JP2011198501A - Solid polymer fuel cell, membrane-electrode assembly, electrode catalyst layer, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane electrode assembly for solid polymer fuel cell capable of enhancing power generation efficiency by increasing all of gas channel, proton conduction path, and three-phase interface without increasing a catalyst layer resistance and utilizing effectively the catalyst in the catalyst layer at the time of obtaining a solid polymer fuel cell, and a manufacturing method of the membrane electrode assembly for solid polymer fuel cell.SOLUTION: In the membrane electrode assembly, at least the electrode catalyst layer on the cathode side is composed of a porous film in which a proton conductive polymer obtained by freezing and drying is formed continuously and a catalyst carrying carbon, and the higher the catalyst density in the electrode catalyst layer is, the nearer it is to the polymer electrolyte membrane, while the lower the density is, the farther it is separated from the polymer electrolyte membrane.

Description

  The present invention relates to a membrane / electrode assembly for a polymer electrolyte fuel cell, a method for producing the membrane / electrode assembly, and a technology for a polymer electrolyte fuel cell using the same.

  A fuel cell is a kind of power generation device that generates electricity by causing reverse reaction of electrolysis of water using hydrogen and oxygen as fuel. Fuel cell power generation has features such as high efficiency, low environmental load, and low noise compared to conventional power generation methods, and is attracting attention as a clean energy source in the future. In particular, polymer electrolyte fuel cells that can be used near room temperature are expected to be used for in-vehicle power sources and household stationary power sources, and in recent years, various research and development have been conducted.

Here, examples of the challenges for the practical application of fuel cells include power density, gas utilization rate, improved durability, and cost reduction.
In order to improve the power density and the gas utilization rate, it is necessary to supply fuel gas and proton sufficiently and to increase the surface area of the oxidation-reduction reaction site in the catalyst electrode. The most demanded for cost reduction is a reduction in the amount of platinum used as a catalyst for the electrode.

  In general, a polymer electrolyte fuel cell is configured by stacking a large number of single cells. The single cell has a structure in which a membrane / electrode assembly is sandwiched between separators having gas flow paths. The membrane / electrode assembly has a structure in which a solid polymer electrolyte membrane is sandwiched between two electrodes, an oxidation electrode and a reduction electrode. Then, oxidation of hydrogen gas occurs at the oxidation electrode, and reduction of hydrogen ions occurs at the reduction electrode. This oxidation-reduction reaction occurs inside the electrode only on the surface of the catalyst that is in contact with both the carbon particles as the electron conductor and the proton conductor and can adsorb the introduced gas. This part where the redox reaction takes place is called the three-phase interface. The large area of the three-phase interface and satisfying the proton and fuel gas supply path to the three-phase interface lead to an improvement in the output density and gas utilization rate of the single cell.

  For this purpose, it is necessary to improve the diffusibility of the gas in the catalyst layer, the drainage of the generated water, the water content of the proton conductive polymer, the proton conductivity, and the like. In addition, platinum catalyst particles that are not located at the three-phase interface do not contribute to the oxidation-reduction reaction of the electrode, and thus do not function at all. In order to reduce the amount of platinum used, it is necessary to reduce the amount of platinum that does not function as much as possible to increase the effective utilization rate of the platinum used.

  Conventionally, the catalyst layer is often formed on a substrate by various coating methods, screen printing methods, and the like using a catalyst ink in which catalyst-supported carbon, a proton conductive polymer, and a solvent are confused. In this case, agglomeration of the catalyst-supported carbon is likely to occur when the coated catalyst ink is dried. As a result, the interface between the catalyst and the proton-conductive polymer is reduced, or the porosity in the catalyst layer is reduced to reduce the fuel. There was a tendency for the power density of the cell to decrease due to the gas path being cut off.

  Thus, attempts have been made to use freeze-drying in order to prevent aggregation of the catalyst-supporting carbon and increase the three-phase interface (see, for example, Patent Documents 1 to 3). This freeze-drying is performed by freezing a material containing water and sublimating ice under vacuum, and the material after freeze-drying can maintain its shape when frozen. This freeze-drying is a drying method conventionally used in the food industry in the food industry and in the medical / pharmaceutical fields.

