JP2015060801A - Method for manufacturing film-electrode assembly, film-electrode assembly, and solid polymer fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film-electrode assembly having electrode catalyst layers which is increased in water retention property without interfering with the reactive gas diffusibility, the removal of water resulting from an electrode reaction or the like, and which shows a high power generating property even under a low-humidification condition; and a method for manufacturing such a film-electrode assembly.SOLUTION: A film-electrode assembly comprises: a pair of electrode catalyst layers; and a polymer electrolytic film held by and between the pair of electrode catalyst layers. The pair of electrode catalyst layers each includes a polymer electrolyte and particles having a catalyst material thereon. At least one electrode catalyst layer is divided into at least two parts composed of a first electrode catalyst part and a second electrode catalyst part which are adjacent to each other in a plane direction of the polymer electrolytic film. In the electrode catalyst layer thus divided, the first electrode catalyst part provided on a gas inlet side is smaller than the second electrode catalyst part provided on a gas outlet side in the value of the pore volume of micropores having diameters of 1.0 μm or less according to the conversion based on a cylinder approximation, which are determined by a mercury press-in method. The difference between the first and second electrode catalyst parts in the value of the pore volume of micropores is 0.1-1.0 mL/g.

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 hydrogen gas-containing fuel gas and an oxygen-containing oxidant gas to undergo reverse reaction of water electrolysis at an electrode including a catalyst. 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 those using proton conductive polymer membranes are called solid polymer fuel cells.

  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. A polymer electrolyte fuel cell is a fuel in which a pair of electrode catalyst layers are arranged on both sides of a polymer electrolyte membrane called a membrane electrode assembly (MEA), and hydrogen is contained in one of the electrodes. The battery is sandwiched between a separator plate having a gas flow path for supplying gas and a separator plate having a gas flow path for supplying an oxidant gas containing oxygen to the other electrode. Here, the electrode for supplying the fuel gas is called a fuel electrode, and the electrode for supplying the oxidant is called an air electrode. These electrodes are composed of an electrode catalyst layer formed by laminating carbon particles carrying a catalyst material such as a platinum-based noble metal and a polymer electrolyte, and a gas diffusion layer having both gas permeability and electron conductivity.

  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 the fuel gas to the three-phase interface, which is the oxidation-reduction 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 along with the supply of the oxidant gas. In order to prevent a phenomenon called so-called “flooding” in which the power generation reaction stops due to the hindrance of mass transport, techniques for improving drainage have been performed so far (for example, Patent Document 1, Patent Document 2, Patent Document 3, (See Patent Document 4).

Issues for the practical application of polymer electrolyte fuel cells include improvement of output density and durability, but the biggest issue is cost reduction (cost reduction).
One way to reduce the cost is to reduce the number of humidifiers. Perfluorosulfonic acid membranes and hydrocarbon membranes are widely used as the polymer electrolyte membrane located at the center of the membrane electrode assembly, but in order to obtain excellent proton conductivity, it is close to a saturated water vapor pressure atmosphere. Moisture management 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, the electrode catalyst layer with improved drainage properties needs to improve the water retention by optimizing the electrode catalyst layer structure because the polymer electrolyte dries up under low humidification conditions. 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 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 these patent documents have a problem that they do not have satisfactory power generation performance. In addition, the manufacturing method is complicated and the cost is high.
Accordingly, in the present invention, an electrode catalyst layer that enhances the diffusibility of the reaction gas, enhances water retention without hindering removal of water produced by the electrode reaction, and exhibits high power generation characteristics even under low humidification conditions It aims at providing the manufacturing method of a membrane electrode assembly provided with this, and the membrane electrode assembly.

