JP2016143595A - Method for manufacturing electrode catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an electrode catalyst capable of exhibiting high activity.SOLUTION: A method for manufacturing an electrode catalyst including: (1) preparing a precursor mixed liquid containing a platinum precursor, a non-platinum metal precursor, and an aggregation preventing agent; (2) preparing a reducing agent mixed liquid containing a reducing agent and an aggregation preventing agent; (3) obtaining a catalyst particle-containing liquid by adding the reducing agent mixed liquid to the precursor mixed liquid and simultaneously reducing the platinum precursor and the non-platinum metal precursor; and (4) obtaining a catalyst particle supporting carrier by adding a carbon carrier to the catalyst particle-containing liquid.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing an electrode catalyst.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, 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. A fuel cell is a clean power generation system in which the product of an electrode reaction is water in principle and has almost no adverse effect on the global environment. In particular, a polymer electrolyte fuel cell (PEFC) is expected as a power source for electric vehicles because it operates at a relatively low temperature. The polymer electrolyte fuel cell generally has a structure in which an electrolyte membrane-electrode assembly (MEA) is sandwiched between separators. The electrolyte membrane-electrode assembly is formed by sandwiching a polymer electrolyte membrane between a pair of electrode catalyst layers and a gas diffusible electrode (gas diffusion layer; GDL).

In the polymer electrolyte fuel cell having the electrolyte membrane-electrode assembly as described above, both the electrodes (cathode and anode) sandwiching the solid polymer electrolyte membrane are represented by the following reaction formulas according to their polarities. Electrode reaction proceeds to obtain electrical energy. First, hydrogen contained in the fuel gas supplied to the anode (negative electrode) side is oxidized by the catalyst component to become protons and electrons (2H ₂ → 4H ⁺ + 4e ⁻ : reaction 1). Next, the generated protons pass through the solid polymer electrolyte contained in the electrode catalyst layer and the solid polymer electrolyte membrane in contact with the electrode catalyst layer, and reach the cathode (positive electrode) side electrode catalyst layer. In addition, the electrons generated in the anode side electrode catalyst layer include the carbon carrier constituting the electrode catalyst layer, and the gas diffusion layer, separator, and external circuit that are in contact with the electrode catalyst layer on the side different from the solid polymer electrolyte membrane. To reach the cathode side electrocatalyst layer. The protons and electrons that have reached the cathode-side electrode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode side to generate water (O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O: Reaction 2). . In the fuel cell, electricity can be taken out through the above-described electrochemical reaction.

  Here, in order to improve the power generation performance, improvement of the activity of the catalyst particles of the electrode catalyst layer is an important key. Conventionally, it was necessary to use platinum as a catalyst component of an electrode catalyst from the viewpoint of improving activity. However, since platinum is a very expensive and rare metal resource, there is a demand for the development of a platinum alloy catalyst that maintains the activity and reduces the platinum content in the catalyst particles.

  As a method for producing such a platinum alloy catalyst, for example, in Patent Document 1, a noble metal salt solution and a salt solution of an alloy element are added to a suspension of carbon black, and a metal salt is used by using a basic compound. A method is described in which the solution is hydrolyzed and reduced with a reducing agent.

JP 2001-85020 A

  However, in the conventional method, the effective surface area of the catalyst particles is not sufficient, and as a result, the area specific activity is not satisfactory.

  Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing an electrode catalyst that can exhibit high activity.

  The present inventor has intensively studied to solve the above problems. As a result, it has been found that the above problem can be solved by adding an aggregation inhibitor to both the metal precursor solution and the reducing agent solution, and the above problem can be solved.

  According to the present invention, by adding a reducing agent solution to a platinum and non-platinum metal precursor solution containing an anti-aggregation agent, particle size increase of particles containing platinum and non-platinum metal and contact between particles are suppressed. be able to. Therefore, a sufficient catalytic effective surface area can be ensured, and the activity of the catalyst particles can be sufficiently exhibited.

It is a schematic sectional drawing which shows the basic composition of the polymer electrolyte fuel cell which concerns on one Embodiment of this invention.

  In the first embodiment of the present invention, (1) a precursor mixed solution including a platinum precursor, a non-platinum metal precursor, and an anti-aggregation agent is prepared; (2) a reducing agent mixed solution including a reducing agent and an anti-aggregation agent. (3) adding the reducing agent mixture to the precursor mixture and simultaneously reducing the platinum precursor and the non-platinum metal precursor to obtain a catalyst precursor particle-containing solution; (4) And adding a carbon support to the catalyst precursor particle-containing liquid to obtain a catalyst precursor particle-supported support.

  This embodiment is characterized in that an aggregation inhibitor is used for both the metal salt solution and the reducing agent solution when the platinum salt particles are obtained by reducing the metal salt solution with a reducing agent. By such a production method, an electrode catalyst having a high effective catalyst surface area and a high area specific activity can be obtained.

  In the method of simultaneously reducing platinum and non-platinum metal precursors with a reducing agent, the effective surface area of the catalyst particles is not sufficient, and as a result, the area specific activity is not satisfactory. In particular, the present inventor has found that when the production amount is increased, the catalytic activity is remarkably lowered as compared with the case where the production amount is small. When the electrode catalyst is used as a membrane-electrode assembly or further as a fuel cell, a large amount of catalyst needs to be synthesized. For this reason, even if it is a case where it scales up in order to increase a production amount, the manufacturing method which can exhibit high activity is desired.

