KR102455396B1 - Catalyst ink for forming electrode catalyst layer of fuel cell and manufacturing method thereof - Google Patents

Abstract

The present specification includes the steps of preparing a mixed solution by mixing an ionomer and a solvent; preparing a dispersion by adding graphite to the mixed solution and then dispersing it at a high pressure of 50 bar or more; and injecting a catalyst into the dispersion liquid.

Description

Catalyst ink for forming a fuel cell electrode catalyst layer and manufacturing method thereof

The present invention relates to a catalyst ink for forming an electrode catalyst layer in a fuel cell and a method for preparing the same.

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

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

Representative examples of such fuel cells include a polymer electrolyte fuel cell (PEMFC) or a direct methanol fuel cell (DMFC) using methanol as a fuel, and the like. Development and research are being actively carried out.

It is the Membrane Electrode Assembly (MEA) that determines the 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 thereby, an anode electrode (aka, “oxidation electrode” or “fuel electrode”) and a cathode electrode. (aka, "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 an external circuit through a conducting wire (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 oxidizing agent, to generate water. At this time, the movement of electrons through the anode, external circuit and cathode is power.

The anode is provided with a catalyst layer for accelerating the oxidation of fuel, and the cathode is provided with a catalyst layer for accelerating the reduction of the oxidizing agent. Research is being actively conducted to increase the reaction rate of such a catalyst layer and to improve the conductivity properties in the electrode through this.

Korean Patent Publication No. 10-2011-0114992

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

An exemplary embodiment of the present specification is

1) preparing a mixed solution by mixing an ionomer and a solvent;

2) preparing a dispersion by adding graphite to the mixed solution and then dispersing it at a high pressure of 50 bar or more; and

3) adding a catalyst to the dispersion

It provides a method for preparing 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 membrane-electrode assembly for a fuel cell including the electrode catalyst layer.

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

When an electrode is manufactured using the catalyst ink prepared according to an exemplary embodiment of the present specification, the ohmic resistance is reduced due to a decrease in the electrode resistance, so that the conductivity in the electrode is improved. There is an advantage in that it is possible to manufacture an electrode assembly.

1 is a view showing a photograph of the electrode surface of Examples 1 and 2 and Comparative Example 1 prepared according to an exemplary embodiment of the present specification.
2 is a diagram showing the 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 an exemplary embodiment of the present specification.
3 is a diagram illustrating electrode resistance values of Examples 1 and 2 and Comparative Examples 1 and 2 manufactured according to an exemplary embodiment of the present specification.
4 schematically shows a fuel cell used in the art.

Hereinafter, the present invention will be described in more detail.

In the case of a conventional membrane-electrode assembly for a fuel cell, there is a problem in that the performance is deteriorated in a low humidity condition because the conductivity between the catalyst and the ionomer is low.

In order to solve this problem, the inventors of the present invention added graphite to a mixed solution of ionomer and solvent in the process of preparing a catalyst ink used for forming a catalyst layer and high-pressure dispersion, thereby forming 50 layers of graphite having a multilayer structure of 100 or more layers. Hereinafter, it was preferably changed to graphene of a monolayer. A catalyst ink based on the thus-prepared graphene-ionomer dispersion was applied to the electrode catalyst layer, and the resistance of the electrode was reduced due to the high conductivity of graphene, which ultimately resulted in improved performance under low humidity conditions. It has been found that manufacturing is possible.

In the present specification, when a part 'includes' a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

In the present specification, when a member is said to be positioned 'on' another member, this includes not only a case in which a member is in contact with another member but also a case in which another member exists between the two members.

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

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

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

When the content of the ionomer is within the above range, the ionomer does not excessively cover the catalyst layer, thereby facilitating 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 the most smooth.

In an exemplary embodiment of the present specification, the mixing of step 1) may be performed by putting the ionomer in a solvent and stirring at a speed of 600 rpm to 1,000 rpm for 12 hours or more.

In an exemplary embodiment of the present specification, the pressure during dispersion in step 2) may be 50 bar or more, preferably 100 bar or more and 1,500 bar or less, and more preferably 100 bar or more and 500 bar or less.

