JP2008130394A - Membrane electrode assembly for fuel cell and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent or restrain degradation of a solid polymer electrolyte membrane. <P>SOLUTION: The membrane electrode assembly for a fuel cell is provided with a membrane deterioration preventing layer containing either a catalyst with precious metal with a particle diameter of 5 nm or more and less than 20 nm as a catalyst ingredient or a catalyst having precious metal by 10 μg/cm<SP>2</SP>or more and 62 μg/cm<SP>2</SP>or less, and the fuel cell uses the same. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a membrane electrode assembly for a fuel cell and a fuel cell.

  Membrane electrode assemblies used in polymer electrolyte fuel cells generally include an oxidant electrode comprising a oxidant electrode catalyst layer and an oxidant electrode substrate, a solid polymer electrolyte membrane, a fuel electrode catalyst layer and a fuel electrode substrate. The fuel electrode is made by joining by heating and pressing by a hot press method. The membrane electrode assembly is sandwiched from both sides by the separator.

  On the surface of the separator facing the membrane electrode assembly, the flow channel is provided so as to meander over substantially the entire surface. The oxidant and the fuel are supplied to the oxidant electrode and the fuel electrode, respectively, through the channel groove. Usually, air or high-concentration oxygen is used as the oxidizer, and hydrogen is used as the fuel.

  Oxygen or hydrogen passes through the solid polymer electrolyte membrane more or less, reaches the counter electrode, reacts, and greatly reduces the cell voltage or wastes the reaction gas. When it reaches the counter electrode and reacts, active species such as hydrogen peroxide or OH radicals are generated, which degrades the solid polymer electrolyte membrane, resulting in a problem that the life of the fuel cell is extremely shortened.

  In order to solve such problems, a membrane electrode assembly in which a crossover prevention layer containing metal oxide particles supporting noble metal particles or carbon particles supporting noble metal particles is sandwiched between solid polymer electrolyte layers has been proposed. (For example, refer to Patent Document 1).

Although such a crossover prevention layer was able to prevent crossover to some extent, further improvement is desired.
JP-A-2005-285356

  An object of the present invention is to prevent or suppress deterioration of a solid polymer electrolyte membrane.

  The present invention relates to a membrane electrode assembly for a fuel cell comprising a solid polymer electrolyte membrane and a fuel electrode and an oxidizer electrode that sandwich the solid polymer electrolyte membrane from both sides. The present invention also relates to a membrane electrode assembly comprising a membrane deterioration preventing layer including a catalyst having a noble metal having a particle diameter of 5 nm or more and less than 20 nm arranged along the fuel electrode or oxidant electrode as a catalyst component.

The present invention also provides a membrane electrode assembly for a fuel cell comprising a solid polymer electrolyte membrane, and a fuel electrode and an oxidizer electrode that sandwich the solid polymer electrolyte membrane from both sides. a membrane electrode assembly in which the fuel electrode or becomes arranged along the oxidant electrode noble metal and having a membrane deterioration preventing layer comprising a catalyst in the following 10 [mu] g / cm ² or more 62μg / cm ^2, about .

  Furthermore, the present invention relates to a fuel cell using the membrane electrode assembly.

  According to the membrane / electrode assembly of the present invention, the durability of the membrane / electrode assembly can be improved by suppressing or preventing the generation of hydrogen peroxide in the solid polymer electrolyte membrane.

  Moreover, according to the fuel cell of the present invention, since the deterioration of the solid polymer electrolyte membrane is suppressed or prevented, the high durability of the fuel cell can be exhibited.

  The film deterioration preventing layer of the present invention will be described with reference to the drawings.

  Conventionally, when a fuel cell is operated, platinum is eluted from a platinum catalyst used for an oxidant electrode or the like into a solid polymer electrolyte membrane, thereby generating hydrogen peroxide in the membrane, and There was a risk of breaking the membrane. As a result, it has been reported that battery performance decreases.

  On the other hand, in the present invention, it has been devised to provide a membrane deterioration preventing layer containing a specific catalyst in the solid polymer electrolyte membrane.

  FIG. 1 is a drawing for explaining a film deterioration preventing layer used in a membrane electrode assembly (MEA) of the present invention.