  The present inventor considered that the reason why the catalytic activity was not sufficiently exhibited was that the nanoparticles produced by the reduction reaction with the reducing agent aggregated and the particle diameter increased. Aggregation of nanoparticles is considered to occur more significantly when the production amount is increased. For this reason, the present invention has been completed by intensive studies on the assumption that the decrease in the activity can be suppressed by suppressing the aggregation of the nanoparticles during the metal reduction reaction. Since colloid formation occurs at the contact portion between metal ions and reducing agent, the presence of an anti-agglomeration agent in both the metal precursor mixture and the reducing agent solution can protect metal nanoparticles more effectively. It is done. As a result, it is possible to significantly reduce the increase in particle size and aggregation due to contact between particles, increase the dispersibility of metal nanoparticles, ensure the effective area of the catalyst particles, and improve the catalyst activity. Presumed.

  In this specification, “X to Y” indicating a range means “X or more and Y or less”. Unless otherwise specified, the operation and physical properties are measured under conditions of room temperature (20 to 25 ° C.) / Relative humidity 40 to 50%.

  Hereinafter, each process of the manufacturing method of 1st embodiment is explained in full detail. However, the present invention is not limited to the following method.

(Step (1) of preparing a precursor mixed solution containing a platinum precursor, a non-platinum metal precursor, and an aggregation inhibitor (hereinafter, also simply referred to as step (1)))
In this step, a mixed solution containing a platinum precursor, a non-platinum metal precursor, and an aggregation inhibitor is prepared.

  The anti-aggregation agent here refers to a compound that prevents aggregation when platinum and non-platinum metal are reduced to form particles.

  The aggregation inhibitor is not particularly limited, but citrate such as sodium citrate and trisodium citrate; citrate hydrate such as trisodium citrate dihydrate; citric acid; polyvinylpyrrolidone Water-soluble polymers such as polyethyleneimine, chitosan, sodium polyacrylate and polyacrylate; sulfur compounds such as decanethiol and hexanethiol; aliphatic quaternary amine salts such as cetyltrimethylammonium bromide and cetyltrimethylammonium chloride Is mentioned.

  Among these, as an anti-aggregation agent, citrate or its hydration is excellent because it has an excellent anti-agglomeration effect and acts as a buffering agent to minimize pH change during the reaction and facilitate the reaction to proceed uniformly. And is more preferably trisodium citrate dihydrate.

  In addition, the said aggregation inhibitor may be used individually by 1 type, or may be used as a 2 or more types of mixture.

  The addition amount of the aggregation inhibitor in the precursor mixed solution is appropriately set so that the effect of preventing aggregation is exhibited, but is 0.5% with respect to 1 mol in total of the platinum precursor and the non-platinum metal precursor. It is preferable that it is -3.0 mol, and it is more preferable that it is 0.8-2.0 mol.

  Moreover, it is preferable that the content weight of the aggregation inhibitor in a precursor liquid mixture is larger than the content weight of the aggregation inhibitor in a reducing agent liquid mixture. By adding a large amount of anti-agglomeration agent in the precursor mixed solution, it becomes possible to sufficiently dispose the anti-aggregation agent around the metal ions before the reaction, and it becomes possible to protect the generated particles more effectively. The weight ratio of the content of the aggregation inhibitor in the precursor mixture and the weight ratio of the aggregation inhibitor in the reducing agent mixture is not particularly limited, but the content of the aggregation inhibitor in the reducing agent mixture: precursor The content of the aggregation inhibitor in the body mixture is preferably 1: 2 to 1:10, more preferably 1: 3 to 1: 8.

  Moreover, it is preferable that the total weight of the aggregation inhibitor in the precursor mixture and the aggregation inhibitor in the reducing agent mixture is 5 to 7 times the weight of the platinum precursor. By setting it as such a range, it becomes possible to arrange | position a coagulation inhibitor fully around a metal ion, and it becomes possible to protect the produced | generated particle | grains more effectively.

Here, the platinum precursor that can be used in this step (1) is not particularly limited, but platinum salts and platinum complexes can be used. More specifically, chloroplatinic acid (typically its hexahydrate; H ₂ [PtCl ₆ ] · 6H ₂ O), nitrates such as dinitrodiammine platinum, sulfates, ammonium salts, amines, tetraammine platinum and Use ammine salts such as hexaammineplatinum, carbonates, bicarbonates, halides such as platinum chloride, inorganic salts such as nitrite and oxalic acid, carboxylates such as formate, hydroxides, alkoxides, etc. Can do. In addition, the said platinum precursor may be used individually by 1 type, or may be used as a 2 or more types of mixture.

  In addition, the non-platinum metal precursor that can be used in this step (1) is not particularly limited, but non-platinum metal salts and non-platinum metal complexes can be used. More specifically, non-platinum metals such as nitrates, sulfates, ammonium salts, amines, carbonates, bicarbonates, halides such as bromides and chlorides, inorganic salts such as nitrites and oxalic acid, formates, etc. And carboxylates, hydroxides, alkoxides, oxides, and the like. That is, a compound in which the non-platinum metal can be converted into a metal ion in a solvent such as pure water is preferable. Of these, halides (particularly chlorides), sulfates and nitrates are more preferred as the non-platinum metal salts. In addition, the said non-platinum metal precursor may be used individually by 1 type, or may be used as a 2 or more types of mixture. The non-platinum metal precursor may be in the form of a hydrate.

Although it does not restrict | limit especially as a non-platinum metal, From a viewpoint of catalyst activity etc., it is preferable that it is a transition metal atom. Here, the transition metal atom refers to a Group 3 element to a Group 12 element, and the type of the transition metal atom is not particularly limited. Catalytic activity, from the viewpoint of forming easiness of L1 ₂ structure, the transition metal atom, vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), copper (Cu) It is preferably selected from the group consisting of zinc (Zn) and zirconium (Zr). Among these, cobalt (Co) is preferable.

