JP7090374B2 - Electrode catalyst layer, membrane electrode assembly and polymer electrolyte fuel cell - Google Patents

Description

The present invention relates to an electrode catalyst layer, a membrane electrode assembly and a polymer electrolyte fuel cell.

A fuel cell is a power generation system that produces electricity from a chemical reaction between hydrogen and oxygen. Compared to conventional power generation methods, it has features such as high efficiency, low environmental load, and low noise, and is attracting attention as a clean energy source in the future. In particular, polymer electrolyte fuel cells that can be used near room temperature are expected to be used for in-vehicle power supplies and stationary power sources for home use, and in recent years, various research and development on polymer electrolyte fuel cells have been carried out. It has been. Issues for its practical application include improvement of battery performance such as power generation characteristics and durability, infrastructure development, and reduction of manufacturing cost.

A polymer electrolyte fuel cell is generally composed of a large number of single cells stacked together. A single cell is a gas flow path and cooling of a film electrode junction formed by sandwiching a polymer electrolyte membrane between two electrodes, a fuel electrode (anode) that supplies fuel gas and an oxygen electrode (cathode) that supplies an oxidizing agent. It has a structure sandwiched between separators having a water flow path. Each of these fuel electrode and oxygen electrode is an electrode catalyst layer containing at least a catalyst substance such as a platinum-based noble metal, a conductive carrier and a polymer electrolyte, and a gas diffusion layer having both gas permeability and conductivity. It is mainly composed.

In a polymer electrolyte fuel cell, electricity can be extracted through the following electrochemical reactions. First, in the electrode catalyst layer on the fuel electrode side, hydrogen contained in the fuel gas is oxidized by the catalytic substance to become protons and electrons. The generated protons pass through the polyelectrolyte in the electrode catalyst layer and the polyelectrolyte film in contact with the electrode catalyst layer, and reach the electrode catalyst layer on the oxygen electrode side. Further, the electrons generated at the same time pass through the conductive carrier in the electrode catalyst layer, the gas diffusion layer in contact with the side different from the polymer electrolyte membrane of the electrode catalyst layer, the separator and the external circuit, and the electrode catalyst layer on the oxygen electrode side. To reach. Then, in the electrode catalyst layer on the oxygen electrode side, protons and electrons react with oxygen contained in the oxidant gas to generate water.

The electrode catalyst layer constituting the membrane electrode assembly may have unevenness generated in the manufacturing process. The unevenness generated in the electrode catalyst layer is due to uneven distribution of the catalyst substance, the conductive carrier and the polymer electrolyte, the difference in the local thermal history inside the electrode catalyst layer, and the variation in the thickness of the electrode catalyst layer. A membrane electrode assembly having an uneven electrode catalyst layer is laminated with a peripheral member to form a cell, and when power is generated, the adhesion between the polymer electrolyte membrane or the gas diffusion layer and the electrode catalyst layer is partially reduced. There is a risk that the generated water will stay or that there will be a locally high electrical load portion inside the electrode catalyst layer. Such a local load tends to accelerate the deterioration of the membrane electrode assembly, and there is a high possibility that the membrane breaks or the like occurs in the long term.

When a membrane electrode assembly having unevenness in the electrode catalyst layer as described above is used for a fuel cell, the battery performance and durability are significantly deteriorated, which causes a problem in the manufacturing process of the membrane electrode assembly. A method of detecting with high accuracy and excluding defective products has been proposed.
To detect the defective portion of the membrane electrode assembly or the gas diffusion layer, there is a method of capturing the transmitted light or the reflected light of the irradiation light in the defective portion and performing image processing. For example, the method described in Patent Document 1 irradiates inspection light from one side of a sheet member, and detects the inspection light transmitted through the defective portion with a detector provided on the other side.

Further, the method described in Patent Document 2 irradiates inspection light from one side of the membrane electrode assembly, and detects the inspection light reflected by the defective portion with a detector.
Further, in the method described in Patent Document 3, the surface of the porous electrode base material is irradiated with inspection light, the transmitted light, the specular reflected light and the scattered light are imaged, and the imaged data thereof is sent to the image processing unit. And analyze it to know the type, location and size of the defect.

Japanese Unexamined Patent Publication No. 2014-190706 Japanese Unexamined Patent Publication No. 2014-225340 Japanese Patent No. 5306053

However, since the method according to Patent Document 1 uses transmitted light as a light source for inspection, there is a problem that it cannot be applied to inspection of unevenness generated in an electrode catalyst layer that does not transmit light.
Further, the method according to Patent Document 2 uses reflected light for inspection, but since the photographic paper is placed on the surface of the membrane electrode assembly, wrinkles can be detected but occur on the surface of the electrode catalyst layer. There was a problem that it was not possible to detect the unevenness.

The method according to Patent Document 3 directly irradiates the surface of the inspection body with inspection light to detect defects, and may be applicable to inspection of the electrode catalyst layer. However, since the size and contrast are different between the defect generated in the porous electrode base material and the unevenness generated in the electrode catalyst layer, it cannot be applied as it is. Further, Patent Document 3 does not mention the electrode catalyst layer, and there is a problem that the criteria for quality of unevenness generated in the electrode catalyst layer are unknown.

