JP2016207419A - Electrode catalyst layer, membrane electrode assembly and solid polymer fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode catalyst layer which exhibits high power generation performance even in low-humidity environment while having drainage necessary and sufficient for avoiding flooding phenomenon, and also to provide a membrane electrode assembly and a solid polymer fuel cell.SOLUTION: An electrode catalyst layer 12 is characterized in being constituted so that, in a cross section in a thickness direction orthogonal to the surface of the electrode catalyst layer 12, a first integration area Sp obtained by integrating an area of a void part whose area is 100 nmor more and 250000 nmor less out of the void part formed in series becomes 25% or more and 30% or less of the cross section S.SELECTED DRAWING: Figure 1

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 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 promising for use in 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 equipment, reduction of manufacturing costs, and the like.

  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, with a gas flow path and cooling. The structure is sandwiched between separators having a water flow path. These electrodes are mainly composed of 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. .

  In the polymer electrolyte fuel cell, electricity can be taken out through the following electrochemical reaction. First, in the fuel electrode-side electrode catalyst layer, hydrogen contained in the fuel gas is oxidized by the catalyst material 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 oxygen electrode side electrode catalyst layer. The simultaneously generated electrons pass through the conductive carrier in the electrode catalyst layer, the gas diffusion layer in contact with the polymer electrolyte membrane on the side different from the polymer electrolyte membrane, the separator, and the external electrode to the oxygen electrode side electrode catalyst layer. Reach. In the oxygen electrode side electrode catalyst layer, protons and electrons react with oxygen contained in the oxidant gas to generate water.

  The pores in the electrode catalyst layer are located in front of the separator through the gas diffusion layer and serve as a passage for transporting a plurality of substances. The pores of the fuel electrode are required to have a function of smoothly supplying fuel gas to the three-phase interface, which is a redox reaction field, and supplying water for conducting the generated protons in the polymer electrolyte. Further, the pores of the oxygen electrode are required to have a function of smoothly supplying the oxidant gas and quickly discharging water generated by the electrode reaction. However, under conditions where the amount of product water to condense increases, the “flooding phenomenon” in which the power generation reaction stops because the product water is not smoothly discharged but closes the pores and hinders mass transport is a problem. It was.

  As a means for avoiding the flooding phenomenon as described above, for example, as described in Patent Document 1 or Patent Document 2, a hydrophobic agent or a water repellent agent is included in the electrode catalyst layer to increase the hydrophilicity of the electrode catalyst layer. Methods have been proposed for reducing and increasing drainage. Further, as another method for avoiding the flooding phenomenon, for example, as described in Patent Document 3, a pore-forming agent is included in the electrode catalyst layer to increase the voids inside the electrode catalyst layer, thereby improving drainage. A way to increase it has been proposed.

Japanese Patent No. 5013740 JP 2006-108031 A JP 2004-158387 A

However, the method according to Patent Document 1 or Patent Document 2 has a problem that the hydrophilicity of the electrode catalyst layer is lowered, so that sufficient proton conductivity cannot be maintained in a low-humidity environment, and power generation performance is lowered. In order to reduce the cost of the entire fuel cell system, it is effective to reduce the humidifier, and an electrode catalyst layer in which sufficient power generation performance cannot be obtained in a low humidity environment is not preferable.
In addition, the method according to Patent Document 3 has a problem in that the pore-forming agent component causes the proton conduction path and the conduction path in the electrode catalyst layer to be reduced or blocked, resulting in a reduction in power generation performance.
The present invention has been made to solve the above-described problem, and has a sufficient drainage property to avoid the flooding phenomenon and can exhibit high power generation performance even in a low humidity environment. An object is to provide an electrode catalyst layer, a membrane electrode assembly, and a polymer electrolyte fuel cell.

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 including at least a catalyst substance, a conductive carrier, and a polymer electrolyte, and is orthogonal to the surface of the electrode catalyst layer. in the thickness direction of the cross section, the first integrated area Sp by integrating the area of 100 nm ² or more 250000Nm ² or less of the gap portion of the area of the void portion formed in stretches is 25% of the cross-sectional area S of the cross section It is configured to be within the range of 30% or less.

