JP2005108827A - Ink for catalyst layer formation and electrode using the same and membrane electrode junction - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen ion conductive polymer electrolyte fuel cell capable of raising battery voltage by improving gaseous diffusion property of a catalyst layer and maintaining the high battery voltage over a long time. <P>SOLUTION: In this ink for catalyst layer formation including, at least, polymer electrolyte having positive ion conductivity, catalyst carrying particles consisting of conductive carbon particles carrying electrode catalyst, and dispersion medium, an average radius of inertia of the polyelectrolyte is set to 150-300 nm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink for forming a catalyst layer that can be suitably used for the production of a polymer electrolyte fuel cell. Furthermore, the present invention relates to a gas diffusion electrode, a membrane electrode assembly, and a polymer electrolyte fuel cell provided with the gas diffusion electrode obtained by using the catalyst layer forming ink.

A polymer electrolyte fuel cell generates electricity and heat simultaneously by electrochemically reacting a fuel gas such as hydrogen and an oxidant gas such as air. A general basic configuration of such a polymer electrolyte fuel cell is schematically shown in FIG.
In the fuel cell 2 shown in FIG. 8, a particulate electrode catalyst made of a noble metal such as platinum is formed on both surfaces of a cation (hydrogen ion) conductive polymer electrolyte membrane 100 that selectively transports cations (hydrogen ions). A catalyst layer 110a mainly composed of conductive carbon particles supporting the carbon is disposed in close contact with a hot press or the like. Further, a gas diffusion layer 110b having both gas permeability and conductivity is disposed in close contact with the outer surface of the catalyst layer 110a by hot pressing or the like. The catalyst layer 110a and the gas diffusion layer 110b constitute a gas diffusion electrode 110.
Conductive separator plates 120a and 120b are disposed outside the gas diffusion electrode 110. The conductive separator plates 120a and 120b mechanically fix a membrane electrode assembly (MEA) formed of the polymer electrolyte membrane 100 having hydrogen ion conductivity and the gas diffusion electrodes 110 disposed on both sides thereof. Adjacent MEAs are electrically connected in series with each other. The conductive separator plates 120a and 120b have gas flow paths 130a and 130b for supplying a reaction gas to the gas diffusion electrode and carrying away a gas generated by the reaction or an excess gas.

The catalyst layer 110a is generally formed by thinly forming a mixture of conductive carbon particles carrying an electrode catalyst made of a noble metal such as platinum, a polymer electrolyte having hydrogen ion conductivity, and a dispersion medium. The As a polymer electrolyte having hydrogen ion conductivity, perfluorocarbon sulfonic acid is generally used.
The method for forming the catalyst layer 110a will be described more specifically. First, conductive carbon particles carrying an electrode catalyst made of a noble metal such as platinum, and conductive carbon coated with a water repellent or water repellent if necessary. The powder is mixed with a solution in which a polymer electrolyte having hydrogen ion conductivity is dispersed in an alcohol-based dispersion medium such as ethanol. Next, an organic solvent having a relatively high boiling point such as isopropyl alcohol or butyl alcohol is added to the mixture to prepare a catalyst layer forming ink.
Next, the catalyst layer 110a is formed by applying the ink for forming the catalyst layer to the polymer electrolyte membrane 100 or the gas diffusion layer 110b using a screen printing method, a spray coating method, a doctor blade method, or the like.
Alternatively, the catalyst layer 110a may be formed by applying and drying a catalyst layer forming ink on a support sheet made of a polymer material such as polypropylene. In this case, the catalyst layer 110a can be formed on the polymer electrolyte membrane 100 by thermocompression bonding the support sheet on which the catalyst layer 110a is arranged to the polymer electrolyte membrane 100 and transferring the catalyst layer 110a. .
The MEA can be produced by laminating the polymer electrolyte membrane 100, the catalyst layer 110a, and the gas diffusion layer 110b and thermocompression bonding with a hot press.

By the way, in the catalyst layer 110a, the size of the reaction area of the three-phase interface formed by the gap serving as the supply path for the reaction gas, the hydrogen ion conductive polymer electrolyte, and the electrode catalyst as the electron conductor is It is one of the most important factors that influence the discharge performance. The larger the three-phase interface is, the longer it is stable, the more durable the fuel cell.
Above all, ensuring a sufficient hydrogen ion conduction path (proton network) by the polymer electrolyte having hydrogen ion conductivity that constitutes one of the three-phase interfaces increases the contact area with the electrode catalyst, This is important because it increases the number of reaction sites.
For example, Patent Document 1 intends to allow platinum in the pores of conductive carbon particles to be coated with a polymer electrolyte (fluorine-containing carbon sulfonate ion exchange resin) having hydrogen ion conductivity. , Technology for reducing the molecular weight of the fluorine-containing carbon sulfonate ion exchange resin (polymer electrolyte) contained in the catalyst layer forming ink (specifically, the melt extrusion temperature of the precursor of the ion exchange resin is set to 80 to 170 ° C.) Technology to adjust) has been proposed. More specifically, attempts have been proposed to shorten the polytetrafluoroethylene (PTFE) type main chain skeleton constituting the polymer electrolyte.
Further, Patent Document 2 proposes an attempt to control the form (state) of the ink for forming a catalyst layer with a dispersion medium, for example, a method in which a polymer electrolyte is colloided and adsorbed on conductive carbon particles carrying platinum. ing.
JP 2000-188110 A JP 08-264190 A

However, even in the prior art including the above-mentioned Patent Documents 1 and 2, there is a possibility that platinum in the pores of the conductive carbon particles can be coated with the polymer electrolyte having hydrogen ion conductivity. However, a large amount of polymer electrolyte is also present in the voids (gas supply path) in the catalyst layer to which the gas is originally supplied, or a catalyst obtained by applying and drying the catalyst layer forming ink. In some cases, the polymer electrolyte was unevenly distributed in the thickness direction of the layer. Electrodes produced using the catalyst layer in this state increase the static electrochemical reaction area measured using cyclic voltammetry, but the current region (gas diffusion used in actual power generation) The voltage improvement in the rate limiting region) is reduced. This causes a decrease in gas diffusibility in the electrode including the catalyst layer, and causes flooding to occur easily.
In particular, in the case of a fuel cell including an electrode including a catalyst layer in the above-described state, even if a three-phase interface is well formed at the initial stage of cell operation, flooding occurs and voltage decreases with time. Sometimes it happened.

