JP5515959B2 - Membrane electrode assembly for polymer electrolyte fuel cell and method for producing the same - Google Patents

Description

  The present invention relates to a membrane electrode assembly constituting a single cell of a polymer electrolyte fuel cell and a method for producing the same.

  A fuel cell is a power generation system that generates electricity by using hydrogen and oxygen as fuel and causing reverse reaction of water electrolysis. This has features such as high efficiency, low environmental load and low noise compared with the conventional power generation method, 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 considered promising for use in in-vehicle power sources and household stationary power sources, and various research and development have been conducted in recent years.

  Issues for the practical application of fuel cells include power density, gas utilization, 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. A single cell has a structure in which a membrane / electrode assembly formed by sandwiching a solid polymer electrolyte membrane between two electrodes of an oxidation electrode (anode) and a reduction electrode (cathode) is sandwiched by a separator having a gas channel. . 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 that are the electron conductor and the proton conductor and that 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 electrode 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 and increase the effective utilization rate of the platinum used.

  A membrane electrode assembly constituting a single cell of a polymer electrolyte fuel cell comprises a polymer electrolyte membrane and a pair of electrode catalyst layers disposed on both sides thereof. In the past, this electrode catalyst layer has often been formed on a substrate by using various coating methods, screen printing methods, or the like, which are a mixture of catalyst-supporting carbon, proton conductive polymer, and solvent. In this case, agglomeration of the catalyst-supporting 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, and the porosity in the electrode catalyst layer is reduced. There was a tendency for the power density of the cells to decrease due to the fuel 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). Freeze-drying is performed by freezing water-containing material and sublimating the ice under vacuum. The material after freeze-drying can maintain its shape when frozen, and is conventionally stored in the food industry. It is a drying method used in the food manufacturing and medical / pharmaceutical fields.

  Patent Document 1 discloses that a catalyst layer-constituting powder is obtained by freeze-drying an ink in which catalyst-supported carbon, proton conductive polymer, and a solvent are mixed, followed by heat treatment and pulverizing, and obtaining the catalyst layer by forming the powder into a sheet. Is. 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.

  In Patent Document 2, a catalyst layer is obtained by adding a solvent to a freeze-dried ink obtained by mixing catalyst-carrying carbon, a proton conductive polymer, and a solvent, and applying the ink again. In the method according to Patent Literature 2, the adsorption of the proton-conductive polymer is peeled off due to dispersion mixing during reinking, and the catalyst-carrying carbon is agglomerated or the pores serving as gas channels are crushed. Not much improvement.

  In Patent Document 3, 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, which is applied to a substrate. Thus, an electrode catalyst layer is obtained. 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.

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

  An object of the present invention is to increase all of the gas channel, proton conduction path, and three-phase interface of an electrode catalyst layer constituting a single cell of a polymer electrolyte fuel cell, and effectively use the catalyst in the electrode catalyst layer. It is to increase power generation efficiency.

In order to solve the above problems, a membrane / electrode assembly for a polymer electrolyte fuel cell of the present invention comprises a polymer electrolyte membrane and a pair of electrode catalyst layers disposed on both sides thereof, and is in the form of a plate in the plane. A membrane electrode assembly constituting a single cell of a polymer electrolyte fuel cell together with a separator having a plurality of gas flow paths, wherein at least the electrode catalyst layer on the cathode side comprises the following (a) to (c) The catalyst-supported carbon particles are adsorbed in the pores of the porous membrane made of a proton conductive polymer, and a layer made of the proton conductive polymer is formed on the surface of the carbon particles. The catalyst density of the porous membrane is higher in the portion corresponding to the gas flow channel than in other portions.
The portion corresponding to the gas flow path refers to the portion that is in contact with the gas flow path when the separator and the electrode catalyst layer are in contact with each other, and when there are inclusions between the separator and the electrode catalyst layer, It refers to a portion facing the gas flow path with an inclusion interposed therebetween.

