JP2017174600A - Manufacturing method of membrane/electrode assembly, membrane/electrode assembly, and solid polymer type fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane/electrode assembly including an electrode catalyst layer which improves diffusibility of a reaction gas, improves water retentivity without blocking removal or the like of water generated by an electrode reaction and indicates a high power generation property even under a low humidification condition, a manufacturing method thereof and a solid polymer type fuel cell.SOLUTION: A membrane/electrode assembly comprises a polymer electrolyte membrane 1 and a pair of electrode catalyst layers 2 and 3 holding the polymer electrolyte membrane 1 therebetween. At least one of the electrode catalyst layers 2 and 3 includes a first electrode catalyst layer (2a or 3a) and a second electrode catalyst part (2b or 3b) which is adjacent to the first electrode catalyst part (2a or 3a) in a plane direction of the polymer electrolyte membrane 1. A value of pore volume equal to or less than 1.0 μm of a diameter of the second electrode catalyst part (2b or 3b) is greater than a value of pore volume equal to or less than 1.0 μm of a diameter of the first electrode catalyst part (2a or 3a) as a conversion value by cylinder approximation of a pore calculated according to a mercury press-in method.SELECTED DRAWING: Figure 1

Description

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

  A fuel cell is a power generation system that generates electricity simultaneously with heat by causing a reverse reaction of water electrolysis at an electrode including a catalyst using a fuel gas containing hydrogen and an oxidant gas containing oxygen. This power generation system has features such as high efficiency, low environmental load, and low noise as compared with conventional power generation systems, and is attracting attention as a clean energy source in the future. There are several types depending on the type of ion conductor used, and a battery using a proton conductive polymer membrane is called a solid polymer fuel cell.

  Among fuel cells, polymer electrolyte fuel cells can be used near room temperature, so they are considered promising for use in in-vehicle power sources and household stationary power sources. In recent years, various research and development have been conducted. Yes. In a polymer electrolyte fuel cell, a membrane electrode assembly (hereinafter sometimes referred to as MEA) in which a pair of electrode catalyst layers is disposed on both sides of a polymer electrolyte membrane is sandwiched between a pair of separator plates. Battery. One separator plate is formed with a gas flow path for supplying a fuel gas containing hydrogen to one of the electrodes, and the other separator plate is supplied with an oxidant gas containing oxygen to the other electrode. A gas flow path is formed for this purpose. Here, the above-mentioned other electrode to which the fuel gas is supplied is referred to as a fuel electrode, and the above-mentioned one electrode to which the oxidant gas is supplied is referred to as an air electrode. These electrodes include an electrode catalyst layer formed by laminating a polymer electrolyte and carbon particles carrying a catalyst substance such as a platinum-based noble metal, and a gas diffusion layer having both gas permeability and electronic conductivity. Yes. Moreover, these electrodes are arrange | positioned so that a gas diffusion layer may oppose a separator.

  Here, with respect to the electrode catalyst layer, efforts have been made to increase gas diffusibility in order to improve the output density of the fuel cell. The pores in the electrode catalyst layer are located in front of the separator plate through the gas diffusion layer and serve as a passage for transporting a plurality of substances. The fuel electrode not only smoothly supplies fuel gas to the three-phase interface, which is a redox reaction field, but also functions to supply water for smoothly conducting the generated protons in the polymer electrolyte membrane. The air electrode functions to smoothly remove water generated by the electrode reaction together with the supply of the oxidant gas. In the polymer electrolyte fuel cell, in order to prevent a so-called “flooding” phenomenon in which the power generation reaction is stopped due to obstruction of material transport in the fuel electrode and the air electrode, a configuration for improving drainage has been studied so far ( For example, see Patent Documents 1 to 4).

In addition, examples of the problem toward the practical application of the polymer electrolyte fuel cell include improvement of output density and durability, but the biggest problem is cost reduction (cost reduction).
One way to reduce the cost is to reduce the number of humidifiers. As the polymer electrolyte membrane located at the center of the membrane electrode assembly, a perfluorosulfonic acid membrane or a hydrocarbon-based membrane is widely used. In order to obtain excellent proton conductivity, water management close to a saturated water vapor pressure atmosphere is required, and water is currently supplied from the outside by a humidifier. Therefore, in order to reduce power consumption and simplify the system, polymer electrolyte membranes that exhibit sufficient proton conductivity even under low humidification conditions that do not require a humidifier are being developed. .

  However, in an electrode catalyst layer with improved drainage, the polymer electrolyte dries up under low humidification conditions, so it is necessary to optimize the electrode catalyst layer structure and improve water retention. Until now, in order to improve the water retention of a fuel cell under low humidification conditions, for example, a method of sandwiching a humidity adjusting film between an electrode catalyst layer and a gas diffusion layer has been proposed.

For example, Patent Document 5 discloses a method in which a humidity adjustment film composed of conductive carbonaceous powder and polytetrafluoroethylene exhibits a humidity adjustment function and prevents dry-up.
Patent Document 6 discloses a method of providing grooves on the surface of the catalyst electrode layer in contact with the polymer electrolyte membrane. That is, a method is disclosed in which a groove having a width of 0.1 to 0.3 mm is formed on the surface of the catalyst electrode layer to suppress a decrease in power generation performance under low humidification conditions.

JP 2006-120506 A JP 2006-332041 A JP 2007-87651 A JP 2007-80726 A JP 2006-252948 A JP 2007-141588 A

  However, the membrane electrode assemblies described in Patent Documents 1 to 6 increase the diffusibility of the reaction gas and increase the water retention without hindering the removal of water generated by the electrode reaction. There was also room for improvement in power generation performance. In addition, the manufacturing method is complicated and the cost is high.

  Therefore, in the present invention, at low cost, the diffusibility of the reaction gas is increased, the water retention is increased without hindering the removal of water generated by the electrode reaction, etc., and high power generation characteristics are obtained even under low humidification conditions. It aims at providing the manufacturing method of a membrane electrode assembly provided with the electrode catalyst layer to show, and the membrane electrode assembly.

  One aspect of the method for producing a membrane electrode assembly of the present invention includes a catalyst ink preparation step for preparing a catalyst ink, and the catalyst ink prepared in the catalyst ink preparation step is applied to a substrate, An electrode film forming step for forming an electrode film to be the electrode catalyst layer; and a first electrode for forming the one electrode catalyst layer by transferring the electrode film to one surface of the polymer electrolyte film while applying pressure. A catalyst layer forming step and a second electrode catalyst layer forming step of forming the other electrode catalyst layer by transferring the electrode membrane to the other surface of the polymer electrolyte membrane while applying pressure, and In at least one of the first electrode catalyst layer forming step and the second electrode catalyst layer forming step, the electrode membrane is transferred to the polymer electrolyte membrane while being pressed, and is adjacent in the planar direction of the polymer electrolyte membrane. The first electrode catalyst And the second electrode catalyst layer portion, and the first electrode at a pressure higher than at the time of transfer in at least one of the first electrode catalyst layer formation step and the second electrode catalyst layer formation step Pressurize the catalyst layer.

  In another aspect of the method for producing a membrane electrode assembly of the present invention, a catalyst ink production step for producing a catalyst ink, and the catalyst ink produced in the catalyst ink production step are applied to a substrate, An electrode film forming step of forming an electrode film to be the electrode catalyst layer on the material; and transferring the electrode film to one surface of the polymer electrolyte film while heating to form one of the electrode catalyst layers An electrode catalyst layer forming step of 1 and a second electrode catalyst layer forming step of transferring the electrode membrane to the other surface of the polymer electrolyte membrane while heating to form the other electrode catalyst layer. The electrode membrane is transferred to the polymer electrolyte membrane while being heated in at least one of the first electrode catalyst layer forming step and the second electrode catalyst layer forming step, and a plane of the polymer electrolyte membrane is provided. First in adjacent positions in the direction An electrode catalyst layer portion and a second electrode catalyst layer portion are formed, and the first electrode catalyst layer portion and the first electrode catalyst layer formation step, and the first electrode catalyst layer formation step and the first electrode catalyst layer portion at a temperature higher than at the time of transfer in at least one of the first electrode catalyst layer formation step and the second electrode catalyst layer formation step. The electrode catalyst layer part is heat-treated.

