KR101483124B1 - Membrane electrode assembly including porous electrode catalyst layer, manufacturing method thereof, and fuel cell employing the same - Google Patents

Abstract

The present invention relates to a membrane electrode assembly for a fuel cell having a porous electrode catalyst layer, a method for manufacturing the membrane electrode assembly, and a membrane electrode assembly for a fuel cell employing the membrane electrode assembly, wherein an electrode including an electrode catalyst layer is provided on both surfaces of the electrolyte membrane, In the electrode catalyst layer, a plurality of pores are uniformly distributed to have porosity. The present invention can provide a high output by stabilizing the reaction efficiency by efficiently supplying the gas by supplying the gas by making the electrode catalyst layer porous, and by reducing the amount of the noble metal catalyst used, the manufacturing cost of the fuel cell is greatly reduced There is an effect that can be done.

Description

TECHNICAL FIELD [0001] The present invention relates to a membrane electrode assembly having a porous electrode catalyst layer, a method of manufacturing the membrane electrode assembly, and a fuel cell employing the membrane electrode assembly,

The present invention relates to a membrane electrode assembly for a fuel cell, a method of manufacturing the same, and a fuel cell employing the membrane electrode assembly. More particularly, the present invention relates to a membrane electrode assembly for a fuel cell, And a fuel cell employing the membrane electrode assembly.

Fuel cells are devices that produce electricity by electrochemically reacting fuel and oxygen. Unlike thermal power generation, fuel cells do not go through a carnot cycle, so their theoretical efficiency is very high. Fuel cells can be applied not only to the supply of electric power for industrial, domestic and vehicular drive, but also to the power supply of small electric / electronic products, especially portable devices.

Currently known fuel cells are classified into a polymer electrolyte membrane (PEM) system, a phosphoric acid system, a molten carbonate system, a solid oxide system, and the like depending on the type of electrolyte used And the operating temperature of the fuel cell, the material of the component parts, and the like are changed depending on the electrolyte used.

The fuel cell includes an externally reforming type in which fuel is converted into a hydrogen-enriched gas through a fuel reformer and then supplied to the anode, and a direct fuel supply type in which gas or liquid fuel is directly supplied to the anode, Or an internal reforming type.

A typical example of a direct fuel type fuel cell is a direct methanol fuel cell (DMFC). In the DMFC, an aqueous methanol solution or a mixed vapor of methanol and water is generally supplied to the anode. DMFCs are known to be the most likely to be miniaturized among various types of fuel cells because they do not require external reformers and are easy to handle fuel.

The electrochemical reaction process of the DMFC is composed of an anode reaction in which a fuel is oxidized and a cathode reaction in which hydrogen ions and oxygen are reduced, and the reaction formula is as follows.

Anode reaction: CH ₃ OH + H ₂ O → 6 H + + 6 e + CO ₂

Cathode reaction: 1.5 O ₂ + 6 H ⁺ + 6 e ^- → 3 H ₂ O

Overall reaction: CH ₃ OH + 1.5 O ₂ → 2 H ₂ O + CO ₂

As shown in the above reaction formula, in the anode, methanol and water react with each other to generate carbon dioxide, 6 hydrogen ions, and 6 electrons. The generated hydrogen ions migrate to the cathode using a hydrogen ion conductive electrolyte membrane positioned between the anode and the cathode as a medium. In the cathode, hydrogen ions, electrons transferred through an external circuit, and oxygen react to produce water. The overall reaction of DMFC is the reaction of methanol with oxygen to produce water and carbon dioxide, in which a significant amount of energy corresponding to the heat of combustion of methanol is converted to electrical energy. In order to promote this reaction, the anode and cathode contain a catalyst.

The hydrogen-ion conductive electrolyte membrane serves not only as a channel for transferring hydrogen ions generated by the oxidation reaction to the cathode at the anode, but also as a separation membrane for separating the anode and the cathode. Generally, the hydrogen ion conductive electrolyte membrane has hydrophilicity and exhibits ion conductivity by humidifying a proper amount of water.

A part of the methanol supplied to the anode diffuses into the hydrogen ion conductive electrolyte membrane having hydrophilic property and moves to the cathode. This phenomenon is called methanol cross-over. In general, a platinum catalyst is used for the cathode of the DMFC. The platinum catalyst accelerates the oxidation reaction of methanol as well as the reduction reaction of oxygen. Thus, the crossover methanol is oxidized at the cathode, and therefore the performance of the DMFC is significantly degraded.

