JP2015038883A - Catalyst ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst ink which forms an electrode catalyst layer showing high power generation characteristics.SOLUTION: The catalyst ink forms the electrode catalyst layer comprising a polymer electrolyte, a catalyst material and carbon particles. For the catalyst material, the polymer electrolyte is embedded in the catalyst material of which the specific surface area is smaller than that of the carbon particle and for the carbon particles, the polymer electrolyte is also embedded in the carbon particles of which the specific surface area is larger than that of the catalyst material. Therefore, proton conductivity on a catalyst surface can be improved beforehand and a reaction active point is increased. By performing processing for reducing the specific surface area of the carbon particles, proton conductivity on the catalyst surface is also improved when forming the electrode catalyst layer, thereby providing the electrode catalyst layer of which the output performance is improved, a membrane electrode assembly and a solid-state polymer type fuel cell.

Description

  The present invention relates to a catalyst ink for a polymer electrolyte fuel cell, and more particularly to a catalyst ink for forming an electrode catalyst layer exhibiting high power generation characteristics using a non-platinum catalyst.

  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 systems, and is attracting attention as a clean energy source in the future. There are several types depending on the type of ion conductor used, and 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. The polymer electrolyte fuel cell comprises a membrane electrode assembly (Membrane and Electrode Assembly; hereinafter referred to as “MEA”) in which a pair of electrodes are disposed on both sides of a polymer electrolyte membrane. In this battery, a fuel gas containing hydrogen is supplied to one of the electrodes, and a gas passage for supplying an oxidant gas containing oxygen to the other electrode is sandwiched between a pair of separator plates. 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 generally comprise an electrode catalyst layer formed by laminating carbon particles carrying a catalyst substance such as a platinum-based noble metal and a polymer electrolyte, and a gas diffusion layer having both gas permeability and electronic conductivity.

  Issues for the practical application of polymer electrolyte fuel cells include improvements in power density and durability, but the biggest issue is cost reduction.

  In current polymer electrolyte fuel cells, expensive platinum is used as an electrode catalyst, and development of alternative materials is strongly required for full-scale spread. In particular, since the air electrode uses more platinum than the fuel electrode, the development of platinum substitute materials (non-platinum catalysts) that exhibit high oxygen reduction catalytic ability in the air electrode is actively performed.

  As an example of the non-platinum catalyst in the air electrode, for example, Patent Document 1 describes a mixture of iron nitride and noble metal, which is a transition metal. Patent Document 2 describes a nitride of molybdenum, which is a transition metal. However, the catalyst materials described in Patent Document 1 and Patent Document 2 have insufficient oxygen reducing ability in the acidic electrolyte, and the catalyst material may be dissolved.

  On the other hand, Non-Patent Document 1 describes a partially oxidized tantalum carbonitride, which indicates that it has excellent stability and catalytic ability. However, although this oxide-based non-platinum catalyst shows high oxygen reduction catalytic ability as a single catalyst, it is not supported on carbon particles like platinum catalyst, and it is necessary to optimize the preparation method of the electrode catalyst layer There is.

  In addition, Patent Document 3 describes MEA using a non-platinum catalyst. The electrode catalyst layer is prepared by using, for example, the platinum catalyst described in Patent Document 4 and Patent Document 5, for example. Therefore, there is a problem that it is not suitable for a non-platinum catalyst.

JP 2005-44659 A JP 2005-63677 A JP 2008-270176 A Japanese Examined Patent Publication No. 2-48632 Japanese Patent Laid-Open No. 5-36418

“Journal of The Electrochemical Society”, Vol. 155, no. 4, p. B400-B406 (2008)

  An object of the present invention is to provide a catalyst ink for a fuel cell exhibiting high power generation characteristics, particularly using an oxide-based non-platinum catalyst as a catalyst substance.

  As a result of intensive studies, the present inventor has been able to solve the above-mentioned problems and has completed the present invention.

The invention according to claim 1 of the present invention is a catalyst ink applied to an electrode catalyst layer for a fuel cell having a polymer electrolyte, a catalyst material, and carbon particles. The catalyst material having a specific surface area smaller than that of the carbon particles and the first polymer electrolyte And embedded in a first polymer electrolyte that is dispersed in a solvent in a weight ratio of 1: 0.01 to 1:30 and dried in a temperature range of 30 ° C. to 140 ° C. A substance, carbon particles having a larger specific surface area than the catalyst particles, and the second polymer electrolyte are dispersed in a solvent within a weight ratio of 1: 0.1 to 1:20, and a temperature range of 30 ° C. to 140 ° C. And the carbon particles embedded in the second polymer electrolyte dried within the range of (1) and the first polymer electrolyte mixed without solvent and heat-treated in the temperature range of 50 ° C to 180 ° C. Embedded with the embedded catalytic material and the second polymer electrolyte Catalyst ink in which carbon particles are dispersed in a solvent together with a third polymer electrolyte.

