JP2009238496A - Membrane-electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane-electrode assembly which exhibits an excellent power generation performance even in a high humidification condition. <P>SOLUTION: In the membrane-electrode assembly, an anode catalyst layer and a cathode catalyst layer which comprise an electrode catalyst in which a catalyst component is carried on a conductive carrier and a polymer electrolyte are arranged in opposition on both sides of a solid polymer electrolyte membrane, and a pair of gas diffusion layers interpose these. Then, at least part of the anode catalyst layer or the cathode catalyst layer has a prescribed pore structure. Specifically, the pore structure has, in a hole distribution by mercury pressure method, a model hole diameter in a range of the hole diameter 0.01-0.10 μm in a range 0.045-0.060 μm. Then, the ratio of the half width to the peak height of a peak of the model hole diameter is 0.045 μm/(cm<SP>3</SP>g<SP>-1</SP>) or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a membrane electrode assembly (MEA). In particular, the present invention relates to a membrane electrode assembly capable of stable power generation at a high power density even under high humidification conditions.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. A fuel cell is a clean power generation system in which the product of an electrode reaction is water in principle and has almost no adverse effect on the global environment. In particular, a polymer electrolyte fuel cell (PEFC) is expected as a power source for electric vehicles because it operates at a relatively low temperature. The structure of a polymer electrolyte fuel cell (hereinafter also simply referred to as “fuel cell”) generally has a structure in which a membrane electrode assembly (MEA) is sandwiched between separators. In the membrane / electrode assembly, an electrode catalyst layer is disposed so as to face both surfaces of a solid polymer electrolyte membrane, and a pair of gas diffusion layers are sandwiched between the electrode catalyst layers.

In the polymer electrolyte fuel cell having the membrane electrode assembly as described above, in both electrode catalyst layers (cathode and anode) sandwiching the polymer electrolyte membrane, an electrode represented by the following reaction formula according to the polarity thereof The reaction proceeds to obtain electrical energy. First, hydrogen contained in the fuel gas supplied to the anode (hydrogen electrode) side is oxidized by the catalyst component to become protons and electrons (2H ₂ → 4H ⁺ + 4e ⁻ : reaction 1). Next, the generated protons are accompanied by a polymer electrolyte (hereinafter also referred to as an ionomer) contained in the electrode catalyst layer and a solid polymer electrolyte membrane in contact with the electrode catalyst layer, accompanied by several water molecules. The cathode (oxygen electrode) catalyst layer. In addition, the electrons generated in the anode catalyst layer pass through the conductive carrier constituting the electrode catalyst layer, the gas diffusion layer in contact with the side of the electrode catalyst layer different from the solid polymer electrolyte membrane, the separator, and an external circuit. Reach the cathode catalyst layer. The protons and electrons that have reached the cathode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode side to generate water (O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O: Reaction 2). In the fuel cell, electricity can be taken out through the above-described electrochemical reaction.

  The above electrochemical reaction takes place at the three-phase interface of electrode catalyst-electrolyte-reactive gas. Therefore, in order to increase the contact area between the electrode catalyst and the electrolyte, a polymer electrolyte made of the same material as the solid polymer electrolyte membrane is usually dispersed around the electrode catalyst. As the polymer electrolyte, perfluorocarbon-based resins having sulfonic acid groups are widely used. Such a perfluorocarbon-based resin does not have a cross-linked structure, and has a structure that easily swells and shrinks depending on the surrounding moisture concentration environment. Furthermore, perfluorocarbon-based resins have a property that proton conductivity decreases when the water content in the resin decreases. Therefore, in order to maintain good proton conductivity, it is preferable to maintain the moisture concentration in the electrode catalyst layer to such an extent that the polymer electrolyte made of such a resin is sufficiently swollen. On the other hand, if water exists excessively in the electrode catalyst layer, water aggregates in the pores of the electrode catalyst layer, so that drainage from the electrode catalyst layer stagnates and gas diffusibility decreases. As a result, the reaction gas used in the electrochemical reaction is not sufficiently supplied, and the output can be reduced.

  In general, in the membrane electrode assembly as described above, the anode catalyst layer has a relatively low humidification condition because water molecules move to the cathode side simultaneously with the movement of protons accompanying the oxidation reaction of the fuel gas. It has been known. On the other hand, the cathode catalyst layer is relatively humidified by the water generated by the electrochemical reaction. For these reasons, it is desired that moisture management of the anode-side and cathode-side electrode catalyst layers be appropriately performed.

  Patent Document 1 is characterized by comprising a gas diffusion electrode containing a catalyst, and among the pores of the gas diffusion electrode, the pore volume having a pore diameter larger than 0.1 μm is 0.4 cc / g or more. An electrode for a polymer electrolyte fuel cell is described. Thereby, it is said that a polymer electrolyte fuel cell having excellent gas diffusibility, high conductivity of the electrode catalyst layer, and low resistance and high output density can be obtained.

Patent Document 2 discloses that the catalyst layer on the anode side and the cathode side is composed of a first catalyst layer having a relatively small pore diameter and pore volume, and a second catalyst layer having a relatively large pore diameter and pore volume. A polymer electrolyte fuel cell comprising a catalyst layer is described. The first catalyst layer is disposed on the reaction gas inlet side, and the second catalyst layer is disposed on the reaction gas outlet side. As a result, the moisture content of the electrolyte membrane can be maintained moderately over the entire region, the gas diffusibility of the catalyst layer can be maintained well, and a polymer electrolyte fuel cell having excellent cell characteristics can be obtained.
JP-A-9-283154 Japanese Patent Laid-Open No. 2002-237306

  However, the gas diffusion electrode described in Patent Document 1 and having a large proportion of pores having a large pore diameter has a problem in that the drainage property under high humidification conditions is insufficient and the desired power generation performance cannot be obtained. It was.

  Further, in Patent Document 2, specifically, the first catalyst layer has a pore diameter of 0.01 to 0.05 μm, a pore volume of 0.05 to 0.4 ml / g, It is described that the pore diameter of the catalyst layer is 0.05 to 0.1 μm and the pore volume is 0.4 to 1.0 ml / g. However, when such two types of catalyst layers are used, there is a problem that drainage is poor and desired power generation performance cannot be obtained. Furthermore, even if only the second catalyst layer having a large pore diameter and pore volume is used, the drainage performance is still insufficient, and a satisfactory output density cannot be obtained particularly under high humidification conditions. It was.

  Accordingly, an object of the present invention is to provide a membrane electrode assembly that exhibits excellent power generation performance even under high humidification conditions.

  The present inventors have intensively studied to solve the above problems. As a result, it has been found that a membrane electrode assembly excellent in drainage and gas diffusibility can be obtained by uniformly having pores having a predetermined pore diameter in the electrode catalyst layer.

That is, in order to achieve the above object, the membrane electrode assembly of the present invention has an anode catalyst layer and a cathode catalyst layer containing an electrode catalyst in which a catalyst component is supported on a conductive carrier, and a polymer electrolyte. The molecular electrolyte membrane is disposed so as to face both surfaces, and is sandwiched between a pair of gas diffusion layers. At least a part of the anode catalyst layer or the cathode catalyst layer has a predetermined pore structure. Specifically, the hole structure has a modest hole diameter in a range of 0.01 to 0.10 μm in a range of 0.045 to 0.060 μm in a hole distribution by a mercury intrusion method. And the ratio of the half value width with respect to the peak height of the peak of the mode hole diameter is 0.045 μm / (cm ³ g ⁻¹ ) or less.