In FIG. 1, Pt ^{n +} eluted from the oxidant electrode 11 into the solid polymer electrolyte membrane A is captured by the membrane deterioration preventing layer 12. Here, the oxidant electrode catalyst layer is made of carbon particles carrying platinum fine particles. Further, hydrogen peroxide generated by the reaction of oxygen and hydrogen leaked from the oxidant electrode 11 and the fuel electrode 13 into the solid polymer electrolyte membrane is not easily decomposed, but the membrane deterioration preventing layer of the present invention. 12 can be used for decomposition. Here, the fuel electrode catalyst layer is made of carbon particles carrying platinum fine particles.

  FIG. 2 is a view for explaining the relationship between the particle diameter or density of platinum of the platinum catalyst used in the film deterioration preventing layer and the decomposition of hydrogen peroxide.

  In FIG. 2A, when the amount of platinum 21a supported is small, hydrogen peroxide is difficult to be reduced to water. In FIG. 2B, when the particle size of platinum 21b supported on the carbon particles 22 is increased and the amount of platinum supported per unit area is optimized, hydrogen peroxide is easily reduced to water. In FIG. 2C, the particle size of the platinum 21c supported on the carbon particles 22 becomes small, and if the amount of platinum supported per unit area is too large, hydrogen peroxide is physically inhibited from moving. It is difficult to reduce to water due to factors.

  Thus, it can be seen that the catalyst constituting the film deterioration preventing layer needs to contain a noble metal having a specific particle size or a catalyst containing a predetermined amount of noble metal per unit area. .

  Next, the film deterioration preventing layer will be described in more detail.

(Membrane degradation prevention layer)
The membrane deterioration preventing layer (also referred to as a crossover layer) of the solid polymer electrolyte membrane used for the fuel cell membrane electrode assembly of the present invention contains a catalyst having a noble metal having a particle diameter of 5 nm or more and less than 20 nm as a catalyst component. Since the precious metal eluted from the electrode into the solid polymer electrolyte membrane can be captured, the generation of hydrogen peroxide can be suppressed or prevented. By setting the particle diameter (diameter) to 5 nm or more, it is possible to provide a sufficient area for one molecule of oxygen to undergo a four-electron reaction. As a result, the four-electron reaction from oxygen to water proceeds rapidly, and even when hydrogen peroxide is generated, it is rapidly reduced to water. In this way, deterioration of the solid polymer electrolyte membrane based on the generation of hydrogen peroxide can be prevented. It is because oxygen activity will become low when it exceeds 20 nm.

Also, membrane deterioration preventing layer of the solid polymer electrolyte membrane used for a fuel cell membrane electrode assembly of the present invention includes a catalytic noble metal is at 62μg / cm ² or less 10 [mu] g / cm ² or more. The surface area indicates the utilization rate and dispersibility of the catalyst. The four-electron reaction proceeds with high utilization. When hydrogen peroxide is produced due to high dispersibility, it is possible to provide an area that can quickly move to the reaction field.

  The catalyst is preferably a catalyst containing platinum, ruthenium, iridium, palladium or a mixture thereof. Among these, a platinum catalyst or a platinum-ruthenium catalyst is more preferable. Further, the catalyst metal such as platinum or ruthenium is preferably supported on a carrier such as carbon.

The catalyst preferably contains 30μg-Pt / cm ² or more 62μg-Pt / cm ² or less platinum. The amount of platinum supported is 30 μg-Pt / cm ² or more, thereby suppressing the generation of hydrogen peroxide and accelerating the oxidation to water. The effect can be obtained with a smaller amount of platinum.

  The catalyst preferably has an electrochemically active catalyst surface area of 70% or more of the catalyst surface area evaluated by gas adsorption. Here, it is assumed that the gas adsorption method usually shows 100% surface area of a Pt-supported catalyst such as platinum.

  When performing electrochemical measurements, due to a failure in the catalyst ink preparation method, the catalyst or ionomer may be agglomerated, so that the part where the catalyst should originally be used may be lost. May rise.

  In addition, in the aqueous solution, reactants such as protons and oxygen are easily disturbed. However, this problem can be solved by improving the dispersibility of the catalyst by the preparation method of the catalyst ink. As this allowable range, the situation where 70% of the catalyst is used is set as the minimum physical property value.

  The surface area indicates the utilization rate and dispersibility of the catalyst. Due to the high utilization rate, the four-electron reaction proceeds. In addition, when hydrogen peroxide is produced due to high dispersibility, it is possible to provide an area that can quickly move to the reaction field. That is, deterioration of the solid electrolyte membrane can be prevented.