The present invention has been made to solve the above-mentioned problems, and it detects unevenness of the electrode catalyst layer, which is a problem in practical use of a polymer electrolyte fuel cell, with high accuracy and excludes defective products for a long period of time. Another object of the present invention is to provide an electrode catalyst layer, a membrane electrode assembly, and a polymer electrolyte fuel cell that do not significantly reduce the battery performance and durability.

In order to solve the above problems, the electrode catalyst layer according to the first aspect of the present invention is an electrode catalyst layer containing at least a catalytic substance, a conductive carrier and a polymer electrolyte, and is formed on the surface of the electrode catalyst layer. Of the positively reflected light when the region having a predetermined area is irradiated with the inspection light incident at Brewster's angle, the amount of reflected light that has passed through the polarizing element that allows only the P-polarizing component to pass is Lp, and is 4096 gradations. When represented, it is characterized in that the standard deviation σ of the reflected light amount Lp obtained by scanning almost the entire surface of the surface of the electrode catalyst layer without overlapping the regions is 30 or more and 150 or less.

Further, in this electrode catalyst layer, it is preferable that the predetermined area of the region is 1600 μm ² or more and 10000 μm ² or less.
Further, in this electrode catalyst layer, it is preferable that the thickness in the direction orthogonal to the surface of the electrode catalyst layer is within the range of 1 μm or more and 30 μm or less, and the thickness is in the range of 2 μm or more and 20 μm or less. It is more preferable that it is configured to be inside.

Further, it is preferable that the electrode catalyst layer is configured such that the ratio of the weight of the polymer electrolyte to the weight of the conductive carrier is 0.8 or more and 1.6 or less.
Further, in order to solve the above-mentioned problems, the membrane electrode assembly according to the second aspect of the present invention has the polymer electrolyte membrane and the first aspect bonded to at least the surface on the oxygen electrode side of the polymer electrolyte membrane. It is characterized by having an electrode catalyst layer according to the above.
Further, in order to solve the above problems, the polymer electrolyte fuel cell according to the third aspect of the present invention is characterized by including the membrane electrode assembly according to the second aspect.

According to the electrode catalyst layer, the membrane electrode junction, and the solid polymer fuel cell according to the present invention, an inspection in which the electrode catalyst layer is incident on the surface of the electrode catalyst layer at a brewer angle in a region having a predetermined area. Of the positively reflected light when irradiated with light, the amount of reflected light that has passed through the polarizing element that allows only the P-polarizing component to pass is Lp, and when expressed in 4096 gradations, the electrode catalyst does not overlap the regions. The standard deviation σ of the reflected light amount Lp obtained by scanning almost the entire surface of the layer is configured to be 30 or more and 150 or less. As a result, the uneven distribution of the catalyst substance, the conductive carrier and the polymer electrolyte, the difference in the local thermal history inside the electrode catalyst layer, and the variation in the thickness of the electrode catalyst layer are suppressed, and the battery performance and durability are suppressed even in the long term. It is possible to provide an electrode catalyst layer, a membrane electrode junction, and a solid polymer fuel cell that do not cause a significant deterioration in properties.

The membrane electrode assembly according to the embodiment of the present invention is shown, (a) is a plan view of the membrane electrode assembly viewed from the upper surface side (oxygen electrode side) of the electrode catalyst layer, and (b) is (a). It is sectional drawing along the XX'line. It is explanatory drawing of the transfer base material with a catalyst layer which formed the electrode catalyst layer which concerns on embodiment of this invention. It is explanatory drawing which shows the structural example at the time of obtaining the reflected light amount Lp on the surface of the electrode catalyst layer which concerns on embodiment of this invention. It is an exploded perspective view which shows the structural example of the polymer electrolyte fuel cell which concerns on embodiment of this invention. It is a figure which shows the mapping image of the reflected light amount Lp of Example 1. It is a histogram of the reflected light amount Lp of Example 1.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the present embodiment is not limited to the embodiments described below, and modifications such as design changes based on the knowledge of those skilled in the art can be added, and such modifications are added. The embodiment is also included in the scope of the present embodiment. In addition, each drawing is exaggerated as appropriate to facilitate understanding.

As a result of diligent studies on the power generation performance and durability performance of the polymer electrolyte fuel cell, the present inventor has found that these performances include the uneven distribution of the catalyst substance, the conductive carrier and the polymer electrolyte in the electrode catalyst layer, and the electrode catalyst. It was found that the difference in the local thermal history inside the layer and the variation in the thickness of the electrode catalyst layer had a great influence. Then, by keeping the variation in the reflected brightness in the electrode catalyst layer within a predetermined range and preventing a local load from occurring in the membrane electrode assembly, deterioration is suppressed and a solid exhibiting high power generation performance even in the long term. We succeeded in obtaining a polymer electrolyte fuel cell.

