JP2001216973A - Electrode and its production as well as fuel cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode with an electrode catalyst layer coating liquid controlled to be infiltrated into an electrode substrate when using a porous conductive sheet having a non-woven cloth structure as the electrode substrate. SOLUTION: The electrode comprises, at least, an electrode substrate and an electrode catalyst layer, the electrode substrate having the porous conductive sheet having the non-woven cloth structure, wherein a conductive intermediate layer containing, at least, an inorganic conductive material and a hydrophobic polymer is provided between the electrode catalyst layer and the electrode substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode used for a fuel cell and a method for manufacturing the same.

[0002]

2. Description of the Related Art A fuel cell is a power generation device with low emission, high energy efficiency and low environmental burden. For this reason, they have been spotlighted again with the recent rise of global environmental protection. As a relatively small-scale distributed power generation facility compared to conventional large-scale power generation facilities, as a power generation device for mobile objects such as cars and ships,
It is a power generator that is expected in the future.

[0003] Fuel cells are classified into a solid polymer type, a phosphoric acid type, a solid oxide type, a molten carbonate type, and an alkaline type depending on the type of electrolyte used. Among them, polymer electrolyte fuel cells have the characteristics of lower operating temperature, shorter start-up time, higher power output, smaller size and lighter weight, strong vibration resistance, etc., compared to other fuel cells. Suitable for body power supply.

[0004] A fuel cell is constituted as a unit in which an anode electrode and a cathode electrode where a reaction responsible for power generation occurs, and an electrolyte serving as an ion conductor between the anode and the cathode are sandwiched between separators. . The electrode is composed of an electrode substrate (also referred to as a current collector) for promoting gas diffusion and collecting (supplying) electricity, and an electrode catalyst layer that actually acts as an electrochemical reaction field. For example, in an anode electrode of a polymer electrolyte fuel cell, a fuel gas reacts on a catalyst surface to generate protons and electrons, the electrons are conducted to an electrode substrate, and the protons are conducted to a proton exchange membrane of an electrolyte. Therefore, the anode electrode is required to have good gas diffusivity, electron conductivity, and ion conductivity. On the other hand, in the cathode electrode, on the surface of the electrode catalyst layer, the oxidizing gas reacts with protons conducted from the electrolyte and electrons conducted from the electrode base material to produce water. Therefore, it is necessary to efficiently discharge generated water as well as gas diffusivity, electron conductivity, and ion conductivity.

In order to satisfy such requirements, various studies have been made on the electrode catalyst layer. Examples of improved gas diffusivity are disclosed in JP-A-8-88007, JP-A-7-183035, and JP-A-6-20.
Japanese Patent Application Laid-Open No. 4-329264, Japanese Patent Application Laid-Open No. 8-213,027, Japanese Patent Application Laid-Open No. 6-236762, and Japanese Patent Application Laid-Open No. 6-203840 disclose techniques for improving proton conductivity. JP, JP-A-7-296818, JP-A-7-254420, JP-A-6-251779, JP-A-9-245
The technology described in Japanese Patent Publication No. 802 has been reported so far.

[0006] In these publications, a catalyst-supporting carbon or a polymer (proton exchange resin is used to improve proton conductivity, and the generated water is discharged to form a porous electrode catalyst layer for the purpose of improving gas diffusivity. PTF for improved performance
E: using polytetrafluoroethylene), an example in which an electrode catalyst layer is prepared by mixing a catalyst-supporting carbon and a proton exchange resin for the purpose of improving proton conductivity, and a case in which a proton is added to the electrode catalyst layer. An example in which an exchange resin is applied and then joined to a proton exchange membrane is described.

[0007] Further, as the prior art of the electrode base material (current collector), there are Japanese Patent Application Laid-Open Nos. 6-20710 and 7-326.
No. 362 or Japanese Patent Application Laid-Open No. 7-220735 has been proposed. The current collectors disclosed therein consist of a porous carbon plate formed by binding carbon fibers of short length with carbon.

[0008]

As described above, an electrode is composed of an electrode substrate and an electrode catalyst layer. These required properties include gas diffusivity, electron conductivity, and ion conductivity, as well as the required properties. It is required to efficiently discharge the water, especially the electrode base material, gas diffusion, electron conductivity,
A porous conductive sheet is used from the viewpoint of drainage. Among such porous conductive sheets, a porous conductive sheet having a so-called nonwoven structure such as a paper-like paper body, a felt or a nonwoven fabric has been used in order to improve gas diffusivity and reduce manufacturing costs. .

In the electrode catalyst layer, in addition to the above-mentioned required characteristics, since the catalyst used is an expensive noble metal, it is necessary to improve the amount of catalyst used effectively. In particular, when the electrode catalyst layer is applied to an electrode substrate made of a porous conductive sheet having a nonwoven structure as described above, the electrode catalyst layer coating liquid greatly penetrates into the electrode substrate, and this impregnation occurs. This is a cause of an increase in useless catalysts that cannot be used effectively because of the impregnation.

[0010] Fuel cells are expected as a power supply source for mobile objects, but a large reduction in cost is required for mass diffusion of automobiles and the like. In particular, the catalyst particles in the electrode catalyst layer are very expensive because noble metals are used,
There is a strong demand to reduce this amount of catalyst. For this reason, it is necessary to reduce as much as possible the amount of the catalyst that has not penetrated into the electrode base material and is not used effectively. The provision of a layer is disclosed. Here, it is disclosed that an intermediate layer containing acetylene black and a proton conductive polymer as a conductive agent has an effect of preventing permeation of a catalyst. However, since the proton conductive polymer is a hydrophilic polymer and easily contains water, there is a concern that discharge of generated water at the cathode may be hindered.

An object of the present invention is to solve the above problems and to provide a high-performance and inexpensive electrode and a method for manufacturing the same.

[0012]

Means for Solving the Problems The present invention has the following arrangement to solve the above-mentioned problems.

That is, the electrode of the present invention comprises at least
An electrode comprising an electrode substrate and an electrode catalyst layer, wherein the electrode substrate has a porous conductive sheet having a nonwoven structure, and at least between the electrode substrate and the electrode catalyst layer. A conductive intermediate layer containing an inorganic conductive substance and a hydrophobic polymer is provided.

Further, according to the method for producing an electrode of the present invention, a conductive intermediate layer containing at least an inorganic conductive substance is provided on an electrode substrate made of a porous conductive sheet having a non-woven structure, An electrode catalyst layer is provided on the layer.

Further, an electrochemical device and a fuel cell according to the present invention are characterized in that the above-mentioned electrodes are applied.

Further, the moving object and the automobile according to the present invention are characterized in that the fuel cell is used as a power supply source.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described.

According to the present invention, there are provided an electrode base material having electronic conductivity,
The purpose of the present invention is to suppress the infiltration of the catalyst into the substrate, which is a problem when using a porous conductive sheet having a nonwoven structure having excellent gas diffusion and drainage properties. An electrode characterized by providing a conductive intermediate layer containing at least an inorganic conductive substance and a hydrophobic polymer between layers.

The form of the inorganic conductive substance contained in the conductive intermediate layer in the present invention is not particularly limited, such as fibrous or particulate, and may be in any shape that cannot be distinguished from any of them, or may be a mixture thereof. There may be. For example, in a fibrous form, the fiber length is preferably 20
μm to 20 mm (more preferably 20 μm to 3 mm),
The diameter is preferably 3 μm to 15 μm (more preferably 5 μm
μm to 10 μm). With respect to the fiber length, it is difficult to produce short carbon fibers having a value lower than the lower limit of the numerical range, and if the fiber length exceeds the upper limit of the numerical range, it becomes difficult to prepare the conductive intermediate layer, which may be undesirable. If the diameter is below the lower limit of the above numerical range, the production of the conductive fiber becomes difficult, and if it exceeds the upper limit of the above numerical range, the production of the conductive intermediate layer becomes difficult, which is not preferable. In the particulate form, the particle size is preferably 1
0 nm to 10 μm (more preferably 20 nm to 100 n
m). If the particle size is below the lower limit of the above numerical range, it becomes difficult to produce conductive particles, and if it exceeds the upper limit of the above numerical range, it becomes difficult to produce the conductive intermediate layer, which may be undesirable.

Examples of the material of the inorganic conductive substance include various graphitic and carbonaceous carbon materials, metals and metalloids, but are not particularly limited. When the electrode of the present invention is used in an electrochemical device, it is preferable to use a carbon material as the inorganic conductive material from the viewpoint of corrosion resistance.

As such a carbon material, carbon black such as oil furnace black, acetylene black, thermal black and channel black is preferable from the viewpoint of the electron conductivity and the specific surface area. Oil furnace black includes Vulcan XC-72, Vulcan P, Black Pearls 88 manufactured by Cabot Corporation.
0, Black Pearls 1100, Black Pearls 13
00, Black Pearls 2000, Legal 400, Ketchen Black EC manufactured by Lion, # 3 manufactured by Mitsubishi Chemical
150, # 3250, etc., and acetylene black includes Denka Black manufactured by Denki Kagaku Kogyo KK

In addition to carbon black, there are fired bodies obtained from organic compounds such as natural graphite, pitch, coke, polyacrylonitrile, phenol resin and furan resin, for example, artificial graphite and carbon. These carbon materials may be in the form of fibers in addition to particles. It is also possible to use carbon materials obtained by post-processing these carbon materials.

Among the above carbon materials, Vulcan XC-72 manufactured by Cabot, Ketchen Black EC manufactured by Lion, Denka Black manufactured by Denki Kagaku Kogyo, Toray ( Torayca Chop Fibers manufactured by Toray Industries, Inc., Torayca Milled Fibers manufactured by Toray Industries, Inc., or a mixture thereof is preferably used.

The conductive intermediate layer in the present invention contains a polymer for the purpose of binding between inorganic conductive substances, and this polymer is a hydrophobic polymer. When a hydrophilic polymer is used for the conductive intermediate layer, a flooding phenomenon in which water generated at the cathode is clogged with the electrode catalyst layer, the conductive intermediate layer, or the electrode base material is likely to occur. If the polymer contained in the conductive intermediate layer is a hydrophobic polymer, the flooding is unlikely to occur.

As such a hydrophobic polymer, although not particularly limited, an inorganic conductive substance is well dispersed,
A polymer that does not degrade in an oxidation-reduction atmosphere in a fuel cell is preferred. Such a polymer includes a polymer having a fluorine atom, and is not particularly limited. For example, polytetrafluoroethylene (PTFE), perfluoroalkyl vinyl ether-tetrafluoroethylene copolymer (PFA), hexa Fluoropropylene-tetrafluoroethylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (CTFE), polyvinylidene fluoride (PVDF), hexafluoropropylene-vinylidene fluoride copolymer Coalescence, polyvinyl fluoride (PV
F) or a copolymer of these monomer units with other monomers such as ethylene and styrene, and further, a blend and the like can also be used. Further, in addition to the above-mentioned polymer having a fluorine atom, a sulfonic acid group, a phosphoric acid group, a carboxyl group, a hydroxyl group, a hydrophilic functional group such as an amino group,
It is also possible to use a polymer having substantially no amide bond, ester bond or the like. The expression "substantially does not have" means that the compound does not have a hydrophilic functional group or the like to such an extent that the hydrophobicity is reduced so as to adversely affect the effect of the present invention. Although not particularly limited, for example,
In the case of the above-mentioned hydrophilic functional group, if the ratio of the monomer units is preferably a hydrophobic monomer unit / hydrophilic monomer unit of preferably 0.1 or less (more preferably 0.05 or less), copolymerization or mixing is possible. No problem. The proportion of these hydrophobic polymers contained in the conductive intermediate layer depends on the inorganic conductive substance, but is 0.5 to 70% by weight.
Is preferably included in the range of, more preferably 1 to
50%, even more preferably 5-40%. If the amount of the hydrophobic polymer is large, the electric resistance increases and the electrode performance decreases. On the other hand, when the amount of the hydrophobic polymer is small, the binding force between the inorganic conductive substance and the electrode substrate decreases, and the conductive intermediate layer peels or falls off.