Moreover, in order to solve the said subject, the membrane electrode assembly which concerns on the 2nd aspect of this invention is equipped with the electrode catalyst layer which concerns on the said 1st aspect, and a polymer electrolyte membrane, The said electrode catalyst layer is the said The polymer electrolyte membrane is joined to at least the surface on the oxygen electrode side of the surface on which the electrode catalyst layer is formed.
Moreover, in order to solve the said subject, the polymer electrolyte fuel cell which concerns on the 3rd aspect of this invention has the membrane electrode assembly which concerns on the said 2nd aspect.

According to one aspect of the present invention, the electrode catalyst layer, in the thickness direction of the cross section perpendicular to its surface, an area of 100 nm ² or more 250000Nm ² or less of the gap portion of the area of the void portion formed in stretch The integrated first integrated area Sp is configured to be in the range of 25% to 30% of the cross-sectional area S of the cross section. As a result, the electrode is capable of exhibiting high power generation performance in both high and low humidity environments by preventing excessive drainage while having sufficient drainage to avoid the flooding phenomenon. A catalyst layer, a membrane electrode assembly and a polymer electrolyte fuel cell can be obtained.

(A) is the top view which looked at the membrane electrode assembly which concerns on embodiment of this invention from the surface side of the electrode catalyst layer, (b) is sectional drawing seen from the AA direction of (a). . It is a cross-section binarized image of the electrode catalyst layer which concerns on embodiment of this invention. It is a disassembled perspective view which shows the structural example of the polymer electrolyte fuel cell which concerns on embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings. 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. The form is also included in the scope of the present embodiment.
As a result of intensive studies on the power generation performance of the polymer electrolyte fuel cell in a high humidity environment and a low humidity environment, the present inventors have found that the ratio of voids in the electrode catalyst layer greatly affects the power generation performance. I found out. And by making the ratio of the voids in the electrode catalyst layer within a predetermined range, there is no reduction in power generation performance due to flooding phenomenon and proton conductivity reduction, and high power generation performance in both high and low humidity environments. We have succeeded in obtaining a solid polymer fuel cell that can be used.

(Configuration of membrane electrode assembly)
Hereinafter, a specific configuration of the membrane electrode assembly according to the present embodiment will be described with reference to FIG.
Fig.1 (a) is the top view which looked at the membrane electrode assembly 1 which concerns on this embodiment from the surface side of 12 A of electrode catalyst layers, FIG.1 (b) is the AA direction of Fig.1 (a). FIG. 6 is a cross-sectional view (a cross-sectional view in the thickness direction orthogonal to the surface of the electrode catalyst layer 12A).
As shown in FIGS. 1 (a) and 1 (b), a membrane / electrode assembly 1 has a pair of electrode catalyst layers 12A and 12F arranged opposite to each other with a polymer electrolyte membrane 11 in between and joined. . In the present embodiment, the electrode catalyst layer 12A is a cathode side catalyst layer constituting an oxygen electrode, and the electrode catalyst layer 12F is an anode side catalyst layer constituting a fuel electrode. Hereinafter, the pair of electrode catalyst layers 12 </ b> A and 12 </ b> F 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 according to this embodiment includes at least a catalyst substance, a conductive carrier, and a polymer electrolyte.
As the catalyst material used in the present embodiment, platinum, palladium, ruthenium, iridium, rhodium, osmium, platinum group elements, iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum It is possible to use metals such as these, alloys thereof, oxides, double oxides, carbides and the like.

  In addition, the conductive carrier supporting these catalysts may be any fine powder that is conductive and is not affected by the catalyst, but carbon particles are generally used. For example, carbon black, graphite, graphite, activated carbon, carbon nanotube, carbon nanofiber, and fullerene can be preferably 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 is reduced or the utilization rate of the catalyst is reduced. Is preferred. More preferably, 10-100 nm is good.

