JP2005285511A - Electrode catalyst ink for fuel cell and manufacturing method of electrode catalyst ink for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electrode ink or the like for a fuel cell electrode with high mass activity. <P>SOLUTION: The electrode catalyst ink for the fuel cell contains an electrolyte polymer, and catalyst particles carrying catalyst metal on a conductive carrier with a peak of a particle size distribution of 1 μm or less and a ratio of a C-O peak to a C-C peak obtained by the peak division of C(1s) measured by XPS of 5% or more. By the introduction of a hydrophilic group, the catalyst particle in the electrode catalyst is excellent in dispersion property and mass activity. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell electrode catalyst having a particle size range in a specific range, and a method for producing a fuel cell electrode catalyst having an increased amount of introduction of hydrophilic groups.

  In recent years, in response to social demands and trends against the background of energy and environmental issues, polymer electrolyte fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. . The solid polymer fuel cell comprises an anode and a cathode, a separator that forms a gas flow path, and a film-like solid polymer electrolyte membrane, and a joined body of the solid polymer electrolyte membrane and both electrodes (hereinafter referred to as “solid polymer electrolyte membrane”). In general, a structure in which a separator is laminated with a separator is built-in, and both electrodes are generally composed of an electrolyte polymer and an electrode catalyst.

  The anode and the cathode generally have an electrode catalyst layer in which a carbon powder such as carbon black is used as a conductive carrier, and an electrode catalyst having noble metal particles supported on the carrier is highly dispersed in an electrolyte polymer having proton conductivity. When a fuel gas such as hydrogen is supplied to the anode, the hydrogen is oxidized by the catalyst particles contained in the anode-side electrode catalyst layer to become protons and electrons. The generated protons reach the cathode via the electrolyte polymer contained in the anode and the solid polymer electrolyte membrane adjacent to the anode, where they react with oxygen supplied to the cathode to generate water and obtain electric energy. . Battery performance is greatly affected by the ionic conduction resistance between the two electrodes. For this reason, it is necessary to reduce the ion conduction resistance by joining the catalyst and the solid polymer electrolyte membrane contained in both electrodes through an ion conduction path. At present, an electrode catalyst obtained by applying and drying a catalyst ink obtained by mixing and stirring an electrolyte polymer and catalyst particles is prepared, the electrode catalyst and the solid polymer electrolyte membrane are pressed under heating, and MEA Is manufactured.

  On the other hand, a polymer in which a sulfonic acid group is introduced into a perfluoro main chain is generally used as an electrolyte polymer responsible for ion conduction. Specific products include Nafion manufactured by DuPont, Flemion manufactured by Asahi Glass Co., Ltd., and Aciplex manufactured by Asahi Kasei Co., Ltd. A perfluoro polymer electrolyte is composed of a perfluoro main chain and a side chain having a sulfonic acid group. The polymer electrolyte is divided into a region mainly composed of a sulfonic acid group and a region mainly composed of a perfluoro main chain. Microphase separation occurs, and the sulfonic acid group phase is said to form clusters. What contributes to ionic conduction is the portion where sulfonic acid groups are gathered to form clusters. A catalytic reaction in a fuel cell is performed at a three-phase interface between electrode catalyst particles, a reaction gas such as hydrogen or oxygen, and an electrolyte polymer. In order to efficiently exchange ions on the catalyst surface at the three-phase interface, it is desirable to ensure a large catalyst surface area, and thus it is desirable that the catalyst particle size distribution is small. Moreover, in order to ensure ionic conductivity, it is preferable that the sulfonic acid group which contributes to ionic conduction is orientated on the catalyst surface, and it is preferable that the catalyst surface is hydrophilic.

As a method for producing MEA using a catalyst layer having a hydrophilic group introduced into catalyst particles, catalyst ink is prepared by mixing catalyst particles that have been subjected to hydrophilic treatment, a hydrogen ion conductive polymer electrolyte, and a solvent. An MEA manufacturing method including a process and a process of dispersing a particle size distribution of carbon particles carrying catalyst particles in the catalyst ink in a predetermined range is disclosed (Patent Document 1). When the hydrophilicity of the catalyst powder decreases, the cohesiveness of the catalyst ink increases, and a dense and smooth coating film cannot be obtained by a normal stirring / dispersing method such as a stirrer or an ultrasonic bath. For this reason, the dispersibility and hydrophilicity of the catalyst-carrying conductive carrier are optimized, and a dense and smooth catalyst layer is realized to produce a membrane electrode assembly that exhibits higher performance. As hydrophilic treatment, an oxidizing agent such as hydrogen peroxide, sodium hypochlorite, potassium permanganate is used.
JP 2002-63909 A

  The electrode catalyst is obtained by supporting a metal having catalytic activity such as platinum on the surface of carbon black particles. The surface of the carbon black particles is originally hydrophobic, and the surface state of the metal surface having catalytic activity cannot be controlled by the influence of impurities. When such catalyst particles and a hydrophilic polymer solution are mixed, the particles remain in the state immediately after mixing due to the surface tension of the catalyst particles, and it becomes difficult to uniformly disperse the catalyst particles, or a large amount of stirring is required. Requires time and rotational force.