In the conductive intermediate layer of the present invention, various additives can be used in addition to the above-mentioned inorganic conductive substance and polymer. Such additives include, but are not particularly limited to, surfactants, alcohols, esters, and the like, which are used to improve the coating performance when applying the conductive intermediate layer to the electrode substrate. It is useful.

In order to provide the conductive intermediate layer of the present invention on a porous conductive sheet having a nonwoven structure, a coating liquid containing an inorganic conductive substance and a hydrophobic polymer for forming the intermediate layer is prepared. (The two may be mixed, or each may be a separate coating liquid, preferably the former.) The coating liquid is applied on a porous conductive sheet and dried. As the coating method, a coating method according to the viscosity or solid content of the coating liquid is selected, and it is not particularly limited. However, a knife coater, a bar coater, a spray, a dip coater, a spin coater, a roll coater, a die coater A general coating method such as a tar coater or a curtain coater is used. The coating liquid of the inorganic conductive substance and the hydrophobic polymer is
A coating liquid viscosity, a solid content, or a solvent according to a polymer type and a coating method is used, and is not particularly limited. When PTFE, PFA, FEP, or the like is used as the hydrophobic polymer, a polymer dispersion of water or various solvents in which these polymers are dispersed is used, and a polymer solution is used for a soluble polymer such as PVDF. The order in which the inorganic conductive substance and the hydrophobic polymer are dispersed or dissolved in the solvent is not particularly limited, but a liquid in which the hydrophobic polymer is dispersed or dissolved in the solvent is prepared in advance, and then the inorganic conductive substance is dispersed. Dispersing is preferable in that a coating liquid having good dispersibility can be obtained.

The thickness of the conductive intermediate layer of the present invention should be appropriately determined according to the ease of penetration of the coating liquid into the electrode substrate and the required electrode performance, and is not particularly limited. When the porosity of the electrode substrate used is high and the coating liquid easily penetrates, the coating is applied thick, and when the penetration of the coating liquid is small, the coating is applied thinly. Generally, 1 to 100 μm
It is. When the thickness of the conductive intermediate layer is too thin, the electrode catalyst coating liquid permeates when the electrode catalyst layer is applied thereon. On the other hand, if the conductive intermediate layer is too thick, gas permeability and water permeability to the electrode catalyst layer are impaired, so that the electrode performance is reduced.

The conductive intermediate layer according to the present invention is characterized by containing an inorganic conductive substance, but the structure of the intermediate layer is not particularly limited. However, it is an effective embodiment to have a porous structure in order to improve electron conductivity, gas diffusivity and drainage. In particular, a three-dimensional network microporous structure composed of an inorganic conductive substance-hydrophobic polymer composite is a further preferred embodiment. That is, the inorganic conductive substance-hydrophobic polymer composite is a composite in which the inorganic conductive particles and the hydrophobic polymer are well dispersed. This composite is characterized in that it has a three-dimensional network microporous structure. In addition, "3D network microporous structure"
The term “state” refers to a state in which the inorganic conductive substance-hydrophobic polymer composite has a three-dimensionally connected three-dimensional network structure.

The three-dimensional network microporous structure of the inorganic conductive substance-hydrophobic polymer composite has a microporous diameter of 0.05
To 5 μm, more preferably 0.1 μm.
1 to 1 μm. The microporous diameter is determined by scanning electron microscope (S
EM) or the like, the average of 20 or more, preferably 100 or more, can be obtained from a photograph of the surface, and usually 100 can be measured. When manufactured by the wet solidification method described below, the conductive intermediate layer having a microporous structure preferably has an average of as many pore diameters as possible because the distribution of the microporous diameter is wide.

The porosity of the three-dimensional network microporous structure is 10
It is preferably about 95%. More preferably 50 to
90%. The porosity is a percentage (%) obtained by subtracting the volume occupied by the inorganic conductive substance-hydrophobic polymer composite from the total volume of the conductive intermediate layer and dividing by the total volume of the conductive intermediate layer. The conductive intermediate layer is subjected to wet coagulation after applying the coating liquid to the electrode substrate, but when it is difficult to determine the porosity of the conductive intermediate layer alone, the porosity of the electrode substrate is determined. It is also possible to determine the porosity including the base material and the conductive intermediate layer in advance, and then determine the porosity of the conductive intermediate layer alone.

The conductive intermediate layer having a three-dimensional network microporous structure has a high porosity, good gas diffusivity, good discharge of generated water, and good electron conductivity. In the conventional porous method, the inorganic conductive particle diameter and the particle diameter of the added polymer are increased, and pores are formed by using a pore-forming agent. The contact resistance between the conductive materials increases. On the other hand, in the three-dimensional network microporous structure formed by the wet solidification method, the hydrophobic polymer composite containing the inorganic conductive substance is in a three-dimensional network, so electrons can easily conduct through this polymer composite. In addition, because of the microporous structure, gas diffusivity and generated water discharge are excellent.

In the conductive intermediate layer having a three-dimensional network microporous structure, the hydrophobic polymer is preferably polyvinylidene fluoride (PVDF) or hexafluoropropylene-vinylidene fluoride copolymer. These hydrophobic polymers can obtain a three-dimensional network microporous structure by a wet coagulation method using an aprotic polar solvent and a protic polar solvent or the like as a coagulating solvent. Solvents for these polymers include N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC),
Examples include propylene carbonate (PC) and dimethylimidazolidinone (DMI). Examples of the coagulating solvent include water, lower alcohols such as methanol, ethanol, and isopropanol; esters such as ethyl acetate and butyl acetate; Various group-based or halogen-based organic solvents are used.

As a method for producing the conductive intermediate layer having a three-dimensional network microporous structure, a method using a wet solidification method is preferable. In this wet coagulation method, after applying an inorganic conductive substance-hydrophobic polymer solution composition, this coating layer is brought into contact with a coagulation solvent for the polymer to coagulate and precipitate the inorganic conductive substance-hydrophobic polymer solution composition. Solvent extraction is performed simultaneously. The inorganic conductive substance-hydrophobic polymer solution composition is one in which the inorganic conductive substance is uniformly dispersed in the hydrophobic polymer solution. If the dispersion state is bad, during wet coagulation,
The inorganic conductive substance and the hydrophobic polymer cannot form a composite, and only the polymer has a three-dimensional network microporous structure, and sufficient performance cannot be obtained.

The method of applying the coating solution to the substrate when producing the conductive intermediate layer having a three-dimensional network microporous structure is not particularly limited, but may be a knife coater, a bar coater, or the like. General coating methods such as spray, dip coater, spin coater, roll coater, die coater, curtain coater and the like are used. Also,
The method of contacting the inorganic conductive substance-hydrophobic polymer composite with the coagulation solvent during wet coagulation is not particularly limited, but the base material is immersed in the coagulation solvent, and only the coating layer is formed of the coagulation solvent. Examples of the method include contacting with a liquid surface, showering or spraying a solidified solvent on a coating layer, and the like.

The electrode substrate used in the present invention has a porous conductive sheet having a non-woven structure. Non-woven structure means that the fibers do not have a regular structure such as woven fabric, knitting, braid, lace, etc., but have an irregular fiber structure such as paper, felt, non-woven fabric, etc. Say what is. The papermaking body is a thin and flat paper-like structure obtained by using a solution in which fibers or particles and a binder are dissolved or dispersed and scooping it up on a net according to the principle of papermaking. Felts and nonwoven fabrics are obtained by entanglement of these fibers with long fibers while using short fibers for the papermaking body. A crocheted fiber is made of felt and entangled with air flow or water flow when a long fiber is hooked and entangled. All of these papermaking bodies, felts, and nonwoven fabrics are characterized by irregularly entangled fibers. On the other hand, a woven fabric or a knitted fabric has a regular structure, so that thickness unevenness is likely to occur. The electrode base material is a porous conductive sheet for achieving both gas diffusivity and electric resistance, and among them, a nonwoven structure in which fibers are irregularly entangled with each other, such as a papermaking body, felt, nonwoven fabric, etc. This is preferable in that the thickness unevenness is small.

Examples of such a porous conductive sheet having a nonwoven structure include a porous conductive sheet containing a conductive inorganic material as a main constituent material. The conductive inorganic material includes a fired body made of polyacrylonitrile. And carbon materials such as graphite and expanded graphite, stainless steel, molybdenum, titanium and the like. The form of the conductive inorganic material is not particularly limited, such as fibrous or particulate, but from the viewpoint of electrode performance, a fibrous inorganic conductive fiber is preferred. Above all, when used in an electrochemical device such as a fuel cell, a porous conductive sheet having a nonwoven structure using carbon fibers, particularly short carbon fibers, is preferable from the viewpoint of corrosion and electric resistance. Carbon paper TGP series and SO series manufactured by Co., Ltd. are preferably used. Although the material of the carbon fiber will be described later, it is preferable to use polyacrylonitrile, pitch, or a low-boiling organic compound as a raw material.

The electrode substrate of the present invention has a thickness of 2.9M in the thickness direction.
When a uniform surface pressure of Pa is applied, the thickness is 0.02 to 0.
It is preferably 3 mm. More preferably 0.04 to
0.2 mm. If the thickness is less than 0.02 mm, the electrode substrate will be buried in the gas flow path of the separator when used in a fuel cell, and the diffusion and permeability in the plane direction will be low, or the strength will be weak and workability will be poor. If it is thicker than 0.3mm,
The electric resistance in the thickness direction increases. In addition, the thickness is sandwiched between two glassy carbon plates having a uniform thickness and a smooth surface by pressing the electrode substrate with a uniform surface pressure of 2.9 MPa, and when the electrode substrate is not sandwiched. It is determined from the difference between the upper and lower indenters at that time. In measuring the interval between the indenters, the interval between the indenters is measured by a micro-displacement detector at both ends sandwiching the center point of the indenter, and the interval between the indenters is calculated as an average value of the intervals between both ends. In order to make the surface pressure uniform, one of the indenters is received by a ball seat, and the angle between the pressing surfaces of the upper and lower indenters is made variable.

When a uniform surface pressure of 2.9 MPa is applied in the thickness direction, the thickness of the carbon fiber paper contained in the electrode base material having the above-mentioned thickness measured at a surface pressure of 13 kPa is 0.1 to 2 m.
m is preferable, and 0.2 to 1.2 mm is more preferable. 2
If it exceeds mm, the carbon fiber paper becomes bulky, the short carbon fibers face the thickness direction, or the strength of the carbon fiber paper becomes weak.
In order to reduce the thickness to less than 0.1 mm, it is necessary to strongly bind short carbon fibers with a large amount of a polymer substance.