One embodiment of the membrane electrode assembly of the present invention comprises a polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane, wherein at least one of the electrode catalyst layers is a first electrode catalyst layer. An electrode catalyst portion; and a second electrode catalyst portion adjacent to the first electrode catalyst portion in a planar direction of the polymer electrolyte membrane, wherein the second electrode catalyst portion has a diameter of 1.0 μm or less. The value of the pore volume is a converted value obtained by approximating the pores in the cylinder obtained by the mercury intrusion method, and is larger than the value of the pore volume of the first electrode catalyst portion having a diameter of 1.0 μm or less.
Moreover, one aspect of the polymer electrolyte fuel cell of the present invention includes the membrane electrode assembly described above.

  According to one embodiment of the present invention, an electrode catalyst layer that enhances the diffusibility of a reaction gas, increases water retention without hindering removal of water generated by an electrode reaction, and exhibits high power generation characteristics even under low humidification conditions. Can be efficiently and economically manufactured easily.

It is an exploded perspective view showing typically the structure in one embodiment of a membrane electrode assembly. It is a disassembled perspective view which shows typically the structure in one Embodiment of a polymer electrolyte fuel cell.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The present invention is not limited to the embodiments described below, and modifications such as design changes can be added based on the knowledge of those skilled in the art. These forms can also be included in the scope of the present invention.

(Membrane electrode assembly)
First, the membrane electrode assembly 11 of this embodiment will be described.
As shown in FIG. 1, a membrane electrode assembly 11 includes a polymer electrolyte membrane 1 and an electrode catalyst layer 2 that holds the polymer electrolyte membrane 1 from the upper and lower surfaces of the polymer electrolyte membrane 1 (upper side in FIG. 1). And an electrode catalyst layer 3 (shown on the lower side in FIG. 1).

<Polymer electrolyte membrane>
The polymer electrolyte membrane 1 only needs to have proton conductivity, and a fluorine polymer electrolyte membrane or a hydrocarbon polymer electrolyte membrane can be used. Examples of the fluorine-based polymer electrolyte membrane 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 membrane, electrolyte membranes such as sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used. In particular, as the polymer electrolyte membrane 1, a Nafion (registered trademark) material manufactured by DuPont can be suitably used.

<Electrocatalyst layer>
At least one of the two electrode catalyst layers 2 and 3 includes catalyst material-carrying particles and a polymer electrolyte.
The two electrode catalyst layers 2 and 3 are each divided into two in the plane direction of the polymer electrolyte membrane 1. More specifically, in FIG. 1, the upper electrode catalyst layer 2 includes a first electrode catalyst portion 2a located on the gas inlet side and a second electrode catalyst portion 2b located on the gas outlet side. Have. The first electrode catalyst portion 2a and the second electrode catalyst portion 2b are continuous in the planar direction of the polymer electrolyte membrane 1 without any overlap or gap.

  Similarly, in FIG. 1, the lower electrode catalyst layer 3 includes a first electrode catalyst portion 3a located on the gas inlet side and a second electrode catalyst portion 3b located on the gas outlet side. . The first electrode catalyst portion 3a and the second electrode catalyst portion 3b are continuous with each other in the plane direction of the polymer electrolyte membrane 1 without any overlap or gap.

Here, the electrode catalyst layers 2 and 3 are formed on both surfaces of the polymer electrolyte membrane 1 using a catalyst ink. The catalyst ink includes at least a polymer electrolyte and a solvent.
The polymer electrolyte contained in the above-described catalyst ink is not particularly limited as long as it has proton conductivity, and the same material as that of the polymer electrolyte membrane 1 can be used. Fluorine polymer electrolyte, hydrocarbon polymer An electrolyte can be used. As an example of the fluorine-based polymer electrolyte, a Nafion (registered trademark) material manufactured by DuPont, etc. can be used. As the hydrocarbon polymer electrolyte, electrolytes such as sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used. In particular, as a fluorine-based polymer electrolyte, a Nafion (registered trademark) material manufactured by DuPont can be suitably used. In consideration of the adhesion between the electrode catalyst layers 2 and 3 and the polymer electrolyte membrane 1, it is preferable to use the same material as the polymer electrolyte membrane 1 for the polymer electrolyte contained in the catalyst ink.

<Catalyst material>
Examples of the catalytic substance (hereinafter sometimes referred to as catalyst particles or catalyst) include platinum, palladium, ruthenium, iridium, rhodium, osmium, platinum group elements, iron, lead, copper, chromium, cobalt, nickel, manganese. Further, a metal such as vanadium, molybdenum, gallium, or aluminum, or an alloy, oxide, or double oxide thereof can be used. When the catalyst particles are one or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium, the electrode reactivity is excellent and the electrode reaction can be performed efficiently and stably. it can. When the catalyst particles are one or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium, the polymer electrolyte fuel cell 12 including the electrode catalyst layers 2 and 3 is provided. It is preferable because it shows high power generation characteristics.

  Moreover, the average particle diameter of the catalyst particles described above is preferably 0.5 nm or more and 20 nm or less, and more preferably 1 nm or more and 5 nm or less. Here, the average particle diameter is an average flow diameter obtained from an X-ray diffraction method in the case of a catalyst supported on a carrier such as carbon particles. In the case of a catalyst not supported on a carrier, the arithmetic average flow diameter obtained from particle size measurement. When the average particle diameter of the catalyst particles is in the range of 0.5 nm or more and 20 nm or less, the activity and stability of the catalyst are improved, which is preferable.

  Generally, carbon particles are used as the electron conductive powder supporting the above-described catalyst substance. The type of carbon particles is not limited as long as they are in the form of fine particles and have conductivity and are not affected by the catalyst, but carbon black, graphite, graphite, activated carbon, carbon fiber, carbon nanotube, fullerene should be used. Can do.

  The average particle diameter of the carbon particles is preferably about 10 nm to 1000 nm, more preferably 10 nm to 100 nm. Here, the average particle diameter is an average flow diameter obtained from an SEM image. When the average particle diameter of the carbon particles is in the range of 10 nm to 1000 nm, the activity and stability of the catalyst are improved, which is preferable. It is preferable because an electron conduction path is easily formed and the gas diffusibility of the two electrode catalyst layers 2 and 3 and the utilization factor of the catalyst are improved.

  The solvent used as a dispersion medium for the catalyst ink is not particularly limited as long as it does not erode the catalyst substance-supporting particles and the polymer electrolyte, and can dissolve or disperse the polymer electrolyte in a highly fluid state as a fine gel. It is not something. However, it is desirable that the solvent contains at least a volatile organic solvent. Examples of the solvent used as the dispersion medium of the catalyst ink include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, pentanol and other alcohols, acetone , Ketone solvents such as methyl ethyl ketone, pentanone, methyl isobutyl ketone, heptanone, cyclohexanone, methyl cyclohexanone, acetonyl acetone, diisobutyl ketone, ether solvents such as tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxy toluene, dibutyl ether, etc. Dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol , It can be used polar solvents such as 1-methoxy-2-propanol. Moreover, you may use the mixed solvent which mixed 2 or more types among the above-mentioned materials as a solvent.

  In addition, a solvent using a lower alcohol as a solvent used as a dispersion medium of the catalyst ink has a high risk of ignition. Therefore, when using a lower alcohol, it is preferable to use a mixed solvent with water. Furthermore, water (water having high affinity) that is compatible with the polymer electrolyte may be contained. The amount of water added is not particularly limited as long as the polymer electrolyte does not separate and cause white turbidity or gelation.

  In order to disperse the catalyst material-carrying particles, the catalyst ink may contain a dispersant. Examples of the dispersant include an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant.