  The method described in Patent Document 1 is characterized in that a smooth catalyst layer is produced. However, since catalyst particles are mixed in an electrolyte polymer solution having a high viscosity, the surface of each catalyst particle is uniformly coated with the electrolyte polymer. Or a strong stirring force is required to mix the catalyst particles and the electrolyte polymer.

The present invention has been made to solve the above-described problems. The catalyst particles are dispersed in an H ₂ O ₂ solution to control the particle size distribution state of the conductive support within a specific range. It aims at improving the ion conductivity of the surface and improving the performance of the fuel cell.

As a result of intensive studies to solve the above problems, the present inventors have added a conductive support carrying a catalyst metal to the H ₂ O ₂ solution, whereby the dispersibility of the catalyst particles is improved and uniformly dispersed. In addition, the conductive carrier is oxidized by H ₂ O ₂ to introduce a hydrophilic group, and when a diluted electrolyte polymer is added thereto, the surface of each catalyst particle is uniformly coated with the electrolyte polymer, so that ion conductivity is improved. The present inventors have found that an excellent catalyst ink can be obtained and completed the present invention. In addition, the catalyst ink obtained through such a process has a catalyst particle size distribution peak of 1 μm or less and a C—O peak value within a specific range. Become ink.

According to the method for producing a catalyst ink of the present invention, the catalyst particles can be highly dispersed in the catalyst ink by using the H ₂ O ₂ solution. In addition, exposure of the catalyst particles to the H ₂ O ₂ solution increases the number of oxidized chemical species on the surface of the catalyst particles, and the affinity between the catalyst particles and the electrolyte polymer can be improved by introducing hydrophilic groups. . Further, the gas diffusion region and the proton conduction path can be controlled, and the catalyst layer can be arbitrarily designed. For this reason, it can contribute also to the water management of a fuel cell, and it becomes cell performance capability improvement.

  In the present invention, by adjusting the concentration of the electrolyte polymer after the addition of the diluted electrolyte polymer, drying of the highly dispersed catalyst particles can be prevented, thereby preventing secondary particle aggregation by the electrolyte polymer-coated particles. . As a method for adjusting the concentration, when the method of sedimenting the catalyst particles and removing the supernatant is performed, the energy required for the separation and concentration of the catalyst particles can be minimized.

  According to the production method of the present invention, a catalyst ink can be produced while maintaining a high dispersion state. For this reason, the catalyst-carrying electrode and MEA produced using the electrode catalyst ink have improved proton conductivity and improved cell performance. As a result, it is possible to construct a high durability and high-performance catalyst layer.

  In the first aspect of the present invention, the particle size distribution peak is 1 μm or less, and the ratio of the C—O peak to the C—C peak obtained by peak splitting of C (1s) measured by XPS is 5% or more. An electrode catalyst ink for a fuel cell comprising catalyst particles carrying a catalyst metal on a conductive carrier and an electrolyte polymer.

  The electrode catalyst ink for fuel cells includes at least catalyst particles in which a catalyst metal is supported on a conductive carrier and an electrolyte polymer, thereby increasing the three-phase interface composed of the catalyst particles, the reactive gas, and the electrolyte polymer. Power generation efficiency can be improved by introducing a hydrophilic group into the conductive carrier. In the present invention, in the catalyst ink used for preparing the catalyst-carrying electrode, the surface area of the catalyst particles is increased, and a hydrophilic group is introduced to increase the three-phase interface, thereby increasing the power generation efficiency. The peak of the particle size distribution was 1 μm or less, and the ratio of the C—O peak to the C—C peak obtained by C (1s) peak division measured by XPS was 5% or more. Hereinafter, the present invention will be described in detail.

  The conductive carrier that can be used in the present invention should be particularly limited as long as it has a BET specific surface area sufficient for carrying the catalyst in a highly dispersed manner and has sufficient electronic conductivity as a current collector. It is not a thing.

As such a conductive carrier, at least one of carbon particles, carbon nanotubes, carbon nanohorns, cup-stacked nanostructures, or carbon fibers can be used as a raw material. The size of these conductive carriers is not particularly limited, but the pulverized or aggregated mass is dissociated by mixing and stirring during the preparation of the catalyst ink. In the present invention, in order to specify the particle size distribution peak of the catalyst particles to be 1 μm or less, the average particle size of the conductive carrier before supporting the catalyst component is 10 nm to several μm. It is an aggregate and is very easy to aggregate and has a wide particle size distribution. Further, the BET specific surface area is preferably several tens to several 1,000 m ² / g, more preferably 200 to 1,000 m ² / g.

  Examples of the catalyst metal include noble metals and alloys of noble metals and base metals.