  The polymer electrolyte contained in the polymer electrolyte membrane 11 and the electrode catalyst layer 12 used in the present embodiment may be any one having proton conductivity, and a fluorine polymer electrolyte or a hydrocarbon polymer electrolyte is used. Is possible. In this case, as the fluorine-based polymer electrolyte, for example, “Nafion (registered trademark)” manufactured by DuPont, “Flemion (registered trademark)” manufactured by Asahi Glass, “Aciplex (registered trademark)” manufactured by Asahi Kasei Corporation, Gore It is possible to use “Gore Select (registered trademark)” manufactured by the company. As the hydrocarbon polymer electrolyte, sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, sulfonated polyphenylene and the like can be used. In particular, as the polymer electrolyte membrane 11, “Nafion (registered trademark)” material manufactured by DuPont or “Gore Select (registered trademark)” material manufactured by Gore can be suitably used.

  Various things can be used as the polymer electrolyte contained in the polymer electrolyte membrane 11 and the electrode catalyst layer 12 according to the present embodiment. However, in consideration of the interface resistance between the polymer electrolyte membrane 11 and the electrode catalyst layer 12 and the dimensional change rate between the polymer electrolyte membrane 11 and the electrode catalyst layer 12 when the humidity changes, the polymer electrolyte membrane 11 is included. The polymer electrolyte and the polymer electrolyte contained in the electrode catalyst layer 12 are preferably the same component.

The electrode catalyst layer 12 of the present invention, FIG. 1 (a) and as (b), in the surface and cross section of the electrode catalyst layer 12, is 100 nm ² or more areas of the gap portion formed in the stretch 250000Nm ² The first integrated area Sp obtained by integrating the areas of the following voids is configured to be 25% or more and 30% or less of the cross-sectional area S in the thickness direction orthogonal to the surface of the electrode catalyst layer 12.

When the first accumulated area Sp is less than 25% of the cross-sectional area S, the water generated and condensed by the power generation is clogged with pores and the gas passage is easily blocked, and such an electrode catalyst layer 12 is used. When is used, the output of the fuel cell is lowered.
In addition, when the first integrated area Sp is larger than 30% of the cross-sectional area S, the proton conductivity of the electrode catalyst layer 12 is insufficient particularly in a low humidity environment, and the catalyst layer resistance is easily improved. When such an electrode catalyst layer 12 is used, the output of the fuel cell is also lowered.

The electrode catalyst layer 12 according to this embodiment, among the air gap, the second integrated area Sps of the area of the stretch is obtained by integrating the area of 100 nm ² or more 20000 nm ² or less of the gap portion, the first integrated area above It is comprised so that it may become 50% or more of Sp. When there are many voids having an area larger than 20000 nm ² so that the second accumulated area Sps is less than 50% of the first accumulated area Sp, the proton conduction path and the conduction path in the electrode catalyst layer are reduced or blocked. When such an electrode catalyst layer is used, the output of the fuel cell decreases.

The area of each void in the cross section of the electrode catalyst layer 12, the first integrated area Sp, and the second integrated area Sps are obtained by, for example, obtaining an image of the cross section of the electrode catalyst layer using a scanning electron microscope (SEM). , Trimming, filtering, binarization, and black pixel measurement. The magnification of the acquired image by SEM is preferably about 10,000 to 30,000 times.
Moreover, as a method of exposing the cross section of the electrode catalyst layer 12, well-known methods, such as ion milling and an ultramicrotome, can be used, for example. 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.

For example, the cross-section of the electrode catalyst layer is exposed using an ion milling device IM4000 manufactured by Hitachi High-Technology Co., Ltd., and the image obtained by imaging the cross-section using FE-SEM S-4800 manufactured by Hitachi High-Technology Co., Ltd. is as described above. When the image processing is performed, a binarized image as shown in FIG. 2 is obtained. In this image, the pixels constituting the voids are represented as black pixels 50, and the area of each void in the cross section of the electrode catalyst layer can be obtained by measuring the number of continuous black pixels 50. . Then, these areas of 100 nm ² or more 250000Nm ² or less of the gap portion of the area of each gap portion obtained could be obtained first integrated area Sp by integrating the, 100 nm ² or more of the area of each air gap The second integrated area Sps can be obtained by integrating the areas of the voids of 20000 nm ² or less.