Next, the uneven distribution of the polymer electrolyte in the catalyst layer will be described in more detail with reference to the drawings. Here, FIGS. 9A and 9B are cross-sectional views schematically showing a conventional catalyst layer.
As shown in FIGS. 9A and 9B, the conventional catalyst layer forming ink includes conductive carbon particles 220 carrying an electrode catalyst 210 made of a noble metal, a high molecular ion conductivity with a short molecular chain. A molecular electrolyte 230 is used.
For example, when a catalyst layer is produced by a transfer method, when a catalyst layer forming ink is applied onto a resin support sheet 240, a polymer electrolyte having hydrogen ion conductivity is produced while the catalyst layer forming ink is dried. 230 is unevenly distributed on the support sheet 240 side. Therefore, the catalyst layer 110a transferred to the polymer electrolyte membrane 100 having hydrogen ion conductivity is in a state in which the polymer electrolyte 230 is unevenly distributed on the gas diffusion layer side (the side opposite to the polymer electrolyte membrane 100). The gas diffusibility and anti-flooding resistance of the resin become low.

In addition, even when the catalyst layer 110a is directly formed on the polymer electrolyte membrane 100 having hydrogen ion conductivity, since many hydrogen ion conductive polymer electrolytes exist in the vicinity of the hydrogen ion conductive polymer electrolyte membrane, The layer is less likely to contribute to the electrochemical reaction. Therefore, the voltage drop due to CO poisoning is large at the anode, and the voltage drop in the high current density region is large at the cathode. Further, such a fuel cell has a large voltage drop due to flooding, particularly during a high humidification operation.
The present invention has been made in view of the above problems, and includes a catalyst layer having sufficient gas diffusibility, and can maintain a high battery voltage while sufficiently preventing occurrence of flooding over a long period of time. It is an object of the present invention to provide a catalyst layer forming ink capable of easily and reliably obtaining a molecular electrolyte fuel cell. The present invention also provides a gas diffusion electrode and a membrane electrode assembly capable of easily and reliably obtaining a polymer electrolyte fuel cell capable of maintaining a high cell voltage while sufficiently preventing the occurrence of flooding over a long period of time. The purpose is to obtain. Furthermore, an object of the present invention is to obtain a polymer electrolyte fuel cell capable of maintaining a high battery voltage while sufficiently preventing the occurrence of flooding over a long period of time.

As a result of intensive studies to achieve the above object, the present inventors have found that the state of the polymer electrolyte in the ink for forming the catalyst layer is the distribution state of the polymer electrolyte in the catalyst layer formed using this. It has been found that this is one factor that greatly affects (the distribution state of the polymer electrolyte effective for the construction of a good three-phase interface).
Furthermore, the present inventors have used an average inertia radius of the polymer electrolyte in the catalyst layer forming ink (hereinafter referred to as “average inertia radius 1” if necessary) or a dispersion usable in the catalyst layer forming ink. The average inertia radius of the polymer electrolyte when dispersed in the medium (hereinafter referred to as “average inertia radius 2” if necessary) is used as an index indicating the state of the polymer electrolyte in the above-described catalyst layer forming ink. I found it effective.
The inventors of the present invention rather than selecting a polymer electrolyte having a specific range of molecular weight as the polymer electrolyte to be contained in the catalyst layer forming ink, rather, the average inertia radius 1 of the polymer electrolyte described above, or The distribution state of the polymer electrolyte in the catalyst layer obtained by using the ink for forming the catalyst layer by adding the polymer electrolyte satisfying the condition that the average inertia radius 2 of the polymer electrolyte is in a specific range. Is in a good state (a state where the uneven distribution of the polymer electrolyte is sufficiently reduced), and is extremely effective for easily and reliably forming a catalyst layer having a good gas diffusibility particularly excellent in flooding resistance. I found.
Furthermore, the present inventors have prepared a catalyst using a polymer electrolyte having a relatively large average inertia radius (average inertia radius 1 or average inertia radius 2) than the polymer electrolyte contained in the conventional catalyst layer forming ink. It has been found that it is extremely effective to constitute a layer forming ink and use this to form a catalyst layer to achieve the above object, and the present invention has been achieved.

That is, in order to solve the above problems, the present invention includes at least a polymer electrolyte having cation conductivity, catalyst-carrying particles composed of conductive carbon particles on which an electrode catalyst is supported, and a dispersion medium,
The average inertia radius of the polymer electrolyte is 150 to 300 nm,
An ink for forming a catalyst layer is provided.

As described above, by forming a catalyst layer using a polymer electrolyte having an average radius of inertia of 150 to 300 nm for the ink for forming the catalyst layer, it is easy to form a catalyst layer with less unevenness of the polymer electrolyte and excellent gas diffusibility. In addition, the three-phase interface formed by the electrode catalyst, the reaction gas, and the polymer electrolyte can be formed in a good state while sufficiently securing a conductive network by the polymer electrolyte.
Further, by using this catalyst layer, it is possible to obtain a gas diffusion electrode, a membrane electrode assembly, and a polymer electrolyte fuel cell that can maintain a high battery voltage for a long time.

Here, the “inertia radius” of the polymer electrolyte having cation conductivity (hydrogen ion conductivity) represents the spread from the center of gravity of the polymer chain present in the catalyst layer forming ink or dispersion medium, The “average inertia radius” indicates the arithmetic average value. Even for the same polymer chain, the radius of inertia can vary depending on the type of dispersion medium. However, in the present invention, when an ink for forming a catalyst layer is prepared by adding conductive carbon particles supporting an electrode catalyst made of a noble metal to a hydrogen ion conductive polymer electrolyte dispersion, another dispersion medium is added. Since it is not added, it is considered that the inertial radius 2 in the dispersion and the inertial radius 1 in the catalyst layer forming ink are substantially the same.
When the average inertia radius (1, 2) is less than 150 nm, the polymer electrolyte is unevenly distributed in the catalyst layer formed using the catalyst layer forming ink. Therefore, the gas diffusibility and battery voltage of the catalyst layer are lowered. On the other hand, when the average inertia radius (1, 2) exceeds 300 nm, when the polymer electrolyte dispersion is mixed with the conductive carbon particles supporting the electrode catalyst, the polymer electrolyte becomes pores of the conductive carbon particles. The electrode catalyst in the pores cannot be covered with the polymer electrolyte. For this reason, the reaction area of a three-phase interface becomes small, and a battery voltage becomes low.

The inertia radius can be obtained using a method known in the art. In the present invention, a polymer electrolyte dispersion having a polymer electrolyte concentration in the range of 0.1 to 1% by mass is prepared as a sample, and the intensity of scattered light emitted from the polymer electrolyte molecules in the polymer electrolyte dispersion And the radius of inertia is obtained by measuring the angle dependence by the static light scattering method.
In the present invention, the “polyelectrolyte dispersion liquid” means a polymer electrolyte partly dissolved in addition to the liquid in which the polymer electrolyte is dispersed, and the other part is dispersed without being dissolved. Including the liquid in the state.
In the present invention, the “dispersion medium” refers to the following liquid. In other words, it may be a liquid that can disperse the polymer electrolyte used, or it may be a liquid that can dissolve the polymer electrolyte. A part of the polymer electrolyte can be dissolved and the other part can be dispersed. It may be a liquid.

