KR102287808B1 - Membrane electrode assembly comprising water retaining layer and fuel cell using the same - Google Patents

Abstract

Disclosed are a catalyst slurry, an electrode manufactured using the same, a membrane electrode assembly including the electrode, and a fuel cell including the membrane electrode assembly. The catalyst slurry may include a catalyst material, a binder resin, inorganic particles having an ionic group, and a hydrophilic oligomer; and solvents.

Description

Membrane electrode assembly comprising a moisturizing layer and a fuel cell comprising the same

It relates to a membrane electrode assembly and a fuel cell including the same.

A fuel cell is a power generation device that directly converts the chemical energy of hydrogen and oxygen in the air, which can be obtained from hydrocarbon-based substances such as natural gas, methanol, and ethanol, into electrical energy, and has high efficiency and high energy density. Such a fuel cell is a clean energy source that can replace fossil energy, has various driving temperatures depending on the choice of electrolyte, and has the advantage of being able to output a wide range of outputs in a stack configuration in which unit cells are stacked. Therefore, fuel cells are attracting attention as an energy source that can be applied in a variety of ways from small and portable power sources to large-scale power generation.

Representative examples of the fuel cell include a polymer electrolyte fuel cell (PEMFC: Polymer Electrolyte Membrane Fuel Cell or Proton Exchange Membrane Fuel Cell) and a direct methanol fuel cell (DMFC: Direct Methanol Fuel Cell). The fuel cell uses a polymer membrane capable of conducting hydrogen ions as an electrolyte.

Such a fuel cell system has a stack structure in which several to hundreds of membrane electrode assemblies (MEA) are connected in series by a bipolar plate. Among them, the membrane electrode assembly, which can be said to be the core of fuel cell technology, has an anode electrode (called “fuel electrode” or “oxidation electrode”) and a cathode electrode (aka, It has a structure in which the "air electrode" or "reduction electrode") is located.

The principle of generating electricity in a fuel cell is as follows. Fuel is supplied to the anode electrode, which is the anode electrode, and is adsorbed to the catalyst of the anode electrode and then oxidized to generate hydrogen ions and electrons. At this time, the generated electrons reach the cathode electrode, which is a reduction electrode, along an external circuit, and hydrogen ions pass through the polymer electrolyte membrane and are transferred to the cathode electrode. Oxygen is supplied to the cathode electrode, and the oxygen, hydrogen ions, and electrons react on the catalyst of the cathode electrode to generate water while generating electricity.

In order to increase the conductivity of hydrogen ions, it is preferable that the water content of the electrolyte membrane is high. On the other hand, in order to obtain high output, it is desirable to operate the fuel cell at a medium temperature of about 120°C. At this temperature, the humidity of the fuel cell is lowered to about 40% or less, so that the output is lowered. Therefore, a membrane electrode assembly capable of obtaining high output under medium temperature and low humidity (120° C., humidity of 40% or less) is required.

One object is to provide a membrane electrode assembly for a fuel cell that can ensure excellent performance even in a low-humidity environment by increasing the water content in the catalyst layer and the electrolyte membrane.

Another object is to provide a fuel cell having excellent performance using the membrane electrode assembly for a fuel cell.

One aspect provides a membrane electrode assembly including a cathode, an anode, and an electrolyte membrane interposed therebetween.

The cathode and the anode may each include a catalyst layer in contact with the electrolyte membrane, a moisturizing layer in contact with the catalyst layer and having hygroscopicity, and a gas diffusion layer in contact with the moisturizing layer.

The moisturizing layer may include porous carbon and a moisture absorption material.

The BET specific surface area of the moisturizing layer is larger than the BET specific surface area of the catalyst layer.

The surface of the porous carbon of the moisture-retaining layer includes -OH groups, and the surface oxygen-to-carbon concentration ratio of the moisture-retaining layer is greater than the surface oxygen-to-carbon concentration ratio of the catalyst layer.

The moisture absorption material may include silica or metal phosphate.

Another aspect provides a fuel cell in which a plurality of the above-described membrane electrode assemblies are connected by a bipolar plate.