  The gas adsorption method is performed by the following method.

<Measurement method of Pt surface area on carbon support>
As a measuring device, Pulse Chemisorb 2700 (Pulse Chemisorb 2700) manufactured by Micromeritex Corporation was used.

  1. The sample is dried in a vacuum oven at 50 ° C. overnight. 2. After drying, cool to room temperature in a desiccator. 3. Purge the sample (about 100 mg) in a U-shaped tube with helium at room temperature for 10 minutes. 4). The temperature is raised to 80 ° C. in 30 minutes under a helium flow. 5. The flow gas is switched to hydrogen and held at a sample temperature of 80 ° C. for 10 minutes. 6). The circulating gas is switched to nitrogen, and the temperature is lowered to 30 ° C. in 30 minutes. 7. This temperature is maintained, and the CO adsorption amount is measured by an operation unique to the measuring instrument. The value obtained is taken as 100%.

  The thickness of the film deterioration preventing layer is preferably 0.01 to 1 μm, more preferably 0.5 to 1 μm. Within this range, deterioration of the solid polymer electrolyte membrane is prevented and proton conduction is not hindered.

  Such a membrane deterioration preventing layer can prevent deterioration of the solid polymer electrolyte membrane and can suppress or prevent the generation of hydrogen peroxide.

(Manufacturing method of film deterioration preventing layer)
An example of a method for producing the film deterioration preventing layer will be described.

  A catalyst, water, and isopropyl alcohol are prepared in a predetermined ratio (mass), for example, in a range of 5: 3: 2 to 5: 4: 1, and stirred for at least 30 minutes with an ultrasonic wave to form an ink for a film deterioration preventing layer. Is made. Here, the same catalyst as the catalyst used for the catalyst layer of the fuel cell can be used as the catalyst except that the particle diameter of the catalyst metal is the above-mentioned size. Specific examples include platinum-supported carbon.

  A part of the obtained ink is dropped on a carbon electrode, and CV (cyclic voltammetry) is measured. ECA (electrochemical reaction area) should be 80 to 100% of the surface area evaluated by BET or the like.

  The obtained ink is transferred onto a Teflon (registered trademark) sheet to obtain a transfer sheet A. The thickness is usually in the above range.

  In this way, a film deterioration preventing layer can be manufactured.

(MEA)
The MEA used in the polymer electrolyte fuel cell includes an oxidant electrode composed of an oxidant electrode catalyst layer and an oxidant electrode substrate; a solid polymer electrolyte membrane; a fuel electrode or an oxidant in the solid polymer electrolyte membrane. containing a catalyst with a noble metal of less than the particle diameter of 5nm or more 20nm consisting disposed along the electrode catalyst as a catalyst component or a noble metal is below 10 [mu] g / cm ² or more 62μg / cm ^2,, of the solid polymer electrolyte membrane Film degradation prevention layer: A fuel electrode composed of a fuel electrode catalyst layer and a fuel electrode base material is joined by heating and pressurizing by a hot press method.

  The film deterioration preventing layer is sandwiched between a pair of solid polymer electrolyte membranes. Accordingly, the length is not particularly limited as long as it can prevent the progress of oxygen or hydrogen traveling in the solid polymer electrolyte toward the counter electrode, but it may have a length from one end to the other end of the solid polymer electrolyte membrane. preferable.

  Of course, the pair of solid polymer electrolyte membranes may be the same or different.

  When the same solid polymer electrolyte membrane is used, the membrane degradation preventing layer is preferably located closer to the oxidizer electrode than the center of the membrane. In particular, the thickness ratio of the A membrane (solid polymer electrolyte membrane on the oxidizer electrode side) and B membrane (solid polymer electrolyte membrane on the fuel electrode side) is in the range of 1: 100 to 1: 2.5. Is preferred. By adopting such an arrangement, it is possible to efficiently capture the catalytic metal dissolved in the solid polymer electrolyte membrane and efficiently prevent the generation of generated hydrogen peroxide. Furthermore, hydrogen leaked from the fuel electrode to the solid polymer electrolyte membrane can be captured.

