JP2018142466A - Electrode catalyst layer membrane-electrode assembly and solid polymer fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode catalyst layer capable of preventing for a long time a cell performance or durability from being considerably reduced, a membrane-electrode assembly and a solid polymer fuel cell.SOLUTION: In an electrode catalyst layer 12, a radio σp/σs of a standard deviation σp of a light quantity (reflection light quantity Lp) of a P polarized component included in multiple regular reflection lights that are obtained in a case where multiple predetermined domains D on a surface of the electrode catalyst layer 12 are irradiated with inspection light that is made incident at a Brewster angle θ, and a standard deviation σs of a light quantity (reflection light quantity Ls) of an S polarized component is set to 0.5 or more and 1.5 or less.SELECTED DRAWING: Figure 3

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 generates electricity from a chemical reaction between hydrogen and oxygen. Compared to conventional power generation systems, it has the features of 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 household stationary power supplies. In recent years, various research and development related to polymer electrolyte fuel cells have been conducted. It has been broken. Issues for practical application include improvement of battery performance such as power generation characteristics and durability, infrastructure development, and reduction of manufacturing costs.
In general, a polymer electrolyte fuel cell is configured by stacking a large number of single cells. A single cell consists of a membrane electrode assembly joined by sandwiching a polymer electrolyte membrane between two electrodes, a fuel electrode (anode) for supplying fuel gas and an oxygen electrode (cathode) for supplying oxidant. And it has the structure pinched | interposed with the separator which has a cooling water flow path. Each of the fuel electrode and the oxygen electrode includes an electrode catalyst layer including at least a catalytic 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 of.

  In the polymer electrolyte fuel cell, electricity can be taken out through the following electrochemical reaction. First, in the electrode catalyst layer on the fuel electrode (anode) side, hydrogen contained in the fuel gas is oxidized by the catalyst substance to become protons and electrons. The generated protons pass through the polymer electrolyte in the electrode catalyst layer and the polymer electrolyte membrane in contact with the electrode catalyst layer, and reach the electrode catalyst layer on the oxygen electrode (cathode) side. In addition, the simultaneously generated electrons pass through the electroconductive carrier in the electrode catalyst layer, the gas diffusion layer in contact with the electrode catalyst layer on the side different from the polymer electrolyte membrane, the separator, and the electrode catalyst layer on the oxygen electrode side through the external circuit. 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 defects such as unevenness and cracks generated in the production process. These defects generated in the electrode catalyst layer are due to uneven distribution of the catalyst substance, the conductive carrier and the polymer electrolyte, a difference in local thermal history inside the electrode catalyst layer, and variations in the thickness of the electrode catalyst layer. Membrane / electrode assemblies having electrode catalyst layers with significant unevenness and cracks are laminated with peripheral members to form cells, and when power is generated, the adhesion between the polymer electrolyte membrane or gas diffusion layer and the electrode catalyst layer is partially There is a possibility that the generated water may be reduced and the electrode catalyst layer may have a portion where a high electrical load is applied locally. Such a local load tends to promote the deterioration of the membrane electrode assembly, and there is a high possibility of causing a membrane breakage in the long term.

When such a membrane electrode assembly having an electrode catalyst layer with remarkable unevenness and cracks is used in a fuel cell, the battery performance and durability are significantly reduced, which causes a problem in the manufacturing process of the membrane electrode assembly. Techniques have been proposed for detecting defects with high accuracy and excluding defective products.
As a technique for detecting a defective part of a membrane electrode assembly or a gas diffusion layer, there is a method in which transmitted light or reflected light of irradiated light in the defective part is imaged and image processing is performed on the captured transmitted light or reflected light image data. is there. For example, in the technique described in Patent Document 1, the inspection light is irradiated from one side of the sheet member, and the inspection light transmitted through the defect portion is detected by a detector provided on the opposite side.

In the technique described in Patent Document 2, inspection light is irradiated from one side of the membrane electrode assembly, and the inspection light reflected by the defect portion is detected by a detector.
Furthermore, in the technique described in Patent Document 3, the surface of the porous electrode base material is irradiated with inspection light, and transmitted light, specular reflected light, and scattered light are imaged, and transmitted light, regular reflected light, and scattered light are captured. The image data is analyzed by image processing to detect the type, location and size of the defect.

JP 2014-190706 A JP 2014-225340 A Japanese Patent No. 5306053

However, the technique described in Patent Document 1 uses transmitted light as a light source for inspection, and thus has a problem that it cannot be applied to inspection of unevenness generated in an electrode catalyst layer that does not transmit light.
Moreover, although the technique described in Patent Document 2 uses reflected light for inspection, since the phase paper is installed on the surface of the membrane electrode assembly, wrinkles can be detected, but the electrode catalyst layer There has been a problem that unevenness generated on the surface cannot be detected.
Furthermore, in the technique described in Patent Document 3, since the defect is detected by directly irradiating the surface of the test object with the inspection light, it may be applicable to the inspection of the electrode catalyst layer. However, since the size and contrast differ between a defect occurring in the porous electrode substrate and a defect such as unevenness occurring in the electrode catalyst layer, it cannot be applied as it is. Moreover, in patent document 3, it did not mention regarding an electrode catalyst layer, but there existed a problem that the reference | standard of the quality of the defect which generate | occur | produced in the electrode catalyst layer was unknown.