  The noble metal is one or more metals selected from the group consisting of platinum, palladium, rhodium, osmium, ruthenium, and iridium. Among these, platinum is preferable. The amount of noble metal fine particles supported on the conductive support is 10 to 80% by mass, more preferably 10 to 70% by mass, and particularly preferably 30 to 50% by mass per catalyst. When it exceeds 80% by mass, it is difficult to uniformly disperse, and it becomes difficult to carry highly dispersed noble metal fine particles.

  The base metal is preferably at least one selected from the group consisting of vanadium, chromium, manganese, iron, cobalt, nickel, copper and zinc. The average particle diameter is 1 to 10 nm, more preferably 2 to 5 nm. This is because the catalyst activity is particularly excellent within this range. Conventionally, platinum and ruthenium are used as the catalyst catalyst for the electrode catalyst as a reaction catalyst for protons and oxygen, but the activity is often insufficient only by using the noble metal alone as the electrode catalyst. When an alloy of a noble metal and a base metal is used, the activity is improved as compared with an electrode catalyst made of a noble metal alone.

  The amount of base metal supported is 0.1 to 1 mol%, more preferably 0.3 to 1 mol%, based on the amount of noble metal. If it exceeds 1 mol%, it is difficult to uniformly disperse, and it becomes difficult to carry highly dispersed base metal fine particles. The noble metal and the base metal may be separately supported on the inner surface and the outer surface of the conductive carrier, but the noble metal and the base metal are supported on the inner and outer surfaces of the conductive carrier as composite fine particles or alloy fine particles. May be.

  In order to support the catalyst metal on the conductive support, the catalyst support can be easily supported on the conductive support by uniformly dispersing and impregnating the conductive support in the catalyst metal-containing solution and administering a reducing agent described later. it can.

  The source of the noble metal is not particularly limited, and compounds containing platinum, palladium, rhodium, osmium, ruthenium, and iridium can be widely used. Examples of such compounds include nitrates, sulfates, ammonium salts, amines, carbonates, bicarbonates, inorganic salts such as halogen salts, nitrites, and oxalic acid, carboxylates and hydroxides such as formate. , Alkoxides, oxides, and the like can be exemplified, and can be appropriately selected depending on the type and pH of the solvent in which these are dissolved. Among these, in the case of industrial use, nitrate, carbonate, oxide, hydroxide, platinum, platinum chloride, dinitrodiamine platinum and the like are preferable. The concentration of these noble metals is preferably 0.1 to 1.0% by mass, more preferably 0.3 to 60% by mass in terms of metal.

  Moreover, as a reducing agent for precipitating or reducing precious metals, organic acids having 1 to 6 carbon atoms such as formic acid, acetic acid and citric acid, aldehydes having 1 to 3 carbon atoms such as formaldehyde, hydrogen, hydrazine, and boronation Sodium hydrogen, sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, sodium borohydride, methanol, ethanol, ethylene, carbon monoxide and the like can be mentioned. Note that a gaseous substance such as hydrogen or carbon monoxide at room temperature can be supplied by bubbling. In the present invention, among these, it is preferable to use organic acids having 1 to 6 carbon atoms such as formic acid, acetic acid and citric acid, and aldehydes having 1 to 3 carbon atoms such as formaldehyde.

  Base metal sources include inorganic vanadium, chromium, manganese, iron, cobalt, nickel, copper and zinc nitrates, sulfates, ammonium salts, amines, carbonates, bicarbonates, halogen salts, nitrites, oxalic acid, etc. Examples thereof include carboxylates such as salts and formate, hydroxides, alkoxides, and the like, which can be appropriately selected depending on the type and pH of the solvent in which these are dissolved.

  In order to support such a base metal on a conductive carrier, it is preferable to use a reducing agent for the base metal. Examples of such a reducing agent include ammonia, aqueous ammonia, tetramethylammonium hydroxide, and the like. Ammonia can also be supplied by bubbling. Note that the catalyst particles may be supported on the conductive support by first supporting either a noble metal or a base metal.

  After the noble metal and / or base metal fine particles are supported on the conductive support, it is isolated from the solution, dried, and then the support is fired at 400 to 800 ° C.

  Drying can be performed by, for example, natural drying, evaporation to dryness, rotary evaporator, spray dryer, drum dryer, or the like. What is necessary is just to select drying time suitably according to the method to be used. Depending on the case, it is good also as drying in a baking process, without performing a drying process.

  The firing temperature is preferably 500 to 800 ° C. when only the noble metal is supported on the conductive support. As a cause of performance deterioration of the electrode catalyst, there is sintering of the catalytic metal fine particles, and the particle diameter of the catalytic metal fine particles is increased by the sintering. 500 ° C is the crystallization temperature of platinum, and firing at a higher temperature can make the catalyst metal fine particles stronger and more stable, reducing the elution, dissolution, aggregation and sintering of the catalyst metal fine particles. This can improve durability. If the temperature exceeds 800 ° C., the sintering of the supported particles increases, and the particle diameter grows to reduce the surface area, which is not suitable. In the case of an alloy of a noble metal and a base metal, it may be fired at 400 to 800 ° C. By firing in this temperature range, sintering can be suppressed and durability can be improved.

