JP2018060715A - Method for manufacturing membrane-electrode assembly, membrane-electrode assembly and solid polymer fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane-electrode assembly which has a high power-generation property even under a low-humidification condition, which can increase the diffusibility of reactive gas, and which can enhance a water retention property without interfering with the removal of water produced by an electrode reaction etc.SOLUTION: A membrane-electrode assembly comprises: a polymer electrolyte membrane 1; and a pair of electrode catalyst layers 2, 3 holding the polymer electrolyte membrane therebetween. In the membrane-electrode assembly, an electrode catalyst layer of at least one of the pair of electrode catalyst layers is provided with at least two electrode catalyst parts consisting of: a first electrode catalyst part 2a (or 3a) provided on a gas inlet side; and a second electrode catalyst part 2b (or 3b) provided on a gas outlet side. The ion exchange capacity of a first polymer electrolyte that a first polymer electrolyte solution in a catalyst ink forming the first electrode catalyst part 2a (or 3a) includes is made larger than that of a second polymer electrolyte that a second polymer electrolyte solution in a catalyst ink forming the second electrode catalyst part 2b(or 3b) includes.SELECTED DRAWING: Figure 1

Description

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

  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 methods, 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 supporting a catalyst material 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 Document 1, Patent Document 2, Patent Document 3, and Patent Document 4.)

In addition, examples of the problem toward the practical application of the polymer electrolyte fuel cell include improvement in 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 the fuel cell under low humidification conditions, for example, a method of sandwiching a humidity adjusting film between the electrode catalyst layer and the gas diffusion layer has been devised.

For example, Patent Document 5 devises 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 devises a method of providing a groove on the surface of the catalyst electrode layer in contact with the polymer electrolyte membrane. A method has been devised 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 power generation performance of the electrode catalyst layer described in these patent documents is insufficient, and further improvement in power generation performance is desired. Further, these electrode catalyst layers have a problem that the production method is complicated and the cost is high.
The present invention has been made paying attention to the above-mentioned problems, and enhances the diffusibility of the reaction gas, enhances the water retention without hindering the removal of water produced by the electrode reaction, and generates high power even under low humidification conditions. It is an object of the present invention to provide a method for producing a membrane electrode assembly, a membrane electrode assembly, and a polymer electrolyte fuel cell.

  According to one aspect of the present invention, a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers, each of the pair of electrode catalyst layers including catalyst-carrying particles and a polymer electrolyte, and at least of the pair of electrode catalyst layers. One electrode catalyst layer includes a first electrode catalyst portion and a second electrode catalyst portion adjacent to the first electrode catalyst portion in the planar direction of the polymer electrolyte membrane. The first catalyst ink in which the catalyst-supporting particles and the first polymer electrolyte solution are dispersed in a solvent is prepared, and after the first catalyst ink is applied and dried, the first electrode catalyst portion is formed. A second high electrolyte comprising a step of forming, a catalyst-supporting particle, and a second polymer electrolyte having an ion exchange capacity smaller than the ion exchange capacity of the first polymer electrolyte contained in the first polymer electrolyte solution. Second catalyst in which molecular electrolyte solution is dispersed in solvent To produce a method for producing a second catalyst ink and forming a second electrode catalyst portion is dried after coating, the a membrane electrode assembly, are provided.

  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 has high power generation characteristics even under low humidification conditions Membrane / electrode assembly including the above can be produced efficiently, economically and easily.

It is a disassembled perspective view which shows typically the structure of an example of the membrane electrode assembly in this invention. It is a disassembled perspective view which shows typically the structure of an example of the polymer electrolyte fuel cell in this invention.