  The invention according to claim 2 of the present invention is the catalyst ink according to claim 1, wherein the catalyst substance is an electrode active material for an oxygen reduction electrode used as an air electrode of a polymer electrolyte fuel cell, and Ta , Nb, Ti, Zr, a catalyst ink containing at least one transition metal element.

The invention according to claim 3 of the present invention is the catalyst ink according to claim 2, wherein the catalyst substance is a partial oxide of a transition metal element carbonitride or an oxide of a transition metal element.

  According to the present invention, in a catalyst ink having a polymer electrolyte, a catalyst material, and carbon particles, a catalyst material in which the polymer electrolyte is embedded in a catalyst material having a specific surface area smaller than that of the carbon particles, and larger than the catalyst material By increasing the proton conductivity of the catalyst surface during the formation of the electrode catalyst layer by embedding a polymer electrolyte in the carbon particles with a specific surface area to make the carbon particles treated to reduce the specific surface area of the carbon particles. Thus, it is possible to provide an electrode catalyst layer, a membrane electrode assembly, and a polymer electrolyte fuel cell with increased reaction active points and improved output performance.

  Further, by embedding the polymer electrolyte in each of the catalyst substance and the carbon particles, the embedding amount can be controlled. As a result, it is possible to easily perform the optimization examination of the embedding amount.

FIG. 1 is a schematic cross-sectional view of a membrane electrode assembly in which the catalyst ink of the present invention is applied to an electrode catalyst layer. FIG. 2 is an exploded schematic view of a polymer electrolyte fuel cell employing a membrane electrode assembly in which the catalyst ink of the present invention is applied to an electrode catalyst layer.

  Below, the membrane electrode assembly which concerns on embodiment of this invention is demonstrated. The embodiments of the present invention are 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. Embodiments to which is added can also be included in the scope of the embodiments of the present invention.

  FIG. 1 is a schematic cross-sectional view showing a membrane electrode assembly 11 in which a catalyst ink according to an embodiment of the present invention is applied to an electrode catalyst layer. As shown in FIG. 1, a membrane electrode assembly 11 in which a catalyst ink according to an embodiment of the present invention is applied to an electrode catalyst layer is provided on one surface of a polymer electrolyte membrane 1 and a polymer electrolyte membrane 1. The electrode catalyst layer 2 on the air electrode side and the electrode catalyst layer 3 on the fuel electrode side provided on the other surface of the polymer electrolyte membrane 1, and further the polymer electrolyte membrane of the electrode catalyst layer 2 on the air electrode side The gas diffusion layer 4 on the air electrode side provided on the surface opposite to the surface in contact with 1, and the gas on the fuel electrode side provided on the surface opposite to the surface in contact with the polymer electrolyte membrane 1 of the electrode catalyst layer 3 on the fuel electrode side A diffusion layer 5 is provided.

  FIG. 2 is an exploded schematic view of the polymer electrolyte fuel cell 12 according to the embodiment of the present invention. A polymer electrolyte fuel cell 12 employing a membrane electrode assembly in which the catalyst ink of the present invention is applied to an electrode catalyst layer includes an electrode catalyst layer 2 on the air electrode side provided on both surfaces of the polymer electrolyte membrane 1 and a fuel electrode. A gas diffusion layer 4 on the air electrode side and a gas diffusion layer 5 on the fuel electrode side are arranged to face the electrode catalyst layer 3 on the side. Thereby, an air electrode (cathode) 6 and a fuel electrode (anode) 7 are formed. Then, a set of separators 10 made of a conductive and impermeable material, which is provided with a gas flow path 8 for gas flow and has a cooling water flow path 9 for cooling water flow on the opposing main surface, is disposed. 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 hydrogen and oxygen gas of the fuel gas in the presence of the catalyst.

  In the polymer electrolyte fuel cell 12 shown in FIG. 2, the polymer electrolyte membrane 1, the electrode catalyst layers 2, 3 and the gas diffusion layers 4, 5 are sandwiched between a pair of separators. Although it is a solid polymer fuel cell having a so-called single cell structure, in the present invention, a plurality of cells can be stacked via a separator 10 to form a fuel cell.