The basis weight of the electrode substrate is 10 to 220 g /
m ² is preferred. More preferably, 20 to 120
g / m ² . If it is less than 10 g / m ² , the strength of the electrode substrate will be low. In addition, when the polymer electrolyte membrane, the electrode catalyst layer, and the electrode base material are integrated or assembled into a battery, the electrode base material becomes thin and buried in the electrode catalyst layer, resulting in insufficient diffusion and transmission effects in the surface direction. Become. If it exceeds 220 g / m ² , the electrode base material becomes thicker when assembled into a battery, and the resistance increases.

The density of the electrode substrate is 2.9MP in the thickness direction.
0.3 to 0.8 g / cm when a uniform surface pressure of a is applied
Preferably it is ³ . More preferably 0.35
0.7 g / cm ³ , and more preferably 0.4 to
0.6 g / cm ³ . The density of the electrode substrate when a uniform surface pressure of 2.9 MPa is applied in the thickness direction is determined by the basis weight of the electrode substrate and the electrode substrate when a uniform surface pressure of 2.9 MPa is applied in the thickness direction. Is calculated from the thickness. The electrode substrate needs to have a high porosity in order to increase the diffusion and permeability, but the density when a uniform surface pressure of 2.9 MPa is applied in the thickness direction is 0.8 g / cm ^3. If it is larger than this, the porosity decreases and the diffusion and permeability become insufficient. On the other hand, when it is smaller than 0.3 g / cm ³ , the resistance value in the thickness direction increases.

The electrode substrate has a pressure loss of 98 Pa (10 mmAq) when air of 14 cm / sec is transmitted in the thickness direction in a state where the pressure is not applied by the surface pressure in the thickness direction.
The following is preferable in view of gas diffusibility of the electrode substrate.
More preferred is 29 Pa (3 mmAq) or less,
More preferably, it is 9.8 Pa (1 mmAq) or less.

The tensile strength of the electrode substrate was 0.49 N /
The width is preferably 10 mm or more, more preferably 1.96 N / 10 mm or more, and even more preferably 4.9 N / 10 mm or more. When the tensile strength is low, there is a problem that the possibility of breakage of the sheet increases in high-order processing in which the sheet is used as a fuel cell current collector.

[0044] In addition to the above electrode substrate,
Including a paper-like sheet obtained by binding inorganic conductive fibers oriented in a random direction in a substantially two-dimensional plane with a polymer substance, the length of the inorganic conductive fibers is at least 3 mm
In addition, a porous conductive sheet having a thickness of at least 5 times the thickness of the sheet can also be used. Here, the thickness of the sheet is measured according to JIS P8118. The surface pressure during measurement is 13 kPa. The meaning that the inorganic conductive fibers are oriented substantially in a two-dimensional plane is as follows.
This means that the inorganic conductive fibers lie roughly to form one surface. This makes it possible to prevent a short circuit with the counter electrode due to the inorganic conductive fiber and breakage of the inorganic conductive fiber.

In order to increase the strength and handleability of the porous conductive sheet and to orient the inorganic conductive fiber substantially in a two-dimensional plane, the length of the inorganic conductive fiber is at least 3 mm or more. It is preferably at least 4.5 mm, more preferably at least 6 mm. If it is less than 3 mm, it is difficult to maintain strength and handling properties. Further, in order to orient the inorganic conductive fibers in a random direction substantially in a two-dimensional plane, the length of the inorganic conductive fibers is at least 5 times, preferably at least 8 times the thickness of the porous conductive sheet, More preferably, it is 12 times or more. If it is less than five times, it is difficult to secure the orientation in two dimensions. The upper limit of the length of the inorganic conductive fiber is preferably 30 mm or less, more preferably 15 mm or less, and still more preferably 8 mm or less in order to substantially orient in a random direction in a two-dimensional plane. If the inorganic conductive fibers are too long, poor dispersion is likely to occur, and many fibers may remain in a bundle. In such a case, the porosity of the bundle-shaped portion is low, and the thickness at the time of pressurization is large, so high pressure is applied at the time of pressurization. Problems, such as a thin layer, are likely to occur.

Further, the form of the inorganic conductive fiber is preferably a straight line so that a short circuit with the counter electrode by the fiber can be more completely prevented. Here, the linear inorganic conductive fiber refers to a linearity with respect to the length L when a length L (mm) in a length direction of the fiber is taken in a state where an external force for bending the inorganic conductive fiber is removed. Is measured from the deviation Δ (mm)
/ L is about 0.1 or less. On the other hand, non-linear fibers have the disadvantage that they tend to be oriented in a three-dimensional direction when oriented in a random direction in a substantially two-dimensional plane.

As a method for orienting the inorganic conductive fibers in a porous conductive sheet in a random direction in a substantially two-dimensional plane, a wet method of dispersing the inorganic conductive fibers in a liquid medium to form a paper is used. Alternatively, there is a dry method in which inorganic conductive fibers are dispersed in the air and accumulated. To ensure that the inorganic conductive fibers are oriented substantially in a two-dimensional plane and to increase the strength of the inorganic conductive fibers, a wet method is preferred. Examples of the carbon fiber include polyacrylonitrile (PAN) -based carbon fiber, phenol-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, and the like. Other examples include carbon fibers made of low-boiling organic compounds as raw materials, such as benzene, naphthalene, and creitol oil. However, among these, PAN-based carbon fibers are preferred. PAN-based carbon fibers have higher compressive strength and tensile elongation at break than pitch-based carbon fibers, and are less likely to break. This is considered to be due to a difference in crystallization of carbon constituting the carbon fiber. In order to obtain carbon fibers that are difficult to break, the heat treatment temperature of the carbon fibers should be 2,
500 ° C. or lower is preferable, and 2,000 ° C. or lower is more preferable.

The short carbon fiber used in the electrode substrate of the present invention satisfies the following expression in relation to the diameter D (μm), the tensile strength σ (MPa), and the tensile modulus E (MPa). Good to be. This is because an electrode substrate including carbon fiber paper made of such short carbon fibers is hard to break. That is, the shorter carbon fibers have a smaller diameter, a higher tensile strength, and a lower tensile modulus, the harder the carbon short fibers are to be broken, and the more difficult the electrode substrate is to be broken when pressurized. .sigma ./ (E.times.D) .gtoreq.0.5.times.10.sup.- ³ where the tensile strength and tensile modulus of the carbon fiber are JIS R
It is measured according to 7601. In the case of a flat carbon fiber, the average value of the major axis (a) and the minor axis (b) ((a + b) /
Let 2) be the diameter. When different types of short carbon fibers are mixed, D, σ, and E are each used as a weighted average value. Preferably, σ / (E × D) ≧ 1.1 × 10
^-3 , more preferably σ / (E × D) ≧ 2.4 × 1
0 ^-3 .

The tensile elongation at break of short carbon fibers is preferably 0.7% or more, more preferably 1.2% or more, and further preferably 1.8%, because of the strength of the electrode substrate.
That is all. The tensile elongation at break is a value obtained by dividing the tensile strength (σ) by the tensile modulus (E).

Further, since breakage of the short carbon fiber occurs in various situations, the tensile strength of the short carbon fiber is preferably 500 MPa or more, more preferably 1,000 MPa or more, and more preferably 2,000 MPa or more. Is more preferred.

The diameter of the inorganic conductive fiber used for the electrode substrate is preferably 20 μm or less. More preferably, it is 12 μm or less, and still more preferably, 8 μm or less. On the surface of the electrode substrate, the diameter of the inorganic conductive fiber is 5 to 5.
A 10 times diameter void is observed. This gap increases as the fiber diameter increases. The conductive intermediate layer of the present invention suppresses a decrease in electrode performance due to the electrode catalyst layer penetrating into the void. If the gap is too large, the conductive intermediate layer needs to be thickened, which impairs gas permeability and water dischargeability. Therefore, the fiber diameter is preferably smaller.
Further, the thinner the inorganic conductive fiber is, the harder it is to break when pressurized in the thickness direction. On the other hand, if the diameter of the inorganic conductive fiber is too small, it is difficult for the electrode catalyst layer to penetrate into the electrode base material during integration, so that the fiber diameter is preferably 2 μm or more. When fibers having different diameters are mixed, the diameter is determined by weight average.

The volume resistivity of the inorganic conductive fiber used for the electrode base material is preferably 200 μΩ · m or less, more preferably 50 μΩ · m or less, to reduce the resistance of the electrode base material.
μΩ · m or less is more preferable. The volume resistivity of the inorganic conductive fiber is measured according to JIS R7601. When the fiber length specified by the measurement prescription cannot be obtained, the measurement is performed using the obtained fiber length.

When carbon fibers are used for the electrode substrate, the ratio of the number of oxygen atoms to the number of carbon atoms on the surface (oxygen atom number / carbon atom number) by X-ray photoelectron spectroscopy is 0.35 or less, preferably 0%. .2, more preferably 0.1 or less. This is because, when a carbon fiber paper is obtained by a wet papermaking method, if the atomic ratio of oxygen atoms to carbon atoms is high, dispersion of short carbon fibers becomes difficult and dispersion failure increases. If it exceeds 0.35, it becomes difficult to obtain a uniform carbon fiber paper. In order to lower the atomic ratio between oxygen atoms and carbon atoms, there are methods to stop the surface treatment of carbon fiber and the application of a sizing agent, and to remove oxygen atoms from the surface by heat treatment in an inert or reducing atmosphere. .

The electrode substrate used in the present invention is also preferably made of a porous conductive sheet in which inorganic conductive particles, particularly flexible inorganic conductive particles, are arranged in a sheet. As a result, the components are less likely to fall off, or hard to break even when mechanical force acts, the electric resistance is low,
In addition, it is possible to provide an inexpensive electrode substrate. In particular, it is preferable to use expanded graphite particles as the inorganic conductive particles having flexibility to achieve the above object.

Here, the expanded graphite particles are defined as graphite particles,
Graphite particles obtained by being intercalated with sulfuric acid, nitric acid, etc., and then expanded by rapid heating. Usually, the interlayer distance in the crystal structure of the expanded graphite particles is about 50 to 500 times that of the raw graphite particles.

The expanded graphite particles themselves are rich in shape deformability. This property is expressed in terms of flexibility.
This flexibility is observed by the morphological compatibility of the expanded graphite particles with the other objects adjacent to the expanded graphite particles. This morphological compatibility is that, when the expanded graphite particles are subjected to a pressurizing action in a state where at least a part of them are overlapped, they are deformed to each other according to the pressurized state, and the particles are at least partially bonded. To be observed. In addition, the morphological compatibility is based on expanded graphite particles and auxiliary materials used when they are arranged in a sheet shape while ensuring gas permeability (for example, a conventionally used flexible material such as carbon black). When the inorganic conductive particles having no property, or the inorganic conductive fibers conventionally used such as carbon fiber) are pressed together, the expanded graphite particles are deformed along the outer shape of the auxiliary material. Is observed by being bonded to this auxiliary material.