By introducing a moisture-absorbing layer having hygroscopicity between the catalyst layer and the gas diffusion layer, the water content in the catalyst layer and the electrolyte membrane is increased, thereby improving the conductivity of the catalyst layer and the electrolyte membrane, thereby providing a fuel cell having excellent performance.

1 is a schematic cross-sectional view of a membrane electrode assembly (MEA) according to an embodiment.
2 is an exploded perspective view illustrating a structure of a fuel cell according to an exemplary embodiment.
3 is a graph of measuring the pore distribution of the membrane electrode assemblies of Example 6 and Comparative Example 1. Referring to FIG.
FIG. 4 is a graph of measuring cell voltage versus current density of unit cells of Examples 1, 3, 4, 6 and Comparative Example 1. FIG.
5 is a graph of measuring AC impedance of unit cells prepared in Examples 3 and 6 and Comparative Example 1. FIG.
6 is a graph of measuring the ohmic overvoltage of the unit cells prepared in Examples 1 to 5 and Comparative Example 1. Referring to FIG.

As used herein, "low relative humidity" means relative humidity in the range greater than 0% and less than or equal to about 80%.

As used herein, the term “ionic group” refers to a functional group having ionicity, such as a sulfonic acid group or a carboxylic acid group.

As used herein, the term “moisture content” refers to a property capable of containing moisture due to high affinity for moisture.

As used herein, the term “pore volume” refers to the volume of pores having a pore diameter of 30 nm or less, for example, 0.1 to 30 nm, and is measured using a mercury porosimeter.

Hereinafter, a fuel cell and a membrane electrode assembly according to embodiments will be described in detail.

1 is an exploded perspective view illustrating an embodiment of a fuel cell.

Referring to FIG. 1 , in the fuel cell 100 , two unit cells 11 are sandwiched by a pair of holders 12 . The unit cell 11 is composed of a membrane electrode assembly 10 and a bipolar plate 20 disposed on both sides of the membrane electrode assembly 10 in the thickness direction. The bipolar plate 20 may be made of conductive metal or carbon. The bipolar plate 20 functions as a current collector by bonding to the membrane electrode assembly 10 , and includes a channel, so that fuel and oxygen can be supplied to the catalyst layer of the membrane electrode assembly 10 .

Although two unit cells 11 are illustrated in the fuel cell 100 of FIG. 1 , the number of unit cells is not limited to two, and may be increased to several tens or hundreds depending on characteristics required for the fuel cell.

FIG. 2 is a schematic cross-sectional view of a membrane electrode assembly (MEA) according to an embodiment constituting the fuel cell of FIG. 1 .

Referring to FIG. 2 , the membrane electrode assembly 10 includes an electrolyte membrane 1 , a catalyst layer 5 disposed on both sides in the thickness direction of the electrolyte membrane 1 , a moisture retention layer 8 on the catalyst layer 5 , and a gas a diffusion layer (9). The catalyst layer 5, the moisture-retaining layer 8 and the gas diffusion layer 9 on one side constitute the anode, and the catalyst layer 5, the moisture-retaining layer 8 and the gas diffusion layer 9 on the other side constitute the cathode. .

The electrolyte membrane 1 is made of an ion conductive polymer. ^{Hydrogen ions (H +} ) generated by ionization of fuel in the catalyst layer 5 of the anode pass through the electrolyte membrane 1 and are transferred to the catalyst layer 5 of the cathode.

The electrolyte membrane 1 is not particularly limited, but for example, poly(perfluorosulfonic acid), poly(perfluorocarboxylic acid), tetrafluoroethylene containing a sulfonic acid group, and fluorovinyl ether Copolymer, defluorinated sulfurized polyetherketone, aryl ketone, poly(2,2'-m-phenylene)-5,5'-bibenzimidazole (Poly(2,2'-(m-phenylene)- At least one polymer electrolyte membrane selected from the group consisting of 5,5'-bibenzimidazole), poly(2,5-benzimidazole), and copolymers thereof may be used.

Since the polymer electrolyte has a hydrophilic group such as a sulfonic acid group, a hydrophilic region is formed by the hydrophilic group. In this hydrophilic region, the attractive force between the hydrogen ion and the sulfonic acid group is relatively weak, so that the hydrogen ion can freely move with water. As the water content in the polyelectrolyte decreases, the electrical conductivity decreases generally linearly.