  The solvent used for the preparation of the mixed solution containing the platinum precursor, the non-platinum metal precursor and the aggregation inhibitor is not particularly limited, and the kind of the platinum precursor, the non-platinum metal precursor and the aggregation inhibitor used. Is appropriately selected. The form of the mixed solution is not particularly limited, and includes a solution, a dispersion, and a suspension. In view of uniform mixing, the mixed solution is preferably in the form of a solution. Specific examples include water, methanol, ethanol, organic solvents such as 1-propanol and 2-propanol, acids, and alkalis. Among these, water is preferable from the viewpoint of sufficiently dissolving the platinum / non-platinum metal ion compound, and it is particularly preferable to use pure water or ultrapure water. The said solvent may be used independently or may be used with the form of a 2 or more types of mixture.

  The concentration in the mixed liquid of the platinum precursor and the non-platinum metal precursor is not particularly limited, but is preferably 0.1 to 3000 (mg / 100 mL), more preferably 0.5 to 2000 (mg) in terms of metal. / 100 mL). In addition, the density | concentration in the liquid mixture of a platinum precursor and a non-platinum metal precursor may be the same, or may differ.

  In addition, the mixing ratio of the platinum precursor and the non-platinum metal precursor is not particularly limited, but is preferably a mixing ratio that can achieve the alloy composition as described above. Specifically, the non-platinum metal precursor is in a proportion of 0.4 to 20 mol, more preferably 0.4 to 18 mol, and particularly preferably 0.5 to 15 mol with respect to 1 mol of the platinum precursor ( It is preferable to mix by metal conversion. With such a mixing ratio, the ratio of platinum atoms and non-platinum metal atoms in the catalyst particles can be appropriately controlled to improve the catalytic activity.

  In the step (1), the method for preparing the mixed solution containing the platinum precursor, the non-platinum metal precursor and the aggregation preventing agent is not particularly limited. For example, after adding an anti-agglomeration agent to the solvent, a platinum precursor and a non-platinum metal precursor are added to the solvent; after adding the anti-agglomeration agent to the solvent, the platinum precursor is dissolved in the solvent and added to the non-platinum Add a metal precursor; after adding an anti-agglomeration agent to the solvent, dissolve the non-platinum metal precursor in the solvent and add the platinum precursor to it; an anti-agglomeration agent, a platinum precursor and a non-platinum metal precursor These may be separately dissolved in a solvent and then mixed; any method of adding an aggregation inhibitor, a platinum precursor and a non-platinum metal precursor to the solvent and mixing them together may be used. Since the aggregation inhibitor can be dissolved in the solution in advance and the aggregation inhibitor can be efficiently arranged around the metal ions, the platinum precursor and the non-platinum metal precursor are added after the aggregation inhibitor is added to the solvent. A method of adding to a solvent is preferred.

  Moreover, it is preferable to stir in order for the said liquid mixture to mix uniformly. Here, the stirring conditions are not particularly limited as long as they can be mixed uniformly. For example, the mixture can be uniformly dispersed and mixed by using an appropriate stirrer such as a stirrer or a homogenizer, or by applying ultrasonic waves such as an ultrasonic dispersing device. Moreover, what is necessary is just to set suitably as stirring time so that an aggregation inhibitor may melt | dissolve in a solvent completely, and it is 1 to 90 minutes normally, Preferably it is 10 to 60 minutes.

  As will be described later, since the solution temperature of the precursor mixed solution at the time of reduction is preferably 20 ° C. or lower, the solution temperature of the precursor mixed solution in step (1) is 20 ° C. or lower, more preferably 10 ° C. It is preferable to make it less than ° C. When the solution temperature exceeds 20 ° C, it is necessary to cool to 20 ° C or lower. The solution temperature may be 20 ° C. or lower at any stage of the step (1), but the condition that the solution temperature is 20 ° C. or lower after adding the anti-aggregating agent to the solvent to make the anti-aggregating agent solution 20 ° C. or lower. Below, it is preferred to add a platinum precursor and a non-platinum metal precursor to the solvent. In addition, the solution temperature of the precursor liquid mixture in a process (1) should just be the temperature used as a solution state, and a minimum is not specifically limited.

(Step (2) of preparing a reducing agent mixed solution containing a reducing agent and an anti-aggregation agent (hereinafter also simply referred to as step (2)))
In this step, a reducing agent mixed solution containing a reducing agent and an aggregation inhibitor is prepared.

  As used herein, the anti-aggregation agent refers to a compound that prevents aggregation when platinum and non-platinum metal are reduced to particles as in the anti-aggregation agent used in step (1).

  Specific examples of the aggregation inhibitor used in the step (2) are the same as those described in the column of the step (1). The aggregation inhibitor used in step (2) may be the same as or different from the aggregation inhibitor used in step (1), but the aggregation inhibitor used in step (2) may be different. The agent is preferably the same as the aggregation preventing agent used in step (1). Among them, the anti-aggregation agent used in step (2) is excellent in anti-aggregation effect and can also act as a buffer, minimizing changes in the solution pH due to the reaction, and the reaction can easily proceed uniformly. Therefore, citrate or a hydrate thereof is preferable, and trisodium citrate dihydrate is more preferable. In the case of a citrate salt or a hydrate thereof, when a borohydride compound that is a suitable reducing agent is used, it is weakly alkaline by making it into an aqueous solution, and the lifetime of the reducing ability of the borohydride compound is increased. Since the role of extending can also be played, it is preferable.