In a preferred embodiment, the porous conductive sheet used for the electrode substrate of the present invention contains, in addition to the conductive fine particles having flexibility, other conductive particles and conductive fibers. When both the conductive fibers and the conductive particles are made of an inorganic material, an electrode substrate excellent in heat resistance, oxidation resistance, and elution resistance can be obtained.

The porous conductive sheet may contain inorganic conductive particles having no flexibility, for example, carbon black powder, graphite powder, metal powder, ceramic powder, etc. % Or more are preferably the inorganic conductive particles having flexibility, more preferably 50% by weight or more, and even more preferably 70% by weight or more.

In addition, the porous conductive sheet used for the electrode substrate of the present invention can contain a water-repellent polymer.
Particularly, fluororesins such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA) are preferably used because they have high water repellency. Can be

When the porous conductive sheet is used as an electrode substrate (collector) for a fuel cell, a water-repellent treatment is indispensable. In this case, the water-repellent polymer is composed of inorganic conductive fibers and inorganic conductive fibers. It also provides an adhesive effect with the conductive particles. This is useful in terms of sheet strength and electrical resistance. PTFE,
FEP and PFA are more preferable because they have high water repellency and oxidation resistance required for a fuel cell current collector, and PTFE and PFA have an effect of lowering electric resistance.

The content of the water-repellent polymer is preferably from 10 to 50% by weight, more preferably from 1 to 50% by weight, based on the total weight of the sheet.
It is 5 to 45% by weight, more preferably 20 to 40% by weight. If the content is small, water repellency and sheet strength will be low,
When the content is large, the electric resistance increases.

The measurement of the electric resistance R of the porous conductive sheet is as follows.
According to the following. Width 50mm, length 200mm, thickness 1.5m
Two test electrode plates are prepared in which a copper foil having a width of 50 mm, a length of 200 mm, and a thickness of 0.1 mm is adhered to one side of a glassy carbon plate having a flat surface of m. The two test electrode plates are maintained at a substantially uniform distance, and the surfaces of the glassy carbon plate are positioned facing each other. One end of each of the two test electrode plates is provided with a terminal for current, and the other end is provided with a terminal for voltage. A sheet cut into a circle having a diameter of 46 mm is inserted into the gap and placed on the center of two test electrode plates. The test electrode plate is moved so that a pressure of 0.98 MPa acts on the placed sheet. At the current terminal, a current of 1 A flows between the two test electrode plates. The voltage V (V) at this time is measured at the voltage terminal. The value of the measured voltage V is used, and the resistance R (mΩ · c
m ² ) is required. R = V × 2.4 × 2.4 × π × 1000 where π is a pi.

The electric resistance of the porous conductive sheet is 100
mΩ · cm ² or less, preferably 50 mΩ · c
m ² or less, more preferably 15 mΩ · cm ² or less. The electric resistance of the porous conductive sheet containing a water-repellent fluororesin is 150 mΩ · cm ²
Preferably less, more preferably 70mΩ · cm ² or less, still more preferably 30 m [Omega] · cm ² or less.

The electrode base material of the present invention becomes strong in compression and tensile strength by binding with a polymer substance, increases strength and handling properties, and may cause inorganic conductive fibers to come off the sheet.
It is possible to prevent the sheet from turning in the thickness direction. As a method of binding the polymer material, when the inorganic conductive fiber is oriented in a random direction in a substantially two-dimensional plane, a method of mixing a fibrous, granular, or liquid polymer material, There is a method of attaching a fibrous, liquid polymer substance to an aggregate in which conductive fibers are oriented in a random direction in a substantially two-dimensional plane. The concept of a liquid includes an emulsion, a dispersion, a latex, and the like, in which fine particles of a polymer substance are dispersed in a liquid and can be handled substantially as a liquid. In order to strengthen the binding of the inorganic conductive fibers and to lower the electrical resistance of the porous conductive sheet and, consequently, the current collector, the polymer substance binding the inorganic conductive fibers is formed of a fibrous, emulsion, or disperse material. John and latex are preferred. In the case of a fibrous polymer substance, it is preferable to use a filament yarn to reduce the content.

As the polymer substance binding the inorganic conductive fiber, a polymer substance having carbon or silicon in the main chain is preferable. For example, polyvinyl alcohol (PVA), polyvinyl acetate (vinyl acetate), polyethylene terephthalate ( PET), polypropylene (PP), polyethylene,
Polystyrene, polyvinyl chloride, polyvinylidene chloride,
Acrylic resin, thermoplastic resin such as polyurethane, phenol resin, epoxy resin, melamine resin, urea resin,
In addition to thermosetting resins such as alkyd resins, unsaturated polyester resins, acrylic resins, and polyurethane resins, thermoplastic elastomers, butadiene / styrene copolymers (SB
R), butadiene / acrylonitrile copolymer (NB
R) and other elastomers, rubbers, cellulose, pulp and the like can be used. A hydrophobic polymer containing a fluorine atom,
That is, using a water-repellent resin such as a fluororesin, the porous conductive sheet may be subjected to a water-repellent treatment simultaneously with the binding of the inorganic conductive fibers.

In order to make the electrode base material less likely to be broken at the time of pressurization, it is preferable that the polymer material binding the inorganic conductive fibers be soft. When the polymer material is used in a fibrous or granular form, a high molecular weight material is required. If the molecular substance is a soft polymer substance such as a thermoplastic resin, an elastomer, rubber, cellulose, pulp or the like, the electrode substrate is not easily broken when pressurized, which is preferable. When the polymer substance is used in a liquid form,
Polymeric substances include thermoplastics, elastomers, rubbers,
A thermosetting resin modified with a soft material such as a thermoplastic resin, an elastomer, or a rubber is preferable, and a thermoplastic resin, an elastomer, or a rubber is more difficult to be broken when the electrode substrate is pressurized, and is more preferable.

The high-molecular substance preferably has a compression elastic modulus at 23 ° C. of 4,000 MPa or less, preferably 2,0 MPa.
More preferably, the pressure is not more than 00 MPa.
More preferably, it is Pa or less. The reason is that the polymer substance having a low compression modulus relieves the stress applied to the binding portion so that the binding is not easily released, and also reduces the stress applied to the inorganic conductive fiber so that the inorganic conductive fiber is hardly broken.

In the polymer electrolyte fuel cell, at the cathode (air electrode, oxygen electrode), water as an electrode reaction product,
Water permeating the electrolyte is generated. At the anode (fuel electrode), the fuel is supplied humidified to prevent the polymer electrolyte membrane from drying. Since the condensation and stagnation of the water and the swelling of the polymer substance due to water hinder the supply of the electrode reactant, the lower the water absorption of the polymer substance, the better. It is preferably at most 20%, more preferably at most 7%.

The content of the polymer substance in the electrode substrate is
Preferably it is in the range of 0.1 to 30% by weight. In order to lower the electrical resistance of the porous conductive sheet, it is better that the content of the polymer substance is small, but if it is less than 0.1% by weight, the strength that can withstand handling is insufficient, and the inorganic conductive fibers often fall off. . Conversely, if the content exceeds 30% by weight, there arises a problem that the electric resistance of the porous conductive sheet increases.
More preferably, it is in the range of 1 to 20% by weight.

The porous conductive sheet may be used as it is as an electrode substrate, or may be used after further post-treatment. Examples of post-treatments include water repellency treatment to prevent gas diffusion and permeability decrease due to water retention, partial water repellency to form a water discharge path, hydrophilic treatment, and treatment to reduce resistance. And the addition of carbonaceous powder.

In general, the electrode substrate is sometimes pressed and broken in the thickness direction when the polymer electrolyte membrane, the electrode catalyst layer, and the electrode substrate are integrated or used as a battery. In addition, when used as a battery, since pressure is applied in the thickness direction while facing the grooved separator, a large pressure is applied to the portion of the grooved separator facing the peak, and in addition to the portion facing the boundary between the peak and valley. Is fragile. When the electrode substrate is broken, the broken fibers may fall off, the strength of the electrode substrate may be reduced, the electric resistance in the surface direction may be increased, and the battery may not be used.

As described above, the porous conductive sheet of the present invention, which can be used as an electrode substrate, applies a uniform surface pressure of 2.9 MPa in the thickness direction for 2 minutes, and after releasing the surface pressure. Is preferably 3% or less.
This is because an electrode substrate having a weight reduction rate of more than 3% is weak after the surface pressure is released, and has a problem that it is easily broken by handling. Thereby, it is hard to be broken at the time of pressurization, and it can be prevented that the fuel cell cannot be used due to the breakage of the electrode substrate. It is preferably at most 2%, more preferably at most 1%.

The measurement of the weight loss rate is performed as follows. First, the electrode substrate is cut into a circle having a diameter of 46 mm, and the weight is measured. Next, the electrode base material, which is larger than the electrode base material and cut by two glassy carbon plates having a smooth surface, is sandwiched between the electrode base materials and 2.9 MPa per area of the electrode base material.
And keep it for 2 minutes. Remove the electrode substrate by removing the pressure and turn the surface of the electrode substrate to the vertical direction.
Drop from a height of 0 mm. After performing this drop 10 times, the weight is measured, and the weight reduction rate is calculated.

In order to prevent breakage of the inorganic conductive fiber and to reduce the weight reduction rate to 3% or less, the fiber used is preferably a short carbon fiber obtained by cutting a carbon fiber. Preferably, it is stretched at the time of heat treatment.

The electrode catalyst layer in the electrode of the present invention is not particularly limited, and a known one can be used. The electrode catalyst layer includes a catalyst and an electrode active material necessary for an electrode reaction, and further includes a substance that contributes to electron conduction and ion conduction that promote the electrode reaction. In addition, when the electrode active material (a substance that oxidizes or reduces) is a gas, it is necessary to have a structure that allows the gas to easily permeate, and a structure that promotes the discharge of the generated material accompanying the electrode reaction is required. is there. When the electrode of the present invention is used for a fuel cell, the electrode active material may be hydrogen, oxygen, or the like, and the catalyst may be preferably a noble metal particle such as platinum. Further, it is preferable to include a material for improving the conductivity of the electrode catalyst layer, and the form is not particularly limited. For example, it is preferable to have conductive particles. As a material for improving conductivity, there is an electronic conductor. Examples of the electron conductor include carbon black and the like, and particularly, platinum-supported carbon and the like are preferably used as the carbon black supporting the catalyst. The electron conductor is carbon black, the ionic conductor is a proton exchange resin, and the reaction product is water. The electrode catalyst layer is required to have a structure in which the catalyst, the electron conductor, and the ionic conductor are in contact with each other, and the active material and the reaction product can efficiently enter and exit. In addition, a polymer compound is preferably used for improving ionic conductivity, improving binding properties of a material, or improving water repellency. It is preferable that the electrode catalyst layer contains at least catalyst particles, conductive particles, and a polymer compound.

When the electrode of the present invention is used in a fuel cell, the catalyst contained in the electrode catalyst layer can be a known catalyst, and is not particularly limited, but may be platinum, palladium, ruthenium, iridium, or the like. A noble metal catalyst such as gold is preferably used. Further, two or more elements such as alloys and mixtures of these noble metal catalysts may be contained.

