JP2021111542A - Membrane electrode complex - Google Patents

Abstract

To provide a membrane electrode complex capable of improving power generation performance by sufficiently humidifying a polymer electrolyte membrane even under a high temperature and low humidification condition and maintaining high proton conductivity.SOLUTION: A membrane electrode complex includes a polymer electrolyte membrane, catalyst layers arranged on both sides of the polymer electrolyte membrane, and a gas diffusion layer containing a carbon sheet arranged on the opposite side of the catalyst layer with respect to the polymer electrolyte membrane. According to the filling rate of the carbon sheet, when a layer closest to the electrolyte membrane side is a layer X, a layer closest to the other surface is a layer Y, and a layer located between the layers X and Y is a layer Z, the filling rate of the layer X is equal to the filling rate of the layer Y, and the filling rate of the layer Z is smaller than the filling rates of the layer X and the layer Y.SELECTED DRAWING: Figure 1

Description

The present invention is a membrane electrode composite for a fuel cell having an anode and cathode electrode base material and an electrolyte membrane sandwiched between them, and by having a gas diffusion layer having high water retention, under low humidification conditions. Also relates to a membrane electrode composite having excellent power generation performance.

A fuel cell is a kind of power generation device that extracts electric energy by electrochemically oxidizing fuels such as hydrogen and methanol, and has been attracting attention as a clean energy supply source in recent years. Among them, polymer electrolyte fuel cells have a low standard operating temperature of around 100 ° C and a high energy density, so they are relatively small-scale distributed power generation facilities and power generation devices for mobile objects such as automobiles and ships. It is expected to have a wide range of applications. It is also attracting attention as a power source for small mobile devices and mobile devices, and is expected to be installed in mobile phones and personal computers in place of secondary batteries such as nickel-metal hydride batteries and lithium-ion batteries.

A fuel cell usually has a gas diffusion layer that supplies fuel gas and oxidation gas to the catalyst layer, an anode and cathode catalyst layer in which a reaction responsible for power generation occurs, and a polymer that serves as a proton conductor between the anode catalyst layer and the cathode catalyst layer. The electrolyte membrane constitutes a membrane electrode composite (hereinafter, may be abbreviated as MEA), and the cell in which this MEA is sandwiched by a separator is configured as a unit. The first characteristic required for the polymer electrolyte membrane is high proton conductivity, and it is particularly necessary to have high proton conductivity even under high temperature and low humidification conditions. Conventionally, Nafion (registered trademark) (manufactured by DuPont), which is a perfluorosulfonic acid-based polymer, has been widely used for polymer electrolyte membranes. While Nafion® exhibits high proton conductivity through proton conduction channels due to the cluster structure, there is a problem with proton conductivity under low humidification conditions. On the other hand, the development of hydrocarbon-based polymer electrolyte membranes that can replace Nafion (registered trademark) has become active in recent years, and in particular, both blocks consisting of hydrophobic segments and hydrophilic segments are aimed at improving proton conductivity. Although some attempts have been made to form microphase-separated structures using polymers, proton conductivity under low humidification conditions remains a problem.

Under these circumstances, it is important to control the water (particularly the water content of the electrolyte membrane) in the membrane electrode complex in the fuel cell. The gas diffusion layer is responsible for managing the water in the membrane electrode composite, and the generated water generated by the electrochemical reaction and the water contained in the supply gas are used for water retention in the membrane electrode composite and as a separator. It is a member that controls the discharge property of the water. Therefore, efforts have been made to try to control water in a fuel cell by controlling the behavior of water in the gas diffusion layer.

In Patent Document 1, as a carbon sheet used for a gas diffusion layer capable of preventing bending into a separator flow path while maintaining high drainage property, the carbon sheet is placed in the direction perpendicular to the sheet surface (hereinafter, the direction perpendicular to the surface). Regarding the layers obtained by dividing into three equal parts, the layer close to one surface and having the highest filling rate is referred to as layer X, and the layers close to the other surface and having a lower filling rate than layer X are referred to as layer Y and layer X. A carbon sheet for a gas diffusion layer is disclosed, wherein when the layer located between the layers Y is the layer Z, the filling rate of the layers decreases in the order of the layer X, the layer Y, and the layer Z. However, in Patent Document 1, since the purpose is to improve the drainage property from the gas diffusion layer, the water retention of the membrane electrode assembly is not mentioned, and the power generation performance is improved under low humidification conditions. It had no effect.

Further, in Patent Document 2, for the purpose of enhancing the water retention of the fuel cell, carbon black is contained in the gas diffusion layer, and organic substances are interposed in the voids formed between the carbon black particles due to the aggregation of the carbon black particles. A gas diffusion layer is described, which is characterized in that it is allowed to flow. However, Patent Document 2 introduces a paste containing carbon black into a carbon sheet by impregnation or coating, and does not mention the filling rate thereof. Further, when carbon black is introduced into the entire pores in the carbon sheet by the above method, there is a concern that the gas diffusibility of the entire carbon sheet may decrease.

Further, in Patent Document 3, for the purpose of improving power generation performance under high temperature and low humidification operating conditions, it is composed of a sheet-like and rubber-like porous member containing conductive particles and a polymer resin as main components. It is described that a gas diffusion layer in which the porosity of the anode gas diffusion layer to be formed is 60% or less and the porosity of the cathode gas diffusion layer is made larger than the porosity of the anode gas diffusion layer is used. However, Patent Document 3 does not mention the filling rate distribution in the gas diffusion layer, and it is difficult to control the filling rate distribution in the anode gas diffusion layer having a sheet-like and rubber-like shape. be.

Japanese Patent No. 5954506 Japanese Unexamined Patent Publication No. 2010-40399 Japanese Unexamined Patent Publication No. 2011-146407

In view of the background of the prior art, the present invention provides a fuel cell capable of improving power generation performance by sufficiently humidifying the polymer electrolyte membrane even under high temperature and low humidification conditions and maintaining high proton conductivity. Is what you do.

The present invention employs the following means in order to solve such a problem.
That is, the membrane electrode composite of the present invention is a membrane electrode composite having an electrolyte membrane and a catalyst layer and a gas diffusion layer provided on both sides of the electrolyte membrane, and the gas diffusion layer is at least a porous carbon sheet and a microporous. Regarding layers X, Y, and Z which are composed of layers and are obtained by dividing the porous carbon sheet into three equal parts in the direction perpendicular to the sheet surface, the layer closest to the electrolyte membrane side is layer X, and the layer close to the other surface. When the layer Y is defined as the layer Y and the layer located between the layers X and the layer Y is the layer Z, the filling ratio of the layers is equal between the layer X and the layer Y, and the layer Z is smaller than the layer X and the layer Y. It is characterized by becoming.

According to the present invention, it is possible to provide a membrane electrode complex having high power generation performance under high temperature and low humidification conditions.

It is a schematic cross-sectional view of the carbon sheet used for the membrane electrode complex of this invention. It is a schematic cross-sectional view for demonstrating the structure of the membrane electrode complex which concerns on 2nd Embodiment of this invention. It is a schematic cross-sectional view for demonstrating the structure of the membrane electrode complex which concerns on 2nd Embodiment of this invention.