When the A film and the B film are different, for example, the hydrogen permeability is 10 ⁻¹¹ to 10 ⁻¹⁰ mol / cm · s · atm for the A film, and the hydrogen permeability is 10 ⁻¹² mol / cm · s · atm or less for the B film. In the case of using a molecular film, it is preferable that the position where the film deterioration preventing layer is installed is closer to the fuel electrode than the center of the film. In this case, in particular, the ratio of the thicknesses of the A film and the B film is preferably in the range of 100: 1 to 10: 5.

Further, when using a polymer membrane having a hydrogen permeability of 10 ⁻¹² mol / cm · s · atm or less for the A film and a hydrogen permeability of 10 ⁻¹¹ to 10 ⁻¹⁰ mol / cm · s · atm for the B film, The position where the film deterioration preventing layer is installed is preferably closer to the fuel electrode than the center of the film. In particular, the ratio of the thicknesses of the A film and the B film is preferably in the range of 1: 100 to 5:10.

  By adopting such an arrangement, it is possible to efficiently capture the catalytic metal dissolved in the solid polymer electrolyte membrane and efficiently prevent the generation of generated hydrogen peroxide. Furthermore, hydrogen leaked from the fuel electrode to the solid polymer electrolyte membrane can be captured.

  As other materials, materials known in the field of fuel cells are used. For example, as the oxidizer electrode catalyst layer, an oxidation produced from a paste composed of carbon particles supporting fine platinum particles and a perfluorosulfonic acid solid polymer electrolyte such as Nafion (registered trademark of DuPont). The electrode catalyst layer is carbon perper as the oxidant electrode substrate, and the perfluorosulfonic acid solid polymer electrolyte such as Nafion is used as the solid polymer electrolyte membrane, and the hydrocarbon type such as polyimide and polyphenylene is used. The solid polymer electrolyte is a paste composed of carbon particles supporting platinum and ruthenium fine particles and a perfluorosulfonic acid solid polymer electrolyte such as Nafion (registered trademark of DuPont) as the fuel electrode catalyst layer. As the fuel electrode base material, the fuel electrode catalyst layer prepared from .

  Thus, by providing a membrane deterioration preventing layer in the solid polymer electrolyte membrane, it is possible to capture noble metal eluted from the electrode to the solid polymer electrolyte membrane, and to prevent or suppress hydrogen crossover, Furthermore, the generation of hydrogen peroxide can be suppressed or prevented, and the oxidation of hydrogen peroxide can be promoted. As a result, deterioration of the solid polymer electrolyte membrane can be suppressed or prevented.

(Method for producing MEA)
An example of the MEA manufacturing method will be described.

  Both the fuel electrode catalyst layer and the oxidant electrode catalyst layer are produced on a Teflon sheet. A solid polymer electrolyte membrane is placed on the fuel electrode catalyst layer, and hot pressing is performed to obtain a sheet B. A sheet C is obtained by placing the solid polymer electrolyte membrane on the oxidant electrode catalyst layer and performing hot pressing. The transfer sheet A is joined on the electrolyte membrane of the sheet C by hot pressing to obtain a sheet D. Further, hot pressing is performed on the electrolyte membrane side of the sheet B and the transfer sheet side of the sheet D together. In this way, MEA is obtained.

  Of course, the sheet D is obtained by bonding the transfer sheet A onto the electrolyte membrane of the sheet B by hot pressing. Further, hot pressing may be performed on the electrolyte membrane side of the sheet C and the transfer sheet side of the sheet D together.

(Fuel cell)
The MEA obtained by the above method can be sandwiched from both sides by a separator to form a fuel cell. The fuel cell obtained in this way can exhibit high durability since the deterioration of the solid polymer electrolyte membrane is prevented. Since it shows high durability, it can also be used as a fuel cell for vehicles.

  Next, although the Example of this invention is described, this Example does not limit this invention.

(Example 1: Preparation of deterioration preventing layer ink slurry, measurement of influence of Pt carrying amount and measurement of H2 crossover amount)
As an electrode catalyst, a platinum-supported carbon catalyst (Pt supported amount: 48.6 wt%, average Pt particle size: 5.5 nm, carrier carbon: Vulcan XC-72 (manufactured by Cabot)) was used. After adding 1/2 times the amount of purified water with respect to the mass of this electrode catalyst, 1/10 times the amount of isopropyl alcohol was added, and Nafion solution (Aldrich 5 wt% Nafion (registered trademark of DuPont) included ) Was added, and the mass of Nafion was adjusted to 1 time. Slurry A was prepared by dispersing the mixed slurry well with an ultrasonic homogenizer, followed by vacuum degassing.
Slurry A was dropped with a micropipette onto the GC substrate of the RRDE electrode, and the amount of Pt supported was changed by changing the amount of dripping to measure H ₂ O ₂ . Table 1 shows the measurement conditions.