  The present invention has been made to solve the above-described problems, and an electrode catalyst layer, a membrane electrode assembly, and a solid polymer fuel that can suppress long-term deterioration of battery performance and durability. It is an object to provide a battery.

In order to solve the above problems, one embodiment of the present invention is (a) an electrode catalyst layer including a catalyst substance, a conductive carrier, and a polymer electrolyte, and (b) predetermined on the surface of the electrode catalyst layer. The standard deviation σp of the reflected light amount Lp, which is the light amount of the P-polarized component, and the light amount of the S-polarized component included in the plurality of specularly reflected light obtained when the inspection light incident at the Brewster angle is irradiated on each of the plurality of regions. The gist is that the ratio σp / σs of the reflected light quantity Ls to the standard deviation σs is 0.5 or more and 1.5 or less.
Another aspect of the present invention is a membrane electrode assembly comprising (a) a polymer electrolyte membrane, and (b) the electrode catalyst layer bonded to the oxygen electrode side surface of the polymer electrolyte membrane. This is the gist.
Furthermore, another aspect of the present invention is a polymer electrolyte fuel cell including the membrane electrode assembly.

  According to the present invention, since the uneven distribution of the catalyst substance, the conductive carrier and the polymer electrolyte, the difference in local thermal history inside the electrode catalyst layer, and the variation in the thickness of the electrode catalyst layer can be suppressed, battery performance and durability can be suppressed. It is possible to provide an electrode catalyst layer, a membrane electrode assembly, and a polymer electrolyte fuel cell that can suppress the deterioration of the property for a long time.

The structure of the membrane electrode assembly which concerns on embodiment is shown, (a) is the top view which looked at the membrane electrode assembly from the oxygen electrode side of the electrode catalyst layer, (b) is fractured | ruptured by the XX 'line of (a) FIG. It is explanatory drawing of the transfer base material with a catalyst layer which has the electrode catalyst layer which concerns on embodiment. It is explanatory drawing which shows the structure at the time of obtaining reflected light quantity Lp and Ls. It is a disassembled perspective view which shows the structure of the polymer electrolyte fuel cell which concerns on embodiment. It is a figure which shows an example of the mapping image of reflected light quantity Lp. It is a figure which shows an example of the histogram of reflected light quantity Lp.

Embodiments of the present invention will be described below with reference to the 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. The form is also included in the scope of the present invention. Each drawing is exaggerated as appropriate for easy understanding.
As a result of earnestly examining the power generation performance and durability performance of the polymer electrolyte fuel cell, the inventors of the present invention have found that these performances include the uneven distribution of the catalyst substance, the conductive carrier and the polymer electrolyte in the electrode catalyst layer, It has been found that the difference in local thermal history inside the electrode catalyst layer and the variation in the thickness of the electrode catalyst layer are greatly affected. In addition, the dispersion of the reflected luminance in the electrode catalyst layer is set within a predetermined range so as not to cause a local load on the membrane electrode assembly, thereby suppressing deterioration and providing a solid power source that exhibits high power generation performance over the long term. We succeeded in obtaining a molecular fuel cell.

(Configuration 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 oxygen electrode (hereinafter also referred to as “upper surface”) side of the electrode catalyst layer 12C, and FIG. It is sectional drawing (sectional drawing fractured | ruptured in the thickness direction orthogonal to the surface of the electrode catalyst layer 12C) in alignment with the XX 'line | wire of Fig.1 (a).
As shown in FIGS. 1A and 1B, the membrane electrode assembly 1 includes a polymer electrolyte membrane 11 and electrode catalyst layers 12C and 12A joined to the respective surfaces of the polymer electrolyte membrane 11. ing. In the present embodiment, the electrode catalyst layer 12C formed on the upper surface of the polymer electrolyte membrane 11 is a cathode side catalyst layer constituting the oxygen electrode, and the electrode catalyst layer 12A formed on the lower surface of the polymer electrolyte membrane 11 is The anode side catalyst layer constituting the fuel electrode. Hereinafter, the pair of electrode catalyst layers 12 </ b> C and 12 </ b> A may be abbreviated as “electrode catalyst layer 12” when it is not necessary to distinguish them. The outer periphery of the electrode catalyst layer 12 may be sealed with a gasket or the like (not shown).

The electrode catalyst layer 12 includes at least a catalyst substance, a conductive carrier, and a polymer electrolyte.
Examples of the catalytic substance include platinum group elements such as platinum, palladium, ruthenium, iridium, rhodium, and osmium, and metals such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. Alloys, oxides, double oxides, carbides, and the like can be used. The conductive carrier may be any conductive carrier as long as it has conductivity and can support the catalyst material without being attacked by the catalyst material, but generally carbon particles are used. . For example, carbon black, graphite, graphite, activated carbon, carbon nanotube, carbon nanofiber, and fullerene can be used. If the particle size of the carbon particles is too small, it becomes difficult to form an electron conduction path. If the particle size is too large, the gas diffusibility of the electrode catalyst layer 12 is reduced or the utilization factor of the catalyst is reduced. About 1000 nm is preferable. More preferably, about 10-100 nm is good.