  As a result, catalyst particles having an average particle diameter of the catalyst metal of 1 to 10 nm, more preferably 2 to 5 nm are obtained. The smaller the average particle size of the catalyst metal, the higher the effective electrode area where the electrochemical reaction proceeds, and thus the higher the oxygen reduction activity. However, in practice, there is a phenomenon that the activity is rather lowered when the catalyst particle diameter is too small. When the average particle diameter is 1 to 10 nm, a surface area necessary for the catalyst activity can be secured, and the catalyst activity per unit mass of the catalyst metal fine particles can be increased. The average particle diameter can be calculated from the crystallite diameter obtained from the half-value width of the diffraction peak of the metal fine particles in X-ray diffraction, or the average value of the average particle diameter of the metal fine particles examined by a transmission electron microscope. .

  The electrolyte polymer used in the present invention is a member having at least high proton conductivity, such as various Nafion manufactured by DuPont (registered trademark: Nafion), ion exchange resin manufactured by Dow Chemical, and other ionic co-polymers. A polymer (electrolyte polymer), Flemion manufactured by Asahi Glass Co., Ltd., and Aciplex manufactured by Asahi Kasei Co., Ltd. can be used. The compounding amount of the electrolyte polymer in the catalyst ink is 0.3 to 1.0 part by mass, more preferably 0.4 to 0.6 part by mass with respect to 1 part by mass of the catalyst particles. This is because a catalyst-supporting electrode having excellent ion conductivity can be prepared within this range.

  In the present invention, the peak of the particle size distribution of the catalyst particles contained in the catalyst ink is 1 μm or less, preferably 250 to 950 nm, particularly preferably 350 to 750 nm. FIG. 1 shows conventional catalyst particles (immediately after mixing with an electrolyte polymer), conventional products treated with a homogenizer for 1 hour, and catalyst particles of the present invention prepared in Example 1 described later (30 minutes with the electrolyte polymer). Particle size distribution). As is apparent from FIG. 1, the peak of the conventional product before homogenization exists in the vicinity of about 10 μm, and even if this is homogenized for 1 hour, the peak exists in a range exceeding 1 μm. However, the catalyst particles contained in the catalyst ink of the present invention have a particle size distribution peak at a position of about 0.5 μm by homogenization for 30 minutes. If it exceeds 1 μm, the surface area per unit weight is reduced, so that the three-phase interface is reduced and the power generation efficiency may be lowered. In order to obtain a particle size distribution with a peak position of 1 μm or less, it can be prepared by mixing, stirring and homogenizing at least the catalyst particles and the electrolyte polymer. However, the conductive support constituting the catalyst particles is derived from the inherent hydrophobicity. Thus, agglomerates are easily formed, and the catalyst particles may aggregate in the drying and firing steps of the catalyst particles. In the present invention, focusing on this point, such agglomeration is dissociated by introducing a hydrophilic group and mixing and stirring the catalyst particles with the electrolyte polymer, and finally the peak of the particle size distribution is set to 1 μm or less. A conventional catalyst particle treated with a homogenizer for 1 hour has a peak at a position of about 1 μm, and the catalyst particle prepared in Example 1 of the present application has a peak at a position of about 0.5 μm by homogenization for 30 minutes. Therefore, the reason why the particle size distribution peak in the present invention is 1 μm is not simply an increase in stirring force due to homogenization, but is considered to depend on introduction of a hydrophilic group described later.

  Further, the ratio of the C—O peak to the C—C peak by C (1s) peak division measured by XPS is preferably 5% or more, more preferably 5 to 50%, and particularly preferably 20 to 40. %. FIG. 2 shows a C—O peak relative to a C—C peak obtained by C (1s) peak splitting measured by XPS. The solid line indicates the sum of the previous peaks, the broken line indicates each peak, and the binding energy 286 e. V. The nearby peak is the C—O peak and 284 e. V. A nearby peak indicates a CC peak. Conventionally, catalyst particles tend to agglomerate by drying, sintering, etc., and therefore it is difficult to prepare catalyst particles having a particle size distribution peak of 1 μm or less. For example, even if hydrophilic groups are introduced, the catalyst particles are subsequently dried. Aggregation of catalyst particles was likely to occur. However, in the present invention, the introduction of the hydrophilic group can be evaluated by the above measurement method, and the peak in the particle size distribution of each catalyst particle can be adjusted to 1 μm or less by the introduction of the hydrophilic group, and at the three-phase interface. It can also contribute to the increase. When the ratio of the C—O peak is less than 5%, the hydrophilicity is inferior, and even in the preparation of the catalyst ink, the dispersibility with the electrolyte polymer is not excellent, and it becomes difficult to prepare an electrode catalyst having excellent power generation efficiency. In addition, the XPS measurement of the catalyst particle in this invention shall be based on the method of the Example description described later.