The present invention also includes at least the catalyst of the present invention as described above, comprising at least a polymer electrolyte having cation conductivity, catalyst-carrying particles made of conductive carbon fine particles carrying an electrode catalyst, and a dispersion medium. Having a catalyst layer formed with a layer forming ink;
A gas diffusion electrode is provided.

The gas diffusion electrode of the present invention described above has a catalyst layer formed using the above-described ink for forming a catalyst layer of the present invention, and therefore can maintain a high battery voltage for a long time. An electrode assembly and a polymer electrolyte fuel cell can be realized.
Here, in the present invention, the “gas diffusion electrode” may consist of (I) a catalyst layer alone, (II) a catalyst layer formed on the gas diffusion layer, that is, a gas diffusion layer and A combination with a catalyst layer may also be used.

Furthermore, the present invention provides a first electrode having a first catalyst layer, a second electrode having a second catalyst layer, and hydrogen ions disposed between the first electrode and the second electrode. A membrane electrode assembly comprising a conductive polymer electrolyte membrane,
At least one of the first catalyst layer and the second catalyst layer comprises at least a polymer electrolyte having cation conductivity, catalyst-carrying particles made of conductive carbon fine particles carrying an electrode catalyst, and a dispersion medium. Including the catalyst layer forming ink of the present invention described above,
A membrane electrode assembly is provided.

The membrane electrode assembly of the present invention described above has a catalyst layer and a gas diffusion electrode formed using the above-described ink for forming a catalyst layer of the present invention, and thus maintains a high battery voltage for a long time. It is possible to realize a polymer electrolyte fuel cell that can be used.
Note that one of the first electrode and the second electrode is an anode and the other is a cathode.

  Furthermore, the present invention provides a polymer electrolyte comprising the membrane electrode assembly described above and a pair of conductive separator plates having a gas flow path for supplying a reaction gas to the membrane electrode assembly. A fuel cell is provided.

  Since the above-described polymer electrolyte fuel cell of the present invention has the membrane electrode assembly of the present invention described above, a high battery voltage can be maintained for a long time.

According to the ink for forming a catalyst layer of the present invention, a catalyst layer with little uneven distribution of a polymer electrolyte and excellent gas diffusibility can be obtained, and a three-phase interface between an electrode catalyst, a reaction gas, and a polymer electrolyte is formed. While being able to make it a favorable state, the conductive network by a polymer electrolyte can fully be ensured. Further, by using this catalyst layer, it is possible to obtain a gas diffusion electrode, a membrane electrode assembly, and a polymer electrolyte fuel cell that can maintain a high battery voltage for a long time.
In addition, according to the gas diffusion electrode of the present invention, since it has a catalyst layer formed using the above catalyst layer forming ink, there is little uneven distribution of the polymer electrolyte, it has excellent gas diffusibility, and a high battery voltage over a long period of time. A membrane electrode assembly and a polymer electrolyte fuel cell that can be maintained can be obtained.
Furthermore, according to the membrane electrode assembly of the present invention, since the gas diffusion electrode of the present invention is provided, a high battery voltage can be maintained for a long time.
In addition, since the polymer electrolyte fuel cell of the present invention includes the membrane electrode assembly of the present invention described above, a high battery voltage can be maintained for a long time.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following description, the same or corresponding parts are denoted by the same reference numerals, and redundant description may be omitted.
FIG. 1 is a schematic cross-sectional view showing a basic configuration of a preferred embodiment of a polymer electrolyte fuel cell of the present invention. Here, the polymer electrolyte fuel cell 1 shown in FIG. 1 is a gas diffusion electrode formed using a preferred embodiment of the catalyst layer forming ink of the present invention (a suitable one of the gas diffusion electrodes of the present invention). Embodiment) and a membrane electrode assembly (a preferred embodiment of the membrane electrode assembly of the present invention) provided with the gas diffusion electrode.
A polymer electrolyte fuel cell 1 shown in FIG. 1 includes a polymer electrolyte membrane 10 having hydrogen ion conductivity, a gas diffusion electrode 11 having a catalyst layer 11a and a gas diffusion layer 11b, and gas flow paths 13a and 13b, respectively. The conductive separator plates 12a and 12b, the gasket 14, the sealing member 15, and the cooling water flow path 16 formed between the conductive separator plates 12a and 12b, respectively, are included.
On both surfaces of the polymer electrolyte membrane 10 having hydrogen ion conductivity, a catalyst layer 11a mainly composed of conductive carbon particles carrying a particulate electrode catalyst made of a noble metal such as platinum is publicly known such as hot press. Arranged in close contact with technology. Further, the gas diffusion layer 11b having both gas permeability and conductivity is disposed in close contact with the outer surface of the catalyst layer 11a by a known manufacturing technique such as hot pressing. A gas diffusion electrode (anode or cathode) 11 is composed of the catalyst layer 11a and the gas diffusion layer 11b. Further, a membrane electrode assembly is constituted by the polymer electrolyte membrane 10 and the pair of gas diffusion electrodes 11.

Conductive separator plates 12 a and 12 b are disposed outside the gas diffusion electrode 11. The conductive separator plates 12a and 12b mechanically fix the membrane electrode assembly MEA and electrically connect adjacent MEAs to each other in series. The conductive separator plates 12a and 12b have gas flow paths 13a and 13b for supplying a reaction gas to the gas diffusion electrode and carrying away a gas generated by the reaction or an excess gas.
A sealing member 15 for preventing water leakage is disposed between the pair of separator plates 12 a and 12 b having the cooling water flow path 16.
The polymer electrolyte membrane 10 has a function of selectively transmitting protons generated in the catalyst layer on the anode side to the catalyst layer on the cathode side along the film thickness direction. Further, the polymer electrolyte membrane 10 also has a function as a diaphragm for preventing hydrogen supplied to the anode and oxygen supplied to the cathode from being mixed.
Examples of the material of the separator plates 12a and 12b include metal, carbon, and a material in which graphite and a resin are mixed, and can be used widely.
Moreover, it does not specifically limit as a material which comprises a gas diffusion layer, A well-known thing can be used in the said field | area. For example, carbon cloth or carbon paper can be used.

Next, a preferred embodiment of the catalyst layer forming ink (the catalyst layer forming ink of the present invention) used for forming the catalyst layer 11a will be described.
This ink for forming a catalyst layer contains conductive carbon particles carrying an electrode catalyst made of a noble metal, a polymer electrolyte having cation (hydrogen ion) conductivity, and a dispersion medium. The average inertia radius (1, 2) of the polymer electrolyte is 150 to 300 nm.
Preferred examples of the polymer electrolyte include those having sulfonic acid groups, carboxylic acid groups, phosphonic acid groups, and sulfonimide groups as cation exchange groups. From the viewpoint of hydrogen ion conductivity, those having a sulfonic acid group are particularly preferred.