In the present invention, the reducing agent is a reducing agent that can reduce both platinum atoms and non-platinum metal atoms (preferably transition metal atoms). Moreover, as a reducing agent, it is preferable that it is a reducing agent which shows a reducing action at 30 degrees C or less, Preferably it is 20 degrees C or less. Examples of such a reducing agent include sodium borohydride (NaBH ₄ ), calcium borohydride (Ca (BH ₄ ) ₂ ), lithium borohydride (LiBH ₄ ), and aluminum borohydride (Al (BH _{4). 3} ), borohydride compounds such as magnesium borohydride (Mg (BH ₄ ) ₂ ); lower alcohols such as ethanol, methanol, propanol; formates such as formic acid, sodium formate and potassium formate; sodium thiosulfate, and Hydrazine (N ₂ H ₄ ) or the like can be used. These may be in the form of hydrates. Moreover, the said reducing agent may be used individually by 1 type, or may be used as a 2 or more types of mixture. Citrate, for example, trisodium citrate dihydrate, is a platinum reducing agent, but is not included in the reducing agent in the present invention because it cannot reduce transition metal atoms. Among these, from the viewpoint of reducing action, it is preferable to use a borohydride compound as a reducing agent, and it is more preferable to use sodium borohydride.

  The solvent used for the preparation of the mixed solution containing the reducing agent and the aggregation preventing agent is not particularly limited, and is appropriately selected depending on the type of the reducing agent and the aggregation preventing agent used. The form of the mixed solution is not particularly limited, and includes a solution, a dispersion, and a suspension. In view of uniform mixing, the mixed solution is preferably in the form of a solution. Further, it is preferable to add the reducing agent in the solution state to the metal salt solution because the reaction rate becomes uniform in the mixed solution and the particle diameter tends to be uniform rather than adding the powdery reducing agent.

  Specific examples of the solvent include water, organic solvents such as methanol, ethanol, 1-propanol, and 2-propanol, acids, and alkalis. Among these, water is preferable from the viewpoint of sufficiently dissolving the reducing agent and the aggregation inhibitor, and it is particularly preferable to use pure water or ultrapure water. The said solvent may be used independently or may be used with the form of a 2 or more types of mixture. Note that the solvent used for the reducing agent solution and the solvent used for the preparation of the mixed solution are not necessarily the same, but are preferably the same in consideration of uniform mixing properties.

  As will be described later, since the solution temperature of the precursor mixture at the time of reduction is preferably 20 ° C. or less, the solution temperature of the mixture in step (2) is 20 ° C. or less, more preferably less than 10 ° C. It is preferable that When solution temperature exceeds 20 degreeC, it is preferable to cool to 20 degrees C or less. The solution temperature may be 20 ° C. or lower in any stage of the step (2), but the condition that the solution temperature is 20 ° C. or lower after adding the anti-aggregating agent to the solvent to make the anti-aggregating agent solution 20 ° C. or lower. Under, it is preferred to add the reducing agent to the solvent. In addition, the solution temperature of the precursor liquid mixture in a process (2) should just be the temperature used as a solution state, and a minimum is not specifically limited.

  In the step (2), the method for preparing the reducing agent mixed solution containing the reducing agent and the aggregation preventing agent is not particularly limited. For example, after adding the anti-aggregation agent to the solvent, the reducing agent is added to the solvent; the anti-aggregation agent and the reducing agent are separately dissolved in the solvent, and then mixed together; Any method of adding to a solvent may be used. In order to exhibit the effect of the aggregation inhibitor more effectively, it is preferable to add the reducing agent to the solvent after adding the aggregation inhibitor to the solvent.

  Moreover, when using the borohydride compound which is a suitable reducing agent as a reducing agent, it is preferable to add a borohydride compound to the aggregation inhibitor solution adjusted to pH 8.5-10. That is, a preferred embodiment of the present invention is an electrode catalyst comprising: adding a borohydride compound to an agglomeration inhibitor solution whose reducing agent is a borohydride compound and having a pH adjusted to 8.5-10. It is a manufacturing method. By controlling the reducing agent aqueous solution to such a pH, the reducing ability of the boron hydride compound, which is the reducing agent, is secured, while the alloy metal, which is the base metal, is prevented from precipitating as an oxide, thereby forming alloy particles. This is preferable. As the pH adjuster used for setting and adjusting the pH within the above range, known acids, bases, or salts thereof can be used. Examples of acids that can be used as a pH adjuster include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, boric acid, carbonic acid, hypophosphorous acid, phosphorous acid, and phosphoric acid, formic acid, acetic acid, and propionic acid. , Butyric acid, pentanoic acid, 2-methylbutyric acid, hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylpentanoic acid, heptanoic acid, 2-methylhexanoic acid, octanoic acid, 2-ethylhexanoic acid, Benzoic acid, hydroxyacetic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, citric acid, lactic acid, diglycolic acid, 2 -Furan carboxylic acid, 2,5-furandicarboxylic acid, 3-furan carboxylic acid, 2-tetrahydrofuran carboxylic acid, methoxyacetic acid, methoxyphenylacetic acid, And phenoxy organic acids such as acetic acid. Bases that can be used as pH adjusters include amines such as aliphatic amines and aromatic amines, organic bases such as quaternary ammonium hydroxide, hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide, and group 2 Examples thereof include elemental hydroxides and ammonia.

  The mixed solution is preferably stirred in order to mix uniformly. Here, the stirring conditions are not particularly limited as long as they can be mixed uniformly. For example, the mixture can be uniformly dispersed and mixed by using an appropriate stirrer such as a stirrer or a homogenizer, or by applying ultrasonic waves such as an ultrasonic dispersing device. Moreover, what is necessary is just to set suitably so that dispersion | distribution may fully be performed as stirring time, and it is 0.5-60 minutes normally, Preferably it is 1-40 minutes.