Hereinafter, the present invention will be described in detail.

[Membrane electrode complex]
The membrane electrode composite of the present invention is provided so as to be in contact with the polymer electrolyte membrane, the catalyst layers provided on both sides of the polymer electrolyte membrane, and the polymer electrolyte membrane of the catalyst layer on opposite sides. It has a gas diffusion layer. At that time, regarding the layers X, Y, and Z obtained by dividing the porous carbon sheet contained in the gas diffusion layer into three equal parts in the vertical direction, the layer closest to the electrolyte membrane side is the layer X, and the other surface. When the layer close to is the layer Y and the layer located between the layers X and the layer Y is the layer Z, the filling ratio of the layers is equal in the layer X and the layer Y, and the layer Z is more than the layer X and the layer Y. By making the size smaller, the water retention of the membrane electrode composite can be enhanced, and high power generation performance can be realized even under high temperature and low humidification conditions.

Here, the method for producing MEA is as follows.
(I) A method of preparing a gas diffusion electrode (GDE) in which a catalyst layer is formed on one surface of a gas diffusion layer and laminating it with an electrolyte membrane (II) Creating an electrolyte membrane (CCM) with a catalyst layer and gas diffusion. It is roughly divided into a method of laminating with a layer.

In the case of the method (I), a gas diffusion electrode (GDE) having a catalyst layer formed on one surface of the gas diffusion layer having the characteristics described in the present application is used. In this case, the carbon in the section from the surface having the 50% filling rate closest to one surface of the porous carbon sheet contained in the gas diffusion layer to the surface having the 50% filling rate closest to the other surface. The effect of the present invention can be obtained by forming a catalyst layer on the surface close to the layer having the second highest filling rate for the layer obtained by dividing the sheet into three equal parts in the direction perpendicular to the plane.

In the case of the method (II), the anode and cathode electrode base materials (gas diffusion layer) are arranged and joined so that the catalyst layer forming surface of the CCM is in direct contact with the gas diffusion layer. The catalyst layer is generally, but is not limited to, formed from carbon black particles on which platinum is supported.

The method for joining the polymer electrolyte membrane and the gas diffusion layer is not particularly limited, and is a known method (for example, the chemical plating method described in Electrochemistry, 1985, 53, p.269., edited by the Electrochemical Society (J. Electrochem. Soc). .), Electrochemical Science and Technology, 1988, 135, 9, p.2209. The heat press bonding method of the gas diffusion electrode described in.) Can be applied.

When the polymer electrolyte membrane and the gas diffusion layer are integrated by a press, the temperature and pressure thereof may be appropriately selected depending on the thickness and water content of the electrolyte membrane, the catalyst layer and the electrode base material. Specific press methods include roll presses that regulate pressure and clearance, flat plate presses that regulate pressure, and the like from the viewpoints of industrial productivity and suppression of thermal decomposition of polymer materials having ionic groups. It is preferable to carry out in the range of 0 ° C. to 250 ° C. The pressurization is preferably as weak as possible from the viewpoint of protecting the electrolyte membrane and electrodes, and in the case of a flat plate press, a pressure of 10 MPa or less is preferable. It is also one of the preferable options from the viewpoint of preventing short-circuiting of the anode and cathode electrodes by superimposing the electrodes and the electrolyte membranes to form a fuel cell without performing the compounding by the pressing process. In the case of this method, when power generation is repeated as a fuel cell, deterioration of the electrolyte membrane, which is presumed to be caused by a short-circuited portion, tends to be suppressed, and the durability of the fuel cell becomes good.

Specifically, it is preferable to produce MEA by laminating an electrolyte membrane, a gas diffusion layer, and a catalyst layer as shown in FIGS. 2 and 3 and pressing them at a constant temperature and pressure. Such laminating and pressing may be performed simultaneously on both sides or one side at a time.

Examples of the method for continuously producing the membrane electrode composite include a method in which a roll-shaped electrolyte membrane is produced, laminated with a gas diffusion layer, and pressed at a constant temperature and pressure. When laminating film-like members such as a base material, an electrolyte membrane, or an electrolyte membrane with a base material, it is preferable to apply tension to each film-like member, and a method of providing a tension cut between each step. It can be changed by such means. The tension cut includes, for example, a roll in which a motor, a clutch, a brake, or the like is installed, and it is preferable to provide a detecting means for detecting the tension applied to the film. Examples of the roller used for tension cutting include a nip roller, a suction roller, or a combination of a plurality of rollers. The nip roller sandwiches the film between the rollers and controls the feed rate of the film by the frictional force generated by the sandwiching pressure, and as a result, the pressure applied to the film can be changed before and after the roller. The suction roller sucks the film-like member by sucking the inside of a roller with many holes on the surface or a roller that is made into a net or a child shape by winding a wire and making it a negative pressure, and by the suction force. The frictional force generated controls the feed rate of the film-like member, and as a result, the pressure applied to the film-like member can be changed before and after the roller.

[Polymer electrolyte membrane]
The polymer electrolyte membrane (hereinafter, may be simply referred to as “electrolyte membrane”) contained in the membrane electrode composite of the present invention is not particularly limited, but is preferably an electrolyte membrane made of an aromatic hydrocarbon-based polymer.

Conventionally, perfluorosulfonic acid-based polymers have been widely used for polymer electrolyte membranes. While this polymer exhibits high proton conductivity through the proton conductive channels due to the cluster structure, it is very expensive because it is manufactured through multi-step synthesis, and in addition, the above-mentioned cluster structure has a large fuel crossover. There was a problem. In addition, there are problems such as loss of mechanical strength and physical durability of the film due to swelling and drying, problems of low softening point and inability to use at high temperature, problems of disposal after use, and difficulty in recycling materials. It has been pointed out.

In order to overcome these drawbacks, it is inexpensive, suppresses fuel crossover, has excellent mechanical strength, has a high softening point, and can withstand use at high temperatures, which can replace perfluorosulfonic acid-based polymers. The development of molecular electrolyte membranes has become active in recent years. In particular, in order to improve the low-humidification proton conductivity, some attempts have been made to form a microphase-separated structure using a block copolymer composed of a hydrophobic segment and a hydrophilic segment.

By using a polymer having such a structure, the hydrophobic interaction between hydrophobic segments and the improvement of mechanical strength due to aggregation, etc., and the electrostatic interaction between ionic groups of hydrophilic segments cause clustering to form an ion conduction channel. The formation improves proton conductivity.

As a mechanism for protons to move in these electrolyte membranes, a vehicle mechanism in which proton-hydrated hydronium ions themselves move and a grotus mechanism in which protons bound to a substrate hopping to another substrate have been proposed. Under low humidification conditions with few water molecules, the movement of sulfonic acid groups by hopping based on the Grotus mechanism becomes dominant.

