KR20190136252A - Catalyst ink for forming electrode catalyst layer of fuel cell and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a method for manufacturing a catalyst ink for forming an electrode catalyst layer of a fuel cell comprising the following steps: mixing an ionomer and a solvent to prepare a mixed liquid; inputting graphite to the mixed liquid, dispersing the same at high pressure over 50 bar and preparing a dispersion liquid; and inputting a catalyst into the dispersion liquid. According to the present invention, since the ohmic resistance is reduced due to a decrease in the electrode resistance, conductivity in an electrode is increased and a membrane-electrode assembly with improved performance at low humidification conditions can be manufactured.

Description

Catalyst ink for forming fuel cell electrode catalyst layer and its manufacturing method {CATALYST INK FOR FORMING ELECTRODE CATALYST LAYER OF FUEL CELL AND MANUFACTURING METHOD THEREOF}

The present invention relates to a catalyst ink for forming a fuel cell electrode catalyst layer and a method of manufacturing the same.

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 a clean energy source that can replace fossil energy and are considered to be the most suitable energy source for the trend of the popularization of portable mobile electronic products with the recent rapid development of the electronic industry. In addition, fuel cells are attracting attention as a power source of high-performance portable electronic products because they exhibit a high energy density while outputting a wide range of outputs compared to batteries used as power sources of portable electronic products.

Representative examples of such fuel cells include polymer electrolyte fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) using methanol as a fuel. Development and research are active.

It is the membrane-electrode assembly (MEA) that determines performance in PEMFC or DMFC. The MEA consists of a solid polymer electrolyte membrane containing a hydrogen ion conductive polymer and two catalyzed electrodes separated by these two electrodes, an anode electrode (also known as an "oxide electrode" or "fuel electrode") and a cathode electrode. (Also called "reduction electrode" or "air electrode").

In the anode electrode, the oxidation reaction of the fuel occurs to generate hydrogen ions and electrons, 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 an external circuit react with oxygen, which is an oxidant, to generate water. At this time, the movement of electrons through the anode, the external circuit, and the cathode is electric 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 speed of the catalyst layer and thereby improve the conductivity characteristics in the electrode, research is being actively conducted.

Republic of Korea Patent Publication No. 10-2011-0114992

It is an object of the present invention to provide a catalyst ink for forming a fuel cell electrode catalyst layer and a method of manufacturing the same.

One embodiment of the present specification

1) mixing a ionomer and a solvent to prepare a mixed solution;

2) preparing a dispersion by adding graphite to the mixture and dispersing the mixture at a high pressure of 50 bar or more; And

3) adding a catalyst to the dispersion

It provides a method for producing a catalyst ink for forming a fuel cell electrode catalyst layer comprising a.

In addition, an exemplary embodiment of the present specification provides a catalyst ink for forming a fuel cell electrode catalyst layer including an ionomer, a catalyst, and graphene.

In addition, an exemplary embodiment of the present specification provides an electrode catalyst layer for a fuel cell including a cured product of the catalyst ink on a gas diffusion layer.

In addition, an exemplary embodiment of the present specification provides a fuel cell membrane-electrode assembly including the electrode catalyst layer.

In addition, an exemplary embodiment of the present disclosure provides a fuel cell including the membrane-electrode assembly.

When the electrode is manufactured using the catalyst ink prepared according to the exemplary embodiment of the present specification, the ohmic resistance is reduced due to the decrease of the electrode resistance, thereby improving conductivity in the electrode, and thus, the membrane has improved performance under low humidity conditions. There is an advantage that the electrode assembly can be manufactured.

1 is a view showing a photograph of the electrode surface of Examples 1, 2 and Comparative Example 1 prepared according to one embodiment of the present specification.
2 is a view showing a relationship between the current density, the battery voltage and the HFR resistance measured in Examples 1 and 2 and Comparative Examples 1 and 2 manufactured according to one embodiment of the present specification.
3 is a view showing electrode resistance values of Examples 1 and 2 and Comparative Examples 1 and 2 manufactured according to one embodiment of the present specification.
4 schematically illustrates a fuel cell used in the art.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In the conventional fuel cell membrane-electrode assembly, since the conductivity between the catalyst and the ionomer is low, there is a problem in that the performance is degraded under low-humidity conditions.