Here, in Patent Document 1, a catalyst ink in which catalyst-supported carbon, a proton conductive polymer, and a solvent are mixed is freeze-dried and then heat-treated and pulverized to obtain a catalyst layer-constituting powder, and the powder is formed into a sheet. It is described that a catalyst layer is obtained.
Patent Document 2 describes that a catalyst layer is obtained by adding a solvent to a freeze-dried catalyst ink obtained by mixing a catalyst-supporting carbon, a proton-conductive polymer, and a solvent, and applying the ink again. Has been.

  Patent Document 3 discloses that a first intermediate obtained by mixing and stirring catalyst-carrying carbon and water is freeze-dried to be porous, and then a Nafion solution is added under reduced pressure to form an electrode paste. It is described that an electrode catalyst layer is obtained by applying to the surface.

JP-A-8-185865 JP 2003-86190 A JP 2009-1117069 A

However, in the method according to Patent Document 1, since the pulverization process is performed even if the reaction point increases, formation of a proton conduction path by the proton conductive polymer is insufficient, and the catalyst layer resistance increases due to the decrease in proton conductivity. Therefore, the power generation performance does not increase so much.
Further, in the method according to Patent Document 2, the adsorption of the proton conductive polymer is peeled off due to the dispersion mixing at the time of reinking, and the catalyst-carrying carbon is aggregated or the pores serving as gas channels are crushed, thereby generating power characteristics. Still does not improve much.

Moreover, in the method according to Patent Document 3, since the catalyst is present at the same frequency in the entire region of the catalyst layer, a catalyst that is not used appears as a result. Moreover, in the method of forming a catalyst layer by applying a paste to a base material, the generated water is not sufficiently discharged, and there is a concern about voltage drop due to flooding.
The present invention has been made to solve the above problems, and in obtaining a polymer electrolyte fuel cell, the gas channel, proton conduction path, and three-phase interface are all increased without increasing the catalyst layer resistance. It is an object of the present invention to provide an electrode catalyst layer, a membrane / electrode assembly, and a polymer electrolyte fuel cell that can increase power generation efficiency by effectively using a catalyst in the catalyst layer.

In order to solve the above problems, the invention described in claim 1 of the present invention is a membrane / electrode assembly including a polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane. A method for producing the electrode catalyst layer used in
Forming a porous membrane by applying a dispersion containing a proton-conducting polymer to the substrate surface, freezing before the solvent dries and drying under vacuum to form a porous membrane of the proton-conducting polymer on the substrate Process,
The proton-conductive polymer porous membrane formed above was impregnated with the catalyst-supported carbon dispersion and dried to impregnate the pores of the proton-conductive polymer porous membrane with the catalyst-supported carbon. A first intermediate forming step for obtaining one intermediate;
By applying the catalyst-supported carbon dispersion to the surface of the first intermediate and drying, the density of the catalyst-supported carbon adsorbed on the pores of the porous membrane of the proton conductive polymer is close to that of the substrate. A second intermediate forming step for obtaining a second intermediate that is set to be higher at a position away from the substrate than at the position;
An impregnation drying step of impregnating the second intermediate with a dispersion of a proton conductive polymer and drying;
It is characterized by having.

  Next, in the invention described in claim 2, the electrode catalyst layer manufactured by the manufacturing method described in claim 1 is disposed at least on the cathode side of the polymer electrolyte membrane, and the glass transition point of the polymer electrolyte membrane is determined. The present invention provides a method for producing a membrane / electrode assembly, wherein the membrane / electrode assembly is brought into close contact with the polymer electrolyte membrane by applying pressure in the following temperature atmosphere.

Next, the invention described in claim 3 is a membrane / electrode assembly comprising a polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane,
At least the cathode-side electrode catalyst layer of the pair of electrode catalyst layers has a porous membrane composed of a continuous proton-conductive polymer and catalyst-supporting carbon, and the catalyst density in the electrode catalyst layer is: It is characterized by being set higher at a position closer to the polymer electrolyte membrane than at a position away from the polymer electrolyte membrane.

  Next, an invention described in claim 4 provides a polymer electrolyte fuel cell comprising the membrane-electrode assembly according to claim 3.

