KR20100068028A - Catalyst layer for fuel cell and method for preparing the same - Google Patents

Abstract

PURPOSE: A catalyst layer for a fuel cell is provided to obtain excellent electrical activity and durability, to prevent a pin hole and cracks from being generated on the surface of the fuel cell, and to offer a membrane-electrode assembly having excellent output density. CONSTITUTION: A catalyst layer for a fuel cell includes a catalyst metal particle and an ionomer. The catalyst layer has concentration gradient of the ionomer. The content of the ionomer is 5-300 parts by weight based on 100.0 parts by weight of the catalyst metal particle. A method for manufacturing the catalyst layer comprises the following steps: drying catalyst slurry(12) after spreading the catalyst slurry including the catalyst metal particle, the ionomer, and a dispersing medium on the upper side of a supporter(11); and repeating a process of increasing the content of the ionomer on the upper side of the dried catalyst slurry and drying the catalyst slurry.

Description

Catalyst layer for fuel cell, and method for preparing the same {Catalyst layer for fuel cell and method for preparing the same}

A fuel cell comprising a catalyst layer for a fuel cell, a method for producing the catalyst layer, an apparatus for drying the catalyst layer, an electrode for a fuel cell including the catalyst layer, a membrane electrode assembly including the electrode, and a membrane electrode assembly are disclosed, and more specifically, Is a fuel cell catalyst layer having a gradient of ionomer in the catalyst layer, the formation of pinholes and cracks is suppressed, a method for producing the catalyst layer, an apparatus for drying the catalyst layer, an electrode for a fuel cell including the catalyst layer, and including the electrode. A fuel cell comprising a membrane electrode assembly and the membrane electrode assembly is disclosed.

With the development of science and technology, the need for a high-capacity power source is increasing. However, the conventional lithium secondary battery does not meet this need, and has a disadvantage in that it has a short time and a long life of recharging after a short time of use. As a solution to this, environmentally friendly, high energy density and long life fuel cells have attracted attention as next generation power sources.

Such fuel cells are polymer electrolyte membrane fuel cells (PEMFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC) depending on the type of electrolyte used. cell), solid oxide fuel cell (SOFC), etc., depending on the electrolyte used, the operating temperature of the fuel cell and the material of the components are different. In addition, according to the fuel supply method to the anode, the external reforming type for converting the fuel to hydrogen-enriched gas through the fuel reformer and supplying to the anode, and the fuel direct supply type for supplying gas or liquid fuel directly to the anode or It can be divided into internal reforming type. A representative example of the direct fuel supply type is a direct methanol fuel cell (DMFC), and a direct methanol fuel cell generally uses an aqueous methanol solution as a fuel and a hydrogen ion conductive polymer electrolyte membrane as an electrolyte. Therefore, DMFC also belongs to PEMFC. PEMFCs can achieve high power density, even at small and light weights. Moreover, the use of PEMFCs simplifies the construction of power generation systems.

The basic structure of a fuel cell typically includes an anode (fuel electrode), a cathode (oxidant electrode), and a polymer electrolyte membrane disposed between the anode and the cathode. 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 the anode, the fuel is oxidized to produce hydrogen ions and electrons, the hydrogen ions are transferred to the cathode through the electrolyte membrane, and the electrons are transferred to the external circuit (load) through the conductor (or current collector). In the cathode, water is generated by combining hydrogen ions transferred through the electrolyte membrane, electrons transferred from an external circuit through a conductor (or current collector), and oxygen. At this time, the movement of electrons via the anode, the external circuit and the cathode is power. As such, the cathode and / or anode of the fuel cell contains a catalyst layer that promotes electrochemical oxidation of the fuel and / or electrochemical reduction of oxygen.

The production process of the catalyst layer of the fuel cell typically includes a spray method, a screen printer method, and the like, and spray methods are often used at a laboratory scale level. However, the spray method requires a large amount of solvent, which increases the number of catalyst coatings and is inefficient in terms of workability. In addition, the catalyst must be dried immediately after application of the catalyst, and when the catalyst slurry is applied again without being dried, catalyst surface cracking occurs even though only a small amount of catalyst is applied. In addition, a large amount of alcohol frequently has a problem of electrode ignition when the catalyst slurry containing a large amount of alcohol components is applied to the dried electrode surface after the one-time application of the catalyst, rather than the catalyst slurry containing the water solvent. If a low catalyst content, such as PEMFC, is required, a catalyst slurry containing a large amount of alcohol component is preferred for one application. However, DMFC still has several application times due to high catalyst requirements. It is very urgent to improve the process to improve the problems caused by the ignition.

One aspect of the present invention is to provide a catalyst layer for a fuel cell having a gradient of ionomer in the catalyst layer and suppressing pinholes and crack formation.

Another aspect of the present invention is to provide a method for producing the catalyst layer.

Another aspect of the present invention is to provide a drying apparatus of the catalyst layer.

Another aspect of the invention is to provide an electrode for a fuel cell comprising the catalyst layer.

Another aspect of the invention to provide a membrane electrode assembly comprising the electrode.

