JP2017050107A - Method for manufacturing membrane-electrode assembly, and method for manufacturing solid polymer fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method to efficiently, economically and readily obtain a membrane-electrode assembly with an electrode catalyst layer, which is high in reactive gas diffusibility, has both of the property of draining water resulting from an electrode reaction and the property of retaining water, and shows a high power generation property even in a low-humidification condition.SOLUTION: A method for manufacturing a membrane-electrode assembly which has a polymer electrolyte film and electrode catalyst layers on one face of the polymer electrolyte film and the other face on its sides opposite to each other comprises the steps of: bonding the first electrode catalyst layer formed on a base to a part of the one face by putting a pressure on the first electrode catalyst layer; and bonding the second electrode catalyst layer formed on a base to another part of the one face by putting a pressure on the second electrode catalyst layer. The step of bonding the second electrode catalyst layer is performed with the pressure lower than that in the step of bonding the first electrode catalyst layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a membrane electrode assembly and a method for producing a polymer electrolyte fuel cell.

A fuel cell is a power generation system that generates electricity simultaneously with heat by causing a hydrogen gas-containing fuel gas and an oxygen-containing oxidant gas to undergo reverse reaction of water electrolysis at an electrode including a catalyst. This power generation system has features such as high efficiency, low environmental load, and low noise as compared with conventional power generation systems, and is attracting attention as a clean energy source in the future. There are several types depending on the type of ion conductor used, and those using proton conductive polymer membranes are called solid polymer fuel cells.
Among fuel cells, polymer electrolyte fuel cells can be used near room temperature, so they are considered promising for use in in-vehicle power sources and household stationary power sources. In recent years, various research and development have been conducted. Yes. A polymer electrolyte fuel cell is a membrane electrode assembly (Membrane Electrode Assembly) in which a pair of electrode catalyst layers are arranged on both sides of a polymer electrolyte membrane, and a fuel gas containing hydrogen is applied to one of the electrodes. The battery is sandwiched between a separator plate having a gas flow path for supply and a separator plate having a gas flow path for supplying an oxidant gas containing oxygen to the other electrode.

The electrode that supplies the fuel gas is called the fuel electrode, and the electrode that supplies the oxidant is called the air electrode. These electrodes are composed of an electrode catalyst layer containing carbon particles supporting a catalyst material such as a platinum-based noble metal and a polymer electrolyte, and a gas diffusion layer having both gas permeability and electron conductivity.
For the electrode catalyst layer, efforts have been made to increase gas diffusibility in order to improve the output density of the fuel cell. The pores in the electrode catalyst layer serve as a passage for transporting a plurality of substances through the gas diffusion layer of the separator plate. The fuel electrode not only smoothly supplies the fuel gas to the three-phase interface, which is the oxidation-reduction reaction field, but also functions to supply water for smoothly conducting the generated protons in the polymer electrolyte membrane. . The air electrode functions to smoothly remove water generated by the electrode reaction along with the supply of the oxidant gas.

In order to prevent a so-called “flooding” phenomenon in which the power generation reaction is stopped due to hindering material transport, a method for improving drainage has been performed on the electrode catalyst layer (for example, Patent Document 1, (See Patent Document 2, Patent Document 3, and Patent Document 4).
Issues for the practical application of polymer electrolyte fuel cells include improvement of output density and durability, but the biggest issue is cost reduction (cost reduction).
One way to reduce costs is to reduce humidifiers. Perfluorosulfonic acid membranes and hydrocarbon membranes are widely used as the polymer electrolyte membrane located at the center of the membrane electrode assembly, but in order to obtain excellent proton conductivity, it is close to a saturated water vapor pressure atmosphere. Moisture management is required, and water is currently supplied from the outside by a humidifier. Therefore, in order to reduce power consumption and simplify the system, polymer electrolyte membranes that exhibit sufficient proton conductivity even under low humidification conditions that do not require a humidifier are being developed. .

However, the electrode catalyst layer with improved drainage properties needs to improve the water retention by optimizing the electrode catalyst layer structure because the polymer electrolyte dries up under low humidification conditions. Until now, in order to improve the water retention of a fuel cell under low humidification conditions, for example, a method of sandwiching a humidity adjusting film between an electrode catalyst layer and a gas diffusion layer has been proposed.
For example, Patent Document 5 describes a method in which a humidity adjusting film composed of conductive carbonaceous powder and polytetrafluoroethylene exhibits a humidity adjusting function to prevent dry-up.

Patent Document 6 describes a method of providing a groove on the surface of a catalyst electrode layer in contact with a polymer electrolyte membrane. In this method, by forming a groove having a width of 0.1 to 0.3 mm, a decrease in power generation performance under low humidification conditions is suppressed.
Patent Document 7 discloses a membrane electrode assembly including an electrode catalyst layer that has high diffusibility of a reaction gas, has both drainage and water retention of water generated by an electrode reaction, and exhibits high power generation characteristics even under low humidification conditions. A method for producing the membrane electrode assembly is described.
The membrane electrode assembly described in Patent Document 7 is a membrane electrode assembly in which a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers, and at least one of the electrode catalyst layers includes a first electrode catalyst portion, In the plane of the polymer electrolyte membrane, it is divided into at least two parts: a second electrode catalyst part adjacent to the first electrode catalyst part. A pore cylinder in which the difference between the pore volume of the first electrode catalyst portion having a diameter of 1.0 μm or less and the pore volume of the second electrode catalyst portion having a diameter of 1.0 μm or less is determined by a mercury intrusion method The conversion value by approximation is 0.1 mL / g or more and 1.0 mL / g or less.

The manufacturing method of the membrane electrode assembly described in Patent Document 7 includes the following first to third steps.
The first step is a step of forming a first electrode catalyst portion by applying a catalyst ink in which particles carrying a catalyst and a polymer electrolyte are dispersed in a solvent and drying. The second step is a step of forming a second electrode catalyst part by applying a catalyst ink in which particles carrying a catalyst and a polymer electrolyte are dispersed in a solvent and drying the catalyst ink.
In the third step, the first electrode catalyst part obtained in the first step and the second electrode catalyst part obtained in the second step are formed on the polymer electrolyte membrane on at least one surface of the polymer electrolyte membrane. It is the process of joining. As a joining method, a hot press method is exemplified.
Further, the pore volume of the first electrode catalyst portion arranged on the gas inlet side is set by making the coating speed of the catalyst ink in the first process larger than the coating speed of the catalyst ink in the second process. Is made smaller than the pore volume of the second electrode catalyst portion arranged on the gas outlet side.

JP 2006-120506 A JP 2006-332041 A JP 2007-87651 A JP 2007-80726 A JP 2006-252948 A JP 2007-141588 A Japanese Patent Laying-Open No. 2015-60801

However, the membrane electrode assemblies described in Patent Documents 1 to 6 have room for improvement in terms of power generation performance, and there is room for improvement in the manufacturing method. Moreover, in the manufacturing method of the membrane electrode assembly described in Patent Document 7, the pore volume of the electrode catalyst layer to be formed is controlled by the coating speed when the catalyst ink is applied. However, the change in the coating speed affects the coating amount of the catalyst ink, and it is necessary to separately adjust the catalyst loading amount, so there is room for improvement in terms of efficiency, economy, and ease.
The object of the present invention is to provide a membrane electrode assembly comprising an electrode catalyst layer that has high diffusibility of a reaction gas, has both drainage and water retention of water produced by an electrode reaction, and exhibits high power generation characteristics even under low humidification conditions. It is to provide an efficient, economical and easily obtainable method.

