KR20120089179A - Electrode for fuel cell, and membrane electrode assembly and fuel cell including the same - Google Patents

Abstract

PURPOSE: An electrode for fuel cells, a membrane electrode assembly including the same and a fuel battery are provided to prevent outflow of phosphoric acid which is moving from a catalyst layer to a diffusion layer, thereby enhancing lifetime of the membrane electrode assembly. CONSTITUTION: An electrode for fuel cells(10) comprises a supporter(11) and a diffusion layer(13) which includes a micro pore layer(12) arranged in the supporter, a catalyst layer(14) which is arranged in order to face the micro pore layer, and a barrier layer(15) which is placed between the catalyst layer and the micro pore layer. The barrier layer has bigger average pore size than the average pore size of the micro pore layer and the catalyst layer. The membrane electrode assembly comprises a cathode, an anode which faces with the cathode, and a polymer electrolyte membrane(20) arranged between the cathode and the anode. One or more of the cathode and anode include the electrode.

Description

Electrode for fuel cell, membrane electrode assembly and fuel cell comprising same {Electrode for fuel cell, and membrane electrode assembly and fuel cell including the same}

An electrode for a fuel cell, a membrane electrode assembly including the same, and a fuel cell are provided.

Fuel cells that are of interest as alternative energy are polymer electrolyte membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC), depending on the electrolyte used and the type of fuel used. ), Phosphate fuel cells (PAFC), molten carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC) and the like.

Among the polymer electrolyte membrane fuel cells (PEMFC), the PEMFC operating at a high temperature of 100 ° C. or higher (eg, 150 ° C. to 180 ° C.) and a non-humidifying condition does not use a humidifier, and PEMFC operates at low temperature because water exists as a vapor. Compared with the water discharge, the water management is easy and the control of the water is easy.

Currently, acid-doped MEAs are commercialized as membrane-electrode assemblies (MEAs) of high-temperature, non-humidified PEMFCs, and non-acid doping-based MEAs have not been commercialized and are being studied.

In the case of a polymer electrolyte membrane fuel cell using a phosphate-doped MEA in an acid doping system, phosphoric acid introduced into the electrode from the electrolyte membrane serves as an important hydrogen ion conductor in the electrode. During operation of the fuel cell, the distribution and amount of phosphate in the electrode are constantly changed by the operating conditions. For example, water generated in the cathode changes the concentration of phosphoric acid. The change in the amount and distribution of phosphoric acid in the electrode affects the performance of the battery by changing the catalyst utilization rate, and the phosphate outflow is promoted when the moisture generated during operation condenses at low temperatures and lowers the concentration of phosphoric acid as the start and stop are repeated. Excessive phosphoric acid outflow during operation of the fuel cell increases the membrane resistance and reduces the catalyst / conductor contact area, resulting in lower reactivity of the catalyst layer. Although the phosphate outflow is controlled to some extent due to the water repellency of the diffusion layer, the capillary phenomenon does not prevent the phosphate migration from the catalyst layer to the diffusion layer. As a result, this situation degrades the cell's performance and degrades its lifetime.

One aspect of the present invention is to provide an electrode for a fuel cell that can reduce the outflow of phosphoric acid during operation of the fuel cell.

Another aspect of the present invention is to provide a membrane electrode assembly including the fuel cell 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 diffusion layer comprising a support and a microporous layer disposed on the support;

A catalyst layer disposed to face the microporous layer; And

A barrier layer disposed between the catalyst layer and the microporous layer,

The barrier layer is provided by a fuel cell electrode having an average pore size larger than the average pore size of the catalyst layer and the microporous layer.

The barrier layer may have a maximum size of pores of 50 μm or less.

The barrier layer may have a minimum size of pores (min size) of 1 nm or more.

The average pore size of the barrier layer may be 25 μm or less.

The average pore size of the barrier layer may be 10 μm or less.

The average pore size of the barrier layer may be, for example, 200nm to 5μm.

The barrier layer may be made of at least one material selected from the group consisting of conductive carbon-based materials, metal materials, polymer materials, and ceramic materials. Here, the carbon-based material includes at least one selected from the group consisting of carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene, carbon nanotube, carbon nanowire, carbon nanohorn and carbon nanoring can do.

The barrier layer may include a particulate material. Here, the particle size of the particulate matter may be 0.1 to 50 μm.

The barrier layer may include at least one metal porous body of a metal mesh and a foamed metal.

The barrier layer may further comprise a water repellent material. Wherein the water repellent material is polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), polyvinylidene fluoride (PVdF), perfluoroalkoxy (PFA), 2,2-bistrifluoromethyl-4,5 At least one selected from the group consisting of: -difluoro-1,3-diosol tetrafluoroethylene copolymer, and sulfonated tetrafluoroethylene-based fluoropolymer-copolymer.