In order to solve such a problem, an attempt has been made to develop a hydrogen ion conductive electrolyte membrane capable of suppressing permeation of methanol and to develop a catalyst for a cathode having low reactivity with methanol.

In addition, the cathode catalyst layer requires an oxygen transfer capability and an effective water removal capability.

 The pore size should be small and the total porosity should be improved. However, if the pore size is small, it is difficult to remove the water in the catalyst layer. If the pore size is too large, There is a problem that the oxygen adsorption ability is deteriorated. Therefore, optimal pore size and porosity within the catalyst bed are required for oxygen transfer capability and effective water removal.

For the design of the cathode catalyst layer having such characteristics, Japanese Unexamined Patent Publication (Kokai) No. 2006-147371 discloses a method for obtaining a catalyst layer film having two different pore sizes by sputtering Pt particles and Fe particles together and then removing only Fe particles using hydrochloric acid. .

The prior art attempts to obtain a high output electrode catalyst for a fuel cell by supplying a reaction gas by producing a catalyst layer having various pore sizes and effectively discharging the generated water.

SUMMARY OF THE INVENTION The present invention provides a membrane electrode assembly for a fuel cell, which has improved oxygen transport capability and effective water removal efficiency by solving the problems described above, a method for manufacturing the membrane electrode assembly, and a fuel cell employing the same.

According to an aspect of the present invention,

A membrane electrode assembly for a fuel cell, comprising an electrode catalyst layer on both surfaces of an electrolyte membrane, wherein the electrode catalyst layer has pores having an average diameter of 3 to 5 nm and a porosity of 40 to 80% The present invention provides a membrane electrode assembly for a fuel cell, which is a porous electrode catalyst layer.

A further object of the present invention is to provide a method of manufacturing a membrane electrode assembly for a fuel cell, each of which has an electrode including a porous electrode catalyst layer on both surfaces of the electrolyte membrane,

a-1) dissolving an inorganic salt in water to prepare an inorganic salt solution;

b-1) A mixture of the metal catalyst, the ionomer and the first solvent is mixed with the solution of the inorganic salt (a-1)

 Preparing a slurry for forming a catalyst layer;

c-1) coating the slurry for forming a catalyst layer on the support film for a transfer film and drying the slurry to form an electrode catalyst layer on the support film to prepare a transfer film for forming a catalyst layer

d-1) transferring the electrode catalyst layer formed on the support film of the transfer film onto the electrolyte membrane, separating and removing the support film therefrom, and transferring the electrode catalyst layer to the electrolyte membrane, Obtaining a membrane (CCM);

(e-1) pre-treating the catalyst coating film (CCM) with a second solvent to form a porous catalyst layer.

Another technical problem of the present invention is

a-2) dissolving an inorganic salt in water to prepare an inorganic salt solution;

b-2) The metal catalyst, the ionomer and the first solvent are mixed with the solution of the inorganic salt a-2)

 Preparing a slurry for forming a catalyst layer;

(c-2) direct coating the catalyst layer onto the membrane by directly coating an electrolyte catalyst layer on the electrolyte membrane to form an electrode catalyst layer on the electrolyte membrane by coating the electrolyte layer with the catalyst layer- step; And

d-2) a step of pre-treating the electrode catalyst layer formed on the electrolyte membrane obtained in the step c-2) with a second solvent to form a porous catalyst layer.

Another technical object of the present invention is achieved by a fuel cell including the membrane electrode assembly described above.

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

The laminated structure of the membrane electrode assembly according to an embodiment of the present invention is as shown in FIG.

1, the direct methanol fuel cell (DMFC) includes an anode 32 to which a fuel is supplied, a cathode 30 to which an oxidizing agent is supplied, and an electrolyte membrane 40 that is disposed between the anode 32 and the cathode 30. [ ). The anode 32 generally comprises an anode diffusion layer 22 and an anode catalyst layer 33 and the cathode 30 comprises a cathode diffusion layer 34 and a cathode catalyst layer 31.

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

The methanol aqueous solution transferred to the catalyst layer 33 of the anode through the diffusion layer 22 of the anode is decomposed into electrons, hydrogen ions, carbon dioxide and the like. The hydrogen ions are transferred to the cathode catalyst layer 31 through the electrolyte membrane 40, the electrons are transferred to the external circuit, and the carbon dioxide is discharged to the outside. In the cathode catalyst layer 31, hydrogen ions transferred through the electrolyte membrane 40, electrons supplied from the external circuit, and oxygen in the air transferred through the cathode diffusion layer 34 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. At this time, the role of the separator means to prevent the unreacted fuel from being transferred to the cathode or the unreacted oxidant to the anode.