In the present embodiment, the thickness of the electrode catalyst layer 12 is configured to be within a range of 1 μm to 50 μm. The thickness of the electrode catalyst layer 12 is more preferably in the range of 1 μm or more and 30 μm or less, and further preferably in the range of 2 μm or more and 15 μm or less.
When the electrode catalyst layer 12 was thicker than 50 μm, the catalyst layer surface was cracked, hindered from diffusing gas or generated water, decreased in conductivity, and used for a fuel cell. Output is reduced. On the other hand, when the thickness is less than 1 μm, the thickness tends to vary, and the in-plane catalyst and polymer electrolyte tend to be non-uniform. Cracks on the surface of the electrode catalyst layer and non-uniform thickness are not preferable because they have a high possibility of adversely affecting 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 is exposed by the method as described above, and five or more cross sections are observed at 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 taken as the thickness of the electrode catalyst layer 12.

  In the present embodiment, the electrode catalyst layer 12 is configured such that the ratio of the polymer electrolyte to the conductive carrier in the electrode catalyst layer 12 is in the range of 0.8 to 1.6. When this ratio is higher than 1.6, the polymer electrolyte may block the pores in the electrode catalyst layer, which may hinder the diffusion of gas and generated water, thereby reducing the output of the fuel cell. . On the other hand, when the 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.

(Method for producing electrode catalyst layer and membrane electrode assembly)
Hereinafter, the manufacturing method of the electrode catalyst layer and membrane electrode assembly of this embodiment will be described.
As a method of forming the electrode catalyst layer on both surfaces of the polymer electrolyte membrane, a method of forming the catalyst layer by directly applying the catalyst ink on the surface of the polymer electrolyte membrane and removing the solvent component from the coating film of the catalyst ink, The catalyst electrolyte is applied to the surface of a substrate that is not a polymer electrolyte membrane, and the catalyst layer transfer sheet is formed by removing the solvent component from the coating film of the catalyst ink to form the catalyst layer. It is possible to use a method of joining and transferring by bringing them into contact and heating and pressurizing.

The catalyst ink is obtained by mixing at least a solvent, a catalyst substance supported on a conductive carrier, and a polymer electrolyte, 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 the 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 material, the conductive carrier, or the polymer electrolyte. There are no particular restrictions.

  The solvent may contain water that is compatible with the polymer electrolyte. Although it is desirable that the catalyst ink contains at least a volatile liquid organic solvent, those using a lower alcohol as the solvent have a high risk of ignition, and when using such a solvent, the solvent is mixed with water. It is preferable to do this. The amount of water added is not particularly limited as long as the polymer electrolyte is not separated to cause white turbidity or gelation.

  Examples of the base material on which the catalyst ink is applied include ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), poly A fluororesin excellent in transferability such as tetrafluoroethylene (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.

As a method for applying the catalyst ink, for example, various coating methods such as die coating, roll coating, curtain coating, spray coating, and squeegee can be used. A die coat that can also be applied is particularly preferably used.
For drying the applied catalyst ink, for example, a warm air oven, IR drying, reduced pressure drying or the like can be used.

When using a catalyst layer transfer sheet and joining and transferring by contacting and heating the polymer electrolyte membrane and the catalyst layer and applying pressure, the pressure applied to the catalyst layer affects the power generation performance of the membrane electrode assembly. Therefore, in order to obtain a membrane electrode assembly with good power generation performance, the pressure applied to the laminate is preferably in the range of 0.5 MPa to 20 MPa, more preferably in the range of 2 MPa to 15 MPa. . When the pressure is higher than 20 MPa, the electrode catalyst layer is excessively compressed, and when the pressure is lower than 0.5 MP, the bondability between the electrode catalyst layer and the polymer electrolyte membrane is lowered, and the power generation performance is lowered.
Also, the temperature at the time of bonding is set near the glass transition point of the polymer electrolyte of the electrode catalyst layer, because the bondability at the interface between the polymer electrolyte membrane and the electrode catalyst layer is improved, and the interface resistance can be suppressed. Effective and desirable.