  ADVANTAGE OF THE INVENTION According to this invention, the membrane electrode assembly which exhibits the outstanding electric power generation performance also under high humidification conditions can be provided.

  Hereinafter, preferred embodiments of the present invention will be described.

In the present embodiment, an anode catalyst layer and a cathode catalyst layer containing an electrode catalyst in which a catalyst component is supported on a conductive carrier and a polymer electrolyte are disposed opposite to both surfaces of the solid polymer electrolyte membrane. The present invention relates to a membrane / electrode assembly formed by sandwiching between a pair of gas diffusion layers. At least a part of the anode catalyst layer or the cathode catalyst layer has a predetermined pore structure. Specifically, the hole structure has a modest hole diameter in a range of 0.01 to 0.10 μm in a range of 0.045 to 0.060 μm in a hole distribution by a mercury intrusion method. And the ratio of the half value width with respect to the peak height of the peak of the mode hole diameter is 0.045 μm / (cm ³ g ⁻¹ ) or less.

  Hereinafter, the present invention will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

[Membrane electrode assembly]
FIG. 1 is a schematic cross-sectional view schematically showing a general overall structure of a membrane electrode assembly of the present invention. As shown in FIG. 1, in the membrane electrode assembly 100 of the present invention, the anode catalyst layer 120 a and the cathode catalyst layer 120 c are arranged to face both surfaces of the solid polymer electrolyte membrane 110. A pair of anode side gas diffusion layer 140a and cathode side gas diffusion layer 140c is sandwiched therebetween. The anode catalyst layer 120a and the cathode catalyst layer 120c include an electrode catalyst and a polymer electrolyte. In this electrode catalyst, a conductive carrier carries a catalyst component.

  Hereinafter, although the member which comprises the membrane electrode assembly of this invention is demonstrated easily, the technical scope of this invention is not restrict | limited only to the following form.

(Electrocatalyst layer)
There are two electrode catalyst layers, an anode catalyst layer and a cathode catalyst layer. Hereinafter, when the anode catalyst layer and the cathode catalyst layer are not distinguished from each other, they are also simply referred to as “electrode catalyst layers”. The electrode catalyst layer has a function of generating electric energy by an electrochemical reaction. In the anode catalyst layer, protons and electrons are generated by the oxidation reaction of hydrogen. Protons and electrons generated here are used for oxygen reduction reaction in the cathode catalyst layer.

At least a part of the anode-side or cathode-side electrode catalyst layer has a predetermined pore structure. Specifically, the hole structure has a modest hole diameter in a range of 0.01 to 0.10 μm in a range of 0.045 to 0.060 μm in a hole distribution by a mercury intrusion method. And the ratio of the half value width with respect to the peak height of the peak of the mode hole diameter is 0.045 μm / (cm ³ g ⁻¹ ) or less. In the following description, it is assumed that all the holes are cylindrical, the hole diameter is D, and the hole volume is V.

Here, the mercury intrusion method is a method in which mercury that does not react with most substances and does not wet is pressed into solid vacancies under pressure, and the pressure applied at that time is pushed (intruded) mercury. This is a technique for measuring the size and volume of vacancies on the sample surface from the relationship of volume. When a cell filled with a sample and mercury is continuously pressurized in a high-pressure vessel, mercury is sequentially injected from a large hole to a small hole. It can be theoretically calculated from the Washburn equation (D = −4σcos θ / P) how much pressure the mercury enters into the pores of which size. Here, P is the applied pressure, D is the pore diameter, σ is the surface tension of mercury, and θ is the contact angle between mercury and the pore wall surface. By treating σ and θ as constants, the relationship between the pressure P applied from the Washburn equation and the hole diameter D is obtained, and the hole diameter and its volume distribution are derived by measuring the intrusion volume at that time. In the following examples, the hole diameter is calculated assuming that the surface tension σ of mercury is 485 dyn cm ⁻¹ and the contact angle between mercury and the hole wall surface is 130 °. Therefore, in comparison between the present invention and a conventionally known technique, it is necessary to recalculate the hole diameter in the conventionally known technique using these values.

Specifically, the electrode catalyst layer according to the present invention is formed on both surfaces of the solid polymer electrolyte membrane to produce a CCM (catalyst coated membrane). The CCM is put into a measurement cell, the measurement cell containing the sample is evacuated and then filled with mercury, the inside of the cell is continuously pressurized, and the mercury intrusion volume (W1 [cm ³ ]) in the process Is detected by a capacitance detector. Separately, the same operation is performed on the solid polymer electrolyte membrane alone before forming the electrode catalyst layer, and the mercury intrusion volume (W0 [cm ³ ]) is detected. The value obtained by dividing the difference between the mercury intrusion volume of the CCM and the mercury intrusion volume of the electrolyte membrane (W1-W0 [cm ³ ]) by the electrode catalyst layer mass (g) is the pore volume V (cm ^{3 of the} electrode catalyst layer). / G).

  In the present invention, the pore distribution means a log differential pore volume distribution. In order to obtain the log differential hole volume distribution, first, the hole volume of the electrode catalyst layer obtained by the mercury intrusion method is set to V, and the hole diameter is set to D. A value (dV / d (logD)) divided by a logarithmic difference value d (logD) of the diameter is obtained. Then, this dV / d (logD) may be plotted against the average pore diameter of each section. The differential hole volume dV refers to an increase in the hole volume between measurement points.

  FIG. 2 is a graph showing the pore distribution of a general pore structure possessed by the electrode catalyst layer according to the present invention. As shown in FIG. 2, the horizontal axis represents the hole diameter (logarithmic scale), and the left vertical axis represents the log differential hole volume. Here, the solid line is a graph for the log differential integral void volume on the left vertical axis, and the broken line is a graph for the accumulated void volume on the right vertical axis.

  The hole structure according to the present invention has a modest hole diameter in a range of 0.01 to 0.10 μm in a range of 0.045 to 0.060 μm in a hole distribution by a mercury intrusion method. This means that the maximum value of the log differential pore volume in the pore diameter range of 0.01 to 0.10 μm exists in the pore diameter range of 0.045 to 0.060 μm. In the following, “moderate hole diameter in the range of 0.01 to 0.10 μm hole diameter” is also simply referred to as “moderate hole diameter”. From the viewpoint of power generation performance under highly humidified conditions, the most frequent pore diameter is preferably in the range of 0.050 to 0.060 μm, and more preferably in the range of 0.052 to 0.057 μm. preferable. If the mode pore size is less than 0.045 μm, there is a possibility that water is not suitably discharged from the electrode catalyst layer. On the other hand, if the mode pore diameter exceeds 0.060 μm, the ionomer network of the electrode catalyst layer is not formed well, and water retention may be reduced. Further, from the viewpoint of the small influence of the humidification condition on the power generation performance (hereinafter also referred to as “humidification robustness”), the mode pore diameter is preferably in the range of 0.045 to 0.050 μm. , Preferably in the range of 0.045 to 0.049 μm. When the mode pore diameter is 0.050 μm or less, an ionomer network is formed satisfactorily and water retention is improved. Thereby, the fall of the power generation performance under low humidification conditions is suppressed. In other words, a fuel cell having a membrane electrode assembly having such a pore structure has little influence on the moisture content of the supplied reaction gas itself and the humidity distribution in the cell that changes in a complicated manner, and stable power generation. Can demonstrate performance.