  The catalyst ink of the present invention embeds a polymer electrolyte in a catalyst material having a specific surface area smaller than that of carbon particles, and further embeds the polymer electrolyte in carbon particles having a specific surface area larger than that of the catalyst material. The reaction active point can be increased by increasing the proton conductivity of the catalyst surface. In the electrode catalyst layer using the conventional catalyst ink that does not embed the polymer electrolyte in the catalyst material and carbon particles, carbon particles with a large specific surface area are preferred in the polymer electrolyte when the electrode catalyst layer is formed. Embedded in the catalyst, the proton conductivity on the catalyst surface is low, and the reaction active sites cannot be increased. In addition, the conventional manufacturing method can also increase the proton conductivity of the catalyst surface by increasing the concentration of the polymer electrolyte, but an excessive amount is added to the carbon particles to improve the output performance. It is difficult.

  When embedding the polymer electrolyte in a catalyst material having a specific surface area smaller than that of the carbon particles, the weight ratio of the catalyst material to the polymer electrolyte is in the range of 1: 0.01 to 1:30. It is preferable. When the weight ratio of the polymer electrolyte to the catalyst substance is less than 0.01, the proton conductivity on the catalyst surface does not change, and it is difficult to increase the reactive site, Output performance may not improve. Further, when the weight ratio of the polymer electrolyte to the catalyst substance exceeds 30, gas diffusivity to the reaction active site may be hindered and output performance may not be improved.

  Further, when the polymer electrolyte is embedded in carbon particles having a specific surface area larger than that of the catalyst material, the weight ratio of the carbon particles to the polymer electrolyte is within the range of 1: 0.1 to 1:20. Preferably there is. When the weight ratio of the polymer electrolyte to the carbon particles is less than 0.1, it is difficult to reduce the specific surface area of the carbon particles, and thus the output performance may not be improved. Further, when the weight ratio of the polymer electrolyte to the carbon particles exceeds 20, an excessive amount is added to the carbon particles, the gas diffusibility to the reaction active point is inhibited, and the output Performance may not improve.

  In addition, in the process of preparing a catalyst ink in which a catalyst material embedded with a polymer electrolyte, carbon particles embedded with a polymer electrolyte, and a polymer electrolyte are dispersed in a solvent, a catalyst ink is prepared. Before the step, it is preferable to include a step of mixing the catalyst material embedded with the polymer electrolyte and the carbon particles embedded with the polymer electrolyte in the absence of a solvent. When this step is not performed, the output performance may not be improved because the contact between the catalyst substance and the carbon particles is low and it is difficult to increase the reaction active point.

  In the above case, it is preferable to provide a heat treatment step after the step of mixing without solvent. If this step is not performed, the reaction active point may decrease in the step of producing the catalyst ink. In this heat treatment step, the temperature is preferably 50 ° C. or higher and 180 ° C. or lower. When the drying temperature is less than 50 ° C., many polymer electrolytes embedding the catalyst substance and carbon particles are dissolved in the solvent in the process of preparing the catalyst ink, and the reaction active sites formed are reduced. Depending on the case, the output performance may not improve. Even when the drying temperature exceeds 180 ° C., the proton conductivity of the polymer electrolyte embedding the catalyst substance and the carbon particles is hindered, and the output performance may not be improved.

  As the catalyst material according to the embodiment of the present invention, a commonly used material such as platinum may be used. In the present invention, preferably, a substance containing at least one transition metal element selected from Ta, Nb, Ti, and Zr, which is used as an air electrode of a polymer electrolyte fuel cell, is used as a platinum substitute material. Good. More preferably, it is a partial oxide of a carbonitride of these transition metal elements or an oxide of these transition metal elements. When platinum is used as the catalyst material, the electrode catalyst layer can be used as an electrode catalyst layer on the air electrode side or an electrode catalyst layer on the fuel electrode side. On the other hand, when a material containing the transition metal element is used as the catalyst material, the electrode catalyst layer is used as an electrode catalyst layer on the air electrode side.

Specifically, the transition metal element carbonitride partial oxide is a substance (TaCNO) obtained by partially oxidizing Ta carbonitride (TaCN) in an oxygen-containing atmosphere, and its specific surface area is: It is about 1 m ² / g or more and 20 m ² / g or less.

The carbon particles according to the embodiment of the present invention may be any particles as long as they are in the form of fine particles and have electrical conductivity and are not affected by the catalyst. Carbon black, graphite, graphite, activated carbon, carbon fiber, Carbon nanotubes and fullerenes can be used. If the particle size of the carbon particles is too small, it becomes difficult to form an electron conduction path. If the particle size is too large, the gas diffusibility of the electrode catalyst layer decreases or the utilization factor of the catalyst decreases. Is preferred. More preferably, it is 10 nm or more and 100 nm or less. The specific surface area of these carbon particles is about 100 m ² / g or more and 1500 m ² / g or less.