The catalyst layer 5 is a layer functioning as an anode (anode electrode) and an oxygen electrode (cathode electrode). The catalyst layer 5 may include catalyst materials 2 and 3 and a binder resin 4 .

The catalyst material may include a carrier 3 and a catalyst metal 2 supported thereon. The carrier 3 may include carbon powder, carbon black, acetylene black, Ketjen black, activated carbon, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanohorn, carbon airgel, carbon crerogel or carbon nanoring. It may be a carbon-based carrier, and may include two or more of them. The carbon-based carrier may have an average diameter in the range of, for example, 20 nm to 50 nm.

The catalyst metal 2 is platinum (Pt), iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), ruthenium (Ru), rhodium (Rh), iridium (Ir), osmium (Os) ), copper (Cu), silver (Ag), gold (Au), tin (Sn), titanium (Ti), chromium (Cr), platinum (Pt)-palladium (Pd) alloy, platinum (Pt)-ruthenium ( Ru) alloy, platinum (Pt)-iridium (Ir) alloy, platinum (Pt)-osmium alloy, platinum (Pt)-M alloy (M is Ti, V, Cr, Mo, W, Mn, Fe, Co, Rh) , Ni, Cu, Ag, Au, Zn, at least one selected from the group consisting of Ga and Sn) or a combination thereof may include at least one selected from the group consisting of, but is not limited thereto. The catalyst metal 2 may be nanoparticles having an average particle diameter of 10 nm or less. If the particle size is greater than 10 nm, the surface area of the particle may be too small, resulting in low activity. For example, the average particle diameter of the catalyst metal particles may be 2 nm to 10 nm or 3 nm to 8 nm.

The catalyst materials 2 and 3 may be, for example, a platinum-based catalyst supported on a carbon-based carrier. The catalyst materials 2 and 3 may be, for example, an alloy of platinum and cobalt (PtCo/C) supported on carbon powder.

The binder resin 4 may be a hydrogen ion conductive polymer resin. Representative examples of the hydrogen ion conductive polymer resin include fluoro-based polymers, benzimidazole-based polymers, polyimide-based polymers, polyetherimide-based polymers, polyphenylene sulfide-based polymers, polysulfone-based polymers, polyethersulfone-based polymers, and polyether ketone-based polymers, polyether-etherketone-based polymers, polyphenylquinoxaline-based polymers, and copolymers thereof. Specifically, the hydrogen ion conductive polymer resin is poly(perfluorosulfonic acid), poly(perfluorocarboxylic acid), a copolymer of tetrafluoroethylene and fluorovinyl ether containing a sulfonic acid group, defluorinated sulfided polyether Ketones, aryl ketones, poly(2,2'-m-phenylene)-5,5'-bibenzimidazole (Poly(2,2'-(m-phenylene)-5,5'-bibenzimidazole), poly (2,5-benzimidazole) or a copolymer thereof.

The catalyst layer 5 may have, for example, a volume of 20-100 nm pores of 0.03-0.06 mL/g.

The catalyst layer 5 may have a thickness of, for example, 1 μm to 100 μm, 5 μm to 80 μm, or 10 μm to 60 μm to effectively activate the electrode reaction and not excessively increase the electrical resistance.

The moisture-retaining layer 8 may supply moisture contained in the moisture-retaining layer 8 to the catalyst layer 5 . The moisture-retaining layer 8 includes a porous material 6 and a moisture-absorbing material 7 . The porous material 6 is, like the carbon-based carrier, carbon powder, carbon black, acetylene black, Ketjen black, activated carbon, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanohorn, carbon airgel, carbon crerogel, or It may be a carbon-based material having good electrical conductivity, such as carbon nanoring, and may include two or more of them. The porous material 6 of the moisturizing layer 8 may be, for example, mesoporous carbon.

The content of the porous material of the moisturizing layer may be, for example, 0.2-2 mg/cm ² or 0.5-1.5 mg/cm ² . On the other hand, the porous material 6 of the moisturizing layer 8 has a larger surface area and a larger pore size than the carrier 3 of the catalyst layer 5 . The larger the surface area, the more water can be adsorbed on the surface, and the larger the pore size, the smoother the supply of gas and moisture to the catalyst layer 5 .