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

In an exemplary embodiment of the present specification, the content of the graphite may be 0.1 wt% to 1 wt%, preferably 0.2 wt% to 0.8 wt%, based on 100 wt% 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.

The carbon support includes, but is not limited to, Graphite (graphite), carbon black, acetylene black, denka black, cathen black, activated carbon, mesoporous carbon, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon nanoring, carbon nanowire, fullerene (C60) and super At least one selected from the group consisting of P may 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 , a transition metal of Co, Ni, Cu, Zn, Sn, Mo, W, Rh, Ru, or a combination thereof), or a combination thereof.

In an exemplary 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 an exemplary 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 the graphite and the catalyst is within the above range, there is an effect of improving the conductivity in the electrode and improving the low-humidity performance.

In an exemplary 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 steps 2) and 3). By cooling the dispersion, the effect of preventing the catalyst from igniting can be obtained.

The method for preparing a catalyst ink for forming a catalyst layer for a fuel cell electrode according to an exemplary embodiment of the present specification may further include the step of dispersing at a high pressure of 50 bar or more after the catalyst is added, which is to be performed 1 to 10 times in a high-pressure disperser. can

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

In an exemplary 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 based on the same graphite input amount, it may be smaller and more evenly distributed on the electrode, so that the reactant conductivity and diffusivity may be improved during fuel cell operation.

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

When the content of the ionomer is within the above range, the ionomer does not excessively cover the catalyst layer, thereby facilitating 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 the most smooth.

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

When the content of the catalyst is 1 wt% or more, the viscosity of the catalyst ink is prevented from being too low, and thus the problem of repeating the coating several times due to the thin thickness of the catalyst layer can be prevented. When the content of the catalyst is 20 wt% or less, it is possible to prevent the viscosity of the catalyst ink from becoming too high, thereby preventing the deterioration of the separation property of the catalyst particles and the non-uniform formation of the catalyst layer.

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

When the content of graphene is 0.1wt% or more, there is an effect of improving the low humidity by improving the conductivity in the electrode, and when the content of graphene is 1wt% or less, it is possible to prevent a decrease in the diffusivity of the reactant.

In the exemplary embodiment of the present specification, the remainder of the catalyst ink other than the ionomer, the 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 the exemplary embodiment of the present specification, the cured product of the catalyst ink refers to a solid state after the applied catalyst ink is dried and the solvent is removed.

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

At this time, as a method of applying the catalyst ink on the gas diffusion layer, printing, tape casting, slot die casting, spraying, rolling, and blade coating (blade). coating), spin coating, inkjet coating, or brushing, but is not limited thereto.

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

Examples of the carbon-based material include graphite (graphite), carbon black, acetylene black, denka black, cashon black, activated carbon, mesoporous carbon, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon nanoring, carbon nanowire, At least one selected from the group consisting of fullerene (C60) and super P may be used, but is not limited thereto.

Examples of the fluorine-based resin include polytetrafluoroethylene, polyvinylidene fluoride (PVdF), polyvinyl alcohol, cellulose acetate, polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), and styrene-butadiene rubber. (SBR) may be used at least one selected from the group consisting of, but 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 for including the electrode catalyst layer for a fuel cell. Referring to FIG. 4 , the fuel cell is formed to include 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). When two or more membrane-electrode assemblies are included, the stack 60 includes a separator interposed therebetween. It prevents the connection and transfers the fuel and oxidizer 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 the fuel stored in the fuel tank 81 to the stack 60 . can be As the fuel, gas or liquid hydrogen or hydrocarbon fuel may be used, and examples of the hydrocarbon fuel include methanol, ethanol, propanol, butanol, or natural gas.

The oxidizing agent supply unit 70 serves to supply the oxidizing agent to the stack. Oxygen is typically used as the oxidizing agent, and oxygen or air may be injected into the pump 82 to be used.

Hereinafter, examples will be given to describe the present specification in detail. However, the embodiments according to the present specification may be modified in various other forms, and the scope of the present specification is not to be construed as being limited to the embodiments described below. The embodiments of the present specification are provided to more completely explain the present specification to those of ordinary skill in the art.