A catalytic metal may be further loaded on the barrier layer. Here, 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), mixtures thereof and alloys thereof.

The barrier layer may have a multilayer structure in which a plurality of porous matrices are stacked. Here, each of the stacked porous matrices may have a different average pore size.

The barrier layer may have a thickness of 5 to 50 μm.

The barrier layer may suppress the outflow of phosphoric acid from the catalyst layer to the diffusion layer.

According to another aspect of the present invention,

Cathode;

An anode disposed opposite the cathode; And

It includes a polymer electrolyte membrane disposed between the cathode and the anode,

A membrane electrode assembly for a fuel cell is provided wherein at least one of the cathode and the anode comprises the electrode.

According to another aspect of the invention, there is provided a fuel cell comprising the membrane electrode assembly.

The fuel cell electrode includes a barrier layer having a larger average pore size between the catalyst layer and the microporous layer, thereby reducing the outflow of phosphoric acid from the catalyst layer to the diffusion layer and improving the life of the membrane electrode assembly.

1 is a cross-sectional view schematically showing the structure of an electrode for a fuel cell according to an embodiment.
2 is an enlarged cross-sectional structure of an electrode for a fuel cell according to an exemplary embodiment, and illustrates a principle of suppressing phosphoric acid outflow to a diffusion layer.
3 schematically illustrates a structure of an electrode for a fuel cell according to another embodiment.
4 schematically shows the structure of an electrode for a fuel cell according to another embodiment.
5 shows the cumulative pore volume distribution of each of the support, the microporous layer (MPL), the catalyst layer, the barrier layer, and the catalyst metal-supported barrier layer used in the fuel cells of Examples 1-4 and Comparative Examples 1-2. The result is.
6 is a graph showing the results of measuring the amount of phosphoric acid after storing the fuel cell unit cells of Comparative Example 1 and Example 1 at 80 ° C. for three weeks.
FIG. 7 is a graph showing results of measuring voltages according to DSS (Daily Start Start) operation for the fuel cells of Comparative Examples 2 and 2 to 4. FIG.
FIG. 8 is a graph showing the results of measuring the amount of phosphoric acid remaining in the MEA after the DSS (Daily Start Start) operation is performed on the fuel cells of Comparative Examples 2 and 2. FIG.

EMBODIMENT OF THE INVENTION Hereinafter, specific embodiment of this invention is described in detail.

An electrode for a fuel cell according to an aspect of the present invention,

A diffusion layer comprising a support and a microporous layer disposed on the support;

A catalyst layer disposed to face the microporous layer; And

A barrier layer disposed between the catalyst layer and the microporous layer,

The barrier layer has an average pore size larger than that of the catalyst layer and the microporous layer.

Here, the "average pore size" is the pore size of the point reaching a volume percentage of 50% in this cumulative curve when the cumulative curve of the pore distribution is obtained with 100% of the total volume. Pore size (hereinafter referred to as “D ₅₀ ”) at a volume of 50%.

The average pore size can be measured by a variety of commonly known methods, for example optical microscopy, electron microscopy, X-ray scattering, gas-adsorption, mercury Cumulative curves of pore volume distribution can be obtained by measuring methods such as intrusion, liquid extrusion, molecular weight cut off method, fluid displacement method, and pulse NMR. At the point where the cumulative frequency of the volume distribution is 50%, the average pore size D ₅₀ can be identified.

In general, in a polymer electrolyte membrane fuel cell using an electrolyte membrane doped with phosphoric acid, phosphoric acid introduced into the electrode from the electrolyte membrane serves as an important hydrogen ion conductor in the electrode. However, as the start and stop of the fuel cell is repeated, the phosphoric acid outflow may be promoted. When the phosphoric acid outflow occurs excessively during operation of the fuel cell, the resistance of the catalyst layer may be lowered as the membrane resistance increases and the catalyst / conductor contact area decreases. In addition, a phenomenon in which the phosphoric acid excessively leaked into the diffusion layer blocks pores of the diffusion layer and thus fuel does not move to the catalyst layer may occur.

However, the fuel cell electrode according to an aspect of the present invention can suppress the outflow of phosphoric acid from the catalyst layer to the diffusion layer by forming a barrier layer that can suppress the outflow of phosphoric acid between the catalyst layer and the diffusion layer. The fuel cell electrode includes a barrier layer having a larger average pore size between the catalyst layer and the diffusion layer, and phosphoric acid, which migrates from the catalyst layer to the diffusion layer, exits the barrier layer due to a sudden decrease in capillary force in the barrier layer. This can reduce the amount of phosphoric acid that migrates to the diffusion layer.

1 is a cross-sectional view schematically showing the structure of an electrode for a fuel cell according to one embodiment.