The electron conductor (conductive material) contained in the electrode catalyst layer is not particularly limited, but an inorganic conductive substance is preferably used from the viewpoint of electron conductivity and contact resistance. Among them, carbon black, graphite or carbonaceous carbon materials, and metals and metalloids are exemplified. As such a carbon material, carbon black such as channel black, thermal black and furnace black is preferable from the viewpoint of electron conductivity and specific surface area.
Oil furnace black includes Vulcan XC-72, Vulcan P, Black Pearls 88 manufactured by Cabot Corporation.
0, Black Pearls 1100, Black Pearls 13
00, Black Pearls 2000, Legal 400, Ketchen Black EC manufactured by Lion, # 3 manufactured by Mitsubishi Chemical
150, # 3250, etc., and acetylene black includes Denka Black manufactured by Denki Kagaku Kogyo KK In addition to carbon black, there are artificial graphite and carbon obtained from organic compounds such as natural graphite, pitch, coke, polyacrylonitrile, phenol resin, and furan resin. These carbon materials may be in the form of fibers in addition to particles. It is also possible to use carbon materials obtained by post-processing these carbon materials. Among such carbon materials, Vulcan XC-72 manufactured by Cabot Corporation is particularly preferably used from the viewpoint of electron conductivity.

The addition amount of these electron conductors should be appropriately determined according to the required electrode characteristics, the specific surface area of the substance to be used, the electronic resistance, and the like. Preferably 80% to 20%.
60% is more preferred. When the amount of the electron conductor is small, the electronic resistance is low. When the amount is large, the gas permeability is impaired or the catalyst utilization rate is reduced, so that the electrode performance is lowered.

It is preferable that the electron conductor is uniformly dispersed with the catalyst particles from the viewpoint of electrode performance. For this reason, a method in which the catalyst particles and the electron conductor are well dispersed in advance as a coating liquid and the coating liquid is coated on a porous conductive sheet provided with a conductive intermediate layer is preferably used.

When the electrode catalyst layer is used in a fuel cell, it is also a preferred embodiment to use a catalyst-supporting carbon in which a catalyst and an electron conductor are integrated. By using this catalyst-supporting carbon, the utilization efficiency of the catalyst is improved, which contributes to cost reduction. Even when the catalyst-supporting carbon is used for the electrode catalyst layer, it is possible to further add a conductive agent. As such a conductive agent, the above-mentioned carbon black is preferably used.

As the ion conductor used for the electrode catalyst layer, known ones can be used without particular limitation. As the ionic conductor, various organic and inorganic materials are known, but when used for a fuel cell, a sulfonic acid group, a carboxylic acid group, which improves proton conductivity,
A polymer having an ion exchange group such as a phosphate group is preferably used. Among them, a polymer having a proton exchange group composed of a fluoroalkyl ether side chain and a fluoroalkyl main chain is preferably used. For example, D
uPont's Nafion, Asahi Kasei's Acip
lex and Flemion manufactured by Asahi Glass Co., Ltd. are preferable. These ion exchange polymers are provided in the electrode catalyst layer in the form of a solution or a dispersion. At this time, the solvent for dissolving or dispersing the proton exchange resin is not particularly limited, but a polar solvent is preferable in view of the solubility of the proton exchange resin. The above-mentioned fluorine atom-containing polymer having a proton exchange group, another polymer such as ethylene or styrene, a copolymer or a blend thereof may be used.

It is important that the ionic conductor is added in advance to a coating liquid as a main constituent substance of the electrode catalyst particles, the electron conductor and the electrode catalyst layer when forming the electrode catalyst layer, and is applied in a uniformly dispersed state. However, the ionic conductor may be applied after the application of the electrode catalyst layer. As a method of applying the ion conductor to the electrode catalyst layer, spray coating, brush coating, dip coating, die coating,
There is no particular limitation on curtain coats, flow coats, and the like.

The amount of the ion conductor contained in the electrode catalyst layer should be appropriately determined according to the required electrode characteristics, the conductivity of the ion conductor used, and the like.
Although not particularly limited, the weight ratio is preferably 1 to 80%, more preferably 5 to 50%. When the ion conductor is small, the ion conductivity is low, and when the ion conductor is large, the gas permeability is impaired.

The electrode catalyst layer may contain various substances in addition to the above-mentioned catalyst, electron conductor and ion conductor. In particular, it is a preferred embodiment to include a polymer other than the above-mentioned proton exchange resin in order to enhance the binding property of a substance contained in the electrode catalyst layer. Examples of such a polymer include polymers containing a fluorine atom, and are not particularly limited. For example, polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), Tetrafluoroethylene, polyperfluoroalkyl vinyl ether (PFA), or the like, a copolymer thereof, a copolymer of these monomer units with another monomer such as ethylene or styrene, or a blend can also be used. The content of these polymers in the electrode catalyst layer is preferably 5 to 40% by weight. If the polymer content is too high, the electron and ionic resistance will increase and the electrode performance will decrease.

In a preferred embodiment of the electrode catalyst layer, the catalyst-polymer composite has a three-dimensional network microporous structure. The catalyst-polymer composite is a polymer composite containing catalyst particles, and is characterized in that the composite has a three-dimensional network microporous structure. The “three-dimensional network microporous structure” refers to a state in which the catalyst-polymer composite has a three-dimensional network structure three-dimensionally connected.

When the electrode catalyst layer has a three-dimensional network microporous structure, the microporous diameter is preferably from 0.05 to 5 μm, and more preferably from 0.1 to 1 μm. The microporous diameter can be measured with a scanning electron microscope (SEM), etc.
From the photograph of the surface, 20 or more, preferably 100
It can be obtained from an average of more than 100 pieces, and can usually be measured with 100 pieces. Since the electrode catalyst layer having a microporous structure of the present invention when produced by a wet coagulation method has a wide distribution of microporous diameters, it is preferable to average as many pore diameters as possible.

The porosity of the three-dimensional network microporous structure is 10
It is preferably about 95%. More preferably 50 to
90%. The porosity is calculated from the total volume of the electrode catalyst layer as follows:
This is a percentage (%) obtained by dividing the volume occupied by the polymer composite by the total volume of the electrode catalyst layer. The electrode catalyst layer is subjected to wet coagulation after being applied to the electrode substrate, the proton exchange membrane, and other substrates, but if it is difficult to obtain the porosity by itself, the electrode substrate Calculate the porosity of the proton exchange membrane and the other base material in advance, determine the porosity including the base material and the electrode catalyst layer, and then determine the porosity of the electrode catalyst layer alone. Is also possible.

The electrode catalyst layer has a high porosity, good gas diffusivity and good discharge of generated water, and good electron conductivity and proton conductivity. In the conventional porous method, the catalyst particle diameter and the particle diameter of the added polymer are increased, and pores are formed by using a pore-forming agent. And the contact resistance between the proton exchange resins becomes larger than that of the electrode catalyst layer. On the other hand, in the three-dimensional network microporous structure by the wet solidification method, since the polymer composite containing the catalyst-supporting carbon is in a three-dimensional network, electrons and protons can easily conduct through this polymer composite, Furthermore, because of the microporous structure, gas diffusibility and generated water discharge are also good.

Even when the electrode catalyst layer has a three-dimensional microporous structure, the same materials as those used in the related art can be used for the catalyst, the electron conductor, and the ion conductor. However, when preparing an electrode catalyst layer having a three-dimensional network microporous structure, it is preferable to use a wet coagulation method, and it is preferable to use a polymer suitable for the wet coagulation method. Polymers that do not degrade in a reducing atmosphere are preferred. Such polymers include:
Examples include polymers containing fluorine atoms, and are not particularly limited. For example, polyvinyl fluoride (PV
F), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), polyperfluoroalkyl vinyl ether (PFA), or a copolymer thereof, or a copolymer of these monomer units with another monomer such as ethylene or styrene. Polymer (for example, hexafluoropropylene-vinylidene fluoride copolymer and the like), and further,
Blends and the like can also be used.

Among them, polyvinylidene fluoride (PV
DF) and hexafluoropropylene-vinylidene fluoride copolymer are obtained by a wet coagulation method using an aprotic polar solvent and a protic polar solvent as a coagulating solvent, and a catalyst having a three-dimensional network microporous structure. It is a particularly preferred polymer in that a polymer composite can be obtained. Examples of the solvent for these polymers include N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), propylene carbonate (PC), dimethylimidazolidinone (DMI), and the like. In addition to lower alcohols such as methanol, ethanol, and isopropanol, esters such as ethyl acetate and butyl acetate, and various aromatic or halogen-based organic solvents are used.

As the polymer of the catalyst-polymer composite, in addition to the above-mentioned polymers, a polymer having a proton exchange group for improving proton conductivity is also preferable. Examples of the proton exchange group contained in such a polymer include a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group, but are not particularly limited. Further, such a polymer having a proton exchange group is also selected without particular limitation, but a polymer having a proton exchange group composed of a fluoroalkyl ether side chain and a fluoroalkyl main chain is preferably used. For example, DuPont's
Nafion and the like are also preferable. Further, a polymer containing the above-described fluorine atom having a proton exchange group, another polymer such as ethylene or styrene, a copolymer or a blend thereof may be used.

The Nafion polymer solution may be obtained by dissolving a commercially available Nafion membrane in an aprotic polar solvent, or using Nafion, a mixed solvent of water-methanol-isopropanol manufactured by Aldrich.
An on solution or a solution obtained by replacing the Nafion solution with a solvent may be used. In this case, the coagulation solvent during wet coagulation is Na
Although it should be appropriately determined depending on the solvent of the fion solution, when the solvent of the Nafion solution is an aprotic polar solvent, as the coagulating solvent, in addition to water, alcohols, and esters, various organic solvents and the like are used. Preferably, in the case of a mixed solvent of water-methanol-isopropanol, esters such as butyl acetate and various organic solvents are preferably used.

As the polymer used in the catalyst-polymer composite, it is also preferable to use a polymer containing a fluorine atom or a polymer containing a proton exchange membrane by copolymerization or blending. In particular, blending polyvinylidene fluoride, poly (hexafluoropropylene-vinylidene fluoride) copolymer, and a polymer such as Nafion, which has a fluoroalkyl ether side chain and a fluoroalkyl main chain in the proton exchange group, can improve electrode performance. It is preferable from the point.

The main components of the catalyst-polymer composite are a catalyst-supporting carbon and a polymer, and their ratio should be appropriately determined according to the required electrode characteristics, and is not particularly limited. The weight ratio of carbon / polymer of 5/95 to 95/5 is preferably used. In particular, when used as an electrode catalyst layer for a polymer electrolyte fuel cell, the catalyst-supporting carbon / polymer weight ratio is 40/60.
~ 85/15 is preferred.

It is also a preferred embodiment to add various additives to the catalyst-polymer composite. For example, a conductive agent such as carbon for improving electron conductivity, a polymer for improving binding, an additive for controlling the pore size of a three-dimensional network microporous structure, and the like, but are not particularly limited. Can be used. The addition amount of these additives is as follows:
The weight ratio to the polymer composite is preferably from 0.1 to 50%, more preferably from 1 to 20%.

