and a pump 82 for supplying the fuel stored in the fuel tank 81 to the stack 60 . As the fuel, gas or liquid hydrogen or hydrocarbon fuel may be used. Examples of the hydrocarbon fuel include methanol, ethanol, propanol, butanol or natural gas.

The oxidant supply part 70 serves to supply an oxidant to the stack. As the oxidizing agent, oxygen is typically used, and oxygen or air can be injected into the pump 82 for use.

Hereinafter, the present invention will be described in detail by way of examples with reference to the drawings. However, the embodiments according to the present disclosure can be modified in various other forms, and the scope of the present specification is not construed as being limited to the embodiments described below. Embodiments of the present disclosure are provided to more fully describe the present disclosure to those of ordinary skill in the art.

< Example >

Example  One.

10 g of propanol as a solvent was added to 1.65 g of commercial Nafion ionomer solution (D2021, Nafion 20% content, Dupont), and then tip type ultrasonic treatment was performed for 15 minutes to prepare an ionomer solution.

The average particle diameter of the ionomer clusters in the prepared solution was measured, and the results are shown in Table 1 below. The measurement was performed with a dynamic light scattering spectrometer (DLS) using a zetasizer from Malven.

After the ionomer solution was cooled, 1 g of Pt / C (TEC10V50E, manufactured by Tanaka) was added to prepare a catalyst ink.

The catalyst ink prepared above was applied to an electrode substrate by an ink-jet coating method to form an electrode catalyst layer, and an SEM photograph of the prepared catalyst layer is shown in FIG.

After forming the catalyst layer, the electrode was dried at 100 ° C. for 1 hour to prepare an electrode. The anode and the cathode were bonded to both surfaces of the polymer electrolyte membrane to prepare a membrane electrode assembly (MEA) for fuel cells.

Example  2.

A membrane-electrode assembly (MEA) for a fuel cell was prepared in the same manner as in Example 1, except that a tip type ultrasonic treatment was performed for 30 minutes to prepare an ionomer solution.

Example  3.

A membrane-electrode assembly (MEA) for a fuel cell was fabricated in the same manner as in Example 2, except that the ionomer solution was prepared by changing the ultrasonic treatment mode to a bath type instead of a tip type.

Example  4.

A membrane-electrode assembly (MEA) for a fuel cell was fabricated in the same manner as in Example 3, except that the ionomer solution was prepared by conducting a bath type ultrasonic treatment for 60 minutes.

Example  5.

A membrane-electrode assembly (MEA) for a fuel cell was prepared in the same manner as in Example 3, except that the ionomer solution was prepared by performing a bath type ultrasonic treatment for 90 minutes.

Example  6.

A membrane-electrode assembly (MEA) for a fuel cell was prepared in the same manner as in Example 3, except that the ionomer solution was prepared by conducting a bath type ultrasonic treatment for 120 minutes.

< Comparative Example >

Comparative Example  One.

A membrane-electrode assembly (MEA) for a fuel cell was prepared in the same manner as in Example 1, except that the ionomer solution was prepared by simple stirring instead of the ultrasonic treatment. SEM photographs of the electrode catalyst layer prepared in this process Is shown in Fig.

Conditions for ionomer solution dispersion Particle size (nm) of ionomer cluster Example 1 Type sonic (15 min.) 224 Example 2 Type sonic (30 min.) 223 Example 3 Bath sonic (30min.) 360 Example 4 Bath sonic (60min.) 311 Example 5 Bath sonic (90min.) 298 Example 6 Bath sonic (120min.) 294 Comparative Example 1 Stirring 674

It can be seen from Table 1 that the particle diameters of the ionomer clusters are remarkably reduced in Examples 1 to 6 in which the ionomer solution was subjected to ultrasonic treatment than in Comparative Example 1 in which the ionomer solution was simply stirred.

In addition, when the SEM photographs of the electrode catalyst layers of FIGS. 2 and 3 are compared, it can be seen that the catalyst layer of Example 1 is much more uniform than the catalyst layer of Comparative Example 1.

60: Stack
70: oxidant supplier
80: fuel supply unit
81: Fuel tank
82: Pump

Claims (10)

1) sonicating a mixture of an ionomer and a solvent; And
2) introducing the catalyst into the ultrasonic treated mixture
And a catalyst layer formed on the catalyst layer. The method according to claim 1, wherein the ultrasonic treatment in step 1) is performed in a tip type or a bath type. The method according to claim 1, wherein an average particle diameter of ionomer clusters is 10 nm to 500 nm, which is a unitary particle formed by aggregating ionomers in the solvent after the completion of the step 1) . The electrode catalyst layer for a fuel cell according to claim 1, wherein the solvent of step 1) is one or more selected from the group consisting of water, methanol, ethanol, butanol, n-propanol, isopropanol, n-butyl acetate, ethylene glycol, and glycerol Wherein the catalyst ink is prepared by a method comprising the steps of: The method according to claim 1, wherein the ionomer is a perfluorosulfonic acid (PFSA) -based polymer or a perfluorocarboxylic acid (PFCA) -based polymer. [Claim 2] The method according to claim 1, wherein the ionomer is contained in an amount of 0.01 to 0.1% by weight based on the total weight of the catalyst ink. The method according to claim 1, wherein the solvent of step 1) is contained in an amount of 50% by weight to 95% by weight based on the total weight of the catalyst ink. The catalyst of claim 1, wherein the catalyst is selected from the group consisting of Pt, Pt / C, Pt / Ir, Pt / Ru, Pt / W, Pt / Ni, Pt / Sn, Pt / Mo, Pt / Pt / Ru / W, Pt / Ru / Mo, Pt / Ru / V, Pt / Fe / Co, Pt / Ru / Rh / Wherein the catalyst layer is formed on the surface of the catalyst layer. The method of claim 1, wherein the catalyst is contained in an amount of 1 wt% to 20 wt% based on the total weight of the catalyst ink. A mixture of an ionomer and a solvent is formed by ultrasonic treatment,
Wherein an average particle size of ionomer clusters which are unit particles formed by agglomerating ionomers in the solvent is 10 nm to 500 nm.

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