(Configuration of polymer electrolyte fuel cell)
Next, a specific configuration of the polymer electrolyte fuel cell according to the present embodiment will be described with reference to FIG. FIG. 3 is an exploded perspective view showing a configuration example of the polymer electrolyte fuel cell 10 to which the membrane electrode assembly 1 is attached. However, FIG. 3 is a configuration example of a single cell, and is not limited to this configuration, and a configuration in which a plurality of single cells are stacked may be employed.

  As shown in FIG. 3, the polymer electrolyte fuel cell 10 includes a membrane electrode assembly 1, a gas diffusion layer 13A, and a gas diffusion layer 13F. The gas diffusion layer 13A is disposed to face the electrode catalyst layer 12A that is the cathode catalyst layer on the oxygen electrode side of the membrane electrode assembly 1, and the gas diffusion layer 13F is the anode on the fuel electrode side of the membrane electrode assembly 1. The electrode catalyst layer 12 </ b> F that is the side catalyst layer is disposed to face the catalyst layer. The electrode catalyst layer 12A and the gas diffusion layer 13A constitute an oxygen electrode 2A, and the electrode catalyst layer 12F and the gas diffusion layer 13F constitute a fuel electrode 2F.

The polymer electrolyte fuel cell 10 further includes a separator 14A disposed facing the oxygen electrode 2A and a separator 14F disposed facing the fuel electrode 2F.
The separator 14A is made of a conductive and gas-impermeable material, and is disposed on the main surface facing the gas flow path 15A and the gas flow path 15A for the reaction gas flow disposed facing the gas diffusion layer 13A. The cooling water flow path 16A for circulating the cooling water is provided. Further, the separator 14F has the same configuration as that of the separator 14A, the gas flow path 15F disposed facing the gas diffusion layer 13F, and the cooling water flow disposed on the main surface facing the gas flow path 15F. Road 16F.

In this polymer electrolyte fuel cell 10, an oxidant such as air or oxygen is supplied to the oxygen electrode 2A through the gas flow path 15A of the separator 14A, and the fuel gas containing hydrogen passes through the gas flow path 15F of the separator 14F. Alternatively, power is generated by supplying organic fuel to the fuel electrode 2F.
Above, integrates the electrode catalyst layer 12 in the thickness direction of the cross section perpendicular to the surface of the electrode catalyst layer 12, the area of the void portion formed in stretches is an area of 100 nm ² or more 250000Nm ² or less of the gap portion The first integrated area Sp is configured to be in the range of 25% to 30% of the cross-sectional area S. As a result, the electrode catalyst layer and the membrane exhibit high power generation performance in both a high humidity environment and a low humidity environment by preventing water from draining too much while having sufficient drainage to avoid the flooding phenomenon. An electrode assembly can be obtained.

Further, an electrode catalyst layer 12, of the air gap, the second integrated area Sps of the area of the stretch is obtained by integrating the area of 100 nm ² or more 20000 nm ² or less of the gap portion is 50% or more of the first integrated area Sp above It comprised so that it might become. As a result, it is possible to obtain an electrode catalyst layer and a membrane electrode assembly that have sufficient proton conductivity even in a low humidity environment and exhibit higher power generation performance.

In addition, since the thickness of the electrode catalyst layer 12 is configured to be within a range of 1 μm or more and 50 μm or less, it is possible to obtain the electrode catalyst layer 12 without problems such as uneven thickness and cracks on the surface, It becomes possible to obtain a membrane electrode assembly excellent in durability.
In addition, since the electrode catalyst layer 12 is configured such that the ratio of the polymer electrolyte to the conductive carrier in the electrode catalyst layer 12 is in the range of 0.8 to 1.6, diffusion of gas and water It is possible to obtain an electrode catalyst layer and a membrane electrode assembly having high proton conductivity while maintaining the properties.

  In addition, since the polymer electrolyte fuel cell 10 is configured using the membrane electrode assembly 1, there is no reduction in power generation performance due to the flooding phenomenon and the decrease in proton conductivity, and high power generation in both high and low humidity environments. It is possible to obtain a polymer electrolyte fuel cell that exhibits performance and excellent durability.