The first aspect of the present invention is a method for producing a membrane electrode assembly having the following constitutions (1) to (3).
(1) A method for producing a membrane electrode assembly having an electrode catalyst layer on one side and the other side of a polymer electrolyte membrane opposite to each other.
(2) a step of joining the first electrode catalyst layer formed on the base material to a part of the one surface by applying pressure to the first electrode catalyst layer; Joining the second electrode catalyst layer to a portion different from the part of the one surface by applying pressure to the second electrode catalyst layer.
(3) The step of joining the second electrode catalyst layer is performed at a lower pressure than the step of joining the first electrode catalyst layer.

The second aspect of the present invention is a method for producing a membrane / electrode assembly having the following constitutions (a) to (c).
(a) A method for producing a membrane electrode assembly having an electrode catalyst layer on one surface and the other surface of the polymer electrolyte membrane opposite to each other.
(b) a step of joining the first electrode catalyst layer formed on the substrate to a part of the one surface by heating the first electrode catalyst layer; and a second layer formed on the substrate. And heating the second electrode catalyst layer to a part different from the part of the one surface.
(c) The step of bonding the second electrode catalyst layer is performed at a lower temperature than the step of bonding the first electrode catalyst layer.

  According to the method of the present invention, a membrane electrode joint having an electrode catalyst layer that has high diffusibility of a reaction gas, has both drainage and water retention of water generated by an electrode reaction, and exhibits high power generation characteristics even under low humidification conditions. The body can be easily obtained efficiently and economically.

It is an exploded schematic diagram showing a membrane electrode assembly manufactured by a method of an embodiment. It is an exploded schematic diagram showing a polymer electrolyte fuel cell manufactured by the method of the embodiment.

<About the first aspect>
The manufacturing method of the membrane electrode assembly according to the first aspect has the following functions and effects by having the configurations (1) to (3).
By performing the step of bonding the second electrode catalyst layer at a lower pressure than the step of bonding the first electrode catalyst layer, the electrode catalyst layer on one side of the manufactured membrane electrode assembly is The pore volume of the electrode catalyst layer is smaller than the pore volume of the second electrode catalyst layer. That is, the first electrode catalyst layer has a denser structure than the second electrode catalyst layer.

Therefore, the membrane electrode assembly produced by this method is used for a polymer electrolyte fuel cell, the first electrode catalyst layer is disposed on the gas inlet side, and the second electrode catalyst layer is disposed on the gas outlet side. In the electrode catalyst part (first electrode catalyst part) on the gas inlet side, the water retention is high, and the drainage property is enhanced in the electrode catalyst part (second electrode catalyst part) on the gas outlet side. Water drainage and water retention under low humidification conditions.
In addition, by changing the coating speed of the catalyst ink when forming the electrode catalyst layer on the substrate, after forming the first electrode catalyst layer and the second electrode catalyst layer having different pore volumes, these Compared with the method of joining the electrode catalyst layer to one surface of the polymer electrolyte membrane, the method of the first aspect is such that the first electrode catalyst layer and the second electrode catalyst layer having different pore volumes are formed on one surface. A membrane electrode assembly can be easily obtained efficiently and economically.

The method of the first embodiment can have the following configuration (4).
(4) having a step of bonding the third electrode catalyst layer formed on the substrate to the other surface by applying pressure to the third electrode catalyst layer, The step of bonding is performed at a lower pressure than the step of bonding the second electrode catalyst layer after the step of bonding the first electrode catalyst layer and the second electrode catalyst layer.
The method of the first aspect preferably has the following configuration (5).
(5) The second electrode catalyst layer in the step of bonding the second electrode catalyst layer to the pressure (P1) applied to the first electrode catalyst layer in the step of bonding the first electrode catalyst layer. The ratio (P2 / P1) of the pressure (P2) applied to is 0.2 or more and 0.8 or less.

The method of the first aspect preferably has the following configuration (6).
(6) The pore volume of 1.0 μm or less in diameter of the first electrode catalyst layer after bonding to the one surface and the diameter of 1.0 μm of the second electrode catalyst layer after bonding to the one surface The difference from the following pore volume is set to 0.1 mL / g or more and 1.0 mL / g or less in terms of a conversion value obtained by approximating the pore cylinder obtained by mercury porosimetry.

<About the second aspect>
The manufacturing method of the membrane electrode assembly of the second aspect has the above-described configurations (a) to (c), and the following effects are obtained.
By performing the step of joining the second electrode catalyst layer at a lower temperature than the step of joining the first electrode catalyst layer, the electrode catalyst layer on the one surface side of the manufactured membrane electrode assembly is The pore volume of the electrode catalyst layer is smaller than the pore volume of the second electrode catalyst layer. That is, the first electrode catalyst layer has a denser structure than the second electrode catalyst layer.
Therefore, the membrane electrode assembly produced by this method is used for a polymer electrolyte fuel cell, the first electrode catalyst layer is disposed on the gas inlet side, and the second electrode catalyst layer is disposed on the gas outlet side. In the electrode catalyst portion on the gas inlet side, the water retention is high, and the drainage property is increased in the electrode catalyst portion on the gas outlet side, so that both the drainage property of the water generated by the electrode reaction and the water retention property under low humidification conditions can be achieved. .

In addition, by changing the coating speed of the catalyst ink when forming the electrode catalyst layer on the substrate, after forming the first electrode catalyst layer and the second electrode catalyst layer having different pore volumes, these Compared with the method of joining the electrode catalyst layer to one surface of the polymer electrolyte membrane, the method of the second aspect is such that the first electrode catalyst layer and the second electrode catalyst layer having different pore volumes are formed on one surface. A membrane electrode assembly can be easily obtained efficiently and economically.
The method of the second embodiment can have the following configuration (d).
(d) There is a step of joining the third electrode catalyst layer formed on the substrate to the other surface by heating the third electrode catalyst layer. The step of joining the third electrode catalyst layer is more than the step of joining the second electrode catalyst layer after the step of joining the first electrode catalyst layer and the second electrode catalyst layer. Perform at low temperature.

The method of the second aspect preferably has the following configuration (e).
(e) The temperature (T1) applied to the first electrode catalyst layer in the step of bonding the first electrode catalyst layer, and the second electrode catalyst layer in the step of bonding the second electrode catalyst layer. The difference (T2−T1) from the temperature (T2) applied to is 2 ° C. or more and 20 ° C. or less.
The method of the second aspect preferably has the following configuration (f).
(f) A pore volume of 1.0 μm or less in diameter having the first electrode catalyst layer after bonding to the one surface, and a diameter of 1.0 μm having the second electrode catalyst layer after bonding to the one surface. The difference from the following pore volume is set to 0.1 mL / g or more and 1.0 mL / g or less in terms of a conversion value obtained by approximating the pore cylinder obtained by mercury porosimetry.

<Embodiment>
Embodiments of the present invention will be described below with reference to the accompanying drawings. The present invention is not limited to the embodiments described below, and modifications such as design changes can be added based on the knowledge of those skilled in the art. These forms can also be included in the scope of the present invention.