As the material of the DMFC electrolyte membrane, a cation exchangeable polymer electrolyte such as a sulfonated highly fluorinated polymer having a main chain composed of fluorinated alkylene and a side chain composed of fluorinated vinyl ether having a sulfonic acid group at the terminal (e.g., Nafion: a product of Dupont) Is used.

 The present invention relates to a membrane electrode assembly for a fuel cell, which is provided with electrodes each including an electrode catalyst layer on both surfaces of an electrolyte membrane, wherein the electrode catalyst layer has an optimal pore size in the catalyst layer for oxygen- And porosity. The electrode catalyst layer is a porous electrode catalyst layer having pores having an average diameter of 3 to 5 nm and a porosity of 40 to 80%.

The electrode catalyst layer of the present invention has excellent oxygen transfer capability and water removal performance due to the above characteristics. If the average diameter of the pores is less than 3 nm, high porosity is achieved and oxygen diffusion is performed. However, since the water discharge is unreliable, the performance of the cell is deteriorated. When the average diameter of the pores exceeds 5 nm, , The oxygen diffusion rate is slow and the performance of the battery is deteriorated.

If the porosity of the electrode catalyst layer according to the present invention is less than 40%, it is difficult to supply and discharge the fuel. If the porosity exceeds 80%, the distance between the catalyst and the ionomer may be distant and hydrogen reaction transfer resistance may increase.

It is further preferable that the electrode catalyst layer of the present invention has a specific surface area of 6 to 10 m ² / g. When the specific surface area of the electrode catalyst layer 6m ² / g is less than if the interface resistance and the electrical resistance of the catalyst layer is reduced, but does not have a specific surface area smaller easy supply and discharge of the fuel 10m exceed ² / g feed and discharge of the fuel is easily However, the ion transporting ability is lowered and the interfacial resistance and electric resistance are increased, which is not preferable.

In the present invention, the average diameter and the specific surface area of the pores of the electrode catalyst layer were measured according to B.E.T. And evaluated by the measurement method. The porosity is a term indicating the ratio of the volume of the pores to the total volume of the electrode catalyst layer, which is evaluated by a porosity meter.

Also, the thickness of the porous electrode catalyst layer is preferably 10-40 mu m, and the amount of catalyst loading is preferably 4-6 mg / cm < ² >. If the thickness of the porous electrode catalyst layer is less than 10 mu m and the amount of catalyst loading is less than 4 mg / cm < 2 >, the electrical resistance is reduced. However, the permeation of the catalyst layer to the fuel is easy and cross- If the thickness of the catalyst layer exceeds 40 μm and the amount of catalyst loading is 6 mg / cm ² , the fuel supply time of the entire catalyst layer becomes long and the reaction efficiency of the catalyst layer becomes low, which is not preferable.

The membrane electrode assembly according to the present invention has a structure in which an electrode including a porous electrode catalyst layer is provided on both surfaces of an electrolyte membrane. The manufacturing process will be described with reference to FIGS.

2A is a schematic flow chart of the present invention using a decal transfer method in which a transfer film for forming an electrode catalyst layer is separately prepared and transferred to an electrolyte membrane to form an electrode catalyst layer, 2b is a schematic flowchart of the present invention using a direct coating method (directly coating the catalyst layer onto the membrane) in which an electrode catalyst layer is formed by directly coating an electrode catalyst layer slurry on an electrode.

FIG. 2C illustrates a CCM and MEA manufacturing process of a direct methanol fuel cell according to an embodiment of the decal transfer method of FIG. 2A according to the present invention.

The manufacturing process of the MEA according to the present invention will be described in detail with reference to the accompanying drawings.

First, an inorganic salt solution is prepared by dissolving an inorganic salt in water. A metal catalyst, a polymer ionomer and a first solvent are mixed with the inorganic salt solution to prepare a slurry for forming an electrode catalyst layer.

The slurry for forming an electrode catalyst layer is coated on a support film 21 for a transfer film and dried to form an electrode catalyst layer 22 on the support film 21 to form a transfer film 20. [ As the support film 21, a polyethylene film (PE film), a Mylar film, a polyethylene terephthalate film, a Teflon film, a polyimide film, a polytetrafluoroethylene film, or the like is used. The method of coating the slurry for forming an electrode catalyst layer is not particularly limited, and a bar coating, a spray coating, a screen printing method, or the like is used.