The obtained results are shown in FIGS. In FIG. 3, it is recognized that the generation rate of hydrogen peroxide is suppressed when the amount of platinum supported is 30 μg-Pt / cm ² or more. In FIG. 4, it can be confirmed whether there is a dependency on the loading amount that can suppress the generation of hydrogen peroxide.

(Measurement of equilibrium potential)
Using an H-type cell, measurement was performed for the case where only the Nafion membrane was used as a diaphragm in the center of the cell and the case where a membrane with a crossover layer sandwiched by Nafion membrane was used.
First, the equilibrium potential was measured in a nitrogen atmosphere, and then hydrogen was bubbled into the cell on one side. Table 2 shows the measurement conditions.

  The obtained results are shown in FIG. In FIG. 5, the Nafion membrane alone decreased the equilibrium potential due to hydrogen permeation, but this decrease was not observed when a crossover layer was present.

(Comparative Example 1: Measurement of H ₂ O ₂ generation by Pt particle size system)
A platinum-supported carbon catalyst (average Pt particle size: 3 nm-Sample A, Pt-supported amount: 45.6 wt%, carrier carbon: Vulcan XC-72 (manufactured by Cabot)) was used as the electrode catalyst, and the same method as in Example 1 was used. An anti-degradation layer ink slurry was prepared.
Slurry A and Sample A were dropped with a micropipette onto the GC substrate of the RRDE electrode, and H ₂ O ₂ was measured. Table 3 shows the measurement conditions.

  The obtained result is shown in FIG. In FIG. 6, since the ring current value increases with time, it is recognized that the generation rate of hydrogen peroxide increases when the Pt particle diameter is 5 nm or less.

(Example 2: Creation of MEA provided with deterioration preventing layer)
The slurry A produced in Example 1 was printed on a 20 μm Nafion film by a screen printing method so as to have a predetermined Pt carrying amount, and dried at 60 ° C. for 3 hours. Thereafter, a 5 wt% Nafion solution was printed on the surface coated with the deterioration preventing layer by the same method until the thickness became 5 μm.
In addition, the active surface area by the electrochemistry of the catalyst of a catalyst deterioration prevention layer was 63 m < ² > / g-Pt, and the surface area by CO adsorption method was 80 m < ² > / g-Pt. The thickness of the film deterioration preventing layer was 1 μm. The amount of Pt supported by the film deterioration preventing layer was 40 μg / cm ² .

(Example 3 and Comparative Example 2; endurance test results)
(Production of fuel cell)
About preparation of the fuel battery cell, it performed as follows in all.
After adding 5 times the amount of purified water to the mass of Pt-supported carbon (Pt-supported amount: 48.6 wt%, average Pt particle size: 3.5 nm, carrier carbon: Vulcan XC-72 (manufactured by Cabot)), A 0.5-fold amount of isopropyl alcohol was added, and a Nafion (DuPont, registered trademark) solution (Aldrich 5 wt. % Nafion (manufactured by DuPont, registered trademark) was added. The mixed slurry was well dispersed with an ultrasonic homogenizer, followed by addition of a vacuum degassing operation to prepare a catalyst slurry.
The catalyst slurry was printed on one side of the Teflon sheet by a screen printing method so as to have a predetermined Pt amount, and dried at 60 ° C. for 3 hours. Thereafter, the surface coated with the catalyst layer is 120 ° C. according to the electrolyte membrane (Example 1) obtained by laminating the deterioration preventing layer 12 obtained in Example 2 or only the fluorine-based electrolyte membrane (Comparative Example 2). Anode and cathode catalyst layers were attached respectively by hot pressing at 1.5 MPa for 10 minutes. The membrane electrode assembly (MEA) of Example 4 and Comparative Example 2 was bonded by bonding together the catalyst layer side of the electrolyte membrane coated with the catalyst layer thus produced and the carbon layer side of the carbon paper coated with the carbon layer. Produced.
In these MEAs, the amount of Pt used was 0.3 mg for the anode and 0.5 mg for the cathode per 1 cm ^{2 of the} apparent electrode area, and the electrode area was 25 cm ² . Further, Nafion (registered trademark, manufactured by DuPont) 112 (thickness: about 50 μm) was used as the electrolyte membrane.
The obtained MEA was put in a state where it was sandwiched by using two GDLs prepared earlier, sandwiched between graphite separators, and further sandwiched between gold-plated stainless steel current collector plates. did.