The BET specific surface area of the moisturizing layer 8 is larger than the BET specific surface area of the catalyst layer, and the BET specific surface area of the moisturizing layer may be, ^{for example, 400-1,000 m 2} /g or 500-800 m ^{2 /g.} In the porous material 6 of the moisturizing layer 8, about 20-80% of the pores may have a pore size of, for example, 100-500 nm or 100-300 nm. When the BET specific surface area and pore size of the moisturizing layer 8 have the above ranges, the supply of gas and moisture may be smooth.

On the other hand, the surface of the porous material 6 of the moisture-retaining layer 8 may include -OH groups, which may increase the moisture content of the moisture-retaining layer 8 . The -OH group on the surface of the porous material 6 may be generated, for example, by irradiating the surface of the porous material 6 with UV in the presence of oxygen. Therefore, the surface oxygen-to-carbon concentration ratio of the moisturizing layer 8 is greater than the surface oxygen-to-carbon concentration ratio of the catalyst layer 5 . The surface oxygen to carbon concentration ratio of the porous material 6 of the moisturizing layer 8 may be, for example, 0.1-0.5 or 0.2-0.4.

Since the moisture-absorbing material 7 has water absorbing power, it is possible to further improve the moisture-retaining ability of the moisture-absorbing layer 8 . The moisture-absorbing material 7 may be 1-20% by weight or 5-15% by weight based on the total weight of the moisture-retaining layer 8 . The size (diameter) of the moisture absorbing material 7 may be 2-30 nm or 10-20 nm. The moisture absorption material 7 may include silica or metal phosphate. Metal phosphates may include, for example, zirconium phosphate, tin phosphate or tungsten phosphate.

The gas diffusion layer 9 is porous so that the fuel and oxygen supplied through the bipolar plate (20 in FIG. 1) can be diffused to the front of the catalyst layer 5, and water formed in the catalyst layer 5 can be quickly discharged. It is advantageous. In addition, in order to transmit the current generated in the catalyst layer 5, it is necessary to have electrical conductivity.

The gas diffusion layer 9 may include a microporous layer (not shown) and a support (not shown). The support (not shown) may be an electrically conductive material such as a metal or a carbon-based material. For example, the support may use a conductive substrate such as carbon paper, carbon cloth, carbon felt, or metal cloth, but is not limited thereto.

The microporous layer (not shown) is generally a conductive powder having a small particle size, for example, carbon powder, carbon black, acetylene black, Ketjen black, activated carbon, carbon nanotube, carbon nanofiber, carbon nanowire, carbon nanohorn, It may be made of carbon airgel, carbon crerogel, carbon nanoring or fullerene. If the particle size of the conductive powder constituting the microporous layer (not shown) is too small, the pressure drop may be severe and diffusion of gas into the catalyst layer may be insufficient. If the particle size is too large, uniform diffusion of the gas may be difficult. Therefore, in consideration of the gas diffusion effect, conductive particles having an average particle diameter in the range of generally 10 nm to 50 nm may be used.

The gas diffusion layer 9 may be prepared by using a commercial product, or by directly coating a microporous layer (not shown) thereon after purchasing only carbon paper. In the micropore layer (not shown), gas diffusion occurs through the pores formed between the conductive particles, and the average pore size of these pores is not particularly limited. For example, the average pore size of the microporous layer (not shown) may be in the range of 1 nm to 1 mm, or in the range of 10 nm to 800 μm, in the range of 100 nm to 600 μm, or in the range of 1 μm to 400 μm. In some cases, the microporous layer (not shown) may be omitted.

The thickness of the gas diffusion layer 9 may be, for example, in the range of 100 μm to 500 μm, 150 μm to 450 μm, or 200 μm to 400 μm in consideration of gas diffusion effects and electrical resistance.

Protons (hydrogen ions) generated by oxidation of fuel in the fuel cell move from the anode electrode to the cathode electrode. At this time, the protons (hydrogen ions) form ions with water and move. Therefore, since a sufficient amount of moisture can be present in the electrolyte membrane and the electrode of the fuel cell for a smooth reaction to occur, the fuel cell is generally operated in a high-humidity environment close to 100%. However, in such a high-humidity environment, there may be a problem that the gas circulation inside the catalyst layer is not smooth, so the necessity of driving the fuel cell in a low-humidity environment is increasing. However, the movement of protons (hydrogen ions) may not be smooth at low humidity.