  Examples of anionic surfactants include alkyl ether carboxylates, ether carboxylates, alkanoyl sarcosine, alkanoyl glutamate, acyl glutamate, oleic acid / N-methyl taurine, potassium oleate / diethanolamine salt, alkyl ether sulfate / trimethyl Ethanolamine salt, polyoxyethylene alkyl ether sulfate / triethanolamine salt, amine salt of special modified polyether ester acid, amine salt of higher fatty acid derivative, amine salt of special modified polyester acid, amine salt of high molecular weight polyether ester acid , Amine salt of special modified phosphate ester, amide amine salt of high molecular weight polyester acid, amide amine salt of special fatty acid derivative, alkylamine salt of higher fatty acid, amide of high molecular weight polycarboxylic acid Carboxylic acid type surfactants such as amine salt, sodium laurate, sodium stearate, sodium oleate, dialkylsulfosuccinate, dialkylsulfosuccinate, 1,2-bis (alkoxycarbonyl) -1-ethanesulfonate, Alkyl sulfonate, alkyl sulfonate, paraffin sulfonate, α-olefin sulfonate, linear alkyl benzene sulfonate, alkyl benzene sulfonate, polynaphthyl methane sulfonate, polynaphthyl methane sulfonate, naphthalene sulfonate-formalin condensate, alkyl naphthalene sulfonate, alkanoyl Methyl tauride, lauryl sulfate sodium salt, cetyl sulfate sodium salt, stearyl sulfate sodium salt, oleyl sulfate ester Tellurium salt, lauryl ether sulfate, sodium alkylbenzene sulfonate, oil-soluble alkylbenzene sulfonate, α-olefin sulfonate, and other sulfonate surfactants, alkyl sulfate, alkyl sulfate, alkyl sulfate, alkyl Ether sulfate, polyoxyethylene alkyl ether sulfate, alkyl polyethoxy sulfate, polyglycol ether sulfate, alkyl polyoxyethylene sulfate, sulfated oil, highly sulfated sulfate type surfactant, phosphoric acid (mono or Di) alkyl salts, (mono or di) alkyl phosphates, (mono or di) alkyl phosphate esters, alkyl polyoxyethylene salts of phosphates, alkyl ether phosphates, alkyl polyethoxy compounds Acid salt, polyoxyethylene alkyl ether, alkylphenyl phosphate polyoxyethylene salt, alkylphenyl ether phosphate, alkylphenyl polyethoxy phosphate, polyoxyethylene alkylphenyl ether phosphate, higher alcohol phosphate monoester Examples thereof include phosphate type surfactants such as disodium salt, higher alcohol phosphate diester disodium salt and zinc dialkyldithiophosphate.

  Examples of cationic surfactants include benzyldimethyl {2- [2- (P-1,1,3,3-tetramethylbutylphenoxy) ethoxy] ethyl} ammonium chloride, octadecylamine acetate, tetradecylamine acetate , Octadecyltrimethylammonium chloride, tallow trimethylammonium chloride, dodecyltrimethylammonium chloride, coconut trimethylammonium chloride, hexadecyltrimethylammonium chloride, behenyltrimethylammonium chloride, coconut dimethylbenzylammonium chloride, tetradecyldimethylbenzylammonium chloride, octadecyldimethylbenzylammonium chloride Dioleoyldimethylammonium chloride, 1-hydroxyethyl 2-tallow imidazoline quaternary salt, 2-heptadecenyl-hydroxyethyl imidazoline, stearamide ethyl diethylamine acetate, stearamide ethyl diethylamine hydrochloride, triethanolamine monostearate formate, alkyl pyridium salt, higher alkyl amine Examples include ethylene oxide adducts, polyacrylamide amine salts, modified polyacrylamide amine salts, and perfluoroalkyl quaternary ammonium iodides.

  Examples of amphoteric surfactants include dimethyl coconut betaine, dimethyl lauryl betaine, sodium laurylaminoethylglycine, sodium laurylaminopropionate, stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, amide betaine, imidazolinium betaine, lecithin, 3- [ ω-fluoroalkanoyl-N-ethylamino] -1-propanesulfonic acid sodium, N- [3- (perfluorooctanesulfonamido) propyl] -N, N-dimethyl-N-carboxymethyleneammonium betaine and the like can be mentioned.

  Examples of nonionic surfactants include coconut fatty acid diethanolamide (1: 2 type), coconut fatty acid diethanolamide (1: 1 type), bovine fatty acid diethanolamide (1: 2 type), and bovine fatty acid diethanolamide (1: 1). Type), oleic acid diethanolamide (1: 1 type), hydroxyethyl lauryl amine, polyethylene glycol lauryl amine, polyethylene glycol coconut amine, polyethylene glycol stearyl amine, polyethylene glycol beef tallow amine, polyethylene glycol beef tallow propylene diamine, polyethylene glycol dioleyl amine, Dimethyl lauryl amine oxide, dimethyl stearyl amine oxide, dihydroxyethyl lauryl amine oxide, perfluoroalkylamine oxide, polyvinyl pyro Don, higher alcohol ethylene oxide adduct, alkylphenol ethylene oxide adduct, fatty acid ethylene oxide adduct, polypropylene glycol ethylene oxide adduct, glycerin fatty acid ester, pentaerythritol fatty acid ester, sorbit fatty acid ester, sorbitan fatty acid ester, Examples include sugar fatty acid esters.

  Among the surfactants mentioned above, sulfonic acid type surfactants such as alkylbenzene sulfonic acid, oil-soluble alkyl benzene sulfonic acid, α-olefin sulfonic acid, sodium alkyl benzene sulfonate, oil-soluble alkyl benzene sulfonate, α-olefin sulfonate, etc. The agent can be suitably used as the dispersant in consideration of the carbon dispersion effect, the change in catalyst performance due to the remaining dispersant, and the like.

  Increasing the amount of polymer electrolyte in the catalyst ink generally decreases the pore volume. On the other hand, increasing the amount of carbon particles in the catalyst ink increases the pore volume. In addition, when a dispersant is used, the pore volume is reduced.

  Further, the catalyst ink is subjected to a dispersion treatment as necessary. The viscosity of the catalyst ink and the size of the particles contained in the catalyst ink can be controlled by the conditions of the catalyst ink dispersion treatment. Distributed processing can be performed using various apparatuses. In particular, the distributed processing method is not limited. For example, as the dispersion treatment, treatment with a ball mill or roll mill, treatment with a shear mill, treatment with a wet mill, ultrasonic dispersion treatment, and the like can be given. Moreover, you may employ | adopt the homogenizer etc. which stir with centrifugal force. As the dispersion time becomes longer, the pore volume becomes smaller due to the destruction of the aggregate of the catalyst material-carrying particles.

  If the solid content in the catalyst ink is too large, the viscosity of the catalyst ink increases, and therefore cracks are likely to occur on the surfaces of the electrode catalyst layers 2 and 3. On the other hand, if the solid content in the catalyst ink is too small, the film formation rate is very slow and the productivity is lowered. Therefore, the solid content in the catalyst ink is preferably 1% by mass (wt%) or more and 50% by mass or less. The solid content is composed of catalyst material-supported particles and a polymer electrolyte. If the content of catalyst material-supported particles is increased in the solid content, the viscosity increases even with the same solid content. On the other hand, when the content of the catalyst substance-supporting particles is reduced in the solid content, the viscosity is lowered even with the same solid content. Therefore, the ratio of the catalyst substance-supporting particles in the solid content is preferably 10% by mass or more and 80% by mass or less. Further, the viscosity of the catalyst ink is preferably about 0.1 cP to 500 cP (0.0001 Pa · s to 0.5 Pa · s), preferably 5 cP to 100 cP (0.005 Pa · s to 0.1 Pa · s). Is more preferable. Further, the viscosity can be controlled by adding a dispersing agent when the catalyst ink is dispersed.

  Further, the catalyst ink may contain a pore forming agent. By removing the pore-forming agent after the formation of the electrode catalyst layer, pores can be formed. Examples include substances that are soluble in acids, alkalis, and water, substances that sublime such as camphor, and substances that thermally decompose. If the pore-forming agent is a substance that is soluble in warm water, it may be removed with water generated during power generation.

