KR102155929B1 - Catalyst composition of fuel cell, catalyst layer manufactured by the same and fuel cell comprising the same - Google Patents

Abstract

The present specification relates to a fuel cell catalyst composition, a catalyst layer prepared therefrom, and a fuel cell including the same.

Description

A fuel cell catalyst composition, a catalyst layer prepared therefrom, and a fuel cell including the same TECHNICAL FIELD [CATALYST LAYER MANUFACTURED BY THE SAME AND FUEL CELL COMPRISING THE SAME}

The present specification relates to a fuel cell catalyst composition, a catalyst layer prepared therefrom, and a fuel cell including the same.

Recently, as the depletion of existing energy resources such as oil and coal is predicted, interest in energy that can replace them is increasing. As one of these alternative energies, a fuel cell is attracting special attention due to its advantages such as high efficiency, no emission of pollutants such as NOx and SOx, and abundant fuel used.

A fuel cell is a power generation system that converts chemical reaction energy between a fuel and an oxidizing agent into electrical energy. Hydrocarbons such as hydrogen, methanol and butane are typically used as fuels, and oxygen is typically used as the oxidizing agent.

Fuel cells include polymer electrolyte fuel cells (PEMFC), direct methanol fuel cells (DMFC), phosphoric acid fuel cells (PAFC), alkaline fuel cells (AFC), molten carbonate fuel cells (MCFC), and solid oxide fuels. Battery (SOFC) and the like.

Korean Patent Publication No. 2003-0045324 (published on June 11, 2003)

The present specification is to provide a fuel cell catalyst composition, a catalyst layer prepared therefrom, and a fuel cell including the same.

The present specification is a catalyst having metal nanoparticles supported on a carbon carrier; Carbon nanofibers to which an ion conductive polymer is physically attached to the surface; And it provides a fuel cell catalyst composition comprising an ionomer.

In addition, the present specification is a catalyst layer for a fuel cell made of the catalyst composition, wherein the hydrogen ion transfer resistance of the catalyst layer is 0.2 ohm·cm ² It provides a catalyst layer for a fuel cell as follows.

In addition, the present specification is a membrane electrode assembly comprising a cathode catalyst layer, an anode catalyst layer, and an electrolyte membrane provided between the cathode catalyst layer and the anode catalyst layer, wherein at least one of the cathode catalyst layer and the anode catalyst layer is a catalyst layer made of the catalyst composition. It provides a membrane electrode assembly.

In addition, the present specification provides a fuel cell including the membrane electrode assembly.

The fuel cell according to the exemplary embodiment of the present specification may increase the connectivity of the ionomer over the entire catalyst layer, thereby lowering the hydrogen ion transfer resistance and improving the hydrogen ion conductivity without impeding gas transfer of the catalyst layer.

1 is a schematic diagram showing a principle of generating electricity in a fuel cell.
2 is a diagram schematically showing the structure of a membrane electrode assembly.
3 is a diagram schematically showing an embodiment of a fuel cell.
4 is a schematic diagram of hydrogen ion conduction in a conventional catalyst layer.
5 is a schematic diagram of conduction of hydrogen ions in a catalyst layer according to an exemplary embodiment of the present specification.
6 is an impedance measurement result graph of Experimental Example 1.
7 is an image obtained by measuring the scanning electron microscope of Example 2.

Hereinafter, the present specification will be described in detail.

The present specification is a catalyst having metal nanoparticles supported on a carbon carrier; Carbon nanofibers to which an ion conductive polymer is physically attached to the surface; And it provides a fuel cell catalyst composition comprising an ionomer.

The catalyst includes metal nanoparticles supported on a carbon carrier.

The type of the metal nanoparticles is not limited as long as it can serve as a catalyst in a fuel cell, but may include one of platinum, a transition metal, and a platinum-transition metal alloy.

Here, the transition metal is an element of Group 3 to 11 in the periodic table, and may be, for example, any one of cobalt, nickel, ruthenium, osmium, palladium, molybdenum, and rhodium.