  In order to obtain catalyst particles in such a range, at least one selected from hydrogen peroxide, sodium hypochlorite, potassium permanganate, hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, hydrofluoric acid, acetic acid, and ozone in advance. There are a method of preparing catalyst particles using a conductive carrier treated with an oxidizing agent, and a method of introducing a hydrophilic group with an oxidizing agent used for the above-mentioned hydrophilic treatment after obtaining catalyst particles.

  When an electrode for a fuel cell is prepared using the catalyst ink of the present invention, the catalyst particles are uniformly coated with the electrolyte polymer by introducing the hydrophilic group, and the three-phase interface is widened, resulting in an electrode having excellent catalytic activity. The catalyst ink of the present invention may be mixed with a water repellent, a pore former, a thickener, a diluting solvent, etc., as long as the specification is not impaired.

The second of the present invention is a step of dispersing an electrode catalyst supporting a catalytic metal on a conductive carrier in an H ₂ O ₂ solution, then adding a dilute electrolyte polymer to the electrode catalyst and stirring, an electrolyte for the catalyst particles It is a manufacturing method of the electrode catalyst ink for fuel cells characterized by including the process of raising a polymer concentration. When a catalyst ink having a hydrophilic group introduced into the catalyst particles and having a peak in the particle size distribution of the catalyst particles of 1 μm or less is used, a catalyst-supporting electrode having excellent mass activity can be obtained. When a method for preparing an electrode for a fuel cell using such an electrode was examined, the method was not limited to the characteristics of the catalyst particles of the first invention, and the electrode catalyst was dispersed in an H ₂ O ₂ solution, It has been found that an electrode for a fuel cell excellent in mass activity can be obtained by performing a step of adding a dilute electrolyte polymer and stirring and a step of concentrating the solution. The difference from the first invention is that there is no limitation of the peak in the particle size distribution of the catalyst particles, and the ratio of the C—O peak to the C—C peak obtained by the peak splitting of C (1s) by XPS measurement. There is nothing. FIG. 3 shows a method for producing the catalyst ink of the present invention and a process for producing MEA using the catalyst ink.

  As the catalyst particles used in the second invention, those described in the first invention can be preferably used.

Then but dispersing the catalyst particles in the _H 2 _{O 2 solution,} the concentration of the H 2 _{O 2} solution is 3 to 10 wt%, more preferably 5-8 wt%. Since the conductive support is oxidized when it is treated with the H ₂ O ₂ solution, a hydrophilic group is introduced, and the ratio of the C—O peak to the C—C peak can be adjusted to 5% or more. Also, oxygen gas bubbles are generated in response to the oxidation reaction with H ₂ O ₂ , whereby the catalyst particle mass is separated and uniformly dispersed in the solution. If the amount exceeds 10% by mass, the amount of generated oxygen may be large and the solution may be scattered. If the dispersed solution contains catalyst particles, the catalyst is lost. On the other hand, if it is less than 3% by mass, it takes a long time to obtain a dispersion effect and an oxidation effect.

The amount of the _H 2 _{O 2} solution, 100-1,000 parts by weight with respect to catalyst particle 1 part by weight, more preferably from 200 to 500 parts by weight. When the amount is less than 100 parts by mass, the liquid ratio of the H ₂ O ₂ solution to the catalyst particles decreases, so that the dispersibility of the catalyst decreases. On the other hand, when the amount exceeds 1,000 parts by mass, the H ₂ O ₂ to the catalyst particles decreases. Since the liquid ratio of the solution becomes too large, the load on the process of the Noh district that is refrained next becomes large, which is inefficient.

The solution temperature at the time of dispersing in the H ₂ O ₂ solution can be appropriately adjusted depending on the state of the catalyst particles, specifically the content of the catalyst metal and the aggregation state. However, in general, the solution temperature is 30 ° C to 90 ° C, more preferably 40 to 80 ° C. If it is the range of 30 to 90 degreeC, the catalyst particle surface can be efficiently hydrophilized by an oxidizing action. The higher the temperature is, the faster the reaction rate is. However, when the temperature is lower than 30 ° C., the reaction rate is slow. Therefore, the appearance of slight bubbles is noticeable, and it takes a long time to complete the reaction. On the other hand, even if it exceeds 90 ° C., the amount of heat is wasted and a sudden bumping may be caused, which is disadvantageous.

  Next, the catalyst particles are stirred by stirring the solution, or adding an electrolyte polymer to the solution and then stirring the mixture at an average of 10,000 to 15,000 rpm for about 1 to 5 hours. It can be pulverized.

  The diluted electrolyte polymer is then added to the solution and stirred. The density | concentration of the diluted electrolyte polymer to add is 0.1-10 mass%, More preferably, it is 0.3-3 mass%. When the amount exceeds 10% by mass, the viscosity of the electrolyte polymer solution to be added becomes too high, and the polymer in the electrolyte polymer solution aggregates during storage, so that sufficient performance cannot be obtained. On the other hand, if the amount is less than 0.1% by mass, the electrolyte polymer layer may become too thin, and subsequent concentration may be difficult. The solvent for diluting the electrolyte polymer is at least one or more of water-soluble organic solvents such as methanol, propanol, isopropanol, butyl alcohol, isobutyl alcohol, methoxyethanol, methoxypropanol, ethoxyethanol, and methyl ethyl ketone. An organic solvent mixed with can be used.