Another aspect of the present invention is to provide a fuel cell including the membrane electrode assembly.

According to one aspect of the invention,

A catalyst layer for a fuel cell comprising catalyst metal particles and ionomers, the catalyst layer having a concentration gradient of the ionomer is provided.

The ionomer may be a fluorine polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer, a polyether ketone polymer, a polyether It may be at least one hydrogen ion conductive polymer selected from the group consisting of an ether ketone-based polymer, and a polyphenylquinoxaline-based polymer.

The concentration of the ionomer may increase from the bottom surface of the catalyst layer for fuel cell to the top surface direction.

The ionomer content may be 5 to 300 parts by weight based on 100 parts by weight of the catalyst metal particles.

The fuel cell catalyst layer may further include a carbon-based support.

The carbon-based support may be at least one selected from the group consisting of carbon black, ketjen black, acetylene black, activated carbon powder, carbon molecular sieve, carbon nanotubes, activated carbon having fine pores, and mesoporous carbon.

The catalytic metal particles may be one or more metal particles selected from the group consisting of a main catalyst metal, an alloy of a main catalyst metal and a cocatalyst metal, and a main catalyst metal doped with a cocatalyst metal.

The main catalyst metal may be platinum, gold, ruthenium or osmium.

The cocatalyst metal may be at least one metal selected from the group consisting of cerium, ruthenium, tin, tungsten, titanium, molybdenum, iron, vanadium, manganese, cobalt, chromium, nickel, palladium, rhodium and iridium.

When the catalyst metal particles are an alloy of the main catalyst metal and the cocatalyst metal, or the main catalyst metal doped with the cocatalyst metal, the atomic ratio between the main catalyst metal and the cocatalyst metal is 9: 1 to 1: 9 days. Can be.

When the catalyst metal particle is an alloy of the main catalyst metal and the cocatalyst metal, or the main catalyst metal doped with the cocatalyst metal, the weight ratio of the main catalyst metal / cocatalyst metal may be 0.3 to 20.

The average particle diameter of the catalyst metal particles may be 1.0 to 10.0 nm.

The content of the carbon-based support may be 10 to 1,000 parts by weight based on 100 parts by weight of the catalyst metal particles.

According to another aspect of the invention (a) applying a catalyst slurry comprising catalyst metal particles, ionomer and dispersion medium on the upper surface of the support and dried; And

(b) repeating the process of increasing the ionomer content of the catalyst slurry on the upper surface of the catalyst slurry dried in the previous step and applying and drying the catalyst slurry.

The number of repetitions may be 1 to 5 times.

The catalyst slurry may further include a carbon support.

The drying may include placing the support on which the catalyst slurry is applied on a lower plate to which a heater is connected and spaced apart from the upper plate to which the cooler is connected on the applied catalyst slurry; And adjusting the temperature of the upper and lower plates.

The spacing between the applied catalyst slurry and the top plate may be 1 to 15 mm.

The temperature of the upper plate may be adjusted to -15 to 5 ℃, the temperature of the lower plate may be adjusted to 0 to 150 ℃.

The method may further include applying an ionomer dispersion to the upper surface of the catalyst slurry dried in the previous step before applying the catalyst slurry in the step (b).

According to another aspect of the present invention is connected to the cooler and the top plate temperature adjustable;

A lower plate opposed to the upper plate and installed to adjust a distance from the upper plate and connected to a heater to control a temperature; And a control unit for controlling the cooler and the heater so that the temperature of the upper and lower plates is adjusted.

According to another aspect of the invention there is provided an electrode for a fuel cell comprising the catalyst layer.

A pair of electrodes comprising a catalyst layer according to another aspect of the present invention; And an electrolyte membrane disposed between the pair of electrodes.

One surface of the catalyst layer may contact the electrolyte membrane, and the other surface may contact the gas diffusion layer.

The catalyst layer may include an ionomer having a concentration that increases in the direction of the electrolyte membrane in the gas diffusion layer.

According to another aspect of the invention a pair of electrodes comprising the catalyst layer; And a membrane electrode assembly including an electrolyte membrane disposed between the pair of electrodes.

According to an aspect of the present invention, it is possible to provide a fuel cell catalyst layer having excellent electrical activity, durability, and economy, and preventing pinholes and cracks on its surface, a high performance membrane electrode assembly having an excellent power density, and a fuel cell.

Hereinafter, a fuel cell catalyst layer according to an embodiment of the present invention, a method for producing the catalyst layer, a drying device of the catalyst layer, a fuel cell electrode including the catalyst layer, a membrane electrode assembly including the electrode and the membrane electrode assembly The fuel cell will be described in more detail.

A catalyst layer for a fuel cell according to an embodiment of the present invention is a catalyst layer for a fuel cell including a carbon-based support, catalyst metal particles, and an ionomer, and the catalyst layer has a gradient of ionomer. That is, the ionomer contained in the catalyst layer is not distributed irregularly, but has a characteristic that the concentration of the ionomer, that is, the content, changes according to a certain orientation.