  The polymer electrolyte contained in the polymer electrolyte membrane 11 and the electrode catalyst layer 12 may be any polymer electrolyte as long as it has proton conductivity, and a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte is used. be able to. As the fluorine-based polymer electrolyte, for example, “Nafion (registered trademark)” manufactured by DuPont, “Flemion (registered trademark)” manufactured by Asahi Glass Co., Ltd., “Aciplex (registered trademark)” manufactured by Asahi Kasei Corporation, etc. Can do. Examples of the hydrocarbon polymer electrolyte that can be used include sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene. The polymer electrolyte contained in the polymer electrolyte membrane 11 and the polymer electrolyte contained in the electrode catalyst layer 12 may be the same as each other or different from each other. However, considering the interfacial resistance between the polymer electrolyte membrane 11 and the electrode catalyst layer 12 and the rate of dimensional change between the polymer electrolyte membrane 11 and the electrode catalyst layer 12 when the humidity changes, the high concentration contained in the polymer electrolyte membrane 11 is considered. The molecular electrolyte and the polymer electrolyte contained in the electrode catalyst layer 12 are preferably the same or similar components.

  Further, as a method of obtaining the membrane electrode assembly 1 by forming the electrode catalyst layer 12 on the upper and lower surfaces of the polymer electrolyte membrane 11, for example, a catalyst substance, a conductive carrier and a polymer are formed on the surface of the polymer electrolyte membrane 11. A method of forming the electrode catalyst layer 12 by directly applying a catalyst ink containing at least an electrolyte and a solvent and then removing the solvent component from the coating film of the catalyst ink can be used. Further, for example, using a transfer substrate 2 with a catalyst layer (see FIG. 2) prepared in advance, the surface of the electrode catalyst layer 12 of the transfer substrate 2 with a catalyst layer and the polymer electrolyte membrane 11 are brought into contact with each other and heated / heated. A method of joining and transferring by pressing can also be used. FIG. 2 is an explanatory diagram of the transfer base material 2 with a catalyst layer (a cross-sectional view in the thickness direction orthogonal to the surface of the electrode catalyst layer 12). The transfer substrate 2 with the catalyst layer is coated with a catalyst ink containing at least a catalyst substance, a conductive carrier, a polymer electrolyte, and a solvent on the surface of the substrate 13, and the solvent component is removed from the coating film of the catalyst ink. The catalyst layer 12 is formed.

The catalyst ink is obtained by mixing at least the above-described catalyst substance, a conductive carrier, a polymer electrolyte, and a solvent, and applying a dispersion treatment. Various methods such as a planetary ball mill, a bead mill, and an ultrasonic homogenizer can be used for the dispersion process.
In addition, the solvent used as a dispersion medium for the catalyst ink may be one that can dissolve or disperse the polymer electrolyte in a highly fluid state without eroding the catalyst substance, the conductive carrier, and the polymer electrolyte. Anything can be used. The solvent may contain water that is compatible with the polymer electrolyte. The catalyst ink preferably contains at least a volatile liquid organic solvent, but those using lower alcohol as the solvent have a high risk of ignition. When using such a solvent, a mixed solvent with water is used. Is preferable. The amount of water added is not particularly limited as long as the polymer electrolyte is not separated to cause white turbidity or gelation.

Moreover, as a method of applying the catalyst ink, various coating methods such as die coating, roll coating, curtain coating, spray coating, squeegee, and the like can be used. In particular, die coating is preferred because the film thickness at the coating intermediate portion is stable and can be applied to intermittent coating. Furthermore, as a method of drying the applied catalyst ink, for example, a warm air oven, IR (far infrared) drying, hot plate, reduced pressure drying, or the like can be used.
When the transfer substrate 2 with the catalyst layer is used and the polymer electrolyte membrane 11 and the electrode catalyst layer 12 are brought into contact with each other and heated and pressurized to perform bonding and transfer, the pressure applied to the electrode catalyst layer 12 is membrane electrode bonding. The power generation performance of the body 1 is affected. In order to obtain the membrane electrode assembly 1 with high power generation performance, the pressure applied to the laminate is preferably 0.5 MPa or more and 20 MPa or less. When the pressure is higher than 20 MPa, the electrode catalyst layer 12 is overcompressed, and when it is lower than 0.5 MP, the bondability between the electrode catalyst layer 12 and the polymer electrolyte membrane 11 is lowered, and the power generation performance is lowered. The temperature at the time of bonding is set near the glass transition point of the polymer electrolyte of the electrode catalyst layer 12 in consideration of the improvement of the bondability at the interface between the polymer electrolyte membrane 11 and the electrode catalyst layer 12 and the suppression of the interface resistance. Is preferred.

  Examples of the base material 13 include ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), polytetra A fluororesin excellent in transferability such as fluoroethylene (PTFE) can be used. Polymer films such as polyimide, polyethylene terephthalate, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyarylate, and polyethylene naphthalate can also be used. Moreover, as the base material 13, a gas diffusion layer can also be used, for example.