Referring to FIG. 1, the diffusion layer 13 may be formed of the support 11 and the microporous layer 12, and the catalyst layer 14 is disposed to face the microporous layer 12 of the diffusion layer 13. The barrier layer 15 is disposed between the microporous layer 12 and the catalyst layer 14. These layers may be arranged adjacent to each other, and layers having other functions may be further inserted between the layers as necessary. An electrolyte membrane 20 is disposed adjacent to the catalyst layer 14.

The diffusion layer 13 includes a support 11 and a microporous layer 12, and the diffusion layer 13 needs to have conductive conductivity in order to transfer current generated in the catalyst layer 14. In addition, the diffusion layer 13 is advantageous to have a porosity to quickly discharge the water formed in the catalyst layer 14, and to facilitate the flow of air.

The support 11 may be an electrically conductive material such as a metal or a carbon-based material. For example, a conductive substrate such as carbon paper, carbon cloth, carbon felt or metal cloth may be used, but is not limited thereto.

The microporous layer 12 is generally a conductive powder having a small particle diameter, such as carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene, carbon nanotube, carbon nanowire, carbon nano horn It may include a carbon nano-horn or a carbon nano-ring (carbon nano-ring). The conductive powder constituting the microporous layer may have insufficient pressure diffusion when the particle size is too small, and insufficient diffusion of gas may be difficult when the particle size is too large. Therefore, in consideration of the diffusion effect of the gas, it is possible to use a conductive powder having an average particle diameter in the range of 10 nm to 50 nm in general. The diffusion layer 13 may use a commercial product, or purchase only carbon paper, and may be prepared by directly coating the microporous layer 12 thereon. The microporous layer 12 is a gas diffusion through the pores formed between the conductive powder, the average pore size of these pores is not particularly limited. For example, the average pore size of the microporous layer 12 may range from 1 nm to 10 μm. For example, the average pore size of the microporous layer 12 may be in the range of 5 nm to 1 μnm, 10 nm to 500 nm, or 50 nm to 400 nm.

The thickness of the diffusion layer 13 may be in the range of 200 μm to 400 μm in consideration of gas diffusion effects and electrical resistance. For example, the thickness of the diffusion layer 13 may be 100 μm to 350 μm, and more specifically 200 μm to 350 μm.

The catalyst layer 14 includes metal catalyst particles, and is not particularly limited as long as it can be generally used in the art. For example, as the metal catalyst particles, platinum (Pt), ruthenium (Ru), tin (Sn), palladium (Pd), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), Iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), aluminum (Al), molybdenum (Mo), selenium (Se), tungsten (W), iridium (Ir), Osmium (Os), rhodium (Rh), niobium (Nb), tantalum (Ta), lead (Pb), mixtures thereof, or alloys thereof can be used, and the average particle diameter of the metal catalyst particles is, for example, 2 nm to May be 10 nm. These metal catalyst particles are generally supported on a carbon carrier to be used as a catalyst layer, and the carbon carrier may have an average diameter in the range of 20 nm to 50 nm. For example, Pt alloy catalysts such as Pt / C, PtCo / C, PtCr / C can be used as the cathode catalyst layer, and alloy catalysts such as Pt / C and PtRu / C can be used as the anode catalyst layer.

In the catalyst layer 14, pores may be formed between the carbon carrier particles on which the metal catalyst particles are supported, and the pores may be formed between the secondary particles while the carbon carrier particles aggregate to form secondary particles. The average pore size of these pores may range from 1 nm to 1 μm. For example, the average pore size of the catalyst layer 14 may range from 10 nm to 700 nm, from 50 nm to 500 nm, or from 70 nm to 200 nm.

The catalyst layer 14 may have a thickness of 10 μm to 100 μm so as to effectively activate the electrode reaction and not excessively increase the electrical resistance. For example, the catalyst layer 14 may have a thickness of 20 μm to 60 μm, and more specifically, may have a thickness of 30 μm to 50 μm.

The catalyst layer 14 may further include a binder resin to improve adhesion of the catalyst layer and transfer hydrogen ions.

It is preferable to use a polymer resin having hydrogen ion conductivity as the binder resin, and more preferably have a cation exchange group selected from the group consisting of sulfonic acid group, carboxylic acid group, phosphoric acid group, phosphonic acid group and derivatives thereof in the side chain. A polymer resin can be used. Preferably, 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 include one or more hydrogen ion conductive polymer selected from ether ketone-based polymer, or polyphenylquinoxaline-based polymer.

The barrier layer 15 is disposed between the microporous layer 12 and the catalyst layer 14 of the diffusion layer 13, and the barrier layer 15 has an average pore size of the catalyst layer 14 and the microporous layer 12. It consists of a porous matrix that is larger than the average pore size. When phosphoric acid escaped through the pores of the catalyst layer 14 arrives at the barrier layer 15, the barrier layer 15 is suddenly reduced because the average pore size of the barrier layer 15 is larger than the average pore size of the catalyst layer 14. It is impossible to escape the pores of (15), and even if it passes through the barrier layer 15, the movement speed is significantly reduced. That is, the barrier layer 15 can control the movement of phosphoric acid from the catalyst layer 14 to the diffusion layer 13 by capillary action.