(Step (3) of adding a reducing agent mixture to the precursor mixture and simultaneously reducing the platinum precursor and the non-platinum metal precursor to obtain a catalyst particle-containing solution (hereinafter also simply referred to as Step (3)) )
In the step (3), the reducing agent mixed solution obtained in the step (2) is added to the precursor mixed solution prepared in the step (1) to contain catalyst particles (platinum-non-platinum metal mixed particles). Obtain a liquid. By this step, platinum ions derived from the platinum precursor and non-platinum metal ions derived from the non-platinum precursor can be reduced simultaneously, and catalyst particles (intermetallic compound of platinum and non-platinum metal) can be obtained.

  Thus, by subjecting platinum and non-platinum metal to reduction precipitation simultaneously, the target product can be obtained in a state where platinum and non-platinum metal are uniformly mixed. Thus, by simultaneously reducing platinum ions and non-platinum metal ions, catalyst particles having many highly active crystal faces exposed can be obtained.

  The addition amount of the reducing agent is not particularly limited as long as it is an amount sufficient to reduce metal ions. Specifically, the addition amount of the reducing agent is preferably 1 to 10 moles, more preferably 1.10 moles per mole of metal ions (total moles of platinum ions and non-platinum metal ions (metal conversion)). 5-7 moles. With such an amount, metal ions (platinum ions and non-platinum ions) can be sufficiently reduced simultaneously. In addition, when using 2 or more types of reducing agents, it is preferable that these total addition amount is the said range.

  The solution temperature of at least one of the precursor mixture and the reducing agent mixture when the reducing agent mixture is added to the precursor mixture is preferably 20 ° C. or less, and more preferably less than 10 ° C. By setting the solution temperature to 20 ° C. or lower, it is possible to reduce the collision frequency between the generated catalyst particles, and aggregation is less likely to occur. In order to further exhibit the effect of reducing the collision frequency during particle generation, at least the solution temperature of the precursor mixed solution is preferably 20 ° C. or less, and more preferably less than 10 ° C. The solution temperature of the precursor mixed solution and the reducing agent mixed solution when the reducing agent mixed solution is added to the precursor mixed solution may be a temperature at which the solution is brought into a solution state, and the lower limit is not particularly limited.

  It is preferable to stir after adding the reducing agent mixture. Thereby, since a platinum precursor, a non-platinum metal precursor, and a reducing agent are mixed uniformly, a uniform reduction reaction becomes possible. Here, the stirring conditions are not particularly limited as long as they can be mixed uniformly. For example, the mixture can be uniformly dispersed and mixed by using an appropriate stirrer such as a stirrer or a homogenizer, or by applying ultrasonic waves such as an ultrasonic dispersing device. Also, the stirring temperature is preferably 20 ° C. or lower, more preferably 0 ° C. or higher and lower than 10 ° C., similarly to the temperature at the time of addition. The stirring time is not particularly limited as long as the platinum precursor, the non-platinum metal precursor, and the reducing agent can be uniformly mixed, but is usually 1 to 60 minutes, and preferably 5 to 40 minutes.

  Catalyst particles are obtained by the reduction reaction. Here, if necessary, the catalyst particles may be isolated from the catalyst particle-containing liquid. Here, the isolation method is not particularly limited, and the catalyst particles may be filtered and dried. If necessary, the catalyst particles may be filtered and then washed (for example, washed with water). Further, the filtration and the washing step may be repeated if necessary. Further, the catalyst particles may be dried after filtration or washing. Here, drying of the catalyst particles may be performed in air or may be performed under reduced pressure. Moreover, although drying temperature is not specifically limited, For example, it can carry out in 10-100 degreeC, Preferably it is room temperature (25 degreeC)-about 80 degreeC. Also, the drying time is not particularly limited, but for example, it can be performed in the range of 1 to 60 hours, preferably about 5 to 50 hours.

(Step (4) of obtaining a catalyst particle-supporting carrier by adding a carbon carrier to the catalyst particle-containing liquid (hereinafter, also simply referred to as step (4)))
In this step, a carbon carrier is added to the catalyst particle-containing liquid obtained in the step (3) to obtain a catalyst particle-supported carrier.

  Specifically, a carbon carrier is put into a catalyst particle-containing liquid which is a dispersion of catalyst particles, and the catalyst particles are adsorbed on the carbon carrier by stirring. Thereafter, the carbon carrier on which the catalyst particles are adsorbed is filtered and washed to obtain a catalyst particle-supported carrier carrying the catalyst particles.

  The carbon carrier functions as a carrier for supporting the catalyst particles and an electron conduction path involved in the exchange of electrons between the catalyst particles and other members. Any carbon carrier may be used as long as it has a specific surface area for supporting the catalyst particles in a desired dispersed state and has sufficient electronic conductivity as a current collector. The main component is carbon. Is preferred. “The main component is carbon” means that the main component contains carbon atoms, and is a concept that includes both carbon atoms and substantially carbon atoms. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by weight or less is allowed.

The BET specific surface area of the carbon support may be a specific surface area sufficient to support highly dispersed catalyst particles, but is preferably 10 to 5000 m ² / g, more preferably 50 to 2000 m ² / g. . With such a specific surface area, sufficient catalyst particles are supported (highly dispersed) on the carbon support, and sufficient power generation performance can be achieved. The “BET specific surface area (m ² / g carrier)” of the carrier is measured by a nitrogen adsorption method.

  Further, the size of the carbon support is not particularly limited, but from the viewpoints of easy loading, catalyst utilization, and control of the electrode catalyst layer thickness within an appropriate range, the average particle size is preferably 5 to 200 nm, preferably Is preferably about 10 to 100 nm. The “average particle size of the carrier” is the average of the crystallite size obtained from the half-value width of the diffraction peak of the carrier particle in X-ray diffraction (XRD), or the average particle size of the carrier examined by a transmission electron microscope (TEM). It can be measured as a value. In the present specification, the “average particle diameter of the carrier” is an average value of the particle diameter of the carrier particles examined from a transmission electron microscope image of a statistically significant number (for example, at least 200) of samples. Here, the “particle diameter” means the maximum distance among the distances between any two points on the particle outline.