According to the membrane electrode assembly for a polymer electrolyte fuel cell of the present invention, at least the electrode catalyst layer on the cathode side adsorbs the catalyst-supporting carbon particles in the pores of the porous membrane made of proton conductive polymer, and the carbon Since it has a structure in which a layer made of a proton conducting polymer is formed on the surface of the particle, at least the cathode-side electrode catalyst layer has a gas channel, a proton conducting path, and a three-phase structure, compared with those having no structure. All of the interfaces can be increased.
Further, at least in the electrode catalyst layer on the cathode side, the catalyst density of the porous membrane is higher in the portion corresponding to the gas flow path where the reaction gas can easily reach than in other portions, so that the power generation efficiency is increased.

The method for producing an electrode catalyst layer for a polymer electrolyte fuel cell according to the present invention includes a separator and a polymer electrolyte membrane each having a plate-like shape and a plurality of gas flow paths formed in a plane, and a single cell of the polymer electrolyte fuel cell Is a method for producing an electrode catalyst layer comprising the following steps (a) to (c) in order.
(a) A liquid layer composed of a liquid in which a proton conductive polymer is dispersed in a solvent is formed on the surface of the substrate, and after the solvent in the liquid layer is frozen, it is dried under vacuum to sublimate the frozen solvent. And a porous film forming step of forming a porous film made of a proton conductive polymer on the substrate by making the portion where the solvent existed into pores.

(b) The catalyst-supported carbon particle dispersion is applied only to the portion of the porous membrane corresponding to the gas flow path of the separator and dried, so that the catalyst is only present in the pores existing in the portion of the porous membrane. A carbon adsorption process for adsorbing supported carbon particles.
(c) Protons that form a layer made of the proton conductive polymer on the surface of the carbon particles by impregnating the porous membrane after the carbon adsorption step with a dispersion of a proton conductive polymer and drying it. Conductive polymer layer forming step.

The method for producing a membrane electrode assembly for a polymer electrolyte fuel cell according to the present invention comprises a polymer electrolyte membrane and a pair of electrode catalyst layers disposed on both sides thereof, and is in the form of a plate and a plurality of gas channels in the plane. Is a method for producing a membrane electrode assembly that constitutes a single cell of a polymer electrolyte fuel cell together with a separator formed with the step of obtaining the electrode catalyst layer by the steps (a) to (c), and the step A step of disposing the electrode catalyst layer obtained in step 1 at least on the cathode side of the polymer electrolyte membrane and pressurizing the electrode catalyst layer at a temperature below the glass transition point of the polymer electrolyte membrane. .
The polymer electrolyte fuel cell of the present invention is a pair of separators each having a plate shape and having a plurality of gas channels formed in a plane, and the membrane electrode assembly of the present invention or the membrane electrode joint obtained by the method of the present invention. It has the single cell of the structure where the body is clamped, It is characterized by the above-mentioned.

According to the membrane electrode assembly for a polymer electrolyte fuel cell of the present invention, the gas channel, proton conduction path, and three-phase interface of the single cell constituting the polymer electrolyte fuel cell are all increased, and the electrode catalyst layer The power generation efficiency of the polymer electrolyte fuel cell can be increased by effectively using the catalyst.
According to the method for producing an electrode catalyst layer for a polymer electrolyte fuel cell of the present invention, the electrode catalyst layer constituting the membrane electrode assembly for a polymer electrolyte fuel cell of the present invention can be produced.
According to the method for producing a membrane electrode assembly for a polymer electrolyte fuel cell of the present invention, the membrane electrode assembly for a polymer electrolyte fuel cell of the present invention can be produced.

  Since the polymer electrolyte fuel cell using the membrane electrode assembly of the present invention has good power generation performance, it can be suitably used particularly for stationary cogeneration systems and electric vehicles. Furthermore, in order to effectively use the catalyst in the electrode catalyst layer, the cost can be reduced by reducing the amount of platinum used.

It is a figure which shows typically the membrane electrode assembly and separator for polymer electrolyte fuel cells corresponding to one Embodiment of this invention. It is a figure explaining the manufacturing method of the electrode catalyst layer for polymer electrolyte fuel cells corresponding to one Embodiment of this invention. FIG. 3 is an enlarged view of a portion A in FIG.