(Cell evaluation by endurance test 1)
A fuel cell single cell (evaluation single cell) was constructed using the produced MEA, and the cell voltage change with respect to the operation time was evaluated by the following method.
Hydrogen was supplied as fuel to the anode side of the fuel cell, and air was supplied to the cathode side. The supply pressure for both gases is atmospheric pressure, the temperature of the fuel cell body is set to 70 ° C., the hydrogen utilization rate is 67%, the anode supply gas dew point is 70 ° C., the air utilization rate is 40%, and the cathode supply gas dew point is 50%. The change in the cell voltage was examined when the load operation was performed for 10 minutes at a current density of 0.2 A / cm ² and 1.0 A / cm ² , respectively.
FIG. 7 shows changes in cell voltage due to load fluctuation operation as a result of power generation characteristics. In FIG. 7, the cell voltage is an average value of the cell voltage of 9 to 10 minutes from the start of 0.2 A / cm ² operation in the load fluctuation operation. As shown in FIG. 7, the fuel cell (single cell) of Example 4 formed using the deterioration preventing layer 12 is compared with the fuel cell of Comparative Example 2 formed without using the deterioration preventing layer 12. It was confirmed that high power generation performance (high potential) can be stably maintained for a long period of time because the amount of decrease in the cell voltage is remarkably reduced. From this, it was found that the durability of the battery provided with the deterioration preventing layer of the present invention can be remarkably improved.

It is drawing explaining the film | membrane deterioration prevention layer used for MEA of this invention. It is a drawing for explaining the relationship between the particle size or density of noble metal and the decomposition of hydrogen peroxide. It is drawing which shows an example of the experimental result by a rotating ring disk. It is drawing which shows the influence of the Pt carrying amount which gives on generation | occurrence | production of hydrogen peroxide. It is drawing which shows an example of the relationship between the presence or absence of a crossover layer, and an equilibrium potential. It is drawing which shows an example of the relationship with the generation | occurrence | production of hydrogen peroxide by the difference in Pt particle size. It is drawing which shows an example of a durability test result.

Explanation of symbols

11 Oxidant electrode,
12 Film degradation prevention layer,
13 Fuel electrode,
21 platinum particles,
22 Carbon particles.

Claims (7)

In a membrane electrode assembly for a fuel cell comprising a solid polymer electrolyte membrane, and a fuel electrode and an oxidizer electrode that sandwich the solid polymer electrolyte membrane from both sides,
The solid polymer electrolyte membrane has a membrane deterioration preventing layer containing a catalyst having a noble metal having a particle diameter of 5 nm or more and less than 20 nm arranged along the fuel electrode or oxidant electrode as a catalyst component. Membrane electrode assembly. In a membrane electrode assembly for a fuel cell comprising a solid polymer electrolyte membrane, and a fuel electrode and an oxidizer electrode that sandwich the solid polymer electrolyte membrane from both sides,
And wherein the solid polymer electrolyte in membrane has a membrane deterioration preventing layer containing a catalyst noble metal comprising disposed along the fuel electrode or oxidant electrode is in 10 [mu] g / cm ² or more 62μg / cm ² or less Membrane electrode assembly.   The membrane electrode assembly according to claim 1 or 2, wherein the catalyst is a catalyst containing platinum, ruthenium, iridium, palladium, or a mixture thereof. The catalyst, 30μg-Pt / cm ² or more 62μg-Pt / cm ² or less in any one membrane electrode assembly according to claim 1 comprising platinum.   The membrane electrode assembly according to any one of claims 1 to 4, wherein the catalyst has an electrochemically active catalyst surface area of 70% or more of a catalyst surface area evaluated by gas adsorption.   The membrane electrode assembly according to any one of claims 1 to 5, wherein the thickness of the membrane deterioration preventing layer is in the range of 0.01 to 1 µm.   A fuel cell comprising the membrane electrode assembly according to claim 1.

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