The electrode catalyst layer 22 formed on the supporting film 21 of the transfer film is transferred onto the electrolyte film 23 and the supporting film 21 is peeled and removed to obtain a catalyst coating film CCM.

Next, the catalyst coating film (CCM) is pretreated with a second solvent to dissolve and remove the inorganic salt to form a porous catalyst layer 22 'on the electrolyte membrane 23.

The second solvent uses an aqueous solution mixture of an acidic solvent and an alcohol. The concentration of the aqueous solution of the acidic solvent and the aqueous solution of the alcohol are each mixed at a concentration of 0.5M to 2M, and the aqueous solution of the acidic solvent and the aqueous solution of the alcohol are mixed at the molar concentration (M) ratio of 3: 0.5 to 1: 1.5. .

The pretreatment is refluxed at a temperature of 80 to 100 DEG C for 2 to 5 hours.

The acidic solvent may be sulfuric acid, nitric acid, hydrochloric acid, nonvolatile organic acid, or the like. As the alcohol, methanol, ethanol, propanol or the like is used, and the acidic solvent and the alcohol can be used in an aqueous solution state.

In the present invention, the inorganic salt constituting the slurry for forming the electrode catalyst layer may contain at least one element selected from the group consisting of Cl ^- , SO4 ^{2 -} , MgSO 4 ^- , MgSO 4 ^- , MgSO 4 ^- , MgSO 4 ^- NO ^{3 -} , and the inorganic salt is preferably used in an amount of 10 to 30 parts by weight per 100 parts by weight of the metal catalyst of the slurry for forming an electrode catalyst layer.

When the content of the inorganic salt is less than 10 parts by weight, the inorganic salt which is a pore forming agent is small in the catalyst layer to make the catalyst layer porous, and if it exceeds 30 parts by weight, pores in the catalyst layer are formed too much and the catalyst layer is collapsed.

The content of water for dissolving the inorganic salt is preferably 250-300 parts by weight based on 100 parts by weight of the inorganic salt.

The metal catalyst may be a conventional Pt or Pt alloy (PtRu) applied to a fuel cell, or a supported catalyst in which the metal catalyst is supported on a separate carrier. As the carrier, for example, a carbon powder, an activated carbon powder, a graphite powder or a powder which is a carbon powder may be used. Specific examples of the activated carbon powder include Vulcan XC-72, Ketjenblack, and the like.

In the slurry for forming an electrode catalyst layer, water, ethylene glycol, isopropyl alcohol, polyalcohol or the like is preferably used as the first solvent, and the content thereof is preferably 250-300 parts by weight based on 100 parts by weight of the metal catalyst.

As the ionomer, a main chain composed of fluorinated alkylene and a sulfonic acid group at the terminal

(For example, Nafion: a trademark of Dupont) having side chains composed of fluorinated vinyl ethers having a number-average molecular weight of from 1,000 to 1,000,000, and all of the polymers having similar properties can be used. The ionomer is dispersed in a solvent of water and alcohol, and the content of the ionomer is preferably 7.5 to 12.5 parts by weight based on 100 parts by weight of the metal catalyst.

A step of laminating a cathode diffusion layer and a backing layer on one side of the pretreated CCM, sequentially stacking an anode diffusion layer and a backing layer on the other side of the CCM, and hot pressing.

When producing a membrane electrode assembly (MEA) of a decal transfer method for transferring to move the electrode catalyst layer to the electrolyte membrane as described above, the hot press conditions are from 100 to 160 ℃ temperature, at a pressure of 0.2 to 0.8tonf / cm ^2, 1 More preferably from 120 to 140 ° C at a pressure of 0.4 to 0.6 tonf / cm ² for 5 to 15 minutes, most preferably at a temperature of 130 ° C to 0.5 tonf / cm 2 It is best to carry out at a pressure of ² for 10 minutes.

In the present invention, the porous catalyst layer may be used either on the cathode or on the anode, or on both the cathode and the anode.

FIG. 2d illustrates a direct methanol fuel cell according to an embodiment of the present invention, in which a slurry for forming an electrode catalyst layer according to the present invention is directly coated on an electrode to form an electrode catalyst layer, CCM and MEA manufacturing processes are emerging.

2C, an inorganic salt solution is prepared by dissolving an inorganic salt in water, and a slurry for forming an electrode catalyst layer is obtained by mixing a metal catalyst, an ionomer and a first solvent. Here, the kind of the inorganic salt and its content, and the composition of the slurry for forming the electrode catalyst layer are the same as in the production method disclosed in Fig. 2C.