In order to solve this problem, the inventors of the present invention injected graphite into a mixture of ionomer and a solvent in a process of preparing a catalyst ink used in forming a catalyst layer and performing high pressure dispersion, thereby obtaining 50 layers of graphite having a multilayer structure of 100 layers or more. Hereinafter, it was changed to graphene of a monolayer. The catalyst ink based on the graphene-ionomer dispersion thus prepared was applied to the electrode catalyst layer, and the resistance of the electrode was reduced due to the high conductivity of graphene, ultimately improving the performance of the membrane-electrode assembly under low humidity conditions. It turns out that preparation is possible.

In the present specification, when a part is used to 'include' a certain component, it means that the component may further include other components, unless the description is specifically stated to the contrary.

In the present specification, when a member is located 'on' another member, this includes not only when one member is in contact with another member but also when another member exists between the two members.

In one embodiment of the present specification, the ionomer may serve to provide a passage for ions generated by the reaction between the fuel and the catalyst such as hydrogen or methanol to move to the electrolyte membrane.

In one embodiment of the present specification, the weight average molecular weight of the ionomer may be 10,000 g / mol to 1,000,000 g / mol.

In one embodiment of the present specification, the ionomer may be a perfluorosulfonic acid (PFSA) -based polymer. As the perfluorosulfonic acid polymer, for example, E-21669A (3M company) or D2021 (Dupont company) may be used, but is not limited thereto.

In one embodiment of the present specification, the solvent may be at least one selected from water, methanol, ethanol, butanol, n-propanol, isopropanol, n-butyl acetate, dipropylene glycol, ethylene glycol and glycerol, preferably Water and 1-propanol can be used together.

In one embodiment of the present specification, the content of the ionomer may be 0.5 wt% to 10 wt% based on 100 wt% of the mixed solution of step 1), and preferably 1 wt% to 5 wt%.

When the content of the ionomer is in the above range, the ionomer does not excessively cover the catalyst layer to facilitate the reaction between the catalyst and the fuel, and the ion transport passage in the catalyst layer is properly formed, so that the movement of ions may be most smooth.

In one embodiment of the present specification, the mixing of step 1) may be performed by adding an ionomer to a solvent and stirring at a speed of 600 rpm to 1,000 rpm for at least 12 hours.

In one embodiment of the present specification, the pressure at the time of dispersion of step 2) may be 50 bar or more, preferably 100 bar or more and 1,500 bar or less, more preferably 100 bar or more and 500 bar or less.

When the dispersion is less than 50bar or when the dispersion is made by simple stirring, there is a problem that the graphite is not sufficiently converted to graphene. Since graphite has lower conductivity and larger particle size than graphene, it is difficult to obtain an effect of improving conductivity and improving material transfer.

In one embodiment of the present specification, the content of graphite may be 0.1wt% to 1wt%, preferably 0.2wt% to 0.8wt% based on 100wt% of the dispersion of 2).

In one embodiment of the present specification, the catalyst may be a metal supported on the surface of the carbon support.

As the carbon support, it is not limited thereto, Graphite (Graphite), Carbon Black, Acetylene Black, Denka Black, Caten Black, Activated Carbon, Mesoporous Carbon, Carbon Nanotube, Carbon Nanofiber, Carbon Nanohorn, Carbon Nano Ring, Carbon Nano Wire, Fullerene (C60) and Super One or more selected from the group consisting of P can be used.

Examples of the metal include, but are not limited to, platinum, ruthenium, osmium, platinum / ruthenium alloy, platinum / osmium alloy, platinum / palladium alloy, platinum / M alloy (M is Ga, Ti, V, Cr, Mn, Fe , Transition metals of Co, Ni, Cu, Zn, Sn, Mo, W, Rh, Ru, or a combination thereof, or a combination thereof.