  In more detail, a membrane electrode assembly in which the catalyst ink according to the embodiment of the present invention is applied to an electrode catalyst layer and a polymer electrolyte fuel cell employing the electrode catalyst layer will be described.

  The polymer electrolyte membrane according to the embodiment of the present invention only needs to have proton conductivity, and a fluorine-based polymer electrolyte and a hydrocarbon-based polymer electrolyte can be used. Examples of the fluoropolymer electrolyte include Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., Aciplex (registered trademark) manufactured by Asahi Kasei Co., Ltd., and Gore Select (registered trademark) manufactured by Gore. Etc. can be used. As the hydrocarbon polymer electrolyte membrane, electrolyte membranes such as sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used. Among these, a Nafion (registered trademark) material manufactured by DuPont can be suitably used as the polymer electrolyte membrane. As the hydrocarbon polymer electrolyte membrane, electrolyte membranes such as sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used.

  The polymer electrolyte according to the embodiment of the present invention may be any one having proton conductivity, and the same fluorine-based polymer electrolyte and hydrocarbon-based polymer electrolyte as the polymer electrolyte membrane can be used. As the fluorine-based polymer electrolyte, for example, a Nafion (registered trademark) material manufactured by DuPont 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. Among these, a Nafion (registered trademark) material manufactured by DuPont can be suitably used as the polymer electrolyte membrane. In consideration of the adhesion between the electrode catalyst layer and the polymer electrolyte membrane, it is preferable to use the same material as the polymer electrolyte membrane.

  The polymer electrolyte of the present invention is embedded in a polymer electrolyte that embeds a catalyst material, a polymer electrolyte that embeds carbon particles, a catalyst material that is embedded in a polymer electrolyte, and a polymer electrolyte. There are polymer electrolytes mixed with carbon particles, but the same polymer electrolytes or different polymer electrolytes may be used.

  The solvent used when embedding the catalyst substance or carbon particles with the polymer electrolyte or the solvent used as the dispersion medium for the catalyst ink flows through the polymer electrolyte without eroding the catalyst substance or the polymer electrolyte. There is no particular limitation as long as it can be dissolved or dispersed as a fine gel in a highly soluble state. However, it is desirable that at least a volatile organic solvent is contained, and although not particularly limited, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl Alcohols such as alcohol, pentanol, acetone, methyl ethyl ketone, pentanone, methyl isobutyl ketone, heptanone, cyclohexanone, methyl cyclohexanone, acetonyl acetone, diisobutyl ketone and other ketone solvents, tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene , Ether solvents such as dibutyl ether, other dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol Le, diethylene glycol, diacetone alcohol, such as a polar solvent such as 1-methoxy-2-propanol is used. Moreover, what mixed 2 or more types of these solvents can also be used.

  In addition, those using lower alcohol as the solvent have a high risk of ignition, and when using such a solvent, it is preferable to use a mixed solvent with water. Water 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 is not separated to cause white turbidity or gelation.

  In order to disperse the catalyst material embedded with the polymer electrolyte and the carbon particles embedded with the polymer electrolyte, 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.

  Specific examples of the anionic surfactant include alkyl ether carboxylate, ether carboxylate, alkanoyl sarcosine, alkanoyl glutamate, acyl glutamate, oleic acid / N-methyltaurine, 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, high molecular weight Polyamine ester acid amine salt, special modified phosphate amine salt, high molecular weight polyester acid amide amine salt, special fatty acid derivative amide amine salt, higher fatty acid alkyl amine salt, high molecular weight polyester Amidoamine salt of carboxylic acid, carboxylic acid type surfactant such as sodium laurate, sodium stearate, sodium oleate, dialkyl sulfosuccinate, dialkyl salt of sulfosuccinic acid, 1,2-bis (alkoxycarbonyl) -1-ethane Sulfonate, alkyl sulfonate, alkyl sulfonate, paraffin sulfonate, alpha olefin sulfonate, linear alkyl benzene sulfonate, alkyl benzene sulfonate, polynaphthyl methane sulfonate, polynaphthyl methane sulfonate, naphthalene sulfonate-formalin condensate, alkyl naphthalene Sulfonate, alkanoylmethyl tauride, lauryl sulfate sodium salt, cetyl sulfate sodium salt, stearyl sulfate ester Sodium salt, oleyl sulfate sodium salt, lauryl ether sulfate ester salt, sodium alkylbenzene sulfonate, oil-soluble alkylbenzene sulfonate, α-olefin sulfonate, etc., alkyl sulfate ester salt, alkyl sulfate salt , Sulfate surfactants such as alkyl sulfate, alkyl ether sulfate, polyoxyethylene alkyl ether sulfate, alkyl polyethoxy sulfate, polyglycol ether sulfate, alkyl polyoxyethylene sulfate, sulfated oil, highly sulfated oil, 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 Fate, alkylpolyethoxy phosphate, polyoxyethylene alkyl ether, alkylphenyl phosphate polyoxyethylene salt, alkylphenyl ether phosphate, alkylphenyl polyethoxy phosphate, polyoxyethylene alkylphenyl ether phosphate And phosphoric acid ester type surfactants such as higher alcohol phosphoric acid monoester disodium salt, higher alcohol phosphoric acid diester disodium salt and zinc dialkyldithiophosphate.