Embodiments of the present invention will be described below. As shown in FIG. 1, a membrane electrode assembly 10 of this embodiment includes a polymer electrolyte membrane 1 and a cathode-side electrode catalyst layer 2 and an anode-side electrode catalyst layer 3 disposed on both sides thereof.
The cathode-side electrode catalyst layer 2 has a portion 2a having a high catalyst density and a portion 2b having a low catalyst density. The portion 2a having a high catalyst density is a portion (a portion corresponding to the gas flow path) that is brought into contact with the gas flow path 5a of the separator 5. The separator 5 is a plate-like member in which a plurality of ribs 5b are formed on one surface, and a gas flow path 5a is formed between adjacent ribs 5b. The portion 2b having a low catalyst density is a portion in contact with the rib 5b.

The cathode-side electrocatalyst layer 2 is manufactured by the method described below (see FIG. 2).
<Porous membrane formation process>
First, a liquid layer 24 made of a liquid in which a proton conductive polymer 22 is dispersed in a solvent 23 is formed on a substrate 21. Next, the solvent 23 in the liquid layer 24 is frozen. FIG. 2A shows this state.
Next, the frozen solvent 23 is sublimated by drying under vacuum. Thereby, the portion where the solvent was present becomes the pore 25. As a result, a porous film 26 made of a proton conductive polymer is formed on the substrate 21. FIG. 2B shows this state.

<Carbon adsorption process>
Next, the catalyst-supported carbon particle dispersion is applied only to the portion of the porous membrane 26 that is in contact with the gas flow path 5a of the separator 5 and dried. As a result, the catalyst-carrying carbon particles are adsorbed only in the holes 25a existing in the portion and are not adsorbed in the other holes 25b.
<Proton conductive polymer layer forming step>
Next, the porous membrane 26 in this state is impregnated with a proton conductive polymer dispersion and dried. Thus, layers 27 and 28 made of proton conductive polymer are formed on the inner surfaces of the pores 25a and 25b of the porous film 26. FIG. 2 (c) shows this state. FIG. 3 corresponds to an enlarged view of a portion A in FIG.

  In the pores 25a where the catalyst-carrying carbon particles are adsorbed, a layer 27 made of a proton conductive polymer is formed on the surface of the carbon particles 62 on which the catalyst particles 61 are carried, as shown in FIG. In addition, since the solvent in which the catalyst-carrying carbon particles are dispersed in the carbon adsorption step appropriately dissolves the surface of the porous membrane 26 made of the proton conductive polymer, the carbon particles 62 on which the catalyst particles 61 are carried are porous membranes. 26 is partially embedded and fixed.

  In this way, a three-phase interface is formed on the surface of the pores 25a of the porous membrane 26 made of proton conductive polymer. Since the pores 25a and 25b of the porous film 26 made of proton conductive polymer are actually three-dimensionally continuous, the three-phase interface is similarly three-dimensionally continuously porous film 26. Exists within. Further, a gas channel is formed by the three-dimensionally continuous holes 25a and 25b, and a proton conduction path is formed by the layer 27 made of the proton conductive polymer.

  Through the above steps, an electrode having a structure in which the catalyst-supporting carbon particles 62 are adsorbed in the pores 25a of the porous film 26 made of a proton conductive polymer and the layer 27 made of the proton conductive polymer is formed on the surface thereof. The catalyst layer 2 is formed on the base material 21. In the electrode catalyst layer 2, the catalyst density of the portion 2a that is in contact with the gas flow path 5a of the separator 5 is higher than that of the portion 2b that is in contact with the rib 5b. This electrode catalyst layer 2 is used for the cathode.

  The member composed of the base material 21 and the electrode catalyst layer 2 is disposed with the electrode catalyst layer 2 side facing the polymer electrolyte membrane 1, and the anode electrode catalyst layer 3 is disposed on the opposite surface of the polymer electrolyte membrane 1. Then, the electrode catalyst layers 2, 3 are brought into close contact with both surfaces of the polymer electrolyte membrane 1 by hot pressing (pressing and adhering step). After adhesion, the substrate 21 is peeled from the electrode catalyst layer 2. Thereby, the membrane electrode assembly 10 shown in FIG. 1 is obtained.