[Membrane electrode assembly]
First, the membrane electrode assembly 11 manufactured by the method of the embodiment will be described.
FIG. 1 is an exploded schematic view showing a membrane electrode assembly 11. As shown in FIG. 1, a membrane electrode assembly 11 includes a polymer electrolyte membrane 1 and an electrode catalyst layer shown on the upper side in the drawing, which holds the polymer electrolyte membrane 1 from the upper and lower surfaces of the polymer electrolyte membrane 1. 2 and an electrode catalyst layer 3 shown on the lower side in the figure.
Further, in the membrane electrode assembly 11, the two electrode catalyst layers 2 and 3 are provided with catalyst material-carrying particles and a polymer electrolyte. Further, the electrode catalyst layer 2 of the membrane electrode assembly 11 is divided into two in the plane direction of the polymer electrolyte membrane 1. More specifically, the electrode catalyst layer 2 shown on the upper side in the drawing has a first electrode catalyst portion 2a located on the gas inlet side and a second electrode catalyst portion 2b located on the gas outlet side.

In the membrane electrode assembly 11, the value of the pore volume with a diameter of 1.0 μm or less calculated by the mercury intrusion method in terms of the cylindrical approximation of the pore is obtained from the first electrode catalyst portion 2a provided on the gas inlet side. However, the second electrode catalyst portion 2b provided on the gas outlet side is large. In other words, the value of the pore volume of the second electrode catalyst part 2b on the downstream side of the gas is larger than the value of the pore volume of the first electrode catalyst part 2a on the upstream side of the gas.
In the membrane electrode assembly 11, the first electrode catalyst part 2 a provided on the gas inlet side has a dense structure as compared with the second electrode catalyst part 2 b provided on the gas outlet side. Water retention is enhanced by the first electrode catalyst portion 2a provided on the side, and water removal is promoted by the second electrode catalyst portion 2b provided on the gas outlet side. Thus, the membrane electrode assembly 11 has both the drainage of water generated by the electrode reaction and water retention under low humidification conditions.

In the membrane / electrode assembly 11, unlike the case of reducing humidity by applying a conventional humidity adjusting film or forming grooves on the surface of the electrode catalyst layer, the power generation characteristics are not deteriorated due to an increase in interface resistance. From this, the solid polymer fuel cell provided with the membrane electrode assembly 11 is remarkably high in power generation characteristics even under low humidification conditions, compared with the solid polymer fuel cell provided with the conventional membrane electrode assembly. There is an effect.
For the pore volume of 1.0 μm or less in diameter calculated by the mercury intrusion method, the pore volume value of the second electrode catalyst portion 2b and the first electrode catalyst portion 2a It is preferable that the difference from the value of the pore volume is 0.1 mL / g or more and 1.0 mL / g or less.

When the difference between the pore volume value of the second electrode catalyst portion 2b and the pore volume value of the first electrode catalyst portion 2a is less than 0.1 mL / g, it is generated by an electrode reaction. It may be difficult to achieve both water drainage and water retention under low humidification conditions.
Further, even when the difference between the pore volume value of the second electrode catalyst portion 2b and the pore volume value of the first electrode catalyst portion 2a exceeds 1.0 mL / g, the electrode reaction It may be difficult to achieve both the drainage of the generated water and water retention under low humidification conditions.
In the membrane electrode assembly 11, the number of divisions of each electrode catalyst layer 3 is not limited to two. The number of divisions of each electrode catalyst layer 2 may be three or more. When the number of divisions of each electrode catalyst layer 2 is 3 or more, the pore volume having a diameter of 1.0 μm or less in terms of the cylindrical approximation of the pores obtained by the mercury intrusion method of 3 or more electrode catalyst layers 2 However, it changes in steps from the upstream side of the gas to the downstream side of the gas. In other words, even in the case of a membrane electrode assembly in which the number of divisions of the electrode catalyst layer is 3 or more, the value of the pore volume in the downstream portion of the gas is larger than the value of the pore volume in the upstream portion of the gas. Change so that becomes larger.

[Solid polymer fuel cell]
Next, the polymer electrolyte fuel cell 12 manufactured by the method of the embodiment will be described.
FIG. 2 is an exploded schematic view of the polymer electrolyte fuel cell 12. The polymer electrolyte fuel cell 12 includes an air electrode side gas diffusion layer 4 and a fuel electrode side gas diffusion layer 5 disposed so as to face the two electrode catalyst layers 2 and 3 of the membrane electrode assembly 11. Is provided. The electrode catalyst layer 2 and the gas diffusion layer 4 form an air electrode (cathode) 6. The electrode catalyst layer 3 and the gas diffusion layer 5 form a fuel electrode (anode) 7.
In addition, a pair of separators 10 and 10 made of a conductive and impervious material, each having a gas flow path 8 for gas flow and a cooling water flow path 9 for flow of cooling water, 5 are arranged on the outside of 5 respectively. For example, hydrogen gas is supplied as a fuel gas from the gas flow path 8 of the separator 10 on the fuel electrode 7 side.

On the other hand, a gas containing oxygen, for example, is supplied as an oxidant gas from the gas flow path 8 of the separator 10 on the air electrode 6 side. An electromotive force can be generated between the fuel electrode and the air electrode by causing an electrode reaction between the hydrogen of the fuel gas and the oxygen gas of the oxidant gas in the presence of the catalyst.
In the polymer electrolyte fuel cell 12, the polymer electrolyte membrane 1, the two electrode catalyst layers 2 and 3, and the gas diffusion layers 4 and 5 are sandwiched between a pair of separators 10 and 10. The polymer electrolyte fuel cell 12 is a single cell fuel cell, but a plurality of cells may be stacked via the separator 10 to form a polymer electrolyte fuel cell.

[Production method of membrane electrode assembly]
Next, the manufacturing method of the membrane electrode assembly 11 is demonstrated.
In this embodiment, the membrane electrode assembly 11 is manufactured by a method including the following first to fourth steps.
(First Step) A step of producing a catalyst ink in which particles carrying a catalyst and a polymer electrolyte are dispersed in a solvent.
(2nd process) The process of apply | coating a catalyst ink and forming a 1st electrode catalyst layer and a 2nd electrode catalyst layer on a base material.
(Third step) A step of bonding the first electrode catalyst layer to the polymer electrolyte membrane to form the first electrode catalyst part.
(4th process) The process of joining a 2nd electrode catalyst layer to a polymer electrolyte membrane, and forming a 2nd electrode catalyst part.
(Fifth Step) A step of joining the third electrode catalyst layer to the surface of the other polymer electrolyte membrane of the first electrode catalyst portion and the second electrode catalyst portion to form an electrode catalyst layer.

In the step of forming the first electrode catalyst portion and the second electrode catalyst portion, respectively, the bonding pressure for forming the second electrode catalyst portion is made lower than the bonding pressure for forming the first electrode catalyst portion. Electrocatalyst portions having different pore volumes can be formed.
The electrode catalyst part is formed by applying a catalyst ink in which catalyst-supported particles and a polymer electrolyte are dispersed in a solvent to form a coating film, removing the solvent in the coating film, and joining the electrolyte film. Is formed. At this time, when the bonding pressure is increased, the pore volume of the formed electrode catalyst portion can be reduced as compared with the case where the pressure is reduced. Further, when the bonding pressure is reduced, the pore volume of the electrode catalyst portion to be formed can be increased as compared with the case where the pressure is increased.