As a method for producing a catalyst-polymer composite having a three-dimensional network microporous structure, a method based on a wet coagulation method is preferable. In the wet coagulation method, after the catalyst-polymer solution composition is applied, the coating layer is brought into contact with a coagulation solvent for the polymer, and coagulation precipitation of the catalyst-polymer solution composition and solvent extraction are simultaneously performed.

This catalyst-polymer solution composition is obtained by uniformly dispersing the catalyst-supporting carbon in the polymer solution.
The above-mentioned catalyst-supporting carbon and polymer are preferably used. The solvent for dissolving the polymer should be appropriately determined according to the polymer used, and is not particularly limited. It is important that the polymer solution disperse the catalyst-supporting carbon well. If the dispersion state is poor, it is not preferable because the catalyst-carrying carbon and the polymer cannot form a composite during wet coagulation.

As for the coating method, a coating method is selected according to the viscosity and solid content of the catalyst-polymer solution composition.
Although not particularly limited, a knife coater,
General coating methods such as a bar coater, a spray, a dip coater, a spin coater, a roll coater, a die coater, and a curtain coater are used.

On the other hand, the coagulation solvent for wet coagulation of the polymer is not particularly limited, but a solvent which is easy to coagulate and precipitate the polymer to be used and which is compatible with the solvent of the polymer solution is preferable. The method of contact with the coagulation solvent in which wet coagulation is actually performed is not particularly limited, but the base material is immersed in the coagulation solvent, the coating layer is brought into contact with the liquid surface of the coagulation solvent, There is no particular limitation, such as showering or spraying the coating layer.

The substrate to which the catalyst-polymer solution composition is applied can be applied to either an electrode substrate provided with a conductive intermediate layer or a solid electrolyte, and then subjected to wet coagulation. . Also, after applying to a substrate (transfer substrate) other than the electrode substrate and the solid electrolyte, and then performing wet solidification to create a three-dimensional network microporous structure, the electrode catalyst layer is applied to the electrode substrate or the solid electrolyte. It may be transferred or sandwiched on the electrolyte. As the transfer substrate in this case, a polytetrafluoroethylene (PTFE) sheet, a glass plate or a metal plate whose surface is treated with a fluorine or silicone release agent, or the like is also used.

The electrode of the present invention is obtained by combining the above-mentioned electrode substrate / conductive intermediate layer / electrode catalyst layer with the solid electrolyte layer to form a membrane-electrode composite (MEA: Membrane Electrode).
Assembly) is also a preferred embodiment.

The solid electrolyte is not particularly limited as long as it is a solid electrolyte used in a normal fuel cell, but a proton exchange membrane is preferably used for exhibiting the fuel cell performance of the present invention. The proton exchange group of the proton exchange membrane is not particularly limited, such as a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group.

This proton exchange membrane is composed of a hydrocarbon such as a styrene-divinylbenzene copolymer having the above proton exchange groups, especially sulfonic acid groups, and a fluorine atom-containing polymer, particularly a fluoroalkyl ether side chain and a fluoroalkyl ether. It is roughly classified into a perfluoro-based copolymer composed of a main chain, and should be appropriately selected according to the use and environment in which the fuel cell is used. This is preferable from the viewpoint of fuel cell life. Further, a partial fluorine film partially substituted with fluorine atoms is also preferably used. For perfluoro membranes, DuPont Nafion, Asahi Kasei Aciplex, Asahi Glass Fle
Examples include mion, Goa-select manufactured by Japan Gore-Tex Co., Ltd., and examples of the partial fluorine film include a polymer of trifluorostyrene sulfonic acid and a material in which a sulfonic acid group is introduced into polyvinylidene fluoride. The proton exchange membrane is not only one kind of polymer, but also a copolymer or a blended polymer of two or more kinds of polymers, a composite membrane in which two or more kinds of membranes are bonded together,
A membrane obtained by reinforcing a proton exchange membrane with a nonwoven fabric, a porous film, or the like can also be used.

The method for producing the membrane-electrode composite is not particularly limited. In general, a conductive intermediate layer is provided on a porous conductive sheet, and an electrode catalyst layer is further provided on the intermediate layer to prepare an electrode of the present invention. This electrode is formed with a solid electrolyte such as a proton exchange membrane. The joining is performed, and the joining conditions should be appropriately determined according to the characteristics of the electrode catalyst layer or the electrochemical device.

The electrode substrate of the present invention / conductive intermediate layer /
The electrode composed of the electrode catalyst layer or the membrane-electrode composite (MEA) composed of the electrode and the solid electrolyte membrane can be applied to various electrochemical devices. Among them, a fuel cell and a water electrolysis layer are preferable, and among the fuel cells, a polymer electrolyte fuel cell is suitable. There are fuel cells that use hydrogen as fuel and fuel cells that use hydrocarbons such as methanol as fuel, but they can be used without any particular limitation.

Further, the use of the fuel cell using the electrode catalyst layer of the present invention can be considered without any particular limitation. However, the power supply source of the moving body, which is a useful application in the polymer electrolyte fuel cell, is considered. It is preferred. In particular, automobiles such as passenger cars, buses and trucks, ships, railways, and the like are also preferable moving bodies.

[0107]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be further described below using embodiments.

Example 1 (1) Preparation of Porous Conductive Sheet Short fibers of PAN-based carbon fiber cut to a length of 12 mm and expanded graphite powder (PF Powder-4, manufactured by Toyo Carbon Co., Ltd.)
Bulk density 0.039 g / cm ³ , average particle size 300 to 5
00 μm) was mixed at a weight ratio of 1: 1 and dispersed in an aqueous solution of sodium carboxymethylcellulose. Using this dispersion, a sheet in which expanded graphite powder was adhered to short fibers of carbon fibers was formed on a wire mesh. The sheet was sandwiched between two pieces of filter paper and lightly pressed to remove moisture. Thereafter, the filter paper was removed and the sheet was dried. After drying, the sheet was pressed at a linear pressure of 490 N / cm (50 kg / cm) by a roll press to produce a porous conductive sheet.

Further, this porous conductive sheet was subjected to a heat treatment in air at 200 ° C. for 30 minutes. The basis weight is 60g / c
m ² . A PTFE dispersion (Polyflon TFE dispersion, manufactured by Daikin Industries, Ltd., diluted to a concentration of 15
The aqueous dispersion in weight% was impregnated. After impregnation, the sheet was sandwiched between two pieces of filter paper and lightly pressed. Thereafter, the filter paper was removed from the sheet and dried. The dried sheet was subjected to a heat treatment at 370 ° C. for 10 minutes while being pressurized to 1.2 MPa (12 kgf / cm ² ) to produce a porous conductive sheet. The amount of PTFE added is 15% by weight.
Met.

(2) Preparation of Conductive Intermediate Layer Carbon black (Vull manufactured by Cabot) was used as the inorganic conductive material.
canXC-72) and a polytetrafluoroethylene (PTFE) dispersion (Polyflon TFE dispersion manufactured by Daikin Industries, Ltd.) as a binder polymer and mixed well, and applied to the porous conductive sheet according to (1) above. After drying, a heat treatment was further performed at 370 ° C. for 10 minutes. The obtained conductive intermediate layer was 1 mg / cm ² (80% by weight of carbon black, 20% by weight of PTFE).

(3) Preparation of Catalyst-Polymer Composition A catalyst-supporting carbon (catalyst;
Pt, carbon; VulcanXC-72, manufactured by Cabot, platinum loading;
(50 wt%) and stirred well to prepare a catalyst-polymer composition.

(4) Preparation of Electrode Catalyst Layer by Applying and Drying Catalyst-Polymer Composition The catalyst prepared in (3) above was placed on the porous conductive sheet provided with the conductive intermediate layer prepared in (2). -The polymer composition was applied and dried. The obtained electrode catalyst layer had a coating amount of platinum of 1 mg / cm ² and a coating amount of Nafion of 0.5 mg / cm ² .

When the catalyst-polymer composition was applied, penetration of the composition was suppressed because of the provision of the conductive intermediate layer. FIG. 1A shows a cross-sectional SEM photograph of the electrode, and FIG. 1B shows the distribution of platinum by XMA analysis.
Shown in The thickness of the conductive intermediate layer was 10 μm, the thickness of the electrode catalyst layer was 15 μm, and there was no penetration of the electrode catalyst layer into the conductive sheet.

(5) Preparation of MEA and fuel cell performance evaluation Using the electrode composed of the porous conductive sheet, the conductive intermediate layer and the electrode catalyst layer prepared in the above (4), proton Nafion1 manufactured by DuPont as an exchange membrane
12 using a hot press (pressure 5 MPa, temperature 150
C.) to produce an MEA. The fuel cell performance of this MEA was measured by current-voltage (IV) measurement. The fuel cell performance was evaluated at a cell temperature of 60 ° C. and a gas pressure of normal pressure. The battery terminal voltage at a current density of 50 mA / cm ² was 0.5.
70 V, and the catalyst was used effectively.

Comparative Example 1 A porous conductive sheet was prepared in the same manner as in Example 1 (1), and the same method as in Examples 1 (3) and (4) was formed on this porous conductive sheet without providing a conductive intermediate layer. Was provided with an electrode catalyst layer.

At this time, when the catalyst-polymer composition was applied, there was no conductive intermediate layer, so that the composition permeated an average of 25 μm into the porous conductive sheet. Section SE of this electrode
An M photograph is shown in FIG. 2 (4), and a distribution of Pt by XMA analysis is shown in FIG. 2 (6). The thickness of the electrode catalyst layer was 35 μm, and the thickness of the layer immersed in the conductive sheet was 25 μm.

Further, in accordance with Example 1 (5), an MEA was prepared using the electrode without the conductive intermediate layer, and the fuel cell was evaluated. The battery terminal voltage at a current density of 50 mA / cm ² was 0.60 V, and the amount of the catalyst used effectively was smaller than that in Example 1.

Example 2 (1) Preparation of Porous Conductive Sheet A porous conductive sheet was prepared in the same manner as in Example 1 (1).

(2) Preparation of Conductive Intermediate Layer Carbon black (Vull manufactured by Cabot) was used as an inorganic conductive substance.
canXC-72) was well dispersed in an N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) as a binder polymer, and applied to the porous conductive sheet described in (1) above at 150 ° C. Dried. In the obtained conductive intermediate layer, (carbon black and PVDF (weight ratio 9:
The amount of 1) was 1 mg / cm ² .

(3) Preparation of Catalyst-Polymer Composition A catalyst-supporting carbon (catalyst;
Pt, carbon; VulcanXC-72, manufactured by Cabot, platinum loading;
(50 wt%) and stirred well to prepare a catalyst-polymer composition.

(4) Preparation of Electrode Catalyst Layer by Applying and Drying Catalyst-Polymer Composition The catalyst prepared in (3) above was placed on the porous conductive sheet provided with the conductive intermediate layer prepared in (2). -The polymer composition was applied and dried. The obtained electrode catalyst layer had a coating amount of platinum of 1 mg / cm ² and a coating amount of Nafion of 0.5 mg / cm ² .

Further, when the catalyst-polymer composition was applied, penetration of the composition was suppressed because the conductive intermediate layer was provided.