  The diluted electrolyte polymer is added so that the electrolyte polymer is 0.2 to 0.6 parts by mass, more preferably 0.2 to 0.3 parts by mass with respect to 1 part by mass of the catalyst particles. . When the amount is less than 0.2 parts by mass, the coating of the polymer is not sufficient, and when the amount exceeds 0.6 parts by mass, the adjustment range in the electrolyte polymer solution to be added in the next step becomes narrow, which is not preferable.

  Stirring is performed at a rotational speed of 9,500 to 17,500 rpm, more preferably 12,000 to 15,000 rpm, and a stirring time of 10 minutes to 5 hours, more preferably 30 minutes to 1 hour. As a result, the surface of the electrode catalyst can be uniformly coated with the electrolyte polymer, and aggregation of the electrode catalyst can be suppressed, so that the electrode catalyst can be uniformly dispersed in the solution.

  In the present invention, the solution is then concentrated. The catalyst ink preferably contains 0.3 to 1.0 parts by mass of an electrolyte polymer with respect to 1 part by mass of the catalyst particles in order to ensure optimal conductivity for proton transfer. In the present invention, since the diluted electrolyte polymer is used as described above, it is necessary to increase the concentration of the electrolyte polymer thereafter. The method is not particularly limited. For example, the electrolyte polymer solution containing the catalyst particles is allowed to stand, the catalyst particles are allowed to settle, and the supernatant solution is decanted while visually confirming the electrolyte solution. The final concentration can be adjusted by mixing the polymers. According to this method, since the catalyst particles do not come into contact with the outside air, the catalyst particles are not dried. Therefore, aggregation of the catalyst particles generated during drying can be prevented.

  Note that the concentration can be adjusted by distillation or dehydration, for example, without depending on such a concentration adjustment method. In addition, as the electrolyte polymer that can be used in the second invention, those described in the first invention can be used. Further, in addition to the catalyst particles and the electrolyte polymer, a water repellent, a pore-forming agent, a thickener, a diluting solvent, and the like may be mixed as long as the specification is not impaired.

  A third aspect of the present invention is a catalyst-carrying electrode prepared by using the fuel cell electrode catalyst ink or the catalyst ink obtained by the method for producing the fuel cell electrode catalyst ink.

  There is no restriction | limiting in particular as a preparation method of a catalyst carrying electrode, What is necessary is just to use the catalyst ink of this invention instead of the conventional catalyst ink. For example, the catalyst ink is made into a paste or slurry, and is applied and dried to a desired thickness by a screen printing method, a deposition method, or a spray method on a gas diffusion layer or a solid polymer electrolyte membrane described later. There is a method of forming an electrode catalyst layer and using it as a catalyst-carrying electrode.

  In the present invention, the fuel cell MEA may further include a solid polymer electrolyte membrane, a cathode and an anode, and the catalyst-supporting electrode as a cathode. For example, as MEA, a gas diffusion layer / electrode (anode) / solid polymer electrolyte membrane / electrode (cathode) / gas diffusion layer is used by using a gas diffusion layer in addition to the solid polymer electrolyte membrane and the catalyst supporting electrode. You may arrange so that it may become.

  As the gas diffusion layer, a fiber woven fabric or the like can be generally used. Further, the solid polymer electrolyte membrane is not particularly limited, and any solid polymer electrolyte membrane can be applied as long as it is conventionally used in MEA. For example, a material composed of a member having at least high proton conductivity is exemplified. A perfluorocarbon polymer having a sulfonic acid group, a material obtained by doping a hydrocarbon polymer compound with an inorganic acid such as phosphoric acid, partly proton Examples include organic / inorganic hybrid polymers substituted with conductive functional groups, and membranes made of solid polymer electrolytes such as proton conductors in which a polymer matrix is impregnated with a phosphoric acid solution or a sulfuric acid solution. More specifically, perfluorosulfonic acid membranes represented by various NAFION and Flemion manufactured by DuPont, ion exchange resin, ethylene-tetrafluoroethylene copolymer resin membrane, trifluorostyrene manufactured by Dow Chemical Co., Ltd. There are commercially available products such as a fluorine-based polymer electrolyte such as a resin film as a base polymer, and a hydrocarbon-based resin film having a sulfonic acid group.

  The MEA of the present invention is characterized in that the catalyst-carrying electrode of the present invention is used. If the catalyst-carrying electrode of the present invention is used instead of the conventional catalyst-carrying electrode, the MEA can be produced according to the conventional method. For example, a method in which an electrode is directly formed on the solid polymer electrolyte membrane and then sandwiched by a gas diffusion layer, a method in which a gas diffusion layer and an electrode are formed on a separator, and this is joined to a solid polymer electrolyte membrane Examples thereof include various methods such as a method of forming an electrode on a flat plate such as a release film, transferring the electrode to a solid polymer electrolyte membrane, and sandwiching it with a gas diffusion layer. When the electrode is formed separately from the solid polymer electrolyte membrane, the electrode and the solid polymer electrolyte membrane are preferably joined by a hot press method or the like.