The concentration of the ionomer may increase in an upward direction from the bottom of the catalyst layer for the fuel cell. That is, when the catalyst layer is formed on a predetermined support, the concentration of the ionomer may be increased in the top direction, which is the height direction of the catalyst layer, from the bottom contacting the support.

In addition, when the fuel cell catalyst layer is interposed between the gas diffusion layer (GDL) and the electrolyte membrane (membrane), the concentration of the ionomer may increase in the direction of the electrolyte membrane in the gas diffusion layer. As a result, the concentration of the ionomer is small in the vicinity of the gas diffusion layer, which obstructs the gas passage less, and at the same time, the ionomer concentration increases in the vicinity of the electrolyte membrane, thereby facilitating the movement of protons, thereby providing a high-performance catalyst layer.

The catalytic metal particles are one or more metal particles selected from the group consisting of a main catalyst metal, an alloy of a main catalyst metal and a cocatalyst metal, and a main catalyst metal doped with a cocatalyst metal.

The main catalyst metal plays a role of directly catalyzing the electrochemical redox reaction of the fuel cell, and non-limiting examples thereof include platinum, gold, ruthenium or osmium.

The cocatalyst metal plays a role of improving the electrical activity of the main catalyst metal, and includes cerium, ruthenium, tin, tungsten, titanium, molybdenum, iron, vanadium, manganese, cobalt, chromium, nickel, palladium, rhodium and iridium. It may be one or more metals selected from the group consisting of.

On the other hand, when the catalyst metal particles are an alloy of the main catalyst metal and the cocatalyst metal, or the main catalyst metal doped with the cocatalyst metal, the atomic ratio between the main catalyst metal and the cocatalyst metal is 9: 1 to 1: 9, the weight ratio of main catalyst metal / cocatalyst metal is, for example, 0.3 to 20, 0.7 to 7.

In the case where an excessive amount of the main catalyst metal is out of the above range, the cost of the main catalyst metal is generally very high, and thus the manufacturing cost may increase, and when the auxiliary catalyst metal is present in an excessive amount, It may not be able to exert sufficient activity as a catalyst for the electrochemical redox reaction.

In addition, the average particle diameter of the catalyst metal particles may be, for example, 1.0 to 10.0 nm. In this case, when the average particle diameter of the catalyst metal particles is less than 1.0 nm, the catalyst may be easily deteriorated, and thus the active capacity may be reduced. When the average particle diameter of the catalyst metal particles is greater than 10.0 nm, the catalytic active area may be reduced to cause performance degradation. have.

The carbon-based support may be included in the metal precursor mixture solution to absorb the metal precursor, thereby bringing the effect of controlling the size of the active metal particles, having a porosity and having a surface area of 150 m ² / g or more, particularly 500 to 1200 m ² / g and an average particle diameter of 10 to 300nm, in particular 20 to 100nm can be used.

As the carbon-based support, one or more selected from the group consisting of carbon black, ketjen black, acetylene black, activated carbon powder, carbon molecular sieve, carbon nanotube, microporous activated carbon, and mesoporous carbon may be used. It is not limited.

The content of the carbon-based support may be 10 to 1,000 parts by weight, 25 to 500 parts by weight, and 50 to 300 parts by weight based on 100 parts by weight of the catalyst metal particles. At this time, when the content of the carbon-based support is less than 10 parts by weight, the amount of the carbon-supported support is insufficient and the effect of the carbon-based support is not effective. It may be inappropriate for direct methanol fuel cells.

The ionomer may be a fluorine polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer, a polyether ketone polymer, a polyether It may be at least one selected from the group consisting of an ether ketone-based polymer, and a polyphenylquinoxaline-based polymer. A specific example is Nafion ^® , DuPont.

The amount of the ionomer may be, for example, 5 to 300 parts by weight, 10 to 200 parts by weight, and 15 to 150 parts by weight based on 100 parts by weight of the catalyst metal particles. When the content of the ionomer is less than 5 parts by weight, the binding of the catalyst powder is weakened. If the content of the ionomer is more than 50 parts by weight, methanol crossover may be induced to provide a cause of deterioration.

In addition, according to one embodiment of the invention, (a) applying a catalyst slurry comprising catalyst metal particles, ionomer and dispersion medium on the upper surface of the support and dried; And (b) repeating the step of applying and drying the ionomer content of the catalyst slurry on the upper surface of the catalyst slurry dried in the previous step and repeating the step of applying and drying the catalyst slurry.

In this case, the number of times to repeat the process of applying and drying the catalyst slurry may be, for example, 1 to 5 times, 1 to 2 times. When the number of repetitions exceeds five times, workability may be degraded.

If the process of applying and drying the catalyst slurry is performed twice in total, the method for preparing a catalyst layer may include applying a first catalyst slurry including catalyst metal particles, ionomers, and a dispersion medium to an upper surface of an electrode support; Drying the applied first catalyst slurry to form a first catalyst layer; Applying a second catalyst slurry including catalyst metal particles, immonia and a dispersion medium to an upper surface of the first catalyst layer; And drying the applied second catalyst slurry to form a second catalyst layer.