  Specific examples of the carbon carrier include carbon blacks such as acetylene black, channel black, oil furnace black, gas furnace black (for example, Vulcan), lamp black, thermal black, ketjen black (registered trademark); black pearl; Graphitized Acetylene Black; Graphitized Channel Black; Graphitized Oil Furnace Black; Graphitized Gas Furnace Black; Graphitized Lamp Black; Graphitized Thermal Black; Graphitized Ketjen Black; Graphitized Black Pearl; Carbon Nanotubes; Carbon nanohorn; carbon fibril; activated carbon; coke; natural graphite; artificial graphite. Further, examples of the carbon carrier include zeolite-templated carbon (ZTC) having a structure in which nano-sized band-shaped graphene is regularly connected in a three-dimensional manner.

The carbon support preferably has at least one functional group selected from the group consisting of a lactone group, a hydroxyl group, an ether group, and a carbonyl group on the surface in a total amount of 0.5 μmol / m ² or more, preferably 0 A carbon support having 8 to 5 μmol / m ² . By using such a carbon support, the activity (particularly the area specific activity) can be further improved. This is considered to be because aggregation of the alloy particles can be suppressed and a decrease in the specific surface area of the entire supported catalyst particles can be suppressed.

The value measured by the temperature programmed desorption method is adopted as the method for measuring the functional group amount. The temperature programmed desorption method is a technique in which a sample is heated at a constant speed under an ultra-high vacuum and gas components (molecules / atoms) released from the sample are detected in real time by a quadrupole mass spectrometer. The temperature at which a gas component is released depends on the adsorption / chemical binding state of that component on the sample surface, ie, components that require large energy for desorption / dissociation are detected at relatively high temperatures. The surface functional groups formed on the carbon are discharged as CO or CO ₂ at different temperatures depending on the type. The temperature-programmed desorption curve obtained for CO or CO ₂ is peak-separated, the integrated intensity T of each peak is measured, and the amount (μmol) of each functional group component can be calculated from the integrated intensity T. From this amount (μmol), the functional group amount is calculated by the following formula.

Desorption gas and temperature due to temperature rise of each functional group are as follows; lactone group CO ₂ (700 ° C.), hydroxyl group CO (650 ° C.), ether group CO (700 ° C.), carbonyl group CO (800 ° C.) .

  Moreover, in this invention, the value measured with the following apparatus and conditions is employ | adopted.

Apparatus: Electronic Science Co., Ltd. WA1000S / W)
Sample chamber vacuum degree: 10 ⁻⁷ to 10 ⁻⁸ Pa order Heating method: infrared ray Temperature rising rate: 60 ° C./min
The method for producing a carbon carrier having a specific functional group is not particularly limited. For example, the carbon materials listed above as a carbon carrier are brought into contact with an acidic solution (hereinafter, this treatment is also referred to as acid treatment). Vapor activation treatment; vapor phase oxidation treatment (ozone, fluorine gas, etc.); liquid phase oxidation treatment (permanganic acid, chloric acid, ozone water, etc.), etc.

  Hereinafter, the acid treatment which is a preferable form will be described.

  Although it does not specifically limit as an acid used for an acidic solution, Hydrochloric acid, a sulfuric acid, nitric acid, perchloric acid etc. can be mentioned. Among these, from the viewpoint of surface functional group formation, it is preferable to use at least one of sulfuric acid and nitric acid.

  The carbon material to be brought into contact with the acidic solution is not particularly limited, but carbon black is preferable because it has a large specific surface area and is stable even by acid treatment.

  The acid treatment may be repeated not only when the carrier is brought into contact with the acidic solution once, but also multiple times. Moreover, when performing acid treatment in multiple times, you may change the kind of acidic solution for every process. The concentration of the acidic solution is appropriately set in consideration of the carbon material, the type of acid, etc., but is preferably 0.1 to 10 mol / L.

  The method of bringing the carbon material into contact with the acidic solution (acid treatment method) is not particularly limited, but the step of preparing the carbon material dispersion by mixing the carbon material with the acidic solution (step X), and the carbon material dispersion It is preferable to include a step (step Y) of applying a functional group to the surface of the carbon material by heating. That is, a preferred embodiment of the present invention can be obtained by performing a heat treatment after the carbon support is brought into contact with an acidic solution.

  In the step X, it is preferable to mix a carbon material into the acidic solution. Moreover, it is preferable to stir the carbon material dispersion in order to mix it sufficiently uniformly. Here, the stirring conditions are not particularly limited as long as they can be mixed uniformly. For example, the mixture can be uniformly dispersed and mixed by using an appropriate stirrer such as a stirrer or a homogenizer, or by applying ultrasonic waves such as an ultrasonic dispersing device. In Step X, the stirring temperature is preferably 5 to 40 ° C. Moreover, what is necessary is just to set suitably so that dispersion | distribution may fully be performed as stirring time, and it is 1 to 60 minutes normally, Preferably it is 3 to 30 minutes.

  Moreover, in the said process Y, the carbon material dispersion liquid prepared at the process X is heated, and a functional group is provided to the surface of a carbon material. Here, the heating condition is not particularly limited as long as the functional group can be imparted to the surface of the carbon material. For example, the heating temperature is preferably 60 to 90 ° C. The heating time is preferably 1 to 4 hours. Under such conditions, sufficient functional groups can be imparted to the surface of the carbon material.