In addition, as shown in FIG. 3, the electrode catalyst layer 12 according to the embodiment has a surface at the surface of the electrode catalyst layer 12 irradiated with inspection light incident at a Brewster angle θ _B on a region D having a predetermined area. Of the regular reflection light, when the polarizer 15 is a polarizer that passes only the P-polarized component, the amount of light reflected by the polarizer 15 is Lp, and the polarizer 15 allows only the S-polarized component to pass. When the reflected light amount of the light that has passed through the polarizer 15 is Ls, the standard deviation of the reflected light amount Lp obtained by scanning almost the entire surface of the electrode catalyst layer 12 without overlapping each region D. The ratio σp / σs between σp and the standard deviation σs of the reflected light amount Ls is configured to be 0.5 or more and 1.5 or less. In other words, included in the plurality of regular reflected light obtained when irradiated with inspection light incident at the Brewster angle theta _B to each of the plurality of regions D determined in advance on the surface of the electrode catalyst layer 12, the P-polarized component light quantity ( The ratio σp / σs between the standard deviation σp of the reflected light amount Lp) and the standard deviation σs of the light amount of the S-polarized component (reflected light amount Ls) is 0.5 or more and 1.5 or less.

  In the example of FIG. 3, the inspection light is irradiated by the light source 14 and reflected by the surface (region D) of the electrode catalyst layer 12. Then, the light transmitted through the polarizer 15 enters the light receiving unit 16, and the amount of reflected light is detected by the light receiving unit 16. At this time, when the polarizer 15 is a polarizer that passes only the P-polarized component, the amount of reflected light detected is Lp, and when the polarizer 15 is a polarizer that passes only the S-polarized component, it is detected. The amount of reflected light is Ls. Therefore, the smaller the standard deviations σp and σs of the reflected light amounts Lp and Ls obtained by scanning almost the entire surface of the electrode catalyst layer 12 without overlapping the region D, the more uniform the surface of the electrode catalyst layer 12 is. It becomes an indicator that there is.

  As a method of calculating the standard deviation σp of the reflected light amount Lp, for example, the inspection light is irradiated from the light source 14 to each of the plurality of regions D on the surface of the electrode catalyst layer 12, and the regular reflection light from each region D is converted into a P-polarized light component. It is possible to adopt a method of obtaining the standard deviation σp by obtaining the reflected light amount Lp by detecting with the light receiving unit 16 through the polarizer 15 that passes only the light, and performing the histogram analysis using the data of all the acquired reflected light amounts Lp. . Further, as a method of calculating the standard deviation σs of the reflected light amount Ls, for example, the inspection light is irradiated from the light source 14 to each of the plurality of regions D on the surface of the electrode catalyst layer 12, and the regular reflection light from each region D is converted to S. A method of obtaining the standard deviation σs by obtaining the reflected light amount Ls by detecting with the light receiving unit 16 after passing through the polarizer 15 that passes only the polarization component, and performing the histogram analysis using the data of all the obtained reflected light amounts Ls. Can be adopted. In the example of FIG. 3, the electrode catalyst layer 12 serving as an object to be inspected with the reflected light amounts Lp and Ls is formed on the surface of the polymer electrolyte membrane 11, but as shown in FIG. It may be formed on the surface.

Here, as the light source 14, for example, an LED (Light Emitting Diode), a halogen lamp, a xenon lamp, or the like can be used. The inspection light is preferably parallel light or highly directional light so that uniform irradiation can be performed over the entire width of the object to be inspected, and a uniform illumination lens or a telecentric lens may be used together. Good.
As the light receiving unit 16, an area camera or a line scan camera having a CCD (Charge Coupled Device) image sensor can be used. In particular, a line scan camera is installed over the entire width of the object to be inspected (electrode catalyst layer 12), and the inspection object (electrode catalyst layer 12) is sequentially inspected while being moved in a direction perpendicular to the light receiving unit 16. In addition to being excellent in inspection accuracy and inspection efficiency, it is possible to cope with various sizes of objects to be inspected (electrode catalyst layer 12). When the effective sizes of the light source 14 and the light receiving unit 16 are sufficiently large, the reflected light amounts Lp and Ls in the plurality of regions D can be obtained without scanning.

Generally, light Brewster angle theta _B on the surface of a smooth object to be inspected if incident, the zero reflectance of P-polarized light component. Therefore, when the light reflected from the surface of the smooth test object passes through the polarizer 15 that passes only the P-polarized component, the light is not incident on the light receiving unit 16. However, when the object to be inspected is the electrode catalyst layer 12, the surface of the electrode catalyst layer 12 has micro unevenness, and light is scattered on the uneven surface, so the polarizer 15 that allows only the P-polarized component to pass is selected. Even if it is done, the inspection light is incident on the light receiving unit 16. Further, when the surface of the electrode catalyst layer 12 has different smoothness and composition, the reflectance is different, so that the light detected by the light receiving unit 16 for each portion of the electrode catalyst layer 12 having different smoothness and composition. The amount of reflected light Lp is different.
In general, when light is incident on the smooth surface of the object to be inspected at the Brewster angle θ _B , the S-polarized component is reflected with a reflectance inherent to the material. However, when the object to be inspected is the electrode catalyst layer 12, if cracks or pinholes exist on the surface of the electrode catalyst layer 12, a part of the incident light to the electrode catalyst layer 12 is transmitted without being reflected. In the portion of the electrode catalyst layer 12 where the light etc. exists, the reflected light amount Ls of the light detected by the light receiving unit 16 is different from the intrinsic reflectance.