(5) Preparation of MEA and Evaluation of Fuel Cell Performance Using the electrode composed of the porous conductive sheet, the conductive intermediate layer, and the electrode catalyst layer prepared in (4) above, Nafion1 manufactured by DuPont as an exchange membrane
Hot pressing was performed using No. 12 to prepare an MEA. The fuel cell performance of this MEA was measured by current-voltage (IV) measurement. The fuel cell performance was evaluated at a cell temperature of 60 ° C. and a gas pressure of normal pressure. The battery terminal voltage at a current density of 50 mA / cm ² was 0.70 V, and the catalyst was effectively used.

Example 3 (1) Preparation of Porous Conductive Sheet Short fibers of PAN-based carbon fiber cut to a length of 12 mm and expanded graphite powder (manufactured by Toyo Carbon Co., Ltd., bulk density 0.14
g / cm ³ and an average particle size of 100 to 200 μm) were mixed at a weight ratio of 1: 1 and dispersed in an aqueous solution of sodium carboxymethylcellulose. Using this dispersion, a sheet in which expanded graphite powder was adhered to short fibers of carbon fibers was formed on a wire mesh. For the purpose of removing water,
The sheet was sandwiched between two filter papers and lightly pressed. Thereafter, the filter paper was removed and the sheet was dried. After drying, the sheet was roll-pressed to produce a porous conductive sheet.

Further, this porous conductive sheet was subjected to a heat treatment in air at 200 ° C. for 30 minutes, and the basis weight was 60 g / cm.
It became ² . PFA dispersion (neoflon PF
A dispersion, manufactured by Daikin Industries, Ltd.) and then the sheet is sandwiched between two pieces of filter paper,
Lightly pressurized. The filter paper was then removed from the sheet and the sheet was dried. The dried sheet is 14.7 kP
a (0.15 kgf / cm ² )
C. for 3 hours to produce a porous conductive sheet. The amount of PFA applied was 15% by weight.

(2) Preparation of Conductive Intermediate Layer Carbon black (Vull manufactured by Cabot) was used as the inorganic conductive substance.
canXC-72) as a binder polymer was well dispersed in an N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF), and applied to the porous conductive sheet described in (1) above. And dried. The obtained conductive intermediate layer was 1 mg / cm ² (carbon black 90% by weight, P
VDF 10% by weight).

(3) Preparation of Catalyst-Polymer Composition A catalyst-supporting carbon (catalyst;
Pt, carbon; VulcanXC-72, manufactured by Cabot, platinum loading;
(50 wt%) and stirred well to prepare a catalyst-polymer composition.

(4) Preparation of Electrode Catalyst Layer by Applying and Drying Catalyst-Polymer Composition The catalyst prepared in (3) above was placed on the porous conductive sheet provided with the conductive intermediate layer prepared in (2). -The polymer composition was applied and dried. The obtained electrode catalyst layer had a coating amount of platinum of 0.5 mg / cm ² and a coating amount of Nafion of 0.4 mg / c.
m ² .

When the catalyst-polymer composition was applied, the conductive intermediate layer was provided, so that the penetration of the composition was suppressed.

(5) Preparation of MEA and fuel cell performance evaluation Using the electrode composed of the porous conductive sheet, the conductive intermediate layer, and the electrode catalyst layer prepared in the above (4), proton Nafion1 manufactured by DuPont as an exchange membrane
Hot pressing was performed using No. 12 to prepare an MEA. The fuel cell performance of this MEA was measured by current-voltage (IV) measurement. The fuel cell performance was evaluated at a cell temperature of 60 ° C. and a gas pressure of normal pressure. The battery terminal voltage at a current density of 50 mA / cm ² was 0.70 V, and the catalyst was effectively used.

Comparative Example 2 A porous conductive sheet was prepared in the same manner as in Example 3 (1), and a conductive intermediate layer was not provided on the porous conductive sheet in the same manner as in Example 3 (3) (4). Was provided with an electrode catalyst layer.

At this time, when the catalyst-polymer composition was applied, there was no conductive intermediate layer, so that the composition permeated an average of 25 μm into the porous conductive sheet.

Further, according to Example 3 (5), an MEA was prepared using the electrode without the conductive intermediate layer, and the fuel cell was evaluated. The battery terminal voltage at a current density of 50 mA / cm ² was 0.60 V, and the amount of the catalyst used effectively was smaller than that in Example 3.

Example 4 (1) Preparation of Porous Conductive Sheet Short fibers of PAN-based carbon fibers cut to a length of 12 mm and expanded graphite powder (PF-4 manufactured by Toyo Carbon Co., Ltd., bulk density 0.039 g / cm ³ , average particle size 300-500μ
m) was mixed 1: 1 by weight and dispersed in aqueous sodium carboxymethylcellulose. Using this dispersion, a sheet in which expanded graphite powder was adhered to short fibers of carbon fibers was formed on a wire mesh. The sheet was sandwiched between two pieces of filter paper and lightly pressed to remove moisture. Thereafter, the filter paper was removed and the sheet was dried. After drying, the sheet was roll-pressed to produce a porous conductive sheet. The basis weight was 60 g / cm ² .

Further, the porous conductive sheet is subjected to a heat treatment in air at 200 ° C. for 30 minutes, and impregnated with PFA dispersion (neoflon PFA dispersion, manufactured by Daikin Industries, Ltd.).
It was sandwiched between two pieces of filter paper and lightly pressed. The filter paper was then removed from the sheet and the sheet was dried. The dried sheet was subjected to a heat treatment at 400 ° C. for 3 hours while being pressed at 14.7 kPa (0.15 kgf / cm ² ) to produce a porous conductive sheet. 15% by weight of PFA
Met.

(2) Preparation of Conductive Intermediate Layer Carbon black (Vull manufactured by Cabot) was used as an inorganic conductive substance.
canXC-72) is well dispersed in an N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) as a binder polymer, and is immediately applied to methanol after being applied to the porous conductive sheet described in (1) above. It was immersed and wet solidified. After 10 minutes, it was taken out and dried at 90 ° C. The obtained conductive intermediate layer was 1 mg / cm ² (carbon black 9
0% by weight and PVDF 10% by weight).

(3) Preparation of Catalyst-Polymer Composition A catalyst-supporting carbon (catalyst;
Pt, carbon; VulcanXC-72, manufactured by Cabot, platinum loading;
(50 wt%) and stirred well to prepare a catalyst-polymer composition.

(4) Preparation of Electrode Catalyst Layer by Applying and Drying Catalyst-Polymer Composition The catalyst prepared in (3) above was placed on the porous conductive sheet provided with the conductive intermediate layer prepared in (2). -The polymer composition was applied and dried. The obtained electrode catalyst layer had a coating amount of platinum of 0.5 mg / cm ² and a coating amount of Nafion of 0.4 mg / c.
m ² .

When the catalyst-polymer composition was applied, penetration of the composition was suppressed * due to the provision of the conductive intermediate layer.

(5) Preparation of MEA and Evaluation of Fuel Cell Performance Using the electrode composed of the porous conductive sheet, the conductive intermediate layer, and the electrode catalyst layer prepared in (4) above, Nafion1 manufactured by DuPont as an exchange membrane
Hot pressing was performed using No. 12 to prepare an MEA. The fuel cell performance of this MEA was measured by current-voltage (IV) measurement. The fuel cell performance was evaluated at a cell temperature of 60 ° C. and a gas pressure of normal pressure. The battery terminal voltage at a current density of 50 mA / cm ² was 0.70 V, and the catalyst was effectively used.

Example 5 (1) Preparation of porous conductive sheet A porous conductive sheet was prepared in the same manner as in Example 4 (1).

(2) Preparation of Conductive Intermediate Layer Acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) was used as the inorganic conductive substance, and N-methylpyrrolidone (NMP) of polyvinylidene fluoride (PVDF) was used as the binder polymer. It was well dispersed in a solution, applied to the porous conductive sheet described in (1) above, and immediately immersed in methanol for wet coagulation. After 10 minutes, it was taken out and dried at 90 ° C. The obtained conductive intermediate layer was made of carbon black and PV.
The attached amount of DF (weight ratio 9: 1) was 1 mg / cm ² .

(3) Preparation of Catalyst-Polymer Composition The catalyst-supporting carbon (catalyst;
Pt, carbon; VulcanXC-72, manufactured by Cabot, platinum loading;
(50 wt%) and stirred well to prepare a catalyst-polymer composition.

(4) Preparation of Electrode Catalyst Layer by Applying and Drying Catalyst-Polymer Composition The catalyst prepared in (3) above was placed on the porous conductive sheet provided with the conductive intermediate layer prepared in (2). -The polymer composition was applied and dried. The obtained electrode catalyst layer had a coating amount of platinum of 0.5 mg / cm ² and a coating amount of Nafion of 0.4 mg / c.
m ² .

When the catalyst-polymer composition was applied, the conductive intermediate layer was provided, so that the penetration of the composition was suppressed.

(5) Preparation of MEA and fuel cell performance evaluation Using the electrode composed of the porous conductive sheet, the conductive intermediate layer, and the electrode catalyst layer prepared in (4) above, Nafion1 manufactured by DuPont as an exchange membrane
Hot pressing was performed using No. 12 to prepare an MEA. The fuel cell performance of this MEA was measured by current-voltage (IV) measurement. The fuel cell performance was evaluated at a cell temperature of 60 ° C. and a gas pressure of normal pressure. The battery terminal voltage at a current density of 50 mA / cm ² was 0.75 V, and the catalyst was used effectively.

Comparative Example 3 A porous conductive sheet was prepared in the same manner as in Example 5 (1), and a conductive intermediate layer was provided as in Example 5 (2). The conductive intermediate layer is 0.5 mg / cm ² (carbon 0.45 mg / c
m ² , PVDF 0.05 mg / cm ² ). An electrode catalyst layer was provided on this porous conductive sheet in the same manner as in Examples 5 (3) and (4).

At this time, when the catalyst-polymer composition was applied, since the conductive intermediate layer was small, this composition had an average of 25 μm soaked in the porous conductive sheet.

Further, in accordance with Example 5 (5), an MEA was prepared using the electrode without the conductive intermediate layer, and the fuel cell was evaluated. The battery terminal voltage at a current density of 50 mA / cm ² was 0.65 V, and the amount of the catalyst used effectively was smaller than that of Example 5.

Example 6 (1) Preparation of Porous Conductive Sheet A porous conductive sheet was prepared in the same manner as in Example 4 (1).

(2) Preparation of Conductive Intermediate Layer Acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) was used as the inorganic conductive material, and N-methylpyrrolidone (NMP) of polyvinylidene fluoride (PVDF) was used as the binder polymer. It was well dispersed in a solution, applied to the porous conductive sheet described in (1) above, and immediately immersed in methanol for wet coagulation. After 10 minutes, it was taken out and dried at 90 ° C. The obtained conductive intermediate layer was made of carbon black and PV.
The amount of DF (weight ratio) is 1 mg / cm ² .

(3) Preparation of Catalyst-Polymer Composition A catalyst-supporting carbon (catalyst;
Pt, carbon; VulcanXC-72, manufactured by Cabot, platinum loading;
(50 wt%) and stirred well to prepare a catalyst-polymer composition.