  Specific examples of the cationic surfactant include benzyldimethyl {2- [2- (2- (P-1,1,3,3-tetramethylbutylphenoxy) ethoxy] ethyl} ammonium chloride, octadecylamine acetic acid. Salt, tetradecylamine acetate, octadecyltrimethylammonium chloride, tallow trimethylammonium chloride, dodecyltrimethylammonium chloride, palm trimethylammonium chloride, hexadecyltrimethylammonium chloride, behenyltrimethylammonium chloride, palm dimethylbenzylammonium chloride, tetradecyldimethylbenzylammonium Chloride, octadecyldimethylbenzylammonium chloride, dioleyldimethylammonium chlora 1-hydroxyethyl-2-tallow imidazoline quaternary salt, 2-heptadecenyl-hydroxyethyl imidazoline, stearamide ethyl diethylamine acetate, stearamide ethyl diethylamine hydrochloride, triethanolamine monostearate formate, alkyl pyridium Examples thereof include a palladium salt, a higher alkylamine ethylene oxide adduct, a polyacrylamideamine salt, a modified polyacrylamideamine salt, and a perfluoroalkyl quaternary ammonium iodide.

  Specific examples of the amphoteric surfactant include dimethyl coconut betaine, dimethyl lauryl betaine, sodium laurylaminoethylglycine, sodium laurylaminopropionate, stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, amide betaine, imidazolinium. Betaine, lecithin, sodium 3- [ω-fluoroalkanoyl-N-ethylamino] -1-propanesulfonate, N- [3- (perfluorooctanesulfonamido) propyl] -N, N-dimethyl-N-carboxymethylene Examples include ammonium betaine.

  Specific 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 cattle. 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 diolylamine, dimethyl lauryl amine oxide, dimethyl stearyl amine oxide, dihydroxyethyl lauryl amine oxide, perfluoroalkylamine ox Id, polyvinyl pyrrolidone, higher alcohol ethylene oxide adduct, alkylphenol ethylene oxide adduct, fatty acid ethylene oxide adduct, polypropylene glycol ethylene oxide adduct, fatty acid ester of glycerin, fatty acid ester of pentaerythritol, fatty acid ester of sorbit, sorbitan Examples include fatty acid esters and sugar fatty acid esters.

  Among the above surfactants, 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 and α-olefin sulfonate are Considering the carbon dispersion effect and the change in catalyst performance due to the remaining dispersant, it is preferable.

  The catalyst ink is subjected to a dispersion treatment as necessary. The viscosity and particle size of the catalyst ink can be controlled by the conditions for the dispersion treatment of the catalyst ink. Distributed processing can be performed using various devices. 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 use the homogenizer etc. which stir with centrifugal force.

  If the content of the solid content in the catalyst ink is too large, the viscosity of the catalyst ink will increase, so that the surface of the electrode catalyst layer will easily crack, and conversely if it is too small, the film formation rate will be very slow and productivity will be low. Since it will fall, it is preferable that they are 1 mass% or more and 50 mass% or less. The solid content is composed of a catalyst substance, carbon particles, and a polymer electrolyte. When the amount of carbon particles is increased, the viscosity is increased even with the same solid content, and when the amount is decreased, the viscosity is decreased. Therefore, the proportion of carbon 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 at this time is preferably about 0.1 cP or more and 500 cP or less, and more preferably 5 cP or more and 100 cP or less. Further, the viscosity can be controlled by adding a dispersing agent when dispersing the catalyst ink.

  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 substance is soluble in hot 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 and monosodium phosphate, polyvinyl alcohol, polyethylene glycol It is also effective to use two or more types in combination.