A separator 5 is attached to the electrode catalyst layer 2 on the cathode side of the membrane electrode assembly 10 by combining the portion 2a having a high catalyst density and the gas flow path 5a, and a separator (not shown) is also attached to the electrode catalyst layer 3 on the anode side. A single cell of a polymer electrolyte fuel cell is assembled by attaching.
Although the reaction gas easily reaches the portion 2a of the electrode catalyst layer 2 in contact with the gas flow path 5a, the power generation efficiency is increased because the catalyst density of the portion 2a is high. Further, although the portion 2b in contact with the rib 5b of the electrode catalyst layer 2 is likely to be clogged with water, gas diffusion and drainage can be promoted because the catalyst density of this portion 2b is low. Therefore, the catalyst in the electrode catalyst layer 2 can be used effectively, and the voltage drop due to gas diffusion or water clogging can be suppressed.

Therefore, according to the membrane electrode assembly of this embodiment, the gas channel, proton conduction path, and three-phase interface of the single cell constituting the polymer electrolyte fuel cell are all increased to effectively use the catalyst in the electrode catalyst layer. Therefore, the power generation efficiency of the polymer electrolyte fuel cell can be increased, and the voltage drop due to gas diffusion or water clogging can be suppressed.
In addition, when the electrode catalyst layer 2 having the high catalyst density portion 2a and the low portion 2b is arranged on the cathode side, the power generation efficiency is increased, and the effect of suppressing the voltage drop due to gas diffusion or water clogging is high. The electrode catalyst layer having the above structure is disposed at least on the cathode side in the membrane electrode assembly of the present invention, but may be used as an electrode catalyst layer on the anode side.

As a catalyst used in the present invention, a platinum group element such as platinum, palladium, ruthenium, iridium, rhodium, osmium, a metal such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, or the like These alloys, oxides, double oxides, carbides, etc. 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 decreases. Conversely, when too small, since stability of a catalyst falls, 0.5 to 50 nm is preferable, More preferably, it is 1 to 5 nm.

The carbon supporting these catalysts used in the present invention may be any carbon as long as it is finely powdered and has conductivity and is not affected by the catalyst. Carbon black, graphite, graphite, activated carbon, carbon Nanotubes and fullerenes can be preferably used.
If the particle size of the carbon is too small, it becomes difficult to form an electron conduction path, and if it is too large, the gas diffusibility of the catalyst layer is reduced or the utilization factor of the catalyst is lowered. More preferably, it is 10 nm or more and 100 nm or less.

Various proton conductive polymers are used, but considering the interface resistance between the polymer electrolyte membrane and the electrode, and the dimensional change rate between the electrode and the electrolyte membrane when the humidity changes, the electrolyte membrane and catalyst to be used The proton conducting polymer in the layer should be the same component.
The proton conductive polymer used in the membrane / electrode assembly of the present invention may be any proton-conductive 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, an electrolyte membrane made of sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, sulfonated polyphenylene, or the like can be used. Of these, Nafion (registered trademark) manufactured by DuPont is particularly suitable.

The solvent used as the dispersion medium in the present invention is not particularly limited as long as it 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 limit. 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 particles in the step (b) and the solvent for dispersing the proton conductive polymer in the step (c) preferably include at least a volatile liquid organic solvent. Those using the are 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.

  Examples of the base material used in the present invention include ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), poly A fluororesin excellent in transferability such as tetrafluoroethylene (PTFE) can be used. Polymer films such as polyimide, polyethylene terephthalate, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyarylate, and polyethylene naphthalate can also be used.

  When using a gas diffusion layer as a base material, it is not necessary to peel the base material after hot pressing the electrode catalyst layer formed on the base material onto the polymer electrolyte membrane. 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 nonwoven 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. In order to obtain a membrane / electrode assembly with good battery performance, the pressure A applied to the porous membrane composed of the base material and the proton conductive polymer is preferably 0.5 MPa ≦ A ≦ 20 MPa, 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 and the polymer electrolyte membrane is lowered, and the battery performance is lowered.

The generation of wrinkles in the membrane / electrode assembly is affected by the pressure applied to the portion of the polymer electrolyte membrane in the hot pressing step. The generation of wrinkles can be suppressed by using a cushioning 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 pressing temperature is set near the glass transition point of the proton conducting polymer of the polymer electrolyte membrane and the electrode catalyst layer, which improves the bondability at the interface between the polymer electrolyte membrane and the electrode catalyst layer, and reduces the interface resistance. It is effective in terms of suppression, and is desirably 100 ° C. or higher.