(Structure of membrane electrode assembly and electrode catalyst layer)
Hereinafter, specific configurations of the membrane electrode assembly and the electrode catalyst layer according to the present embodiment will be described.
FIG. 1A is a plan view of the membrane electrode assembly 1 according to the present embodiment as viewed from the upper surface side (oxygen electrode side) of the electrode catalyst layer 12C, and FIG. 1B is FIG. 1A. It is a cross-sectional view along the XX'line (cross-sectional view in the thickness direction orthogonal to the surface of the electrode catalyst layer 12C).

As shown in FIGS. 1 (a) and 1 (b), in the membrane electrode assembly 1, a pair of electrode catalyst layers 12C and 12A are arranged and bonded to each other with the polymer electrolyte membrane 11 interposed therebetween. In the present embodiment, the electrode catalyst layer 12C formed on the upper surface of the polymer electrolyte film 11 is a cathode-side catalyst layer constituting an oxygen electrode, and the electrode catalyst layer 12A formed on the lower surface of the polymer electrolyte film 11 is a fuel. It is an anode side catalyst layer constituting a pole. Hereinafter, the pair of electrode catalyst layers 12C and 12A may be abbreviated as "electrode catalyst layer 12" when it is not necessary to distinguish them.

The outer peripheral portion of the electrode catalyst layer 12 may be sealed with a gasket or the like (not shown).
The electrode catalyst layer 12 according to the present embodiment contains at least a catalyst substance, a conductive carrier, and a polymer electrolyte.
The catalytic material used in this embodiment includes platinum, palladium, ruthenium, iridium, rhodium, and osmium, as well as platinum group elements, as well as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. Metals such as, and alloys, oxides, compound oxides, carbides and the like thereof can be used.

Further, the conductive carrier that supports these catalysts may be any kind as long as it is in the form of a fine powder and has conductivity and is not affected by the catalyst, but carbon particles are generally used. For example, carbon black, graphite, graphite, activated carbon, carbon nanotubes, carbon nanofibers, and fullerenes can be preferably used. If the particle size of the carbon particles is too small, it becomes difficult to form an electron conduction path, and if it is too large, the gas diffusivity of the electrode catalyst layer decreases and the utilization rate of the catalyst decreases, so it is about 10 to 1000 nm. Is preferable. More preferably, 10 to 100 nm is preferable.

The polyelectrolyte contained in the polyelectrolyte film 11 and the electrode catalyst layer 12 used in the present embodiment may be any as long as it has proton conductivity, and a fluoropolymer electrolyte or a hydrocarbon-based polyelectrolyte should be used. Is possible. In this case, examples of the fluoropolymer electrolyte include "Nafion (registered trademark)" manufactured by DuPont, "Flemion (registered trademark)" manufactured by Asahi Glass Co., Ltd., "Aciplex (registered trademark)" manufactured by Asahi Kasei Corporation, and the like. Can be used. Further, as the hydrocarbon-based polymer electrolyte, sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, sulfonated polyphenylene and the like can be used. In particular, as the polymer electrolyte membrane 11, it is possible to preferably use a "Nafion (registered trademark)" material manufactured by DuPont. Further, various polyelectrolytes contained in the electrode catalyst layer 12 can be used. However, considering the interface resistance between the polyelectrolyte film 11 and the electrode catalyst layer 12 and the dimensional change rate between the polyelectrolyte film 11 and the electrode catalyst layer 12 when the humidity changes, the polyelectrolyte film 11 is included. It is preferable that the polyelectrolyte to be used and the polyelectrolyte contained in the electrode catalyst layer 12 have the same or similar components.

As a method of forming the electrode catalyst layer 12 on the upper surface and the lower surface of the polymer electrolyte membrane 11 to obtain the membrane electrode joint 1, the catalyst substance, the conductive carrier, and the polymer electrolyte are directly formed on the surface of the polymer electrolyte membrane 11. Using a method of applying a catalyst ink containing at least a catalyst and removing a catalyst component from the coating film of the catalyst ink to form an electrode catalyst layer 12, or a transfer substrate 2 with a catalyst layer (see FIG. 2) prepared in advance. Therefore, a method of bonding and transferring by contacting the surface of the polymer electrolyte membrane 11 and the surface of the electrode catalyst layer 12 with heating and pressurization can be used.

FIG. 2 is an explanatory view of the transfer base material 2 with a catalyst layer (cross-sectional view in the thickness direction orthogonal to the surface of the electrode catalyst layer 12). As shown in FIG. 2, in the transfer base material 2 with a catalyst layer, a catalyst ink containing at least a catalyst substance, a conductive carrier, a polymer electrolyte, and a solvent is applied to the surface of the base material 13, and the coating film of the catalyst ink is used. The electrode catalyst layer 12 is formed by removing the solvent component.
The catalyst ink is obtained by mixing at least the above-mentioned catalyst substance, a conductive carrier, a polyelectrolyte, and a solvent, and subjecting them to a dispersion treatment. For the dispersion treatment, for example, various methods such as a planetary ball mill, a bead mill, and an ultrasonic homogenizer can be used.