In this embodiment, by introducing a moisturizing layer between the catalyst layer and the gas diffusion layer, the moisture content of the membrane electrode assembly can be improved, so that protons (hydrogen ions) can move smoothly in a low humidity environment.

The fuel cell may be driven, for example, at a driving temperature of 60-250° C. and a relative humidity of 0-80%.

The fuel cell may be, for example, a hydrogen ion exchange membrane fuel cell (PEMFC), a direct methanol fuel cell (DMFC), or a phosphoric acid fuel cell (PAFC). The structure and manufacturing method of such a fuel cell are not particularly limited, and specific examples are well known in various documents, and thus will not be described in detail herein.

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

Example One

(a) Preparation of catalyst coated membrane

Pt-supported carbon catalyst (Pt/C) (Tanaka Co.) and ionomer (Aquivion™ R79-20BS) (molar equivalent 790 g/mol SO ₃ H, weight of polymer per mole of sulfuric acid) were mixed at a weight ratio of 7:3 (Pt/C) : A catalyst layer slurry containing ionomer) was printed on a PTFE (polytetrafluoroethylene) sheet to form a catalyst layer on two PTFE. Two catalyst layers on PTFE were transferred to both sides of an electrolyte membrane (Aquivion™ R79-02S) (molar equivalent: 790 g/mol SO ₃ H) having a thickness of 20 μm, respectively, to form a catalyst coating membrane consisting of a catalyst layer/electrolyte membrane/catalyst layer. At this time, the Pt content in each catalyst layer was 0.4 mg/cm ² , the formation area of the ^{catalyst layer was 10 cm 2} , and the thickness of the catalyst layer was 15 μm.

(b) formation of a moisturizing layer

A moisturizing layer slurry containing 0.5 mg/cm ² of mesoporous carbon (surface area 670 m ² /g, particle size 100-1000 nm) and 5% by weight of PVDF binder was printed on a PTFE sheet and placed on two PTFE sheets. of the moisture layer was formed. The moisture-retaining layers on the two PTFE were transferred to both sides of the catalyst coating film, respectively, to form a moisture-retaining layer with a thickness of 10 μm on both sides of the catalyst coating film.

(c) Preparation of membrane electrode assembly and unit cell

The electrolyte membrane, in which the catalyst layer and the moisturizing layer are bonded on both sides, is inserted between two sheets of carbon paper serving as a gas diffusion layer and the gasket, and then inserted between the two carbon plates having gas flow channels of a certain shape. An electrode assembly was formed. And this was fastened using a SUS end plate to manufacture a unit cell.

Example 2

A membrane electrode assembly and a unit cell were prepared in the same manner as in Example 1, except that a moisturizing layer further containing 2 wt% silica was used.

Example 3

If a meso content of the porous carbon moisturizing layer using a 0.5 mg / cm ² instead of 0.6 mg / cm ^2, and except for using a 9 wt% instead of 2% by weight of silica moisturizing layer, using the same method as in Example 2 Thus, a membrane electrode assembly and a unit cell were prepared.

Example 4

If a meso content of the porous carbon moisturizing layer using a 0.5 mg / cm ² instead of 0.6 mg / cm ^2, and except for using 13 wt% instead of 2% by weight of silica moisturizing layer, using the same method as in Example 2 Thus, a membrane electrode assembly and a unit cell were prepared.

Example 5

A membrane electrode assembly and a unit cell were prepared in the same manner as in Example 2, except that 1 mg/cm ^{2 was used instead of 0.5 mg/cm 2} for the mesoporous carbon content of the moisturizing layer.

Example 6

The same method as in Example 2 was used, except that 1 mg/cm ^{2 was used instead of 0.5 mg/cm 2} for the content of mesoporous carbon in the moisture layer, and 9 wt % of the silica of the moisture layer was used instead of 2 wt %. Thus, a membrane electrode assembly and a unit cell were prepared.

comparative example One

A membrane electrode assembly and a unit cell were prepared in the same manner as in Example 1, except that the moisturizing layer was not used.