  Thereafter, it is also preferable to perform cleaning, and the cleaning may be performed a plurality of times. It is preferable to dry after washing. In this way, an acid-treated carbon carrier (a carbon carrier having a specific functional group) can be obtained.

  The acid-treated carbon carrier (carbon carrier having a specific functional group) may be added to a suitable solvent (for example, ultrapure water) to form a suspension. This suspension is preferably stirred until mixed with the catalyst particle-containing liquid.

  The mixing ratio of the catalyst particles and the carbon support is not particularly limited, but is preferably an amount such that the supported concentration (supported amount) of the catalyst particles is 2 to 70% by weight with respect to the total amount of the electrode catalyst. . It is preferable to set the support concentration in such a range because aggregation of the catalyst particles is suppressed and an increase in the thickness of the electrode catalyst layer can be suppressed. The supported concentration is more preferably 5 to 60% by weight, even more preferably more than 5% by weight and 50% by weight or less.

  Further, it is preferable to stir after adding the carbon support to the catalyst particle-containing liquid. Thus, since the catalyst particles and the carbon support are uniformly mixed, the catalyst particles can be highly dispersed and supported on the carbon support. Moreover, since the reduction reaction of the unreduced platinum precursor and the non-platinum metal precursor with the reducing agent occurs simultaneously by the stirring treatment, it is possible to further promote the high dispersion and loading of the catalyst particles on the carbon support. . Here, the stirring conditions are not particularly limited as long as they can be mixed uniformly. For example, the mixture can be uniformly dispersed and mixed by using an appropriate stirrer such as a stirrer or a homogenizer, or by applying ultrasonic waves such as an ultrasonic dispersing device. The stirring temperature is preferably 0 to 50 ° C, more preferably 5 to 40 ° C. The stirring time is preferably 1 to 90 hours, more preferably 5 to 80 hours. Under such conditions, the catalyst particles can be highly dispersed and supported by the carbon support. Further, since the unreduced platinum precursor or non-platinum metal precursor can be further reduced with a reducing agent, the catalyst particles can be efficiently dispersed and supported by the carbon carrier. In addition, the carbon carrier may be added to the catalyst particle-containing liquid by adding only the carbon carrier or as a suspension as described above.

  By the above-described supporting treatment, a carbon support (catalyst particle support support or support support) on which catalyst particles are supported is obtained. Here, if necessary, this carrier may be isolated. Here, the isolation method is not particularly limited, and the supported carrier may be filtered and dried. If necessary, the supported carrier may be filtered and then washed (for example, washed with water). Further, the filtration and the washing step may be repeated if necessary. Further, after the filtration or washing, the supported carrier may be dried. Here, the support carrier may be dried in air or under reduced pressure. Moreover, although drying temperature is not specifically limited, For example, it can carry out in the range of about 10-100 degreeC, More preferably, room temperature (25 degreeC)-about 80 degreeC. Also, the drying time is not particularly limited, but is, for example, 1 to 60 hours, preferably 5 to 48 hours.

  In the above, the catalyst particles are supported on the carbon support by the impregnation method, but the present invention is not limited to the above method. In addition to the above methods, known methods such as a liquid phase reduction support method, an evaporation to dryness method, a colloid adsorption method, a spray pyrolysis method, and a reverse micelle (microemulsion method) can be used. However, in the present invention, any method is used for simultaneous reduction.

  The electrode catalyst thus obtained can ensure a catalyst effective surface area and exhibit high activity (area specific activity) even with a small platinum content.

  Moreover, you may further have the heat processing process which heat-processes the electrode catalyst obtained at the said process (4). The catalytic activity can be improved by appropriately selecting the heat treatment conditions (heat treatment temperature and heat treatment time).

  Specifically, when the heat treatment temperature is 350 to 450 ° C., the heat treatment is preferably performed for a time exceeding 120 minutes, more preferably 240 minutes or more.

  The upper limit of the heat treatment time at the heat treatment temperature is not particularly limited as long as it is a temperature at which the catalyst particles can be supported on the carbon support, and is appropriately selected depending on the particle size and type of the catalyst particles. For example, the heat treatment time is usually 36 hours or less, preferably 24 hours or less, more preferably 10 hours or less, and even more preferably 5 hours or less.

The heat treatment atmosphere when the heat treatment temperature is 350 to 450 ° C. is not particularly limited, but the heat treatment is to suppress and prevent oxidation of the alloy (platinum and non-platinum metal) and / or reduction to platinum or non-platinum metal. It is preferable to carry out in a non-oxidizing atmosphere in order to further advance the process. Examples of the non-oxidizing atmosphere include an inert gas atmosphere and a reducing gas atmosphere. Here, the inert gas is not particularly limited, but helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), nitrogen (N ₂ ), and the like can be used. The said inert gas may be used independently or may be used with the form of 2 or more types of mixed gas. The reducing gas atmosphere is not particularly limited as long as the reducing gas is contained, but a mixed gas atmosphere of the reducing gas and the inert gas is more preferable. Here, the reducing gas is not particularly limited, but hydrogen (H ₂ ) gas and carbon monoxide (CO) gas are preferable. Further, the concentration of the reducing gas contained in the inert gas is not particularly limited, but the content of the reducing gas in the inert gas is preferably 10 to 100% by volume, more preferably 50 to 100% by volume. It is. With such a concentration, the oxidation of the alloy (platinum and non-platinum metal) can be sufficiently suppressed / prevented. Among the above, the heat treatment is preferably performed in a reducing gas atmosphere. Under such conditions, an increase in catalyst particle diameter can be suppressed.