  The membrane electrode assembly according to one embodiment of the present invention is a membrane electrode assembly in which a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers. At least one of the pair of electrode catalyst layers includes at least two of the first electrode catalyst part and the second electrode catalyst part adjacent to the first electrode catalyst part in the planar direction of the polymer electrolyte membrane. It is divided into two. The method for manufacturing a membrane electrode assembly according to one aspect of the present invention includes a step of forming a first electrode catalyst portion by applying and drying a first catalyst ink, and applying a second catalyst ink. And forming a second electrode catalyst part by drying. The coating speed of the first catalyst ink in the step of forming the first electrode catalyst portion is higher than the coating speed of the second catalyst ink in the step of forming the second electrode catalyst portion.

  According to the present invention, the pore volume with a diameter of 1.0 μm or less in terms of the cylindrical approximation of the pores determined by the mercury intrusion method is larger than the value of the first electrode catalyst portion provided on the gas inlet side. The value of the second electrode catalyst portion provided on the outlet side of the electrode is increased, the water content is increased without impeding the removal of water produced by the electrode reaction, and the electrode catalyst exhibits high power generation characteristics even under low humidification conditions A membrane electrode assembly including a layer can be easily produced efficiently and economically.

It is a cross-sectional schematic diagram of the membrane electrode assembly which concerns on embodiment of this invention. 1 is an exploded cross-sectional view of a polymer electrolyte fuel cell according to an embodiment of the present invention.

<Embodiment>
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 a schematic cross-sectional view showing a membrane electrode assembly 11 according to this embodiment. As shown in FIG. 1, the membrane electrode assembly 11 includes a polymer electrolyte membrane 1 and electrode catalyst layers 2 and 3 that sandwich the polymer electrolyte membrane 1. Further, in the membrane electrode assembly 11, at least one of the electrode catalyst layers 2 and 3 includes catalyst substance-supporting particles and a polymer electrolyte. Furthermore, the electrode catalyst layers 2 and 3 of the membrane electrode assembly 11 are divided into two in the plane direction of the polymer electrolyte membrane 1. More specifically, the 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. Similarly, the 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.

  In the membrane electrode assembly 11, the value of the pore volume with a diameter of 1.0 μm or less calculated by the mercury intrusion method and converted by the cylindrical approximation of the pore is the first electrode catalyst portion 2a (on the gas inlet side). Alternatively, the second electrode catalyst portion 2b (or 3b) provided on the gas outlet side is larger than 3a). 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 getting bigger.

  In the membrane electrode assembly 11, the first electrode catalyst portions 2a and 3a provided on the gas inlet side are made denser than the second electrode catalyst portions 2b and 3b provided on the gas outlet side. The first electrode catalyst portions 2a and 3a provided on the gas inlet side enhance water retention, and the second electrode catalyst portions 2b and 3b provided on the gas outlet side promote water removal. 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. 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.

  The pore volume value of the second electrode catalyst portion 2b (or 3b) and the first electrode for the pore volume of 1.0 μm or less in diameter calculated by the mercury intrusion method in terms of the cylinder approximation The difference from the pore volume value of the catalyst part 2a (or 3a) is preferably 0.1 mL / g or more and 1.0 mL / g or less. When the difference between the pore volume value of the second electrode catalyst part 2b (or 3b) and the pore volume value of the first electrode catalyst part 2a (or 3a) is less than 0.1 mL / g In this case, it may be difficult to achieve both the drainage of water generated by the electrode reaction and the water retention under low humidification conditions. When the difference between the pore volume value of the second electrode catalyst part 2b (or 3b) and the pore volume value of the first electrode catalyst part 2a (or 3a) exceeds 1.0 mL / g Even in this case, 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.

  In the membrane electrode assembly 11, the number of divisions of the electrode catalyst layers 2 and 3 is not limited to two. The number of divisions of the electrode catalyst layers 2 and 3 may be three or more. When the number of divisions of the electrode catalyst layers 2 and 3 is three or more, the pore volume of 1.0 μm or less in diameter in terms of the cylindrical approximation of the pores obtained by the mercury intrusion method of the electrode catalyst layers 2 and 3 , Change step by step. In other words, even in the case of a membrane electrode assembly in which the number of divisions of the electrode catalyst layer is 3 or more, the value of the pore volume in the downstream portion of the gas is larger than the value of the pore volume in the upstream portion of the gas. Change so that becomes larger.