And in the said void | hole structure, ratio of the half value width with respect to the peak height of the peak of a mode hole diameter is 0.045 micrometer / (cm < ³ > g < ^-1 >) or less. In the following, “the ratio of the half-value width to the peak height of the peak of the mode pore diameter” is also simply referred to as “half-value width / peak height”. The peak of the most frequent pore diameter refers to a peak including the maximum value of the log differential pore volume. Peak height refers to the distance from the baseline to the peak top. Here, in the pore distribution in the present invention, the value of the log differential pore volume when the pore diameter is 0.50 μm is defined as 0 cm ³ g ⁻¹ . This is because the value of the accumulated pore volume when the pore diameter is 0.50 μm is defined as 0 cm ³ g ⁻¹ . A line having a log differential pore volume value of 0 cm ³ g ⁻¹ is defined as a baseline. That is, in the present invention, the baseline is the horizontal axis of the log differential pore volume distribution graph. Therefore, the peak height corresponds to the value from the horizontal axis to the peak top, that is, the maximum value of the peak. The full width at half maximum is an index representing the extent of the spread of a certain peak, and refers to the peak width at half the height of the peak. The half width / peak height is preferably 0.044 μm / (cm ³ g ⁻¹ ) or less, and more preferably 0.043 μm / (cm ³ g ⁻¹ ) or less. When the half width / peak height exceeds 0.045 μm / (cm ³ g ⁻¹ ), the uniformity of the pore structure is lowered, and the drainage and gas diffusibility may be lowered. In view of the humidifying robustness, it is preferable that the half width / peak height is 0.025μm ^{/ (cm 3 g -1)} or ^{less, 0.021μm / (cm 3 g -1} ) that less is Is more preferable. When the full width at half maximum / peak height is 0.025 μm / (cm ³ g ⁻¹ ) or less, vacancies are present more uniformly, so that an ionomer network is well formed and water retention is further improved. And thereby, the fall of the power generation performance under low humidification conditions is suppressed. The half-value width / peak height is theoretically a value exceeding 0 and is preferably as small as possible. However, in consideration of a practically manufacturable limit, it is preferably 0.010 μm / (cm ³ g ⁻¹ ). That's it.

  Satisfying these two numerical ranges means that pores of a suitable size are uniformly present in the electrocatalyst layer. Therefore, the membrane electrode assembly in which the electrode catalyst layer having such a pore structure is arranged exhibits excellent power generation performance.

  Moreover, in the hole distribution by the mercury intrusion method, the half-value width of the peak of the most frequent hole diameter is preferably 0.045 μm or less. In the following, the “half-value width of the peak of the most frequent pore diameter” is also simply referred to as “half-value width”. From the viewpoint of power generation performance under highly humidified conditions, the full width at half maximum is more preferably 0.043 μm or less, and still more preferably 0.042 μm or less. When the half-value width is 0.045 μm or less, pores contributing to drainage and gas diffusibility are present more uniformly, and therefore drainage and gas diffusibility are further improved. Further, from the viewpoint of humidification robustness, the half width is more preferably 0.030 μm or less, and further preferably 0.026 μm or less. When the full width at half maximum is 0.030 μm or less, the above-mentioned pores having the most frequent pore diameter suitable for improving the humidification robustness are uniformly present in the electrode catalyst layer, so that an ionomer network is formed favorably. Water retention is improved. Thereby, the fall of the power generation performance under low humidification conditions is suppressed. The half-value width is theoretically a value exceeding 0 and is preferably as small as possible. However, in consideration of a practically manufacturable limit, it is preferably 0.010 μm or more, more preferably 0.019 μm or more. is there.

Furthermore, in the above-mentioned hole structure, it is preferable that the total hole volume with a hole diameter in the range of 0.01 to 0.50 μm is 0.40 to 0.60 cm ³ g ⁻¹ . In the following, the “total pore volume in which the pore diameter is in the range of 0.01 to 0.5 μm” is also simply referred to as “total pore volume”. From the viewpoint of power generation performance under highly humidified conditions, the total pore volume is more preferably 0.47 to 0.60 cm ³ g ⁻¹ , further preferably 0.49 to 0.56 cm ³ g ^−1. It is. When the total pore volume is 0.40 to 0.60 cm ³ g ⁻¹ , pores in a form preferable for power generation are sufficiently present in the catalyst layer, and the power generation performance is improved. When the total pore volume is 0.40 cm ³ g ⁻¹ or more, there is a sufficient number of pores, and thus power generation performance is improved. Further, if the total pore volume is 0.60 cm ³ g ⁻¹ or less, the strength of the catalyst layer is maintained. In view of the humidifying robustness, more preferably Zensoraana volume is 0.40~0.50cm ³ g ^-1, and more preferably 0.42~0.45cm ³ g ^-1 . When the total pore volume is 0.40 to 0.50 cm ³ g ⁻¹ , there are sufficient pores in the catalyst layer that can contribute to improvement of water retention in which an ionomer network is well formed. Thereby, the fall of the power generation performance under low humidification conditions is suppressed.

  The membrane / electrode assembly of the present invention may have the above-described pore structure on at least a part of the anode side or the cathode catalyst layer. In other words, in the electrode catalyst layer, there may be a region having a pore structure that does not satisfy the above numerical range in addition to a region having a pore structure that satisfies the above numerical range. At this time, for evaluation of the pore distribution of the pore structure, an electrode catalyst layer having a region of 20% by volume or more is used for evaluation based on the total volume of the anode side or cathode catalyst layer used in the membrane electrode assembly. Use as a sample. That is, it is only necessary that at least one evaluation sample out of the evaluation samples randomly selected from the anode or cathode catalyst layer has a pore structure that satisfies the above numerical range. Further, the ratio of the region having the pore structure according to the present invention is preferably 30 to 100% by volume, more preferably 40 to 100% by volume, based on the total volume of the anode or cathode catalyst layer. Further, it is preferably 50 to 100% by volume, particularly preferably 60 to 100% by volume, and most preferably 100% by volume (whole). If the pore structure is included in at least a part of the anode or cathode catalyst layer, excellent power generation performance can be exhibited even under highly humidified conditions. However, when the region where the pore structure exists increases, The effect is further enhanced.

  In particular, the cathode catalyst layer is likely to be in a relatively high humidification condition due to water generated by the electrochemical reaction as compared with the anode catalyst layer. Therefore, the membrane / electrode assembly of the present invention preferably has the above-described pore structure in at least a part of the cathode catalyst layer. When the pore structure is included in at least a part of the cathode catalyst layer, excellent power generation performance can be exhibited even under high humidification conditions by water generated by an electrochemical reaction.

(Solid polymer electrolyte membrane)
The solid polymer electrolyte membrane is composed of a polymer electrolyte having proton conductivity, and selectively generates protons generated in the anode catalyst layer during the operation of the solid polymer fuel cell to the cathode catalyst layer along the film thickness direction. It has a function of transmitting. The solid polymer electrolyte membrane also has a function as a partition for preventing the fuel gas supplied to the anode side and the oxidant gas supplied to the cathode side from being mixed.