As such, the barrier layer 15 may have an average pore size larger than the average pore size of the catalyst layer 14 and the microporous layer 12, or at least the catalyst layer 14, and the range is not particularly limited. That is, when the predetermined catalyst layer 14 and the microporous layer 12 are determined, the barrier layer 15 may be formed by selecting the porous matrix material to have an average pore size in a range larger than their average pore size. The average pore size of the barrier layer 15 is larger than the average pore size of the catalyst layer 14 and the microporous layer 12, for example, may be 25 μm or less. For example, the average pore size of the barrier layer 15 may be larger than the average pore size of the catalyst layer 14 and the microporous layer 12, and may be 10 μm or less, 5 μm or less, or 1 μm or less.

Meanwhile, the barrier layer 15 preferably has a maximum size of pores of 50 μm or less. This is because when the maximum pore size exceeds 50 μm, the outflow of phosphoric acid may occur due to diffusion (diffusion) rather than the effect of inhibiting the outflow of phosphoric acid using a capillary phenomenon. The maximum size of the pores of the barrier layer 15 may be, for example, 30 μm or less, or 25 μm or less.

In addition, the barrier layer 15 may have a minimum size (min size) of pores of 1 nm or more. If the minimum pore size is less than 1 nm, it may not be easy to discharge gas such as water or fuel gas at high temperatures. The minimum size of the pores of the barrier layer 15 may be, for example, 3 nm or more, 5 nm or more, 10 nm or more, or 20 nm or more.

The pores formed in the barrier layer 15 may be interconnected in the thickness direction, and may form a passage through which gas may pass between the catalyst layer 14 and the microporous layer 12 of the diffusion layer 13. The passage formed by these pores inhibits the movement of phosphoric acid while the gas discharge such as water or fuel gas can be made through the passage between the pores.

As described above, the barrier layer 15 has a pore size that can prevent the outflow of phosphoric acid to the diffusion layer 13 in terms of its structure. The material is not particularly limited.

However, the barrier layer 15 must have conductivity, so that the electrons generated in the catalyst layer 14 pass through the diffusion layer 13 of the electrode, and are made of a material that is not corrosive and insoluble in phosphoric acid so as not to be oxidized even at a high voltage. There is a need. As long as the material satisfies these conditions, the barrier layer 15 is not particularly limited. For example, the barrier layer 15 may include a conductive material as at least one material selected from the group consisting of a carbonaceous material, a metal material, a polymer material, and a ceramic material.

For example, examples of the carbon-based material include carbon powder, carbon black, acetylene black, activated carbon, carbon fibres, fullerenes, carbon nanotubes, carbon nanowires, carbon nanohorns, carbon nanorings, and the like.

Examples of the metal material include gold (Au), silver (Ag), platinum (Pt), palladium (Pd), copper (Cu), rhodium (Rh), ruthenium (Ru), iridium (Ir), osmium (Os) And rhenium (Re).

Examples of the polymer material include polyacetylene, polyaniline, polypyrrole, polythiophene, poly sulfur nitride, and polyparaphenylin As long as the carbon atoms in the polymer have a chain structure in which a single bond and a double bond are alternately repeated, such as a para phenylene type, the π-conjugated polymer material having electrical conductivity due to the free movement of π-electrons is limited. It can be used without.

In addition, examples of the ceramic material include compounds containing at least one of transition metals and / or lanthanide metals between Groups 3 and 8 on the periodic table, and include oxides, carbides, It may be nitride or boride, and can be used without limitation as long as it has electrical conductivity. For example, indium tin oxide (ITO), fluorine doped tin oxide (FTO), molybdenum doped indium oxide, aluminum doped zinc oxide zinc oxide), and other metal compounds such as Ti may be used. The barrier layer 15 may be used alone, or two or more thereof may be mixed or combined in a composite form, and a plurality of porous matrices may be stacked to form a multilayer structure. . In the case of the multi-layered barrier layer 15, it is possible to design materials of each porous matrix differently, or design different pore sizes.

The barrier layer 15 may be a porous matrix made of a particulate material. In particular, when the catalyst layer 14 and the microporous layer 12 are made of a particulate material, the average pore size of each layer can be easily adjusted in consideration of the particle size of each layer. Therefore, it is possible to easily control the capillary phenomenon thereby reducing the outflow of phosphoric acid.