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

In one embodiment of the present specification, the weight ratio of the graphite and the catalyst may be 1:99 to 20:80, preferably 1:99 to 15:85. When the weight ratio of graphite and catalyst is in the above range, there is an effect of improving conductivity and low-humidity performance in the electrode.

In one embodiment of the present specification, the weight ratio of the ionomer and carbon included in the catalyst may be 0.6: 1 to 1: 1, preferably 0.7: 1 to 0.9: 1.

The method for preparing a catalyst ink for forming a fuel cell electrode catalyst layer according to an exemplary embodiment of the present specification may further include cooling the dispersion to 5 ° C. or less between the steps 2) and 3). By cooling the dispersion liquid, the effect of preventing the catalyst from igniting can be obtained.

The method of preparing a catalyst ink for forming a fuel cell electrode catalyst layer according to an exemplary embodiment of the present specification may further include dispersing at a high pressure of 50 bar or more after the catalyst is input, which may be performed once to 10 times in a high pressure dispersion machine. Can be.

In one embodiment of the present specification, the catalyst ink for forming a fuel cell electrode catalyst layer is prepared according to the above-described manufacturing method.

An exemplary embodiment of the present specification provides a catalyst ink for forming a fuel cell electrode catalyst layer including an ionomer, a catalyst, and graphene.

In an exemplary embodiment of the present specification, each configuration of the catalyst ink for forming a fuel cell electrode catalyst layer may refer to a description of a method of preparing the catalyst ink for forming a fuel cell electrode catalyst layer.

In one embodiment of the present specification, the graphene may have a single layer structure. When graphene has a single layer structure, it may have high conductivity, and the reactant conductivity and diffusivity may be improved during fuel cell operation because it may be smaller and more evenly distributed on the electrode based on the same graphite dosage.

In one embodiment of the present specification, the content of the ionomer may be 0.5wt% to 10wt%, preferably 1wt% to 5wt% based on 100wt% of the catalyst ink.

When the content of the ionomer is in the above range, the ionomer does not excessively cover the catalyst layer to facilitate the reaction between the catalyst and the fuel, and the ion transport passage in the catalyst layer is properly formed, so that the movement of ions may be most smooth.

In one embodiment of the present specification, the content of the catalyst may be 1wt% to 20wt%, preferably 5wt% to 10wt% based on 100wt% of the catalyst ink.

When the content of the catalyst is 1wt% or more, since the viscosity of the catalyst ink is prevented from being too low, the thickness of the catalyst layer is thin, thereby preventing the problem of repeating the coating 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 phase separation of the catalyst particles and the uneven formation of the catalyst layer can be prevented.

In one embodiment of the present specification, the graphene content may be 0.1 wt% to 1 wt% based on 100 wt% of the catalyst ink, and preferably 0.2 wt% to 0.8 wt%.

When the content of graphene is 0.1wt% or more, there is a low-humidity improvement effect through the conductivity enhancement in the electrode, and when the content is less than 1wt%, it is possible to prevent the decrease in the diffusivity of the reactants.

In one embodiment of the present specification, the remainder other than ionomer, catalyst, and graphene may be a solvent.

An exemplary embodiment of the present specification provides an electrode catalyst layer for a fuel cell including a cured product of the catalyst ink described above on a gas diffusion layer.

In one embodiment of the present specification, the cured product of the catalyst ink refers to a solidified state after the solvent is removed after the applied catalyst ink is dried.

In one embodiment of the present specification, the electrode catalyst layer may be prepared according to a conventional method known in the art, and may be formed, for example, by applying and drying the catalyst ink on a gas diffusion layer. At this time, a plurality of catalyst layers may be formed by sequentially applying and drying catalyst inks having different ionomer contents.

In this case, the method of coating the catalyst ink on the gas diffusion layer may include printing, tape casting, slot die casting, spraying, rolling, and blade coating. coating, spin coating, inkjet coating, or brushing, but are not limited thereto.