  Therefore, in the electrode catalyst layer 12 according to the embodiment, the standard deviation σp of the reflected light amount Lp and the standard of the reflected light amount Ls obtained by scanning almost the entire surface of the electrode catalyst layer 12 without overlapping each region D. The ratio σp / σs with respect to the deviation σs is configured to be 0.5 or more and 1.5 or less. When the ratio σp / σs is larger than 1.5, the catalyst material, the conductive carrier and the polymer electrolyte are unevenly distributed, the difference in the local thermal history of the electrode catalyst layer 12, and the variation in the thickness of the electrode catalyst layer 12 When the power is generated by stacking with peripheral members to generate cells, the battery output and durability are significantly reduced. This is because the adhesion between the polymer electrolyte membrane 11 or the gas diffusion layer (not shown) and the electrode catalyst layer 12 is partially reduced, or the electrode catalyst layer 12 and the membrane electrode assembly 1 are locally electrically high. This is thought to be due to the presence of parts that are loaded. On the other hand, when the ratio σp / σs is smaller than 0.5, the conductive support is too densely packed, and water generated and condensed by power generation is easily clogged with pores and easily blocks the gas path. For this reason, the output and durability of the battery are reduced.

Area of the region D is preferably 1600 .mu.m ² or more 10000 ² below. When the area of the region D is larger than 10000 μm ² , a wide area is averaged, so that defects existing in the electrode catalyst layer 12 cannot be accurately detected. In addition, when the area of the region D is smaller than 1600 μm ² , the light receiving unit 16 with very high resolution is required, and it takes a long time to scan the entire area of the electrode catalyst layer 12. It is not practical.
The thickness of the electrode catalyst layer 12 is preferably 1 μm or more and 30 μm or less. In particular, in consideration of manufacturing variations and the like, 2 μm or more and 20 μm or less is more preferable. If the thickness is greater than 30 μm, cracks are likely to occur, and when used in a fuel cell, the diffusibility and conductivity of the gas and water produced are reduced, resulting in a reduction in output. When the thickness is less than 1 μm, the layer thickness tends to vary, and the internal catalyst material and polymer electrolyte are likely to be non-uniform. Cracks on the surface of the electrode catalyst layer 12 and uneven thickness are not preferable because they are likely to adversely affect 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 as follows, for example. First, the cross section of the electrode catalyst layer 12 is exposed. Subsequently, five or more observation points on the exposed cross section are observed at a magnification of about 3000 to 10,000 times using a scanning electron microscope (SEM). Three or more thicknesses are measured at each observation point, and the average value is used as a representative value at each observation point. The average value of these representative values is the thickness of the electrode catalyst layer 12. As a method for exposing the cross section of the electrode catalyst layer 12, a known method such as ion milling or ultramicrotome can be used. When performing the processing for exposing the cross section, it is preferable to perform the processing while cooling the electrode catalyst layer 12 in order to reduce damage to the polymer electrolyte constituting the electrode catalyst layer 12.
The ratio of the mass of the polymer electrolyte to the mass of the conductive carrier in the electrode catalyst layer 12 is preferably 0.6 or more and 1.4 or less. When the mass ratio is higher than 1.4, the polymer electrolyte may block the pores in the electrode catalyst layer 12, thereby preventing the diffusion of gas and generated water, thereby reducing the output of the fuel cell. There is. On the other hand, when the mass ratio is lower than 0.6, there is a possibility that the proton conduction path of the polymer electrolyte is reduced or cut off and the output of the fuel cell is lowered.

(Configuration of polymer electrolyte fuel cell)
Next, a specific configuration of the polymer electrolyte fuel cell 3 including the membrane electrode assembly 1 according to the embodiment will be described with reference to FIG. FIG. 4 is an exploded perspective view showing a configuration example of the polymer electrolyte fuel cell 3 to which the membrane electrode assembly 1 is attached. FIG. 4 shows a configuration example of a single cell, and the polymer electrolyte fuel cell 3 is not limited to this configuration, and may have a configuration in which a plurality of single cells are stacked.
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 17 </ b> C is disposed so as to face the electrode catalyst layer 12 </ b> C that is the cathode catalyst layer on the oxygen electrode side of the membrane electrode assembly 1. The gas diffusion layer 17 </ b> A is disposed to face the electrode catalyst layer 12 </ b> A that is the anode-side catalyst layer on the fuel electrode side of the membrane electrode assembly 1. The electrode catalyst layer 12C and the gas diffusion layer 17C constitute an oxygen electrode 4C, and the electrode catalyst layer 12A and the gas diffusion layer 17A constitute a fuel electrode 4A.