Further, the solvent used as the dispersion medium of the catalyst ink is one that can dissolve the polymer electrolyte or disperse it as a fine gel in a highly fluid state without eroding the catalyst substance, the conductive carrier or the polymer electrolyte. There are no particular restrictions.
The solvent may contain water that is familiar with the polyelectrolyte. It is desirable that the catalyst ink contains at least a volatile liquid organic solvent, but those using a lower alcohol as the solvent have a high risk of ignition, and when such a solvent is used, it should be mixed with water. It is preferable to do so. The amount of water added is not particularly limited as long as the polyelectrolyte does not separate and cause cloudiness or gelation.

As a method of applying the catalyst ink, for example, various coating methods such as die coat, roll coat, curtain coat, spray coat, and squeegee can be used, but the film thickness of the coating intermediate portion is stable and intermittent. It is possible to particularly preferably use a die coat that can be used for coating.
Further, for drying the applied catalyst ink, for example, a warm air oven, IR drying, a hot plate, vacuum drying or the like can be used.

When bonding and transfer are performed by contacting the polymer electrolyte film 11 and the electrode catalyst layer 12 with the transfer base material 2 with the catalyst layer to heat and pressurize, the pressure applied to the electrode catalyst layer 12 is the membrane electrode assembly. It affects the power generation performance of body 1. Therefore, in order to obtain the membrane electrode assembly 1 having good power generation performance, the pressure applied to the laminated body is preferably in the range of 0.5 MPa or more and 20 MPa or less, and more preferably in the range of 2 MPa or more and 15 MPa or less. desirable. If the pressure is higher than 20 MPa, the electrode catalyst layer 12 is compressed too much, and if the pressure is lower than 0.5 MPa, the bondability between the electrode catalyst layer 12 and the polymer electrolyte film 11 is lowered, and the power generation performance is lowered.

Further, setting the temperature at the time of bonding near the glass transition point of the polymer electrolyte of the electrode catalyst layer improves the bondability of the interface between the polymer electrolyte film 11 and the electrode catalyst layer 12 and suppresses the interface resistance. Effective and desirable in terms of points.
The base material 13 includes, for example, ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), and polytetrafluoro. A fluororesin having excellent transferability such as ethylene (PTFE) can be used. Further, polymer films such as polyimide, polyethylene terephthalate, polyamide (nylon), polysulfone, polyether sulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyallylate, and polyethylene naphthalate can also be used.

Further, a gas diffusion layer can also be used as the base material 13.
The electrode catalyst layer 12 according to the embodiment of the present invention is the surface of the electrode catalyst layer 12 as shown in FIG. 3 when the region D having a predetermined area is irradiated with the inspection light incident on the Brewster angle θ _B. Of the specularly reflected light, the amount of reflected light that has passed through the polarizing element 15 that allows only the P polarization component to pass is Lp, and when expressed in 4096 gradations, the surface of the electrode catalyst layer 12 does not overlap the region D. The standard deviation σ of the reflected light amount Lp obtained by scanning the entire area is configured to be 30 or more and 150 or less. The inspection light is emitted from the light source 14, reflected on the surface of the electrode catalyst layer 12, and the light transmitted through the polarizing element 15 is incident on the light receiving unit 16 and detected. The amount of reflected light of the light detected at this time is Lp.

That is, the standard deviation σ of the reflected light amount Lp obtained by scanning almost the entire surface of the surface of the electrode catalyst layer 12 without overlapping the regions D is that the smaller the standard deviation σ is, the more uniform the electrode catalyst layer 12 is, and the larger the catalyst substance and conductivity. It is an index that the uneven distribution of the sex carrier and the polymer electrolyte, the difference in the local thermal history of the electrode catalyst layer 12, and the variation in the thickness are large.
The method of calculating the standard deviation σ of the reflected light amount Lp is all obtained by irradiating the surface of the electrode catalyst layer 12 with the inspection light and detecting the reflected light with the light receiving unit 16 through the polarizing element 15 that allows only the P polarization component to pass through. It is obtained by performing a histogram analysis on the data of the reflected light amount Lp of.

Here, in FIG. 3, the electrode catalyst layer 12 is formed on the surface of the polymer electrolyte membrane 11, but may be formed on the surface of the base material 13.
Here, as the light source 14, for example, an LED (Light Emitting Diode), a halogen lamp, a xenon lamp, or the like is used. The inspection light is preferably parallel light or highly directional so that uniform irradiation can be performed on the entire width of the object to be inspected, and a uniform illumination lens or a telecentric lens may be used in combination.

Further, as the light receiving unit 16, an area camera or a line scan camera using a CCD (Charge Coupled Device) image sensor is used. In particular, when a line scan camera is installed for the entire width of the inspected object and the inspected object is sequentially inspected while moving in the direction perpendicular to the light receiving portion 16, the inspection accuracy and the inspection efficiency are excellent, and various inspections are performed. It is possible and suitable for the size of the object to be inspected.

When the effective sizes of the light source 14 and the light receiving unit 16 are sufficiently large, it is possible to obtain the reflected light amount Lp in the plurality of regions D without scanning.
Generally, when light is incident on the surface of a smooth object to be inspected at a Brewster's angle, the reflectance of P-polarized light is 0, and only S-polarized light is reflected. That is, when the light reflected on the surface of the inspection body passes through the polarizing element 15 that allows only the P polarization component to pass through, the light is not incident on the light receiving unit 16.