FIG. 2 schematically shows a barrier layer 15 ′ containing particulate matter between the microporous layer 13 and the catalyst layer 14. As shown in FIG. 2, the barrier layer 15 ′ may be composed of particles having a larger size than the particles constituting the microporous layer 13 and the catalyst layer 14, and pores are formed between the particles. Through these pores, a passage through which gas can pass may be formed between the microporous layer 13 and the catalyst layer 14. Fuel gas or water generated in the catalyst layer 14, such as steam in a high temperature PEMFC, may pass into the microporous layer 12 through a gap formed between the particles. However, in the case of phosphoric acid, even if the catalyst layer 14 exits due to a capillary phenomenon, the capillary force is rapidly weakened in the barrier layer 15 ′ having pores of a wide size, and the outflow of phosphoric acid is suppressed.

The average size of the particles forming the barrier layer 15 ′ is larger than the size of each particle forming the microporous layer 13 and the catalyst layer 14, and may be 50 μm or less. The particle size of the barrier layer 15 ′ may be, for example, 100 nm to 50 μm, and more specifically, for example, 1 μm to 10 μm.

The material of the particles forming the barrier layer 15 'is not particularly limited, and the above-described carbon-based material, metal material, polymer material, ceramic material, and the like can be used. For example, the particles of the barrier layer 15 ′ may be formed of a carbon-based material, and may include carbon powder, carbon black, acetylene black, activated carbon, carbon fiper, fullerene, carbon nanotube, carbon nanowire, and carbon nano. And at least one carbon-based material selected from horns and carbon nanorings.

According to another embodiment, the porous matrix may be made of a metal porous body such as a metal mesh or a foamed metal in addition to the carbon-based material. For example, Figure 3 shows that the barrier layer 15 "disposed between the microporous layer 13 and the catalyst layer 14 is made of a metal mesh. The capillary phenomenon can be controlled by the gap of the metal mesh. In this case, the shape of the metal mesh may be variously modified, and is not limited to the form shown in FIG. 3.

According to another embodiment, the barrier layer 15 may include a porous matrix in which a plurality of holes are formed at predetermined intervals in the thickness direction. For example, in FIG. 4, the barrier layer 15 ″ ′ disposed between the microporous layer 13 and the catalyst layer 14 has a plurality of holes formed in the thickness direction, and the capillary phenomenon is controlled by adjusting the size of the holes. The leakage of phosphoric acid may be reduced by adjusting the barrier layer 15 ″. The barrier layer 15 ″ ′ may be modified in various shapes and arrangements of a plurality of holes, but is not limited to the form illustrated in FIG. 4.

As described above, the form that the porous matrix may have been described with reference to the drawings, but this is merely illustrative, and those skilled in the art may have various modifications and equivalent other embodiments. Of course it is possible.

Meanwhile, according to one embodiment, the barrier layer 15 may further include a water repellent material on the surface of the porous matrix. The water repellent material may be coated on the surface except the pores of the porous matrix to impart water repellency around the pores, and may pass gas more effectively without the phosphoric acid entering the pores. According to such a water repellent treatment of the barrier layer 15, in the case of the barrier layer composed of particles, for example, the contact resistance between the adjacent particles may be increased, but the diffusion efficiency of the gas is higher than the overvoltage caused by the contact between the particles. Due to the much larger diffusion overvoltage due to the water repellent treatment, the overall battery performance can be improved.

Examples of the water-repellent material include polytetrafluoroethylene (PTFE), fluorinated ethylene propylne (FEP), polyvinylidene fluoride (PVdF), perfluoroalkoxy (PFA), 2,2-bis Trifluoromethyl-4,5-difluoro-1,3-diosol tetrafluoroethylene copolymer, sulfonated tetrafluoroethylene-based fluoropolymer-copolymer, etc .; Teflon-based polymers such as Fluorosarf (trade name), Asahi Glass's CYTOP (trade name) and Dupont's Nafion (trade name) can be used. These water repellent materials can be used individually or in mixture of 2 or more. Such a water repellent material can be used simply by mixing with the material constituting the porous matrix or by coating the surface of the material constituting the porous matrix and forming a barrier layer.

According to one embodiment, the barrier layer 15 may be supported with a catalytic metal in a porous matrix. In particular, when the barrier layer includes a porous matrix of a carbonaceous material, the catalyst metal may be supported using the carbonaceous porous matrix as a support. Catalysts that can be supported include platinum (Pt), iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), and iridium ( Ir, copper (Cu), silver (Ag), gold (Au), tin (Sn), titanium (Ti), chromium (Cr), mixtures thereof and alloys thereof. As described above, the barrier layer 15 loaded with the catalyst metal not only prevents phosphoric acid leakage but also contributes to activating the electrode reaction at the anode or the cathode, like the catalyst layer 14.

The barrier layer 15 may have a structure including the porous matrix as a single layer as described above, or may have a multilayer structure in which two or more porous matrices are stacked. At this time, the porous matrix of each layer constituting the multi-layer structure may have different pore sizes.