Under such circumstances, in the case of a fluorine-based electrolyte membrane or the like, the acid dissociation constant of the sulfonic acid group contained in the molecular structure is small and the protons are easily dissociated, so that proton conduction by hopping is likely to proceed. On the other hand, in the hydrocarbon-based electrolyte membrane, the acid dissociation constant of the sulfonic acid group in the molecule is larger than that in the fluorine-based electrolyte membrane, and the dissociation of protons is less likely to occur. It is larger than the fluoroelectrolyte film.

The acid dissociation constant here is one of the indexes for expressing the acid strength of a certain substance, and is represented by the negative common logarithm pKa of the equilibrium constant in the dissociation reaction in which a proton is released from the acid. The smaller the pKa value, the easier it is for protons to be released, indicating that the acid is stronger. The acid dissociation constant in the present application is a value in water at 25 ° C.

As described above, since the hydrocarbon-based electrolyte membrane having a large acid dissociation constant has a larger decrease in proton conductivity under low humidification conditions than the fluorine-based electrolyte membrane, gas diffusion with high water retention is higher than that of the hydrocarbon-based electrolyte membrane. The effect of the present invention is more prominently exhibited by forming a membrane electrode assembly composed of layers.

Specific examples of aromatic hydrocarbon-based polymers include polysulfone, polyethersulfone, polyphenylene oxide, polyarylene ether-based polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyarylene-based polymer, polyarylene ketone, and polyether ketone. , Polyarylene phosphinhoxide, polyether phosphinhoxide, polybenzoxazole, polybenzthiazole, polybenzimidazole, aromatic polyamide, polyimide, polyetherimide, polyimide sulfone and other polymers having an aromatic ring in the main chain. ..

Note that the polyether sulfone is a general term for polymers having a sulfone bond in its molecular chain. Moreover, polyetherketone is a general term for polymers having ether bonds and ketone bonds in their molecular chains, and polyetherketoneketone, polyetheretherketone, polyetheretherketoneketone, polyetherketoneetherketoneketone, It contains polyetherketonesulfone and the like, and does not limit a specific polymer structure.

Among these polymers, polysulfone, polyethersulfone, polyphenylene oxide, polyyleneether-based polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyarylene ketone, polyetherketone, polyarylenephosphinhoxide, polyetherphosphinehoxide, etc. Polymers are often used in terms of mechanical strength, physical durability, processability and hydrolysis resistance.

The method for synthesizing the aromatic hydrocarbon-based electrolyte polymer is not particularly limited as long as the above-mentioned properties and requirements can be satisfied. Such a method is described, for example, in the Journal of Membrane Science, 197, 2002, p.231-242.

As an example, preferable polymerization conditions in the case of synthesizing an aromatic hydrocarbon polymer by a polycondensation reaction are shown below. The polymerization can be carried out in the temperature range of 0 to 350 ° C, but is preferably at a temperature of 50 to 250 ° C. If the temperature is lower than 0 ° C, the reaction tends not to proceed sufficiently, and if the temperature is higher than 350 ° C, decomposition of the polymer tends to start. The reaction is preferably carried out in a solvent. Examples of the solvent that can be used include N, N-dimethylacetamide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, hexamethylphosphontriamide and the like. The aprotic polar solvent of the above can be mentioned, but the solvent is not limited thereto, and any solvent may be used as a stable solvent in the aromatic nucleophilic substitution reaction. These organic solvents may be used alone or as a mixture of two or more kinds.

When the condensation reaction is carried out in a solvent, it is preferable to add the monomers so that the obtained polymer concentration is 5 to 50% by weight. If it is less than 5% by weight, the degree of polymerization tends to be difficult to increase. On the other hand, when it is more than 50% by weight, the viscosity of the reaction system becomes too high, and the post-treatment of the reaction product tends to be difficult.

Examples of the method of introducing an ionic group into an aromatic hydrocarbon polymer include a method of polymerizing using a monomer having an ionic group and a method of introducing an ionic group by a polymer reaction. As a method of polymerizing using a monomer having an ionic group, a monomer having an ionic group may be used in the repeating unit, and if necessary, an appropriate protecting group may be introduced to carry out deprotection group after polymerization. good.

The method of introducing an ionic group will be described by way of example. As a method of sulfonation of an aromatic ring, that is, a method of introducing a sulfonic acid group, for example, Japanese Patent Application Laid-Open No. 2-16126 or Japanese Patent Application Laid-Open No. 2-208322 Etc.

Specifically, for example, the aromatic ring can be sulfonated by reacting it with a sulfonate such as chlorosulfonic acid in a solvent such as chloroform, or by reacting it in concentrated sulfuric acid or fuming sulfuric acid. The sulfonate agent is not particularly limited as long as it sulfonates an aromatic ring, and sulfur trioxide or the like can be used in addition to the above. When the aromatic ring is sulfonated by this method, the degree of sulfonation can be easily controlled by the amount of the sulfonate agent used, the reaction temperature and the reaction time. The introduction of a sulfonimide group into an aromatic polymer is possible, for example, by a method of reacting a sulfonic acid group with a sulfonamide group.

As the ionic group, a functional group having a negative charge is preferable, and a functional group having a proton exchange ability is particularly preferable. As such a functional group, a sulfonic acid group, a sulfonimide group, a sulfate group, a phosphonic acid group, a phosphoric acid group and a carboxylic acid group are preferably used. Here, the sulfonic acid group represents a group represented by the following general formula (f1), and the sulfonimide group represents a group represented by the following general formula (f2) [in the general formula (f2), R represents an arbitrary organic group. .. ], The sulfate group is represented by the following general formula (f3), the phosphonic acid group is represented by the following general formula (f4), and the phosphoric acid group is represented by the following general formula (f5) or (f6). Group and carboxylic acid group mean a group represented by the following general formula (f7).

Such an ionic group shall include the case where the functional groups (f1) to (f7) are salts. Examples of the cation forming the salt include an arbitrary metal cation and NR ⁴⁺ (R is an arbitrary organic group). In the case of a metal cation, its valence is not particularly limited. Specific examples of preferable metal ions include Li, Na, K, Rh, Mg, Ca, Sr, Ti, Al, Fe, Pt, Rh, Ru, Ir and Pd. Among them, as the block copolymer used in the present invention, inexpensive and easily proton-substitutable Na, K, and Li are preferably used.

Two or more kinds of these ionic groups can be contained in the polymer, and the combination can be appropriately determined depending on the structure of the polymer and the like. Among them, it is more preferable to use a sulfonic acid group, a sulfonimide group or a sulfate group from the viewpoint of high proton conductivity, and it is most preferable to have a sulfonic acid group from the viewpoint of raw material cost.

The film thickness of the electrolyte membrane is not particularly limited, but if it is thicker than 20 μm, the power generation performance is lowered, and if it is less than 5 μm, the durability and handleability are significantly lowered. Therefore, it is preferably 5 μm or more and 20 μm or less. When the thickness of the electrolyte membrane is 5 μm or more and 20 μm or less, the amount of water retained in the membrane is small, the membrane dries early under low humidification conditions, and the power generation performance is significantly deteriorated. Application is preferred.