  The catalyst ink of the present invention is obtained by preparing an ink in which a catalyst substance and carbon particles embedded in a polymer electrolyte are dispersed in a solvent together with the polymer electrolyte, and drying the ink. For example, it can be obtained by applying a catalyst material and carbon particles embedded in a polymer electrolyte, and an ink in which the polymer electrolyte is dispersed in a solvent, to a transfer sheet and drying it. Alternatively, the catalyst material and carbon particles embedded in the polymer electrolyte can be directly obtained by spraying in a dry atmosphere.

  The temperature range for drying the ink is preferably 30 ° C. or more and 140 ° C. or less. If the temperature at which the ink is dried is less than 30 ° C., the output performance may not be improved because many polymer electrolytes embedding the catalyst substance are dissolved in the solvent in the step of preparing the ink. is there. Even when the temperature at which the ink is dried exceeds 140 ° C., the proton conductivity of the polymer electrolyte that embeds the catalyst substance is hindered, and the output performance may not be improved.

  In the catalyst ink of the present invention, in the step of producing an electrode catalyst layer from a catalyst material embedded in a polymer electrolyte, carbon particles embedded in the polymer electrolyte, and a catalyst ink in which the polymer electrolyte is dispersed in a solvent, A catalyst ink is applied on a substrate, and an electrode catalyst layer is formed through a drying process. When a gas diffusion layer or a transfer sheet is used as the substrate, the electrode catalyst layers are bonded to both surfaces of the polymer electrolyte membrane by a bonding process. In the membrane / electrode assembly of the present invention, a polymer electrolyte membrane is used as a base material, a catalyst ink is directly applied to both sides of the polymer electrolyte membrane, and an electrode catalyst layer is directly formed on both sides of the polymer electrolyte membrane. You can also

  At this time, as a coating method, a doctor blade method, a dipping method, a screen printing method, a roll coating method, a spray method, or the like can be used. For example, spraying methods such as pressure spraying, ultrasonic spraying, and electrostatic spraying are not likely to agglomerate when the coated catalyst ink is dried, resulting in a homogeneous and highly porous catalyst layer. Can do.

  As described above, it is preferable to use any one selected from a gas diffusion layer, a transfer sheet, and a polymer electrolyte membrane as the substrate in the method for producing an electrode catalyst layer of the present invention.

  The transfer sheet used as the substrate may be any material that has good transferability, such as ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroperfluoro. A fluorine resin such as an alkyl vinyl ether copolymer (PFA) or polytetrafluoroethylene (PTFE) can be used. Also, polymer sheets such as polyimide, polyethylene terephthalate, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyarylate, polyethylene naphthalate, etc. are transferred. It can be used as a sheet. When a transfer sheet is used as the base material, the electrode catalyst layer is bonded to the polymer electrolyte membrane, and then the transfer sheet is peeled off to obtain a membrane / electrode assembly having catalyst layers on both sides of the polymer electrolyte membrane.

  As the gas diffusion layer, a material having gas diffusibility and conductivity can be used. Specifically, porous carbon materials such as carbon cloth, carbon paper, and non-woven fabric can be used as the gas diffusion layer. The gas diffusion layer can also be used as a substrate. At this time, it is not necessary to peel off the base material that is the gas diffusion layer after the joining step.

  When the gas diffusion layer is used as a base material, a coating layer may be formed on the gas diffusion layer in advance before applying the catalyst ink. 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. Such a sealing 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 be integrated. In addition, when the separator or the electrode catalyst layer functions as a gas diffusion layer, the gas diffusion layer may be omitted. The fuel cell is manufactured by assembling other accompanying devices such as a gas supply device and a cooling device.

  The catalyst ink in the present invention and the method for producing a fuel cell electrode catalyst layer using the catalyst ink of the present invention will be described below with reference to specific examples and comparative examples. However, the present invention is limited by the following examples. Is not to be done.

  (Example) and (Comparative Example) will be described.

(Example)
[Method of forming catalyst material embedded in polymer electrolyte]
A catalyst material (TaCNO, specific surface area 9 m ² / g) and a 20% by mass polymer electrolyte solution (Nafion: registered trademark, manufactured by DuPont) are mixed in a solvent, and a planetary ball mill (trade name: P-7, Fritsch) is mixed. (Distributed by Japan). Ball mill pots and balls made of zirconia were used. The composition ratio of the ink was 1: 0.25 in terms of the mass ratio of the catalyst substance and the polymer electrolyte. The solvent was ultrapure water and 1-propanol in a volume ratio of 1: 1, and the solid content was 14% by mass. A PTFE sheet was used as a substrate for drying the ink. The ink was applied onto the substrate with a doctor blade and dried in air at 80 ° C. for 5 minutes. Thereafter, the catalyst material embedded with the polymer electrolyte was recovered from the substrate.