Then, the electrode catalyst layer slurry is coated on the electrolyte 23 membrane and dried to form an electrode catalyst layer 22 on the electrolyte membrane 23. Here, the drying is carried out at 100 to 125 ° C, and the drying time is variable for 12 to 24 hours, depending on the drying temperature.

The method of coating the electrode catalyst layer slurry is not particularly limited, and may be bar coating, screen printing, or the like.

Thereafter, the electrode catalyst layer 22 formed on the electrolyte membrane 23 is pretreated with a second solvent as in the manufacturing method shown in FIG. 2C to form a porous catalyst layer 22 'on the electrolyte membrane 23 do.

According to the manufacturing process, the membrane electrode assembly including the electrode including the porous electrode catalyst layer according to the present invention can be manufactured.

When the membrane electrode assembly (MEA) is fabricated by the direct coating method in which the electrode catalyst layer is directly coated on the electrolyte membrane as described above, the hot press condition is a pressure of 0.2 to 0.8 ton / cm ² at a temperature of 100 to 160 ° C, More preferably from 120 to 140 DEG C at a pressure of 0.1 to 0.3 tonf / cm < ² > for 5 minutes to 15 minutes, and most preferably at about 130 DEG C 0.2 tonf / cm ² , m It is best to perform for 10 minutes.

In particular, when a membrane electrode assembly is manufactured by a decal transfer method in which an electrode catalyst layer is transferred to an electrolyte membrane, it is necessary to take the electrolyte membrane and the catalyst layer at a high pressure in order to increase the interface therebetween. (MEA) by direct coating method, the catalyst layer is formed directly on the electrolyte membrane, so that the interface resistance is low, and the porosity of the catalyst layer can be arbitrarily adjusted to have the optimum performance.

The fuel cell is preferably a methanol fuel cell.

Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited thereto.

Example  One ( The catalyst layer On the electrolyte membrane  Warrior moving Decal  When using the judicial method)

A reactor of 20ml 0.4g MgSO ₄ (20 parts by weight based on 100 parts by weight of the catalyst), 1 g of water was added, and MgSO ₄ was completely dissolved. Then, 2 g of Pt-black was added. 1.25 g of a 20 wt% naphthenic solution and 3 g of ethylene glycol (EG) were placed and mixed with a high-speed rotary mixer (Thinky) for 3 minutes to prepare a cathode slurry. This mixing was carried out three times to make the slurry state uniform.

A polytetrafluoroethylene (PTFE) film, which is a supporting film for a transfer film, is placed on a bar-coater equipment on a flat glass plate, and a polyethylene (PTFE) film, which is a mask for patterning the cathode catalyst layer, Film (thickness: 110 mu m). The slurry for forming a cathode catalyst layer obtained in the above procedure was poured in two portions on the resultant product, and then the bar-coater was slowly moved to prepare a uniform cathode catalyst layer on the support film for the transfer film covered with the mask . The resultant was dried in a vacuum oven at 120 캜 for 24 hours to form a transfer film for forming a cathode catalyst layer Prepared.

Separately, a transfer film for forming an anode catalyst layer was prepared according to the following procedure.

2 g of PtRu-black, 1.25 g of 20 wt% Nafion solution and 3 g of ethylene glycol (EG) were placed in a 20 mL reactor, and the mixture was mixed with a high-speed rotary mixer (Thinky) for 3 minutes to prepare an anode-forming slurry. This mixing was carried out three times to make the slurry state uniform. The loading amount of the anode catalyst is adjusted to be in the range of 5 to 6 mg / cm < ^{2 &} gt ;.

A polytetrafluoroethylene (PTFE) film as a supporting film for a transfer film was placed on a flat glass plate, and a polyethylene film (thickness: 110 μm) as a mask for patterning the anode catalyst layer was coated on a predetermined region of the PTFE film. The anode catalyst layer-forming slurry obtained in the above procedure was poured in two portions on the resultant product, and then the bar-coater was slowly moved to prepare a uniform anode catalyst layer on the supporting film for the transfer film covered with the mask . The resultant was dried in a vacuum oven at 120 캜 for 24 hours to prepare a transfer film for forming an anode catalyst layer

Placing an anode catalyst layer transfer for the transfer film and the cathode catalyst layer to form a film obtained according to the process of the electrolyte membrane on both sides and transferring the anode catalyst layer and cathode catalyst layer to the electrolyte membrane in 130 ℃, 0.5ton / cm ^2, the conditions of 10min Then, the polyethylene film as the support film was peeled off from the cathode catalyst layer and the anode catalyst layer.