  The polymer electrolyte having a sulfonic acid group preferably has an ion exchange capacity of 0.5 to 1.5 meq / g dry resin. When the ion exchange capacity of the polymer electrolyte is less than 0.5 meq / g dry resin, the resistance value of the obtained catalyst layer may increase during power generation, which is not preferable. The ion exchange capacity is 1.5 mm. If it is more than equivalent / g dry resin, the water content of the obtained catalyst layer is increased, the resin layer tends to swell, and the pores may be blocked, which is not preferable. The ion exchange capacity is particularly preferably 0.8 to 1.2 meq / g dry resin.

As the polymer _{electrolyte, CF 2 = CF- (OCF 2} CFX) m -O p - (CF 2) a perfluorovinyl compound represented by _n -SO ₃ H (m is an integer of 0 to 3, n Represents an integer of 1 to 12, p represents 0 or 1, and X represents a fluorine atom or a trifluoromethyl group.) And a copolymer comprising a polymer unit based on tetrafluoroethylene. Preferably there is.

  Preferable examples of the fluorovinyl compound include compounds represented by the following formulas (3) to (5). However, in the following formula, q is an integer of 1 to 8, r is an integer of 1 to 8, and t is an integer of 1 to 3.

_{CF 2 = CFO (CF 2)} q -SO 3 H ··· (3)
CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) _r —SO ₃ H (4)
_{CF 2 = CF (OCF 2 CF} (CF 3)) t O (CF 2) 2 -SO 3 H ··· (5)

Specific examples of the polymer electrolyte include “Nafion” (trade name) manufactured by Aldrich, “Flemion” (trade name) manufactured by Asahi Glass Co., Ltd., and the like. Moreover, you may use the polymer electrolyte mentioned above as a constituent material of a polymer electrolyte membrane.
Here, as described above, the average inertia radius of the polymer electrolyte contained in the catalyst layer forming ink is 150 to 300 nm. When the average inertial radius is within this range, the catalyst layer 11a with less uneven distribution of the polymer electrolyte and excellent gas diffusibility can be obtained easily and reliably, and between the electrode catalyst, the reaction gas, and the polymer electrolyte. The three-phase interface can be in a good state, and a conductive network by the polymer electrolyte can be sufficiently secured.
Moreover, by using this catalyst layer 11a, the gas diffusion electrode 11, the membrane electrode assembly MEA, and the polymer electrolyte fuel cell 1 that can maintain a high battery voltage for a long time can be obtained.

When the average inertial radius is less than 150 nm, the polymer layer is unevenly distributed in the catalyst layer formed using the catalyst layer forming ink, so that the gas diffusibility of the catalyst layer and the battery voltage are lowered.
On the other hand, when the average inertia radius exceeds 300 nm, the polymer electrolyte can enter the pores of the conductive carbon particles when the polymer electrolyte dispersion is mixed with the conductive carbon particles supporting the electrode catalyst. Therefore, the electrode catalyst in the pores cannot be coated with the polymer electrolyte. For this reason, the reaction area of a three-phase interface becomes small, and a battery voltage becomes low.

The polymer electrolyte satisfying the above-described average inertia radius (1, 2) preferably has an average molecular weight of 200,000 to 300,000. A polymer electrolyte having a molecular weight in such a range has a larger radius of inertia than a polymer electrolyte used in a catalyst layer of a conventional fuel cell.
Therefore, uneven distribution of the polymer electrolyte 23 does not occur in the step of applying and drying the catalyst layer forming ink to form the catalyst layer, as shown in FIG. Here, FIG. 2 is a cross-sectional view schematically showing a catalyst layer formed using the ink for forming a catalyst layer of the present invention.

  The electrode catalyst used in the present invention is used by being supported on conductive carbon particles (powder) and is composed of metal particles. The metal particles are not particularly limited, and various metals can be used. For example, one selected from the group consisting of platinum, gold, silver, ruthenium, rhodium, palladium, osmium, iridium, chromium, iron, titanium, manganese, cobalt, nickel, molybdenum, tungsten, aluminum, silicon, zinc and tin The above is preferable. Among them, an alloy of noble metal or platinum is preferable, and an alloy of platinum and ruthenium is particularly preferable because the activity of the catalyst is stabilized.

The conductive carbon particles preferably have a specific surface area of 50 to 1500 m ² / g. When the specific surface area is less than 50 m ² / g, it is difficult to increase the loading ratio of the electrode catalyst, and the output characteristics of the obtained catalyst layer may be deteriorated, which is not preferable. The specific surface area exceeds 1500 m ² / g. In some cases, the pores are too fine, making it difficult to coat with a polymer electrolyte, and the output characteristics of the resulting catalyst layer may be reduced, which is not preferable. The specific surface area is particularly preferably 200 to 900 m ² / g.

  Furthermore, it is more preferable that the electrode catalyst particles have an average particle diameter of 1 to 5 nm. Electrocatalysts having an average particle size of less than 1 nm are not preferred because they are difficult to prepare industrially, and if it exceeds 5 nm, the activity per mass of the electrode catalyst is lowered, which leads to an increase in the cost of the fuel cell.

  Furthermore, the conductive carbon particles preferably have an average particle size of 0.1 to 1.0 μm. If it is less than 0.1 μm, the resulting catalyst layer has a dense structure and low gas diffusibility, and is prone to flooding. This is not preferable, and if it exceeds 1.0 μm, it is difficult to coat the electrode catalyst with the polymer electrolyte. Since the covering area decreases and the performance of the catalyst layer decreases, it is not preferable.

As the dispersion medium used for preparing the ink for forming the catalyst layer of the present invention, a liquid containing alcohol that can dissolve or disperse the polymer electrolyte (including a dispersed state in which the polymer electrolyte is partially dissolved) is used. Is preferred.
The dispersion medium preferably contains at least one of water, methanol, propanol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol and tert-butyl alcohol. These water and alcohol may be used alone or in combination of two or more. The alcohol is particularly preferably a straight chain having one OH group in the molecule, and ethanol is particularly preferable. This alcohol includes those having an ether bond such as ethylene glycol monomethyl ether.

  The catalyst layer forming ink preferably has a solid content concentration of 0.1 to 20% by mass. When the solid content concentration is less than 0.1% by mass, a catalyst layer having a predetermined thickness can be obtained unless the catalyst layer is repeatedly sprayed or applied many times when the catalyst layer is prepared by spraying or applying the ink for forming the catalyst layer. The production efficiency is worsened. On the other hand, if the solid content concentration is more than 20% by mass, the viscosity of the mixed solution becomes high and the resulting catalyst layer may be non-uniform. The solid content concentration is particularly preferably 1 to 10% by mass.