  Examples of pore-forming agents that are soluble in acids, alkalis and water include acid-soluble inorganic salts such as calcium carbonate, barium carbonate, magnesium carbonate, magnesium sulfate and magnesium oxide, inorganic salts soluble in alkaline aqueous solutions such as alumina, silica gel and silica sol, aluminum Metals soluble in acids or alkalis such as zinc, tin, nickel and iron, water-soluble inorganic salts such as sodium chloride, potassium chloride, ammonium chloride, sodium carbonate, sodium sulfate, monosodium phosphate, polyvinyl alcohol, polyethylene glycol Water-soluble organic compounds such as Moreover, although the pore former mentioned above may be used individually by 1 type or in combination of 2 or more types, it is preferable to use in combination of 2 or more types.

  As a coating method for coating the catalyst ink on the substrate, a doctor blade method, a dipping method, a screen printing method, a roll coating method, or the like can be employed.

A transfer sheet can be used as a base material used for manufacturing the electrode catalyst layers 2 and 3.
The transfer sheet used as the substrate may be any material having good transferability. For example, ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroper Fluorocarbon resins such as fluoroalkyl vinyl ether copolymer (PFA) and polytetrafluoroethylene (PTFE) can be used. In addition, polyimide, polyethylene terephthalate, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyarylate, polyethylene naphthalate, polymer sheets and polymer films are transferred. It can be used as a sheet. When a transfer sheet is used as the substrate, the electrode sheet, which is a coating film after removal of the solvent, is bonded to the polymer electrolyte membrane 1, and then the transfer sheet is peeled off. The electrode catalyst is formed on both surfaces of the polymer electrolyte membrane 1. It can be set as the membrane electrode assembly 11 provided with the layers 2 and 3.

[pore]
Each of the electrode catalyst layers 2 and 3 of the membrane electrode assembly 11 has pores that serve as passages for transporting a plurality of substances. In the membrane electrode assembly 11, the value of the pore volume of the first electrode catalyst portion 2 a provided on the gas inlet side is provided on the gas outlet side with a conversion value obtained by approximating the cylinder of the pores obtained by the mercury intrusion method. It is preferably smaller than the value of the pore volume of the second electrode catalyst part 2b.

  The pore volume value of the first electrode catalyst part 2a provided on the gas inlet side is preferably smaller than the pore volume value of the second electrode catalyst part 2b provided on the gas outlet side. In other words, the value of the pore volume of the second electrode catalyst part 2b (or 3b) on the downstream side of the gas is larger than the value of the pore volume of the first electrode catalyst part 2a (or 3a) on the upstream side of the gas. Is preferably large. Here, the “pore volume” refers to the value of the pore volume having a diameter of 1.0 μm or less, which is obtained by mercury porosimetry and is converted by cylindrical approximation of the pores.

  The first electrode catalyst parts 2a and 3a provided on the gas inlet side are provided on the gas inlet side by making the first electrode catalyst parts 2a and 3a denser than the second electrode catalyst parts 2b and 3b provided on the gas outlet side. Water retention is enhanced by the first electrode catalyst portions 2a and 3a, and water removal is promoted by the second electrode catalyst portions 2b and 3b provided on the gas outlet side. Thus, the membrane electrode assembly 11 has both the drainage of water generated by the electrode reaction and water retention under low humidification conditions.

  In addition, since there is no overlap or gap between the first electrode catalyst portions 2a and 3a and the second electrode catalyst portions 2b and 3b in the electrode catalyst layers 2 and 3, a decrease in power generation characteristics and durability due to this is suppressed. .

  Furthermore, in the membrane / electrode assembly 11, unlike the case where low humidity is achieved by applying a conventional humidity adjusting film or forming a groove on the surface of the electrode catalyst layer, the power generation characteristics are not deteriorated due to an increase in interface resistance. . From this, the solid polymer fuel cell provided with the membrane electrode assembly 11 is remarkably high in power generation characteristics even under low humidification conditions, compared with the solid polymer fuel cell provided with the conventional membrane electrode assembly. There is an effect.

  In addition, the value of the pore volume of the second electrode catalyst portion 2b (or 3b) having a diameter of 1.0 μm or less and the value of the pore volume of the first electrode catalyst portion 2a (or 3a) having a diameter of 1.0 μm or less. Is a conversion value by cylindrical approximation of pores obtained by the mercury intrusion method, and is preferably 0.1 mL / g or more and 1.0 mL / g or less. When the difference between the pore volume values mentioned above is less than 0.1 mL / g, it becomes difficult to achieve both the drainage of water produced by the electrode reaction and the water retention under low humidification conditions. There is. Moreover, even when the difference in the above-mentioned pore volume values exceeds 1.0 mL / g, it becomes difficult to achieve both the drainage of water produced by the electrode reaction and the water retention under low humidification conditions. There is a case.

  Note that the number of divisions of the electrode catalyst layers 2 and 3 is not limited to two (for example, the first electrode catalyst portion 2a and the second electrode catalyst portion 2b). The number of divided electrode catalyst layers 2 and 3 may be three or more. When the number of divisions of each of the electrode catalyst layers 2 and 3 is 3 or more, pores having a diameter of 1.0 μm or less in the electrode catalyst layers 2 and 3 in terms of a converted value by cylindrical approximation of the pores obtained by the mercury intrusion method The volume changes stepwise from the upstream side of the gas to the downstream side of the gas. In other words, even if the number of divisions of the electrode catalyst layer is 3 or more, the pore volume in the region downstream of the gas is larger than the value of the pore volume in the region upstream of the gas in the electrode catalyst layers 2 and 3. To increase the value of.

In addition, only one of the two electrode catalyst layers 2 and 3 (electrode catalyst layer 2 or 3) formed on both surfaces of the polymer electrolyte membrane 1 is divided into two or more regions having different pore volumes. May be.
When only one of the electrode catalyst layers 2 or 3 is divided into two or more regions having different pore volumes, water is generated by the electrode reaction in the electrode catalyst layer divided into two or more regions having different pore volumes. It is preferably disposed on the air electrode (cathode) (indicated by the upper electrode catalyst layer 2 in FIG. 1). However, the electrode catalyst layer divided into two or more regions having different pore volumes may be formed on both surfaces of the polymer electrolyte membrane 1 from the viewpoint of water retention of the polymer electrolyte membrane 1 under low humidification conditions. More preferable.

(Solid polymer fuel cell)
Next, the polymer electrolyte fuel cell 12 of this embodiment will be described.
As shown in FIG. 2, the polymer electrolyte fuel cell 12 is opposed to the gas diffusion layer 4 on the air electrode side disposed to face the electrode catalyst layer 2 of the membrane electrode assembly 11, and to the electrode catalyst layer 3. And a gas diffusion layer 5 on the fuel electrode side arranged in such a manner.
That is, the electrode catalyst layer 2 and the gas diffusion layer 4 form an air electrode (cathode) 6. The electrode catalyst layer 3 and the gas diffusion layer 5 form a fuel electrode (anode) 7.

  As the gas diffusion layers 4 and 5, a material having gas diffusibility and conductivity can be used. For example, porous carbon materials such as carbon cloth, carbon paper, and nonwoven fabric can be used as the gas diffusion layers 4 and 5.

Also, a set of separators made of a material having conductivity and impermeability, including a gas flow path 8 (8a, 8b) for gas flow and a cooling water flow path 9 (9a, 9b) for flow of cooling water. 10 (10a, 10b) are arranged outside the gas diffusion layers 4 and 5, respectively.
For example, hydrogen gas is supplied as the fuel gas from the gas flow path 8b of the separator 10b on the fuel electrode 7 side. On the other hand, for example, oxygen gas is supplied as an oxidant gas from the gas flow path 8a of the separator 10a on the air electrode 6 side. An electromotive force can be generated between the fuel electrode and the air electrode by causing an electrode reaction between hydrogen of the fuel gas and oxygen of the oxidant gas in the presence of the catalyst.