[Method of forming carbon particles embedded in polymer electrolyte]
Carbon particles (Ketjen Black, trade name: EC-300J, manufactured by Lion, specific surface area 800 m ² / g) and a 20% by mass polymer electrolyte solution (Nafion: registered trademark, manufactured by DuPont) were mixed in a solvent, Dispersion treatment was performed with a planetary ball mill (trade name: P-7, manufactured by Fritsch Japan). Ball mill pots and balls made of zirconia were used. The composition ratio of the ink was 1: 0.5 in terms of the mass ratio between the carbon particles and the polymer electrolyte. The solvent was ultrapure water and 1-propanol in a volume ratio of 1: 1, and the solid content was 14% by mass. A PTFE sheet was used as a substrate for drying the ink. The ink was applied onto the substrate with a doctor blade and dried in air at 80 ° C. for 5 minutes. Thereafter, the carbon particles embedded with the polymer electrolyte were recovered from the substrate.

[Mixing and heat treatment of catalyst material embedded with polymer electrolyte and carbon particles embedded with polymer electrolyte]
The catalyst material embedded with the polymer electrolyte and the carbon particles embedded with the polymer electrolyte were mixed without solvent in a planetary ball mill. Ball mill pots and balls made of zirconia were used. The composition ratio of the catalyst material embedded with the polymer electrolyte and the carbon particles embedded with the polymer electrolyte was 1: 1 as the mass ratio of the catalyst material and the carbon particles.

[Preparation of catalyst ink]
A mixture of a catalyst material embedded with a polymer electrolyte and carbon particles embedded with a polymer electrolyte and a 20% by mass polymer electrolyte solution are mixed in a solvent and dispersed with a planetary ball mill. Went. Ball mill pots and balls made of zirconia were used. The composition ratio of the catalyst ink was 1: 1: 0.8 in terms of the mass ratio of the catalyst substance, carbon particles, and polymer electrolyte. The solvent was 1: 1 by volume ratio of ultrapure water and 1-propanol. The solid content was 14% by mass. A PTFE sheet was used as a transfer sheet.

[Method for forming electrode catalyst layer]
The catalyst ink was applied to the transfer sheet with a doctor blade and dried at 80 ° C. for 5 minutes in an air atmosphere. The thickness of the electrode catalyst layer was adjusted so that the amount of the catalyst substance supported was 0.4 mg / cm ^2, and the electrode catalyst layer 2 on the air electrode side was formed.

(Comparative example)
[Preparation of catalyst ink]
The catalyst substance, carbon particles, and 20% by mass polymer electrolyte solution were mixed in a solvent, and dispersed with a planetary ball mill. Ball mill pots and balls made of zirconia were used. The composition ratio of the catalyst ink was such that the mass ratio of the catalyst substance, the carbon particles, and the polymer electrolyte was 1: 1: 0.8. The solvent used was ultrapure water and 1-propanol in a volume ratio of 1: 1. The solid content was 14% by mass. The same transfer sheet as in the example was used as the substrate.

[Method for producing electrode catalyst layer]
In the same manner as in the example, the catalyst ink was applied to the transfer sheet and dried. The thickness of the electrode catalyst layer was adjusted so that the amount of the catalyst substance supported was 0.4 mg / cm ^2, and the electrode catalyst layer 2 on the air electrode side was formed.

[Preparation of electrode catalyst layer for fuel electrode]
A platinum-supported carbon catalyst (trade name: TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) having a platinum-supporting amount of 50% by mass and a 20% by mass polymer electrolyte solution were mixed in a solvent and subjected to dispersion treatment with a planetary ball mill. A catalyst ink having a dispersion time of 60 minutes was used. The composition ratio of the catalyst ink was 1: 1 in the mass ratio of carbon in the platinum-supported carbon and the polymer electrolyte, and the solvent was 1: 1 in the volume ratio of ultrapure water and 1-propanol. The solid content was 10% by mass. In the same manner as in the electrode catalyst layer 2, the catalyst ink was applied to the substrate and dried. The thickness of the electrode catalyst layer was adjusted so that the amount of the catalyst material supported was 0.3 mg / cm ^2, and the electrode catalyst layer 3 on the fuel electrode side was formed.