[Catalyst layer]
The catalyst layer of the present invention is composed of an ionic conductor and catalyst-supported particles in which a catalyst is supported on a carrier. Precious metal species such as platinum, gold, ruthenium, and iridium, which have high activity in oxidation and reduction reactions, are preferably used as the catalyst, but the catalyst is not limited thereto. As the carrier, carbon particles having conductivity, high chemical stability, and a high surface area are preferable, and examples thereof include acetylene black, ketjen black, and vulcan carbon.

[Gas diffusion layer]
The gas diffusion layer of the present invention includes a carbon sheet and a microporous layer. That is, it can be produced by forming a microporous layer on a carbon sheet. In the present invention, the gas diffusion layer of the present invention can be obtained by forming a microporous layer on the surface closest to the layer X of the carbon sheet.

The microporous layer is composed of a water-repellent resin such as PTFE and a conductive filler. As the conductive filler, carbon powder is preferable. Carbon powders include carbon blacks such as furnace black, acetylene black, lamp black and thermal black, graphite such as scaly graphite, scaly graphite, earthy graphite, artificial graphite, expanded graphite, and flake graphite, carbon nanotubes, and wire. Graphite, milled fiber of carbon fiber and the like can be mentioned. Among them, carbon black is more preferably used as the carbon powder as the filler, and acetylene black is preferably used because there are few impurities.

In the present invention, it is preferable to reduce the amount of the water-repellent resin used for the microporous layer from the viewpoint of increasing water retention. Further, by using a hydrophilic resin having a binding property instead of the water-repellent resin, the water retention as a membrane electrode assembly can be further enhanced.

[Carbon sheet]
The carbon sheet of the present invention has a high gas diffusibility for diffusing the gas supplied from the separator into the catalyst layer and a high drainage property for discharging the water generated by the electrochemical reaction to the separator. It is important that it is porous. Further, the carbon sheet of the present invention preferably has high conductivity in order to take out the generated current. Therefore, in order to obtain a carbon sheet, it is preferable to use a porous body having conductivity. More specifically, the porous body used to obtain the carbon sheet includes, for example, a porous body containing carbon fibers such as carbon fiber woven fabric, carbon paper and carbon fiber non-woven fabric, and a carbonaceous foamed porous body containing carbon fibers. It is a preferable mode to use.

Above all, since it has excellent corrosion resistance, it is preferable to use a porous body containing carbon fibers in order to obtain a carbon sheet, and further, a dimensional change in the direction perpendicular to the surface of the electrolyte membrane (thickness direction). Since it is excellent in the property of absorbing carbon fiber, that is, "springiness", it is preferable to use carbon paper obtained by binding a carbon fiber paper-making body with a carbide (binding material).

Then, in the first embodiment of the carbon sheet of the present invention, with respect to the layers X, Y, and Z obtained by dividing the carbon sheet into three equal parts in the vertical direction of the sheet surface, the layer closest to the electrolyte membrane side is the layer X, and the other surface. When the layer close to is the layer Y and the layer located between the layers X and the layer Y is the layer Z, the filling rate of the layers is equal in the layer X and the layer Y, and the layer Z is more than the layer X and the layer Y. It is characterized by becoming smaller. Here, the layer filling rate means an average value obtained by using the filling rate of the surfaces forming the layer.

Since the filling rate of the layer Z is lower than that of the other two layers, the diameter of the pores existing in the layer Z becomes large. Thereby, gas diffusion and water discharge can be effectively performed. Further, by making the filling rate of the layer X equal to the filling rate of the layer Y, the generated water generated in the layer Z by the power generation is uniformly supplied to the layer X and the layer Y. Therefore, it is possible to supply water to the electrolyte membrane and drain water to the separator in a well-balanced manner. On the other hand, since the layer Y has a higher filling rate than the layer Z, the layer Y has a rigid flat surface and does not bend when the separator is pressed. By arranging the layers so that the filling rate of the layers is equal to that of the layer X and the layer Y is smaller than that of the layer X and the layer Y, it is possible to prevent water retention and bending of the separator surface. be.

In the first embodiment of the present invention, the filling rate of the layer for achieving water retention and prevention of bending is preferably such that the filling rate of the layer Y is 1 when the filling rate of the layer X is 1. Yes, the filling rate of layer Z is 0.97 or less. Hereinafter, the filling rate of each layer when the filling rate of the layer X is 1, is defined as the filling rate ratio of each layer.

The filling rate of the layer Z is more preferably 0.8 or less, still more preferably 0.7 or less, when the filling rate of the layer X is 1. By reducing the filling rate of the layer Z, the diffusivity of the gas inside the carbon sheet and the drainage property of the water generated inside are remarkably improved, and the flooding resistance is improved. The lower limit of the filling rate ratio of the layer Z is not particularly limited, but is preferably 0.14 or more in consideration of the strength required for post-processing and use in the fuel cell stack.

In such an invention, when the filling rate of the layer X, the layer Y, and the layer Z is 5 to 35%, the carbon sheet is well-balanced in the mechanical strength required for use as a gas diffusion layer for a fuel cell. It is preferable to become. When the filling rate of layer X, layer Y, and layer Z is 5% or more, the carbon sheet is prevented from being destroyed by the force received from the separator even when assembled as a fuel cell stack, and carbon sheet production and higher processing are performed. The handleability at the time is good. Further, when the filling rate of the layer X, the layer Y, and the layer Z is 35% or less, the mass transfer in the carbon sheet becomes easy, the diffusivity of the gas and the drainage of the generated water are efficiently performed, and the fuel cell Power generation performance is significantly improved. The filling rate of the layer X and the layer Y is more preferably 8 to 25%, still more preferably 10 to 20%. The filling rate of layer Z is 5 to 20%, more preferably 7 to 15%. By setting the filling rates of the layers X, Y, and Z to preferable ranges, it is possible to optimally achieve both mechanical strength and power generation performance.
[Measuring method of filling rate of layer X, layer Y, and layer Z]
The method for measuring the filling rate of the carbon sheet obtained by the above method will be specifically described below.

The filling factors of layers X, Y, and Z are obtained by three-dimensional measurement X-ray CT. The three-dimensional data of the carbon sheet is acquired by scanning the entire area in the perpendicular direction from one surface of the carbon sheet toward the other surface at regular lengths with a three-dimensional X-ray CT. By analyzing such three-dimensional data, the filling rate on the measured surface can be obtained, and the filling rate on a specific layer can be obtained. The above-mentioned constant length (hereinafter referred to as slice pitch) can be arbitrarily set, but it is set to one-third or less of the average diameter of the single fibers of the carbon fibers constituting the carbon sheet.

The filling rate of the surface at a predetermined position in the direction perpendicular to the sheet surface of the carbon sheet is the maximum brightness and brightness of the sliced image of the position in the three-dimensional data using the image processing program "J-trim". Is divided into 256 steps at the minimum, and binarization is performed with the portion from the minimum to 175 gradation steps as the threshold value. The ratio of the binarized bright side area to the total area is the filling rate of the surface at a predetermined position.