Thereafter, as the number of times of repeating the application and drying of the catalyst slurry is increased, the third to more catalyst layers may be continuously formed on the second catalyst layer.

The catalyst slurry may further include a carbon-based support in addition to the catalyst metal particles, the ionomer, and the dispersion medium. At this time, the carbon-based support, the catalyst metal particles, the ionomer are as described above.

The dispersion medium may be one or a mixture of two or more selected from the group consisting of water and alcohol. The alcohol may be methanol, ethanol, 1-propanol, 2-propanol, butanol, ethylene glycol or a mixture thereof, but is not limited thereto.

In particular, when the catalyst slurry is applied to the hydrophobic support, when the dispersion medium is made of only water, it may be difficult to apply effectively, it may contain 10% or more of the solvent of the alcohols. At this time, when selecting alcohol should be selected to the boiling point similar to water. This is because alcohol has a property of wetting the support more easily, and the surface tension is weak and spreads evenly, so that the surface of the catalyst layer may be cracked if it is easily volatilized after wetting the surface of the already applied catalyst layer.

The content of the dispersion medium may be 100 to 10,000 parts by weight, 100 to 2,000 parts by weight, and 100 to 1,000 parts by weight based on 100 parts by weight of the catalyst metal particles. In this case, when the content of the dispersion medium is less than 100 parts by weight, the dispersing effect of the catalyst metal particles and the ionomer may be reduced, and when the content of the dispersion medium is more than 10,000 parts by weight, the number of operations may be greatly increased during application of the catalyst slurry, thereby reducing work efficiency.

The coating method of the catalyst slurry can be applied as long as it is a conventional method, for example, can be applied using a bar coater, a slit die, an inkjet or a screen printer.

The coating amount of the catalyst slurry, for example, one may be a Hall about 0.1mg / cm ² to 6mg / cm ^2, from about 1mg / cm ² to about ^{4mg / cm 2, 1.5mg / cm} 2 to about 2.5mg / cm ^2. If the coating amount is less than 0.1mg / cm ² It can significantly increase the number of operations when forming the catalyst layer, if it is more than 6mg / cm ² may cause cracking of the surface of the catalyst layer.

The drying of the applied catalyst slurry may include: placing a support on which the catalyst slurry is applied on a lower plate to which a heater is connected and spaced apart from the upper plate to which the cooler is connected on the applied catalyst slurry; And adjusting the temperature of the upper and lower plates.

This drying step has the advantage that it is possible to prevent the pinholes and cracks on the surface of the catalyst layer to be finally produced by slowly drying the slurry from the bottom surface in contact with the support while slowing the top surface of the catalyst slurry.

For this purpose, the spacing between the applied catalyst slurry and the top plate can be adjusted as close as possible within the range that the top plate does not come into contact with the catalyst slurry, for example 1 to 15 mm. If the interval is less than 1mm is not practical control, if the interval is more than 15mm can not give a cooling effect to the surface of the applied catalyst slurry may cause cracking of the surface of the catalyst layer.

The temperature of the top plate may be adjusted to, for example, -15 to 30 ℃, -10 to 5 ℃ using a connected cooler. If the temperature of the upper plate is less than -15 ℃, the drying of the upper surface of the catalyst slurry may not be sufficient, and if the temperature of the upper plate is higher than 30 ℃ drying rate of the upper surface of the catalyst slurry is rapidly progressed to pinholes and cracks of the surface of the catalyst layer produced It may not be prevented.

In addition, the temperature of the lower plate may be adjusted to, for example, 0 to 150 ℃, 5 to 40 ℃ using a heater connected. In this case, when the temperature of the lower plate is less than 0 ° C., the overall drying of the catalyst slurry may be insufficient, and if it is more than 150 ° C., cracks and pinholes on the surface of the catalyst layer may not be prevented.

In the method of preparing the catalyst layer, the method may further include applying an ionomer dispersion to the upper surface of the catalyst slurry dried in the previous step before applying the catalyst slurry in the step (b). That is, an ionomer dispersion having affinity with the catalyst slurry is added in the middle so that the catalyst slurry to be applied can be effectively applied to the upper surface of the dried catalyst slurry.

In the case of preparing the catalyst layer by applying and drying the catalyst slurry only once in the conventional manner, the ionomer in the catalyst layer sinks to the bottom of the catalyst layer, and when the prepared catalyst layer is interposed between the electrolyte diffusion membrane and the electrolyte membrane in the gas diffusion layer, Not only can the ionomer block pores of the support, but also the resistance of the proton is reduced as the specific gravity of the ionomer near the electrolyte membrane is lowered.

Therefore, in the method for producing a catalyst layer according to an embodiment of the present invention, the catalyst slurry is applied and dried at least twice without applying and drying the catalyst slurry only once, and further, the catalyst on the upper surface of the catalyst slurry dried in the previous step. The ionomer content of the slurry is increased to repeat the application and drying process. As a result, in the portion in contact with the support, the concentration of the ionomer is decreased, and then the catalyst slurry prepared by repeatedly applying and drying the catalyst slurry prepared to increase the concentration of the ionomer is increased from the bottom of the catalyst layer toward the top surface. It becomes possible to manufacture.