Specifically, the metal nanoparticles are made of platinum, ruthenium, osmium, platinum-cobalt alloy, platinum-nickel alloy, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-molybdenum alloy, and platinum-rhodium alloy. It may be used that is selected from the group, but is not limited thereto.

The carbon carriers include graphite (graphite), carbon black, acetylene black, denka black, kaetchen black, activated carbon, mesoporous carbon, carbon nanofiber, carbon nanohorn, carbon nanoring, fullerene (C60), and super P black ( Any one or a mixture of two or more selected from the group consisting of Super P black) may be a preferred example.

In the fuel cell catalyst composition, an appropriate catalyst and ionomer content may be selected according to a method of coating the catalyst composition on an electrode substrate.

The fuel cell catalyst composition includes carbon nanofibers to which an ion conductive polymer is physically attached to a surface. In this case, since the ion conductive polymer is attached to the surface of the carbon nanofiber, the carbon nanofibers provided with the ion conductive polymer decreases electron conductivity and increases the ion conductivity by the ion conductive polymer. In addition, since the ion conductive polymer is not located randomly but is continuously provided on the surface of the linear carbon nanofibers in the longitudinal direction, the connection between the ionomer and the ionomer can be increased, thereby improving the ability of ion transfer in the electrode.

The fuel cell catalyst composition includes an ion conducting network, and the ion conducting network includes carbon nanofibers with an ion conducting polymer.

Here, the carbon nanofiber means a fibrous carbon body having a high aspect ratio. Specifically, the carbon nanofibers are not particularly limited as long as they have a fibrous shape even if carbon does not have a regular molecular structure as well as carbon nanotubes having a regular or regular molecular structure. Specifically, the carbon nanofibers include at least one of carbon nanowires, carbon nanotubes, and carbon fibers manufactured by carbonizing polymer fibers.

The average length of the carbon nanofibers may be 300 nm or more and 100 μm or less. Carbon nanofibers within this range are easy to connect between catalyst particles of several tens of nm, and it is possible to rapidly transfer ions in the thickness direction of the catalyst layer.

Based on the total weight of the catalyst, the content of carbon nanofibers to which the ion conductive polymer is physically attached to the surface may be 0.1% by weight or more and 30% by weight or less. If it is less than 0.1% by weight, it does not affect the hydrogen ion conductivity of the catalyst layer, and if it is more than 30% by weight, the reactivity of the catalyst layer may be inhibited due to too much carbon content without catalytic activity.

The ionomer serves to provide a passage for ions generated by a reaction between a catalyst such as hydrogen or methanol and a fuel to move to the electrolyte membrane.

The ionomer may be a polymer having a cation exchange group selected from the group consisting of a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a phosphonic acid group and derivatives thereof in the side chain.

The ionomer may be a hydrocarbon-based polymer, a partially fluorine-based polymer, or a fluorine-based polymer.

The ionomer is a fluorine-based polymer, a benzimidazole-based polymer, a polyimide-based polymer, a polyetherimide-based polymer, a polyphenylene sulfide-based polymer, a polysulfone-based polymer, a polyethersulfone-based polymer, a polyetherketone-based polymer, and a polyether. -It may contain at least one hydrogen ion conductive polymer selected from an ether ketone polymer or a polyphenylquinoxaline polymer.

The ionomer may be different from or identical to the ion conductive polymer attached to the carbon nanofiber.

Based on the sum (C) of the weight of the carbon carrier and the carbon nanofiber, the percentage of the ratio (I/C) of the sum (I) of the weight of the ion conductive polymer and the ionomer may be 30% or more and 150% or less, More preferably, it may be 50% or more and 120% or less. This can be appropriately selected depending on the type of catalyst particles used.

The fuel cell catalyst composition may further include a solvent.

The type of the solvent is not particularly limited, and one or two or more solvents may be used by selecting an appropriate one in the art.

Based on the total weight of the fuel cell catalyst composition, the content of the solvent may be 70% or more and 99.9% or less. An appropriate amount may be selected according to a method of forming a catalyst layer using the catalyst composition.

The present specification provides a catalyst layer for a fuel cell made of the catalyst composition.

When forming the catalyst layer with the catalyst composition, carbon nanofibers to which the ion conductive polymer is physically attached to the surface may form a network of ionomers in the catalyst layer.