<Example: Preparation of catalyst ink>

Example 1.

0.424 g of a fluorine-based polymer ionomer (E-21669A, 3M) was placed in a solvent composed of 1 g of water and 13 g of 1-propanol, and stirred at 800 rpm at room temperature overnight. Then, after cooling to 5° C. or less, 0.05 g of graphite (C-therm002, Imerys) was added and dispersed 10 times at room temperature in a high-pressure disperser (200 bar). After cooling the dispersion to 5° C. or less, 0.95 g of TEC10F50E (TKK), a Pt/C catalyst, was added, and then dispersed 5 times in a high-pressure disperser (200 bar) at room temperature 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 changed to 0.9 g in Example 1.

Comparative Example 1.

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

Comparative Example 2.

0.424 g of a fluorine-based polymer ionomer (E-21669A, 3M) 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, 0.05 g of graphite (C-therm002, Imerys) was added and stirred overnight at 800 rpm at room temperature. After cooling the dispersion to 5° C. or less, 0.95 g of TEC10F50E (TKK), a Pt/C catalyst, was added, and then dispersed 5 times at room temperature in a high-pressure disperser (200 bar) to prepare a catalyst ink.

<Experimental Example: Comparison of performance of membrane-electrode assembly>

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

A membrane-electrode assembly (MEA) for a fuel cell was prepared by bonding the prepared electrode to both surfaces of the polymer electrolyte membrane with an anode electrode and a cathode electrode, and the catalyst loading amount 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, relative humidity was 32%, and the stoichiometry ratio of the flow rate was anode (hydrogen):cathode ( The performance was evaluated under the condition of air) = 1.5:2.0.

A load was applied at intervals of 100mA/cm ² from a low current to a high current, and the voltage and high frequency resistance (HFR) corresponding to each step were measured, and the results are shown in FIG. 2, and the electrode resistance was measured in the potentiostat mode. is shown in FIG. 3 .

Referring to FIG. 2 , Comparative Example 2 in which graphite was added during the production of catalyst ink improved performance under a low humidity condition of 32% relative humidity compared to Comparative Example 1 in which graphite was not added, but graphite was mixed with graphene through high pressure dispersion It can be seen that the performance is not good compared to Examples 1 and 2 converted to . That is, in Examples 1 and 2, the HFR was reduced due to the graphene input, and thus, the performance was improved compared to Comparative Examples 1 and 2.

Referring to FIG. 3, the highest resistance was measured in Comparative Example 1 in which graphite was not used in the manufacturing process, and in Comparative Example 2, in which graphite was added and dispersed by simple stirring, the graphite was not converted to graphene in Example It can be seen that a much higher resistance value was 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 the ionomer, it can be seen that the electrode resistance was measured as low as 45 mOhm·cm ² /mg or less.

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

Claims (13)

1) preparing a mixed solution by mixing an ionomer and a solvent;
2) preparing a dispersion by adding graphite to the mixed solution and then dispersing it at a high pressure of 50 bar or more; and
3) adding a catalyst to the dispersion
A method for producing a catalyst ink for forming a catalyst layer for a fuel cell electrode, comprising: the dispersion liquid comprising graphene. The method according to claim 1, wherein the ionomer is a perfluorosulfonic acid (PFSA)-based polymer. The catalyst ink for forming a fuel cell electrode catalyst layer according to 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. manufacturing method. The method according to claim 1 , further comprising cooling the dispersion to 5° C. or less between steps 2) and 3). The method according to claim 1, wherein a weight ratio of the graphite to 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 a carbon support, and the weight ratio of the ionomer to the carbon is 0.6:1 to 1:1. A catalyst ink for forming a catalyst layer for a fuel cell electrode comprising an ionomer, a catalyst, and graphene, and prepared by the method of claim 1 . The catalyst ink according to claim 7, wherein the graphene has a monolayer structure. The catalyst ink for forming a fuel cell electrode catalyst layer according to claim 7, wherein the weight ratio of the graphene and the catalyst is 1:99 to 20:80. The catalyst ink for forming a fuel cell electrode catalyst layer according to 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 the 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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