Hereinafter, the results of comparing the performance of the fuel cell including the membrane electrode assembly according to the example of the present invention and the fuel cell including the membrane electrode assembly according to the comparative example will be described.
Example 1
A platinum-supported carbon catalyst A (primary particle size of about 30 nm, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), water, a mixed solvent of ethanol and a polymer electrolyte (Nafion (registered trademark), manufactured by Dupont) dispersion are mixed, and a planetary ball mill is used. A dispersion treatment was performed for 30 minutes to prepare a catalyst ink. At that time, the weight ratio x 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 by a slit die coater, and then the PTFE film coated with the catalyst ink is placed in a warm air oven at 80 ° C. and dried until there is no catalyst ink tack. The cathode side catalyst layer was formed on the PTFE surface. Moreover, the anode side catalyst layer was formed in the PTFE surface 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 surfaces of the polymer electrolyte membrane (Nafion 212 (registered trademark), manufactured by Dupont), and this laminate is The membrane electrode assembly of Example 1 was obtained by peeling the PTFE film after hot pressing at 120 ° C. and 10 MPa.

(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 except that the weight ratio x of the polymer electrolyte to the carbon support was 0.8 when preparing the catalyst ink.

Example 4
A membrane / electrode assembly of Example 4 was obtained in the same manner as in Example 1 except that the weight ratio x 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 except that the dispersion time was 300 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 except that the weight ratio x of the polymer electrolyte to the carbon support was 0.7 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 except that the weight ratio x of the polymer electrolyte to the carbon support was 1.7 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 except that the coating amount of the cathode side catalyst layer was 5 times.
(Comparative Example 5)
A comparative example was prepared in the same manner as in Example 1 except that platinum-supported carbon catalyst B (primary particle size of about 50 nm, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was used instead of platinum-supported carbon catalyst A when preparing the catalyst ink. 5 membrane electrode assemblies were obtained.

(Evaluation)
Hereinafter, the thickness of the electrode catalyst layer and the first integrated area in the cross section of the electrode catalyst layer of each of the fuel cells including the membrane electrode assemblies of Examples 1 to 4 and the membrane electrode assemblies of Comparative Examples 1 to 5 above. A result of comparing the ratio of Sp to the cross-sectional area S and the ratio of the second integrated area Sps to the first integrated area Sp and the power generation performance will be described.

(Measurement of electrode catalyst layer thickness)
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, the 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 a magnification of 5000 using a FE-SEM S-4800 manufactured by Hitachi High-Technology Co., Ltd., and the three-point thickness was measured within the field of view 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 the thickness of the electrode catalyst layer.

(Measurement of the first integrated area Sp and the second integrated area Sps in the cross section of the electrode catalyst layer)
For the first integrated area Sp and the second integrated area Sps in the cross section of the electrode catalyst layer, an image of the cross section of the electrode catalyst layer is obtained using a scanning electron microscope (SEM), and trimming, filtering, binarization, black pixels It is obtained by performing image processing such as measurement. Specifically, using the cross section used in the measurement of the thickness of the electrode catalyst layer, an image was acquired at 15000 times using FE-SEM S-4800 manufactured by Hitachi High-Technology Co., Ltd., trimming, filtering, binary Obtained by measuring black pixels.

(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 surfaces of a membrane electrode assembly and tightened to a predetermined surface pressure was used as a single cell for evaluation. Then, IV measurement was performed generally in accordance with the method described in “Cell Evaluation Analysis Protocol” which is a booklet published by the New Energy and Industrial Technology Development Organization (NEDO). The anode relative humidity and the cathode relative humidity were changed from the conditions described in the “Cell Evaluation Analysis Protocol”. When the anode relative humidity and the cathode relative humidity were set to 100% RH, the anode relative humidity and the cathode relative humidity were high. When the humidity was 25% RH, the humidity was low.