According to the membrane / electrode assembly of the present invention, the gas channel can be formed without increasing the catalyst layer resistance by comprising a porous membrane comprising a continuous proton conductive polymer obtained by freeze-drying and catalyst-supporting carbon. The proton conduction path and all three-phase interfaces can be increased.
In addition, by setting the catalyst density in the electrode catalyst layer higher as it is closer to the polymer electrolyte membrane, the catalyst is present in the vicinity of the polymer electrolyte membrane where protons are likely to reach at a high supported density, generating power efficiently, and gas diffusion. Since gas diffusion and drainage can be promoted on the layer side, the catalyst in the catalyst layer can be used effectively.

  That is, according to the inventions according to claims 1 and 3, it is possible to produce an electrode catalyst layer in which all of the gas channel, proton conduction path, and three-phase interface are increased without increasing the catalyst layer resistance. it can. Furthermore, it is possible to provide an electrode catalyst layer in which the catalyst loading density is changed in the thickness direction without complicated steps.

According to the invention of claim 2, the gas channel, proton conduction path, and three-phase interface all increase, and a membrane / electrode assembly that can effectively use the catalyst in the catalyst layer can be manufactured. .
According to the invention of claim 4, a fuel cell with good power generation efficiency can be obtained.

1 is a schematic cross-sectional view of a membrane / electrode assembly using an electrode catalyst layer according to the present invention. It is a schematic diagram of the three-phase interface of the electrode catalyst layer which concerns on this invention. It is a schematic cross section of a mode change in each process of an electrode catalyst layer by a manufacturing method of the present invention.

Embodiments of the present invention will be described below with reference to the drawings. Note that this embodiment is an example of the present invention and does not limit the present invention.
(Solid polymer fuel cell)

A polymer electrolyte fuel cell is configured by stacking a large number of single cells. The single cell has a structure in which a membrane / electrode assembly is sandwiched between separators having gas flow paths.
(Membrane / electrode assembly)

As shown in FIG. 1, the membrane / electrode assembly has a structure in which a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers.
In the membrane-electrode assembly of the present embodiment, at least the cathode catalyst layer 1 (upper side in FIG. 1) of the pair of electrode catalyst layers is a porous membrane in which proton conductive polymers are continuously formed. And catalyst-supporting carbon. The catalyst density in the electrode catalyst layer 1 is set to be higher as it is closer to the polymer electrolyte membrane and lower as it is farther from the polymer electrolyte membrane.
The polymer electrolyte membrane 18 and the electrode catalyst layer 1 are joined as follows, for example.

That is, as will be described later, the electrode catalyst layer 1 formed on the surface of the substrate 12 is disposed on at least the cathode side of the polymer electrolyte membrane 18 and hot-pressed to thereby make the electrode catalyst layer 1 the polymer electrolyte membrane 18. Adhere to. The hot pressing is performed by applying pressure in a temperature atmosphere below the glass transition point of the polymer electrolyte membrane 18.
After adhesion, the substrate 12 is peeled from the electrode catalyst layer 1 to obtain a membrane / electrode assembly 19. As described above, the membrane / electrode assembly 19 has a high support density of the catalyst 4 in the vicinity of the electrolyte membrane 18, and the support density of the catalyst 4 decreases as the distance from the polymer electrolyte membrane 18 increases.
(Method for producing electrode catalyst layer)

  The electrode catalyst layer 1 containing the catalyst-supporting carbon and the proton conductive polymer is manufactured, for example, as follows.

  That is, a proton conductive polymer porous body 10 (porous membrane) is obtained by applying a dispersion containing a proton conductive polymer to the surface of the substrate 12, freezing the solvent before drying, and drying under vacuum. (Porous membrane formation process). Next, the proton-conducting polymer porous body 10 is impregnated with a dispersion of catalyst-supporting carbon and dried (first intermediate formation step). Next, by applying a catalyst-supported carbon dispersion on the surface and drying, the density of the catalyst-supported carbon adsorbed on the pores of the porous membrane 10 of the proton conductive polymer is lower as the base material 12 is closer, The higher the intermediate body 3 is, the higher the distance from the substrate 12 is (second intermediate forming step). Further, the electrode catalyst layer 1 is obtained by impregnating the second intermediate 3 with a dispersion of a proton conductive polymer and drying (impregnation drying step).