  Here, in the separator 10a, the direction in which the gas flow path 8a is formed (the direction in which the gas flows) is the direction in which the electrode catalyst layer 2 is divided (the direction of the boundary between the first electrode catalyst portion 2a and the second electrode catalyst portion 2b). It arrange | positions so that it may cross substantially orthogonally. In the separator 10b, the direction in which the gas flow path 8b is formed (the direction in which the gas flows) is substantially the same as the direction in which the electrode catalyst layer 3 is divided (the direction of the boundary between the first electrode catalyst portion 3a and the second electrode catalyst portion 3b). It arrange | positions so that it may orthogonally cross. Thereby, the 1st electrode catalyst part 2a of the electrode catalyst layer 2 is located in the upstream of the gas flow path 8a, and the 2nd electrode which has a pore volume larger than the pore volume of the 1st electrode catalyst part 2a The catalyst part 2b is located downstream of the gas flow path 8a. Similarly, the second electrode having the pore volume larger than the pore volume of the first electrode catalyst portion 3a, the first electrode catalyst portion 3a of the electrode catalyst layer 3 being located upstream of the gas flow path 8b. The catalyst part 3b is located downstream of the gas flow path 8b.

  As the separator 10 (10a, 10b), a carbon type or a metal type can be used. The gas diffusion layers 4 and 5 and the separators 10 (10a and 10b) may each have an integral structure.

In the polymer electrolyte fuel cell 12, a polymer electrolyte membrane 1, two electrode catalyst layers 2 and 3, and gas diffusion layers 4 and 5 are sandwiched between a pair of separators 10 a and 10 b.
Here, although the polymer electrolyte fuel cell 12 is a fuel cell having a single cell structure, a plurality of cells may be stacked via the separator 10a or 10b to form a polymer electrolyte fuel cell. That is, when the separator 10 (10a, 10b) or the electrode catalyst layers 2, 3 fulfills the function of the gas diffusion layers 4, 5, the gas diffusion layers 4, 5 may be omitted. The polymer electrolyte fuel cell 12 can be manufactured by assembling other accompanying devices such as a gas supply device and a cooling device.

(Method for producing membrane electrode assembly)
Next, the manufacturing method of the membrane electrode assembly 11 of this embodiment is demonstrated.
The manufacturing method of the membrane electrode assembly 11 of this embodiment includes the following first to fourth steps. In addition, in the manufacturing method of the membrane electrode assembly 11 of this embodiment, the electrode catalyst layer 2 of the membrane electrode assembly 11 has the 1st electrode catalyst part 2a and the 2nd electrode catalyst part 2b, and an electrode catalyst layer 3 has the 1st electrode catalyst part 3a and the 2nd electrode catalyst part 3b.

(First step) Step of producing catalyst ink by dispersing particles carrying catalyst and polymer electrolyte in a solvent (second step) Constructing air electrode (cathode) 6 by applying catalyst ink to substrate A step of forming an electrode film to be the electrode catalyst layer 2 and an electrode film to be the electrode catalyst layer 3 constituting the fuel electrode (anode) 7 on the substrate (third step). The first electrode catalyst portion (2a, 3a) and the second electrode catalyst are transferred by transferring the electrode film that becomes the electrode catalyst layer 2 and the electrode film that becomes the electrode catalyst layer 3 that constitutes the fuel electrode (anode) 7. Steps for forming the parts (2b, 3b) (fourth step) The first electrode catalyst part 2a constituting the electrode catalyst layer 2 and the first electrode catalyst part 3a constituting the electrode catalyst layer 3 are pressurized and heated. Process

The first step corresponds to the catalyst ink preparation step, and the second step corresponds to the electrode film formation step.
The third step includes forming the first electrode catalyst portion and the second electrode catalyst portion in the first electrode catalyst layer forming step and the first electrode catalyst portion and the second electrode in the second electrode catalyst layer forming step. These electrode catalyst parts are simultaneously formed.
The fourth step includes pressurizing / heating treatment of the first electrode catalyst portion in the first electrode catalyst layer forming step and pressurizing / heating treatment of the first electrode catalyst portion in the second electrode catalyst layer forming step. Is a step of simultaneously performing.

  Each of the electrode catalyst layers 2 and 3 forms a coating film by applying a catalyst ink in which particles carrying a catalyst and a polymer electrolyte are dispersed in a solvent to a base material, and removing the solvent in the coating film. It is formed by transferring a coating film after solvent removal (hereinafter sometimes referred to as an electrode film) to the polymer electrolyte membrane 1. At this time, the pore volume of each of the electrode catalyst layers 2 and 3 after the treatment can be adjusted by applying pressure treatment to the electrode catalyst layer. That is, when the pressure of the pressure treatment is increased, the pore volume of the formed electrode catalyst layers 2 and 3 can be reduced.

  For this reason, the first electrode catalyst portion in the fourth step (the first electrode catalyst portion (2a, 3a) and the second electrode catalyst portion (2b, 3b) in the third step) than the transfer pressure at the time of formation. 2a, 3a) Increase the pressure of the pressure treatment. Thereby, the electrode catalyst part (1st electrode catalyst part (2a, 3a), 2nd electrode catalyst part (2b, 3b)) from which pore volume differs can be formed.

  In the manufacturing method of the membrane electrode assembly 11, the pressure in the step of applying pressure to the first electrode catalyst portion (2a, 3a) (fourth step) is changed between the first electrode catalyst portion (2a, 3a) and the second electrode catalyst portion (2a, 3a). The transfer pressure of the electrode film in the step (third step) for forming the electrode catalyst portions (2b, 3b) is made larger. Thus, the second electrode catalyst part (2b) formed by transferring the pore volume of the first electrode catalyst part (2a, 3a) formed by pressure treatment in the fourth process in the third process. , 3b) can be made smaller than the pore volume.

  The transfer pressure in the step (third step) for forming the first electrode catalyst portion (2a, 3a) and the second electrode catalyst portion (2b, 3b) and the first electrode catalyst portion (2a, 3a) are added. The pressure ratio in the pressure treatment step (fourth step) is preferably in the range of 1: 1.25 to 1: 5. When the ratio between the transfer pressure in the third step and the pressure in the fourth step is less than 1: 1.25, the pore volume of the formed first electrode catalyst portion (2a, 3a) and the second electrode The difference from the pore volume of the catalyst part (2b, 3b) becomes small. For this reason, in membrane electrode assembly 11, it may become difficult to make compatible the drainage nature of the water generated by electrode reaction, and the water retention under low humidification conditions. When the ratio between the transfer pressure in the third step and the transfer pressure in the fourth step exceeds 1: 5, the pore volume of the formed first electrode catalyst portion (2a, 3a) and the second electrode The difference from the pore volume of the catalyst part (2b, 3b) becomes large. For this reason, in membrane electrode assembly 11, it may become difficult to make compatible the drainage nature of the water generated by electrode reaction, and the water retention under low humidification conditions.

  In addition, each electrode catalyst portion is formed by applying a catalyst ink in which particles supporting a catalyst and a polymer electrolyte are dispersed in a solvent to form a coating film, and removing the solvent in the coating film. It is formed by transferring the coating film (electrode film) after removing the solvent to the polymer electrolyte membrane 1. At this time, the pore volume of each electrode catalyst part after a process can be adjusted by heat-processing with respect to an electrode catalyst layer. That is, when the temperature of the heat treatment is increased, the pore volume of the formed electrode catalyst part can be reduced.

For this reason, the first electrode catalyst portion in the fourth step (the first electrode catalyst portion (2a, 3a) and the second electrode catalyst portion (2b, 3b) in the third step) than the transfer temperature at the time of formation. 2a, 3a) Increase the temperature of the heat treatment. Thereby, the electrode catalyst part (1st electrode catalyst part (2a, 3a), 2nd electrode catalyst part (2b, 3b)) from which pore volume differs can be formed.
In the manufacturing method of the membrane electrode assembly 11, the temperature in the step (fourth step) of heat-treating the first electrode catalyst portion (2a, 3a) is set to the first electrode catalyst portion (2a, 3a) and the second The temperature is higher than the transfer temperature of the electrode film in the step (third step) of forming the electrode catalyst portions (2b, 3b).
Thus, the pore volume of the first electrode catalyst part (2a, 3a) formed by heat treatment in the fourth step is transferred to the second electrode catalyst part (2b, 3a) formed by transferring in the third step. It can be made smaller than the pore volume of 3b).