The barrier layer 15 may have a thickness of 10 μm to 50 μm. If the thickness of the barrier layer 15 is too thick, the electrical resistance may be increased, and if the thickness is too thin, it may be difficult to control the capillary phenomenon, thereby making it difficult to reduce the movement of phosphoric acid. Therefore, the barrier layer 15 may be formed to a thickness within the above range, thereby reducing the outflow of phosphoric acid without excessively increasing the electrical resistance.

According to another aspect of the present invention,

Cathode;

An anode disposed opposite the cathode; And

It includes a polymer electrolyte membrane disposed between the cathode and the anode,

At least one of the cathode and the anode is provided with a membrane electrode assembly for a fuel cell comprising the electrode described above.

According to an embodiment, any one of a cathode and an anode in the membrane electrode assembly may be the above electrode, which solves the problem of leakage of phosphoric acid due to the discharge of water formed at the cathode when at least the cathode is composed of the electrode. Useful at In addition, when both the cathode and the anode is composed of the above-described electrode, it is useful in that it can prevent the phosphate leakage that can occur in the membrane electrode assembly to the maximum.

The polymer electrolyte membrane is not particularly limited, but may be polybenzimidazole (PBI), crosslinked polybenzimidazole, poly (2,5-benzimidazole) (ABPBI), polyurethane, and It may be one or more selected from the group consisting of modified polytetrafluoroethylene (modified PTFE).

The polymer electrolyte membrane may be impregnated with phosphoric acid or organic phosphoric acid, and other acids may be used in addition to phosphoric acid. The concentration of the phosphoric acid is not particularly limited, but an aqueous solution of 80 to 100% by weight, in particular 85% by weight, of phosphoric acid may be used.

According to another aspect of the invention there is provided a fuel cell comprising the membrane electrode assembly.

The fuel cell includes the membrane electrode assembly described above, and the production of such a fuel cell can use a conventional method known in various literatures, and thus a detailed description thereof is omitted here.

Hereinafter, the present invention will be exemplified by the following examples, but the protection scope of the present invention is not limited only to the following examples.

Comparative example  One (Support / MPL Of Electrolyte membrane Of MPL / Support)

First, to compare how much phosphoric acid escapes by barrier layer formation, a microporous layer (MPL) is coated with ketjen black of about 40 μm on 280 μm thick carbon paper to prepare a diffusion layer, and two diffusion layers without a catalyst layer. A polybenzoxazine impregnated with phosphoric acid was assembled through a polymer electrolyte membrane to form a fuel cell unit cell, and Comparative Example 1 was used.

Example  One (Support / MPL Of Barrier layer Of Electrolyte membrane Of Barrier layer Of MPL / Support)

A barrier layer consisting of 97% by weight of carbon powder and 3% by weight of PVdF binder is coated on a diffusion layer coated with a microporous layer (MPL) in ketjen black of about 40 μm on 280 μm thick carbon paper. And it dried at 80 degreeC for 1 hour. The fuel cell unit cell was assembled through the polybenzoxazine polymer electrolyte membrane impregnated with phosphoric acid between the two diffusion layers coated with the barrier layer.

The pore distribution of the support, MPL and barrier layer used in each layer was measured by Mercury Porosimeter, and the cumulative curve of the pore distribution was calculated from the larger pore size to the smaller pore size. The pore volume distribution thus accumulated is shown in FIG. 5. As shown in Figure 5, when looking at the average pore size at the 50% cumulative frequency, it can be seen that the average pore size of the barrier layer is larger than the average pore size of the MPL.

Evaluation example  One: On the barrier layer  Phosphoric Acid Runoff Test

After storing the fuel cell unit cells assembled according to Comparative Examples 1 and 1 for three weeks at 80 ° C., the diffusion layer electrode and the polymer electrolyte membrane were separated from the fuel cell unit cell, diluted in water, and then distributed in water. Was titrated with 0.1 M NaOH solution and the results are shown in FIG. 6.

As shown in FIG. 6, in Comparative Example 1 in which the barrier layer was not inserted, more than 50% of the phosphoric acid impregnated in the first electrolyte membrane was leaked and lost, and about 5% was leaked to the diffusion layer. have. On the contrary, in Example 1 in which the barrier layer was inserted between the microporous layer and the electrolyte membrane, only about 24% of the phosphoric acid impregnated in the first electrolyte membrane was leaked and lost, and the amount of the phosphoric acid was also reduced. Can be.

Comparative example  2  (Support / MPL Of Cathode catalyst layer Of Electrolyte membrane Of Anode catalyst layer Of MPL / Support)

Pt / C 0.5g, NMP 2g and PBOA (Polybenzoxazine) on diffusion layer coated with microporous layer (MPL) in ketjen black of about 40μm on 280μm thick carbon paper Binder solution (5% in H ₂ O) A catalyst slurry containing 0.25 g was coated and dried in an oven at 80 ° C. for 1 hour, at 120 ° C. for 30 minutes, and at 150 ° C. for 10 minutes to prepare a cathode and an anode electrode. After assembling the MEA through the polybenzoxazine polymer membrane impregnated with phosphoric acid between the cathode electrode and the anode electrode thus prepared, a fuel cell was manufactured using the same.