Then, the resultant was refluxed at 95 ° C. for 4 hours using a mixture of 500 g of 1 M aqueous sulfuric acid solution and 500 g of 1 M aqueous methanol solution to pre-treat the CCM.

After the pretreated CCM was dried with a gel-dryer, the cathode diffusion layer, the backing layer, the anode diffusion layer, and the backing layer were attached to the cathode catalyst layer and the anode catalyst layer, respectively, followed by hot pressing to complete the MEA.

Example  2( The catalyst layer On the electrolyte membrane  Decal transfer method of  When used)

0.3g MgSO ₄ (15 parts by weight based on 100 parts by weight of the catalyst) and 1 g of water were added to completely dissolve MgSO _{4. Thus} , an MEA was completed.

Example  3 ( The catalyst layer On the electrolyte membrane  Directly coated direct  Coating method)

After the same slurry as in Example 1 was prepared, a Nafion-115 membrane (Nafion Corp.) was placed on a vacuum plate on a bar-coater equipped with a vacuum device, and a cathode catalyst layer And a polyethylene film (thickness: 110 mu m) which is a mask for patterning is covered.

The slurry for forming the cathode catalyst layer obtained in the above procedure was poured in two portions on the resultant product, and then the bar-coater was slowly moved to prepare a uniform cathode catalyst layer on the electrolyte membrane covered with the mask. The resultant was dried in a vacuum oven at 120 캜 for 24 hours to coat the cathode catalyst layer directly on the electrolyte membrane. After the cathode catalyst layer coating is completed, the same anode slurry as in Example 1 is prepared and directly coated and dried on the electrolyte membrane in the same manner as above.

The PTFE film was placed on both sides of the obtained CCM, and the CCM was subjected to hot pressing under the conditions of 120 ° C, 0.1 ton / cm ² , and 10 minutes, and the film was peeled and removed.

The following procedure is followed by the same procedure as in Example 1 to prepare an MEA.

Example  4 ~ Example  11: The catalyst layer On the electrolyte membrane  Directly coated direct  When coating method is used

An MEA was prepared in the same manner as in Example 3 except that the CCM hot-press conditions were changed as shown in Table 1 below.

Comparative Example  One

The MEA was completed in the same manner as in Example 1, except that MgSO ₄ was not included in the formation of the cathode catalyst layer.

 [Table 1]

CCM manufacturing method
MgSO4 g / catalyst g Hot press condition Power density (mW / cm ² )
Active cell
(0.3 V, 50 < 0 > C)
Temperature (℃) pressure
(Tonf / cm2) Comparative Example 1 Decal transfer method

0 130 0.5 62.2 Example 1 0.2 130 0.5 67.5 Example 2 0.15 130 0.5 65.3 Example 3 Direct coating method







0.2 120 0.1 96.5 Example 4 0.2 120 0.2 92.9 Example 5 0.2 120 0.3 80.7 Example 6 0.2 130 0.1 83.4 Example 7 0.2 130 0.2 95.6 Example 8 0.2 130 0.3 66.3 Example 9 0.2 140 0.1 86.6 Example 10 0.2 140 0.2 62.3 Example 11 0.2 140 0.3 82.5

Referring to Table 1, the power density was improved in the case of Example 1 and Example 2 by the decal transfer method in which the catalyst layer was transferred to the electrolyte membrane, as compared with Comparative Example 1. In the case of Examples 3 to 11 by the direct coating method in which the catalyst layer was directly coated on the electrolyte membrane, high power density was obtained even when the hot press was performed at a lower pressure than in the case of Example 1-2, 130 ° C and 0.2ton _f / cm ² , respectively.

This is because the thickness of the catalyst layer formed by the direct coating method in which the catalyst layer is directly coated on the electrolyte membrane is about three times thicker than the decal transfer method in which the catalyst layer is transferred to the electrolyte membrane, This is because emissions are desirable.

 [Table 2]

Sample Specific surface area (m 2 / g) ^a Porosity (%) ^b Average diameter of pores (nm) Example 1 8.25 46.5 3 Example 2 6.75 40.12 3 Example 3 9.15 77.14 3 Example 7 9.03 77.01 3 Comparative Example 1 4.95 26.1 N / A

※ a: measurement of BET method, b: measurement of porositimeter.