As shown in FIG. 4, in general, hydrogen ion transfer in the catalyst layer is performed through randomly distributed ionomers. The thickness of the ionomer attached to the catalyst surface is very thin, ranging from several to tens of nm, and its connectivity is also random. Therefore, the rate of hydrogen ion transfer through the ionomer in the catalyst layer is slow.

As shown in FIG. 5, the catalyst layer of the present specification has an ionomer network formed by carbon nanofibers to which an ion conductive polymer is physically attached to the surface, thereby increasing the connectivity of the ionomer channel inside the catalyst layer, thereby forming a random ionomer channel. Inert ionomers and catalysts that have not yet been linked can be utilized. In addition, through a linear ionomer network having low tortuosity, a larger amount of ionomer can be transferred into the catalyst layer faster.

In conclusion, the ionomer network can increase the connectivity of the ionomer throughout the catalyst layer, thereby lowering the hydrogen ion transfer resistance and improving the hydrogen ion conductivity without inhibiting gas transfer of the catalyst layer.

The hydrogen ion transfer resistance of the catalyst layer may be 0.5 ohm·cm ² or less, and specifically 0.3 ohm·cm ² or less. In this case, there is an advantage that the catalyst utilization rate can be improved by smooth hydrogen ion transfer. At this time, the lower the hydrogen ion transfer resistance of the catalyst layer is, the better it is, so the lower limit thereof is not particularly limited.

In a fuel cell including the catalyst layer, the hydrogen ion conductivity (σ) of the catalyst layer can be calculated by Equation 1 below.

[Equation 1]

R=t/Aσ

In Equation 1, R is the hydrogen ion transfer resistance of the catalyst layer, t is the average thickness of the catalyst layer, and A is the area of the catalyst layer.

When the average thickness of the catalyst layer is 10 μm and the area of the catalyst layer is 25 cm ² , the hydrogen ion conductivity of the catalyst layer may be 0.02 mS cm ^{-1 or} more, and specifically 0.03 mS cm ^{-1 or} more. In this case, there is an advantage that the catalyst utilization rate can be improved by smooth hydrogen ion transfer. At this time, the higher the hydrogen ion conductivity of the catalyst layer is, the better it is, and the upper limit thereof is not particularly limited.

The average thickness of the catalyst layer may be 3 µm or more and 15 µm or less, and specifically, 5 µm or more and 12 µm or less based on 0.3 mg _Pt /cm ² (the weight of Pt per reference area (1 cm ² ) is 0.3 mg). I can. In this case, there is an advantage of securing appropriate porosity and hydrogen ion conductivity.

In this case, the catalyst layer using the catalyst composition may be formed on the substrate by using various coating methods such as bar coating, spraying, screen printing, and slot die, but is not limited thereto.

The present specification is a membrane electrode assembly comprising a cathode catalyst layer, an anode catalyst layer, and an electrolyte membrane provided between the cathode catalyst layer and the anode catalyst layer, wherein at least one of the cathode catalyst layer and the anode catalyst layer is a catalyst layer made of the catalyst composition. It provides a membrane electrode assembly.

The electrolyte membrane may be a polymer electrolyte membrane.

The polymer electrolyte membrane is provided between the cathode catalyst layer and the anode catalyst layer, and the polymer included in the polymer electrolyte membrane may be an ion conductive polymer.

The ion conductive polymer may be a hydrocarbon-based polymer, a partially fluorine-based polymer, or a fluorine-based polymer. Specifically, the polymer electrolyte membrane may be a hydrocarbon-based polymer electrolyte membrane or a fluorine-based polymer electrolyte membrane.

The hydrocarbon-based polymer may be a hydrocarbon-based sulfonated polymer without a fluorine group, on the contrary, the fluorine-based polymer may be a sulfonated polymer saturated with a fluorine group, and the partially fluorine-based polymer is not saturated with a fluorine group. It may be a non-sulfonated polymer.