  The specific configuration of the solid polymer electrolyte membrane is not particularly limited, and a membrane made of a polymer electrolyte that is conventionally known in the technical field of fuel cells can be appropriately employed. Solid polymer electrolyte membranes are roughly classified into fluorine-based solid polymer electrolyte membranes and hydrocarbon-based solid polymer electrolyte membranes according to the type of polymer electrolyte that is a constituent material.

  Examples of the polymer electrolyte constituting the fluorine-based solid polymer electrolyte membrane include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.). Such as perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride -Perfluorocarbon sulfonic acid type polymer etc. are mentioned. From the viewpoint of power generation performance such as heat resistance and chemical stability, these fluorine-based solid polymer electrolyte membranes are preferably used, and more preferably fluorine-based solid polymer electrolyte membranes composed of perfluorocarbon sulfonic acid polymers. Is used.

  Examples of the polymer electrolyte constituting the hydrocarbon-based solid polymer electrolyte membrane include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, and phosphonated polybenzimidazole alkyl. Sulfonated polystyrene, sulfonated polyetheretherketone (S-PEEK), sulfonated polyphenylene (S-PPP), and the like. These hydrocarbon-based solid polymer electrolyte membranes are preferably used from the viewpoint of production such that the raw materials are inexpensive, the production process is simple, and the material selectivity is high. In addition, as for the ion exchange resin mentioned above, only 1 type may be used independently and 2 or more types may be used together.

  Materials other than the polymer electrolyte constituting the solid polymer electrolyte membrane described above may be used as the polymer electrolyte. As such materials, for example, liquids, solids, and gel materials having high proton conductivity can be used, and solid acids such as phosphoric acid, sulfuric acid, antimonic acid, stannic acid, and heteropoly acid, phosphoric acid, and the like. Hydrocarbon polymer compound doped with a non-organic acid, organic / inorganic hybrid polymer partially substituted with proton conductive functional group, gel impregnated with phosphoric acid solution or sulfuric acid solution in polymer matrix And the like proton conductive material. A mixed conductor having both proton conductivity and electron conductivity can also be used as a polymer electrolyte.

  The thickness of the solid polymer electrolyte membrane is appropriately determined in consideration of the characteristics of the membrane electrode assembly and the polymer electrolyte, and is not particularly limited. However, the thickness of the solid polymer electrolyte membrane is preferably 5 to 300 μm, more preferably 5 to 200 μm, still more preferably 10 to 150 μm, and particularly preferably 15 to 50 μm. When the thickness is within such a range, the balance of strength during film formation, durability during use, and output characteristics during use can be appropriately controlled.

(Gas diffusion layer)
There are two gas diffusion layers, an anode side gas diffusion layer and a cathode side gas diffusion layer. Hereinafter, when the anode side gas diffusion layer and the cathode side gas diffusion layer are not distinguished, they are simply referred to as “gas diffusion layer”. The gas diffusion layer has a function of promoting the diffusion of a reaction gas supplied through a gas flow path of a separator described later to the catalyst layer and a function as an electron conduction path.

  The material which comprises the base material of a gas diffusion layer is not specifically limited, A conventionally well-known knowledge can be referred suitably. For example, a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper body, a felt, and a non-woven fabric can be used. The thickness of the substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. If the thickness of the substrate is within such a range, the balance between mechanical strength and diffusibility such as gas and water can be appropriately controlled.

  The gas diffusion electrode may further include another member (layer) as necessary. For example, the gas diffusion layer may have a carbon particle layer containing carbon particles on the catalyst layer side of the base material in order to promote the discharge of excess moisture present in the catalyst layer and suppress the occurrence of the flooding phenomenon. Good.

  The carbon particles contained in the carbon particle layer are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately employed. Among them, it is preferable to use carbon black such as oil furnace black, channel black, lamp black, thermal black, and acetylene black because of excellent electron conductivity and a large specific surface area. The average particle diameter of the carbon particles is preferably about 10 to 100 nm. Thereby, while being able to obtain the high drainage property by capillary force, it becomes possible to improve contact property with a catalyst layer.

  The carbon particle layer may contain a water repellent. Examples of the water repellent include fluorine-based polymer materials such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Examples include polypropylene and polyethylene. Among these, it is preferable to use a fluorine-based polymer material because it is excellent in water repellency, corrosion resistance during electrode reaction, and the like.

  The electrode catalyst layer includes an electrode catalyst in which a catalyst component is supported on a conductive carrier and a polymer electrolyte.

(Conductive carrier)
The conductive carrier is a carrier that supports the catalyst component and has conductivity. Any conductive carrier may be used as long as it has a specific surface area sufficient to support the catalyst component in a desired dispersed state and sufficient electron conductivity. In the composition of the conductive carrier, the main component is preferably carbon. Specific examples of the material for the conductive carrier include carbon black, activated carbon, coke, natural graphite, and artificial graphite. “The main component is carbon” means that the main component contains carbon atoms, and is a concept that includes both carbon atoms and substantially carbon atoms. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, “consisting essentially of carbon atoms” means that contamination of about 2 to 3% by mass or less of impurities can be allowed.

The BET (Brunauer-Emmet-Teller) specific surface area of the conductive carrier is not particularly limited as long as it is a specific surface area sufficient to carry the catalyst component in a highly dispersed state, but is preferably 100-1500 m ² / g, more Preferably it is 600-1000 m < ² > / g. When the specific surface area of the conductive support is in such a range, the balance between the dispersibility of the catalyst component on the conductive support and the effective utilization rate of the catalyst component can be appropriately controlled.

  Although there is no restriction | limiting in particular also about the average particle diameter of an electroconductive support | carrier, Usually, it is 5-200 nm, Preferably it is about 10-100 nm. As the value of “average particle diameter of conductive carrier”, a value calculated by a primary particle diameter measurement method using a transmission electron microscope (TEM) is employed.

(Catalyst component)
The catalyst component has a function of catalyzing the electrochemical reaction. The catalyst component supported on the conductive carrier is not particularly limited as long as it has a catalytic action for promoting the above-described electrochemical reaction, and conventionally known catalyst components can be appropriately employed. Specific examples of catalyst components include platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and alloys thereof. Etc. Of these, the catalyst component preferably contains at least platinum from the viewpoint of excellent catalytic activity, elution resistance, and the like. The composition of the alloy when the alloy is used as the catalyst component of the electrode catalyst layer varies depending on the type of metal to be alloyed and can be appropriately selected by those skilled in the art. Other metals are about 10 to 70 atomic%. Note that an “alloy” is a general term for a metal element having one or more metal elements or non-metal elements added and having metallic properties. The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be used in the present application. Here, the alloy composition can be specified by using an ICP emission analysis method.

  The shape and size of the catalyst component are not particularly limited, and the same shape and size as those of conventionally known catalyst components can be appropriately employed. However, the shape of the catalyst component is preferably granular. And the average particle diameter of a catalyst component particle becomes like this. Preferably it is 0.5-30 nm, More preferably, it is 1-20 nm. When the average particle size of the catalyst component particles is within such a range, the balance between the catalyst utilization rate related to the effective electrode area where the electrochemical reaction proceeds and the ease of loading can be appropriately controlled. In the present invention, the value of the “average particle diameter of the catalyst component particles” is the crystal component diameter determined from the half-value width of the diffraction peak of the catalyst component particles in X-ray diffraction, or the catalyst component examined from the transmission electron microscope image. It can be calculated as the average value of the particle diameters.