  In the present invention, it is preferable to prepare the ink for forming the catalyst layer so that the mass ratio of the electrode catalyst to the polymer electrolyte is 50:50 to 85:15 in terms of solid content. Thereby, the polymer electrolyte can efficiently coat the electrode catalyst, and the three-phase interface can be increased when a membrane electrode assembly is produced. In addition, when the amount of the electrode catalyst is less than 50:50 at this mass ratio, the pores of the conductive carbon particles as the support are crushed by the polymer electrolyte, and the reaction field is reduced. Therefore, as a polymer electrolyte fuel cell There is a risk of performance degradation. Furthermore, when the amount of the catalyst is larger than 85:15 in this mass ratio, the electrode catalyst may be insufficiently covered with the polymer electrolyte, and the performance as a polymer electrolyte fuel cell may be deteriorated. It is particularly preferable that the mass ratio of the electrode catalyst and the polymer electrolyte is adjusted to be 60:40 to 80:20.

Furthermore, the catalyst layer forming ink of the present invention preferably has a Casson yield value in the range of 1.5 to 2.3 Pa. If the Casson yield value is within this range, the polymer electrolyte is less likely to be unevenly distributed in the step of applying and drying the catalyst layer forming ink, and the catalyst layer forming ink has a viscosity suitable for coating. . Further, when this catalyst layer forming ink is used, as shown in FIG. 2, a catalyst layer having a structure in which the polymer electrolyte 23 is not unevenly distributed can be realized.
If the Casson yield value is less than 1.5, coating is possible, but uneven distribution of the polymer electrolyte is likely to occur in the drying step, and if it exceeds 2.3, coating tends to be very difficult.

Here, the Casson yield value will be described. The Casson yield value is a characteristic value of the catalyst layer forming ink that is measured and calculated by a cone plate type rotational viscometer called an E type viscometer. The Casson yield value can be obtained using the Casson formula of Formula (6).
The Casson formula of the following formula (6) indicates that the following (7) and the following (8) are in a linear relationship. The point that extrapolates the straight line represented by the Casson equation of the following mathematical formula (6) and cuts the axis of the following (7) is the following (9), and the Casson yield value is obtained by squaring this.

  The ink for forming a catalyst layer of the present invention can be prepared based on a conventionally known method except that a polymer electrolyte that satisfies the above-described condition of the radius of inertia is used. Specifically, the dispersion liquid is pushed from a narrow part by applying high pressure such as using a stirrer such as a homogenizer or homomixer, using a high-speed rotating jet flow method, or a high-pressure emulsifier. The method of giving a shearing force to a dispersion liquid by taking out is mentioned.

When the ink for forming a catalyst layer of the present invention obtained as described above is filtered using a membrane filter having a pore size of 0.2 μm, the capture ratio A (%) of the polymer electrolyte trapped on the membrane filter However, it is preferable that the conditions of following formula (1) and following formula (2) are satisfy | filled simultaneously.
50 ≦ A ≦ 90 (1)
A = (1-C / B) × 100 (2)
[In the formula (2), B is the mass of the polymer electrolyte in the catalyst layer forming ink / (the mass of the polymer electrolyte in the catalyst layer forming ink + the mass of the dispersion medium in the catalyst layer forming ink), C is The mass of the polymer electrolyte in the filtrate obtained after filtration / the mass of the filtrate). ]

  As described above, when the ink for forming a catalyst layer of the present invention is filtered using a membrane filter having a pore diameter of 0.2 μm after preparation, the capture ratio A (% of the polymer electrolyte captured on the membrane filter) ) Is adjusted so as to satisfy the condition of the above-mentioned formula (1) {ie, A is 50 or more and 90 or less}, the polymer electrolyte contained in the catalyst layer forming ink is preferably at least 0.2 μm (200 nm). It can be confirmed afterwards that it has an average radius of inertia (1). Therefore, if the catalyst layer forming ink of the present invention satisfying the above conditions is used, a catalyst layer with less uneven distribution of the polymer electrolyte and excellent gas diffusibility can be formed, and a high battery voltage can be maintained for a long time. A gas diffusion electrode, a membrane electrode assembly, and a polymer electrolyte fuel cell can be obtained.

Here, B is represented by {mass of polymer electrolyte in catalyst layer forming ink / (mass of polymer electrolyte in catalyst layer forming ink + mass of dispersion medium in catalyst layer forming ink)}. This value can be obtained from the composition ratio of the constituent elements of the catalyst layer forming ink.
C is represented by (mass of polymer electrolyte in filtrate obtained after filtration / mass of filtrate). This value can be determined, for example, by removing the dispersion medium by drying the filtrate and measuring the mass of the polymer electrolyte. The drying is performed by experimentally obtaining conditions under which the polymer electrolyte is not decomposed and the dispersion medium is sufficiently removed. The filtration conditions are adjusted so that the filtrate does not contain catalyst-carrying particles.

Here, when the value A {= (1−C / B) × 100} in the formula (1) is less than 50, the average inertia radius (1) of the polymer electrolyte contained in the catalyst layer forming ink is small. Thus, it is difficult to obtain a catalyst layer having an unevenly distributed polymer electrolyte and excellent gas diffusibility, and if it exceeds 90, the average inertia radius of the polymer electrolyte is too large. Since molecular electrolyte cannot enter and the reaction area decreases, it is not preferable.
When obtaining the value A {= (1−C / B) × 100} of the above formula (2), the values of B and C are used so that the respective units are the same. .

  Furthermore, when the ink for forming a catalyst layer of the present invention is filtered using a membrane filter having a pore size of 1.0 μm, the average inertia radius (2) of the polymer electrolyte contained in the filtrate is analyzed by diluting the filtrate. It is preferable that it is 150-300 nm.

  As described above, when the catalyst layer forming ink of the present invention was filtered using a membrane filter having a pore size of 1.0 μm after preparation, the filtrate was diluted and analyzed, and the average inertia of the polymer electrolyte contained in the filtrate was analyzed. If the radius is 150 to 300 nm, it can be confirmed later that the polymer electrolyte contained in the catalyst layer forming ink has a preferred average radius of inertia. If the ink for forming a catalyst layer of the present invention that satisfies the above conditions is used, a catalyst layer with little uneven distribution of polymer electrolyte and excellent gas diffusibility can be formed, and a high battery voltage can be maintained for a long time. A gas diffusion electrode, a membrane electrode assembly, and a polymer electrolyte fuel cell can be obtained.

  Here, the filtrate obtained by filtering the prepared catalyst layer forming ink using a membrane filter having a pore diameter of 1.0 μm has a concentration of the polymer electrolyte of 0.1 to 1% by mass as described above. Then, the scattered light intensity and angle dependence emitted from the polyelectrolyte molecules in the diluted filtrate are measured by the static light scattering method.