The ion conductive polymer is a perfluorosulfonic acid polymer, a hydrocarbon polymer, an aromatic sulfone polymer, an aromatic ketone polymer, a polybenzimidazole polymer, a polystyrene polymer, a polyester polymer, a polyimide polymer, a polyvinylidene fluorine. Ride-based polymer, polyethersulfone-based polymer, polyphenylene sulfide-based polymer, polyphenylene oxide-based polymer, polyphosphazene-based polymer, polyethylene naphthalate-based polymer, polyester-based polymer, doped polybenzimidazole-based polymer, It may be one or two or more polymers selected from the group consisting of polyetherketone-based polymers, polyetheretherketone-based polymers, polyphenylquinoxaline-based polymers, polysulfone-based polymers, polypyrrole-based polymers, and polyaniline-based polymers. The polymer may be sulfonated and used, and may be a single copolymer, an alternating copolymer, a random copolymer, a block copolymer, a multiblock copolymer, or a graft copolymer, but is not limited thereto.

When the polymer electrolyte membrane includes a hydrocarbon-based polymer, it may be a hydrocarbon-based polymer, which is a block-type copolymer including a hydrophilic block and a hydrophobic block.

The average thickness of the polymer electrolyte membrane may be 1 μm or more and 100 μm or less.

The membrane electrode assembly further includes a cathode gas diffusion layer provided on a surface of the cathode catalyst layer opposite to a surface provided with an electrolyte membrane, and an anode gas diffusion layer provided on a surface of the anode catalyst layer opposite to a surface provided with the electrolyte membrane can do.

The anode gas diffusion layer and the cathode gas diffusion layer are provided on one surface of the catalyst layer, respectively, and serve as a current conductor and a passage for a reaction gas and water, and have a porous structure. Accordingly, the gas diffusion layer may include a conductive substrate.

As the conductive substrate, a conventional material known in the art may be used, but for example, carbon paper, carbon cloth, or carbon felt may be preferably used, and limited thereto. It doesn't work.

The average thickness of the gas diffusion layer may be 100 μm or more and 500 μm or less. In this case, there is an advantage in that the reactant gas transfer resistance through the gas diffusion layer is minimized and the optimum state is achieved in terms of proper moisture content in the gas diffusion layer.

The present specification provides a fuel cell including the membrane electrode assembly.

1 schematically shows the principle of generating electricity in a fuel cell. In a fuel cell, the most basic unit for generating electricity is a membrane electrode assembly (MEA), which is an electrolyte membrane (M) and the electrolyte membrane (M). It consists of an anode (A) and a cathode (C) formed on both sides of the. Referring to Fig. Showing the electricity generating principle of a fuel cell 1, an anode (A) in the hydrogen or methanol, butane and the oxidation of the fuel (F) of the hydrocarbon and so on up the hydrogen ions (H ⁺⁾ and electron (e ^-), such as Is generated, and hydrogen ions move to the cathode (C) through the electrolyte membrane (M). In the cathode (C), hydrogen ions transferred through the electrolyte membrane (M), an oxidizing agent (O) such as oxygen, and electrons react to generate water (W). This reaction causes the movement of electrons to the external circuit.

As shown in FIG. 2, the membrane electrode assembly may include an electrolyte membrane 10 and a cathode 50 and an anode 51 positioned to face each other with the electrolyte membrane 10 interposed therebetween. Specifically, the cathode includes a cathode catalyst layer 20 and a cathode gas diffusion layer 30 sequentially provided from the electrolyte membrane 10, and the anode catalyst layer 21 and the anode sequentially provided from the electrolyte membrane 10 It may include a gas diffusion layer (31).

3 schematically shows a structure of a fuel cell, and the fuel cell includes a stack 60, an oxidant supply unit 70, and a fuel supply unit 80.

The stack 60 includes one or two or more membrane electrode assemblies described above, and when two or more membrane electrode assemblies are included, a separator interposed therebetween. The separator serves to prevent the membrane electrode assemblies from being electrically connected and to deliver fuel and oxidizing agent supplied from the outside to the membrane electrode assemblies.

The oxidant supply unit 70 serves to supply the oxidant to the stack 60. Oxygen is typically used as the oxidizing agent, and oxygen or air may be injected into the pump 70 to be used.