The one measurement field of view for calculating the surface filling rate depends on the slice pitch, but the average value is obtained by performing multiple measurements so that ^{the total measurement field of view is 5 mm 2 or more, and the layer is filled.} Find the rate.

The X-ray CT used for the measurement shall be SMX-160CTS manufactured by Shimadzu Corporation or an equivalent device. Further, in the examples described later, since the average diameter of the carbon fiber single fibers is 7 μm, the slice pitch is 2.1 μm, the measurement field of view is 1070 μm, the measurement field of view is 5 mm, ² or more, and the surface filling rate is obtained. The number of measurements when determining the filling rate of one surface was set to 7 times.

[Manufacturing method of carbon sheet]
Next, a method suitable for producing the carbon sheet of the present invention will be specifically described below, using carbon paper using a carbon fiber papermaking body as a porous body as a typical example.

<Perforated body>
Examples of carbon fibers include polyacrylonitrile (PAN) -based, pitch-based and rayon-based carbon fibers. Among them, PAN-based carbon fibers and pitch-based carbon fibers are preferably used in the present invention because of their excellent mechanical strength.

The carbon fibers in the carbon sheet of the present invention and the porous body such as the papermaking body used for obtaining the carbon fibers preferably have an average diameter of single fibers in the range of 3 to 20 μm, more preferably in the range of 5 to 10 μm. Inside. When the average diameter of the single fiber is 3 μm or more, the diameter of the pores becomes large, the drainage property is improved, and flooding can be suppressed. On the other hand, when the average diameter of the single fibers is 20 μm or less, it is easy to control the thickness range of the carbon sheet, which will be described later, which is preferable.

The carbon fibers used in the present invention preferably have an average length of single fibers in the range of 3 to 20 mm, more preferably in the range of 5 to 15 mm. When the average length of the single fiber is 3 mm or more, the carbon sheet has excellent mechanical strength, conductivity and thermal conductivity. On the other hand, when the average length of the single fibers is 20 mm or less, the carbon fibers have excellent dispersibility during papermaking, and a homogeneous carbon sheet can be obtained. Carbon fibers having such an average length of single fibers can be obtained by a method of cutting continuous carbon fibers to a desired length or the like.

The average diameter and average length of single fibers in carbon fibers are usually measured by directly observing the carbon fibers as a raw material, but can also be measured by observing a carbon sheet.
A carbon fiber papermaking body formed by papermaking, which is a form of a porous body used to obtain a carbon sheet, has two-dimensional carbon fibers for the purpose of maintaining in-plane conductivity and thermal conductivity isotropically. It is preferably in the form of a sheet randomly dispersed in a plane. The carbon fiber papermaking for obtaining the carbon fiber papermaking body may be performed only once or may be laminated a plurality of times.

In the present invention, in order to prevent internal peeling of the carbon sheet, when the carbon sheet is formed to a desired thickness, it is preferable that the carbon sheet is continuously formed in one step. If the carbon sheet is formed thick by a method such as papermaking multiple times, a discontinuous surface will be formed in the direction perpendicular to the surface, and stress will be concentrated when the carbon sheet is bent, causing internal peeling. Sometimes.

From the viewpoint of preventing internal peeling, specifically, the average diameter of the carbon fiber single fibers is the average diameter of the carbon fiber single fibers obtained from one surface of the carbon sheet and the carbon fibers obtained from the other surface. It is preferable that the ratio of the average diameter of the single fibers of the above is 0.5 or more and 1 or less. Here, when the average diameters are the same, the ratio is 1, and when the average diameters are different, the ratio is small average diameter / large average diameter.

Further, it is preferable that the difference between the average length of the carbon fiber single fibers obtained from one surface and the average length of the carbon fiber single fibers obtained from the other surface is 0 mm or more and 10 mm or less. When the ratio and the difference are within these ranges, the dispersed state of the carbon fibers can be made uniform in the porous body containing the carbon fibers, and variations in the density and thickness of the porous body can be reduced. Since the carbon sheet and the gas diffusion layer made of such a porous body have excellent surface smoothness, a uniform adhesion state with the catalyst layer and the electrolyte membrane can be realized when the membrane electrode assembly is formed, and good power generation performance can be achieved. can get.

<Impregnated resin composition>
When obtaining the carbon sheet of the present invention, a resin composition serving as a binder is impregnated into a porous body containing carbon fibers such as a carbon fiber papermaking body.

In the present invention, as a method of impregnating a porous body containing carbon fibers with a resin composition serving as a binder, a method of immersing the porous body in a solution containing the resin composition and a method of immersing the porous body in a solution containing the resin composition are used. A method of applying to the film, a method of laminating a porous body on a film made of a resin composition, and the like are used. Among them, a method of immersing the porous body in a solution containing a resin composition is particularly preferably used because of its excellent productivity. A porous body containing carbon fibers impregnated with a resin composition serving as a binder may be referred to as a "pre-impregnated body".

The carbon sheet of the present invention is characterized in that the filling rate of the layers is equal in the layer X and the layer Y, and the layer Z is smaller than the layer X and the layer Y. In the present invention, if the difference between the numerical values of the filling rate is 0.2% or less, it is considered to be equal. On the contrary, if the difference between the numerical values of the filling rates is larger than 0.2%, it is considered that one filling rate is smaller than the other filling rate. In such a carbon sheet of the present invention, when the porous body is impregnated with the resin composition, the amount of the resin composition to be impregnated is equal in the layer X and the layer Y, and the layer Z is smaller than the layer X and the layer Y. It can be obtained by doing so. Therefore, the papermaking body containing carbon fibers is uniformly impregnated with the resin composition as a binder by dipping or the like, and then the resin composition excessively adhered before drying is removed. By controlling and distributing the amount of the resin composition in the direction perpendicular to the surface of the carbon sheet, the filling rate of each layer can be controlled.

As an example, after immersing the carbon fiber paper machine in the solution containing the resin composition, the solution containing the resin composition is sucked from both surfaces before drying, or on both sides of the carbon fiber paper machine. It can be passed through a drawing roll. As a result, the amount of adhesion in the vicinity of the surface X and the surface Y can be made uniform by the drawing roll. On the other hand, in the resin composition, since the solvent volatilizes from the surface in the drying step, a large amount of the resin composition can be distributed on the surface, and as a result, in the carbon sheet, the amount of the binder is the layer X and the layer Y. Equally, layer Z can be varied to be less than layer X as well as layer Y.

The resin composition used in producing the pre-impregnated body is preferably a resin composition that is carbonized at the time of firing to be a binder which is a conductive carbide. The resin composition used in producing the pre-impregnated body refers to a resin component to which a solvent or the like is added as needed. Here, the resin component includes a resin such as a thermosetting resin or a thermoplastic resin, and further contains an additive such as a carbon powder or a surfactant, if necessary.

More specifically, it is preferable that the carbonization yield of the resin component contained in the resin composition used for producing the pre-impregnated body is 40% by mass or more. When the carbonization yield is 40% by mass or more, the carbon sheet has excellent mechanical properties, conductivity and thermal conductivity. The carbonization yield of the resin component in the resin composition is not particularly limited, but is usually about 60% by mass.