Further, the polymer electrolyte fuel cell 3 includes a separator 18C disposed to face the oxygen electrode 4C, and a separator 18A disposed to face the fuel electrode 4A.
The separator 18C includes a reaction gas circulation gas channel 19C formed on a surface facing the gas diffusion layer 17C, and a cooling water circulation cooling formed on a surface opposite to the surface on which the gas passage 19C is formed. A water flow path 20C. The separator 18A has the same configuration as the separator 18C, and includes a gas channel 19A formed on a surface facing the gas diffusion layer 17A, and a surface opposite to the surface on which the gas channel 19A is formed. The cooling water flow path 20A formed in the above. The separators 18C and 18A are made of a conductive and gas impermeable material.
In the polymer electrolyte fuel cell 3, an oxidant 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 containing hydrogen passes through the gas flow path 19A of the separator 18A. Gas or organic fuel is supplied to the fuel electrode 4A to generate power.

As described above, in the electrode catalyst layer 12 according to the embodiment, of the regular reflection light when the inspection light incident at the Brewster angle θ _B is applied to the region D having a predetermined area on the surface of the electrode catalyst layer 12, polarized light is included. When the polarizer 15 is a polarizer that passes only the P-polarized component, the amount of light reflected by the polarizer 15 is Lp, and when the polarizer 15 is a polarizer that passes only the S-polarized component, the polarizer 15. The standard deviation σp of the reflected light amount Lp and the standard deviation of the reflected light amount Ls obtained by scanning almost the entire surface of the electrode catalyst layer 12 without overlapping the region D, where Ls is the reflected light amount of the light that has passed through The ratio σp / σs to σs was configured to be 0.5 or more and 1.5 or less. In other words, included in the plurality of regular reflected light obtained when irradiated with inspection light incident at the Brewster angle theta _B to each of the plurality of regions D determined in advance on the surface of the electrode catalyst layer 12, the P-polarized component light quantity ( The ratio σp / σs between the standard deviation σp of the reflected light amount Lp) and the standard deviation σs of the light amount of the S-polarized component (reflected light amount Ls) was set to be 0.5 or more and 1.5 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 of the electrode catalyst layer 12, and the variation in the thickness of the electrode catalyst layer 12 are made appropriate and laminated with the peripheral members. It is possible to obtain the electrode catalyst layer 12 and the membrane electrode assembly 1 which are excellent in output and durability of the battery when generated into a cell.

The area of the region D, is constructed as a 1600 .mu.m ² or more 10000 ² below. Therefore, defects existing in the electrode catalyst layer 12 can be accurately detected at a practically appropriate speed.
Furthermore, the thickness of the electrode catalyst layer 12 was configured to be 1 μm or more and 30 μm or less, preferably 2 μm or more and 20 μm. Therefore, it becomes possible to obtain the electrode catalyst layer 12 having no problems such as uneven layer thickness and cracks, and the membrane electrode assembly 1 having excellent durability can be obtained.
Furthermore, the mass ratio of the polymer electrolyte to the conductive carrier in the electrode catalyst layer 12 was configured to be 0.6 or more and 1.4 or less. Therefore, it becomes possible to obtain the electrode catalyst layer 12 and the membrane electrode assembly 1 having high proton conductivity while maintaining the diffusibility of gas and water.
Moreover, the polymer electrolyte fuel cell 3 was comprised using the membrane electrode assembly 1 which concerns on embodiment. Therefore, it is possible to obtain a polymer electrolyte fuel cell 3 that suppresses a decrease in power generation performance due to a flooding phenomenon and a decrease in proton conductivity, exhibits high power generation performance, and is excellent in durability.

Hereinafter, the results of comparing the performance of the polymer electrolyte fuel cell 3 provided with the membrane electrode assembly 1 according to the example and the polymer electrolyte fuel cell 3 provided with the membrane electrode assembly 1 according to the comparative example are shown. explain.
Example 1
In Example 1, a platinum-supported carbon catalyst (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), a mixed solvent of water and ethanol, and a polymer electrolyte (Nafion (registered trademark), manufactured by Dupont) dispersion are mixed to form a planetary ball mill. Then, a dispersion treatment was carried out for 30 minutes to prepare a catalyst ink. At that time, the mass ratio of the polymer electrolyte to the carbon support 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 90 ° hot air oven and dried until there is no catalyst ink tack. The cathode side catalyst layer 12C was formed on the PTFE surface. Moreover, the anode side catalyst layer 12A was formed on the PTFE surface by the same method.
Then, the cathode side catalyst layer 12C and the anode side catalyst layer 12A formed on the PTFE film are arranged so as to face both surfaces of the polymer electrolyte membrane 11 (Nafion 211 (registered trademark), manufactured by Dupont), respectively. The laminated body was hot-pressed and bonded at 120 ° C. and 10 MPa, and then the PTFE film was peeled off to obtain a membrane electrode assembly 1.

(Example 2)
In Example 2, a membrane electrode assembly 1 was obtained in the same manner as in Example 1 except that the coating amount of the cathode side catalyst layer 12C was doubled.
(Example 3)
In Example 3, a membrane / electrode assembly 1 was obtained in the same manner as in Example 1 except that the mass ratio of the polymer electrolyte to the carbon carrier was set to 0.8 when preparing the catalyst ink.
(Example 4)
In Example 4, a membrane electrode assembly 1 was obtained in the same manner as in Example 1 except that the mass ratio of the polymer electrolyte to the carbon support was set to 1.4 when preparing the catalyst ink.