The fuel supply unit 80 serves to supply fuel to the stack 60, 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 configured. As the fuel, gaseous or liquid hydrogen or hydrocarbon fuel may be used. Examples of hydrocarbon fuels include methanol, ethanol, propanol, butanol or natural gas.

The present specification provides a method of manufacturing a fuel cell catalyst composition comprising adding a catalyst having metal nanoparticles supported on a carbon carrier, carbon nanofibers with an ion conductive polymer, and an ionomer to a solvent.

The method for preparing the fuel cell catalyst composition comprises: preparing carbon nanofibers; And coating the ion conductive polymer on the surface of the carbon nanofibers.

The present specification is a method for manufacturing a membrane electrode assembly including a cathode catalyst layer, an anode catalyst layer, and an electrolyte membrane provided between the cathode catalyst layer and the anode catalyst layer, wherein a catalyst having metal nanoparticles supported on a carbon carrier, and an ion conductive polymer are provided. Preparing a fuel cell catalyst composition by adding carbon nanofibers and ionomers to a solvent; It provides a method of manufacturing a membrane electrode assembly comprising forming at least one of the cathode catalyst layer and the anode catalyst layer by using the fuel cell catalyst composition.

The method of manufacturing the membrane electrode assembly may include forming a polymer electrolyte membrane; Forming a cathode catalyst layer on one surface of the polymer electrolyte membrane; And forming an anode catalyst layer on the other surface of the polymer electrolyte membrane, and at least one of the cathode catalyst layer and the anode catalyst layer may be formed using the fuel cell catalyst composition.

The step of forming the polymer electrolyte membrane may include forming a pure membrane with a polymer electrolyte membrane composition, impregnating the polymer electrolyte membrane composition with a porous substrate to form a reinforcing membrane, or forming a composite membrane including at least one pure membrane and at least one reinforcing membrane. .

The method of introducing the catalyst layer into the polymer electrolyte membrane may be formed by coating the catalyst composition directly on the polymer electrolyte membrane, forming a catalyst layer on the releasable substrate and then thermally compressing the polymer electrolyte membrane and removing the releasable substrate, or coating the gas diffusion layer. Thus, the catalyst layer can be formed, and the catalyst layer can be introduced by assembling the gas diffusion layer provided with the catalyst layer and the polymer electrolyte membrane. At this time, the coating method of the catalyst composition is not particularly limited, but spray coating, tape casting, screen printing, blade coating, inkjet coating, die coating or spin coating method, or the like may be used.

Hereinafter, the present specification will be described in more detail through examples. However, the following examples are for illustrative purposes only and are not intended to limit the present specification.

[Example]

[Production Example 1]

VGCNF (Vapor grown carbon nanofiber) carbon nanofibers having a thickness (diameter) of about 300 nm and a length of about 30 μm and a fluorine-based ionomer (EW 825) manufactured by 3M as an ion conductive polymer were added to 1-propanol at a mass ratio of 1:1. This was dispersed for a sufficient time using ultrasonic waves and dried in an oven at 70° C. for 12 hours or longer to obtain a carbon nanofiber/ionomer composite with an ion conductive polymer.

In the subsequent process, in order to prevent the ion conductive polymer attached to the surface of the carbon nanofiber from being desorbed again, heat treatment was performed in an oven at 130° C. for 10 minutes.

[Production Example 2]

A carbon/ionomer composite was prepared using a Ketjen black carrier. Ketjen black (300D) carbon particles and a fluorine-based ionomer (EW 825) manufactured by 3M as an ion conductive polymer were added to 1-propanol at a mass ratio of 1:1. After dispersing this for a sufficient time using ultrasonic waves, it was dried in an oven at 70° C. for 12 hours or longer to obtain a Ketjen black/ionomer composite with an ion conductive polymer.

Then, heat treatment was performed in an oven at 130° C. for 10 minutes.

[Production Example 3]

Sulfonated polystyrene was synthesized through chemical bonding on the surface of the carbon nanofibers used in Preparation Example 1.