Hereinafter, a membrane electrode assembly to which an embodiment of the present invention is applied will be described with reference to the drawings. However, the same reference numerals are given to portions corresponding to each other in the drawings to be described below, and description of the overlapping portions will be omitted as appropriate. Each drawing is exaggerated as appropriate for easy explanation.
Furthermore, the embodiment of the present invention exemplifies a configuration for embodying the technical idea of the present invention, and specifies the material, shape, structure, arrangement, dimensions, etc. of each part as follows. Not. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

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 according to the present embodiment will be described.
FIG. 1 is an exploded perspective view schematically showing a configuration of a membrane electrode assembly 11 according to the present embodiment. 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). Further, the two electrode catalyst layers 2 and 3 of the membrane electrode assembly 11 are divided into two regions in the planar direction of the polymer electrolyte membrane 1. More specifically, the electrode catalyst layer 2 shown on the upper side in FIG. 1 has 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. . Similarly, the electrode catalyst layer 3 shown on the lower side in the drawing has 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.

  In the membrane electrode assembly 11, the value of the ion exchange capacity of the polymer electrolyte in the electrode catalyst layers 2 and 3 is closer to the gas outlet than the first electrode catalyst portion 2a (or 3a) provided on the gas inlet side. The provided second electrode catalyst part 2b (or 3b) is smaller. In other words, the value of the second electrode catalyst part 2b (or 3b) on the downstream side of the gas is higher than the value of the ion exchange capacity in the polymer electrolyte of the first electrode catalyst part 2a (or 3a) on the upstream side of the gas. The value of the ion exchange capacity in the molecular electrolyte is smaller.

In the membrane electrode assembly 11, the value of the ion exchange capacity in the polymer electrolyte of the first electrode catalyst part 2a (or 3a) provided on the gas inlet side is set to the second electrode catalyst part 2b (on the gas outlet side). Alternatively, the second electrode catalyst part 2b (or the second electrode catalyst part 2b (or 3a) provided on the gas inlet side can be increased by increasing the water retention by the first electrode catalyst part 2a (or 3a) provided on the gas inlet side. 3b) promotes the removal of water. 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 the membrane / electrode assembly 11, unlike the case of reducing humidity by applying a conventional humidity adjusting film or forming grooves on the surface of the electrode catalyst layer, the power generation characteristics are not deteriorated due to an increase in interface resistance. Therefore, compared with the conventional polymer electrolyte fuel cell provided with the membrane electrode assembly, the polymer electrolyte fuel cell provided with the membrane electrode assembly 11 has a remarkable effect that it has high power generation characteristics even under low humidification conditions. Play.

[Solid polymer fuel cell]
Next, the polymer electrolyte fuel cell 12 provided with the membrane electrode assembly 11 according to the present embodiment will be described.
FIG. 2 is an exploded perspective view schematically showing the polymer electrolyte fuel cell 12. The polymer electrolyte fuel cell 12 includes a gas diffusion layer 4 on the air electrode side disposed so as to face the electrode catalyst layer 2 of the membrane electrode assembly 11 and a fuel disposed so as to face the electrode catalyst layer 3. A gas diffusion layer 5 on the pole side. 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. Also, a set of separators made of a material having conductivity and impermeability, including gas flow paths 8 (8a, 8b) for gas flow and cooling water flow paths 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.

  In the polymer electrolyte fuel cell 12 shown in FIG. 2, a polymer electrolyte membrane 1, two electrode catalyst layers 2, 3 and gas diffusion layers 4 and 5 are sandwiched between a pair of separators 10a and 10b. This is a single-cell fuel cell. Here, a single cell structure fuel cell is used as the polymer electrolyte fuel cell 12, but a polymer electrolyte fuel cell may be configured by stacking a plurality of cells via the separator 10a or 10b. .