In the manufacturing method of the membrane electrode assembly 11, the bonding pressure in the step of forming the first electrode catalyst portion (third step) is the same as the bonding pressure in the step of forming the second electrode catalyst portion (fourth step). Larger than. By increasing the bonding pressure, the pore volume of the formed electrode catalyst part can be reduced. Further, the bonding pressure in the step of forming the electrode catalyst layer (fifth step) is made smaller than the bonding pressure in the step of forming the second electrode catalyst part (fourth step), so that the first electrode The pore volume of the catalyst part and the second electrode catalyst part is prevented from changing.
The ratio of the bonding pressure when forming the first electrode catalyst portion and the bonding pressure when forming the second electrode catalyst portion is in the range of 1: 0.2 to 1: 0.8. It is preferable. The first electrode to be formed when the ratio of the bonding pressure when forming the first electrode catalyst part and the bonding pressure when forming the second electrode catalyst part is less than 1: 0.2 The difference in pore volume between the catalyst portion and the second electrode catalyst portion becomes large, and it may be difficult to achieve both the drainage of water generated by the electrode reaction and the water retention under low humidification conditions.

Further, when the ratio of the bonding pressure when forming the first electrode catalyst part and the bonding pressure when forming the second electrode catalyst part exceeds 1: 0.8, the first electrode to be formed is formed. The difference in pore volume between the electrode catalyst part and the second electrode catalyst part is reduced, and it may be difficult to achieve both the drainage of water generated by the electrode reaction and the water retention under low humidification conditions. .
Further, in the step of forming the first electrode catalyst portion and the second electrode catalyst portion, the bonding temperature for forming the second electrode catalyst portion is made lower than the bonding temperature for forming the first electrode catalyst portion. Thus, electrode catalyst parts having different pore volumes can be formed.

The electrode catalyst part is formed by applying a catalyst ink in which catalyst-supported particles and a polymer electrolyte are dispersed in a solvent to form a coating film, removing the solvent in the coating film, and joining the electrolyte film. Is formed.
At this time, when the bonding temperature is increased, the pore volume of the electrode catalyst portion formed can be reduced as compared with the case where the bonding temperature is decreased. Further, when the bonding pressure is lowered, the pore volume of the electrode catalyst portion to be formed can be increased as compared with the case where the bonding pressure is increased.

The manufacturing method of the membrane electrode assembly 11 includes the bonding temperature in the step of forming the first electrode catalyst portion (third step) and the bonding temperature in the step of forming the second electrode catalyst portion (fourth step). Higher than. By increasing the bonding temperature, the pore volume of the formed electrode catalyst portion can be reduced. Moreover, the temperature of the junction in the step of forming the electrode catalyst layer (fifth step) is made lower than the temperature of the junction in the step of forming the second electrode catalyst portion (fourth step), so that the first electrode The pore volume of the catalyst part and the second electrode catalyst part is prevented from changing.
The difference between the bonding temperature when forming the first electrode catalyst portion and the bonding temperature when forming the second electrode catalyst portion is preferably in the range of 2 ° C. or more and 20 ° C. or less. If the difference between the bonding temperature when forming the first electrode catalyst portion and the bonding temperature when forming the second electrode catalyst portion is less than 2 ° C., the first electrode catalyst portion to be formed The difference in pore volume with the second electrode catalyst portion is reduced, and it may be difficult to achieve both the drainage of water generated by the electrode reaction and the water retention under low humidification conditions.

In addition, when the difference in bonding temperature when forming the first electrode catalyst part exceeds 20 ° C., the difference in pore volume between the first electrode catalyst part and the second electrode catalyst part to be formed is large. Therefore, it may be difficult to achieve both the drainage of water generated by the electrode reaction and the water retention under low humidification conditions.
The difference between the value of the pore volume of 1.0 μm or less in diameter in the first electrode catalyst part and the value of the pore volume of 1.0 μm or less in diameter in the second electrode catalyst part is determined by a mercury intrusion method. It is preferably 0.1 mL / g or more and 1.0 mL / g or less in terms of a converted value by cylindrical approximation of the holes.
When the difference between the pore volume value of the second electrode catalyst portion and the pore volume value of the first electrode catalyst portion is less than 0.1 mL / g, the drainage of water generated by the electrode reaction It may be difficult to achieve both water retention under low humidification conditions. Moreover, even when the difference in pore volume exceeds 1.0 mL / g, it may be difficult to achieve both the drainage of water generated by the electrode reaction and the water retention under low humidification conditions. .

[Details]
Hereinafter, the membrane electrode assembly 11 and the polymer electrolyte fuel cell 12 will be described in more detail.
The polymer electrolyte membrane 1 only needs to have proton conductivity, and a fluorine polymer electrolyte membrane or a hydrocarbon polymer electrolyte membrane can be used. Examples of the fluorine-based polymer electrolyte membrane include Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., Aciplex (registered trademark) manufactured by Asahi Kasei Co., Ltd., and Gore Select (registered trademark) manufactured by Gore. Etc. can be used.
As the hydrocarbon polymer electrolyte membrane, electrolyte membranes such as sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used. In particular, as the polymer electrolyte membrane 1, a Nafion (registered trademark) material manufactured by DuPont can be suitably used.

The electrode catalyst layer is formed on both surfaces of the polymer electrolyte membrane using a catalyst ink. The catalyst ink includes at least a polymer electrolyte and a solvent.
The polymer electrolyte contained in the above-described catalyst ink is not particularly limited as long as it has proton conductivity, and the same material as the polymer electrolyte membrane can be used. Fluorine polymer electrolyte, hydrocarbon polymer electrolyte Can be used. As an example of the fluorine-based polymer electrolyte, a Nafion (registered trademark) material manufactured by DuPont, etc. can be used.
As the hydrocarbon polymer electrolyte, electrolytes such as sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used. In particular, as a fluorine-based polymer electrolyte, a Nafion (registered trademark) material manufactured by DuPont can be suitably used. In consideration of the adhesion between the electrode catalyst layer and the polymer electrolyte membrane, the same material as that of the polymer electrolyte membrane 1 is preferably used.

Catalyst materials (hereinafter sometimes referred to as catalyst particles or catalysts) include platinum, palladium, ruthenium, iridium, rhodium, osmium, platinum group elements, iron, lead, copper, chromium, cobalt, nickel, manganese, A metal such as vanadium, molybdenum, gallium, or aluminum, an alloy thereof, an oxide, a double oxide, or the like can be used.
Moreover, since the activity of a catalyst will fall when the particle size of said catalyst is too large, and stability of a catalyst will fall when it is too small, the particle size of a catalyst has preferable 0.5-20 nm. More preferably, 1-5 nm is good. In addition, when the catalyst particles are one or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium, the electrode particles are excellent in electrode reactivity, and the electrode reaction is performed efficiently and stably. be able to.

When the catalyst particles are one or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium, the polymer electrolyte fuel cell including the electrode catalyst layer has high power generation characteristics. This is preferable.
In general, carbon particles are used as the electron conductive powder supporting the catalyst material. The type of carbon particles is not limited as long as they are in the form of fine particles and have conductivity and are not affected by the catalyst, but carbon black, graphite, graphite, activated carbon, carbon fiber, carbon nanotube, fullerene should be used. Can do. If the particle size of the carbon particles is too small, it becomes difficult to form an electron conduction path.