(Comparison result)
The thickness of the electrode catalyst layer of each of the fuel cells using the membrane electrode assemblies of Examples 1 to 4 and the membrane electrode assemblies of Comparative Examples 1 to 5, and the first integrated area Sp in the cross section of the electrode catalyst layer Table 1 shows the ratio (Sp / S) to the cross-sectional area S, the ratio (Sps / Sp) of the second integrated area Sps to the first integrated area Sp, and the power generation performance. Regarding the power generation performance, the current at a voltage of 0.6 V was described as “X” when the humidity was high, and “A” was 20 A or less, and “A” was 10 A or less when the humidity was low.

  In this example, in all of Examples 1 to 4, the thickness of the catalyst layer was in the range of 1 μm to 50 μm. Further, the ratio of the first integrated area Sp to the cross-sectional area S in the cross section of the electrode catalyst layer is in the range of 25% to 30%, and the ratio of the second integrated area Sps to the first integrated area Sp is in the range of 50% or more. It became. The power generation performance under high and low humidification was “◯”. That is, in Examples 1 to 4 above, membrane electrode assemblies capable of constituting a fuel cell with excellent power generation performance were obtained.

  On the other hand, in the comparative example, the thickness of the catalyst layer was in the range of 1 μm to 50 μm in all of Comparative Examples 1 to 5. However, the ratio of the first integrated area Sp to the cross-sectional area S in the cross section of the electrode catalyst layer was less than 25% in Comparative Examples 1, 3, and 4, and exceeded 30% in Comparative Example 5. The ratio of the second integrated area Sps to the first integrated area Sp was less than 50% in Comparative Examples 2 and 5. And about the power generation performance under high humidification, it became "x" in comparative examples 3 and 4, and about the power generation performance under low humidification, all of comparative examples 1-5 became "x". That is, the power generation performance deteriorated because each ratio (Sp / S and Sps / Sp) occupied by the voids was outside the above ranges.

According to the present invention, an electrocatalyst layer and a membrane exhibiting high power generation performance in both high humidity environment and low humidity environment without deterioration of power generation performance due to flooding phenomenon and proton conductivity decrease, and excellent durability An electrode assembly and a polymer electrolyte fuel cell can be obtained.
Therefore, the present invention has performance that can be suitably used for a stationary cogeneration system, a fuel cell vehicle, and the like using a polymer electrolyte fuel cell, and has a great industrial utility value.

DESCRIPTION OF SYMBOLS 1 ... Membrane electrode assembly 2A ... Oxygen electrode 2F ... Fuel electrode 10 ... Solid polymer fuel cell 11 ... Polymer electrolyte membrane 12A, 12F ... Electrode catalyst layer 13A, 13F ... Gas diffusion layer 14A, 14F ... Separator 15A, 15F ... Gas flow paths 16A, 16F ... Cooling water flow paths 50 ... Black pixels (voids)

Claims (6)

An electrode catalyst layer comprising at least a catalyst substance, a conductive carrier and a polymer electrolyte,
In the cross section in the thickness direction perpendicular to the surface of the electrode catalyst layer,
The first integrated area Sp by integrating the area of 100 nm ² or more 250000Nm ² or less of the gap portion of the area of the void portion formed in human followed,
An electrode catalyst layer configured to be in a range of 25% to 30% of the cross-sectional area S of the cross section. Of the area of the void portion formed in the stretch, the second integrated area Sps is obtained by integrating the area of 100 nm ² or more 20000 nm ² or less,
The electrode catalyst layer according to claim 1, wherein the electrode catalyst layer is configured to be 50% or more of the first integrated area Sp.   The electrode catalyst layer according to claim 1 or 2, wherein a thickness in a direction perpendicular to the surface of the electrode catalyst layer is within a range of 1 µm or more and 30 µm or less.   The ratio of the weight of the polymer electrolyte to the weight of the conductive carrier contained is configured to be 0.8 or more and 1.6 or less, any one of claims 1 to 3. 2. The electrode catalyst layer described in item 1.   5. The electrode catalyst layer according to claim 1, and a polymer electrolyte membrane, wherein the electrode catalyst layer includes at least oxygen on a surface of the polymer electrolyte membrane on which the electrode catalyst layer is formed. A membrane electrode assembly, wherein the membrane electrode assembly is bonded to a pole-side surface.   A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 5.

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