Table 1 shows the mesoporous carbon content and silica content of the moisturizing layers of Examples 1 to 6 and Comparative Example 1.

pore distribution measurement

FIG. 3 is a graph of measuring the pore distribution of the membrane electrode assemblies of Example 6 and Comparative Example 1. FIG. The distribution of pores was measured using the method of a mercury porosimeter.

Referring to the graph of FIG. 3 , the pore size distribution of Example 6 has a distribution of a small peak of about 10-50 nm and a large peak of 100-500 nm, whereas the pore size of Comparative Example 1 has only a peak of about 10-50 nm. has a distribution of The size of 100-500 nm in the pore distribution of Example 6 is due to the pores of the moisturizing layer. The space between the mesoporous carbon particles contributes to the pores of 100-500 nm to facilitate the supply of gas and moisture. The mesoporous pores in the mesoporous carbon particles can increase the surface area of the mesoporous carbon particles to increase the amount of moisture adsorption.

evaluation example

For the unit cells prepared in Examples 1 to 6 and Comparative Example 1, after supplying hydrogen to the anode electrode side and air to the cathode electrode side, respectively, at a temperature of 120° C. and a relative humidity of 40%, power density (power density) ) was measured. At this time, the pressure was 0.7 bar, the flow rate of hydrogen was 52 sccm, and the flow rate of air was 200 sccm. The results are shown in FIG. 4 and Table 1 below.

Mesoporous carbon content (mg/cm ² ) Silica content
(weight%) power density
(mW/cm ² @0.7V ) Example 1 0.5 0 160 Example 2 0.5 2 unmeasured Example 3 0.6 9 210 Example 4 0.6 13 170 Example 5 One 2 unmeasured Example 6 One 9 180 Comparative Example 1 0 0 150

Referring to Table 1, it was found that the output density of the unit cells of Examples 1 to 6 using the moisturizing layer was higher than that of Comparative Example 1 in which the moisturizing layer was not used. In addition, the output density of the unit cells of Examples 3, 4 and 6 containing silica was higher than that of Example 1 without silica.

4 is a graph of measuring cell potential with respect to current density of the unit cells of Examples 1, 3, 4, 6, and Comparative Example 1. FIG. As shown in FIG. 4 , the cell potential of the unit cell was large in the order of Example 3, Example 6, Example 4, Example 1, and Comparative Example 1. This is considered to be because the greater the moisture retention of the moisture-retaining layer, the higher the moisture content of the electrolyte membrane, thereby improving the hydrogen ion conduction characteristics, thereby improving the output of the fuel cell. In addition, it is considered that the moisturizing properties of the moisturizing layer are optimized when the content of mesoporous carbon and the content of silica are in an appropriate range.

5 is a graph of measuring the impedance of the membrane electrode assembly of the unit cell prepared in Examples 3, 6, and Comparative Example 1. Referring to FIG. In the graph of FIG. 5, Z' is the real part of the impedance, and Z" is the imaginary part of the impedance. The AC impedance of the membrane electrode assembly of the unit cell was measured at a current density of 0.2 A/cm 2 (10 kHz-0.001 Hz).

In the graph of FIG. 5 , the impedance of the membrane electrode assembly is determined by the position and size of the semicircle. The first x-axis (ie, abscissa) intercept of the semicircle represents the resistance of the electrolyte membrane, and the difference between the first x-axis intercept and the second x-axis intercept of the semicircle represents the electrode resistance. Referring to the graph of FIG. 5 , the size of the semicircle of impedance, the size of the first x-axis intercept, and the size of the second x-axis intercept are all smaller in the order of Example 3, Example 6, and Comparative Example 1. From this, it can be seen that the resistance of the electrolyte membrane and the resistance of the electrode were small in the order of Example 3, Example 6, and Comparative Example 1. On the other hand, it can be seen from the impedance graph of FIG. 5 that the difference in the resistance of the electrode is particularly large between Examples 3, 6, and Comparative Example 1, which is due to the introduction of the moisture-retaining layer in the membrane electrode assembly of the Example. It is believed that this is due to the increase in the migration resistance of hydrogen ions.