Moreover, since the gas diffusibility of the two electrode catalyst layers 2 and 3 will fall or the utilization factor of a catalyst will fall when too large, about 10-1000 nm is preferable. More preferably, 10-100 nm is good.
The solvent used as a dispersion medium for the catalyst ink is not particularly limited as long as it does not erode the catalyst substance-supporting particles and the polymer electrolyte, and can dissolve or disperse the polymer electrolyte in a highly fluid state as a fine gel. It is not something. However, it is desirable that at least a volatile organic solvent is contained.

The following are mentioned as an example of the solvent used as a dispersion medium of a catalyst ink.
Alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, and pentaanol.
Ketone solvents such as acetone, methyl ethyl ketone, pentanone, methyl isobutyl ketone, heptanone, cyclohexanone, methyl cyclohexanone, acetonyl acetone, diisobutyl ketone.
Ether solvents such as tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene and dibutyl ether.
Polar solvents such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol, 1-methoxy-2-propanol;

Moreover, you may use what mixed 2 or more types among the above-mentioned solvents.
In addition, a solvent using a lower alcohol as a solvent used as a dispersion medium of the catalyst ink has a high risk of ignition. Therefore, when using a lower alcohol, it is preferable to use a mixed solvent with water. Furthermore, water (water having high affinity) that is compatible with the polymer electrolyte may be contained. The amount of water added is not particularly limited as long as the polymer electrolyte does not separate and cause white turbidity or gelation.
In order to disperse the catalyst material-carrying particles, the catalyst ink may contain a dispersant. Examples of the dispersant include an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant.

The following are mentioned as an example of the said anionic surfactant.
Alkyl ether carboxylate, ether carboxylate, alkanoyl sarcosine, alkanoyl glutamate, acyl glutamate, oleic acid / N-methyl taurine, potassium oleate / diethanolamine salt, alkyl ether sulfate / triethanolamine salt, polyoxyethylene alkyl Ether sulfate triethanolamine salt, amine salt of special modified polyetherester acid, amine salt of higher fatty acid derivative.

Amine salt of special modified polyester acid, amine salt of high molecular weight polyether ester acid, amine salt of special modified phosphate ester, high molecular weight amide amine salt of polyester acid, amide amine salt of special fatty acid derivative, alkylamine salt of higher fatty acid, high molecular weight Amidoamine salt of polycarboxylic acid.
Carboxylic acid type surfactants such as sodium laurate, sodium stearate and sodium oleate, dialkyl sulfosuccinate, dialkyl sulfosuccinate, 1,2-bis (alkoxycarbonyl) -1-ethanesulfonate, alkyl sulfonate, Alkyl sulfonate, paraffin sulfonate, α-olefin sulfonate, linear alkyl benzene sulfonate, alkyl benzene sulfonate, polynaphthyl methane sulfonate, polynaphthyl methane sulfonate, naphthalene sulfonate-formalin condensate, alkyl naphthalene sulfonate, alkanoyl methyl tauride .

Lauryl sulfate sodium salt, cetyl sulfate sodium salt, stearyl sulfate sodium salt, oleyl sulfate sodium salt, lauryl ether sulfate sodium salt, alkylbenzene sulfonate sodium, oil-soluble alkyl benzene sulfonate, α-olefin sulfonate, etc. Sulfonic acid type surfactant, alkyl sulfate ester salt, alkyl sulfate salt.
Sulfate ester surfactants such as alkyl sulfates, alkyl ether sulfates, polyoxyethylene alkyl ether sulfates, alkyl polyethoxy sulfates, polyglycol ether sulfates, alkyl polyoxyethylene sulfates, sulfated oils, highly sulfated oils, phosphorus Acid (mono or di) alkyl salt, (mono or di) alkyl phosphate, (mono or di) alkyl phosphate ester salt, alkyl polyoxyethylene salt of phosphate.

  Alkyl ether phosphate, alkyl polyethoxy phosphate, polyoxyethylene alkyl ether, alkylphenyl phosphate polyoxyethylene salt, alkylphenyl ether phosphate, alkylphenyl polyethoxy phosphate, polyoxyethylene alkylphenyl Phosphate-type surfactants such as ether phosphate, higher alcohol phosphate monoester disodium salt, higher alcohol phosphate diester disodium salt, zinc dialkyldithiophosphate.

Examples of the cationic surfactant include the following.
Benzyldimethyl {2- [2- (P-1,1,3,3-tetramethylbutylphenoxy) ethoxy] ethyl} ammonium chloride, octadecylamine acetate, tetradecylamine acetate, octadecyltrimethylammonium chloride, beef tallow trimethyl Ammonium chloride, dodecyltrimethylammonium chloride, coconut trimethylammonium chloride, hexadecyltrimethylammonium chloride.
Behenyltrimethylammonium chloride, palm dimethylbenzylammonium chloride, tetradecyldimethylbenzylammonium chloride, octadecyldimethylbenzylammonium chloride, dioleyldimethylammonium chloride, 1-hydroxyethyl-2-tallow imidazoline quaternary salt, 2-heptadecenyl-hydroxy Ethyl imidazoline.

Stearamide ethyl diethylamine acetate, stearamide ethyl diethylamine hydrochloride, triethanolamine monostearate formate, alkyl pyridium salt, higher alkyl amine ethylene oxide adduct, polyacrylamide amine salt, modified polyacrylamide amine salt, perfluoroalkyl Quaternary ammonium iodide and the like.
Examples of the amphoteric surfactants include dimethyl coconut betaine, dimethyl lauryl betaine, sodium laurylaminoethylglycine, sodium laurylaminopropionate, stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, amide betaine, imidazolinium betaine, lecithin, 3 -[Ω-fluoroalkanoyl-N-ethylamino] -1-propanesulfonic acid sodium, N- [3- (perfluorooctanesulfonamido) propyl] -N, N-dimethyl-N-carboxymethyleneammonium betaine It is done.

The following are mentioned as an example of the said nonionic surfactant.
Palm fatty acid diethanolamide (1: 2 type), palm fatty acid diethanolamide (1: 1 type), bovine fatty acid diethanolamide (1: 2 type), bovine fatty acid diethanolamide (1: 1 type), oleic acid diethanolamide (1 1 type), hydroxyethyl lauryl amine, polyethylene glycol lauryl amine, polyethylene glycol coconut amine, polyethylene glycol stearyl amine, polyethylene glycol beef tallow amine, polyethylene glycol beef tallow propylene diamine.

  Polyethylene glycol dioleyl amine, dimethyl lauryl amine oxide, dimethyl stearyl amine oxide, dihydroxyethyl lauryl amine oxide, perfluoroalkyl amine oxide, polyvinyl pyrrolidone, higher alcohol ethylene oxide adduct, alkylphenol ethylene oxide adduct, fatty acid ethylene oxide adduct, polypropylene Glycolethylene oxide adduct, fatty acid ester of glycerin, fatty acid ester of pentaerythritol, fatty acid ester of sorbit, fatty acid ester of sorbitan, fatty acid ester of sugar, etc.