  A fourth aspect of the present invention is a fuel cell using the catalyst-carrying electrode or the fuel cell MEA. The fuel cell is useful as a power source for a moving body such as a vehicle, a stationary power source, and the like, and can stably supply a high power generation amount under a high current density operation condition.

  The type of fuel cell is not particularly limited as long as desired cell characteristics can be obtained, but it is used as a polymer electrolyte fuel cell (also simply referred to as “PEFC”) from the viewpoints of practicality and safety. Is preferred.

  The fuel cell of the present invention can be prepared by a conventional method by using these of the present invention instead of the conventional catalyst-carrying electrode and MEA. Since the fuel cell using the catalyst-carrying electrode and MEA of the present invention has high mass activity, the fuel cell is small and can supply an excellent power generation amount as compared with the conventional one. Therefore, it is possible to provide an efficient fuel cell in a small space as a power source for a moving body such as a vehicle or a stationary power source.

  Hereinafter, the present invention will be specifically described based on examples. In addition, this invention is not limited only to these Examples. In the examples, “%” represents a mass percentage unless otherwise specified.

(Example 1)
1 g of conductive carbon black (Vulcan XC-72: manufactured by Cabot) powder was sufficiently dispersed in 100 g of a chloroplatinic acid aqueous solution containing 0.4% by mass of platinum using a homogenizer, and then sodium citrate was added thereto. 3 g was added, and the mixture was heated to 80 ° C. using a reflux reactor, and platinum was supported for reduction. After the solution was allowed to cool to 30 ° C., the carbon on which platinum was supported was filtered off to obtain Pt-supported carbon black powder (Pt / C). The average particle diameter of platinum in Pt / C was about 2.9 nm from the result of observation with a transmission electron microscope. Further, as a result of examining the amount of Pt supported by inductively coupled plasma emission spectroscopy, it was confirmed that 40.6% by mass of Pt was supported.

  10 g of the obtained Pt-supported catalyst was added to 1 L of hydrogen peroxide (40 ° C.) adjusted to 3% by mass. After adding the catalyst particles, oxygen was sufficiently generated to disperse the catalyst particles in the solution. In anticipation of the generation of oxygen, 40 g of 5% by weight electrolyte polymer (DuPont, 5% Nafion Dispersion Solution DE520, solvent water / isopropanol mixed solution) solution was gradually added with stirring. . After stirring for 30 minutes, the catalyst particles were allowed to stand to settle.

  The supernatant solution was decanted while visually confirmed to recover the electrolyte polymer-coated catalyst. The catalyst particles could be recovered without drying, and an aggregate of the electrolyte polymer-coated catalyst was not formed.

  The collected electrolyte polymer-coated catalyst was weighed, and 5% by mass of the electrolyte polymer solution was combined with the previously collected electrolyte polymer, and the polymer solution was added so as to have the same amount as the platinum mass supported on the catalyst particles. Then, water was added as a solvent so that it might become a viscosity of 150-300 mPa * sec, stirring and mixing.

  The obtained electrode paste was stirred and mixed in a homogenizer for 30 minutes. This was used as an electrode paste.

  When the particle size distribution of the catalyst particles was measured for the obtained electrode paste, the peak top of the particle size distribution curve was 1 μm or less.

  Further, when performing XPS measurement of the catalyst particles contained in the electrode paste, the influence of the CC signal contained in the solvent occurs when the solvent coexists. Therefore, the solvent contained in the electrode paste was removed to obtain a solid state, and the XPS measurement was performed on the catalyst particles contained in the solid material to obtain the XPS measurement of the catalyst particles contained in the catalyst ink. Specifically, the electrode paste was applied smoothly to a base film such as PTFE on the electrode catalyst, and the solvent was removed by drying at 60 to 100 ° C. or by drying under reduced pressure. Provided. About the obtained solid substance, the peak division of the C (ls) peak was performed from the measurement by X-ray photoelectron spectroscopy (XPS: ESCA-5600 manufactured by PHI). The (CO peak area) / (CC peak area) ratio of the C (ls) peak was 0.05 or more.

  The electrode paste described above as a gas diffusion layer <GDL> is obtained in advance by a screen printing method on one side of carbon paper, and finally obtained a condition that the electrode catalyst layer thickness measured by cutting after hot pressing is 10 μm, Under the conditions, the catalyst slurry was printed and dried at 60 ° C. for 24 hours. The cathode and the electrolyte membrane (Nafion12, thickness: about 50 μm) were joined by hot pressing the surface on which the catalyst layer was applied to the electrolyte membrane at 120 ° C. and 0.1 MPa for 10 minutes.