<Sample 1: Example of the present invention>
<Preparation of electrode sheet>
The electrode catalyst layer 2 was formed on the base material 21 by the procedure shown in FIG.
First, a liquid layer 24 is formed by applying a commercially available proton-conducting polymer (Nafion (registered trademark)) solution made by DuPont to an ETFE sheet (base material) 21. Before the solvent 23 is dried, the liquid layer 24 is liquid nitrogen. Soaked and frozen. Before it is melted, it is dried with a freeze dryer (FD-81-TA manufactured by Tokyo Rika Kikai Co., Ltd.) to form a porous film 26 made of a proton conductive polymer on the ETFE sheet (base material) 21. did.

On the other hand, a platinum-supported carbon catalyst (trade name: TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) and a mixed solvent of water and ethanol were mixed and subjected to dispersion treatment with a planetary ball mill to prepare a dispersion of catalyst-supported carbon particles.
After the dispersion liquid of catalyst-carrying carbon particles is discharged only to the part corresponding to the gas flow path part of the separator with the inkjet coating machine, the solvent is removed by drying under reduced pressure, and the part of the porous film 26 is removed. The catalyst-supporting carbon particles were adsorbed only in the pores 25a existing in the catalyst. In this state, the porous membrane 26 is immersed in a commercially available proton conductive polymer (Dafon Nafion (registered trademark)) solution and dried in an oven at 80 ° C., whereby the electrode catalyst layer 2 is formed on the substrate 21. As a result, an electrode sheet was obtained.

<hot press>
The obtained electrode sheet was punched into a square to obtain two electrode plates. Two electrode plates sandwich both sides of a polymer electrolyte membrane (Nafion (registered trademark) 212 manufactured by DuPont), and the electrode catalyst layer 2 side is arranged facing the polymer electrolyte membrane, and is 120 ° C., 60 kgf / cm. ^2. Hot pressing was performed for 30 minutes. Thus, a joined body in which the polymer electrolyte membrane was sandwiched between the two electrode plates was obtained. The substrate 21 was removed from the joined body to obtain a membrane / electrode assembly comprising a pair of electrode catalyst layers 2 and a polymer electrolyte membrane.

<Evaluation 1>
The power generation performance of the obtained membrane electrode assembly was measured.
Membrane electrode assembly produced by a pair of separators made of a conductive and gas-impermeable material having a gas flow path for reaction gas flow and a cooling water flow path for cooling water flow on the opposite main surface Was used as a measuring cell. At this time, the gas flow path part of the separator and the high catalyst density part of the membrane electrode assembly were made to coincide.
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.

<Sample 2: Comparative Example of the Present Invention>
<Preparation of electrode 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. This catalyst ink was applied on a base material made of an ETFE sheet and dried in an oven at 80 ° C. to obtain an electrode sheet of a comparative example in which an electrode catalyst layer was formed on the base material.

<hot press>
The obtained electrode sheet of the comparative example was punched into a square to obtain two electrode plates. Two electrode plates sandwich both sides of a polymer electrolyte membrane (Nafion (registered trademark) 212 manufactured by DuPont), with the electrode catalyst layer side facing the polymer electrolyte membrane, 120 ° C., 60 kgf / cm ^2. The hot pressing was performed under the condition of 30 minutes. Thus, a joined body in which the polymer electrolyte membrane was sandwiched between the two electrode plates of the comparative examples was obtained. The base material was removed from the joined body to obtain a membrane / electrode assembly comprising a pair of electrode catalyst layers and a polymer electrolyte membrane.

<Evaluation 1>
Using the obtained membrane / electrode assembly, a measurement cell was prepared in the same manner as in Sample 1, and power generation performance was measured. The evaluation conditions were the same as those of Sample 1.
<Evaluation 2>
Using the measurement cell used in Evaluation 1, cyclic voltammetry measurement was performed under the same evaluation conditions as Sample 1.
As a result, since the catalyst density of the sample 1 cell is high at the portion in contact with the gas flow path of the separator, the reaction gas easily reaches the three-phase interface, and a higher current density than that of the sample 2 cell is obtained. It was. In addition, the cell of sample 1 had a higher Q value than the cell of sample 2, suggesting that the three-phase interface was well formed.