It can be seen from Table 2 that in the case of Example 1 and Example 2 in which MgSO ₄ of the present invention was added to form pores in the catalyst layer, 78% to 54% of the porosity of the comparative example in which MgSO ₄ was not added was increased by 78% Respectively. As shown in FIG. 3, in Examples 1, 2, 3, and 7, the average pore diameter was uniformly formed to 3 nm due to MgSO ₄ used as a pore-forming agent. On the other hand, in Comparative Example 1 in which the pore-forming agent is not present, the distribution of the total pores is widely distributed.

In addition, the porosity of the catalyst layer directly coated on the electrolyte membrane (Examples 1 and 2) was 70% or more higher than that of the catalyst layers formed by the decal transfer method with the same amount of catalyst loading (Examples 3 and 7). This is because of the advantage of the direct coating method which can bring the porosity to a high level while reducing the interfacial resistance of the electrolyte membrane. This can play a key role in greatly improving performance.

The prepared MEA was supplied with 1M methanol to the anode at a flow rate of 0.3 lmL / min · A and supplied with air at 52.5 mL / min · A to the cathode. The temperature of the cell was 50 ° C, The results of electrochemical analysis at 0.35 V are shown in FIG. 4 and Table 3 below.

[Table 3]

Sample The loading amount of the catalyst
(mg / cm ²⁾ The thickness of the catalyst layer
(탆) Single cell test
(Single cell test)
(mW / cm ² ) Comparative Example 1 5.23 12 62.2 Example 1 5.12 15 67.5 Example 2 5.10 15 64.3 Example 3 5.14 35 96.5 Example 7 5.11 33 95.6

As can be seen from FIG. 4 and Table 3, Example 1-2, in which MgSO ₄ was used as a pore-forming agent, showed a loading of 67.5 mW / cm ² And 64.3 mW / cm < ² >, respectively. However, Comparative Example 1 in which the pore-forming agent was not used showed a performance of 62.2 mW / cm < ² >. As described above, it has been found that the formation of pores in the cathode catalyst layer using MgSO ₄ as the pore former makes the reduction reaction of oxygen excellent and facilitates the discharge of water as a by-product.

In Examples 3 and 7 in which the porosity of the catalyst layer was increased by the direct coating method, the interfacial resistance and the supply and discharge of the fuel were facilitated to improve the reaction efficiency and the performance was greatly improved, compared with Examples 1 and 2 by the decal method Able to know.

According to the present invention, the electrode catalyst layer is made porous to improve the oxygen reduction reaction, to facilitate the discharge of water as a by-product, to reduce the amount of the noble metal catalyst to be used, The efficiency is stabilized and the efficiency of the fuel cell is improved.

1 is a view showing a laminated structure of a membrane electrode assembly according to the present invention,

2A is a schematic flow diagram of a decal transfer method for transferring an electrode catalyst layer according to the present invention to an electrolyte membrane

FIG. 2B is a schematic flow diagram of a direct coating method (directly coating the catalyst layer onto the membrane) in which the electrode catalyst layer according to the present invention is directly coated on the electrolyte membrane,

2C shows a specific manufacturing process for the decal transfer method according to the present invention,

FIG. 2D shows a specific manufacturing process for the direct coating method according to the present invention,

3 shows the pore distribution and specific surface area of the electrode catalyst layer of the decal transfer method according to the present invention,

4A and 4B are graphs showing the I-V curve and the power density with time in a fuel cell employing the cathode catalyst manufactured according to Example 1, Example 2 and Comparative Example 1 of the present invention,

5A and 5B are graphs showing power densities of fuel cells manufactured according to the hot press conditions (temperature, pressure) of Examples 3 to 11, in which a catalyst layer is directly coated on the electrolyte membrane according to the present invention.

Claims (24)