  Next, the anode was prepared in the same manner as the cathode, and the catalyst layer was bonded to the surface opposite to the cathode bonding surface of the electrolyte membrane to form an electrode (membrane-electrode assembly; MEA). The thickness of the anode and cathode catalyst layers was in the range of 8 to 12 μm for both cells.

In the obtained MEA, the amount of Pt used for both the anode and the cathode was 0.5 mg per 1 cm ^{2 of the} apparent electrode area, and the electrode area was 9 cm ² .

  The obtained MEA was sandwiched between carbon plates provided with gas flow channel grooves to form fuel cells.

  This fuel cell was subjected to a power generation durability test. First, hydrogen was supplied as fuel to the anode side, and air was supplied to the cathode side. The supply pressure for both gases is atmospheric pressure, hydrogen is saturated at 80 ° C and air is 50 ° C, the temperature of the fuel cell body is set to 65 ° C, the hydrogen utilization rate is 50%, and the air utilization rate is 33%. As a driving. The power generation characteristics are shown in FIG.

(Comparative Example 1)
The same treatment as in Example 1 was performed to obtain Pt-supported catalyst particles. A 5% by mass electrolyte polymer solution is added to 9 g of the Pt-supported catalyst particles so that the supported Pt mass and the electrolyte polymer mass are 1: 1, and an alcohol / pure water mixed solution is used so that the viscosity becomes 300 mPa · sec. The mixture was stirred and mixed with a homogenizer for 30 minutes to obtain a paste for a comparative electrode.

  When the particle size distribution of the catalyst particles in the reference electrode paste was measured in the same manner as in Example 1, the peak top of the distribution curve was 1 μm or more. Moreover, about the electrode catalyst in the paste for comparison electrodes obtained similarly, when the peak division of C (ls) peak was performed from the measurement by X-ray photoelectron spectroscopy (XPS), the (C- Peak splitting was performed for the calculation of (O peak area) / (CC peak area), but no significance was found in the peak splitting results.

  Using the comparative electrode paste, an MEA was produced in the same manner as in Example 1, a fuel cell was constructed, and the power generation characteristics were evaluated. The results are shown in FIG. The fuel cell according to the present invention had a higher cell voltage than the fuel cell of the comparative example.

  The fuel cell electrode catalyst ink of the present invention is useful as a fuel cell electrode because the catalyst particles are uniformly dispersed, the three-phase interface is increased, the ion conductivity is excellent, the mass activity is high.

It is a figure which shows the particle size distribution of the catalyst particle | grains of a conventional product and this invention product. It is a figure which shows the CC peak and CO peak which are obtained by the peak division of C (1s) measured by XPS. It is process drawing which manufactures the catalyst ink of this invention. It is the figure which comprised the fuel cell from MEA prepared in Example 1 and Comparative Example 1, and evaluated the electric power generation characteristic.

Claims (10)

  A catalyst metal is applied to a conductive support having a particle size distribution peak of 1 μm or less and a ratio of C—O peak to C—C peak obtained by C (1s) peak division measured by XPS of 5% or more. A fuel cell electrode catalyst ink comprising supported catalyst particles and an electrolyte polymer. A step of dispersing an electrocatalyst carrying a catalytic metal on a conductive support in an H ₂ O ₂ solution, a step of adding a dilute electrolyte polymer to the electrocatalyst and stirring, and a step of increasing the concentration of the electrolyte polymer relative to the catalyst particles A method for producing an electrode catalyst ink for a fuel cell. The _H 2 _{O 2 H} 2 _{O 2} concentrations the solution is 3 to 10 wt%, the manufacturing method of a fuel cell electrode catalyst ink according to claim 2. 4. The method for producing an electrode catalyst ink for a fuel cell according to claim 2, wherein the amount of the H ₂ O ₂ solution added is 100 to 1,000 parts by mass with respect to 1 part by mass of the catalyst particles. The method for producing an electrode catalyst ink for a fuel cell according to any one of claims 2 to 4, wherein the step of dispersing in the H ₂ O ₂ solution is performed at a solution temperature of 30 to 90 ° C.   The manufacturing method of the electrode catalyst ink for fuel cells in any one of Claims 2-5 whose density | concentration of the said diluted electrolyte polymer is 0.1-10 mass%.   The method for producing a fuel cell electrode catalyst ink according to any one of claims 2 to 6, wherein the addition amount of the diluted electrolyte polymer is 0.2 to 0.6 parts by mass with respect to 1 part by mass of the catalyst particles.   A catalyst-carrying electrode prepared from the catalyst ink obtained by the method for producing a fuel cell electrode catalyst ink according to claim 1 or the fuel cell electrode catalyst ink according to any one of claims 2 to 7.   An MEA for a fuel cell comprising a solid polymer electrolyte membrane, a cathode and an anode, and comprising the catalyst-supporting electrode according to claim 8 as a cathode.   A fuel cell using the catalyst-carrying electrode according to claim 8 or the MEA for fuel cell according to claim 9.

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