(4) Preparation of Electrode Catalyst Layer by Applying and Drying Catalyst-Polymer Composition The catalyst prepared in (3) above is provided on the porous conductive sheet provided with the conductive intermediate layer prepared in (2). -The polymer composition was applied and dried. The obtained electrode catalyst layer had a coating amount of platinum of 0.5 mg / cm ² and a coating amount of Nafion of 0.4 mg / c.
m ² .

When the catalyst-polymer composition was applied, penetration of the composition was suppressed because of the provision of the conductive intermediate layer.

(5) Preparation of MEA and Evaluation of Fuel Cell Performance Using the electrode composed of the porous conductive sheet, the conductive intermediate layer, and the electrode catalyst layer prepared in (4) above, proton Nafion1 manufactured by DuPont as an exchange membrane
Hot pressing was performed using No. 12 to prepare an MEA. The fuel cell performance of this MEA was measured by current-voltage (IV) measurement. The fuel cell performance was evaluated at a cell temperature of 60 ° C. and a gas pressure of normal pressure. The battery terminal voltage at a current density of 50 mA / cm ² was 0.80 V, and the catalyst was used effectively.

Example 7 (1) Preparation of Porous Conductive Sheet A porous conductive sheet was prepared in the same manner as in Example 4 (1).

(2) Preparation of Conductive Intermediate Layer Acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) as an inorganic conductive substance, and N-methylpyrrolidone (NMP) of polyvinylidene fluoride (PVDF) as a binder polymer It was well dispersed in a solution, applied to the porous conductive sheet described in (1) above, and immediately immersed in methanol for wet coagulation. After 10 minutes, it was taken out and dried at 90 ° C. The obtained conductive intermediate layer was made of carbon black and PV.
The amount of DF applied (weight ratio 9: 1) was 1 mg / cm ² .

(3) Preparation of Catalyst-Polymer Composition A catalyst carrying carbon (catalyst;
Pt, carbon; VulcanXC-72, manufactured by Cabot, platinum loading;
(50 wt%) and stirred well to prepare a catalyst-polymer composition.

(4) Preparation of Electrode Catalyst Layer by Applying and Drying Catalyst-Polymer Composition The catalyst prepared in (3) above was provided on the porous conductive sheet provided with the conductive intermediate layer prepared in (2). -Immediately after application of the polymer composition, it was immersed in methanol. After immersion for 10 minutes, it was dried at 90 ° C. The obtained electrode catalyst layer had a coating amount of platinum of 0.5 mg / cm ² and a coating amount of Nafion of 0.4 mg / cm ² .
/ Cm ² , and had a three-dimensional network prepared porous structure.

When the catalyst-polymer composition was applied, penetration of the composition was suppressed because of the provision of the conductive intermediate layer.

(5) Preparation of MEA and fuel cell performance evaluation Using the electrode composed of the porous conductive sheet, the conductive intermediate layer, and the electrode catalyst layer prepared in (4) above, Nafion1 manufactured by DuPont as an exchange membrane
Hot pressing was performed using No. 12 to prepare an MEA. The fuel cell performance of this MEA was measured by current-voltage (IV) measurement. The fuel cell performance was evaluated at a cell temperature of 60 ° C. and a gas pressure of normal pressure. The battery terminal voltage at a current density of 50 mA / cm ² was 0.85 V, and the catalyst was used effectively.

Example 8 (1) Preparation of Porous Conductive Sheet A porous conductive sheet was prepared in the same manner as in Example 4 (1).

(2) Preparation of Conductive Intermediate Layer Ketjen Black (manufactured by Lion Corporation) as an inorganic conductive material and N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) as a binder polymer are often used. It was dispersed, applied to the porous conductive sheet described in (1) above, and dried at 90 ° C. The obtained conductive intermediate layer is
Attached amount of carbon black and PVDF (weight ratio 9: 1)
It was 1 mg / cm ² .

(3) Preparation of Catalyst-Polymer Composition A catalyst-supporting carbon (catalyst;
Pt, carbon; VulcanXC-72, manufactured by Cabot, platinum loading;
(50 wt%) and stirred well to prepare a catalyst-polymer composition.

(4) Preparation of Electrode Catalyst Layer by Applying and Drying Catalyst-Polymer Composition The catalyst prepared in (3) above was provided on the porous conductive sheet provided with the conductive intermediate layer prepared in (2). The polymer composition was dried at 90 ° C. The obtained electrode catalyst layer had a coating amount of platinum of 0.5 mg / cm ² and a coating amount of Nafion of 0.4.
mg / cm ² .

In addition, when the catalyst-polymer composition was applied, the conductive intermediate layer was provided, so that the penetration of the composition was suppressed.

(5) Preparation of MEA and Evaluation of Fuel Cell Performance Using the electrode composed of the porous conductive sheet, the conductive intermediate layer, and the electrode catalyst layer prepared in (4) above, Nafion1 manufactured by DuPont as an exchange membrane
Hot pressing was performed using No. 12 to prepare an MEA. The fuel cell performance of this MEA was measured by current-voltage (IV) measurement. The fuel cell performance was evaluated at a cell temperature of 60 ° C. and a gas pressure of normal pressure. The battery terminal voltage at a current density of 50 mA / cm ² was 0.7 V, and the catalyst was used effectively.

Example 9 (1) Preparation of porous conductive sheet A porous conductive sheet was prepared in the same manner as in Example 4 (1).

(2) Preparation of Conductive Intermediate Layer Milled carbon fiber (Trecamyl Fiber MLD-30 manufactured by Toray Industries, Inc.) was used as the inorganic conductive material, and N-polyvinylidene fluoride (PVDF) was used as the binder polymer. Well dispersed in methylpyrrolidone (NMP) solution,
It was dried at 90 ° C. after application to the porous conductive sheet described. The obtained conductive intermediate layer is 1 mg / cm ² (carbon 90% by weight, PVDF 10% by weight).

(3) Preparation of Catalyst-Polymer Composition A catalyst-supporting carbon (catalyst;
Pt, carbon; VulcanXC-72, manufactured by Cabot, platinum loading;
(50 wt%) and stirred well to prepare a catalyst-polymer composition.

(4) Preparation of Electrode Catalyst Layer by Applying and Drying Catalyst-Polymer Composition The catalyst prepared in (3) above was provided on the porous conductive sheet provided with the conductive intermediate layer prepared in (2). The polymer composition was dried at 90 ° C. The obtained electrode catalyst layer had a coating amount of platinum of 0.5 mg / cm ² and a coating amount of Nafion of 0.4.
mg / cm ² .

Further, when the catalyst-polymer composition was applied, penetration of the composition was suppressed because the conductive intermediate layer was provided.

(5) Preparation of MEA and Evaluation of Fuel Cell Performance Using the electrode composed of the porous conductive sheet, the conductive intermediate layer, and the electrode catalyst layer prepared in (4) above, proton Nafion1 manufactured by DuPont as an exchange membrane
Hot pressing was performed using No. 12 to prepare an MEA. The fuel cell performance of this MEA was measured by current-voltage (IV) measurement. The fuel cell performance was evaluated at a cell temperature of 60 ° C. and a gas pressure of normal pressure. The battery terminal voltage at a current density of 50 mA / cm ² was 0.75 V, and the catalyst was used effectively.

[0174]

According to the present invention, by providing a conductive intermediate layer, it is possible to reduce the amount of catalyst that is not effectively used because it penetrates into the electrode substrate, and the amount of expensive catalyst in the electrode catalyst layer is reduced. As a result, a significant cost reduction is achieved. Further, by the hydrophobic polymer of the conductive intermediate layer,
The water generated at the cathode is an electrode catalyst layer, a conductive intermediate layer,
Alternatively, the flooding phenomenon in which the electrode base material is clogged hardly occurs, and the hydrophobic polymer also exerts a function of binding between the inorganic conductive substances of the conductive intermediate layer.

[Brief description of the drawings]

FIG. 1 is a cross section of an embodiment of the present invention.

FIG. 2 is a cross section of a comparative example.

[Explanation of symbols]

1: Scanning electron micrograph of the cross section of the embodiment of the present invention 2: Sectional display of the cross section of the embodiment of the present invention 3: Distribution map of platinum by X-ray microanalysis of the cross section of the embodiment of the present invention 4: Scanning of the cross section of the comparative example Type electron micrograph 5: Sectional display of comparative example 6: Platinum distribution diagram by X-ray microanalysis of cross section of comparative example

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H018 AA06 AS01 CC06 DD05 DD06 DD08 EE03 EE05 EE06 EE08 EE18 EE19 5H026 AA06 CX02 CX03 CX05 EE02 EE05 EE06 EE19

Claims (23)

[Claims] 1. An electrode comprising at least an electrode substrate and an electrode catalyst layer, wherein the electrode substrate has a porous conductive sheet having a nonwoven structure, wherein the electrode substrate and the electrode An electrode, wherein a conductive intermediate layer containing at least an inorganic conductive substance and a hydrophobic polymer is provided between the catalyst layer and the catalyst layer. 2. The electrode according to claim 1, wherein the inorganic conductive substance has a particulate or fibrous form. 3. The electrode according to claim 1, wherein the inorganic conductive substance is mainly composed of a carbon material. 4. The carbon material is a carbon black, a fired body from polyacrylonitrile, a fired body from pitch, graphite,
4. The electrode according to claim 3, wherein at least one selected from the group consisting of these processed substances is an essential component. 5. The electrode according to claim 1, wherein the hydrophobic polymer has a fluorine atom. 6. The electrode according to claim 1, wherein the porous conductive sheet uses inorganic conductive fibers. 7. The method according to claim 6, wherein the inorganic conductive fibers are carbon fibers.
The electrode according to 1. 8. The electrode according to claim 7, wherein the carbon fiber is made of polyacrylonitrile, pitch or a low-boiling organic compound. 9. The method according to claim 9, wherein the porous conductive sheet is made of paper, felt,
The electrode according to any one of claims 1 to 8, wherein the electrode is any one of a nonwoven fabric. 10. The electrode according to claim 1, wherein the porous conductive sheet contains inorganic conductive particles. 11. The electrode according to claim 10, wherein the inorganic conductive particles are flexible inorganic conductive particles. 12. The electrode according to claim 11, wherein the flexible inorganic conductive particles are expanded graphite. 13. The electrode according to claim 1, wherein the porous conductive sheet contains a water-repellent polymer. 14. The electrode according to claim 1, wherein the electrode catalyst layer contains at least catalyst particles, conductive particles, and a polymer compound. 15. The electrode according to claim 14, wherein the catalyst particles contain at least one element selected from platinum, ruthenium, palladium, iridium, and gold. 16. The electrode according to claim 14, wherein the polymer compound contains a fluorine atom. 17. The electrode according to claim 14, wherein the polymer compound has a proton exchange group. 18. The method according to claim 1, wherein a conductive intermediate layer containing at least an inorganic conductive substance is provided on the porous conductive sheet, and an electrode catalyst layer is provided on the conductive intermediate layer. A method for producing an electrode according to any one of the above. 19. An electrochemical device using the electrode according to claim 1. 20. A fuel cell using the electrode according to claim 1. 21. The electrolyte according to claim 2, wherein the electrolyte is a solid polymer type.
0 fuel cell. 22. A moving object using the fuel cell according to claim 20 as a power supply source. 23. An automobile using the fuel cell according to claim 20 as a power supply source.