Among the above surfactants, sulfonic acid type surfactants such as alkylbenzene sulfonic acid, oil-soluble alkylbenzene sulfonic acid, α-olefin sulfonic acid, sodium alkylbenzene sulfonate, oil-soluble alkylbenzene sulfonate, α-olefin sulfonate, etc. Can be suitably used as a dispersant in consideration of carbon dispersion effects, changes in catalyst performance due to the remaining dispersant, and the like.
Increasing the amount of polymer electrolyte in the catalyst ink generally decreases the pore volume. On the other hand, increasing the amount of carbon particles in the catalyst ink increases the pore volume. In addition, when a dispersant is used, the pore volume is reduced.

  Further, the catalyst ink is subjected to a dispersion treatment as necessary. The viscosity of the catalyst ink and the size of the particles can be controlled by the conditions for the dispersion treatment of the catalyst ink. Distributed processing can be performed using various apparatuses. In particular, the distributed processing method is not limited. For example, as the dispersion treatment, treatment with a ball mill or roll mill, treatment with a shear mill, treatment with a wet mill, ultrasonic dispersion treatment, and the like can be given. Moreover, you may employ | adopt the homogenizer etc. which stir with centrifugal force. Further, as the dispersion time becomes longer, the aggregates of the catalyst material-carrying particles are destroyed and the pore volume becomes smaller.

If the solid content in the catalyst ink is too large, the viscosity of the catalyst ink becomes high, so that the electrode catalyst layer surfaces 2 and 3 are likely to crack. On the other hand, if the solid content in the catalyst ink is too small, the film formation rate is very slow and the productivity is lowered. Therefore, the solid content in the catalyst ink is preferably 1 to 50% by mass (wt%). The solid content is composed of catalyst material-supported particles and a polymer electrolyte. If the content of catalyst material-supported particles is increased in the solid content, the viscosity increases even with the same solid content.
On the other hand, when the content of the catalyst substance-supporting particles is reduced in the solid content, the viscosity is lowered even with the same solid content. Therefore, the ratio of the catalyst substance-supporting particles in the solid content is preferably 10 to 80% by mass. The viscosity of the catalyst ink is preferably about 0.1 to 500 cP (0.0001 to 0.5 Pa · s), more preferably 5 to 100 cP (0.005 to 0.1 Pa · s). Further, the viscosity can be controlled by adding a dispersing agent when the catalyst ink is dispersed.

Further, the catalyst ink may contain a pore forming agent. By removing the pore-forming agent after the formation of the electrode catalyst layer, pores can be formed. Examples include substances that are soluble in acids, alkalis, and water, substances that sublime such as camphor, and substances that thermally decompose. If the pore-forming agent is a substance that is soluble in warm water, it may be removed with water generated during power generation.
Examples of pore-forming agents that are soluble in acids, alkalis and water include acid-soluble inorganic salts such as calcium carbonate, barium carbonate, magnesium carbonate, magnesium sulfate and magnesium oxide, inorganic salts soluble in alkaline aqueous solutions such as alumina, silica gel and silica sol, aluminum Metals soluble in acids or alkalis such as zinc, tin, nickel and iron, water-soluble inorganic salts such as sodium chloride, potassium chloride, ammonium chloride, sodium carbonate, sodium sulfate, monosodium phosphate, polyvinyl alcohol, polyethylene glycol Water-soluble organic compounds such as

Moreover, although the said pore making agent may be used individually by 1 type or in combination of 2 or more types, it is preferable to use in combination of 2 or more types.
As a coating method for coating the catalyst ink on the substrate, a doctor blade method, a dipping method, a screen printing method, a roll coating method, or the like can be employed.
A transfer sheet can be used as a substrate in the production of the electrode catalyst layer.
The transfer sheet used as the substrate may be any material having good transferability. For example, ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroper Fluorocarbon resins such as fluoroalkyl vinyl ether copolymer (PFA) and polytetrafluoroethylene (PTFE) can be used.

In addition, polyimide, polyethylene terephthalate, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyarylate, polyethylene naphthalate, polymer sheets and polymer films are transferred. It can be used as a sheet.
When a transfer sheet is used as the substrate, only the electrode catalyst layer is bonded to the polymer electrolyte membrane 1 by peeling the transfer sheet after bonding the electrode catalyst layer to the polymer electrolyte membrane 1. That is, the electrode catalyst layer is transferred from the substrate to the polymer electrolyte membrane 1.

As the gas diffusion layer, a material having gas diffusibility and conductivity can be used. For example, porous carbon materials such as carbon cloth, carbon paper, and non-woven fabric can be used.
As the separator, a carbon type or a metal type can be used. The gas diffusion layer and the separator may have an integral structure. When the separator or the electrode catalyst layer functions as a gas diffusion layer, the gas diffusion layer may be omitted. The polymer electrolyte fuel cell 12 can be manufactured by assembling other accompanying devices such as a gas supply device and a cooling device.

Hereinafter, the method for producing an electrode catalyst layer for a polymer electrolyte fuel cell according to this embodiment will be described with reference to specific examples and comparative examples. However, this embodiment is limited by the following examples and comparative examples. It is not something.
<Example 1>
[Adjustment of catalyst ink]
A platinum-supported carbon catalyst (trade name: TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) having a platinum support amount of 50% by mass and a 20% by mass polymer electrolyte solution (trade name: Nafion (registered trademark), manufactured by DuPont) are used as solvents. The mixture was mixed and dispersed with a planetary ball mill. At this time, the dispersion time was set to 30 minutes, and the catalyst ink was adjusted. The composition ratio of the starting material of the prepared catalyst ink was 1: 1 by mass ratio between the carbon support and the polymer electrolyte. The solvent of the catalyst ink was 1: 1 by volume ratio of ultrapure water and 1-propanol. The solid content was 12% by mass.

〔Base material〕
A polytetrafluoroethylene (PTFE) sheet as a transfer sheet was used as a substrate.
[Method for forming electrode catalyst layer on substrate]
The catalyst ink prepared as described above was applied onto a substrate by a doctor blade method and dried at 70 ° C. in an air atmosphere. The amount of catalyst ink applied was adjusted so that the electrode catalyst layer serving as the anode had a platinum loading of 0.1 mg / cm ² and the electrode catalyst layer serving as the cathode had a platinum loading of 0.3 mg / cm ² .

[Production of membrane electrode assembly]
The anode sheet in which the electrode catalyst layer to be the anode was formed on the base material was punched out to 5 cm × 5 cm to obtain one anode piece. Moreover, the cathode sheet in which the electrode catalyst layer used as a cathode was formed in the base material was punched out into 5 cm x 2.5 cm, and two cathode pieces were obtained.
Next, the electrode catalyst layer of the cathode piece is brought into contact with a portion on the gas inlet side of one surface of the polymer electrolyte membrane (trade name: Nafion (registered trademark), manufactured by DuPont), and 135 ° C., 8.0 × 10 After hot pressing under the condition of ⁶ Pa, the substrate was peeled from the electrode catalyst layer. As a result, the first electrode catalyst layer was joined to the portion on the gas inlet side of one surface of the polymer electrolyte membrane to form the first electrode catalyst portion.