In addition, according to an embodiment of the present invention, a drying apparatus for effectively performing the drying step of the above-described method for producing a catalyst layer, the drying apparatus is connected to the cooler and the temperature control panel; A lower plate opposed to the upper plate and installed to adjust a distance from the upper plate and connected to a heater to control a temperature; And a control unit for controlling the cooler and the heater so that the temperature of the upper plate and the lower plate is adjusted.

Referring to the drying apparatus in detail with reference to FIG. 1, the upper plate 1 and the lower plate 2 are provided to face each other, and the lower plate 2 has a support 11 coated with a catalyst slurry 12 on an upper surface thereof. Can be. At this time, the lower end of the lower plate 2 is provided with a height adjusting unit 3 for adjusting the gap between the catalyst slurry and the upper plate (1).

In addition, the cooler 6 and the heater 5 are respectively connected to the upper board 1 and the lower board 2, respectively. Through the control unit 4 connected to the cooler 6 and the heater 5, the upper surface of the catalyst slurry may be dried more slowly than the bottom surface to adjust the temperature so as to suppress the occurrence of pinholes and cracks in the catalyst layer.

In addition, according to an embodiment of the present invention, there is provided a fuel cell electrode including the catalyst layer, a membrane electrode assembly including the electrode, and a fuel cell including the membrane electrode assembly.

An electrode for a fuel cell according to an embodiment of the present invention may include an electrode substrate, a catalyst layer, a gas diffusion layer, and the like of the embodiment of the present invention as described above.

For example, the fuel cell electrode may be a carbon powder such as carbon black, acetylene black, carbon nanotubes, carbon nanowires, carbon nanohorns or carbon nanofibers on an electrode substrate such as carbon paper; Binders such as polytetrafluoroethylene (PTFE: polytetrafluoroethylene), polyvinylidene fluoride (PVdF: polyvinylidenefluoride), and fluorinated ethylene propylene (FEP); And a dispersion medium such as water, ethanol, methanol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, and the like, which are coated by a tape casting, spray, or screen printing method. Thereby forming a gas diffusion layer with a uniform thickness, and then forming a catalyst layer according to an embodiment of the present invention on the gas diffusion layer.

The gas diffusion layer serves to make the reaction gas easily accessible to the catalyst layer, and also serves to prevent performance degradation due to water generated as a by-product when the battery is driven.

Membrane Electrode Assembly (MEA) according to an embodiment of the present invention comprises a pair of electrodes (anode and cathode) comprising a catalyst layer; And an electrolyte membrane disposed between the pair of electrodes.

The electrode is an electrode according to an embodiment of the present invention, and as the electrolyte membrane, a sulfonate high fluorinated polymer having a main chain generally composed of fluorinated alkylene and a side chain composed of fluorinated vinyl ether having a sulfonic acid group at its terminal (eg Polymer electrolytes such as Nafion (trademark of Dupont) may be used. The polymer electrolyte membrane exhibits excellent ion conductivity by moistening an appropriate amount of water. Bonding of the electrode and the electrolyte membrane may be performed by a thermal pressure method, a thermal fusion method, or the like.

The catalyst layer is catalytic metal particles; A catalyst layer for a fuel cell comprising a carbon-based support and an ionomer, wherein the catalyst layer includes an ionomer having a concentration gradient of the ionomer and having a concentration that increases in the direction of the electrolyte membrane in the gas diffusion layer.

Accordingly, one surface of the catalyst layer in the membrane electrode assembly may contact the electrolyte membrane and the other surface may contact the gas diffusion layer. In this case, the catalyst layer may include an ionomer having a concentration that increases in the direction of the electrolyte membrane in the gas diffusion layer.

In addition, an embodiment of the present invention provides a fuel cell including the membrane electrode assembly, and the fuel cell includes at least one electricity generating unit, a fuel supply unit, and a gas supply unit. The electricity generating unit includes a positive electrode, a negative electrode, and a separator formed on both sides of the polymer electrolyte membrane, and the electrode and the separator may be integrally manufactured by using a metal mesh. The fuel supply unit serves to supply hydrogen or hydrogen-containing fuel, that is, alcohols such as methanol to the electricity generator, and the gas supply unit serves to supply oxygen or air including oxygen to the electricity generator.

Hereinafter, a direct methanol fuel cell of a fuel cell according to an embodiment of the present invention will be described with reference to FIG. 2.

As shown in FIG. 2, the DMFC includes an anode 20 to which fuel is supplied, a cathode 30 to which an oxidant is supplied, and an electrolyte membrane 40 positioned between the anode 20 and the cathode 30. . In general, the anode 20 consists of an anode diffusion layer 22 and an anode catalyst layer 21, and the cathode 30 is a cathode diffusion layer (the diffusion layer is used in the same sense as the gas diffusion layer) 32 and the cathode catalyst layer 31. ) The anode catalyst layer and the cathode catalyst layer is made of a supported catalyst prepared by the manufacturing method according to an embodiment of the present invention described above.