VGCNF (Vapor grown carbon nanofiber) 1 g of carbon nanofibers, 50 g of styrene monomer, and 0.15 g of isobisisobutyronitrile (AIBN) as an initiator were mixed and polymerized at 65° C. for 12 hours. This was dried, mixed with a 10M sulfuric acid solution, and reacted for 24 hours or more to attach a sulfonic acid group to prepare an ion conductive polymer composite chemically bonded to the carbon nanofiber surface.

[Example 1]

1 g of a catalyst (PtCo/C) in which platinum/cobalt nanoparticles are supported on carbon black as a carbon carrier, 0.048 g of a carbon nanofiber/ionomer composite provided with an ion conductive polymer prepared in Preparation Example 1, and a fluorine-based 3M company as an ionomer 1.9 g of the ionomer solution was added to 8 g of 1-propanol as a solvent to prepare a catalyst composition. In this case, the mass of the carbon nanofiber composite with the ion conductive polymer is 10 wt% of the mass of the carbon carrier in the catalyst.

At this time, the percentage of the ratio (I/C) of the sum (I) of the ion conductive polymer and the ionomer was 81% based on the sum (C) of the weight of the carbon carrier and the carbon nanofiber.

[Example 2]

A catalyst composition was prepared in the same manner as in Example 1, except that 0.096 g of the carbon nanofiber/ionomer composite provided with the ion conductive polymer prepared in Preparation Example 1 was added.

At this time, the percentage of the ratio (I/C) of the sum (I) of the ion conductive polymer and the ionomer was 82% based on the sum (C) of the weight of the carbon carrier and the carbon nanofiber.

[Comparative Example 1]

It was prepared in the same manner as in Example 1, except that the catalyst composition was prepared without carbon nanofibers with an ion conductive polymer.

At this time, the percentage of the ratio (I/C) of the sum (I) of the ionomers was 80% based on the sum (C) of the carbon carriers.

[Comparative Example 2]

Instead of the composite prepared in Preparation Example 1, a catalyst composition was prepared in the same manner as in Example 1, except that 0.048 g of a carbon/ionomer composite with an ion conductive polymer prepared in Preparation Example 2 was added.

In this case, the mass of the carbon nanofiber composite with the ion conductive polymer is 10 wt% of the mass of the carbon carrier in the catalyst, as in Example 1.

[Comparative Example 3]

Instead of the composite prepared in Preparation Example 1, a catalyst composition was prepared in the same manner as in Example 1, except that 0.048 g of a carbon/ionomer composite provided with an ion conductive polymer chemically bonded with the carrier prepared in Preparation Example 3 was added. Manufactured.

At this time, the mass of the carbon/ionomer composite with the ion conductive polymer chemically bonded to the carrier is 10 wt% of the mass of the carbon carrier in the catalyst, as in Example 1.

[Experimental Example 1]

After sufficiently stirring the catalyst composition prepared in Example 1-2 and Comparative Example 1-3, the catalyst layer was prepared by coating and drying the substrate to a uniform thickness.

In order to prepare the MEA using this, a Nafion 211 membrane was used as an ion conductive polymer membrane, and a Pt/C catalyst layer in which a carbon/ionomer composite was not mixed was used as an anode. MEA was prepared by thermocompression bonding the catalyst layers prepared from the catalyst compositions of Examples 1-2 and 1-3 as a cathode, with Nafion 211 membrane and anode, respectively.

Through electrochemical analysis using the impedance of Example 1-2 and Comparative Example 1-3, the hydrogen ion conductivity in the catalyst layer was directly measured.

The impedance was measured under the following conditions when the current of the MEA was 0 A/cm ² .

-Anode/cathode = H ₂ /N ₂

-Cell temperature 70 ℃

-Relative humidity 50%

As a result, also it was obtained a graph of six and a length of 45 ^o upward region that appears at a high frequency region of the graph is proportional to the electrode hydrogen ion transfer resistance (Rcl). From FIG. 6, it can be seen that the hydrogen ion transfer resistance of Example 1 was significantly reduced compared to the Comparative Example, the catalyst layer of Example 1 had a hydrogen ion transfer resistance (R _cl ) of 0.180 Ω cm ² , and the catalyst layer of Comparative Example 1 was hydrogen The ion transfer resistance (R _cl ) was 0.281 Ω cm ^2, and it was confirmed that the hydrogen ion transfer resistance of Example 1 was reduced by 35.9% compared to Comparative Example 1.