Examples of the resin constituting the resin component in the resin composition used in producing the pre-impregnated body include thermosetting resins such as phenol resin, epoxy resin, melamine resin and furan resin. Among them, phenol resin is preferably used because of its high carbonization yield.

Further, as an additive to be added to the resin component as needed, the purpose is to improve the mechanical properties, conductivity and thermal conductivity of the carbon sheet as the resin component in the resin composition used when producing the pre-impregnated body. Therefore, carbon powder can be used. Here, the carbon powder includes carbon black such as furnace black, acetylene black, lamp black and thermal black, graphite such as flake graphite such as flake graphite, phosphorus graphite, earthy graphite, artificial graphite and expanded graphite, and carbon. Hydroxite, linear carbon, milled fiber of carbon fiber and the like can be used.

As the resin composition used for producing the pre-impregnated body, the resin component obtained by the above-mentioned constitution can be used as it is, or if necessary, impregnation property into a porous body such as a carbon fiber papermaking body can be obtained. Various solvents can be included for the purpose of enhancing. Here, as the solvent, methanol, ethanol, isopropyl alcohol and the like can be used.

The resin composition used for producing the pre-impregnated body is preferably in a liquid state at a temperature of 25 ° C. and 0.1 MPa. When the resin composition is liquid, the impregnation property into the papermaking body is excellent, and the obtained carbon sheet is excellent in mechanical properties, conductivity and thermal conductivity.

When impregnating, it is preferable to impregnate the resin composition so that the resin component is 30 to 400 parts by mass with respect to 100 parts by mass of the carbon fiber in the pre-impregnated body, and the amount is 50 to 300 parts by mass. Is more preferably impregnated with. When the resin component is 30 parts by mass or more with respect to 100 parts by mass of the carbon fiber in the pre-impregnated body, the carbon sheet has excellent mechanical properties, conductivity and thermal conductivity. On the other hand, when the resin component is 400 parts by mass or less with respect to 100 parts by mass of the carbon fibers in the pre-impregnated body, the carbon sheet has excellent in-plane gas diffusivity and in-plane gas diffusivity.

<Lasting and heat treatment>
In the present invention, after forming a pre-impregnated body impregnated with a resin composition in a porous body such as a carbon fiber papermaking body, the pre-impregnated body is bonded or the pre-impregnated body is heat-treated prior to carbonization. Can be done.

In the present invention, a plurality of pre-impregnated bodies can be bonded together for the purpose of making the carbon sheet having a predetermined thickness. In this case, a plurality of pre-impregnated bodies having the same properties can be bonded together, or a plurality of pre-impregnated bodies having different properties can be bonded together. Specifically, a plurality of carbon fibers having different average diameters and average lengths of single fibers, the texture of porous carbon fibers such as carbon fiber paper machines used to obtain a pre-impregnated body, and the amount of impregnation of resin components are different. It is also possible to attach the pre-impregnated body of.

On the other hand, by bonding, a discontinuous surface is formed in the direction perpendicular to the surface, which may cause internal isolation. Therefore, in the present invention, only one sheet is used without bonding a porous body such as a carbon fiber paper machine. It is desirable to use it in the above and to perform heat treatment on it.

In addition, the pre-impregnated body can be heat-treated for the purpose of thickening and partially cross-linking the resin composition in the pre-impregnated body. As a method for heat treatment, a method of blowing hot air, a method of heating by sandwiching a hot plate such as a pressing device, a method of sandwiching between continuous belts, and the like can be used.

<Carbonization>
In the present invention, a porous body such as a carbon fiber paper machine is impregnated with the resin composition to form a pre-impregnated body, and then the resin composition is carbonized by firing in an inert atmosphere. For this firing, a batch type heating furnace can be used, or a continuous type heating furnace can be used. Further, the inert atmosphere can be obtained by flowing an inert gas such as nitrogen gas or argon gas into the furnace.

The maximum temperature for firing is preferably in the range of 1300 to 3000 ° C, more preferably in the range of 1700 to 3000 ° C, and even more preferably in the range of 1900 to 3000 ° C. When the maximum temperature is 1300 ° C. or higher, carbonization of the resin component in the pre-impregnated body proceeds, and the carbon sheet becomes excellent in conductivity and thermal conductivity. On the other hand, when the maximum temperature is 3000 ° C. or lower, the operating cost of the heating furnace is low.

In the present invention, a porous body such as a carbon fiber paper machine impregnated with a resin composition and then carbonized may be referred to as a "carbon fiber fired body". That is, the carbon sheet means a carbon fiber fired body, and both the carbon fiber fired body before the water repellent treatment and the carbon fiber fired body after the water repellent treatment correspond to the carbon sheet.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[Synthesis of electrolyte membrane]
[Synthesis Example 1]
Synthesis of 2,2-bis (4-hydroxyphenyl) -1,3-dioxolane (K-DHBP) represented by the following general formula (G1)

In a 500 ml flask equipped with a stirrer, a thermometer and a distilling tube, 49.5 g of 4,4'-dihydroxybenzophenone, 134 g of ethylene glycol, 96.9 g of trimethyl orthoformate and 0.50 g of p-toluenesulfonic acid monohydrate were charged and dissolved. do. Then, the mixture was kept warm and stirred at 78 to 82 ° C. for 2 hours. Further, the internal temperature was gradually raised to 120 ° C., and the mixture was heated until the distillation of methyl formate, methanol and trimethyl orthoformate was completely stopped. The reaction solution was cooled to room temperature, the reaction solution was diluted with ethyl acetate, the organic layer was washed with 100 ml of a 5% aqueous potassium carbonate solution, separated, and then the solvent was distilled off. 80 ml of dichloromethane was added to the residue to precipitate crystals, which were filtered and dried to obtain 52.0 g of 2,2-bis (4-hydroxyphenyl) -1,3-dioxolane. GC analysis of this crystal revealed 99.8% 2,2-bis (4-hydroxyphenyl) -1,3-dioxolane and 0.2% 4,4'-dihydroxybenzophenone.

[Synthesis Example 2]
Synthesis of disodium 3,3'-disulfonate-4,4'-difluorobenzophenone represented by the following general formula (G2)

109.1 g (Aldrich reagent) of 4,4'-difluorobenzophenone was reacted in _{150 mL (Wako Pure Chemical Industries, Ltd.) of fuming sulfuric acid (50% SO 3} ) at 100 ° C. for 10 hours. Then, it was gradually added to a large amount of water, neutralized with NaOH, and then 200 g of salt was added to precipitate the synthetic product. The obtained precipitate was separated by filtration and recrystallized from an aqueous ethanol solution to obtain disodium 3,3'-disulfonate-4,4'-difluorobenzophenone represented by the above general formula (G2). The purity was 99.3%. The structure was ^{confirmed by 1 1} H-NMR. Quantitative analysis of impurities was performed by capillary electrophoresis (organic matter) and ion chromatography (inorganic matter).