The electrode catalyst layer 1 increases all of the gas channel, proton conduction path, and three-phase interface without increasing the catalyst layer resistance, and the catalyst is present at a high supported density in the vicinity of the polymer electrolyte membrane where protons can easily reach. The gas diffusion layer side promotes gas diffusion and drainage to effectively use the catalyst in the catalyst layer.
Here, in the first intermediate forming step, since the solvent in which the catalyst-supporting carbon is dispersed dissolves the surface of the proton conductive polymer porous body 10 appropriately, the carbon particles 16 supporting the catalyst particles 15 are protons. The conductive polymer porous body 10 is partially embedded and fixed.

Further, by embedding it with the proton conductive polymer 17 in the impregnation drying step, a three-phase interface and a proton path are formed.
In FIG. 2, the schematic diagram of the three-phase interface of the electrode catalyst layer 1 in this embodiment is shown. FIG. 2 shows in detail the portion 14 having the three-phase interface shown in FIG.

Next, the state change in each step of electrode catalyst layer production will be described with reference to FIG.
FIG. 3 is a schematic cross-sectional view of a state change for each step of the electrode catalyst layer according to the manufacturing method of the present embodiment.
The porous body 10 which is a porous membrane of a proton conductive polymer is coated with a dispersion containing the proton conductive polymer on the surface of the substrate 12 and then frozen and vacuum dried before the solvent is dried (porous membrane forming step). Can be obtained.

FIG. 3A shows a state in which a dispersion containing a proton conductive polymer is applied to the surface of the substrate 12 and frozen before the solvent is dried. The frozen solvent 11 actually exists three-dimensionally continuously in a state where the proton conductive polymer is dispersed.
FIG. 3 (b) shows a state of further drying under vacuum from the state shown in FIG. 3 (a), and the solvent sublimated from the portion where the frozen solvent 11 was present to become pores 13.

FIG. 3C shows a state after the first intermediate formation step in which the proton-conductive polymer porous body 10 is impregnated with a catalyst-supported carbon dispersion and dried. By the first intermediate formation step, the first intermediate 2 in which the catalyst-supporting carbon is uniformly adsorbed on the pore surfaces of the proton conductive polymer porous body 10 is obtained.
FIG. 3D shows a state after a second intermediate formation step in which a catalyst-supported carbon dispersion is applied to the upper surface of the first intermediate 2 and dried. By this second intermediate formation step, the density of the catalyst-carrying carbon adsorbed on the pore surface is higher in the portion close to the upper surface, and the density of the catalyst-carrying carbon adsorbed on the pore surface is lower as it is closer to the substrate 12. Intermediate 3 is obtained.

The second intermediate 3 is impregnated with a proton conductive polymer dispersion and dried (impregnation drying step), whereby a three-phase interface is formed on the pore surface of the proton conductive polymer porous body 10. Actually, since the proton conductive polymer porous body 10 and the pores 13 exist three-dimensionally continuously, the portion 14 having a three-phase interface also exists three-dimensionally in the same manner. .
In addition, although the electrode catalyst layer 1 of this embodiment can be arrange | positioned at both the anode side of the polymer electrolyte membrane 18, and the cathode side, it is more preferable to arrange | position at the cathode side. By disposing on the cathode side, the power generation efficiency can be improved, and furthermore, a voltage drop due to clogging of generated water and blocking of the pores can be suppressed.

  Here, examples of the catalyst include platinum, palladium, ruthenium, iridium, rhodium, osmium, platinum group elements, and metals such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. Alternatively, alloys thereof, oxides, double oxides, carbides, or the like can be used.

  Moreover, when the particle size of these catalysts is too large, the specific surface area per mass of the catalyst decreases, and as a result, the current value obtained per unit mass of the catalyst becomes small. On the other hand, if it is too small, the stability of the catalyst is lowered, so that it is preferably from 0.5 nm to 50 nm, more preferably from 1 nm to 5 nm.

Any carbon may be used as long as it supports the catalyst used in the present embodiment as long as it is finely powdered and has conductivity and is not affected by the catalyst. For example, carbon black, graphite, graphite, activated carbon, carbon nanotube, and fullerene can be preferably used.
If the particle size of the carbon is too small, it is difficult to form an electron conduction path, and if it is too large, the gas diffusibility of the catalyst layer is lowered or the utilization factor of the catalyst is lowered. For this reason, about 10 nm-1000 nm are preferable, More preferably, 10 nm or more and 100 nm or less are good.