However, when micro-concavities and convexities are present such as on the surface of the electrode catalyst layer 12, light is scattered on the concavo-convex surface. Is incident. Further, when there are portions having different smoothness and composition on the surface of the electrode catalyst layer 12, the reflectances are different, so that the reflected light amount Lp of the light incident on the light receiving portion 16 and being detected is different.
In the electrode catalyst layer 12 according to the embodiment of the present invention, the standard deviation σ of the reflected light amount Lp obtained by scanning almost the entire surface of the electrode catalyst layer 12 without overlapping the regions D is 30 or more and 150 or less. It is configured to be.

When the standard deviation σ of the reflected light amount Lp is larger than 150, the catalyst substance, the conductive carrier, and the polymer electrolyte are unevenly distributed, and the difference in the local thermal history and the thickness of the electrode catalyst layer 12 are large, and the periphery is large. When the battery is laminated with a member to form a cell and generate power, the output and durability of the battery are significantly reduced. This is because the adhesion between the polymer electrolyte film 11 or the gas diffusion layer and the electrode catalyst layer 12 is partially reduced, or the electrode catalyst layer 12 or the membrane electrode assembly 1 is locally subjected to a high electrical load. It is thought that this is because it exists. On the other hand, when the standard deviation σ of the reflected light amount Lp is smaller than 30, the conductive carrier is in a state of being too tightly clogged, and the water generated and condensed by power generation clogs the pores and blocks the gas passage. Because it is easy, the output of the battery decreases.

More preferably, the predetermined area of the region D is 1600 μm ² or more and 10000 μm ² or less. When the area of the region D is larger than 10000 μm ² , the wider area is averaged, so that the unevenness existing in the electrode catalyst layer 12 cannot be accurately detected. Further, when the area of the region D is smaller than 1600 μm ² , a very high resolution light receiving portion is required, and it takes a long time to scan the entire area of the electrode catalyst layer, so that it is practical from the viewpoint of the manufacturing process. Not the target.

Further, the thickness of the electrode catalyst layer 12 according to the embodiment of the present invention is preferably in the range of 1 μm or more and 30 μm or less, and is in the range of 2 μm or more and 20 μm or less in consideration of manufacturing variations and the like. Is more preferable.
When the thickness of the electrode catalyst layer 12 is thicker than 30 μm, the surface of the electrode catalyst layer is cracked, the diffusion of gas and generated water is hindered, and the conductivity is lowered, so that the fuel cell is used. The output is reduced. Further, when the thickness of the electrode catalyst layer 12 is thinner than 1 μm, the layer thickness tends to vary, and the internal catalyst substance and the polymer electrolyte tend to become non-uniform. Cracks on the surface of the electrode catalyst layer 12 and non-uniformity in thickness are not preferable because they are likely to adversely affect the durability when used as a fuel cell and operated for a long period of time.

The thickness of the electrode catalyst layer 12 can be confirmed, for example, as follows. First, the cross section of the electrode catalyst layer 12 is exposed, and five or more cross sections are observed using a scanning electron microscope (SEM) at a magnification of 3000 to 10000 times. Measure the thickness at 3 or more points at each observation point, and use the average value as the representative value at each observation point. The average value of these representative values is taken as the thickness of the electrode catalyst layer 12.

As a method for exposing the cross section of the electrode catalyst layer 12, for example, a known method such as ion milling or ultramicrotome can be used. When processing to expose the cross section, it is preferable to perform processing while cooling the electrode catalyst layer 12 in order to reduce damage to the polymer electrolyte constituting the electrode catalyst layer 12.
Further, the electrode catalyst layer 12 is configured such that the ratio of the weight of the polymer electrolyte to the weight of the conductive carrier in the electrode catalyst layer 12 is in the range of 0.8 or more and 1.6 or less. If the weight ratio is higher than 1.6, the polyelectrolyte may block the pores in the electrode catalyst layer, hindering the diffusion of gas and generated water and reducing the output of the fuel cell. .. Further, when the weight ratio is lower than 0.8, the proton conduction path of the polymer electrolyte may be reduced or blocked, and the output of the fuel cell may be reduced.

(Construction of polymer electrolyte fuel cell)
Next, with reference to FIG. 4, a specific configuration of the polymer electrolyte fuel cell provided with the membrane electrode assembly according to the embodiment of the present invention will be described. FIG. 2 is an exploded perspective view showing a configuration example of the polymer electrolyte fuel cell 3 equipped with the membrane electrode assembly 1. However, FIG. 4 is an example of a single cell configuration, and the configuration is not limited to this, and a configuration in which a plurality of single cells are stacked may be used.