The anode separator 50 has a flow path for supplying fuel to the anode, and serves as an electron conductor for transferring electrons generated from the anode to an external circuit or an adjacent unit cell. The cathode separator 60 has a flow path for supplying an oxidant to the cathode, and serves as an electron conductor for transferring electrons supplied from an external circuit or an adjacent unit cell to the cathode. In DMFC, an aqueous methanol solution is mainly used as the fuel supplied to the anode, which is supplied from a fuel supply section, and air is mainly used as an oxidant supplied to the cathode, which is supplied from a gas supply section.

The aqueous methanol solution transferred to the anode catalyst layer 21 through the anode diffusion layer 22 is decomposed into electrons, hydrogen ions, carbon dioxide, and the like. Hydrogen ions are transferred to the cathode catalyst layer 31 through the electrolyte membrane 40, electrons are transferred to an external circuit, and carbon dioxide is discharged to the outside. In the cathode catalyst layer 31, hydrogen ions delivered through the electrolyte membrane 40, electrons supplied from an external circuit, and oxygen in the air delivered through the cathode diffusion layer 32 react to generate water.

In such a DMFC, the electrolyte membrane 40 serves as a hydrogen ion conductor, an electronic insulator, a separator, and the like. In this case, the role of the separator means that unreacted fuel is delivered to the cathode, or unreacted oxidant is prevented from being delivered to the anode.

Hereinafter, the present invention will be described in more detail with reference to the following examples. The following examples are only intended to help a clear understanding of the present invention, and the scope of the present invention is not limited to the following examples.

Example

Example: Preparation of Electrode and Membrane Electrode Assembly

(1) Preparation of Cathode Electrode

2.5g of 70wt% PtCo / Vulcan (DC1, Dongjin Semichem) and 10% Nafion dispersion (Nafion ^® , DuPont) were mixed with 7g of water and stirred for 10 minutes at a speed of about 400rpm using a homogenizer. A catalyst slurry of the type fuel cell was prepared.

Sufficiently wet the surface with 0.5 wt% Nafion dispersion on the surface of SGL 24BC (SGL Technology), a carbon paper, so that the coating amount of Nafion per unit area is about 0.1 mg / cm ^2. Applied. The catalyst slurry prepared above was applied to a dry content of about 2.5 mg / cm ² . Thereafter, the lower plate was set to 30 ° C. and the upper plate was set to 0 ° C. using the dryer according to FIG. 1, and then the electrode support to which the catalyst slurry was applied was placed on the lower plate.

The gap between the catalyst slurry and the top plate is maintained at about 1 mm so as not to contact. When the applied catalyst slurry is dried, the surface is wetted with 0.5 wt% Nafion dispersion again, so that the coating amount of Nafion per unit area is about 0.1 mg / cm ^2. Applied. Thereafter the catalyst slurry was applied again so that the catalyst dry content was about 1.5 mg / cm ² . Nafion solution for bonding (10% Nafion: Isopropyl Alcohol (IPA): DI = 1: 1: 1) was used to reduce the dry content of Nafion to facilitate the bonding with the electrolyte membrane on the top surface of the wet catalyst slurry. 0.5-1.5 mg / cm <^2> was applied. The drying process was repeated again with the wet slurry applied. The dried electrode was re-dried at 80 ° C. to fix the ionomer in the catalyst layer.

(2) Preparation of the anode electrode

Add 2.5g of 60wt% PtRu / Vulcan (DA1, Dongjin Semichem) and 10% Nafion dispersion (Nafion ^® , DuPont) and mix 7g of water and stir for 10 minutes at about 400rpm using a homogenizer. A catalyst slurry of an electrolyte fuel cell was prepared. 0.5 wt% Nafion dispersion on the surface of TCP (Toray Carbon Paper) coated with hydrophobic material and microporous layer (MPL) is sufficiently wetted so that the coating amount of Nafion per unit area is about 0.01 mg / cm ^2. Applied. The catalyst slurry was applied thereon to a dry content of about 2.0 mg / cm ² . Thereafter, the lower plate was set to 30 ° C. and the upper plate was set to 0 ° C. using the dryer according to FIG. 1, and then the electrode support to which the catalyst slurry was applied was placed on the lower plate.

The gap between the catalyst slurry and the top plate is maintained at about 1 mm so as not to contact. When the applied catalyst slurry is dried, the surface is sufficiently wetted with 0.5 wt% Nafion dispersion again so that the coating amount of Nafion per unit area is about 0.01 mg / cm ^2. Applied. Thereafter, the catalyst slurry was applied again so that the catalyst dry content was about 1.0 mg / cm ² .

Nafion solution for bonding (10% Nafion: Isopropyl Alcohol (IPA): DI = 1: 1: 1) was used to reduce the dry content of Nafion to facilitate the bonding with the electrolyte membrane on the top surface of the wet catalyst slurry. 0.5-1.5 mg / cm <^2> was applied. The drying process was repeated again with the wet slurry applied. The dried electrode was re-dried at 80 ° C. to fix the ionomer in the catalyst layer.