  Further, in the membrane electrode assembly 11, only one of the electrode catalyst layers 2 or 3 of the electrode catalyst layers 2 and 3 formed on both surfaces of the polymer electrolyte membrane 1 is divided into portions having different pore volumes. May be. When only one electrode catalyst layer 2 or 3 is divided into different pore volumes, the electrode catalyst layer divided into different pore volumes may be arranged on the air electrode (cathode) side where water is generated by the electrode reaction. preferable. However, it is more preferable that the electrode catalyst layers divided into different pore volumes 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.

[Solid polymer fuel cell]
Next, the polymer electrolyte fuel cell 12 according to this embodiment will be described.
FIG. 2 is an exploded cross-sectional view of the polymer electrolyte fuel cell 12 according to the present embodiment. The polymer electrolyte fuel cell 12 includes an air electrode side gas diffusion layer 4 and a fuel electrode side gas diffusion layer 5 which are disposed so as to face the electrode catalyst layers 2 and 3 of the membrane electrode assembly 11. . 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. In addition, a pair of separators 10 made of a conductive and impermeable material, each having a gas flow path 8 for gas flow and a cooling water flow path 9 for flowing cooling water, are provided for the gas diffusion layers 4 and 5. Arranged on the outside respectively. For example, hydrogen gas is supplied as a fuel gas from the gas flow path 8 of the separator 10 on the fuel electrode 7 side. On the other hand, a gas containing oxygen, for example, is supplied as an oxidant gas from the gas flow path 8 of the separator 10 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 the fuel gas hydrogen and oxygen gas in the presence of a catalyst.

  In the polymer electrolyte fuel cell 12, the polymer electrolyte membrane 1, the electrode catalyst layers 2 and 3, and the gas diffusion layers 4 and 5 are sandwiched by a set of separators 10. The polymer electrolyte fuel cell 12 is a single cell fuel cell, but a plurality of cells may be stacked via the separator 10 to form a polymer electrolyte fuel cell.

[Production method of membrane electrode assembly]
Next, a manufacturing method of the membrane electrode assembly 11 according to this embodiment will be described.
In the manufacturing method of the membrane electrode assembly 11 according to the present embodiment, the following first to third steps are included.
(First Step) A step of forming a first electrode catalyst portion by applying a catalyst ink in which particles carrying a catalyst and a polymer electrolyte are dispersed in a solvent and drying the catalyst ink (second step) Catalyst A step of forming a second electrode catalyst part by applying a catalyst ink in which particles carrying a catalyst and a polymer electrolyte are dispersed in a solvent and drying the catalyst ink (third step) polymer electrolyte membrane Forming a first electrode catalyst portion and a second electrode catalyst portion on at least one surface of

  In the step of forming the first electrode catalyst portion and the second electrode catalyst portion, the electrode catalyst portions having different pore volumes can be formed by changing the coating speed of the catalyst ink. The electrode catalyst part is formed by applying a catalyst ink in which particles carrying a catalyst and a polymer electrolyte are dispersed in a solvent to form a coating film and removing the solvent in the coating film. At this time, when the coating speed of the catalyst ink is increased, the pore volume of the formed electrode catalyst portion can be decreased as compared with the case where the coating speed is decreased. Further, when the coating speed of the catalyst ink is decreased, the pore volume of the formed electrode catalyst portion can be increased as compared with the case where the coating speed is increased.

  That is, in the method of manufacturing the membrane electrode assembly 11, the coating speed of the catalyst ink in the step of forming the first electrode catalyst portion (first step) is set to the step of forming the second electrode catalyst portion (second step). ) To be larger than the coating speed of the catalyst ink. By increasing the coating speed of the catalyst ink, the shear stress to the catalyst ink is increased, and the pore volume of the electrode catalyst portion to be formed can be reduced. Further, by reducing the coating speed of the catalyst ink, the shear stress to the catalyst ink is weakened, and the pore volume of the electrode catalyst portion to be formed can be increased.