  The transfer temperature in the step (third step) for forming the first electrode catalyst portion (2a, 3a) and the second electrode catalyst portion (2b, 3b) and the first electrode catalyst portion (2a, 3a) are added. The temperature difference in the pressure treatment step (fourth step) is preferably in the range of 2 ° C. or higher and 20 ° C. or lower. When the difference between the transfer temperature in the third step and the temperature in the fourth step is less than 2 ° C., the pore volume of the formed first electrode catalyst portion (2a, 3a) and the second electrode catalyst portion (2b) , 3b), the difference from the pore volume becomes small, and it may be difficult to achieve both the drainage of the water produced by the electrode reaction and the water retention under low humidification conditions. When the difference between the transfer temperature in the third step and the temperature in the fourth step exceeds 20 ° C., the pore volume of the formed first electrode catalyst portion (2a, 3a) and the second electrode catalyst portion ( The difference between the pore volume of 2b and 3b) becomes large, and it may be difficult to achieve both the drainage of the water generated by the electrode reaction and the water retention under low humidification conditions.

  The value of the pore volume of 1.0 μm or less in diameter in the first electrode catalyst part (2a, 3a) and the value of the pore volume of 1.0 μm or less in diameter in the second electrode catalyst part (2b, 3b) It is preferable to adjust the transfer pressure or the transfer temperature of the electrode film so that the difference is a conversion value by cylindrical approximation of the pores determined by the mercury intrusion method and is 0.1 mL / g or more and 1.0 mL / g or less. . If the difference between the pore volume values described above is less than 0.1 mL / g, it may be difficult to achieve both the drainage of water produced by the electrode reaction and the water retention under low humidification conditions. . Moreover, even when the difference in the above-mentioned pore volume values exceeds 1.0 mL / g, it is difficult to achieve both the drainage of the water generated by the electrode reaction and the water retention under low humidification conditions. There is a case.

  Hereinafter, the method for producing an electrode catalyst layer for a polymer electrolyte fuel cell according to this embodiment will be described with reference to specific examples and comparative examples. However, this embodiment is limited by the following examples and comparative examples. It is not something.

Example 1
<Adjustment of catalyst ink>
A platinum-supported carbon catalyst (trade name: TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) having a platinum support amount of 50% by mass and a 20% by mass polymer electrolyte solution (trade name: Nafion (registered trademark), manufactured by DuPont) The mixture was mixed in a solvent and dispersed with a planetary ball mill. At this time, the dispersion time was set to 30 minutes, and the catalyst ink was adjusted. The composition ratio of the starting material of the prepared catalyst ink was 1: 1 by mass ratio of carbon carrier: polymer electrolyte. The solvent of the catalyst ink was 1: 1 by volume ratio of ultrapure water and 1-propanol. The solid content in the catalyst ink was 10% by mass.

〔Base material〕
A polytetrafluoroethylene (PTFE) sheet, which is a transfer sheet, was used as a substrate.

<Formation of electrode catalyst layer on substrate>
The catalyst ink prepared as described above was applied onto the substrate by the doctor blade method, and dried at 80 ° C. in an air atmosphere. The amount of catalyst ink applied was 0.1 mg / cm ^{2 for the} platinum supported amount in the electrode catalyst layer serving as the fuel electrode (anode), and 0.3 mg / cm ² for the platinum supported amount in the electrode catalyst layer serving as the air electrode (cathode). Each was adjusted to be.

<Preparation of membrane electrode assembly>
The base material on which the electrode catalyst layer to be the anode and the electrode catalyst layer to be the cathode were formed was punched into 5 cm × 5 cm, respectively. It was formed by transferring on a polymer electrolyte membrane (trade name: Nafion (registered trademark), manufactured by DuPont) under the conditions of a transfer temperature of 130 ° C. and a transfer pressure of 4.0 × 10 ⁶ Pa. Pressure treatment was performed on 5 cm × 2.5 cm on the gas inlet side so that the first electrode catalyst portion was disposed on the gas inlet side and the second electrode catalyst portion was disposed on the gas outlet side. The first electrode catalyst part was subjected to pressure treatment under conditions of a temperature of 130 ° C. and a pressure of 9.0 × 10 ⁶ Pa.

A first electrode catalyst portion treated under conditions of a temperature of 130 ° C. and a pressure of 9.0 × 10 ⁶ Pa, and a second electrode catalyst portion treated under conditions of a transfer temperature of 130 ° C. and a transfer pressure of 4.0 × 10 ⁶ Pa The pore volume was measured with a mercury porosimeter. As a result, the cylinder of the second electrode catalyst portion provided on the gas outlet side is smaller than the pore volume of 1.0 μm or less in diameter in terms of the cylinder approximation of the first electrode catalyst portion provided on the gas inlet side. The pore volume with a diameter of 1.0 μm or less in terms of approximation increased, and the difference was 0.16 mL / g.

(Example 2)
<Adjustment of catalyst ink>
The same adjustment as that of the catalyst ink of Example 1 was performed.
<Base material>
A polytetrafluoroethylene (PTFE) sheet was used in the same manner as the base material of Example 1.

<Formation of electrode catalyst layer on substrate>
Similar to the electrode catalyst layer of Example 1, an electrode catalyst layer serving as an anode and an electrode catalyst layer serving as a cathode were formed.

<Preparation of membrane electrode assembly>
The base material on which the electrode catalyst layer to be the anode and the electrode catalyst layer to be the cathode were formed was punched into 5 cm × 5 cm, respectively. It was formed by transferring on a polymer electrolyte membrane (trade name: Nafion (registered trademark), manufactured by DuPont) under the conditions of a transfer temperature of 130 ° C. and a transfer pressure of 4.0 × 10 ⁶ Pa. Heat treatment was performed on 5 cm × 2.5 cm on the gas inlet side so that the first electrode catalyst portion was disposed on the gas inlet side and the second electrode catalyst portion was disposed on the gas outlet side. The first electrode catalyst part was heat-treated under conditions of a temperature of 140 ° C. and a pressure of 4.0 × 10 ⁶ Pa.

A first electrode catalyst portion treated under conditions of a temperature of 140 ° C. and a pressure of 4.0 × 10 ⁶ Pa, and a second electrode catalyst portion treated under conditions of a transfer temperature of 130 ° C. and a transfer pressure of 4.0 × 10 ⁶ Pa The pore volume was measured with a mercury porosimeter. As a result, the cylinder of the second electrode catalyst portion provided on the gas outlet side is smaller than the pore volume of 1.0 μm or less in diameter in terms of the cylinder approximation of the first electrode catalyst portion provided on the gas inlet side. The pore volume with a diameter of 1.0 μm or less in terms of approximation increased, and the difference was 0.19 mL / g.

(Example 3)
<Adjustment of catalyst ink>
The same adjustment as that of the catalyst ink of Example 1 was performed.
<Base material>
A polytetrafluoroethylene (PTFE) sheet was used in the same manner as the base material of Example 1.

<Formation of electrode catalyst layer on substrate>
Similar to the electrode catalyst layer of Example 1, an electrode catalyst layer serving as an anode and an electrode catalyst layer serving as a cathode were formed.

<Preparation of membrane electrode assembly>
The base material on which the electrode catalyst layer to be the anode and the electrode catalyst layer to be the cathode were formed was punched into 5 cm × 5 cm, respectively. It was formed by transferring on a polymer electrolyte membrane (trade name: Nafion (registered trademark), manufactured by DuPont) under the conditions of a transfer temperature of 130 ° C. and a transfer pressure of 4.0 × 10 ⁶ Pa. Pressure treatment was performed on 5 cm × 2.5 cm on the gas inlet side so that the first electrode catalyst portion was disposed on the gas inlet side and the second electrode catalyst portion was disposed on the gas outlet side. The first electrode catalyst part was pressurized under the conditions of a temperature of 130 ° C. and a pressure of 21 × 10 ⁶ Pa.

The first electrode catalyst part processed under the conditions of a temperature of 130 ° C. and a pressure of 21 × 10 ⁶ Pa, and the second electrode catalyst part processed under the conditions of a transfer temperature of 130 ° C. and a transfer pressure of 4.0 × 10 ⁶ Pa. The pore volume was measured with a mercury porosimeter. As a result, the cylinder of the second electrode catalyst portion provided on the gas outlet side is smaller than the pore volume of 1.0 μm or less in diameter in terms of the cylinder approximation of the first electrode catalyst portion provided on the gas inlet side. The pore volume with a diameter of 1.0 μm or less in terms of approximation increased, and the difference was 0.82 mL / g.