  The cell of sample 1 uses a proton conductive polymer porous membrane obtained by freeze-drying the solvent as the electrode catalyst layer, and the catalyst density is low at the portion in contact with the rib of the separator. The passage of water is well formed, and even when the relative humidity is high, power generation performance is not deteriorated due to water clogging. In addition, the proton conductive polymer porous membrane obtained by freeze-drying the solvent is used for the electrode catalyst layer, so that a proton conduction path is well formed, so that a high current density can be obtained even when the relative humidity is low. The power generation performance was excellent.

DESCRIPTION OF SYMBOLS 1 Polymer electrolyte membrane 2 Electrode catalyst layer 2a of cathode side High catalyst density part 2b Low catalyst density part 21 Base material 22 Proton conductive polymer 23 Frozen solvent 24 Liquid layer 25 Pore 25a Catalyst carrying | support carbon particle is adsorbed Pores 25b pores in which catalyst-carrying carbon particles are not adsorbed 26 porous membranes 27 and 28 made of proton-conductive polymer layer 3 layer made of proton-conductive polymer 5 anode-side electrode catalyst layer 5 separator 5a gas flow Path 5b Rib 10 Membrane electrode assembly 61 Catalyst particle 62 Carbon particle

Claims (4)

A method for producing an electrode catalyst layer that constitutes a single cell of a polymer electrolyte fuel cell, together with a separator and a polymer electrolyte membrane that are plate-shaped and have a plurality of gas flow paths formed in-plane,
A liquid layer composed of a liquid in which a proton conductive polymer is dispersed in a solvent is formed on the surface of the substrate, and after the solvent in the liquid layer is frozen, it is dried under vacuum to sublimate the frozen solvent to obtain a solvent. A porous film forming step of forming a porous film made of a proton-conducting polymer on the base material by making the portion where the
The catalyst-carrying carbon particle dispersion liquid is applied only to the part of the porous membrane corresponding to the gas flow path of the separator and dried, so that the catalyst-carrying carbon particle is only in the pores existing in the part of the porous membrane. Carbon adsorption process for adsorbing,
The porous membrane after the carbon adsorption step is impregnated with a dispersion of a proton conductive polymer and dried to form a layer made of the proton conductive polymer on the surface of the carbon particles. A method for producing an electrode catalyst layer for a polymer electrolyte fuel cell, comprising: a molecular layer forming step in order. A membrane comprising a polymer electrolyte membrane and a pair of electrocatalyst layers disposed on both sides thereof, and comprising a single cell of a solid polymer fuel cell together with a plate-like separator having a plurality of gas flow paths formed in the surface A method for producing an electrode assembly,
The step of obtaining the electrode catalyst layer by the method according to claim 1, and the electrode catalyst layer obtained in the step is disposed at least on the cathode side of the polymer electrolyte membrane, and the glass transition point of the polymer electrolyte membrane. A method of producing a membrane electrode assembly for a polymer electrolyte fuel cell, comprising the step of pressurizing and adhering at the following temperature. A membrane comprising a polymer electrolyte membrane and a pair of electrocatalyst layers disposed on both sides thereof, and comprising a single cell of a solid polymer fuel cell together with a plate-like separator having a plurality of gas flow paths formed in the surface An electrode assembly comprising:
The electrode catalyst layer on at least the cathode side is manufactured by the method according to claim 1 , wherein the catalyst-supporting carbon particles are adsorbed in the pores of the porous film made of a proton conductive polymer, and the surface of the carbon particles A solid polymer fuel characterized in that a layer made of a proton-conducting polymer is formed, and the catalyst density of the porous membrane is higher in the portion corresponding to the gas flow path than in other portions. Battery membrane electrode assembly. A pair of separators which a plurality of gas passages in the plane of a plate-like is formed, the structure obtained membrane electrode assembly in claim 3, wherein the membrane electrode assembly or claim 2 wherein the method is sandwiched A solid polymer fuel cell comprising a single cell.

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