(Production of membrane electrode assembly)
The base material on which the air electrode side electrode catalyst layer 2 produced in (Example) and (Comparative Example) was formed and the base material on which the fuel electrode side electrode catalyst layer 3 was formed were punched into a square of 5 cm ² to form a polymer. A transfer sheet was placed so as to face both surfaces of the electrolyte membrane (Nafion (registered trademark) 212, manufactured by DuPont), and hot pressing was performed at 130 ° C. for 10 minutes to obtain a membrane electrode assembly 12. Carbon papers 4 and 5 each having a sealing layer formed as a gas diffusion layer are disposed on both surfaces of the membrane electrode assembly 12 thus obtained, and are further sandwiched between a pair of separators 10 to provide a single cell solid polymer fuel. A battery was produced.

[Power generation characteristics]
(Evaluation conditions)
Using a fuel cell measuring device manufactured by NF Circuit Design Block Co., Ltd., power generation characteristics were evaluated at a cell temperature of 80 ° C. and at 100% RH for both the anode and cathode. Using pure hydrogen as the fuel gas and pure oxygen as the oxidant gas, the flow rate was controlled at a constant flow rate.

(Measurement result)
The membrane / electrode assembly produced in (Example) showed power generation performance superior to the membrane / electrode assembly produced in (Comparative Example). In particular, the power generation performance in the vicinity of 0.6 V was improved, and (Example) showed power generation performance about 2.2 times that of (Comparative Example). In (Example), the proton conductivity of the catalyst surface is increased by embedding the catalyst substance with a polymer electrolyte, and the specific surface area of the carbon particles is adjusted, thereby increasing the reaction active point. I guessed that. On the other hand, in (Comparative Example), the catalyst material, the carbon particles, and the polymer electrolyte are dispersed in a solvent in one step, so the polymer electrolyte is preferential to the carbon particles having a larger specific surface area than the catalyst material. It was presumed that sufficient proton conductivity was not ensured on the surface of the catalyst material by adsorbing on the surface of the catalyst material.

  The present invention is a catalyst ink for forming an electrocatalyst layer having a polymer electrolyte and a catalyst substance and carbon particles, a catalyst substance for embedding the polymer electrolyte in a catalyst substance having a specific surface area smaller than that of the carbon particles, By making the carbon particles embedding the polymer electrolyte with respect to carbon particles having a specific surface area larger than that of the catalyst substance, the proton conductivity on the catalyst surface can be increased in advance, the reaction active point is increased, By performing the treatment for reducing the specific surface area of the carbon particles, the proton conductivity on the catalyst surface can be increased when the electrode catalyst layer is formed. As a result, an electrode catalyst layer, a membrane electrode assembly and a polymer electrolyte fuel cell with improved output performance can be provided. In particular, the catalyst ink using an oxide-based non-platinum catalyst as the catalyst material has a remarkable effect that the potential of the catalyst material can be brought out more than the conventional catalyst ink, and thus has high industrial utility value. .

DESCRIPTION OF SYMBOLS 1 Polymer electrolyte membrane 2 Electrode catalyst layer on the air electrode side 3 Electrode catalyst layer on the fuel electrode side 4 Gas diffusion layer on the air electrode side 5 Gas diffusion layer on the fuel electrode side 6 Air electrode (cathode)
7 Fuel electrode (anode)
8 Gas channel 9 Cooling water channel 10 Separator 11 Membrane electrode assembly 12 Polymer electrolyte fuel cell

Claims (3)

In the catalyst ink of the electrode catalyst layer for a fuel cell having a polymer electrolyte, a catalyst substance and carbon particles,
A catalyst material having a specific surface area smaller than that of carbon particles and the first polymer electrolyte are dispersed in a solvent within a weight ratio of 1: 0.01 to 1:30, and a temperature range of 30 ° C. to 140 ° C. A catalyst material embedded in a first polymer electrolyte dried with
The carbon particles having a specific surface area larger than that of the catalyst particles and the second polymer electrolyte are dispersed in a solvent within a weight ratio of 1: 0.1 to 1:20, and the temperature range is 30 ° C. or higher and 140 ° C. or lower. Carbon particles embedded with a second polymer electrolyte that is dried within the range;
A catalyst material embedded in the first polymer electrolyte and carbon particles embedded in the second polymer electrolyte, which are mixed without solvent and heat-treated in a temperature range of 50 ° C. or higher and 180 ° C. or lower; A catalyst ink which is dispersed in a solvent together with a third polymer electrolyte.   The catalyst material is an electrode active material for an oxygen reduction electrode used as an air electrode of a polymer electrolyte fuel cell, and contains at least one transition metal element selected from Ta, Nb, Ti, and Zr. The catalyst ink according to claim 1.   The catalyst ink according to claim 2, wherein the catalyst material is a partial oxide of the transition metal element carbonitride or an oxide of the transition metal element.