[Synthesis Example 3]
Synthesis of polyetherketone-based polymer electrolyte membrane composed of polymer represented by the following general formula (G5)

6.91 g of potassium carbonate, 7.30 g of disodium 3,3'-disulfonate-4,4'-difluorobenzophenone having an ionic group obtained in Synthesis Example 1, and the hydrolyzable group obtained in Synthesis Example 2 Hydrolysis in N-methylpyrrolidone (NMP) at 210 ° C. with 10.3 g of 2,2-bis (4-hydroxyphenyl) -1,3-dioxolane and 5.24 g of 4,4'-difluorobenzophenone. went.

A 25 wt% N-methylpyrrolidone (NMP) solution in which the obtained block polymer is dissolved is pressure-filtered using a glass fiber filter, cast-coated on a glass substrate, dried at 100 ° C. for 4 hours, and then nitrogen. Heat treatment was performed at 150 ° C. for 10 minutes to obtain a polyketal ketone film. The solubility of the polymer was extremely good. It was immersed in a 10 wt% sulfuric acid aqueous solution at 95 ° C. for 24 hours for proton substitution and deprotection reaction, and then immersed in a large excess amount of pure water for 24 hours for thorough washing to obtain a polymer electrolyte membrane.
[Measurement of proton conductivity]
After immersing the electrolyte membrane in pure water at 25 ° C for 24 hours, it is held in a constant temperature and humidity chamber at 80 ° C and a relative humidity of 25 to 90% for 30 minutes at each step, and the proton conductivity is measured by the constant potential AC impedance method. It was measured. As the electrolyte membrane, a polyether ketone polymer electrolyte membrane using an aromatic hydrocarbon polymer and a commercially available perfluorocarbon electrolyte membrane (Nafion (registered trademark) 211) were used.

As a measuring device, a Solartron electrochemical measurement system (Solartron 1287 Electrochemical Interface and Solartron 1255B Frequency Response Analyzer) was used, and constant potential impedance measurement was performed by a two-terminal method to determine proton conductivity. The AC amplitude was 50 mV. The sample used was a film having a width of 10 mm and a length of 50 mm. The measuring jig was made of phenol resin, and the measuring part was opened. A platinum plate (thickness 100 μm, 2 plates) was used as the electrode. The electrodes were arranged at a distance of 10 mm between the electrodes on the front side and the back side of the sample film so as to be parallel to each other and orthogonal to the longitudinal direction of the sample film. Proton conductivity was measured at a measurement temperature of 80 ° C. and a relative humidity of 25% and 90%.

[Preparation of carbon sheet]
-Manufacture of carbon sheet with a thickness of 150 μm Toray Industries, Inc.'s polyacrylic nitrile carbon fiber "Treca" (registered trademark) T300 (average diameter of single fiber: 7 μm) is cut into an average length of short fiber of 12 mm and placed in water. The paper was continuously made by the wet paper making method. Further, a 10 mass% aqueous solution of polyvinyl alcohol as a binder was applied to the paper machine and dried to prepare a carbon fiber paper machine having a carbon fiber texture of 10.0 g / m2. The amount of polyvinyl alcohol applied was 22 parts by mass with respect to 100 parts by mass of the carbon fiber papermaking body.

Next, a resin composition obtained by mixing a resole-type phenol resin and a novolak-type phenol resin at a mass ratio of 1: 1 as a thermosetting resin, scaly graphite (average particle size 5 μm) as a carbon powder, and methanol as a solvent. Thermosetting resin / carbon powder / solvent = 10 parts by mass / 5 parts by mass / 85 parts by mass of these were mixed and stirred for 1 minute using an ultrasonic disperser to uniformly disperse the resin. The composition was obtained.

Next, a carbon fiber paper machine cut into a size of 15 cm × 12.5 cm was horizontally immersed in an impregnating solution of a resin composition filled in an aluminum vat, sandwiched between rolls, and impregnated by drawing. At this time, two rolls were arranged horizontally with a certain clearance, and the carbon fiber papermaking body was pulled up vertically to adjust the total amount of the resin composition adhered. Further, by squeezing the sandwiching liquid with rolls having the same shape from both sides, the amount of the resin composition adhered was made uniform. Then, it was heated at a temperature of 100 ° C. for 5 minutes and dried to prepare a pre-impregnated body. Next, the heat treatment was performed at a temperature of 180 ° C. for 5 minutes while pressurizing with a flat plate press. A spacer was placed on the flat plate press during pressurization, and the spacing between the upper and lower press face plates was adjusted so that the thickness of the pre-impregnated body after the heat treatment was 50 μm. In this way, a high-density pre-impregnated body for a carbon sheet having a thickness of 50 μm was produced. Further, by adjusting the amount of removing the resin composition in the adhesion of the resin of the pre-impregnated body, a pre-impregnated body for a carbon sheet having a medium density and a thickness of 50 μm was prepared. Two pre-impregnated bodies for high-density carbon sheets and one pre-impregnated body for medium-density carbon sheets were laminated in the order of high density, medium density, and high density, and heat and pressure were applied.

The base material obtained by heat-pressurizing the pre-impregnated body was introduced into a heating furnace having a maximum temperature of 2400 ° C. maintained in a nitrogen gas atmosphere in a heating furnace to obtain a carbon sheet made of a carbon fiber fired body.

The carbon sheet prepared above is used as an aqueous dispersion of PTFE resin (“Polyflon” (registered trademark) PTFE dispersion D-1E (manufactured by Daikin Industries, Ltd.) or FEP resin (“Neophron” (registered trademark) FEP dispersion). The carbon fiber fired body was impregnated with a water-repellent material by immersing it in an aqueous dispersion of John ND-110 (manufactured by Daikin Industries, Ltd.), and then heated in a dryer furnace at a temperature of 100 ° C. for 5 minutes. The carbon sheet was dried and water-repellent to prepare a carbon sheet. When the carbon sheet was dried, the carbon sheet was placed vertically and the vertical direction was changed every minute. After drying, the carbon sheet was diluted to an appropriate concentration to give 5 parts by mass of a water-repellent material to 95 parts by mass of the carbon sheet. A carbon sheet having a grain size of 45 g / m2 and a thickness of 150 μm was prepared. ..

[Preparation of gas diffusion layer]
[material]
-Carbon powder A: Acetylene black: "Denka black" (registered trademark) (manufactured by Denki Kagaku Kogyo Co., Ltd.)
-Carbon powder B: Linear carbon: "VGCF" (registered trademark) (manufactured by Showa Denko KK) Aspect ratio 70
-Material C: Water-repellent material: PTFE resin (using "Polyflon" (registered trademark) PTFE dispersion D-1E (manufactured by Daikin Industries, Ltd.), which is an aqueous dispersion containing 60 parts by mass of PTFE resin)
-Material D: Surfactant "TRITON" (registered trademark) X-100 (manufactured by Nacalai Tesque Co., Ltd.)
Each of the above materials was mixed using a disperser to form a filler-containing coating liquid. This filler-containing coating liquid is applied in a planar manner on one surface of a water-repellent carbon sheet using a slit die coater, and then at a temperature of 120 ° C. for 10 minutes, followed by a temperature of 380 ° C. for 10 minutes. It was heated. In this way, a microporous layer was formed on the water-repellent carbon sheet to prepare a gas diffusion layer. As the filler-containing coating liquid used here, carbon powder, a water-repellent material, a surfactant and purified water were used, and the composition of the carbon coating liquid shown in the table was adjusted so that the blending amount was described in parts by mass. I used the one. The blending amount of the material C (PTFE resin) shown in the table represents not the blending amount of the aqueous dispersion of the PTFE resin but the blending amount of the PTFE resin itself.