Next, the electrode catalyst layer of the cathode piece is brought into contact with a portion (adjacent to the first electrode catalyst portion) on one side of the polymer electrolyte membrane, and the conditions of 135 ° C. and 5.0 × 10 ⁶ Pa are satisfied. Then, the substrate was peeled from the electrode catalyst layer. Thereby, the 2nd electrode catalyst layer was joined to the part used as the gas outlet side of one surface of a polymer electrolyte membrane, and the 2nd electrode catalyst part was formed.
Next, the electrode catalyst layer of the anode piece is brought into contact with the other surface of the polymer electrolyte membrane, hot pressing is performed at 135 ° C. and 4.0 × 10 ⁶ Pa, and then the substrate is peeled from the electrode catalyst layer. did. As a result, the third electrode catalyst layer was joined to the portion opposite to the first and second electrode catalyst portions with the polymer electrolyte membrane interposed therebetween.
In addition, the pore measurement of the 1st electrode catalyst part heat-processed on condition of 135 degreeC and 8.0 * 10 < ⁶ > Pa, and the 2nd electrode catalyst part heat-processed on condition of 135 degreeC and 5.0 * 10 < ⁶ > Pa. As a result of performing the measurement using a mercury porosimeter, the pore volume with a diameter of 1.0 μm or less in terms of the cylinder approximation is larger than the value of the first electrode catalyst portion provided on the gas inlet side. The value of the electrode catalyst part of 2 was large, and the difference was 0.20 mL / g.

<Example 2>
[Adjustment of catalyst ink]
The same adjustment as that of the catalyst ink of Example 1 was performed.
〔Base material〕
A polytetrafluoroethylene (PTFE) sheet was used in the same manner as the base material of Example 1.
[Method for forming electrode catalyst layer on substrate]
Similar to the electrode catalyst layer of Example 1, an electrode catalyst layer serving as an anode and an electrode catalyst layer serving as a cathode were formed.

[Production of membrane electrode assembly]
The anode sheet in which the electrode catalyst layer to be the anode was formed on the base material was punched out to 5 cm × 5 cm to obtain one anode piece. Moreover, the cathode sheet in which the electrode catalyst layer used as a cathode was formed in the base material was punched out into 5 cm x 2.5 cm, and two cathode pieces were obtained.
Next, the electrode catalyst layer of the cathode piece is brought into contact with the portion on the gas inlet side of one surface of the polymer electrolyte membrane (trade name: Nafion (registered trademark), manufactured by DuPont) at 145 ° C., 5.0 × 10 5. After hot pressing under the condition of ⁶ Pa, the substrate was peeled from the electrode catalyst layer. As a result, the first electrode catalyst layer was joined to the portion on the gas inlet side of one surface of the polymer electrolyte membrane to form the first electrode catalyst portion.
Next, the electrode catalyst layer of the cathode piece is brought into contact with a portion (adjacent to the first electrode catalyst portion) on one side of the polymer electrolyte membrane, and the conditions of 135 ° C. and 5.0 × 10 ⁶ Pa are satisfied. Then, the substrate was peeled from the electrode catalyst layer. Thereby, the 2nd electrode catalyst layer was joined to the part used as the gas outlet side of one surface of a polymer electrolyte membrane, and the 2nd electrode catalyst part was formed.

Next, the electrode catalyst layer of the anode piece is brought into contact with the other surface of the polymer electrolyte membrane, hot pressing is performed at 130 ° C. and 5.0 × 10 ⁶ Pa, and then the substrate is peeled from the electrode catalyst layer. did. As a result, the third electrode catalyst layer was joined to the portion opposite to the first and second electrode catalyst portions with the polymer electrolyte membrane interposed therebetween.
In addition, the pore measurement of the 1st electrode catalyst part heat-processed on the conditions of 145 degreeC and 5.0 * 10 < ⁶ > Pa, and the 2nd electrode catalyst part heat-processed on the conditions of 135 degreeC and 5.0 * 10 < ⁶ > Pa. As a result of performing the measurement using a mercury porosimeter, the pore volume with a diameter of 1.0 μm or less in terms of the cylinder approximation is larger than the value of the first electrode catalyst portion provided on the gas inlet side. The value of the electrode catalyst part 2 was large, and the difference was 0.19 mL / g.

<Comparative example>
[Adjustment of catalyst ink]
The catalyst inks of Example 1 and Example 2 were prepared in the same manner.
〔Base material〕
A polytetrafluoroethylene (PTFE) sheet was used in the same manner as the base materials of Example 1 and Example 2.
[Method for forming electrode catalyst layer on substrate]
Similarly to the electrode catalyst layers of Example 1 and Example 2, an electrode catalyst layer to be an anode and an electrode catalyst layer to be a cathode were formed.
[Production of membrane electrode assembly]
The base material on which the electrode catalyst part is formed is punched into a square of 25 cm ² (5 cm × 5 cm), the electrode catalyst part is arranged so as to face both surfaces of the polymer electrolyte membrane, and 135 ° C., 5.0 × 10 ⁶ Pa Hot pressing was performed under conditions to obtain a membrane electrode assembly. That is, no difference in pore volume was formed between the upstream and downstream electrode catalyst layers of the gas at the cathode.

<Evaluation>
[Power generation characteristics]
Carbon paper used as a gas diffusion layer was bonded and placed in a power generation evaluation cell so as to sandwich the membrane electrode assemblies produced in Examples and Comparative Examples. Using the fuel cell measurement device, the cell voltage was set to 80 ° C., and current voltage measurement was performed under the following two operating conditions. Hydrogen was used as the fuel gas and air was used as the oxidant gas, and the flow rate was controlled at a constant utilization rate. The back pressure was 100 kPa.
[Operating conditions]
1. Full humidification: anode 100% RH, cathode 100% RH
2. Low humidification: anode 30% RH, cathode 30% RH

〔Measurement result〕
The membrane / electrode assembly produced in Example 1 and Example 2 exhibited better power generation performance under low humidification operating conditions than the membrane / electrode assembly produced in Comparative Example. Moreover, the membrane electrode assembly produced in Example 1 and Example 2 had the same level of power generation performance as that in the fully humidified operating condition even under the low humidified operating condition. In particular, the power generation performance near a current density of 0.5 A / cm ² is improved, and the membrane electrode assembly produced in Example 1 has a current density of 0.5 A / cm ² compared to the membrane electrode assembly produced in the comparative example. The cell voltage of 68 mV was high, and the membrane electrode assembly produced in Example 2 exhibited power generation characteristics with a cell voltage at a current density of 0.5 A / cm ² being 46 mV.

From the results of the power generation characteristics of the membrane / electrode assembly produced in Example 1 and Example 2 and the membrane / electrode assembly produced in the comparative example, the pore volume of the electrode catalyst layer was provided on the gas inlet side. The membrane electrode assembly in which the value of the second electrode catalyst part provided on the gas outlet side is larger than the value of the electrode catalyst part of 1 increases the water retention, and the power generation characteristics under the low humidifying operation condition are full. It was confirmed that the power generation characteristics were the same as in the humidified operating conditions.
Further, under the full humidification operating conditions, the membrane electrode assembly produced in Example 1 has a cell voltage of 41 mV higher at a current density of 0.5 A / cm ² than the membrane electrode assembly produced in the comparative example. The membrane / electrode assembly produced in Example 2 exhibited a power generation characteristic with a cell voltage of a current density of 0.5 A / cm ^{2 and} a high 35 mV. Based on the results of power generation characteristics of the membrane electrode assemblies produced in Example 1 and Example 2 and the membrane electrode assemblies produced in Comparative Examples, the diffusibility of the reaction gas, the removal of water generated by the electrode reaction, and the like are inhibited. It was confirmed that they did not.