As shown in FIG. 4, the polymer electrolyte fuel cell 3 includes a membrane electrode assembly 1, a gas diffusion layer 17C, and a gas diffusion layer 17A. The gas diffusion layer 17C is arranged so as to face the electrode catalyst layer 12C which is the cathode side catalyst layer on the oxygen electrode side of the membrane electrode assembly 1, and the gas diffusion layer 17A is the anode on the fuel electrode side of the membrane electrode assembly 1. It is arranged so as to face the electrode catalyst layer 12A which is a side catalyst layer. The oxygen electrode 4C is composed of the electrode catalyst layer 12C and the gas diffusion layer 17C, and the fuel electrode 4A is composed of the electrode catalyst layer 12A and the gas diffusion layer 17A.

Further, the polymer electrolyte fuel cell 3 includes a separator 18C arranged to face the oxygen electrode 4C and a separator 18A arranged to face the fuel electrode 4A.
The separator 18C is made of a conductive and gas impermeable material, and is arranged on the gas flow path 19C for the reaction gas flow arranged facing the gas diffusion layer 17C and the main surface facing the gas flow path 19C. The cooling water flow path 20C for flowing the cooling water is provided. Further, the separator 18A has the same configuration as the separator 18C, and has a gas flow path 19A arranged facing the gas diffusion layer 17A and a cooling water flow arranged on the main surface facing the gas flow path 19A. It is provided with a road 20A.

In the solid polymer fuel cell 3, an oxidizing agent such as air or oxygen is supplied to the oxygen electrode 4C through the gas flow path 19C of the separator 18C, and the fuel gas containing hydrogen passes through the gas flow path 19A of the separator 18A. Alternatively, organic fuel is supplied to the fuel electrode 4A to generate power.

As described above, in the present embodiment, among the specularly reflected light when the electrode catalyst layer 12 is irradiated with the inspection light incident on the region D having a predetermined area at the Brewster angle θ _B on the surface of the electrode catalyst layer 12. When the amount of reflected light that has passed through the polarizing element 15 that allows only the P-polarizing component to pass is Lp and expressed in 4096 gradations, the entire surface of the surface of the electrode catalyst layer 12 is scanned without overlapping the regions D. The standard deviation σ of the amount of reflected light Lp obtained is 30 or more and 150 or less. As a result, when the catalyst substance, the conductive carrier and the polymer electrolyte are unevenly distributed, and the difference in the local thermal history and the variation in the thickness of the electrode catalyst layer 12 are set to an appropriate state, they are laminated with the peripheral members to form a cell and generate power. In addition, it is possible to obtain an electrode catalyst layer and a membrane electrode assembly having excellent battery output and durability.

Further, the predetermined area of the region D on the surface of the electrode catalyst layer 12 is set to 1600 μm ² or more and 10000 μm ² or less. This makes it possible to accurately detect the unevenness existing in the electrode catalyst layer 12 at a practically appropriate speed.
Further, since the thickness of the electrode catalyst layer 12 is configured within the range of 1 μm or more and 30 μm or less, it is possible to obtain the electrode catalyst layer 12 without problems such as uneven layer thickness and surface cracks, and further, durability. It is possible to obtain an excellent membrane electrode assembly 1.

Further, since the electrode catalyst layer 12 is configured such that the weight ratio of the polymer electrolyte to the conductive carrier in the electrode catalyst layer 12 is within the range of 0.8 or more and 1.6 or less, gas or water. It is possible to obtain an electrode catalyst layer and a membrane electrode assembly having high proton conductivity while maintaining diffusivity.
Further, since the polymer electrolyte fuel cell 3 is configured by using the membrane electrode assembly 1, there is no deterioration in power generation performance due to a flooding phenomenon and a decrease in proton conductivity, high power generation performance is exhibited, and durability is also excellent. It becomes possible to obtain a polymer electrolyte fuel cell.

Hereinafter, the results of comparing the performances of the fuel cell provided with the membrane electrode assembly according to the embodiment of the present invention and the fuel cell provided with the membrane electrode assembly according to the comparative example will be described.
(Example 1)
A platinum-supported carbon catalyst (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), a mixed solvent of water and ethanol, and a polyelectrolyte (Nafion (registered trademark), manufactured by Dupont) dispersion are mixed and dispersed in a planetary ball mill for 30 minutes. This was done to prepare the catalyst ink. At that time, the weight ratio of the polymer electrolyte to the carbon carrier was set to 1.0.

The adjusted catalyst ink is applied to the surface of the PTFE film in a rectangular shape with a slit die coater, and then the PTFE film coated with the catalyst ink is placed in a warm air oven at 80 degrees and dried until the catalyst ink is no longer tacked. The cathode side catalyst layer was formed on the surface of the PTFE. Moreover, the anode side catalyst layer was formed on the surface of PTFE by the same method.
Then, the cathode side catalyst layer and the anode side catalyst layer formed on the PTFE film are arranged so as to face both sides of the polymer electrolyte membrane (Nafion 211 (registered trademark), manufactured by Dupont), and this laminate is placed. The PTFE film was peeled off after hot pressing at 120 ° C. and 10 MPa to obtain a membrane electrode assembly of Example 1.

(Example 2)
A membrane electrode assembly of Example 2 was obtained in the same manner as in Example 1 except that the coating amount of the cathode side catalyst layer was doubled.
(Example 3)
A membrane electrode assembly of Example 3 was obtained in the same manner as in Example 1 above, except that the weight ratio of the polymer electrolyte to the carbon carrier was 0.8 when the catalyst ink was prepared.