Example  2  (Support / MPL Of Barrier layer Of Cathode catalyst layer Of Electrolyte membrane Of Anode catalyst layer Of MPL / Support)

A barrier layer consisting of 97% by weight of carbon powder and 3% by weight of PVdF binder is coated on a diffusion layer coated with a microporous layer (MPL) in ketjen black of about 40 μm on 280 μm thick carbon paper. And it dried at 80 degreeC for 1 hour.

Meanwhile, a catalyst slurry containing 0.5 g of Pt / C, ₂ g of H ₂ O and 0.25 g of PBOA binder solution (5% in H ₂ O) was coated on a polybenzoxazine polymer membrane impregnated with phosphoric acid and then heated at 60 ° C. for 10 minutes in an oven. Drying prepared the cathode electrode.

Separately, 0.5 g of Pt / C, 2 g of NMP, and 0.25 g of PBOA binder solution (5% in H ₂ O) were included on a diffusion layer coated with a microporous layer (MPL) of approximately 40 μm Ketjen Black on 280 μm thick carbon paper. The prepared catalyst slurry was coated and dried in an oven at 80 ° C. for 1 hour, at 120 ° C. for 30 minutes, and at 150 ° C. for 10 minutes to prepare an anode electrode.

Using the barrier layer coated on the diffusion layer, the polymer film coated on the cathode electrode, and the anode electrode coated on the diffusion layer, an MEA having a barrier layer formed only on the cathode electrode side was assembled, and then, a fuel cell was manufactured. It was.

Example  3  (Support / MPL Of Water repellent Barrier layer Of Cathode catalyst layer Of Electrolyte membrane Of Anode catalyst layer Of MPL / Support)

As the barrier layer in Example 2, except that a barrier layer was formed using 80 wt% of carbon powder having a particle size of about 1-2 μm and 20 wt% of Nafion binder, the same as in Example 2 above. A fuel cell was produced. Example 3 imparted water repellency to the barrier layer by using a Nafion binder having a much higher water repellency than the PVdF binder.

Example  4  (Support / MPL / Catalyst metal Supported Barrier layer Of Cathode catalyst layer Of Electrolyte membrane Anode catalyst layer MPL / Support)

A catalyst slurry containing 0.5 g of Pt / C, 2 g of NMP, and 0.25 g of PBOA binder solution (5% in H2O) on a diffusion layer coated with a microporous layer (MPL) of approximately 40 μm Ketjen Black on 280 μm thick carbon paper The coating layer was dried in an oven at 80 ° C. for 1 hour, at 120 ° C. for 30 minutes, and at 150 ° C. for 10 minutes to prepare a barrier layer having first pores.

Meanwhile, a catalyst slurry containing 0.5 g of Pt / C, ₂ g of H ₂ O and 0.25 g of PBOA binder solution (5% in H ₂ O) was coated on a polybenzoxazine polymer membrane impregnated with phosphoric acid and then heated at 60 ° C. for 10 minutes in an oven. It was dried to prepare a cathode electrode having a second pore. In this case, Pt / C particles of the barrier layer and the cathode electrode layer were selected such that the first pore is larger than the pore size than the second pore.

Separately, 0.5 g of Pt / C, 2 g of NMP, and 0.25 g of PBOA binder solution (5% in H ₂ O) were included on a diffusion layer coated with a microporous layer (MPL) of approximately 40 μm Ketjen Black on 280 μm thick carbon paper. The prepared catalyst slurry was coated and dried in an oven at 80 ° C. for 1 hour, at 120 ° C. for 30 minutes, and at 150 ° C. for 10 minutes to prepare an anode electrode.

Using the barrier layer coated on the diffusion layer, the polymer film coated on the cathode electrode, and the anode electrode coated on the diffusion layer, an MEA having a catalyst layer supported only on the cathode electrode was assembled, and then used. To produce a fuel cell.

The preparation conditions of the support, the microporous layer (MPL) and the barrier layer used in the fuel cells of Example 2-4 and Comparative Example 2 are the same as in Example 1 and Comparative Example 1. 5 shows cumulative pore volume distribution measurement results of the support, MPL, barrier layer, catalyst metal-supported barrier layer, and (cathode / anode) catalyst layer used in the fuel cells of Examples 2-4 and Comparative Example 2. It was. As shown in Figure 5, it can be seen that the average pore size of the barrier layer is larger than the average pore size of the MPL and barrier layer.