  The ratio of the catalyst ink coating speed when forming the first electrode catalyst portion to the catalyst ink coating speed when forming the second electrode catalyst portion is 1: 0.2 or more and 1: 0. It is preferably within the range of .9 or less. When the ratio between the coating speed of the catalyst ink when forming the first electrode catalyst portion and the coating speed of the catalyst ink when forming the second electrode catalyst portion is less than 1: 0.2, The difference in pore volume between the first electrode catalyst part and the second electrode catalyst part to be formed becomes large, and it is difficult to achieve both the drainage of water produced by the electrode reaction and the water retention under low humidification conditions. It may become. When the ratio of the catalyst ink coating speed when forming the first electrode catalyst portion to the catalyst ink coating speed when forming the second electrode catalyst portion exceeds 1: 0.9 The difference in pore volume between the first electrode catalyst part and the second electrode catalyst part to be formed is reduced, and both the drainage of water produced by the electrode reaction and the water retention under low humidification conditions can be achieved. It can be difficult.

The difference between the value of the pore volume of 1.0 μm or less in diameter in the first electrode catalyst part and the value of the pore volume of 1.0 μm or less in diameter in the second electrode catalyst part is determined by a mercury intrusion method. It is preferably 0.1 mL / g or more and 1.0 mL / g or less in terms of a converted value by cylindrical approximation of the holes. When the difference between the pore volume value of the second electrode catalyst portion and the pore volume value of the first electrode catalyst portion is less than 0.1 mL / g, the drainage of water generated by the electrode reaction It may be difficult to achieve both water retention under low humidification conditions. Moreover, even when the difference in pore volume exceeds 1.0 mL / g, it may be difficult to achieve both the drainage of water generated by the electrode reaction and the water retention under low humidification conditions. .
Further, the catalyst ink used when forming the first electrode catalyst portion and the catalyst ink used when forming the second electrode catalyst portion may be the same or different. .

[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 layer is formed on both surfaces of the polymer electrolyte membrane 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 the polymer electrolyte membrane can be used. Fluorine polymer electrolyte, hydrocarbon polymer 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 layer and the polymer electrolyte membrane, the same material as that of the polymer electrolyte membrane 1 is preferably 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. Further, metals such as nickel, manganese, vanadium, molybdenum, gallium, and aluminum, alloys thereof, oxides, double oxides, and the like can be used. Moreover, since the activity of a catalyst will fall when the particle size of said catalyst is too large, and stability of a catalyst will fall when it is too small, the particle size of a catalyst has preferable 0.5-20 nm. More preferably, 1-5 nm is good. In addition, when the catalyst particles are one or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium, the electrode particles are excellent in electrode reactivity, and the electrode reaction is performed efficiently and stably. be able to. When the catalyst particles are one or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium, the polymer electrolyte fuel cell including the electrode catalyst layer has high power generation characteristics. This is preferable.

  In general, carbon particles are used as the electron conductive powder supporting the catalyst material. 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. If the particle size of the carbon particles is too small, it becomes difficult to form an electron conduction path. Moreover, since the gas diffusibility of the electrode catalyst layers 2 and 3 will fall or the utilization factor of a catalyst will fall when too large, about 10-1000 nm is preferable. More preferably, 10-100 nm is good.

  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 at least a volatile organic solvent is contained. Examples of the solvent used as a dispersion medium for the catalyst ink include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, Alcohols such as pentaanol, acetone, methyl ethyl ketone, pentanone, methyl isobutyl ketone, heptanone, cyclohexanone, methyl cyclohexanone, acetonyl acetone, diisobutyl ketone and other ketone solvents, tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxy toluene, Ether solvents such as dibutyl ether, other 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 what mixed 2 or more types among the above-mentioned solvents.

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.
The solvent used as the dispersion medium for the catalyst ink includes a solvent for the first catalyst ink used for forming the first electrode catalyst portion and a second electrode used for forming the second electrode catalyst portion. However, they may be the same solvent or different solvents.