  Various proton conductive polymers are used, but considering the interface resistance between the polymer electrolyte membrane and the electrode, and the dimensional change rate of the electrode and the electrolyte membrane when the humidity changes, the electrolyte membrane to be used, The proton conductive polymer in the catalyst layer may be the same component.

  The proton conducting polymer used in the membrane / electrode assembly of the present embodiment may be any proton-conducting polymer as long as it has proton conductivity, and a fluorine-based polymer electrolyte and a hydrocarbon-based polymer electrolyte can be used. Examples of the fluoropolymer electrolyte include Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., Aciplex (registered trademark) manufactured by Asahi Kasei Co., Ltd., and Gore Select (registered trademark) manufactured by Gore. Etc. can be used. As the hydrocarbon polymer electrolyte, sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, sulfonated polyphenylene and the like can be used. Among these, a Nafion (registered trademark) material manufactured by DuPont can be suitably used as the polymer electrolyte membrane. As the hydrocarbon polymer electrolyte membrane, electrolyte membranes such as sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used.

  The solvent used as the dispersion medium in the present embodiment is any solvent that does not erode the catalyst particles and the proton conductive polymer and can dissolve or disperse the proton conductive polymer in a highly fluid state as a fine gel. There is no particular limitation. The solvent may contain water that is compatible with the proton conductive polymer. The amount of water added is not particularly limited as long as the proton conductive polymer is not separated to cause white turbidity or gelation.

  The solvent for dispersing the catalyst-supporting carbon in the first intermediate formation step and the second intermediate formation step and the solvent for dispersing the proton conductive polymer in the impregnation drying step include at least a volatile liquid organic solvent. However, those using a lower alcohol as a solvent have a high risk of ignition, and when using such a solvent, it is preferable to use a mixed solvent with water.

  The volatile liquid organic solvent is not particularly limited. Specifically, for example, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, Alcohols such as pentanol, acetone, methyl ethyl ketone, pentanone, methyl isobutyl ketone, heptanone, cyclohexanone, methyl cyclohexanone, acetonyl acetone, diisobutyl ketone and other ketone solvents, tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, di Ether solvents such as butyl ether, other dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol Lumpur, diacetone alcohol, 1 such as a polar solvent such as methoxy-2-propanol can be exemplified.

Although these can also be used independently, what mixed 2 or more types of these solvents can also be used.
Distributed processing can be performed using various apparatuses. Examples thereof include a ball mill, a roll mill, a shear mill, a wet mill, and an ultrasonic dispersion treatment. Moreover, you may use the homogenizer etc. which stir with centrifugal force.

  The substrate 12 used in the present embodiment is, for example, an ethylene tetrafluoroethylene copolymer (ETFE), a tetrafluoroethylene-hexafluoropropylene copolymer (FEP), a tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA). Fluorine resin excellent in transferability such as polytetrafluoroethylene (PTFE) can be used. Polymer films such as polyimide, polyethylene terephthalate, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyarylate, and polyethylene naphthalate can also be used.

  When the substrate 12 is a gas diffusion electrode, it is not necessary to peel off the gas diffusion layer that is the substrate after hot pressing. As a gas diffusion layer, what is used for the normal fuel cell can be used. Specifically, porous carbon materials such as carbon cloth, carbon paper, and non-woven fabric can be used as the gas diffusion layer. A sealing layer may be formed between the gas diffusion layer and the electrode catalyst layer. The sealing layer is a layer that prevents the catalyst ink from permeating into the gas diffusion layer, and deposits on the sealing layer to form a three-phase interface even when the coating amount is small. Such a sealing layer can be formed, for example, by kneading carbon particles and a fluorine resin and sintering them at a temperature equal to or higher than the melting point of the fluorine resin. As the fluororesin, polytetrafluoroethylene (PTFE) or the like can be used.

  The pressure applied to the electrode catalyst layer in the hot pressing step affects the battery performance of the membrane / electrode assembly 19. In order to obtain a membrane / electrode assembly having good battery performance, the pressure A applied to the base material 12 and the proton conductive polymer porous body 10 is preferably 0.5 MPa ≦ A ≦ 20 MPa, and more preferably 2 MPa ≦ A ≦ 15 MPa. When the pressure is higher than this, the electrode catalyst layer is excessively compressed, and when the pressure is lower than this, the bondability between the electrode catalyst layer 1 and the polymer electrolyte membrane 18 is lowered, and the battery performance is lowered.