6 is a graph of the ohmic overvoltage versus the mesoporous carbon content of the unit cells of Examples 1 to 5 and Comparative Example 1. FIG. "Ohmic overvoltage" refers to a voltage decrease caused by the movement resistance of hydrogen ions in the electrolyte membrane. The ohmic overvoltage was calculated by multiplying the ohmic resistance obtained from the impedance measurement by the current. Referring to the graph of FIG. 5 , the overvoltage of Comparative Example 1 was the highest, and the overvoltage was low in the order of Examples 4 and 2, Example 3, and Example 1 and Example 5. The order of the overvoltage was different from the order of the power density, because the smaller the voltage decrease caused by the ohmic resistance, the higher the power density. From the graph of FIG. 6, it was found that the overvoltage decreased by 3-6 mV due to the introduction of the moisturizing layer.

In the above, the preferred embodiments according to the present invention have been described with reference to the drawings and examples, but these are merely exemplary, and various modifications and equivalent other embodiments are possible by those skilled in the art. will be able to understand Accordingly, the protection scope of the present invention should be defined by the appended claims.

1: Electrolyte membrane 2: Catalyst metal
3: carrier 4: binder resin
5: Catalyst layer 6: Porous material
7: moisture absorption material 8: moisture layer
9: diffusion layer 10: membrane electrode assembly
11: unit cell 12: holder
20: bipolar plate 100: fuel cell

Claims (18)

A membrane electrode assembly comprising a cathode, an anode and an electrolyte membrane interposed therebetween,
The cathode and the anode are each
a catalyst layer in contact with the electrolyte membrane;
a moisturizing layer in contact with the catalyst layer and having hygroscopicity; and
a gas diffusion layer in contact with the moisturizing layer;
The moisture layer includes a porous material and a moisture absorption material,
The surface of the porous material of the moisturizing layer contains -OH groups,
The porous material of the moisturizing layer is mesoporous carbon,
The hygroscopic material includes silica or metal phosphate,
The moisture absorption material is 1-20 wt% based on the total weight of the moisture-absorbing layer membrane electrode assembly. delete According to claim 1,
A membrane electrode assembly having a BET specific surface area of the moisturizing layer greater than a BET specific surface area of the catalyst layer. According to claim 1,
A membrane electrode assembly having a BET specific surface area of the moisturizing layer of 400-1,000m ^{2 /g.} delete According to claim 1,
A membrane electrode assembly having a surface oxygen-to-carbon concentration ratio of the moisturizing layer greater than a surface oxygen-to-carbon concentration ratio of the catalyst layer. According to claim 1,
A membrane electrode assembly having a surface oxygen to carbon concentration ratio of 0.1-0.5 of the porous material of the moisturizing layer. According to claim 1,
The content of the porous material of the moisture-retaining layer is 0.2-2 mg/cm ² A membrane electrode assembly. delete delete According to claim 1,
20-80% of the pores of the porous material of the moisturizing layer have a pore size of 100-500 nm. delete According to claim 1,
The size of the moisture absorption material is 2-30nm membrane electrode assembly. delete According to claim 1,
The catalyst layer is a membrane electrode assembly comprising a catalyst metal supported on a carbon-based support. 16. The method of claim 15,
The catalyst metal is platinum (Pt), iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), copper (Cu), silver (Ag), gold (Au), tin (Sn), titanium (Ti), chromium (Cr), and at least one membrane electrode assembly selected from the group consisting of alloys of two or more thereof. According to claim 1,
The electrolyte membrane is poly(perfluorosulfonic acid), poly(perfluorocarboxylic acid), a copolymer of tetrafluoroethylene and fluorovinyl ether containing a sulfonic acid group, defluorinated sulfided polyether ketone, aryl ketone, poly (2,2'-m-phenylene)-5,5'-bibenzimidazole (Poly(2,2'-(m-phenylene)-5,5'-bibenzimidazole), poly(2,5-benzimidazole) A membrane electrode assembly comprising at least one polymer electrolyte membrane selected from the group consisting of imidazole) or copolymers thereof. A plurality of claims 1, 3, 4, 6 to 8, 11, 13, and the membrane electrode assembly according to any one of claims 15 to 17 on a bipolar plate connected fuel cell.

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