  The ratio of the content of the conductive support and the catalyst component in the electrode catalyst is not particularly limited. However, the content (supported amount) of the catalyst component is preferably 5 to 70% by mass, more preferably 10 to 60% by mass, and further preferably 30 to 55% by mass with respect to the total mass of the electrode catalyst. %. When the content of the catalyst component is 5% by mass or more, the catalyst performance of the electrode catalyst is sufficiently exerted, which contributes to the improvement of the power generation performance of the polymer electrolyte fuel cell. On the other hand, the catalyst component content of 70% by mass or less is preferable because aggregation of the catalyst components on the surface of the conductive support is suppressed and the catalyst components are supported in a highly dispersed state. In addition, as a value of the ratio of content mentioned above, the value measured by ICP emission spectrometry shall be employ | adopted.

(Polymer electrolyte)
The polymer electrolyte has a function of improving the proton conductivity of the electrode catalyst layer. There is no restriction | limiting in particular in the specific form of the polymer electrolyte contained in an electrode catalyst layer, The conventionally well-known knowledge can be referred suitably in the technical field of a fuel cell. For example, as the polymer electrolyte contained in the electrode catalyst layer, the polymer electrolyte constituting the solid polymer electrolyte membrane described above can be similarly used. Therefore, details of the specific form of the polymer electrolyte are omitted here. The polymer electrolyte contained in the electrode catalyst layer may be one kind alone or two or more kinds.

  The ion exchange capacity of the polymer electrolyte contained in the electrode catalyst layer is preferably 0.8 to 1.5 mmol / g, and preferably 1.0 to 1.5 mmol / g from the viewpoint of excellent ion conductivity. It is more preferable. The “ion exchange capacity” of the polymer electrolyte means the number of moles of sulfonic acid groups per unit dry mass of the polymer electrolyte. The value of “ion exchange capacity” can be calculated by removing the dispersion medium of the polymer electrolyte dispersion by heat drying or the like to obtain a solid polymer electrolyte, and performing neutralization titration.

  There is no restriction | limiting in particular also about content of the polymer electrolyte in an electrode catalyst layer. However, the mass ratio of the content of the polymer electrolyte to the content of the electroconductive carrier in the electrode catalyst layer (the mass ratio of the polymer electrolyte / the electroconductive carrier) is preferably 0.5 to 2.0, and more preferably. Is 0.6 to 1.5, more preferably 0.8 to 1.3. The mass ratio of ionomer / conductive carrier is preferably 0.8 or more from the viewpoint of suppressing the internal resistance value of the membrane / electrode assembly. On the other hand, the ionomer / conductive carrier mass ratio is preferably 1.3 or less from the viewpoint of suppressing flooding.

[Production method of membrane electrode assembly]
The manufacturing method of the membrane electrode assembly of the present invention is not particularly limited, and can be manufactured by appropriately referring to conventionally known knowledge in the field of manufacturing membrane electrode assemblies. Hereinafter, although the manufacturing method of the membrane electrode assembly of this invention is demonstrated easily, the technical scope of this invention should be defined based on description of a claim, and is not restrict | limited only to the following forms.

  The membrane / electrode assembly of the present invention can be produced by forming anode-side and cathode-side electrode catalyst layers on both sides of a solid polymer electrolyte membrane and sandwiching them between gas diffusion layers. The electrode catalyst layer is formed by spraying a catalyst ink comprising the above electrode catalyst, polymer electrolyte and solvent onto a solid polymer electrolyte membrane, a screen printer coating / transfer method (hereinafter also simply referred to as “transfer method”). It can manufacture by apply | coating using conventionally well-known methods, such as.

  The electrode catalyst is prepared by supporting a catalyst component on a conductive carrier. In order to support the catalyst component on the conductive carrier, a conventionally known method such as impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle method (microemulsion method) is used. You can use it. Moreover, you may use the electrode catalyst marketed.

  It does not restrict | limit especially as a solvent, The normal solvent used in forming an electrode catalyst layer can be used similarly. Specifically, water, lower alcohols such as cyclohexanol, ethanol (EtOH), 1-propanol (NPA), and 2-propanol can be used. The amount of the solvent used is not particularly limited, and the same amount as known can be used. The amount of the electrocatalyst contained in the catalyst ink is not particularly limited as long as the amount can sufficiently exhibit a desired action, that is, an action of catalyzing an oxidation reaction of hydrogen on the anode side or an oxygen reduction reaction on the cathode side. . The amount of the electrode catalyst in the catalyst ink is preferably 3 to 30% by mass, more preferably 5 to 20% by mass. The polymer electrolyte is also preferably present in the same amount / ratio as the electrode catalyst.

  Further, when the catalyst ink is applied by a transfer method, a thickener may be included. The use of a thickener is effective when the catalyst ink cannot be successfully applied onto a transfer mount. The thickener that can be used in this case is not particularly limited, and a known thickener can be used. Examples thereof include glycerin, ethylene glycol (EG), polyvinyl alcohol (PVA), and propylene glycol (PG). Of these, propylene glycol (PG) is preferably used. The amount of the thickener added when using the thickener is not particularly limited as long as it does not interfere with the above effect of the present invention, but is preferably 5 to 40 with respect to the total mass of the catalyst ink. % By mass.

  The catalyst ink can be prepared by mixing and dispersing the above electrode catalyst, polymer electrolyte, solvent and the like. The polymer electrolyte may be used as a polymer electrolyte dispersion previously dispersed in the above solvent. When preparing the catalyst ink, the dispersibility of the conductive carrier may be adjusted by adjusting the stirring time and the like. Thereby, the hole diameter, porosity, surface resistance value, etc. in the obtained electrode catalyst layer can be adjusted. Examples of the agitation means include conventionally known means such as a homogenizer, an ultrasonic dispersion device, a sand mill, a jet mill, and a bead mill. At this time, the average volume particle diameter (secondary particle diameter) of the catalyst component particles in the catalyst ink for obtaining the pore structure as described above is generally 0.1 to 2.0 μm, preferably Is 0.3 to 1.0 μm, more preferably 0.450 to 0.900 μm. In addition, the value obtained with the laser diffraction and scattering type particle size distribution measuring apparatus is employ | adopted for an average volume particle diameter here.

A conventionally well-known method can be used for formation of an electrode catalyst layer. For example, there is a method of directly applying to a solid polymer electrolyte membrane and drying. In addition, there is a method in which a catalyst ink is applied on a substrate (for example, a polytetrafluoroethylene (PTFE) sheet) and dried to form an electrode catalyst layer, which is transferred to a solid polymer electrolyte membrane. An electrode catalyst layer may be formed on one side of the gas diffusion layer. As a coating method, a conventionally known method such as a spray method, a screen printer method, a doctor blade method, or a die coater method can be used. The coating amount of the catalyst ink with the solid polymer electrolyte membrane is not particularly limited as long as the electrode catalyst can sufficiently exert the action of catalyzing the electrochemical reaction, but the mass of the catalyst component per unit area is 0.05 to It is preferable to apply so as to be 1 mg / cm ² . Moreover, it is preferable to apply | coat so that the thickness of the catalyst ink to apply | coat may be 5-30 micrometers after drying. The application amount and thickness of the catalyst ink need not be the same on the anode side and the cathode side, and can be adjusted as appropriate.