The pore volume of the electrode catalyst layer depends on the composition of the catalyst ink and the dispersion conditions, and varies depending on the amount of the polymer electrolyte, the type of the dispersion solvent, the dispersion method, the dispersion time, etc., so at least one of these, preferably Preferably, two or more are used in combination, and the pore volume of the electrode catalyst layer is controlled so as to increase from the side close to the gas diffusion layer toward the polymer electrolyte membrane 1.
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 the anionic surfactant include alkyl ether carboxylate, ether carboxylate, alkanoyl sarcosine, alkanoyl glutamate, acyl glutamate, oleic acid / N-methyl taurine, potassium oleate / diethanolamine salt, alkyl ether sulfate / Triethanolamine 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 of high molecular weight polyether ester acid Salts, special modified phosphate ester amine salts, high molecular weight polyester acid amido amine salts, special fatty acid derivative amido amine salts, higher fatty acid alkyl amine salts, high molecular weight polycarboxylic acid amines Doamine salts, carboxylic acid type surfactants such as 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 sodium salt, lauryl ether sulfate ester salt, alkylbenzene sulfonate sodium salt, oil-soluble alkylbenzene sulfonate salt, α-olefin sulfonate surfactant, alkyl sulfate ester salt, alkyl sulfate salt, 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 salt, (mono or di) alkyl phosphate, (mono or di) alkyl phosphate ester salt, alkyl polyoxyethylene salt of phosphate, alkyl ether phosphate, alkyl polyethoxy Phosphate, polyoxyethylene alkyl ether, alkylphenyl phosphate polyoxyethylene salt, alkylphenyl ether phosphate, alkylphenyl polyethoxy phosphate, polyoxyethylene alkylphenyl ether phosphate, higher alcohol monophosphate Examples thereof include phosphate type surfactants such as ester disodium salt, higher alcohol phosphate diester disodium salt, and zinc dialkyldithiophosphate.

  Examples of the cationic surfactant include benzyldimethyl {2- [2- (P-1,1,3,3-tetramethylbutylphenoxy) ethoxy] ethyl} ammonium chloride, octadecylamine acetate, tetradecylamine acetic acid. Salt, octadecyltrimethylammonium chloride, tallow trimethylammonium chloride, dodecyltrimethylammonium chloride, coconut trimethylammonium chloride, hexadecyltrimethylammonium chloride, behenyltrimethylammonium chloride, coconut dimethylbenzylammonium chloride, tetradecyldimethylbenzylammonium chloride, octadecyldimethylbenzylammonium chloride Chloride, dioleyldimethylammonium chloride, 1-hydroxy Chill-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 Examples include amine ethylene oxide adducts, polyacrylamide amine salts, modified polyacrylamide amine salts, perfluoroalkyl quaternary ammonium iodides, and the like.

  Examples of the amphoteric surfactants include dimethyl coconut betaine, dimethyl lauryl betaine, sodium laurylaminoethylglycine, sodium laurylaminopropionate, stearyldimethylbetaine, 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. .

  Examples of the nonionic surfactant 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 palm 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 Loridone, 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 above surfactants, sulfonic acid type surfactants such as alkylbenzene sulfonic acid, oil-soluble alkylbenzene sulfonic acid, α-olefin sulfonic acid, sodium alkylbenzene sulfonate, oil-soluble alkylbenzene sulfonate, α-olefin sulfonate, etc. Can be suitably used as a dispersant in consideration of carbon dispersion effects, changes 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 can be controlled by the conditions for the dispersion treatment of the catalyst ink. 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. Further, as the dispersion time becomes longer, the aggregates of the catalyst material-carrying particles are destroyed and the pore volume becomes smaller.

  If the solid content in the catalyst ink is too large, the viscosity of the catalyst ink becomes high, so that the electrode catalyst layer surfaces 2 and 3 are likely to crack. 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 to 50% by mass (wt%). 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 to 80% by mass. The viscosity of the catalyst ink is preferably about 0.1 to 500 cP (0.0001 to 0.5 Pa · s), more preferably 5 to 100 cP (0.005 to 0.1 Pa · s). 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 said pore making agent 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.