The gas diffusion layer is not particularly limited so long as it is a substrate having conductivity and 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 μm. If the value is within the above range, the balance between the mechanical strength and the diffusivity of gas and water can be appropriately controlled. The gas diffusion layer may further include a fine pore layer formed on one surface of the conductive substrate, and the fine pore layer may include a carbon material and a fluorine resin. The microporous layer may inhibit the occurrence of flooding phenomenon by promoting the discharge of excess moisture present in the catalyst layer.

Examples of the carbon-based material include graphite (graphite), carbon black, acetylene black, denka black, canyon black, activated carbon, mesoporous carbon, carbon nanotubes, carbon nanofibers, carbon nanohorns, carbon nanorings, carbon nanowires, One or more selected from the group consisting of fullerenes (C60) and super P may be used, but is not limited thereto.

Examples of the fluorine resin include polytetrafluoroethylene, polyvinylidene fluoride (PVdF), polyvinyl alcohol, cellulose acetate, copolymers of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) and styrene-butadiene rubber. One or more selected from the group consisting of (SBR) may be used, but is not limited thereto.

The fuel cell including the fuel cell electrode catalyst layer may be formed using materials and methods known in the art, except that the fuel cell electrode catalyst layer is described above. 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 in the case where two or more membrane electrode assemblies are included, the stack 60 includes separators interposed therebetween. It prevents the connection and transfers fuel and 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 fuel and a pump 82 for supplying fuel stored in the fuel tank 81 to the stack 60. Can be. The fuel may be a gas or liquid hydrogen or hydrocarbon fuel, examples of the hydrocarbon fuel may be methanol, ethanol, propanol, butanol or natural gas.

The oxidant supply unit 70 serves to supply an oxidant to the stack. Oxygen is representatively used as the oxidant, and may be used by injecting oxygen or air into the pump 82.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present disclosure may be modified in various other forms, and the scope of the present specification is not interpreted to be limited to the embodiments described below. The embodiments of the present specification are provided to more fully describe the present specification to those skilled in the art.

Example: Preparation of Catalytic Ink

Example 1.

0.424 g of ionomer (E-21669A, 3M), a fluorine-based polymer, was placed in a solvent composed of 1 g of water and 13 g of 1-propanol, and stirred overnight at 800 rpm at room temperature. Then, the mixture was cooled to 5 ° C. or less, and then 0.05 g of graphite (C-therm002, Imerys, Inc.) was dispersed 10 times at room temperature in a high pressure disperser (200 bar). After the dispersion was cooled to 5 ° C. or less, 0.95 g of a Pt / C catalyst, TEC10F50E (TKK Co., Ltd.) was added thereto, and then dispersed five times at room temperature in a high pressure dispersion machine (200 bar) to prepare a catalyst ink.

Example 2.

A catalyst ink was prepared in the same manner as in Example 1 except that the graphite input amount was changed to 0.1 g and the catalyst input amount was 0.9 g in Example 1.

Comparative Example 1.

In Example 1, the catalyst ink was prepared in the same manner as in Example 1 except that graphite was not added and the amount of the catalyst was changed to 1 g.

Comparative Example 2.

0.424 g of ionomer (E-21669A, 3M), a fluorine-based polymer, was added to a solvent consisting of 1 g of water and 13 g of 1-propanol and stirred overnight at room temperature at 800 rpm. Then, 0.05 g of graphite (C-therm002, Imerys, Inc.) was added thereto, and the mixture was stirred overnight at 800 rpm at room temperature. After the dispersion was cooled to 5 ° C. or less, 0.95 g of a Pt / C catalyst, TEC10F50E (TKK Co., Ltd.) was added thereto, and the catalyst ink was prepared by dispersing five times at room temperature in a high pressure dispersion machine (200 bar).

Experimental Example: Performance Comparison of Membrane-electrode Assembly

The catalyst inks prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were applied to a gas diffusion layer by an inkjet coating method, and then dried at 100 ° C. for 1 hour to prepare electrodes. The electrode surface photographs taken with an optical microscope of the electrodes coated with the catalyst inks of Examples 1, 2 and Comparative Example 1 are shown in FIG. 1. It can be seen from FIG. 1 that the cracks of the electrode surfaces of Examples 1 and 2 to which graphene is added are reduced compared to those of the electrode of Comparative Example 1.