  In the method for producing an electrode catalyst layer according to the present invention, a conventionally known method can be appropriately employed as described above, and a particularly preferable embodiment will be described below.

  As a method for applying the catalyst ink, it is particularly preferable to use a transfer method or a spray method. When using the transfer method, it is preferable to add the above-mentioned thickener to the catalyst ink from the viewpoint of uniformly applying the catalyst ink. Among the thickeners, propylene glycol is preferably used. And it is preferable to dry the catalyst ink after application | coating on the conditions by which a dispersion medium volatilizes at a speed | rate of 0.7 mg / min or less. At this time, the catalyst ink may be appropriately heated for drying. By drying the catalyst ink relatively slowly as described above, pores having a relatively large pore diameter contributing to drainage and gas diffusibility can be uniformly formed. Moreover, when using a spray method, it is preferable to dry the catalyst ink after application | coating on the conditions which a dispersion medium volatilizes at a speed | rate of 0.7 mg / min or more. At this time, the catalyst ink may be appropriately heated for drying. By thus drying the catalyst ink relatively quickly, the holes having a relatively small hole diameter can be uniformly formed in the electrode catalyst layer. Such pores not only have good drainage and gas diffusibility, but also have a good ionomer network, and an electrocatalyst layer with high water retention can be obtained.

  The membrane electrode assembly of the present invention further has a gas diffusion layer. A conventionally known method can be used for forming the membrane electrode assembly. For example, a membrane electrode assembly can be produced by sandwiching an electrode catalyst layer formed on a solid polymer electrolyte membrane between a pair of gas diffusion layers and bonding them. Alternatively, it may be produced by forming an electrode catalyst layer on one side of the gas diffusion layer, sandwiching the solid polymer electrolyte membrane between the pair of gas diffusion layers so that the electrode catalyst layers face each other, and bonding them. .

[Fuel cell]
The fuel cell of the present invention comprises a pair of membrane electrode assemblies of the present invention, a pair of anode side separators having a fuel gas flow path through which fuel gas flows and a cathode side separator having an oxidant gas flow path through which oxidant gas flows. And a separator.

  FIG. 3 is a schematic cross-sectional view schematically showing a general overall structure of a polymer electrolyte fuel cell (PEFC) which is an embodiment of the fuel cell of the present invention. FIG. 3 shows a single cell of a polymer electrolyte fuel cell.

  A polymer electrolyte fuel cell 200 shown in FIG. 3 has the membrane electrode assembly 100 of the present invention. In the polymer electrolyte fuel cell 200, the membrane electrode assembly 100 is sandwiched between a pair of separators including an anode side separator 150a and a cathode side separator 150c. Here, the anode side gas diffusion layer 140a side surface of the anode side separator 150a is provided with a fuel gas passage 152a through which fuel gas flows during operation, and the coolant flows through the opposite surface during operation. A cooling flow path (not shown) is provided. On the other hand, an oxidant gas passage 152c through which an oxidant gas flows during operation is provided on the cathode side gas diffusion layer 140c side surface of the cathode side separator 150c, and a coolant is provided on the opposite surface during operation. A cooling flow path (not shown) through which is circulated is provided. A gasket 160 is disposed around the polymer electrolyte fuel cell 200 so as to surround the pair of gas diffusion electrodes.

  The fuel cell having the membrane electrode assembly of the present invention as described above exhibits excellent power generation performance under high humidification conditions.

  Hereinafter, although the member which comprises the fuel cell of this invention is demonstrated easily, the technical scope of this invention is not restrict | limited only to the following form.

(Separator)
The separator has a function of electrically connecting each cell in series when a plurality of single cells of a fuel cell such as a polymer electrolyte fuel cell are connected in series to form a fuel cell stack. The separator also functions as a partition that separates the fuel gas, the oxidant gas, and the coolant from each other. Therefore, as described above, each separator is provided with a gas flow path and a cooling flow path. As a material constituting the separator, conventionally known materials such as dense carbon graphite, carbon such as a carbon plate, and metal such as stainless steel can be appropriately employed without limitation. The thickness and size of the separator and the shape and size of each flow path provided are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics of the obtained fuel cell.

(gasket)
The gasket is disposed around the fuel cell so as to surround the pair of electrode catalyst layers and the gas diffusion layer, and has a function of preventing the gas supplied to the catalyst layer from leaking to the outside. A gas diffusion electrode refers to a joined body of a gas diffusion layer and an electrode catalyst layer. The material constituting the gasket is not particularly limited, but rubber materials such as fluoro rubber, silicon rubber, ethylene propylene rubber (EPDM), polyisobutylene rubber, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), Examples thereof include fluorine polymer materials such as polyhexafluoropropylene and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and thermoplastic resins such as polyolefin and polyester. Moreover, there is no restriction | limiting in particular also in the thickness of a gasket, Preferably it is 50 micrometers-2 mm, More preferably, what is necessary is just to be about 100 micrometers-1 mm.

[Operating method of fuel cell]
Furthermore, the present invention provides a method for operating the fuel cell. As described above, the electrode catalyst layer according to the present invention has high gas diffusibility and water retention. Therefore, the fuel cell of the present invention having this electrode catalyst layer has excellent power generation performance particularly under high humidification conditions. Therefore, the effect of the present invention becomes more prominent by operating the fuel cell by supplying fuel gas or oxidant gas to the electrode catalyst layer having the pore structure under high humidification conditions.

  In the fuel cell operating method of the present invention, when at least a part of the anode catalyst layer has the above-described pore structure, the fuel gas is supplied at a relative humidity of 70 to 100%, and at least a part of the cathode catalyst layer is In the case of having the pore structure, the oxidizing gas is supplied under the condition of relative humidity of 70 to 100%. The relative humidity of the fuel gas or oxidant gas is preferably 80 to 100%, more preferably 90 to 100%, and still more preferably 95 to 100%. When the relative humidity of the fuel gas or the oxidant gas is 70 to 100%, the power generation performance of the fuel cell of the present invention is further improved as compared with the conventional fuel cell. The relative humidity of the fuel gas or oxidant gas is the relative humidity in the vicinity of the entrance to the cell of the gas flow path.

  Other conditions such as the type of fuel gas and oxidant gas, supply amount, supply temperature, and operating temperature of the fuel cell are not particularly limited, and conventionally known operating methods in the technical field of fuel cells can be appropriately employed.

  Among these operating methods, preferably, at least a part of the cathode catalyst layer has the above-described pore structure, and the fuel gas is supplied under the condition of a relative humidity of 70 to 100%. Since the cathode catalyst layer is likely to be in a high humidification condition as compared with the anode side, the power generation performance of the fuel cell of the present invention is further improved by such an operation method.

[vehicle]
A vehicle equipped with the above-described fuel cell or fuel cell stack of the present invention is also included in the technical scope of the present invention. Since the fuel cell and fuel cell stack of the present invention are very excellent in output performance under high humidification conditions, they are suitable for vehicle applications that require high output.

  The effect of this invention is demonstrated using a following example and a comparative example. However, the technical scope of the present invention is not limited only to the following examples.

  In the following Examples and Comparative Examples, membrane electrode assemblies were prepared by changing the mode pore diameter and the half-value width / peak height, half-value width, and total pore volume of the cathode catalyst layer. The power generation performance of a single polymer electrolyte fuel cell unit was evaluated.