[Production method of membrane electrode assembly]
Next, an example of the manufacturing method of the membrane electrode assembly 11 according to the present embodiment will be described.
The manufacturing method of the membrane electrode assembly 11 according to the present embodiment includes the following steps.
(First Step) A step of preparing a first catalyst ink by dispersing particles carrying a catalyst and a first polymer electrolyte solution in a solvent; and a particle carrying a catalyst and a second polymer electrolyte solution. Step of producing second catalyst ink by dispersing in solvent (second step) Step of forming first electrode catalyst portion by applying first catalyst ink to substrate and drying, and second catalyst Step of forming second electrode catalyst portion by applying ink to substrate and drying (third step) First electrode catalyst portions 2a, 3a and second electrode catalyst portion on at least one surface of the polymer electrolyte membrane Step of forming electrode catalyst parts 2b and 3b The first step corresponds to the step of forming the catalyst ink, the second step corresponds to the step of forming the electrode catalyst layer, and the third step is the step of forming the membrane electrode assembly Corresponding to

  In the preparation process of the catalyst ink in the first step, the ion exchange capacity of the first polymer electrolyte contained in the first polymer electrolyte solution in the first catalyst ink is the second polymer in the second catalyst ink. It is larger than the ion exchange capacity of the second polymer electrolyte contained in the electrolyte solution. By doing in this way, the ion exchange capacity of the polymer electrolyte of the first electrode catalyst parts 2a and 3a formed by the formation process of the electrode catalyst layer in the second process is the same as that of the second electrode catalyst parts 2b and 3b. It becomes larger than the ion exchange capacity of the polymer electrolyte. As a result, the first electrode catalyst parts 2a and 3a can retain water generated by the electrode reaction even under low humidification conditions. Further, the ion exchange capacity of the polymer electrolyte of the second electrode catalyst parts 2b and 3b is smaller than the ion exchange capacity of the polymer electrolyte of the first electrode catalyst parts 2a and 3a, so that the diffusibility of the reaction gas is increased. Can be increased.

  The ion exchange capacity of the first polymer electrolyte contained in the first polymer electrolyte solution in the first step is preferably in the range of 0.9 meq / g to 3.0 meq / g. When the ion exchange capacity of the first polymer electrolyte is less than 0.9 meq / g, it is difficult to retain water in the polymer electrolyte of the first electrode catalyst part, and the catalyst activity may be reduced. In addition, when the ion exchange capacity of the first polymer electrolyte exceeds 3.0 meq / g, the polymer electrolyte in the first electrode catalyst part holds excessive water, and it is difficult to ensure the diffusibility of the reaction gas. It may become.

  The ion exchange capacity of the second polymer electrolyte contained in the second polymer electrolyte solution in the first step is preferably within the range of 0.8 meq / g to 2.8 meq / g. When the ion exchange capacity of the second polymer electrolyte is less than 0.8 meq / g, it is difficult to retain water in the polymer electrolyte of the second electrode catalyst part, and the catalyst activity may be reduced. Further, when the ion exchange capacity of the second polymer electrolyte exceeds 2.8 meq / g, the polymer electrolyte in the second electrode catalyst part holds excessive water, and it is difficult to ensure the diffusibility of the reaction gas. It may become.

[Details]
Hereinafter, the membrane electrode assembly 11 and the polymer electrolyte fuel cell 12 according to this embodiment will be described in more detail.
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.

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.

  The catalyst substance used in the present embodiment (hereinafter sometimes referred to as catalyst particles or catalyst) includes platinum, palladium, ruthenium, iridium, rhodium, osmium, platinum group elements, iron, lead, copper, chromium, cobalt. In addition, metals such as nickel, manganese, vanadium, molybdenum, gallium, and aluminum, or alloys, oxides or double oxides thereof can be used. When the catalyst particles are one or two or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium, they have excellent electrode reactivity and can perform electrode reaction efficiently and stably. . 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 high. It is preferable because it has 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 determined from an SEM (Scanning Electron Microscope) 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-carrying 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 a thing. 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-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 as the aggregates of the catalyst-carrying particles are broken.

  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-supported particles and a polymer electrolyte. If the content of the catalyst-supported particles in the solid content is increased, the viscosity increases even with the same solid content. On the other hand, if the content of the catalyst-carrying particles in the solid content is decreased, the viscosity is lowered even with the same solid content. Therefore, the ratio of the catalyst-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 removing the solvent, is bonded to the polymer electrolyte membrane 1, and then the transfer sheet is peeled off. It can be set as the membrane electrode assembly 11 provided with the layers 2 and 3. FIG.