In the catalyst layer of Example 2, as the content of the linear ionomer complex was further increased, the hydrogen ion transfer resistance was further reduced compared to Example 1. However, as the concentration of the catalyst in the catalyst layer decreased, the actual MEA performance observation result showed a lower value compared to Example 1. (Based on current density at 0.6 V)

Since the same Nafion211 membrane and the same anode catalyst layer were used in Example 1-2 and Comparative Example 1-3, the ohmic resistance of the membrane electrode assembly (MEA) indicated by the intersection point of the graph and the X-axis was the same. It can be seen that this difference in the hydrogen ion transfer resistance originates from the cathode. Therefore, it can be seen that the hydrogen ion conductivity of the cathode catalyst layer is improved through the formation of an ionomer network in the cathode catalyst layer.

In particular, in the case of Comparative Example 3, the resistance was slightly reduced compared to Comparative Example 1 without the composite by using a composite chemically combined with carbon nanofibers and sulfonated polystyrene as an ion transport network, but carbon and sulfonated polystyrene on the carbon nanofibers were It can be seen that the chemically bonded portion corresponds to a part, so that the sulfonated polystyrene chemically bonded on the carbon nanofibers could not be linearly connected and disconnected, thereby having a higher resistance than Example 1-2.

Hydrogen ion transfer resistance in catalyst layer (R _cl , Ω cm ² ) MEA ohmic resistance (Ω cm ² ) Current density @0.6V (mA cm ^-2 ) Example 1 0.180 0.106 1206 Example 2 0.163 0.104 1166 Comparative Example 1 0.281 0.125 1140 Comparative Example 2 0.210 0.105 1188 Comparative Example 3 0.265 0.107 1087

[Experimental Example 2]

Scanning electron microscope (SEM) measurement

The surfaces of the catalyst layers of Comparative Example 1, Comparative Example 2, and Example 1 were observed using SEM. The results are shown in FIG. 7.

In Comparative Example 1, it could be observed that the catalyst layer was formed only with the catalyst and the ionomer. In Comparative Example 2, since the Ketjen black/ionomer complex was included in the catalyst layer, the formation of the ionomer network was judged to be superior to that of Comparative Example 1, but the shape could not be distinguished after being uniformly dispersed with the catalyst. Accordingly, it can be determined that the formation of the ionomer network through the Ketjen black/ionomer complex has the same form as the formation of a random ionomer network through dispersion of the catalyst.

In the results of Example 1, it can be observed that the carbon nanofibers/ionomer composites are well dispersed over the table/section of the catalyst layer, and through this, it can be confirmed that a linear ionomer network is formed in the catalyst layer.

Claims (7)

As a catalyst layer for a fuel cell made of a catalyst composition,
The catalyst composition may include a catalyst having metal nanoparticles supported on a carbon carrier; Carbon nanofibers to which an ion conductive polymer is physically attached to the surface; And an ionomer,
Based on the total weight of the catalyst, the content of carbon nanofibers to which the ion conductive polymer is physically attached to the surface is 0.1% by weight or more and 30% by weight or less,
Based on the sum (C) of the weight of the carbon carrier and the carbon nanofibers, the percentage of the ratio (I/C) of the sum (I) of the ion conductive polymer and the ionomer is 30% or more and 150% or less,
The catalyst layer for a fuel cell, wherein the catalyst layer has a hydrogen ion transfer resistance of 0.2 ohm·cm ² or less. delete delete The catalyst layer for a fuel cell according to claim 1, wherein the ion conductive polymer and the ionomer are different or identical to each other. delete A membrane electrode assembly comprising a cathode catalyst layer, an anode catalyst layer, and an electrolyte membrane provided between the cathode catalyst layer and the anode catalyst layer,
At least one of the cathode catalyst layer and the anode catalyst layer is a catalyst layer for a fuel cell according to claim 1 or 4, wherein the membrane electrode assembly. A fuel cell comprising the membrane electrode assembly of claim 6.

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