  Specifically, the membrane electrode assemblies of Examples 1 to 6 and Comparative Examples 1 to 3 were produced as follows.

[Production of membrane electrode assembly]
(Preparation of cathode catalyst ink)
<Example 1>
16 g of a catalyst carrier (platinum content: 46% by mass) in which platinum is supported as a catalyst component on carbon black as a conductive carrier, a polymer electrolyte dispersion (ion exchange capacity: 1.0 mmol / g, electrolyte content: 12% by mass, 70 g of ion-exchanged water content (88% by mass), 3 g of ion-exchanged water, 16 g of 1-propanol, and 49 g of propylene glycol were mixed, and mixed and dispersed for 10 minutes using a sand mill, whereby the cathode catalyst ink (average volume of catalyst particles) A particle diameter of 0.770 μm) was obtained.

<Example 2>
By mixing 16 g of the same catalyst carrier as in Example 1, 70 g of the same polymer electrolyte dispersion as in Example 1, 3 g of ion exchange water, 16 g of ethanol, and 49 g of propylene glycol, and mixing and dispersing for 10 minutes using a sand mill. A catalyst ink for cathode (average volume particle diameter of catalyst particles 0.820 μm) was obtained.

<Example 3>
16 g of the catalyst carrier as in Example 1, 70 g of the polymer electrolyte dispersion as in Example 1, 19 g of ion exchange water, 16 g of 1-propanol, and 32 g of propylene glycol are mixed and dispersed for 10 minutes using a sand mill. Thus, a catalyst ink for cathode (average volume particle diameter of catalyst particles 0.840 μm) was obtained.

<Example 4>
16 g of the catalyst support similar to that of Example 1, 37 g of the polymer electrolyte dispersion similar to that of Example 1, 18 g of ion-exchanged water, and 78 g of propylene glycol were mixed and dispersed for 10 minutes using a sand mill. A catalyst ink (average volume particle diameter of catalyst particles 0.860 μm) was obtained.

<Example 5>
By mixing 7 g of the same catalyst carrier as in Example 1, 30 g of the same polymer electrolyte dispersion as in Example 1, 2 g of ion-exchanged water, and 112 g of 1-propanol, and mixing and dispersing for 30 minutes using a sand mill, Catalyst ink (average volume particle diameter of catalyst particles 0.488 μm) was obtained.

<Example 6>
7 g of the catalyst support similar to Example 1, 30 g of the polymer electrolyte dispersion similar to Example 1, 57 g of ion exchange water, and 56 g of propylene glycol were mixed and dispersed for 30 minutes using a sand mill. Catalyst ink (average particle diameter of catalyst particles 0.538 μm) was obtained.

<Comparative Example 1>
By mixing 7 g of the catalyst carrier as in Example 1, 16 g of the polymer electrolyte dispersion as in Example 1, 78 g of ion-exchanged water, and 49 g of 1-propanol, and mixing and dispersing for 120 minutes using a sand mill, Catalyst ink (average volume particle diameter of catalyst particles 0.380 μm) was obtained.

<Comparative Example 2>
By mixing 7 g of the catalyst carrier as in Example 1, 16 g of the polymer electrolyte dispersion as in Example 1, 78 g of ion-exchanged water, and 49 g of 1-propanol, and mixing and dispersing for 30 minutes using a sand mill, Catalyst ink (average volume particle diameter of catalyst particles 0.528 μm) was obtained.

<Comparative Example 3>
A catalyst for cathode is prepared by mixing 7 g of the same catalyst carrier as in Example 1, 30 g of the same polymer electrolyte dispersion as in Example 1, 57 g of ion exchange water, and 56 g of methanol, and mixing and dispersing for 30 minutes using a sand mill. An ink (average volume particle diameter of catalyst particles: 0.489 μm) was obtained.

(Preparation of catalyst ink for anode)
5 g of a catalyst carrier (platinum content 46 mass%) carrying platinum as a catalyst component on carbon black as a conductive carrier, a polymer electrolyte dispersion (ion exchange capacity 1.0 mmol / g, electrolyte content 22 mass%) 1-propanol content 42 mass%, ion-exchange water content 36 mass%) 11 g, ion-exchange water 81 g and 1-propanol 52 g are mixed and dispersed for 30 minutes by using a sand mill, whereby anode catalyst ink (The average volume particle diameter of the catalyst particles was 0.420 μm).

(Production of electrode catalyst layer-solid polymer electrolyte membrane assembly)
<Examples 1-4>
Two sheets of polytetrafluoroethylene (PTFE) 80 mm square and 80 μm thick were prepared. The cathode catalyst ink was applied to one side of this PTFE sheet so as to be 0.3 mg-Pt / cm ² using a screen printer, and then dried in a dry oven at 130 ° C. for 30 minutes. The anode catalyst ink was applied to one side of another PTFE sheet so as to be 0.1 mg-Pt / cm ² using a screen printer, and then dried in a 130 ° C. dry oven for 30 minutes.

  A solid polymer electrolyte membrane (manufactured by DuPont, NAFION NRE-211) having a square of 80 mm square and a thickness of 25 μm was prepared. The PTFE sheet on which the anode electrode catalyst layer was formed and the PTFE sheet on which the cathode electrode catalyst layer was formed were overlapped with the solid polymer electrolyte membrane interposed therebetween so that both electrode catalyst layers were opposed to each other. Further, it was sandwiched between two stainless steel plates each having a square of 80 mm and a thickness of 0.5 mm, and a PTFE sheet was hot pressed at 130 ° C. for 10 minutes at a pressure of 0.8 MPa. After cooling, only the PTFE sheet was peeled off to transfer the catalyst layer to the polymer electrolyte membrane to obtain an electrode catalyst layer-solid polymer electrolyte membrane assembly.

<Examples 5 and 6 and Comparative Examples 1-3>
A solid polymer electrolyte membrane (manufactured by DuPont, NAFION NRE-211) having a square of 80 mm square and a thickness of 25 μm was prepared. The anode catalyst ink was applied by spray coating on one surface of the solid polymer electrolyte membrane so as to be 0.1 mg-Pt / cm ^2, and then dried on a hot plate at 80 ° C. for 15 minutes. The cathode catalyst ink was applied to the other surface of the solid polymer electrolyte membrane by spray coating so as to be 0.3 mg-Pt / cm ^2, and then dried on an 80 ° C. hot plate for 15 minutes (Example) No. 6 was further dried in a dry oven at 130 ° C. for 30 minutes) to obtain an electrode catalyst layer-solid polymer electrolyte membrane assembly.

(Preparation of single fuel cell for evaluation)
Two gas diffusion layers (SGL Carbon, GDL25BC) are stacked so that the carbon particle layers of the gas diffusion layers face each other so as to sandwich the electrode catalyst layer-solid polymer electrolyte membrane assembly produced above. An electrode assembly was obtained. This was sandwiched in the order of two graphite separators, two gold-plated stainless steel current collector plates, and two stainless steel end plates to form a single fuel cell for evaluation.