<Summary>
The present embodiment relates to a membrane electrode assembly that exhibits high power generation characteristics under low humidification conditions, a method for manufacturing the membrane electrode assembly, and a polymer electrolyte fuel cell including the membrane electrode assembly.
The membrane electrode assembly according to the present embodiment is a membrane electrode assembly in which a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers. Here, one of the electrode catalyst layers is divided into at least two parts: a first electrode catalyst part and a second electrode catalyst part adjacent to the first electrode catalyst part in the plane of the polymer electrolyte membrane. ing.
The method for producing a membrane electrode assembly includes a step of adjusting a catalyst ink, a step of applying a catalyst ink on a substrate to form an electrode catalyst layer, and a step of bonding the electrode catalyst layer to an electrolyte membrane. Have. The ratio of the pressure when forming the first electrode catalyst portion to the pressure when forming the second electrode catalyst portion is in the range of 1: 0.2 or more and 1: 0.8 or less. Further, the difference between the temperature at which the first electrode catalyst part is formed and the temperature at which the second electrode catalyst part is formed is in the range of 2 ° C. or more and 20 ° C. or less.

In addition, it is a conversion value obtained by approximating the pores in the cylinder obtained by the mercury intrusion method, and the pore volume of the first electrode catalyst part having a diameter of 1.0 μm or less and the second electrode catalyst part having a diameter of 1.0 μm or less. The difference from the pore volume is 0.1 mL / g or more and 1.0 mL / g or less.
The polymer electrolyte fuel cell according to the present embodiment includes the above-described membrane electrode assembly.
According to this embodiment, the pore volume having a diameter of 1.0 μm or less in terms of the cylindrical approximation of the pores determined by the mercury intrusion method is compared with the value of the first electrode catalyst portion provided on the gas inlet side, The value of the second electrode catalyst portion provided on the gas outlet side is increased, the water retention is increased without hindering the removal of water generated by the electrode reaction, and the electrode exhibits high power generation characteristics even under low humidification conditions It is possible to provide a membrane electrode assembly including a catalyst layer and a production method capable of producing the same efficiently and economically.

  The membrane electrode assembly according to the present embodiment is a membrane electrode assembly in which a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers, and the electrode catalyst layer includes particles carrying a polymer electrolyte and a catalyst substance. Further, the electrode catalyst layer is divided into at least two in a direction perpendicular to the stacking direction, and the electrode catalyst layer has a diameter of 1.0 μm or less in terms of a cylindrical approximation of pores obtained by mercury porosimetry. The value of the second electrode catalyst part provided on the gas outlet side is larger than the value of the first electrode catalyst part provided on the gas inlet side, and the difference is 0.1 mL / g or more. It is 1.0 mL / g or less.

The first and second electrode catalyst portions can increase the water retention of the electrode catalyst layer without hindering the diffusibility of the reaction gas, the removal of water generated by the electrode reaction, and the like. Unlike the conventional application of humidity control film and low humidity by forming grooves on the surface of the electrode catalyst layer, the power generation characteristics are not reduced due to the increase in interface resistance, and the conventional membrane electrode assembly is provided. Compared with the solid polymer fuel cell, the polymer electrolyte fuel cell provided with the membrane electrode assembly according to the present embodiment has a remarkable effect of exhibiting high power generation characteristics even under low humidification conditions. The utility value of is high.
As mentioned above, although embodiment of this invention was explained in full detail, actually, it is not restricted to said embodiment, Even if there is a change of the range which does not deviate from the summary of this invention, it is included in this invention.

DESCRIPTION OF SYMBOLS 1 ... Polymer electrolyte membrane 2 ... Electrode catalyst layer 3 ... Electrode catalyst layer 2a ... 1st electrode catalyst part 2b ... 2nd electrode catalyst part 4 ... Gas diffusion layer 5 ... Gas diffusion layer 6 ... Air electrode (cathode)
7. Fuel electrode (anode)
8 ... Gas channel 9 ... Cooling water channel 10 ... Separator 11 ... Membrane electrode assembly 12 ... Polymer electrolyte fuel cell

Claims (8)

A method for producing a membrane / electrode assembly having an electrode catalyst layer on one side and the other side of the polymer electrolyte membrane opposite to each other,
Bonding the first electrode catalyst layer formed on the substrate to a part of the one surface by applying pressure to the first electrode catalyst layer;
Bonding the second electrode catalyst layer formed on the substrate to a portion different from the part of the one surface by applying pressure to the second electrode catalyst layer;
Have
The method for producing a membrane electrode assembly is characterized in that the step of joining the second electrode catalyst layer is performed at a lower pressure than the step of joining the first electrode catalyst layer. Having a step of bonding the third electrode catalyst layer formed on the substrate to the other surface by applying pressure to the third electrode catalyst layer,
The step of joining the third electrode catalyst layer includes:
After performing the step of joining the first electrode catalyst layer and the second electrode catalyst layer,
The method for producing a membrane / electrode assembly according to claim 1, wherein the pressure is lower than that in the step of joining the second electrode catalyst layer.   Applying to the second electrode catalyst layer in the step of bonding the second electrode catalyst layer to the pressure (P1) applied to the first electrode catalyst layer in the step of bonding the first electrode catalyst layer. The method for producing a membrane / electrode assembly according to claim 1, wherein the ratio (P2 / P1) of the pressure (P2) is 0.2 or more and 0.8 or less. A method for producing a membrane / electrode assembly having an electrode catalyst layer on one side and the other side of the polymer electrolyte membrane opposite to each other,
Bonding the first electrode catalyst layer formed on the substrate to a part of the one surface by heating the first electrode catalyst layer;
A step of heating and bonding the second electrode catalyst layer formed on the substrate to a portion different from the part of the one surface by heating the second electrode catalyst layer;
Have
The method for producing a membrane electrode assembly is characterized in that the step of joining the second electrode catalyst layer is performed at a temperature lower than the step of joining the first electrode catalyst layer. A step of heating and bonding the third electrode catalyst layer formed on the substrate to the other surface by heating the third electrode catalyst layer;
The step of joining the third electrode catalyst layer includes:
After performing the step of joining the first electrode catalyst layer and the second electrode catalyst layer,
The manufacturing method of the membrane electrode assembly of Claim 4 performed at temperature lower than the process of joining a said 2nd electrode catalyst layer.   The temperature (T1) applied to the first electrode catalyst layer in the step of bonding the first electrode catalyst layer, and the temperature applied to the second electrode catalyst layer in the step of bonding the second electrode catalyst layer. The method for producing a membrane / electrode assembly according to claim 4, wherein a difference (T2-T1) from the temperature (T2) is 2 ° C or higher and 20 ° C or lower. The first electrode catalyst layer after bonding to the one surface has a pore volume of 1.0 μm or less in diameter and the second electrode catalyst layer after bonding to the one surface has a fine diameter of 1.0 μm or less. The difference from the pore volume
The method for producing a membrane / electrode assembly according to any one of claims 1 to 6, wherein the conversion value is obtained by cylindrical approximation of pores determined by a mercury intrusion method and is 0.1 mL / g or more and 1.0 mL / g or less. . A process for producing a membrane electrode assembly by the production method according to claim 7,
A method for producing a polymer electrolyte fuel cell, wherein the first electrode catalyst layer is disposed on a gas inlet side, and the second electrode catalyst layer is disposed on a gas outlet side.

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