(Example 4)
A membrane electrode assembly of Example 4 was obtained in the same manner as in Example 1 above, except that the weight ratio of the polymer electrolyte to the carbon carrier was 1.6 when the catalyst ink was prepared.
(Comparative Example 1)
A membrane electrode assembly of Comparative Example 1 was obtained in the same manner as in Example 1 above except that the dispersion time was set to 10 minutes when preparing the catalyst ink.

(Comparative Example 2)
A membrane electrode assembly of Comparative Example 2 was obtained in the same manner as in Example 1 above except that the dispersion time was set to 300 minutes when preparing the catalyst ink.
(Comparative Example 3)
A membrane electrode assembly of Comparative Example 3 was obtained in the same manner as in Example 1 above, except that the weight ratio of the polymer electrolyte to the carbon carrier was 0.7 when the catalyst ink was prepared.

(Comparative Example 4)
A membrane electrode assembly of Comparative Example 4 was obtained in the same manner as in Example 1 above, except that the weight ratio of the polymer electrolyte to the carbon carrier was 1.7 when the catalyst ink was prepared.
(Comparative Example 5)
A membrane electrode assembly of Comparative Example 5 was obtained in the same manner as in Example 1 above except that the coating amount of the cathode side catalyst layer was increased by 5 times.

(Comparative Example 6)
A membrane electrode assembly of Comparative Example 6 was obtained in the same manner as in Example 1 above except that the air volume of the hot air oven was tripled.
(evaluation)
Hereinafter, the weight ratio of the polymer electrolyte to the carbon carrier of each of the membrane electrode assembly of Examples 1 to 4 and the membrane electrode assembly of Comparative Examples 1 to 6 and the cathode electrode catalyst layer The result of comparing the thickness, the standard deviation σ of the reflected light amount Lp on the surface of the electrode catalyst layer, the power generation performance, and the durability will be described.

(Measurement of thickness of electrode catalyst layer)
The thickness of the electrode catalyst layer was obtained by observing the cross section of the electrode catalyst layer using a scanning electron microscope (SEM). Specifically, first, a cross section of the electrode catalyst layer was exposed using an ion milling device IM4000 manufactured by Hitachi High-Technology. Next, the obtained cross section was observed at 5000 times using FE-SEM S-4800 manufactured by Hitachi High Technology Co., Ltd., and the thickness of 3 points was measured in the field of view at 5 observation points, and the average thereof was measured. The values were taken as representative values at each observation point. The average value of the representative values at the five observation points was taken as the thickness of the electrode catalyst layer.

(Calculation of standard deviation σ of reflected light amount Lp on the surface of the electrode catalyst layer)
The standard deviation σ of the reflected light amount Lp on the surface of the electrode catalyst layer is the data of all the reflected light amount Lp acquired by the method of irradiating the surface of the electrode catalyst layer with inspection light and detecting the reflected light through a P-polarizer with a line CCD camera. Calculated by performing histogram analysis.

Specifically, first, the membrane electrode assembly was placed on an inspection stage using a porous vacuum adsorption plate without wrinkles or slack, and fixed using a vacuum pump. Highly directional linear illumination installed so that the incident angle is 50 degrees, which is the Brewster's angle, is used as the inspection light source, and the inspection light is reflected by the electrode catalyst layer portion of the membrane electrode assembly fixed to the porous vacuum adsorption plate. I let you. The reflected inspection light was detected by a line CCD camera through a polarizing element installed so as to transmit only P-polarized light. At that time, the effective width of the inspection light source, the spectrometer and the line CCD camera is set to be equal to or larger than the width of the electrode catalyst layer, and the reflected light amount Lp is sequentially moved while the inspection stage is moved in the direction orthogonal to the main scanning direction of the inspection light source and the line CCD camera. Data was acquired. The size of one pixel of the CCD camera corresponding to the area D was 6400 μm ² . Histogram analysis was performed on all the acquired data of the reflected light amount Lp, and the standard deviation σ was obtained. Specifically, the standard deviation σ was obtained by the following procedures (1) to (3). FIG. 5 is a diagram showing an example of a mapping image of the reflected light amount Lp captured by the CCD camera, and FIG. 6 is an example of a histogram of the reflected light amount Lp .
(1) The entire surface of the electrode catalyst layer is scanned without overlapping the imaging region D.
(2) Acquire the data of the reflected light amount Lp for each region D, and obtain the data.
(3) The standard deviation is calculated directly from the data using the general formula for calculating the standard deviation (formula (1) below).

(Measurement of power generation performance)
For the measurement of power generation performance, a cell in which a gas diffusion layer, a gasket, and a separator were arranged on both sides of the membrane electrode assembly and tightened to a predetermined surface pressure was used as a single cell for evaluation. Then, the IV measurement was carried out in accordance with the method described in the "Cell Evaluation and Analysis Protocol", which is a booklet published by the New Energy and Industrial Technology Development Organization (NEDO).