[High temperature and low humidification power generation evaluation (power generation performance)]
The film electrode composite produced by the method described in the examples was set in a JARI standard cell "Ex-1" (electrode area 25 cm ² ) manufactured by Eiwa Co., Ltd. to form a power generation evaluation module, and power generation evaluation was performed under the following conditions. The current was swept ^{from 0 A / cm 2} to 1.2 A / cm ² until the voltage fell below 0.2 V. In the present invention, the voltages at a current density of 1 A / cm at ^{2 o'clock were compared.} When the membrane electrode complex was set in the cell, a pressure of 0.7 GPa was applied.
Electronic load device; Electronic load device "PLZ664WA" manufactured by Kikusui Electronics Co., Ltd.
Cell temperature; always 80 ° C
Gas humidification conditions; 30% RH or 90% RH
Gas utilization: 70% stoichiometry for anode and 40% stoichiometry for cathode.

[Example 1]
A polyetherketone-based polymer electrolyte membrane (thickness: 10 μm) was prepared by using the synthesis method described in [Synthesis of Electrolyte Membrane] above. The proton conductivity of the prepared electrolyte membrane was 0.12 S / cm2 at 25% relative humidity and 8 S / cm2 at 90% relative humidity. A transfer sheet with an anode catalyst (size: 50 x 50 mm) and a transfer sheet with a cathode catalyst (size: 50 x 50 mm) are placed on both sides of this electrolyte membrane (size: 70 mm x 70 mm) at 160 ° C., 4.5 MPa, 5 min. To prepare a catalyst layer-coated electrolyte membrane (CCM) by heating and pressing.

An anode gas diffusion layer and a cathode gas diffusion layer were prepared using the production method described in [Preparation of gas diffusion layer] above. As the carbon sheet contained in the anode gas diffusion layer and the cathode gas diffusion layer, a carbon sheet having the characteristics described in [Preparation of carbon sheet] was used. When the filling rate of this carbon sheet was measured by the method described in [Measuring method of filling rate of layer X, layer Y, and layer Z], the filling rate of layer X and layer Y was 17.5%, that of layer Z. The filling rate was 16.7%.
The above CCM, an anode gas diffusion layer (size: 50 mm × 50 mm), and a cathode gas diffusion layer (size: 50 mm × 50 mm) were arranged as shown in FIG. 2 (cross-sectional view). A membrane electrode complex was prepared by hot pressing at 160 ° C. for 5 minutes at 4.5 Ma.
The power generation performance was 0.50 V at 30% RH and 0.65 V at 90% RH.

[Example 2]
A polyether ketone polymer electrolyte membrane (thickness: 10 μm, size: 70 mm × 70 mm) prepared under the same conditions as in Example 1 and an anode electrode (size: 50 mm × 50 mm) which is a gas diffusion electrode (GDE). And the cathode electrode (size: 50 mm × 50 mm) was arranged as shown in FIG. 3 (cross-sectional view). As the gas diffusion layer contained in the anode and the cathode gas diffusion electrode, a gas diffusion layer containing a carbon sheet prepared under the same conditions as in Example 1 was used. A membrane electrode complex was prepared by hot pressing at 160 ° C. for 5 minutes at 4.5 Ma.

The power generation performance was 0.50 V at 30% RH and 0.65 V at 90% RH.

[Comparative Example 1]
In the above [Preparation of carbon sheet], the carbon sheet was prepared according to the method described in Example 1 except that three pre-impregnated bodies for carbon sheets having a medium density and a thickness of 50 μm were laminated and heated and pressed. A carbon sheet having a uniform filling rate as a whole was prepared. When the filling rate of this carbon sheet was measured by the method described in [Measuring method of filling rate of layer X, layer Y, and layer Z], the filling rate of layer X, layer Y, and layer Z was 16.7%. Met. A membrane electrode complex was prepared under the same conditions as in Example 1 except that this carbon sheet was used as the carbon sheet contained in the gas diffusion layer.

The power generation performance was 0.30 V at 30% RH and 0.65 V at 90% RH.

[Comparative Example 2]
When the proton conductivity was measured using a commercially available perfluorocarbon-based polymer electrolyte membrane (film thickness: 25 μm), it was 1 S / cm2 at a relative humidity of 25% and 6 S / cm2 at a relative humidity of 90%. A membrane electrode composite was prepared under the same conditions as in Example 1 except that this perfluorocarbon-based polymer electrolyte membrane (size: 70 mm × 70 mm) was used as the electrolyte membrane.

The power generation performance was 0.50 V at 30% RH and 0.60 V at 90% RH.

[Comparative Example 3]
A membrane electrode complex was prepared under the same conditions as in Comparative Example 1 except that the same perfluorocarbon-based polymer electrolyte membrane as in Comparative Example 2 was used as the electrolyte membrane.

The power generation performance was 0.40 V at 30% RH and 0.60 V at 90% RH.

1: Carbon sheet 2: Surface X
3: Surface Y
4: Layer X
5: Layer Z
6: Layer Y
7: Gas diffusion layer 8: Catalyst layer 9: Electrolyte membrane

Claims (4)

A membrane electrode assembly having an electrolyte membrane and a catalyst layer and a gas diffusion layer provided on both sides of the electrolyte membrane. The gas diffusion layer is composed of at least a porous carbon sheet and a microporous layer, and the porous carbon sheet is formed. Regarding the layers X, Y, and Z obtained by dividing the sheet surface into three equal parts in the vertical direction, the layer closest to the electrolyte membrane side is the layer X, the layer closest to the other surface is the layer Y, and between the layer X and the layer Y. A membrane electrode assembly characterized in that, when the layer to be located is layer Z, the filling rate of the layers is equal between layer X and layer Y, and layer Z is smaller than layer X and layer Y. The membrane electrode complex according to claim 1, wherein the filling rate of the layer Z is 0.97 or less when the filling rate of the layers X and Y of the gas diffusion layer is 1. The electrolyte membrane is a block copolymer composed of a hydrophilic segment having a sulfonic acid group and a hydrophobic segment having no sulfonic acid group, and the acid dissociation constant of the sulfonic acid group is -10 or more. The membrane electrode composite according to claim 1 or 2. The membrane electrode complex according to any one of claims 1 to 3, wherein the electrolyte membrane is made of an aromatic hydrocarbon-based polymer.

Images