The generation of wrinkles in the membrane / electrode assembly 19 is affected by the pressure B applied to the portion of the polymer electrolyte membrane 18 in the hot press process. When B is small and the difference from A is large, wrinkles are likely to occur in the portion of the polymer electrolyte membrane 18. B can be defined by the ratio A / B of A to B, and preferably 1 <A / B ≦ 3. More preferably, 1 <A / B ≦ 2.
The above pressure condition can be reproduced by using a buffer material having an appropriate compression rate. The cushioning material may be of a size that covers all of the laminate to be hot pressed. Moreover, what is compressed in the direction parallel to a pressurization direction when pressurized in the thickness direction is good.

  The hot press temperature is set in the vicinity of the glass transition point of the proton conducting polymer of the polymer electrolyte membrane 18 and the electrode catalyst layer 1 to improve the bondability at the interface between the polymer electrolyte membrane 18 and the electrode catalyst layer 1. However, it is effective in that the interface resistance can be suppressed, and is preferably 100 ° C. or higher.

<Preparation of transfer sheet>
A commercially available proton conductive polymer (Nafion: registered trademark of DuPont) solution was applied to an ETFE sheet and immersed in liquid nitrogen and frozen before the solvent dried. Before this was melted, it was dried with a freeze dryer (FD-81-TA manufactured by Tokyo Rika Kikai Co., Ltd.) to obtain a proton conductive polymer porous sheet. On the other hand, a platinum-supported carbon catalyst (trade name: TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), a mixed solvent of water and ethanol was mixed, and dispersion treatment was performed using a planetary ball mill to prepare a carbon-supported dispersion liquid. After immersing the proton conductive polymer porous sheet in a carbon dispersion during catalyst loading, the solvent was removed by drying under reduced pressure to obtain a first intermediate. Subsequently, a catalyst-supported carbon dispersion having a higher solid content ratio than the previous step was applied to the surface of this intermediate, and the solvent was removed by drying under reduced pressure to obtain a second intermediate.

  The second intermediate was immersed in a commercially available proton conductive polymer (Nafion: registered trademark of DuPont) solution and dried in an oven at 80 ° C. to obtain a transfer sheet of the electrode catalyst layer.

<hot press>
The transfer sheet of the electrode catalyst layer is punched into a square shape, and the transfer sheet is arranged so as to face both surfaces of the polymer electrolyte membrane (Nafion 212: registered trademark, manufactured by Dupont) to form a laminate, which is 120 ° C., 60 kgf / cm 2, 30 The film electrode assembly shown in FIG. 1 was obtained by performing hot pressing under the conditions of minutes, joining and laminating.
<Evaluation 1>

The power generation performance of the produced membrane / electrode assembly was measured.
Membrane / electrode joint made of a pair of separators made of a conductive and gas-impermeable material with a gas flow channel for reaction gas flow and a cooling water flow channel for cooling water flow on the opposite main surface A measurement cell that sandwiched the body and clamped both poles with bolts was used.

The evaluation conditions were a cell temperature of 80 ° C., the reaction gas was hydrogen at the oxidation electrode and air at the reduction electrode. The relative humidity of the reaction gas was 30% and 100%. The performance was evaluated by the current density when the voltage was 0.7V and 0.3V.
<Evaluation 2>

Cyclic voltammetry measurement was performed using the measurement cell used in Evaluation 1.
The evaluation conditions were a cell temperature of 80 ° C., hydrogen gas was passed through the oxidation electrode, and nitrogen gas was passed through the reduction electrode, and the relative humidity of the reaction gas was 30% and 100%. The performance was evaluated by the peak charge amount Q value of hydrogen oxidative desorption.
(Comparative example)

<Preparation of transfer sheet>
A platinum-supported carbon catalyst (trade name: TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) and a 20% by mass polymer electrolyte solution (Nafion: registered trademark, manufactured by Dupont) are mixed with a mixed solvent of water and ethanol. Dispersion treatment was performed to prepare a catalyst ink. A catalyst ink was applied using an ETFE sheet as a base material and dried in an oven at 80 ° C. to prepare a transfer sheet.
<hot press>

A membrane electrode assembly was obtained in the same manner as in Example.
<Evaluation 1>
The power generation performance was measured and the performance was evaluated and compared in the same manner as in the examples.
<Evaluation 2>
The power generation performance was measured and the performance was evaluated and compared in the same manner as in the examples.