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.
As the separator 10 (10a, 10b), a carbon type or a metal type can be used. In addition, the gas diffusion layers 4 and 5 and the separators 10 (10a and 10b) may each have an integral structure. Further, 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.
Below, the specific example and comparative example are given and demonstrated about the manufacturing method of the membrane electrode assembly in this embodiment. In addition, this embodiment is not restrict | limited by the following Example and comparative example.

<Example>
[Adjustment of catalyst ink]
20 masses including a platinum-supported carbon catalyst having a loading density of 50 mass% and a first polymer electrolyte comprising a fluorine-based polymer electrolyte having an ion exchange capacity of 1.2 meq / g as the first polymer electrolyte solution. % Polymer electrolyte solution was mixed in a solvent and subjected to a dispersion treatment for 30 minutes with a planetary ball mill to prepare a first catalyst ink. Next, a platinum-supported carbon catalyst having a supporting density of 50% by mass and a second polymer electrolyte comprising a fluorine-based polymer electrolyte having an ion exchange capacity of 1.0 meq / g as the second polymer electrolyte solution are included. Then, a 20% by mass polymer electrolyte solution was mixed in a solvent and subjected to a dispersion treatment for 30 minutes with a planetary ball mill to prepare a second catalyst ink. The composition ratio of the starting materials in each catalyst ink was 1: 1 as the mass ratio of carbon support: polymer electrolyte in the platinum-supported carbon catalyst. The solvent of each catalyst ink was 1: 1 by volume ratio of ultrapure water and 1-propanol. The solid content in each catalyst ink was adjusted to 10% by mass.

[Formation of electrode catalyst layer]
The prepared catalyst ink was applied to a base material of a polytetrafluoroethylene (PTFE) sheet by a doctor blade method and dried at 80 ° C. in an air atmosphere. The coating amount of the first catalyst ink is adjusted so that the platinum loading amount is 0.1 mg / cm ² as the fuel electrode (anode) and the platinum loading amount is 0.3 mg / cm ² as the air electrode (cathode). Then, an electrode catalyst layer was formed. Also, the coating amount of the second catalyst ink is adjusted so that the platinum loading amount is 0.1 mg / cm ² as the fuel electrode (anode) and the platinum loading amount is 0.3 mg / cm ² as the air electrode (cathode). Then, an electrode catalyst layer was formed.

[Production of membrane electrode assembly]
The base material on which each electrode catalyst layer is formed is punched out to 5 cm × 2.5 cm, and arranged such that the first electrode catalyst part is on the gas inlet side and the second electrode catalyst part is on the gas outlet side. The electrode catalyst layer was 5 cm × 5 cm. This electrode catalyst layer was disposed on both surfaces of the polymer electrolyte membrane 1, and hot pressing was performed under the conditions of a transfer temperature of 130 ° C. and a transfer pressure of 5.0 × 10 ⁶ Pa to obtain a membrane electrode assembly 11.

<Comparative example>
[Adjustment of catalyst ink]
A 20% by mass polymer electrolyte solution comprising a platinum-supported carbon catalyst having a supported density of 50% by mass, and a fluorine-based polymer electrolyte having an ion exchange capacity of 1.2 meq / g as the first polymer electrolyte solution; As a second polymer electrolyte solution, a 20% by mass polymer electrolyte solution containing a fluorine polymer electrolyte having an ion exchange capacity of 1.0 meq / g is mixed in a solvent, and dispersed for 30 minutes with a planetary ball mill. To prepare a catalyst ink. The composition ratio of the starting materials in the catalyst ink was 2: 1: 1 in terms of the mass ratio of carbon support: first polymer electrolyte: second polymer electrolyte in the platinum-supported carbon catalyst. 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 adjusted to 10% by mass.