(Measurement of durability)
For the measurement of durability, a single cell for evaluation used for measuring the power generation performance was used. Then, the humidity cycle test was carried out in accordance with the method described in the "Cell Evaluation and Analysis Protocol", which is a booklet published by the New Energy and Industrial Technology Development Organization (NEDO).

(Comparison result)
The weight ratio of the polymer electrolyte to each carbon carrier of the fuel cell provided with the membrane electrode assembly of Examples 1 to 4 and the membrane electrode assembly of Comparative Examples 1 to 6 and the thickness of the cathode electrode catalyst layer. Table 1 shows the standard deviation σ of the reflected light amount Lp on the surface of the electrode catalyst layer, and the power generation performance and durability. Regarding the power generation performance, a current of 20 A or more at a voltage of 0.6 V is described as “◯” and a current of less than 20 A is described as “x”. Regarding the durability, the hydrogen cross leak current after 8000 cycles is described as "◯" when it is less than 10 times the initial value, and "x" when it is 10 times or more the initial value.

In this example, in each of the above Examples 1 to 4, the weight ratio of the polymer electrolyte to the carbon carrier is 0.8 or more and 1.6 or less, and the thickness of the cathode electrode catalyst layer is in the range of 2 μm or more and 20 μm or less. It became inside. Further, the standard deviation σ of the reflected light amount Lp on the surface of the electrode catalyst layer was within the range of 30 or more and 150 or less. The power generation performance and durability were all marked with "○". That is, in Examples 1 to 4, a membrane electrode assembly capable of forming a fuel cell having excellent power generation performance and durability was obtained.

On the other hand, in Comparative Example, the weight ratio of the polymer electrolyte to the carbon carrier is 0.8 or more and 1.6 or less in Comparative Examples 1, 2, 5 and 6, but in Comparative Examples 3 and 4, it is in this range. It wasn't inside. The thickness of the cathode electrode catalyst layer was within the range of 2 μm or more and 20 μm or less in Comparative Examples 1 to 4 and Comparative Example 6, but was not within this range in Comparative Example 5. Further, the standard deviation σ of the reflected light amount Lp on the surface of the electrode catalyst layer was not in the range of 30 or more and 150 or less in any of Comparative Examples 1 to 5. The power generation performance was "x" in Comparative Examples 1, 2 and 4, and the durability was "x" in Comparative Examples 1 and 3 to 6. That is, when the standard deviation σ of the reflected light amount Lp on the surface of the electrode catalyst layer, which is an index showing the unevenness of the electrode catalyst layer, is out of each of the above ranges, at least one of the power generation performance and the durability is deteriorated.

According to the present invention, unevenness of the electrode catalyst layer, which is a problem in the operation of a polymer electrolyte fuel cell, is detected with high accuracy to exclude defective products, and the battery output and durability can be improved even when used for a long period of time. Excellent electrode catalyst layers, membrane electrode assemblies and polymer electrolyte fuel cells can be obtained.
Therefore, the present invention has a performance that can be suitably used for a stationary cogeneration system, a fuel cell vehicle, or the like using a polymer electrolyte fuel cell, and has great industrial utility value.

1 ... Membrane electrode assembly 2 ... Transfer substrate with catalyst layer 3 ... Solid polymer fuel cell 4C ... Oxygen electrode 4A ... Fuel electrode 11 ... Polymer electrolyte membrane 12, 12C, 12A ... Electrode catalyst layer 13 ... Base material 14 ... Light source 15 ... Polarizer 16 ... Light receiving unit 17C, 17A ... Gas diffusion layer 18C, 18A ... Separator 19C, 19A ... Gas flow path 20C, 20A ... Cooling water flow path

Claims (7)

An electrode catalyst layer containing at least a catalyst substance, a conductive carrier, and a polymer electrolyte.
On the surface of the electrode catalyst layer, the amount of reflected light that has passed through a polarizing element that allows only the P-polarizing component to pass through the specularly reflected light when the inspection light incident on the region having a predetermined area at Brewster's angle is irradiated. Is Lp, and when expressed in 4096 gradations, the standard deviation σ of the reflected light amount Lp obtained by scanning the entire surface of the surface of the electrode catalyst layer without overlapping the regions is 30 or more and 150 or less. The electrode catalyst layer is characterized by. The electrode catalyst layer according to claim 1, wherein the predetermined area of the region is 1600 μm ² or more and 10000 μm ² or less. The electrode catalyst layer according to claim 1 or 2, wherein the thickness in the direction orthogonal to the surface of the electrode catalyst layer is set to be within the range of 1 μm or more and 30 μm or less. The electrode catalyst layer according to claim 3, wherein the thickness in the direction orthogonal to the surface of the electrode catalyst layer is set to be within a range of 2 μm or more and 20 μm or less. The invention according to any one of claims 1 to 4, wherein the ratio of the weight of the polymer electrolyte to the weight of the conductive carrier is 0.8 or more and 1.6 or less. Electrode catalyst layer. The membrane electrode according to any one of claims 1 to 5, which comprises a polyelectrolyte film and an electrode catalyst layer bonded to at least a surface on the oxygen electrode side of the polyelectrolyte film. Joined body. A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 6.

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