Example 4
<Adjustment of catalyst ink>
The same adjustment as that of the catalyst ink of Example 1 was performed.
<Base material>
A polytetrafluoroethylene (PTFE) sheet was used in the same manner as the base material of Example 1.

<Formation of electrode catalyst layer on substrate>
Similar to the electrode catalyst layer of Example 1, an electrode catalyst layer serving as an anode and an electrode catalyst layer serving as a cathode were formed.

<Preparation of membrane electrode assembly>
The base material on which the electrode catalyst layer to be the anode and the electrode catalyst layer to be the cathode were formed was punched into 5 cm × 5 cm, respectively. It was formed by transferring on a polymer electrolyte membrane (trade name: Nafion (registered trademark), manufactured by DuPont) under the conditions of a transfer temperature of 130 ° C. and a transfer pressure of 4.0 × 10 ⁶ Pa. Heat treatment was performed on 5 cm × 2.5 cm on the gas inlet side so that the first electrode catalyst portion was disposed on the gas inlet side and the second electrode catalyst portion was disposed on the gas outlet side. The first electrode catalyst part was heat-treated under conditions of a temperature of 165 ° C. and a pressure of 4.0 × 10 ⁶ Pa.

A first electrode catalyst portion treated under conditions of a temperature of 165 ° C. and a pressure of 4.0 × 10 ⁶ Pa, and a second electrode catalyst portion treated under conditions of a transfer temperature of 130 ° C. and a transfer pressure of 4.0 × 10 ⁶ Pa The pore volume was measured with a mercury porosimeter. As a result, the cylinder of the second electrode catalyst portion provided on the gas outlet side is smaller than the pore volume of 1.0 μm or less in diameter in terms of the cylinder approximation of the first electrode catalyst portion provided on the gas inlet side. The pore volume with a diameter of 1.0 μm or less in terms of approximation increased, and the difference was 0.75 mL / g.

(Comparative Example 1)
<Adjustment of catalyst ink>
The same adjustment as that of the catalyst ink of Example 1 was performed.
<Base material>
A polytetrafluoroethylene (PTFE) sheet was used in the same manner as the base material of Example 1.

<Formation of electrode catalyst layer on substrate>
Similar to the electrode catalyst layer of Example 1, an electrode catalyst layer serving as an anode and an electrode catalyst layer serving as a cathode were formed.

<Preparation of membrane electrode assembly>
The base material on which the electrode catalyst part is formed is punched into a 25 cm ² (5 cm × 5 cm) square, the electrode catalyst part is disposed so as to face both surfaces of the polymer electrolyte membrane, a transfer temperature of 130 ° C., and a transfer pressure of 4.0 ×. The film was transferred under the condition of 10 ⁶ Pa to obtain a membrane electrode assembly. In other words, no difference in pore volume was formed between the gas catalyst upstream and downstream electrode catalyst layers.

(Evaluation)
<Power generation characteristics>
Carbon paper used as a gas diffusion layer is bonded and placed in a power generation evaluation cell so as to sandwich the membrane electrode assemblies produced in Example 1, Example 2, Example 3, Example 4, and Comparative Example 1. did. Using the fuel cell measurement device, the cell voltage was set to 80 ° C., and current voltage measurement was performed under the following two operating conditions. Hydrogen was used as the fuel gas and air was used as the oxidant gas, and the flow rate was controlled at a constant utilization rate. The back pressure was 100 kPa.
[Operating conditions]
1. Full humidification: relative humidity anode 100% RH, cathode 100% RH
2. Low humidification: Relative humidity Anode 30% RH, Cathode 30% RH

〔Measurement result〕
The membrane / electrode assembly produced in Example 1, Example 2, Example 3 and Example 4 has better power generation performance under low humidification operating conditions than the membrane / electrode assembly produced in Comparative Example 1. Indicated.
In addition, the membrane electrode assemblies produced in Example 1, Example 2, Example 3, and Example 4 have the same level of power generation performance as in the fully humidified operating condition even under the low humidified operating condition. It was. In particular, the power generation performance near a current density of 0.5 A / cm ² was improved.
The cell voltage at a current density of 0.5 A / cm ² of the membrane electrode assembly produced in Example 1 is 69 mV compared to the cell voltage at a current density of 0.5 A / cm ² of the membrane electrode assembly produced in Comparative Example 1. It showed high power generation characteristics.
Further, the cell voltage at a current density of 0.5A / cm ² of the membrane electrode assembly produced in Example 2 as compared to the cell voltage at a current density of 0.5A / cm ² of the membrane electrode assembly fabricated in Comparative Example 1 The power generation characteristics were 47 mV higher.
Further, the cell voltage at a current density of 0.5A / cm ² of the membrane electrode assembly produced in Example 3 as compared to the cell voltage at a current density of 0.5A / cm ² of the membrane electrode assembly fabricated in Comparative Example 1 The power generation characteristic is 22 mV higher.
Further, the cell voltage at a current density of 0.5A / cm ² of the membrane electrode assembly produced in Example 4 as compared to the cell voltage at a current density of 0.5A / cm ² of the membrane electrode assembly fabricated in Comparative Example 1 The power generation characteristics were 28 mV higher.

  Thus, from the results of the power generation characteristics of the membrane electrode assemblies produced in Example 1, Example 2, Example 3, and Example 4 and the membrane electrode assemblies produced in Comparative Example 1, the gas inlet The membrane electrode assembly in which the value of the pore volume of the second electrode catalyst part provided on the gas outlet side is larger than the value of the pore volume of the first electrode catalyst part provided on the side increases the water retention In addition, it was confirmed that the power generation characteristics under the low humidifying operation condition show the power generation characteristics equivalent to those under the full humidifying operation condition.

Moreover, under the full humidification operation conditions, the cell voltage at the current density of 0.5 A / cm ² of the membrane electrode assembly produced in Example 1 was 0.5 A / cm ² of the membrane electrode assembly produced in Comparative Example 1. The power generation characteristic was 41 mV higher than the cell voltage at / cm ² .
Further, the cell voltage at a current density of 0.5A / cm ² of the membrane electrode assembly produced in Example 2 as compared to the cell voltage at a current density of 0.5A / cm ² of the membrane electrode assembly fabricated in Comparative Example 1 The power generation characteristics are as high as 32 mV.
Further, the cell voltage at a current density of 0.5A / cm ² of the membrane electrode assembly produced in Example 3 as compared to the cell voltage at a current density of 0.5A / cm ² of the membrane electrode assembly fabricated in Comparative Example 1 The power generation characteristics were 13 mV higher.
Further, the cell voltage at a current density of 0.5A / cm ² of the membrane electrode assembly produced in Example 4 as compared to the cell voltage at a current density of 0.5A / cm ² of the membrane electrode assembly fabricated in Comparative Example 1 The power generation characteristic was 21 mV higher.
Thus, from the result of the power generation characteristic of the membrane electrode assembly produced in Example 1, Example 2, Example 3, and Example 4 and the membrane electrode assembly produced in Comparative Example 1, the reaction gas It was confirmed that diffusivity and removal of water generated by electrode reaction were not hindered.

  As described above, the present embodiment relates to a membrane / electrode assembly that exhibits high power generation characteristics under low humidification conditions, a method for producing the membrane / electrode assembly, and a polymer electrolyte fuel cell including the membrane / electrode assembly.

  The membrane electrode assembly according to the present embodiment is a membrane electrode assembly in which a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers. Here, at least one of the electrode catalyst layers is divided into at least two parts: a first electrode catalyst part and a second electrode catalyst part adjacent to the first electrode catalyst part in the planar direction of the polymer electrolyte membrane. ing. And the value of the pore volume of 1.0 μm or less in diameter of the second electrode catalyst part is larger than the value of the pore volume of 1.0 μm or less in diameter of the first electrode catalyst part.