  Next, when the catalyst layer is formed using the catalyst layer forming ink of the present invention, the catalyst layer is formed on the support sheet. Specifically, the catalyst layer may be formed by spraying or coating the catalyst layer forming ink on the support sheet and drying the liquid film formed of the catalyst layer forming ink on the support sheet. .

Here, the gas diffusion electrode of the present invention may be composed of only (I) the catalyst layer, and (II) one in which the catalyst layer is formed on the gas diffusion layer, that is, the gas diffusion layer and the catalyst layer. It may be a combination.
In the case of (I), only the catalyst layer obtained by peeling from the support sheet may be produced as a product (gas diffusion electrode), or a product in which the catalyst layer is formed to be peelable on the support sheet is produced as a product. May be. As this support sheet, as will be described later, a synthetic resin sheet having no solubility in the mixed solution for forming the catalyst layer, a laminate film having a structure in which a layer made of a synthetic resin, a layer made of a metal is laminated, Examples thereof include metallic sheets, ceramic sheets, inorganic organic composite sheets, and polymer electrolyte membranes.

  In the case of (II), one or more other layers such as a water repellent layer may be disposed between the gas diffusion layer and the catalyst layer. Further, a product in which the support sheet is releasably bonded to the surface of the catalyst layer opposite to the gas diffusion layer may be manufactured as a product.

The support sheet is made of (i) a polymer electrolyte membrane, (ii) a gas diffusion layer made of a porous material having gas diffusibility and electronic conductivity, or (iii) a synthetic resin having a property of not dissolving in a mixed solution. Examples thereof include any one of a sheet, a layer made of a synthetic resin, a laminate film having a structure in which a layer made of a metal is laminated, a metal sheet, a sheet made of ceramic, and a sheet made of an inorganic-organic composite material.
Examples of the synthetic resin include polypropylene, polyethylene terephthalate, ethylene / tetrafluoroethylene copolymer, and polytetrafluoroethylene.

  As a coating method of the mixed solution when forming the catalyst layer, a method using an applicator, a bar coater, a die coater, a spray, or the like, a screen printing method, a gravure printing method, or the like can be applied.

  From the viewpoint of more reliably obtaining the effects of the present invention, it is preferable that the two catalyst layers of the membrane electrode assembly have a thickness of 3 to 50 μm independently. If the thickness is less than 3 μm, it is difficult to form a uniform catalyst layer, and the durability due to insufficient catalyst amount is reduced, which is not preferable. If the thickness exceeds 30 μm, the gas supplied in the catalyst layer is diffused. This is not preferable because the reaction becomes difficult to proceed. From the viewpoint of obtaining the effects of the present invention more reliably, it is particularly preferable that the two catalyst layers of the membrane electrode assembly have a thickness of 5 to 20 μm independently.

The catalyst layer obtained by the catalyst layer forming step as described above can be suitably used for the production of gas diffusion electrodes, membrane electrode assemblies, and polymer electrolyte fuel cells.
At that time, when the polymer electrolyte membrane of (i) above was used as the support sheet, a catalyst layer was formed on both sides to obtain a membrane electrode assembly, and then the whole was made of carbon paper, carbon cloth or It may be sandwiched between gas diffusion layers such as carbon felt and bonded by a known technique by hot pressing or the like.

When the gas diffusion layer (ii) is used as a support sheet, the polymer electrolyte membrane is sandwiched between two gas diffusion layers with a catalyst layer so that the catalyst layer faces the polymer electrolyte membrane. And what is necessary is just to join by a well-known technique with a hot press etc. FIG.
Furthermore, when the catalyst layer is formed on the support sheet of (iii) above, the support sheet with the catalyst layer is brought into contact with at least one of the polymer electrolyte membrane and the gas diffusion layer, and the support The catalyst layer may be transferred by peeling the sheet and bonded by a known technique.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

<< Examples 1-3 >>
(A) Preparation of catalyst layer forming ink The mass ratio of conductive carbon particles (average particle size: 0.1 to 1.0 μm, TEC10E50E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) and platinum as an electrode catalyst is 1: 1 is dispersed in a hydrogen ion conductive polymer electrolyte ethanol dispersion so that the mass ratio of the polymer electrolyte to the conductive carbon is 1: 1, thereby forming a catalyst layer on the cathode side. Ink was obtained.
Here, the concentration of the polymer electrolyte in the polymer electrolyte dispersion was 10% by mass. Further, as the hydrogen ion conductive polymer electrolyte, perfluorocarbon sulfonic acid (EW1100) having an average radius of inertia (2) and a molecular weight in 100% ethanol shown in A to C of Table 1 was used.

The catalyst on the cathode side except that conductive carbon particles (average particle size: 0.1 to 1.0 μm, TEC61E54E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) carrying platinum ruthenium instead of platinum were used as the electrode catalyst. In the same manner as the layer forming ink, an anode side catalyst layer forming ink was obtained.
At this time, the average inertia radii of the perfluorocarbon sulfonic acids contained in the cathode side catalyst layer forming ink and the anode side catalyst layer forming ink used in the same battery were the same.

The Casson yield value was calculated | required about the ink for catalyst layer formation containing the perfluorocarbon sulfonic acid from which an average inertia radius differs. Here, the cone diameter of the rotational viscometer used was 35 mm, the cone angle was 2 °, and the shear rate was measured in the range of 0.1 to 100 S ⁻¹ . The measurement temperature was 25 ° C. The ratio of each component of each ink for forming the catalyst layer was the same, and the catalyst-supporting particles were 16.6% by mass, the polymer electrolyte was 8.3% by mass, and the ethanol was 75.1% by mass.
Table 1 shows the Casson yield values calculated using the above-mentioned Casson equation for each catalyst layer forming ink.

Next, after preparing the above ink for forming a catalyst layer, it is filtered using a membrane filter having a pore size of 0.2 μm (cellulose mixed ester type membrane filter manufactured by Advantech Toyo Co., Ltd.) and captured on the membrane filter. The polymer electrolyte capture ratio A (%) was determined based on the following formula (2).
A = (1-C / B) × 100 (2)
The B value {= the mass of the polymer electrolyte in the ink for forming the catalyst layer / (the mass of the polymer electrolyte in the ink for forming the catalyst layer + the mass of the dispersion medium in the ink for forming the catalyst layer) is the formation of the catalyst layer before filtration. It was determined by measuring the mass of the polymer electrolyte and the dispersion medium contained in the ink for use. The C value {= the mass of the polymer electrolyte in the filtrate obtained after filtration / the mass of the filtrate)} was determined by measuring the mass of the filtrate and the polymer electrolyte in the filtrate.

  Further, the catalyst layer forming ink is filtered using a membrane filter having a pore size of 1.0 μm (cellulose mixed ester type membrane filter manufactured by Advantech Toyo Co., Ltd.) to obtain a filtrate, and the concentration of the polymer electrolyte with ethanol Was diluted to 0.1 to 1% by mass, and the average inertial radius was determined as described above. The average inertial radius measured in the polymer electrolyte dispersion used for the preparation of the catalyst layer forming ink was It was almost the same.