Evaluation example  2: DSS  Voltage measurement by operation

For the fuel cells of Comparative Example 2 and Examples 2 to 4, the battery was operated at 150 ° C. while flowing about 250 ccm of air on the cathode side and 100 ccm of hydrogen on the anode side. After 2 hours of operation the current was stopped and the fuel supply and cell heating were stopped. When the cell dropped to a temperature below 40 ° C., the cell heating started again. When the cell reached 150 ° C., fuel supply was started and operation started at a current density of 0.2 A / cm ² . After 2 hours of operation, the battery was stopped again and this stop-start operation was repeated. The voltage according to 100 DSS (Daily Stop Start) operation was measured, and the results are shown in FIG. 7.

As shown in FIG. 7, it can be seen that the fuel cells of Examples 2 to 4 are significantly improved in voltage reduction compared to Comparative Example 2 in a situation of starting and stopping 100 times daily.

Evaluation example  3: DSS  Phosphoric acid measurement after driving

For the fuel cells of Comparative Examples 2 and 2, DSS (Daily Stop Start) operation was performed under the same conditions as in Evaluation Example 2, and the amount of phosphoric acid remaining in the MEA was measured. 8 is shown.

As shown in FIG. 8, in the fuel cell of Comparative Example 2, the phosphoric acid amount of the fuel cell of Comparative Example 2 decreased by about 11% after DSS 350 operations, whereas the fuel cell of Example 1 was operated after DSS 415 operations. Phosphoric acid was reduced by only about 5%. Through this, it can be seen that the fuel cell of Example 2 significantly reduced the outflow of phosphoric acid by applying a barrier layer between the catalyst layer and the diffusion layer, and improved life characteristics of the MEA.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, . Accordingly, the scope of protection of the present invention should be determined by the appended claims.

10: electrode 11: support
12: microporous layer 13: diffusion layer
14: catalyst layer 15, 15 ', 15 ", 15"': barrier layer
20: electrolyte membrane

Claims (21)

A diffusion layer comprising a support and a microporous layer disposed on the support;
A catalyst layer disposed to face the microporous layer; And
A barrier layer disposed between the catalyst layer and the microporous layer,
The barrier layer has an average pore size larger than the average pore size of the catalyst layer and the microporous layer. The method of claim 1,
The barrier layer is a fuel cell electrode having a maximum size (pore size) of 50μm or less. The method of claim 1,
The barrier layer has a minimum pore size (min size) of 1 nm or more electrode for a fuel cell. The method of claim 1,
An electrode for a fuel cell, wherein the barrier layer has an average pore size of 25 μm or less. The method of claim 1,
And an average pore size of the barrier layer is 10 μm or less. The method of claim 1,
An electrode for a fuel cell having an average pore size of the barrier layer is 200nm to 5μm. The method of claim 1,
And the barrier layer is formed of at least one material selected from the group consisting of a carbon-based material, a metal material, a polymer material, and a ceramic material having conductivity. The method of claim 7, wherein
The carbonaceous material includes at least one fuel selected from the group consisting of carbon powder, carbon black, acetylene black, activated carbon, carbon wiper, fullerene, carbon nanotubes, carbon nanowires, carbon nanohorns and carbon nanorings. Battery electrode. The method of claim 1,
The barrier layer is a fuel cell electrode containing a particulate matter. 10. The method of claim 9,
The particle size of the particulate matter of 0.1 to 50 μm fuel cell electrode. The method of claim 1,
The barrier layer is a fuel cell electrode comprising a metal porous body of at least one of a metal mesh and a foamed metal. The method of claim 1,
The barrier layer further comprises a water repellent material electrode for a fuel cell. The method of claim 12,
The water repellent material is polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), polyvinylidene fluoride (PVdF), perfluoroalkoxy (PFA), 2,2-bistrifluoromethyl-4,5-di A fuel cell cell comprising at least one selected from the group consisting of a fluoro-1,3-diosol tetrafluoroethylene copolymer and a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer. The method of claim 1,
A fuel cell electrode in which a catalyst metal is supported on the barrier layer. 15. The method of claim 14,
The catalyst metal is platinum (Pt), iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), copper A fuel cell electrode selected from the group consisting of (Cu), silver (Ag), gold (Au), tin (Sn), titanium (Ti), chromium (Cr), mixtures thereof and alloys thereof. The method of claim 1,
The barrier layer is a fuel cell electrode having a multilayer structure in which a plurality of porous matrices are stacked. The method of claim 16,
Each of the stacked porous matrices has a different average pore size. The method of claim 1,
The barrier layer is a fuel cell electrode having a thickness of 5 to 50μm. The method of claim 1,
The barrier layer is a fuel cell electrode for suppressing the outflow of the inorganic acid or organic acid from the catalyst layer to the diffusion layer. Cathode;
An anode disposed opposite the cathode; And
It includes a polymer electrolyte membrane disposed between the cathode and the anode,
20. A membrane electrode assembly for a fuel cell, wherein at least one of the cathode and the anode comprises an electrode according to any one of claims 1 to 19. A fuel cell comprising the membrane electrode assembly according to claim 20.

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