A catalyst ink is applied on a substrate and dried to form an electrode catalyst layer. When a gas diffusion layer or a transfer sheet is used as the substrate, the electrode catalyst layer is bonded to both surfaces of the polymer electrolyte membrane. In the membrane / electrode assembly, a polymer electrolyte membrane may be used as a base material, and a catalyst ink may be directly applied to both sides of the polymer electrolyte membrane to directly form an electrode catalyst layer on both sides of the polymer electrolyte membrane.
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.

As a substrate in the production of the electrode catalyst layer, a gas diffusion layer, a transfer sheet, or a polymer electrolyte membrane can be used.
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 is peeled after the electrode catalyst layer is bonded to the polymer electrolyte membrane 1, and the membrane electrode assembly is provided with electrode catalyst layers on both sides of the polymer electrolyte membrane 1. 11 can be used.

  As the gas diffusion layer, a material having gas diffusibility and conductivity can be used. For example, porous carbon materials such as carbon cloth, carbon paper, and non-woven fabric can be used. The gas diffusion layer can also be used as a substrate on which the catalyst ink is applied. When the gas diffusion layer is used as a substrate on which the catalyst ink is applied, it is not necessary to peel off the substrate that is the gas diffusion layer after the electrode catalyst layer is bonded to the polymer electrolyte membrane.

  When the gas diffusion layer is used as a substrate on which the catalyst ink is applied, an eye layer may be formed on the gas diffusion layer in advance before the catalyst ink is applied to the gas diffusion layer. The mesh layer is a layer that prevents the catalyst ink from permeating into the gas diffusion layer, and deposits on the mesh layer to form a three-phase interface even when the coating amount of the catalyst ink is small. The filler layer can be formed, for example, by dispersing carbon particles in a fluorine resin solution and sintering at a temperature equal to or higher than the melting point of the fluorine resin. As the fluororesin, polytetrafluoroethylene (PTFE) or the like can be used.

  As the separator, a carbon type or a metal type can be used. The gas diffusion layer and the separator may have an integral structure. When the separator or the electrode catalyst layer functions as a gas diffusion layer, the gas diffusion layer 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.

Hereinafter, a method for producing a membrane electrode assembly for a polymer electrolyte fuel cell according to the present embodiment will be described with reference to specific examples and comparative examples. The present embodiment will be described with reference to the following examples and comparative examples. It is not limited.
<Example>
[Preparation 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) are used as solvents. The mixture was mixed and dispersed with a planetary ball mill. At this time, the dispersion time was 30 minutes to prepare a catalyst ink. The composition ratio of the starting materials of the prepared catalyst ink was 1: 1 by mass for the carbon support and the polymer electrolyte, and 1: 1 for the dispersion solvent by 1-propanol and 2-propanol by volume. . The solid content was 15% by mass.

〔Base material〕
A polytetrafluoroethylene (PTFE) sheet, which is a transfer sheet, was used as a substrate.
[Method for forming electrode catalyst layer on substrate]
The catalyst ink prepared as described above was applied onto the substrate at a coating speed of 150 mm / s by the doctor blade method, and dried at 80 ° C. in an air atmosphere to obtain a first electrode catalyst part. Similarly, the catalyst ink prepared as described above was applied onto a substrate at a coating speed of 100 mm / s and dried at 80 ° C. in an air atmosphere to obtain a second electrode catalyst part. At this time, the amount of catalyst ink applied was adjusted so that the amount of platinum supported was 0.3 mg / cm ² . As a result of measuring the pores of the obtained electrode catalyst parts with a mercury porosimeter, the pore volume with a diameter of 1.0 μm or less in terms of cylinder approximation is the value of the first electrode catalyst part provided on the gas inlet side. The value of the second electrode catalyst portion provided on the gas outlet side was larger than that, and the difference was 0.18 mL / g.