(Comparative Example 1)
In Comparative Example 1, a membrane electrode assembly 1 was obtained in the same manner as in Example 1 except that the dispersion time was 5 minutes when preparing the catalyst ink.
(Comparative Example 2)
In Comparative Example 2, a membrane electrode assembly 1 was obtained in the same manner as in Example 1 except that the dispersion time was 300 minutes when preparing the catalyst ink.
(Comparative Example 3)
In Comparative Example 3, a membrane electrode assembly 1 was obtained in the same manner as in Example 1 except that the mass ratio of the polymer electrolyte to the carbon carrier was set to 0.5 when preparing the catalyst ink.

(Comparative Example 4)
In Comparative Example 4, a membrane electrode assembly 1 was obtained in the same manner as in Example 1 except that the mass ratio of the polymer electrolyte to the carbon carrier was set to 1.5 when preparing the catalyst ink.
(Comparative Example 5)
In Comparative Example 5, a membrane electrode assembly 1 was obtained in the same manner as in Example 1 except that the coating amount of the cathode side catalyst layer 12C was five times.
(Comparative Example 6)
In Comparative Example 6, a membrane / electrode assembly was obtained in the same manner as in Example 1 except that the air volume of the hot air oven was tripled.

(Evaluation)
Hereinafter, the mass ratio of the polymer electrolyte to the carbon support in each of the polymer electrolyte fuel cells 3 including the membrane electrode assemblies 1 of Examples 1 to 4 and the membrane electrode assemblies 1 of Comparative Examples 1 to 6, and The result of comparing the thickness of the cathode side catalyst layer 12C, the ratio σp / σs of the standard deviation σp of the reflected light amount Lp on the surface of the electrode catalyst layer 12 and the standard deviation σs of the reflected light amount Ls, power generation performance, and durability. explain.

(Measurement of electrode catalyst layer thickness)
The thickness of the electrode catalyst layer 12 was measured by observing a cross section of the electrode catalyst layer 12 using a scanning electron microscope (SEM). Specifically, first, the cross section of the electrode catalyst layer 12 was exposed using an ion milling device IM4000 manufactured by Hitachi High Technology. Next, the exposed cross section was observed at a magnification of 5000 using a FE-SEM S-4800 manufactured by Hitachi High-Technology Co., Ltd., and the thickness of three points was measured within the visual field at five observation points. The value was a representative value 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 12.

(Calculation of standard deviation σp of reflected light amount Lp on the electrode catalyst layer surface)
The standard deviation σp of the reflected light amount Lp on the surface of the electrode catalyst layer 12 is obtained by irradiating the surface of the electrode catalyst layer 12 with inspection light and detecting the reflected light with a line CCD camera through a P polarizer, and all the obtained reflections are obtained. It calculated by performing a histogram analysis about the data of the light quantity Lp.
Specifically, first, the membrane electrode assembly 1 was placed on an inspection stage using a porous vacuum suction plate without wrinkles or slack, and fixed using a vacuum pump. Electrocatalyst of membrane electrode assembly 1 fixed to a porous vacuum adsorption plate using high-directivity linear illumination installed so that the incident angle is 50 ° which is Brewster's angle θ _B as an inspection light source (light source 14) Inspection light was reflected by the layer 12 portion. The reflected inspection light is detected by a 12-bit line CCD camera (light receiving unit 16) through a polarizer 15 installed so as to transmit only the P-polarized component, and data of the reflected light amount Lp is obtained as shown in FIG. . FIG. 5 is a diagram illustrating an example of a mapping image of the reflected light amount Lp captured by the CCD camera (light receiving unit 16). At that time, the effective width of the inspection light source (light source 14), the polarizer 15 and the line CCD camera (light receiving unit 16) is set to be equal to or larger than the width of the electrode catalyst layer 12, and the inspection light source (light source 14) and the line CCD camera (light receiving unit 16). The data of the reflected light amount Lp was sequentially acquired while moving the inspection stage in the direction orthogonal to the main scanning direction. Note that the size of one pixel corresponding to the region D was 6400 μm ² . Further, the light amount of the inspection light source (light source 14) was adjusted so that the average of all the reflected light amounts Lp was approximately in the middle of 4096 gradations. Subsequently, as shown in FIG. 6, a histogram analysis was performed on the acquired data of all reflected light amounts Lp to obtain a standard deviation σp. FIG. 6 is a diagram illustrating an example of a histogram of the reflected light amount Lp.

(Calculation of standard deviation σs of reflected light amount Ls on the electrode catalyst layer surface)
The standard deviation σs of the reflected light amount Ls on the surface of the electrode catalyst layer 12 is obtained by irradiating the surface of the electrode catalyst layer 12 with inspection light and detecting the reflected light with a line CCD camera through an S polarizer. It calculated by performing histogram analysis about the data of the light quantity Ls.
Specifically, the calculation was performed in the same procedure as the calculation of the standard deviation σp of the reflected light amount Lp on the surface of the electrode catalyst layer 12 except that the polarizer 15 that transmits the reflected light was an S polarizer.