(3) Preparation of membrane electrode assembly

An electrolyte membrane / electrode assembly was prepared by contacting the cathode and anode electrodes prepared above to both sides of the polymer electrolyte membrane Nafion 112 (DuPont) membrane and bonding them by a hot fusion method. At this time, the bonding was performed at 130 ^o C, 3 min, pressure 100kg / cm ² .

Comparative example

Comparative Example: Preparation of Electrode and Membrane Electrode Assembly

(1) Preparation of Cathode Electrode

Add 2.5g of 70wt% PtCo / Vulcan (DC1, Dongjin Semichem) and 10% Nafion (Nafion ^® , DuPont) dispersion, mix 7g of water, and stir for 10 minutes at about 400rpm using a homogenizer. A catalyst slurry of the type fuel cell was prepared.

Sufficiently wet the surface with 0.5 wt% Nafion dispersion on the surface of SGL 24BC (SGL Technology), a carbon paper, so that the coating amount of Nafion per unit area is about 0.1 mg / cm ^2. Applied. The prepared catalyst slurry was applied thereon to a dry content of about 4.0 mg / cm ² . Thereafter, the resultant was dried at 50 ° C. using a dryer. To facilitate bonding with the electrolyte membrane on the dried catalyst layer, Nafion solution (10% Nafion: Isopropyl Alcohol (IPA): DI = 1: 1: 1) was used to reduce the dry content of Nafion. 0.5-1.5 mg / cm <^2> was applied. The dried electrode was re-dried at 80 ° C. to fix the ionomer in the catalyst layer.

(2) Preparation of the anode electrode

1 g of 60 wt% PtRu / Vulcan (DA1, Dongjin Semichem) and 10 g of Nafion dispersion (Nafion ^® , DuPont) were mixed with 7 g of water and stirred for 10 minutes at a speed of about 400 rpm using a homogenizer. A catalyst slurry of the type fuel cell was prepared. Apply 0.5 wt% Nafion dispersion on the surface of Toray Carbon Paper (TCP) coated with hydrophobic material and microporous layer (MPL) sufficiently so that the amount of Nafion applied per unit area is about 0.01 mg / cm ^2. Applied. The catalyst slurry was applied thereon to a dry content of about 3.0 mg / cm ² . Thereafter, the resultant was dried at 50 ° C. using a dryer. To facilitate bonding with the electrolyte membrane on the dried catalyst layer, Nafion solution (10% Nafion: Isopropyl Alcohol (IPA): DI = 1: 1: 1) was used to reduce the dry content of Nafion. 0.5-1.5 mg / cm <^2> was applied. The dried electrode was re-dried at 80 ° C. to fix the ionomer in the catalyst layer.

(3) Preparation of membrane electrode assembly

An electrolyte membrane / electrode assembly was prepared by contacting the cathode and anode electrodes prepared above to both sides of the polymer electrolyte membrane Nafion 112 (DuPont) membrane and bonding them by a hot fusion method. At this time, the bonding was carried out at 130 ℃, 3min, pressure 100kg / cm ² .

Experiment result

Unit cell experiments were carried out with the membrane electrode assemblies prepared in Examples and Comparative Examples. Experimental conditions are as follows.

The fuel supply was supplied at 1 cc / min with 4 vol% methanol aqueous solution, while at the same time the air flow rate was supplied at 150 cc / min. The I-V curve was measured according to the temperature, the power value was calculated, and the I-P curve was obtained.

Referring to FIG. 3, when looking at the values of current and power density based on a constant voltage, for example 0.4 V, the comparative example shows a current of about 0.8 A and a power density of 70 mW / cm ² . A current of about 1.2 A and a power density of 100 mW / cm ² are shown. Therefore, it can be seen that the fuel cell according to the embodiment exhibits excellent performance with a higher power density at a constant voltage than in the case of the comparative example.

The present invention is not limited to the above-described specific preferred embodiments, and various modifications can be made by any person having ordinary skill in the art without departing from the gist of the present invention claimed in the claims. Of course, such changes will fall within the scope of the claims.

1 is a view showing a drying device of a catalyst layer according to an embodiment of the present invention.

2 illustrates a fuel cell according to an embodiment of the present invention.

3 is a graph showing the evaluation results of the unit cell experiment of the membrane electrode assembly prepared in Examples and Comparative Examples.