The prepared electrodes were bonded to both surfaces of the polymer electrolyte membrane using an anode electrode and a cathode electrode to prepare a fuel cell membrane-electrode assembly (MEA), wherein the catalyst loading of the anode and the cathode was 0.3 mg / cm ^2, respectively.

The prepared membrane-electrode assembly was assembled in a single cell of a hydrogen ion exchange membrane fuel cell, and the unit cell temperature was 70 ° C., a relative humidity of 32%, and the stoichiometry ratio of the flow rate was measured in terms of anode (hydrogen): cathode ( Air) = 1.5: 2.0 to evaluate the performance.

Load the load at a low current from 100mA / cm ² at high current and measure the voltage and high frequency resistance (HFR) corresponding to each step, and the results are shown in FIG. 2, and the electrode resistance was measured in Potentiostat mode. Is shown in FIG. 3.

Referring to FIG. 2, Comparative Example 2, in which graphite is added in the preparation of catalyst ink, has improved performance under low humidity conditions of 32% relative humidity compared to Comparative Example 1, in which graphite is not added. It can be seen that the performance is not as good as compared to Examples 1 and 2 converted to. That is, in Examples 1 and 2, the HFR is reduced due to the graphene input, thereby improving performance compared to Comparative Examples 1 and 2.

Referring to FIG. 3, the highest resistance was measured in Comparative Example 1 in which no graphite was used in the manufacturing process, and in Comparative Example 2 in which graphite was added and dispersed by simple stirring, the graphite could not be converted into graphene. It can be seen that much higher resistance values were measured compared to 1 and 2. On the other hand, in the case of Examples 1 and 2 using the catalyst ink prepared based on the dispersion of graphene and ionomer, it can be seen that the electrode resistance is measured as low as 45mOhm · cm ² / mg or less.

60: stack
70: oxidant supply unit
80: fuel supply unit
81: fuel tank
82: pump

Claims (13)

1) mixing a ionomer and a solvent to prepare a mixed solution;
2) preparing a dispersion by adding graphite to the mixed solution and dispersing the mixture at a high pressure of 50 bar or more; And
3) adding a catalyst to the dispersion
Method of producing a catalyst ink for forming a fuel cell electrode catalyst layer comprising a. The method of claim 1, wherein the ionomer is a perfluorosulfonic acid (PFSA) polymer. The catalyst ink of claim 1, wherein the solvent is at least one selected from water, methanol, ethanol, butanol, n-propanol, isopropanol, n-butyl acetate, dipropylene glycol, ethylene glycol, and glycerol. Method of preparation. The method of claim 1, further comprising cooling the dispersion to 5 ° C. or lower between steps 2) and 3). The method of claim 1, wherein the weight ratio of the graphite and the catalyst is 1:99 to 20:80. The method according to claim 1, wherein the catalyst is a metal supported on the surface of the carbon support, the weight ratio of the ionomer and the carbon is 0.6: 1 to 1: 1 method for producing a catalyst ink for a fuel cell electrode catalyst layer forming. Catalyst ink for forming a fuel cell electrode catalyst layer comprising an ionomer, a catalyst, and graphene. The catalyst ink of claim 7, wherein the graphene has a monolayer structure. The catalyst ink of claim 7, wherein the graphene and the catalyst have a weight ratio of 1:99 to 20:80. The catalyst ink of claim 7, wherein the graphene content is 0.1 wt% to 1 wt% based on 100 wt% of the catalyst ink. An electrode catalyst layer for a fuel cell comprising a cured product of the catalyst ink according to any one of claims 7 to 10 on a gas diffusion layer. A membrane-electrode assembly for a fuel cell comprising the electrode catalyst layer according to claim 11. A fuel cell comprising the membrane-electrode assembly according to claim 12.

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