[Formation of electrode catalyst layer]
The prepared catalyst ink was applied to a base material of a polytetrafluoroethylene (PTFE) sheet by a doctor blade method and dried at 80 ° C. in an air atmosphere. The coating amount of the catalyst ink was adjusted so that the supported amount of platinum was 0.1 mg / cm ² as the fuel electrode (anode) and the supported amount of platinum was 0.3 mg / cm ² as the air electrode (cathode). Formed.
[Production of membrane electrode assembly]
The base material on which each electrode catalyst layer is formed is punched out to 5 cm × 5 cm, and this electrode catalyst layer is disposed on both sides of the polymer electrolyte membrane, under the conditions of a transfer temperature of 130 ° C. and a transfer pressure of 5.0 × 10 ⁶ Pa. Hot pressing was performed to obtain a membrane electrode assembly.

<Evaluation>
[Power generation characteristics]
Carbon paper was bonded as a gas diffusion layer on both sides of the membrane electrode assembly so as to sandwich the membrane electrode assemblies produced in the examples and comparative examples, and was installed in a power generation evaluation cell for power generation evaluation. 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 50 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 11 produced in the example showed better power generation performance under low humidification operating conditions than the membrane electrode assembly produced in the comparative example. In addition, the membrane / electrode assembly produced in the example had the same level of power generation performance as that under full humidification even under low humidification conditions. 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 11 produced in the example is 0. 0 compared with the cell voltage at a current density of 0.5 A / cm ² of the membrane electrode assembly produced in the comparative example. The power generation characteristic is 22V higher. From the results of the power generation characteristics of the membrane / electrode assembly 11 produced in the example and the membrane / electrode assembly produced in the comparative example, the membrane / electrode assembly 11 of the example has increased water retention and is operated under low humidification operating conditions. It was confirmed that the power generation characteristics were equivalent to those under the fully humidified operating conditions.

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 11 produced in the example is 0.5 A / cm in the current density of the membrane electrode assembly produced in the comparative example. The power generation characteristic was higher by 0.27 V than the cell voltage at cm ² . From the results of the power generation characteristics of the membrane / electrode assembly 11 produced in the example and the membrane / electrode assembly produced in the comparative example, the diffusibility of the reaction gas, the removal of water generated by the electrode reaction, and the like are not inhibited. Was confirmed.

<Summary>
The present embodiment relates to a membrane electrode assembly having high power generation characteristics under low humidification conditions, a method for producing the membrane electrode assembly, and a polymer electrolyte fuel cell comprising the membrane electrode assembly.
In the electrode catalyst layers 2 and 3 of the membrane electrode assembly 11 according to this embodiment, the value of the ion exchange capacity in the polymer electrolyte of the first electrode catalyst part 2a (or 3a) provided on the gas inlet side By increasing the size compared with the second electrode catalyst part 2b (or 3b) provided on the outlet side, the water retention is increased by the first electrode catalyst part 2a (or 3a) provided on the gas inlet side, and the gas outlet The removal of water can be promoted by the second electrode catalyst portion 2b (or 3b) provided on the side.

  Therefore, water retention can be enhanced without hindering removal of water generated by the electrode reaction, and high power generation characteristics can be obtained even under low humidification conditions. In addition, since the first electrode catalyst part 2a (or 3a) and the second electrode catalyst part 2b (or 3b) can be realized by different ion exchange capacities, a significant change in the manufacturing process, etc. In addition, high power generation characteristics can be obtained without a significant increase in cost.

  In the above embodiment, the case where the first electrode catalyst portion and the second electrode catalyst portion are provided in each of the electrode catalyst layers 2 and 3 has been described. However, the present invention is not limited to this. Each of 2 and 3 may be provided with three or more electrode catalyst portions. When three or more electrode catalyst portions are provided in each of the electrode catalyst layers 2 and 3, the ion exchange capacity of the electrode catalyst portion becomes closer to the upstream side of the gas, and the ion exchange capacity of the electrode catalyst portion on the downstream side of the gas. What is necessary is just to make it larger compared with.