<Short description of drawing symbols>

1: top plate 2: bottom plate

3: height adjustment part 4: control part

5: burner 6: cooler

11: support 12: catalyst slurry

20: anode 30: cathode

40: electrolyte membrane 50: anode separator

60: cathode separator 22: anode diffusion layer

21: anode catalyst layer 31: cathode catalyst layer

32: cathode diffusion layer

Claims (28)

Catalytic metal particles; And an ionomer, wherein the catalyst layer is a fuel cell catalyst layer, wherein the catalyst layer has a concentration gradient of the ionomer. The method of claim 1, wherein the ionomer is a fluoropolymer, a benzimidazole-based polymer, a polyimide-based polymer, a polyetherimide-based polymer, a polyphenylene sulfide-based polymer, a polysulfone-based polymer, a polyether sulfone-based polymer, a polyether A catalyst layer for a fuel cell, characterized in that at least one selected from the group consisting of a ketone-based polymer, a polyether-etherketone-based polymer, and a polyphenylquinoxaline-based polymer. The catalyst layer for a fuel cell according to claim 1, wherein the concentration of the ionomer increases in an upward direction from the bottom of the catalyst layer for fuel cell. The catalyst layer for a fuel cell according to claim 1, wherein the ionomer is 5 to 300 parts by weight based on 100 parts by weight of catalyst metal particles. The catalyst layer for a fuel cell according to claim 1, further comprising a carbon-based support. The method of claim 5, wherein the carbon-based support is at least one selected from the group consisting of carbon black, Ketjen black, acetylene black, activated carbon powder, carbon molecular sieve, carbon nanotubes, activated carbon having fine pores, mesoporous carbon A catalyst layer for a fuel cell, characterized in that. The fuel cell according to claim 1, wherein the catalyst metal particles are at least one metal particle selected from the group consisting of a main catalyst metal, an alloy of the main catalyst metal and the cocatalyst metal, and a main catalyst metal doped with the cocatalyst metal. Catalyst bed. 8. The catalyst layer for a fuel cell according to claim 7, wherein the main catalyst metal is platinum, gold, ruthenium or osmium. 8. The method of claim 7, wherein the cocatalyst metal is at least one metal selected from the group consisting of cerium, ruthenium, tin, tungsten, titanium, molybdenum, iron, vanadium, manganese, cobalt, chromium, nickel, palladium, rhodium and iridium. A catalyst layer for a fuel cell, characterized in that. 8. The atomic ratio between the main catalyst metal and the cocatalyst metal according to claim 7, wherein the catalyst metal particles are alloys of the main catalyst metal and the cocatalyst metal or doped with the cocatalyst metal. Catalyst layer for fuel cell, characterized in that 1 to 1: 9. The weight ratio of the main catalyst metal to the cocatalyst metal is 0.3 to 20 when the catalyst metal particles are alloys of the main catalyst metal and the cocatalyst metal or doped with the cocatalyst metal. A catalyst layer for a fuel cell, characterized in that. The catalyst layer for a fuel cell according to claim 1, wherein the catalyst metal particles have an average particle diameter of 1.0 to 10.0 nm. The catalyst layer for a fuel cell according to claim 5, wherein the content of the carbonaceous support is 10 to 1,000 parts by weight based on 100 parts by weight of the catalyst metal particles. (a) applying and drying a catalyst slurry comprising catalyst metal particles, ionomers and dispersion medium on the support surface; And (b) repeating the step of applying and drying the ionomer content of the catalyst slurry on the upper surface of the catalyst slurry dried in the previous step; and drying. The method for producing a catalyst layer for a fuel cell according to claim 14, wherein the number of repetitions is 1 to 5 times. 15. The method of claim 14, wherein the catalyst slurry further comprises a carbon support. 15. The method of claim 14, wherein the drying step comprises: placing a support to which the catalyst slurry is applied on a lower plate to which a heater is connected and spaced apart from the top plate to which the cooler is connected on the applied catalyst slurry; And controlling the temperature of the upper and lower plates. 18. The method of producing a catalyst layer for a fuel cell according to claim 17, wherein the interval between the applied catalyst slurry and the top plate is 1 to 15 mm. The method of claim 17, wherein the temperature of the upper plate is adjusted to −15 to 30 ° C., and the temperature of the lower plate is adjusted to 0 to 150 ° C. 18. 15. The method of claim 14, further comprising applying an ionomer dispersion to the upper surface of the catalyst slurry dried in the previous step before applying the catalyst slurry in step (b). A top plate connected to the cooler and capable of temperature control; A lower plate opposed to the upper plate and installed to adjust a distance from the upper plate and connected to a heater to control a temperature; And And a control unit for controlling the cooler and the heater so that the temperature of the upper and lower plates is controlled. An electrode for a fuel cell comprising the catalyst layer according to any one of claims 1 to 13. A pair of electrodes comprising a catalyst layer according to claim 1; And an electrolyte membrane disposed between the pair of electrodes. 24. The membrane electrode assembly of claim 23, wherein one surface of the catalyst layer is in contact with the electrolyte membrane and the other surface is in contact with the gas diffusion layer. 25. The membrane electrode assembly of claim 24, wherein the catalyst layer comprises an ionomer having a concentration that increases in the direction of the electrolyte membrane in the gas diffusion layer. A pair of electrodes comprising a catalyst layer according to claim 1; And a membrane electrode assembly including an electrolyte membrane disposed between the pair of electrodes. 27. The fuel cell of claim 26, wherein one surface of the catalyst layer is in contact with the electrolyte membrane and the other surface is in contact with the gas diffusion layer. 28. The fuel cell of claim 27, wherein the catalyst layer comprises an ionomer having a concentration that increases in the direction of the electrolyte membrane in the gas diffusion layer.

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