[Production of membrane electrode assembly]
The base material on which the first electrode catalyst portion and the second electrode catalyst portion were formed was punched into 5 cm × 2.5 cm. On the polymer electrolyte membrane (trade name: Nafion (registered trademark), manufactured by DuPont), the first electrode catalyst part is disposed on the gas inlet side, and the second electrode catalyst part is disposed on the gas outlet side. A 5 cm electrode catalyst layer was obtained. This electrode catalyst layer was arrange | positioned on both surfaces of a polymer electrolyte membrane, and it hot-pressed on 130 degreeC and the conditions of 6.0 * 10 < ⁶ > Pa, and obtained the membrane electrode assembly.

<Comparative example>
[Adjustment of catalyst ink]
A catalyst ink was prepared in the same manner as in the examples.
〔Base material〕
The same substrate as in the example was used.
[Method for producing electrode catalyst layer]
A second electrode catalyst part was formed in the same manner as in the example.
[Production of membrane electrode assembly]
5. The base material on which the second electrode catalyst part is formed is punched into a 25 cm ² (5 cm × 5 cm) square, and the second electrode catalyst part is disposed so as to face both surfaces of the polymer electrolyte membrane. Hot pressing was performed under the condition of 0 × 10 ⁶ Pa to obtain a membrane electrode assembly.

<Evaluation>
[Power generation characteristics]
Carbon paper used as a gas diffusion layer was bonded and placed in a power generation evaluation cell so as to sandwich the membrane electrode assemblies produced in Examples and Comparative Examples. 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: anode 100% RH, cathode 100% RH
2. Low humidification: anode 40% RH, cathode 40% RH

〔Measurement result〕
The membrane / electrode assembly produced in the example shows better power generation performance under low humidification operating conditions than the membrane / electrode assembly produced in the comparative example, and the membrane / electrode assembly produced in the example is less humidified. Even under the above operating conditions, the power generation performance was at the same level as in the fully humidified operating conditions. In particular, the power generation performance in the vicinity of 0.7 V was improved, and the membrane electrode assembly produced in the example showed 1.7 times the power generation characteristics compared to the membrane electrode assembly produced in the comparative example. From the results of the power generation characteristics of the membrane electrode assembly produced in the example and the membrane electrode assembly produced in the comparative example, the first electrode catalyst portion in which the pore volume of the electrode catalyst layer is provided on the gas inlet side The membrane electrode assembly in which the value of the second electrode catalyst portion provided on the gas outlet side is larger than the value of the above has increased water retention, and the power generation characteristics under the low humidifying operation condition are It was confirmed that the power generation characteristics were equivalent to Moreover, the membrane electrode assembly produced in the Example showed 1.3 times the power generation characteristics as compared with the membrane electrode assembly produced in the comparative example under the fully humidified operating conditions. From the results of the power generation characteristics of the membrane electrode assembly produced in the example and the membrane electrode assembly produced in the comparative example, it was confirmed that the diffusibility of the reaction gas, removal of water generated by the electrode reaction, etc. were not hindered. confirmed.

<Summary>
The present embodiment relates to a membrane electrode assembly that exhibits high power generation characteristics under low humidification conditions, a method for manufacturing 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.

  In the method of manufacturing the membrane electrode assembly, the first catalyst ink is applied and dried to form the first electrode catalyst portion, and the second catalyst ink is applied and dried. And forming a second electrode catalyst part. The coating speed of the first catalyst ink in the step of forming the first electrode catalyst portion is higher than the coating speed of the second catalyst ink in the step of forming the second electrode catalyst portion. More specifically, the coating speed when the first catalyst ink is applied in the step of forming the first electrode catalyst portion, and the second catalyst ink is applied in the step of forming the second electrode catalyst layer. The ratio with the coating speed at the time of working is in the range of 1: 0.2 to 1: 0.9.