(Measurement of power generation performance)
For measurement of power generation performance, a cell in which gas diffusion layers 17C and 17A and gaskets and separators 18C and 18A are arranged on both surfaces of the membrane electrode assembly 1 and tightened to a predetermined surface pressure is used as a single cell for evaluation. It was. And the IV measurement as described in the "cell evaluation analysis protocol" which is a booklet published by New Energy and Industrial Technology Development Organization (NEDO) was performed.

(Durability measurement)
For the durability measurement, the same single cell as the evaluation single cell used for the measurement of the power generation performance was used as the evaluation single cell. The humidity cycle test described in “Cell Evaluation Analysis Protocol”, which is a booklet published by the New Energy and Industrial Technology Development Organization (NEDO), was conducted.

(Comparison result)
The mass ratio of the polymer electrolyte to each carbon carrier of the fuel cell provided with the membrane electrode assembly 1 of Examples 1 to 4 and the membrane electrode assembly 1 of Comparative Examples 1 to 6, the thickness of the cathode catalyst layer, Table 1 shows the ratio σp / σs of the standard deviation σp of the reflected light amount Lp on the surface of the electrode catalyst layer 12 and the standard deviation σs of the reflected light amount Ls, the power generation performance, and the durability. In addition, regarding the power generation performance, a case where the current when the voltage is 0.6 V is 20 A or more is “◯”, and a case where the current is less than 20 A is “X”. As for durability, the case where the hydrogen cross-leakage current after 8000 cycles was less than 10 times the initial value was “◯”, and the case where it was 10 times or more was “x”.

  As shown in Table 1, in all of Examples 1 to 4, the mass ratio of the polymer electrolyte to the carbon support is 0.6 or more and 1.4 or less, and the thickness of the cathode catalyst layer 12C is 2 μm or more and 20 μm or less. It was. The ratio σp / σs between the standard deviation σp of the reflected light amount Lp and the standard deviation σs of the reflected light amount Ls on the surface of the electrode catalyst layer 12 was 0.5 or more and 1.5 or less. And about electric power generation performance and durability, all became "(circle)". That is, in Examples 1-4, the membrane electrode assembly 1 which can comprise the fuel cell excellent in electric power generation performance and durability was obtained.

  On the other hand, in the comparative examples, the mass ratio of the polymer electrolyte to the carbon support was in the range of 0.6 to 1.4 in the comparative examples 1, 2, 5, and 6, but the comparative examples 3, 4 Was out of this range. The thickness of the cathode side catalyst layer 12C was in the range of 2 μm or more and 20 μm or less in Comparative Examples 1 to 4 and Comparative Example 6, but was out of this range in Comparative Example 5. Further, the ratio σp / σs of the standard deviation σp of the reflected light amount Lp and the standard deviation σs of the reflected light amount Ls on the surface of the electrode catalyst layer 12 is in the range of 0.5 to 1.5 in all of Comparative Examples 1 to 5. It was outside. The power generation performance was “X” in Comparative Examples 1, 2, and 4, and the durability was “X” in Comparative Examples 1 and 3-6. That is, when the ratio σp / σs between the standard deviation σp of the reflected light amount Lp and the standard deviation σs of the reflected light amount Ls on the surface of the electrode catalyst layer 12 that is an index indicating the defect of the electrode catalyst layer 12 is out of the above range, At least one of the power generation performance and durability deteriorated.

  According to the present invention, the unevenness of the electrode catalyst layer, which is a problem in the operation of the polymer electrolyte fuel cell, is detected with high accuracy, and defective products are excluded. An excellent electrode catalyst layer, membrane electrode assembly, and polymer electrolyte fuel cell can be obtained. Therefore, this invention has the performance which can be used suitably for a stationary cogeneration system, a fuel cell vehicle, etc. using a polymer electrolyte fuel cell, and its industrial utility value is great.

  DESCRIPTION OF SYMBOLS 1 ... Membrane electrode assembly, 2 ... Transfer base material 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 part, 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 comprising a catalyst material, a conductive carrier and a polymer electrolyte,
The reflected light amount Lp, which is the light amount of the P-polarized component, contained in the plurality of specular reflection lights obtained when the inspection light incident at the Brewster angle on each of the plurality of predetermined regions on the surface of the electrode catalyst layer is irradiated. A ratio σp / σs between the standard deviation σp and the standard deviation σs of the reflected light amount Ls, which is the light amount of the S-polarized component, is 0.5 or more and 1.5 or less. The area of each region of the plurality of regions, the electrode catalyst layer according to claim 1, characterized in that a 1600 .mu.m ² or more 10000 ² below.   The electrode catalyst layer according to claim 1 or 2, wherein the electrode catalyst layer has a thickness of 1 µm or more and 30 µm or less.   The electrode catalyst layer according to claim 3, wherein the electrode catalyst layer has a thickness of 2 μm or more and 20 μm or less.   5. The electrode catalyst layer according to claim 1, wherein a ratio of a mass of the polymer electrolyte to a mass of the conductive carrier is 0.6 or more and 1.4 or less.   A membrane electrode assembly comprising: a polymer electrolyte membrane; and the electrode catalyst layer according to any one of claims 1 to 5 joined to an oxygen electrode side surface of the polymer electrolyte membrane.   A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 6.

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