The above-described method for manufacturing a membrane electrode assembly includes a step of producing a catalyst ink, a step of applying the catalyst ink on a substrate to form an electrode film, and transferring the electrode film to a polymer electrolyte membrane. Forming the electrode catalyst layer and the second electrode catalyst layer, and pressurizing the first electrode catalyst layer.
Further, the ratio of the transfer pressure in the step of forming the first electrode catalyst portion and the second electrode catalyst portion and the pressure in the step of pressurizing the first electrode catalyst portion at the time of forming any of the electrode catalyst layers Is in the range of 1: 1.25 or more and 1: 5 or less.
Further, the difference between the transfer temperature in the step of forming the first electrode catalyst portion and the second electrode catalyst portion and the temperature in the step of pressurizing the first electrode catalyst portion is within a range of 2 ° C. or more and 20 ° C. or less. It is said.

  The transfer temperature in the step (third step) for forming the first electrode catalyst portion (2a, 3a) and the second electrode catalyst portion (2b, 3b) and the first electrode catalyst portion (2a, 3a) are added. The temperature difference in the pressure treatment step (fourth step) is preferably in the range of 2 ° C. or higher and 20 ° C. or lower. When the difference between the transfer temperature in the third step and the temperature in the fourth step is less than 2 ° C., the pore volume of the formed first electrode catalyst portion (2a, 3a) and the second electrode catalyst portion (2b) , 3b), the difference from the pore volume becomes small, and it may be difficult to achieve both the drainage of the water produced by the electrode reaction and the water retention under low humidification conditions. When the difference between the transfer temperature in the third step and the temperature in the fourth step exceeds 20 ° C., the pore volume of the formed first electrode catalyst portion (2a, 3a) and the second electrode catalyst portion ( The difference between the pore volume of 2b and 3b) becomes large, and it may be difficult to achieve both the drainage of the water generated by the electrode reaction and the water retention under low humidification conditions.

Further, in the membrane electrode assembly manufactured by the method for manufacturing the membrane electrode assembly according to the present embodiment, the value of the pore volume of the second electrode catalyst portion having a diameter of 1.0 μm or less is obtained by the mercury intrusion method. The first and second electrode catalyst portions are formed so as to be larger than the value of the pore volume of the first electrode catalyst portion having a diameter of 1.0 μm or less by a conversion value obtained by approximating the pores to a cylinder. Furthermore, the membrane electrode assembly manufactured by the method for manufacturing a membrane electrode assembly according to the present embodiment has a pore volume of a diameter of 1.0 μm or less of the second electrode catalyst part and a diameter of the first electrode catalyst part. The first and second so that the difference from the pore volume of 1.0 μm or less is 0.1 mL / g or more and 1.0 mL / g or less as a converted value by cylindrical approximation of the pores obtained by the mercury intrusion method. The electrode catalyst part is formed.
Moreover, the polymer electrolyte fuel cell according to the present embodiment includes the above-described membrane electrode assembly.

  For this reason, the membrane / electrode assembly manufactured by the method for manufacturing a membrane / electrode assembly according to the present embodiment increases water retention without hindering removal of water generated by the electrode reaction, and is high even under low humidification conditions. The power generation characteristics are shown. Moreover, the manufacturing method of the membrane electrode assembly which concerns on this embodiment can manufacture the above membrane electrode assembly efficiently efficiently easily.

  As mentioned above, although embodiment of this invention was explained in full detail, actually, it is not restricted to said embodiment, Even if there is a change of the range which does not deviate from the summary of this invention, it is included in this invention.

DESCRIPTION OF SYMBOLS 1 ... Polymer electrolyte membrane 2 ... Electrode catalyst layer 2a ... 1st electrode catalyst part 2b ... 2nd electrode catalyst part 3 ... Electrode catalyst layer 3a ... 1st electrode catalyst part 3b ... 2nd electrode catalyst part 4 ... Gas diffusion layer 5 ... Gas diffusion layer 6 ... Air electrode (cathode)
7. Fuel electrode (anode)
8, 8a, 8b ... gas flow paths 9, 9a, 9b ... cooling water flow paths 10, 10a, 10b ... separator 11 ... membrane electrode assembly 12 ... polymer electrolyte fuel cell

Claims (8)

A catalyst ink production process for producing a catalyst ink;
An electrode film forming step of applying the catalyst ink prepared in the catalyst ink preparation step to a substrate and forming an electrode film to be the electrode catalyst layer on the substrate;
A first electrode catalyst layer forming step of transferring the electrode film while applying pressure to one surface of the polymer electrolyte membrane to form one of the electrode catalyst layers;
A second electrode catalyst layer forming step of transferring the electrode film to the other surface of the polymer electrolyte membrane while applying pressure to form the other electrode catalyst layer;
Including
In at least one of the first electrode catalyst layer forming step and the second electrode catalyst layer forming step, the electrode membrane is transferred to the polymer electrolyte membrane while being pressed, and the planar direction of the polymer electrolyte membrane is And forming the first electrode catalyst layer portion and the second electrode catalyst layer portion at adjacent positions in at least one of the first electrode catalyst layer forming step and the second electrode catalyst layer forming step. A method for producing a membrane electrode assembly, wherein the first electrode catalyst layer portion is subjected to pressure treatment at a pressure higher than that during transfer.   The ratio of the transfer pressure at the time of formation of at least one of the first electrode catalyst part and the second electrode catalyst layer forming step to the pressure in the pressurizing process of the first electrode catalyst part is 1: 1. The method for producing a membrane / electrode assembly according to claim 1, wherein the method is in the range of 25 to 1: 5. A catalyst ink production process for producing a catalyst ink;
An electrode film forming step of applying the catalyst ink prepared in the catalyst ink preparation step to a substrate and forming an electrode film to be the electrode catalyst layer on the substrate;
A first electrode catalyst layer forming step of transferring the electrode film to one surface of the polymer electrolyte membrane while heating to form one of the electrode catalyst layers;
A second electrode catalyst layer forming step of transferring the electrode film to the other surface of the polymer electrolyte membrane while heating and forming the other electrode catalyst layer;
Including
In at least one of the first electrode catalyst layer forming step and the second electrode catalyst layer forming step, the electrode film is transferred to the polymer electrolyte membrane while being heated, and in the plane direction of the polymer electrolyte membrane At the time of transfer in which at least one of the first electrode catalyst layer forming step and the second electrode catalyst layer forming step, the first electrode catalyst layer portion and the second electrode catalyst layer portion are formed at adjacent positions. The manufacturing method of the membrane electrode assembly which heat-processes the said 1st electrode catalyst layer part at higher temperature.   The difference between the transfer temperature in at least one of the first electrode catalyst part and the second electrode catalyst layer forming step and the temperature in the heat treatment of the first electrode catalyst part is in the range of 2 ° C. or more and 20 ° C. or less. The method for producing a membrane electrode assembly according to claim 3, wherein the membrane electrode assembly is in the inside. A polymer electrolyte membrane;
A pair of electrode catalyst layers sandwiching the polymer electrolyte membrane;
With
At least one of the electrode catalyst layers has a first electrode catalyst part and a second electrode catalyst part adjacent to the first electrode catalyst part in the planar direction of the polymer electrolyte membrane,
The value of the pore volume of the second electrode catalyst portion having a diameter of 1.0 μm or less is a conversion value obtained by approximating the pore cylinder obtained by mercury porosimetry, and the diameter of the first electrode catalyst portion is 1.0 μm or less. A membrane electrode assembly having a pore volume larger than that of the membrane electrode assembly.   The difference between the pore volume of the second electrode catalyst portion having a diameter of 1.0 μm or less and the value of the pore volume of the first electrode catalyst portion having a diameter of 1.0 μm or less is a fine value determined by a mercury intrusion method. The membrane electrode assembly according to claim 5, which is a conversion value by cylindrical approximation of the hole and is 0.1 mL / g or more and 1.0 mL / g or less.   A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 5. A pair of separators having a gas flow path for sandwiching the membrane electrode assembly and supplying gas to the electrode catalyst layer;
The solid electrode according to claim 7, wherein the first electrode catalyst part is disposed on the upstream side of the gas flow path, and the second electrode catalyst part is disposed on the downstream side of the gas flow path. Molecular fuel cell.

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