  In addition, it is a conversion value obtained by approximating the pores in the cylinder obtained by the mercury intrusion method, and the pore volume of the first electrode catalyst part having a diameter of 1.0 μm or less and the second electrode catalyst part having a diameter of 1.0 μm or less. The difference from the pore volume is 0.1 mL / g or more and 1.0 mL / g or less. Thus, the coating speed of the catalyst ink is controlled.

The polymer electrolyte fuel cell according to the present embodiment includes the above-described membrane electrode assembly.
According to this embodiment, the pore volume having a diameter of 1.0 μm or less in terms of the cylindrical approximation of the pores determined by the mercury intrusion method is compared with the value of the first electrode catalyst portion provided on the gas inlet side, The value of the second electrode catalyst portion provided on the gas outlet side is increased, the water retention is increased without hindering the removal of water generated by the electrode reaction, and the electrode exhibits high power generation characteristics even under low humidification conditions It is possible to provide a membrane electrode assembly including a catalyst layer and a production method capable of producing the same efficiently and economically.

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, and the electrode catalyst layer includes particles carrying a polymer electrolyte and a catalyst substance. Further, the electrode catalyst layer is divided into at least two in a direction perpendicular to the stacking direction, and the electrode catalyst layer has a diameter of 1.0 μm or less in terms of a cylindrical approximation of pores obtained by mercury porosimetry. The value of the second electrode catalyst part provided on the gas outlet side is larger than the value of the first electrode catalyst part provided on the gas inlet side, and the difference is 0.1 mL / g or more. It is 1.0 mL / g or less. The first and second electrode catalyst portions can increase the water retention of the electrode catalyst layer without hindering the diffusibility of the reaction gas, the removal of water generated by the electrode reaction, and the like. Unlike the conventional application of humidity control film and low humidity by forming grooves on the surface of the electrode catalyst layer, the power generation characteristics are not reduced due to the increase in interface resistance, and the conventional membrane electrode assembly is provided. Compared with the solid polymer fuel cell, the polymer electrolyte fuel cell comprising the membrane electrode assembly according to the present embodiment has a remarkable effect of exhibiting high power generation characteristics even under low humidification conditions. The above utility value is high.
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)
DESCRIPTION OF SYMBOLS 8 ... Gas flow path 9 ... Cooling water flow path 10 ... Separator 11 ... Membrane electrode assembly 12 ... Solid polymer fuel cell

Claims (6)

A method for producing a membrane electrode assembly in which a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers,
At least one of the pair of electrode catalyst layers 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. Divided into at least two
Forming the first electrode catalyst portion by applying and drying a first catalyst ink; and
Forming the second electrode catalyst portion by applying and drying a second catalyst ink; and
Have
The coating speed of the first catalyst ink in the step of forming the first electrode catalyst portion is higher than the coating speed of the second catalyst ink in the step of forming the second electrode catalyst portion. A method for producing a membrane electrode assembly, comprising:   Coating speed when applying the first catalyst ink in the step of forming the first electrode catalyst portion, and applying the second catalyst ink in the step of forming the second electrode catalyst layer 2. The method for producing a membrane electrode assembly according to claim 1, wherein the ratio of the coating speed to the coating speed is in the range of 1: 0.2 or more and 1: 0.9 or less.   It is a conversion value obtained by a cylindrical approximation of the pores determined by the mercury intrusion method, and the pore volume of the first electrode catalyst portion having a diameter of 1.0 μm or less and the second electrode catalyst portion having a diameter of 1.0 μm or less. The membrane electrode assembly according to claim 2, wherein the coating speed of the catalyst ink is controlled so that the difference from the pore volume is 0.1 mL / g or more and 1.0 mL / g or less. Production method. A membrane electrode assembly in which a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers,
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. A membrane electrode assembly characterized by comprising:   It is a conversion value obtained by a cylindrical approximation of the pores determined by the mercury intrusion method, and the pore volume of the first electrode catalyst portion having a diameter of 1.0 μm or less and the second electrode catalyst portion having a diameter of 1.0 μm or less. The membrane electrode assembly according to claim 4, wherein the difference from the pore volume 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 4 or 5.

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