(B) Production of Gas Diffusion Electrode and Membrane Electrode Assembly (MEA) The cathode side catalyst layer forming ink is placed on a support sheet (50 μm thick polypropylene sheet) with a platinum mass of 0.35 mg / cm ^2. Thus, the coating was carried out with a bar coater and dried at room temperature to form a cathode-side catalyst layer on the support sheet.
Next, the support sheet with the catalyst layer on the cathode side was cut into a predetermined size (60 mm square) with a punching die. The catalyst layer formed on the cut support sheet was thermally transferred at 130 ° C. and 50 kg / cm ² to one surface of a hydrogen ion conductive polymer electrolyte membrane (Gore select membrane manufactured by Gore).

Similarly, the ink for forming the catalyst layer on the anode side was applied to a support sheet (a polypropylene sheet having a thickness of 50 μm) with a bar coater so that the mass of platinum ruthenium was 0.35 mg / cm ² and dried at room temperature. Then, the anode-side catalyst layer was formed on the support sheet.
Next, the support sheet with the catalyst layer on the anode side was cut into a predetermined size (60 mm square) with a punching die. The catalyst layer formed on the cut support sheet was thermally transferred to the other surface of the hydrogen ion conductive polymer electrolyte membrane at 130 ° C. and 50 kg / cm ² .

Next, a 400 μm-thick carbon cloth (GF-20-31E manufactured by Nippon Carbon Co., Ltd.) was impregnated in a fluororesin-containing aqueous dispersion (Neoflon ND1 manufactured by Daikin Industries, Ltd.) and dried at room temperature. Water repellent treatment was applied.
Subsequently, a dispersion obtained by dispersing conductive carbon particles in a dispersion obtained by mixing distilled water and Triton X-100 as a surfactant is mixed with an aqueous dispersion containing a fluororesin (Daikin Industries ( Co., Ltd. Polyflon D1) was added and stirred and mixed with a planetary mixer to prepare a water repellent layer ink. The water repellent layer ink obtained here was an aqueous dispersion containing 73% by weight distilled water, 2% by weight Triton X-100, 21% by weight conductive carbon particles, and 4% by weight fluororesin ( Polyflon D1).

The water repellent layer ink was applied to one surface of the carbon cloth subjected to the water repellent treatment as described above using a doctor blade method so that the ink solid content application mass was 4 mg / cm ^2. And dried. After drying, it was baked at 380 ° C. for 10 minutes to form a water repellent layer.
The carbon cloth with a water repellent layer thus obtained was punched with a punching die of a predetermined size (60 mm square) in order to use it as a gas diffusion layer. The gas diffusion layers obtained by punching in this way were arranged on the catalyst layers on both sides of the hydrogen ion conductive polymer electrolyte membrane so that the water-repellent layers faced inward with the water-repellent layers facing inward.

Furthermore, a composite gasket having a three-layer structure of silicone rubber / polyethylene terephthalate / silicone rubber was positioned and arranged at the peripheral edge of a gas diffusion electrode composed of a catalyst layer and a gas diffusion layer.
The polymer electrolyte membrane, the two catalyst layers, the two gas diffusion layers, and the gasket were thermocompression bonded at 130 ° C. and 50 kgf / cm ² for 10 minutes to obtain a membrane electrode assembly (MEA). Cells A, B, and C were respectively constituted by using MEAs containing perfluorocarbon sulfonic acids having different average radii of inertia.

<< Comparative Examples 1 and 2 >>
Further, MEA and comparative batteries 1 and 2 were obtained in the same manner as in Example 1 except that the hydrogen ion conductive polymer electrolyte was changed to the molecular weight and average inertia radius shown in D to E of Table 1.

[Evaluation]
The batteries A to C and the comparative batteries 1 and 2 produced as described above were evaluated as follows.

(1) Measurement of cross-sectional direction distribution of polymer electrolyte in catalyst layer First, in the above examples and comparative examples, conductive polymer in the cross-sectional direction of the catalyst layer formed by coating and drying on a support (polypropylene sheet). The distribution of the electrolyte was examined using an EPMA (Electron Probe Microanalyzer).
From the measurement results, the mass ratio (polymer electrolyte / conductive carbon particles) of the polymer electrolyte (perfluorocarbon sulfonic acid) to the conductive carbon particles on the support sheet side and the catalyst layer surface side was calculated. The obtained results are shown in FIG. FIG. 3 is a graph showing the distribution of the polymer electrolyte in the cross-sectional direction of the catalyst layer in the batteries of Examples and Comparative Examples.

As the average inertia radius of the polymer electrolyte is large and the Casson yield value of the ink for forming the catalyst layer is increased, the distribution of the hydrogen ion conductive polymer electrolyte in the cross-sectional direction of the catalyst layer is made uniform. That is, it approached the polymer electrolyte / conductive carbon particle ratio (= 1.0) of the catalyst layer forming ink.
This is presumably because the flow after application of the ink for forming the catalyst layer could be suppressed by increasing the average inertia radius of the hydrogen ion conductive polymer electrolyte.

(2) Battery initial characteristics Initial battery IV characteristics were measured for batteries A to C and comparative batteries 1 and 2 at a battery temperature of 70 ° C. At this time, hydrogen (H ₂ ) humidified so that the dew point was 70 ° C. was supplied to the anode at 1 atm, and air humidified so that the dew point was 70 ° C. was supplied to the cathode at normal pressure. The hydrogen utilization rate was set to 70% and the oxygen utilization rate was set to 50%. The obtained results are shown in FIG.
FIG. 4 shows initial IV characteristics when H ₂ and air are supplied to the batteries of the example and the comparative example. Here, graph a shows battery A, graph b shows battery B, graph c shows battery C, graph d shows comparative battery 1, and graph e shows comparative battery 2 (FIGS. 5 to 7). The same applies to the above).

FIG. 4 shows that the battery voltages of the batteries A to C are higher than those of the comparative batteries 1 and 2. In particular, since the difference between the battery voltages of the batteries A to C and the battery voltages of the comparative batteries 1 and 2 is large in the high current density region, the uneven distribution of the hydrogen ion conductive polymer electrolyte in the cross-sectional direction of the catalyst layer is improved. This is considered to be because the gas diffusibility at the cathode was improved.
Moreover, in the comparative battery 2, since the average inertia radius of the hydrogen ion conductive polymer electrolyte is too large, the polymer electrolyte cannot enter into the pores of the conductive carbon particles, and therefore, in the catalyst layer, It is considered that the reaction area was lowered and the battery voltage was lowered at the total current density.