[Evaluation of pore structure of electrode catalyst layer]
Cathode catalyst ink was applied to both sides of the solid polymer electrolyte membrane so as to be 0.3 mg-Pt / cm ² . Otherwise, the electrode catalyst layer-solid polymer electrolyte membrane assembly of Examples 1 to 6 and Comparative Examples 1 to 4 was produced in the same manner as the production of the electrode catalyst layer-solid polymer electrolyte membrane assembly. did. The obtained electrode catalyst layer-solid polymer electrolyte membrane assembly was cut into 20 cm ² and introduced into a measuring cell having a cell volume of about 6 cc and a stem volume of about 0.39 cc. This measurement cell was set in Autopore IV 9510 type (manufactured by Micromeritics), and the mercury intrusion amount was measured, and the accumulated pore volume (cm ³ / g-Pt) having a pore diameter in the range of 400 μm to 3 nm. ) And log differential pore volume (cm ³ / g-Pt).

[Measurement of electrolyte resistance]
The electrolyte resistance value was calculated by electrochemical AC impedance measurement using a potentio galvanostat that controls the potential and current connected to a frequency response analyzer (FRA). The FRA has a built-in sine wave transmission circuit and automatically scans the modulation frequency to determine the impedance spectrum. A sine wave signal is sent from the FRA to the potentio galvanostat, and the potentio galvanostat applies sine wave potential modulation to the cell to measure the response current. The modulation potential and the modulation current are output from the potentio galvanostat to the FRA, and the impedance at each frequency is determined. Here, the measurement conditions were an applied potential of 450 mV, a potential amplitude of 10 mV, and a frequency range of 100 mHz to 15 kHz.

The impedance obtained in this way is displayed on a complex plane (Nyquist plot), and from this Nyquist plot, the literature (M. Lefebvre et al, Elec. & Solid State Letters, 2 (6) 259-261 (1999)) is described. The electrolyte resistance value was calculated by the method. Specifically, the electrolyte resistance value in the catalyst layer was calculated by multiplying the difference between the intersection of the linear portion of the Nyquist plot and the real axis and the intersection of the real axis of the plot by three times.
[Evaluation of single fuel cell]
The temperature of the single fuel cell was set to 80 ° C., and the relative humidity (RH) near the entrance to the cell of the gas flow path was set to 40%, 70%, or 100%. Then, under normal pressure, the fuel cell single cell was operated by supplying hydrogen from the anode side at a flow rate of 4 L / min and supplying air from the cathode side at a flow rate of 8 L / min. Under this condition, the single cell voltage at a current density of 1 A / cm ² was measured. Moreover, the change of the voltage (measurement voltage) measured on each RH condition on the basis of the maximum voltage (maximum voltage) among the voltages measured on 40% RH, 70% RH, and 100% RH conditions The rate (%) was calculated according to Equation 1 below.

  The results are shown in Table 1.

From the results shown in Table 1, the mode pore diameter is in the range of 0.045 to 0.060 μm, and the ratio of the half-value width to the peak height of the peak of the mode pore diameter is 0.045 μm / (cm ³ g ^{− 1} ) The following Examples 1 to 6 are higher when the relative humidity is 100% compared to Comparative Examples 1 to 3 that do not have the most frequent pore diameter and half width / peak height values in the range. The power density is shown. Among Examples, Examples 1 to 4 having a modest hole diameter in the range of 0.050 to 0.060 μm are much higher than those of Examples 5 and 6 at a relative humidity of 100%. The power density is shown. On the other hand, the mode hole diameter is in the range of 0.045 to 0.050 μm, and the ratio of the half-value width to the peak height of the peak of the mode hole diameter is 0.025 μm / (cm ³ g ⁻¹ ) or less. Certain Examples 5 and 6 have a higher power density at 40% relative humidity than Examples 1-4, and the absolute value of the rate of change (%) with respect to the maximum voltage under each relative humidity condition. Was small. That is, it was shown that Examples 5 and 6 were superior in humidification robustness compared to Examples 1 to 4 and had good power generation performance even in a wide humidification range.

It is the cross-sectional schematic which represented typically the general whole structure of the membrane electrode assembly of this invention. It is a graph showing the hole distribution of the general hole structure which the electrode catalyst layer which concerns on this invention has. 1 is a schematic cross-sectional view schematically showing a general overall structure of a polymer electrolyte fuel cell which is an embodiment of a fuel cell of the present invention.

Explanation of symbols

100 membrane electrode assembly,
110 solid polymer electrolyte membrane,
120a anode catalyst layer,
120c cathode catalyst layer,
140a anode side gas diffusion layer,
140c cathode side gas diffusion layer,
150a anode side separator,
150c cathode side separator,
152a fuel gas flow path,
152c oxidant gas flow path,
160 gasket,
200 Solid polymer fuel cell.

Claims (13)

An anode catalyst layer catalyst layer and a cathode catalyst layer containing an electrode catalyst in which a catalyst component is supported on a conductive carrier and a polymer electrolyte are disposed opposite to both surfaces of the solid polymer electrolyte membrane, A membrane electrode assembly sandwiched between gas diffusion layers,
In at least a part of the anode catalyst layer or the cathode catalyst layer, in the pore distribution by the mercury intrusion method, (1) the modest pore diameter in the range of 0.01 to 0.10 μm is 0.045 to 0. (2) There is a pore structure in which the ratio of the half-value width to the peak height of the peak of the most frequent pore diameter is 0.045 μm / (cm ³ g ⁻¹ ) or less. A membrane electrode assembly.   The membrane electrode assembly according to claim 1, wherein the full width at half maximum is 0.045 μm or less. ^3. The membrane / electrode assembly according to claim ¹ , wherein in the pore structure, the total pore volume in the range of pore diameters of 0.01 to 0.50 μm is 0.40 to 0.60 cm ³ g ^−1. . The mode hole diameter is in the range of 0.045 to 0.050 μm, and the ratio of the half-value width to the peak height of the peak of the mode hole diameter is 0.025 μm / (cm ³ g ⁻¹ ) or less. The membrane electrode assembly according to any one of claims 1 to 3.   The membrane electrode assembly according to any one of claims 2 to 4, wherein the full width at half maximum is 0.030 µm or less. The said void | hole structure WHEREIN: The total void | hole volume of the range of void | hole diameters 0.01-0.50 micrometer is 0.40-0.50cm < ³ > g < ^-1 >, Any one of Claims 3-5. Membrane electrode assembly.   The membrane electrode assembly according to any one of claims 1 to 3, wherein the most frequent pore diameter is in a range of 0.050 to 0.060 µm. 8. The hole structure according to claim 3, wherein in the hole structure, a total hole volume in a range of a hole diameter of 0.01 to 0.50 μm is 0.47 to 0.60 cm ³ g ^−1. Membrane electrode assembly.   The membrane electrode assembly according to any one of claims 1 to 8, wherein at least a part of the cathode catalyst layer has the pore structure. The membrane electrode assembly according to any one of claims 1 to 9,
A pair of separators comprising an anode side separator having a fuel gas flow path through which fuel gas flows and a cathode side separator having an oxidant gas flow path through which oxidant gas flows;
A fuel cell. When the pore structure is present in at least a part of the anode catalyst layer, the fuel gas is supplied at a relative humidity of 70 to 100%,
11. The method of operating a fuel cell according to claim 10, wherein when the pore structure is present in at least a part of the cathode catalyst layer, the oxidant gas is supplied at a relative humidity of 70 to 100%.   The method for operating a fuel cell according to claim 10, wherein the pore structure exists in at least a part of the cathode catalyst layer, and the fuel gas is supplied under a condition of a relative humidity of 70 to 100%.   A vehicle equipped with the fuel cell according to claim 10.

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