  Further, in the membrane electrode assembly 11, the electrode catalyst layers 2 and 3 formed on both surfaces of the polymer electrolyte membrane 1 have only one electrode catalyst layer 2 or 3 and the first electrode catalyst portion and the second electrode catalyst layer 2. An electrode catalyst part may be provided. When the first electrode catalyst portion and the second electrode catalyst portion are provided only on one of the electrode catalyst layers 2 or 3, the electrode catalyst layer having two electrode catalyst portions is an air electrode that generates water by an electrode reaction ( It is preferable to arrange on the cathode) side. However, it is more preferable that the electrode catalyst layers having two electrode catalyst portions are formed on both surfaces of the polymer electrolyte membrane 1 from the viewpoint of water retention of the polymer electrolyte under low humidification conditions.

Moreover, in FIG. 1, the 1st electrode catalyst part of the electrode catalyst layer 2 or 3 and the 2nd electrode catalyst part are divided into two by the equivalent area (area of the 1st electrode catalyst part with respect to the electrode catalyst layer 2) The rate is 50%), but the present invention is not limited to this. The area ratio of the first electrode catalyst portion relative to the electrode catalyst layer 2 or 3 is preferably 15% or more and 60% or less from the viewpoint of gas reactivity. When the area ratio of the 1st electrode catalyst part with respect to the electrode catalyst layer 2 or 3 is less than 15%, the water retention effect in low humidification conditions is weak, and a high electric power generation characteristic is not acquired. In addition, when the area ratio of the first electrode catalyst portion with respect to the electrode catalyst layer 2 or 3 exceeds 60%, a flooding phenomenon in which the power generation reaction stops due to hindering material transport in the fuel electrode and the air electrode occurs. Characteristics are not obtained.
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 (4)

A polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers, each of the pair of electrode catalyst layers includes catalyst-supporting particles and a polymer electrolyte, and at least one of the pair of electrode catalyst layers includes: A method for producing a membrane electrode assembly comprising: a first electrode catalyst part; and a second electrode catalyst part adjacent to the first electrode catalyst part in a planar direction of the polymer electrolyte membrane,
A first catalyst ink in which the catalyst-carrying particles and the first polymer electrolyte solution are dispersed in a solvent is prepared, and the first electrode ink is applied and then dried to form the first electrode catalyst portion. And a process of
A second polymer electrolyte solution comprising the catalyst-supported particles and a second polymer electrolyte having an ion exchange capacity smaller than the ion exchange capacity of the first polymer electrolyte contained in the first polymer electrolyte solution A second catalyst ink dispersed in a solvent, and applying the second catalyst ink and then drying to form the second electrode catalyst portion;
A process for producing a membrane electrode assembly, comprising: The first polymer electrolyte has an ion exchange capacity of 0.9 meq / g or more and 3.0 meq / g or less,
The second polymer electrolyte has an ion exchange capacity smaller than that of the first polymer electrolyte and in a range of 0.8 meq / g to 2.8 meq / g. The manufacturing method of the membrane electrode assembly of Claim 1. A membrane electrode assembly in which a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers,
Each of the pair of electrode catalyst layers includes catalyst-supporting particles and a polymer electrolyte, and at least one of the pair of electrode catalyst layers includes a first electrode catalyst portion and the polymer electrolyte membrane. A second electrode catalyst portion adjacent to the first electrode catalyst portion in the planar direction,
The membrane electrode assembly, wherein the ion exchange capacity of the polymer electrolyte contained in the first electrode catalyst part is smaller than the ion exchange capacity of the polymer electrolyte contained in the second electrode catalyst part. A pair of separators having a gas flow path for sandwiching the membrane electrode assembly according to claim 3 and supplying gas to the electrode catalyst layer,
3. The polymer electrolyte fuel cell according to claim 1, wherein the first electrode catalyst part is located upstream of the gas flow path, and the second electrode catalyst part is located downstream of the gas flow path.

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