  In the examples, since the catalyst has a loading density suitable for each of the electrolyte membrane side and the gas diffusion layer side, a higher current density than that of the comparative example was obtained even with the same amount of catalyst in the entire catalyst layer. In addition, since the proton conducting path is well formed by using the proton conducting polymer porous material obtained by lyophilization, a high current density is obtained even when the relative humidity is low, and the power generation performance is improved. It was excellent. In addition, the use of a proton-conductive polymer porous material obtained by freeze-drying provides a good channel for gas channels and produced water, so that even when relative humidity is high, power generation performance is reduced due to water clogging. Does not occur. Further, in the examples, the Q value is high, suggesting that the three-phase interface is well formed.

  The membrane / electrode assembly and the electrode catalyst layer of the present invention increase all of the gas channel, proton conduction path, and three-phase interface without effectively increasing the catalyst layer resistance, and effectively use the catalyst in the catalyst layer. Therefore, the polymer electrolyte fuel cell using the electrode catalyst layer of the present invention has good power generation performance. Therefore, the present invention can be suitably used for a fuel cell using a polymer electrolyte membrane, particularly a stationary cogeneration system and an electric vehicle. Furthermore, since the catalyst in the catalyst layer is effectively used, the amount of platinum used can be reduced and the cost can be reduced, so that the industrial utility value is great.

DESCRIPTION OF SYMBOLS 1 ... Electrode catalyst layer based on this invention 2 ... 1st intermediate body 3 ... 2nd intermediate body 4 ... Catalyst 5 shown typically ... Electrode catalyst layer 10 ... Proton-conductive polymer porous body 11 ... Frozen solvent DESCRIPTION OF SYMBOLS 12 ... Base material 13 ... Hole 14 ... Part 15 which has a three-phase interface ... Catalyst particle 16 ... Carbon particle 17 ... Proton conductive polymer 18 ... Polymer electrolyte membrane 19 ... Membrane / electrode assembly

Claims (4)

A method for producing the electrode catalyst layer used in a membrane / electrode assembly comprising a polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane,
Forming a porous membrane by applying a dispersion containing a proton-conducting polymer to the substrate surface, freezing before the solvent dries and drying under vacuum to form a porous membrane of the proton-conducting polymer on the substrate Process,
The proton-conductive polymer porous membrane formed above was impregnated with the catalyst-supported carbon dispersion and dried to impregnate the pores of the proton-conductive polymer porous membrane with the catalyst-supported carbon. A first intermediate forming step for obtaining one intermediate;
By applying the catalyst-supported carbon dispersion to the surface of the first intermediate and drying, the density of the catalyst-supported carbon adsorbed on the pores of the porous membrane of the proton conductive polymer is close to that of the substrate. A second intermediate forming step for obtaining a second intermediate that is set so that the position away from the substrate is higher than the position;
An impregnation drying step of impregnating the second intermediate with a dispersion of a proton conductive polymer and drying;
A process for producing an electrode catalyst layer, comprising:   The electrode catalyst layer produced by the production method according to claim 1 is arranged at least on the cathode side of the polymer electrolyte membrane, and the polymer electrolyte membrane is pressurized in a temperature atmosphere below the glass transition point of the polymer electrolyte membrane. A method for producing a membrane / electrode assembly, wherein the membrane / electrode assembly is adhered to an electrolyte membrane. A membrane / electrode assembly comprising a polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane,
At least the cathode-side electrode catalyst layer of the pair of electrode catalyst layers has a porous membrane composed of a continuous proton-conductive polymer and catalyst-supporting carbon, and the catalyst density in the electrode catalyst layer is: A membrane / electrode assembly characterized in that it is set higher at a position closer to the polymer electrolyte membrane than at a position away from the polymer electrolyte membrane.   A polymer electrolyte fuel cell comprising the membrane-electrode assembly according to claim 3.

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