Next, instead of H ₂ , reformed simulation gas (SRG) (H ₂ : 70%, CO ₂ : 20%, CO: 20 ppm) was used at a battery temperature of 70 ° C. in the same manner as described above. The initial IV characteristics of C and comparative batteries 1 and 2 were measured. Here, the reformed simulation gas humidified so that the dew point was 70 ° C. was supplied to the anode at 1 atmosphere, and air humidified so that the dew point was 70 ° C. was supplied to the cathode at normal pressure. The hydrogen utilization rate at this time was 70%, and the oxygen utilization rate was 50%. The obtained results are shown in FIG. FIG. 5 shows initial IV characteristics at the time of SRG / air supply of the polymer electrolyte fuel cells of Examples and Comparative Examples.
Further, FIG. 6 shows a voltage difference ΔV between the generated voltage by hydrogen and the generated voltage by SRG. FIG. 6 shows the difference ΔV between the voltage when hydrogen is used and the voltage when SRG is used in the polymer electrolyte fuel cells of Examples and Comparative Examples.

FIG. 5 shows that the battery voltages of the batteries A to C are higher than the battery voltages of the comparative batteries 1 and 2. This is also considered to be because the uneven distribution of the hydrogen ion conductive polymer electrolyte in the cross-sectional direction of the catalyst layer was improved and the gas diffusibility at the cathode was improved, as in the case of using hydrogen as the fuel gas.
Moreover, it turns out that the voltage drop by using SRG is small in battery AC from FIG. From this result, it is considered that the gas diffusibility is also improved in the anode, and the CO poisoning resistance is improved.

(3) Battery durability A durability test was conducted when the current density was 0.2 A / cm ² . At this time, the modified simulated gas (SRG) (H ₂ : 70%, CO ₂ : 20%, CO: 20 ppm) humidified so that the dew point is 70 ° C. is supplied to the anode at 1 atm, and the dew point is 70 ° C. Humid air was supplied to the cathode at normal pressure. The hydrogen utilization rate at this time was 70%, and the oxygen utilization rate was 50%. The obtained results are shown in FIG. FIG. 7 is a graph showing the change with time of voltage at a constant current density (0.2 A / cm ² ) in the polymer electrolyte fuel cells of Examples and Comparative Examples.

  From FIG. 7, it can be seen that, in the comparative batteries 1 and 2, the rate of voltage drop increases with time. However, the batteries A to C maintain the initial high voltage even after a long time has elapsed. This result shows that the fuel cell using the catalyst layer of the present invention can maintain a stable voltage for a long time.

  By using the catalyst layer forming ink of the present invention, it is possible to provide a fuel cell capable of maintaining a stable high voltage for a long time. This fuel cell can be suitably used for an automobile fuel cell using a polymer electrolyte, a home cogeneration system using a polymer electrolyte fuel cell, and the like.

It is a schematic sectional drawing which shows the basic composition of suitable one Embodiment of the polymer electrolyte fuel cell of this invention. It is sectional drawing which shows typically the catalyst layer formed using the ink for catalyst layer formation of this invention. It is a graph showing distribution of the hydrogen ion conductive polymer electrolyte of the cross-sectional direction of the catalyst layer in the battery of an Example and a comparative example. It is a graph showing the initial the I-V characteristic at the time of H ₂ / air supply of polymer electrolyte fuel cells of Examples and Comparative Examples. It is a graph which shows the initial IV characteristic at the time of SRG / air supply of the polymer electrolyte fuel cell of an Example and a comparative example. It is a graph which shows the difference (DELTA) V of the voltage when using hydrogen and the voltage when using SRG of the polymer electrolyte fuel cell of an Example and a comparative example. It is a graph which shows the time-dependent change of the voltage in the constant current density (0.2 A / cm < ₂ >) in the polymer electrolyte fuel cell of an Example and a comparative example. It is a schematic sectional drawing which shows the basic composition of an example of the conventional polymer electrolyte fuel cell. It is sectional drawing which shows the conventional catalyst layer typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Polymer electrolyte membrane 11 Gas diffusion electrode 11a Catalyst layer 11b Gas diffusion layer 12 Conductive separator plate 13 Gas flow path 14 Gasket 15 Sealing member 16 Cooling water flow path 210 Electrode catalyst 220 Conductive carbon particle 230 Polymer electrolyte 240 Support sheet 250 Polymer electrolyte membrane

Claims (9)

A polymer electrolyte having cationic conductivity, catalyst-carrying particles made of conductive carbon particles carrying an electrode catalyst, and a dispersion medium,
The average inertia radius of the polymer electrolyte is 150 to 300 nm;
An ink for forming a catalyst layer.   The ink for forming a catalyst layer according to claim 1, wherein the Casson yield value is 1.5 to 2.3 Pa.   The catalyst layer forming ink according to claim 1, wherein an average particle diameter of the catalyst-carrying particles is 0.1 to 1.0 μm. When filtration is performed using a membrane filter having a pore diameter of 0.2 μm, the capture ratio A (%) of the polymer electrolyte trapped on the membrane filter satisfies the conditions of the following formula (1) and the following formula (2). Charging at the same time,
The ink for forming a catalyst layer according to any one of claims 1 to 3.
50 ≦ A ≦ 90 (1)
A = (1-C / B) × 100 (2)
[In Formula (2), B is the mass of the polymer electrolyte / (the mass of the polymer electrolyte + the mass of the dispersion medium), and C is the mass of the polymer electrolyte / the mass of the filtrate obtained after the filtration. ). ] When filtered using a membrane filter having a pore diameter of 1.0 μm, the filtrate was diluted and analyzed, and the average inertia radius of the polymer electrolyte contained in the filtrate was 150 to 300 nm.
The ink for forming a catalyst layer according to any one of claims 1 to 4. The dispersion medium contains at least one selected from the group consisting of water, methanol, propanol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol and tert-butyl alcohol;
The ink for forming a catalyst layer according to any one of claims 1 to 5. The catalyst according to any one of claims 1 to 6, comprising at least a polymer electrolyte having cation conductivity, catalyst-carrying particles composed of conductive carbon fine particles carrying an electrode catalyst, and a dispersion medium. Having a catalyst layer formed with a layer forming ink;
A gas diffusion electrode characterized by. A first electrode having a first catalyst layer; a second electrode having a second catalyst layer; a polymer electrolyte membrane disposed between the first electrode and the second electrode; A membrane electrode assembly comprising:
At least one of the first catalyst layer and the second catalyst layer is a polymer electrolyte having cation conductivity, catalyst-carrying particles made of conductive carbon fine particles carrying an electrode catalyst, a dispersion medium, Is formed with the medium layer forming ink according to any one of claims 1 to 6,
A membrane electrode assembly characterized by the above.   9. A polymer electrolyte fuel cell comprising: the membrane electrode assembly according to claim 8; and a pair of conductive separator plates having a gas flow path for supplying a reaction gas to the membrane electrode assembly. .

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