1. A membrane-electrode assembly for a fuel cell comprising an electrolyte membrane and electrodes each including an electrode catalyst layer on both surfaces thereof, The electrode catalyst layer, Wherein the membrane electrode assembly is a porous electrode catalyst layer having an average diameter of 3 to 5 nm and a porosity of 40 to 80% and a specific surface area of 6.75 to 9.15 m ² / g. delete The membrane electrode assembly for a fuel cell according to claim 1, wherein the porous electrode catalyst layer has a thickness of 10-40 μm and the loading amount of the catalyst is 4-6 mg / cm ² . 1. A method of manufacturing a membrane electrode assembly for a fuel cell, the method comprising the steps of: a-1) preparing an inorganic salt solution by dissolving at least one inorganic salt selected from magnesium sulfate, magnesium chloride, magnesium nitrate, calcium chloride, calcium sulfate and calcium nitrate in water; b-1) mixing a metal catalyst, an ionomer and a first solvent in the solution of the inorganic salt of a-1) to prepare a slurry for forming a catalyst layer; c-1) coating the slurry for forming a catalyst layer on the support film for a transfer film and drying the slurry to form an electrode catalyst layer on the support film to prepare a transfer film for forming a catalyst layer; d-1) transferring the electrode catalyst layer formed on the support film of the transfer film to the electrolyte membrane, and peeling and removing the support film therefrom to obtain a catalyst coating film (CCM); (e-1) pre-treating the catalyst coating film (CCM) with a second solvent to form a porous catalyst layer. 5. The method according to claim 4, wherein the pretreatment is carried out by refluxing at a temperature of 80 to 100 占 폚.  The method of claim 4, further comprising the steps of: (f-1) laminating a cathode diffusion layer and a backing layer on one side of the pre-treated CCM, laminating an anode diffusion layer and a backing layer on the other side of the CCM, (MEA) for a fuel cell according to any one of the preceding claims. The method of manufacturing a membrane electrode assembly (MEA) for a fuel cell according to claim 6, wherein the hot press is performed at a temperature of 120 to 140 캜 at a pressure of 0.4 to 0.6 ton / cm ² . delete 5. The method according to claim 4, wherein the inorganic salt is 10-30 parts by weight based on 100 parts by weight of the metal catalyst of the catalyst layer-forming slurry. The method for producing a membrane electrode assembly (MEA) for a fuel cell according to claim 4, wherein the porous catalyst layer has pores having an average diameter of 3 to 5 nm. The method for producing a membrane electrode assembly (MEA) for a fuel cell according to claim 4, wherein the porosity of the porous catalyst layer is 40 to 80%. 5. The method according to claim 4, wherein the thickness of the porous electrode catalyst layer is 10-40 mu m and the loading amount of the catalyst is 4-6 mg / cm < ² >.  The method according to claim 4, wherein the second solvent is a mixture of an acidic solvent and an alcohol.  14. The method according to claim 13, wherein the acidic solvent is at least one selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, and nonvolatile organic acids or an aqueous solution thereof. 14. The method according to claim 13, wherein the acidic solvent and the alcohol are mixed at a molar ratio (M) of 3: 0.5 to 1: 1.5.  5. The method of claim 4, wherein the porous catalyst layer is at least one selected from the group consisting of a cathode catalyst layer and an anode catalyst layer. 1. A method of manufacturing a membrane electrode assembly for a fuel cell, comprising the steps of: a-2) dissolving at least one inorganic salt selected from magnesium sulfate, magnesium chloride, magnesium nitrate, calcium chloride, calcium sulfate and calcium nitrate in water to prepare an inorganic salt solution; b-2) mixing a metal catalyst, an ionomer and a first solvent in the solution of the inorganic salt (a-2) to prepare a slurry for forming a catalyst layer; c-2) coating the slurry for forming a catalyst layer on the electrolyte membrane and drying the slurry to form an electrode catalyst layer on the electrolyte membrane; And d-2) pre-treating the electrode catalyst layer formed on the electrolyte membrane obtained in the step c-2) with a second solvent to form a porous catalyst layer. 18. The method according to claim 17, wherein the pre-treatment is refluxed at a temperature of 80 to 100 占 폚.  18. The method according to claim 17, further comprising the steps of: e-2) laminating a cathode diffusion layer and a backing layer on one surface of the porous catalyst layer, d-2) laminating an anode diffusion layer and a backing layer on the other surface of the porous catalyst layer, (MEA) for a fuel cell, characterized by further comprising the step of hot-pressing the membrane electrode assembly (MEA). The method of manufacturing a membrane electrode assembly (MEA) for a fuel cell according to claim 19, wherein the hot press is performed at a temperature of 120 to 140 캜 and a pressure of 0.1 to 0.3 ton / cm ² .  18. The method for producing a membrane electrode assembly (MEA) for a fuel cell according to claim 17, wherein the second solvent is a mixture of an acidic solvent and an alcohol. 22. The method of claim 21, wherein the acidic solvent and the alcohol are mixed at a molar ratio (M) of 3: 0.5 to 1: 1.5.  18. The method of manufacturing a membrane electrode assembly (MEA) for a fuel cell according to claim 17, wherein the porous catalyst layer is at least one of a cathode catalyst layer and an anode catalyst layer. A fuel cell comprising the membrane electrode assembly according to claim 1 or 3.

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