  When the heat treatment temperature is higher than 450 ° C. and lower than or equal to 750 ° C., the heat treatment is preferably performed for 10 minutes or longer, more preferably for 20 minutes or longer. The upper limit of the heat treatment time at the heat treatment temperature is not particularly limited as long as it is a temperature at which the catalyst particles can be supported on the carbon support, and is appropriately selected depending on the particle size and type of the catalyst particles. For example, the heat treatment time is usually 36 hours or less, preferably 24 hours or less, more preferably 10 hours or less, and even more preferably 5 hours or less.

  The heat treatment atmosphere when the heat treatment temperature is higher than 450 ° C. and lower than 750 ° C. is not particularly limited, but the heat treatment is performed to suppress and prevent oxidation of the alloy (platinum and non-platinum metal) and / or platinum or non-platinum metal. In order to make the reduction to more proceed, it is preferably performed in a non-oxidizing atmosphere. Here, since the non-oxidizing atmosphere has the same definition as that in the case where the heat treatment temperature is 350 to 450 ° C. or lower, description thereof is omitted here. Among the above, the heat treatment is preferably performed in an inert gas atmosphere or a reducing gas atmosphere. Under such conditions, the catalyst particles can be prevented from aggregating on the carrier, and an increase in the catalyst particle diameter can be suppressed.

  Furthermore, when the heat treatment temperature exceeds 750 ° C., it is preferable to perform the heat treatment in a reducing gas atmosphere for 10 to 45 minutes, more preferably 20 to 40 minutes. Alternatively, when the heat treatment temperature exceeds 750 ° C., the heat treatment is performed in an inert gas atmosphere for 10 to 120 minutes, more preferably 30 to 100 minutes, particularly preferably more than 45 minutes and 90 minutes or less. It is preferable.

  The upper limit of the heat treatment temperature is not particularly limited as long as it is a temperature at which the catalyst particles can be supported on the carbon support, and is appropriately selected depending on the particle size and type of the catalyst particles. Further, the particle diameter tends to increase due to sintering in proportion to the temperature and time during the heat treatment. Considering the above points, for example, the heat treatment temperature may be 1000 ° C. or less. Under such conditions, an increase in the catalyst particle diameter can be suppressed, and further aggregation of the obtained catalyst particles (alloy particles) on the carrier can be suppressed. In the above, “inert gas atmosphere” and “reducing gas atmosphere” have the same definitions as those in the case where the heat treatment temperature is 350 to 450 ° C. or less, and thus the description thereof is omitted here. Under such conditions, the catalyst particles can be prevented from aggregating on the carrier, and an increase in the catalyst particle diameter can be suppressed.

  From the above, according to a preferred embodiment of the present invention, the heat treatment of the catalyst particle-supported carrier is performed in (a) a reducing gas atmosphere or an inert gas atmosphere at a temperature of 350 to 450 ° C. for a time exceeding 120 minutes. (B) performed at a temperature of 450 ° C. or higher and 750 ° C. or lower for 10 minutes or more in a reducing gas atmosphere or an inert gas atmosphere; (c) at a temperature of 750 ° C. or higher in an inert gas atmosphere; For 10 to 120 minutes; or (d) for 10 to 45 minutes at a temperature exceeding 750 ° C. in a reducing gas atmosphere.

  The electrode catalyst obtained by the production method described above can be suitably used for an electrolyte membrane-electrode assembly (MEA) and a fuel cell. That is, the present invention also provides an electrolyte membrane-electrode assembly (MEA) containing the electrode catalyst obtained by the above production method, and a fuel cell containing the electrolyte membrane-electrode assembly (MEA).

[Fuel cell]
A fuel cell comprises a pair of separators comprising an electrolyte membrane-electrode assembly (MEA), an anode side separator having a fuel gas flow path through which fuel gas flows, and a cathode side separator having an oxidant gas flow path through which oxidant gas flows. And have. The fuel cell of the present invention is excellent in durability and can exhibit high power generation performance.

  Hereinafter, an embodiment of the catalyst particles of the present invention, and an embodiment of an electrode, an electrolyte membrane-electrode assembly (MEA) and a fuel cell using the same will be described in detail with reference to the drawings as appropriate. However, the present invention is not limited only to the following embodiments. Each drawing is exaggerated for convenience of explanation, and the dimensional ratio of each component in each drawing may be different from the actual one. Further, in the case where the embodiment of the present invention is described with reference to the drawings, the same reference numerals are given to the same elements in the description of the drawings, and redundant description is omitted.

  FIG. 1 is a schematic diagram showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 according to an embodiment of the present invention. The PEFC 1 first includes a solid polymer electrolyte membrane 2 and a pair of catalyst layers (an anode catalyst layer 3a and a cathode catalyst layer 3c) that sandwich the membrane. The laminate of the solid polymer electrolyte membrane 2 and the catalyst layers (3a, 3c) is further sandwiched between a pair of gas diffusion layers (GDL) (anode gas diffusion layer 4a and cathode gas diffusion layer 4c). Thus, the polymer electrolyte membrane 2, the pair of catalyst layers (3a, 3c), and the pair of gas diffusion layers (4a, 4c) constitute an electrolyte membrane-electrode assembly (MEA) 10 in a stacked state. To do.

  In PEFC1, the MEA 10 is further sandwiched between a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 1, the separators (5 a, 5 c) are illustrated so as to be positioned at both ends of the illustrated MEA 10. However, in a fuel cell stack in which a plurality of MEAs are stacked, the separator is generally used as a separator for an adjacent PEFC (not shown). In other words, in the fuel cell stack, the MEAs are sequentially stacked via the separator to form a stack. In an actual fuel cell stack, a gas seal portion is disposed between the separator (5a, 5c) and the solid polymer electrolyte membrane 2, or between the PEFC 1 and another adjacent PEFC. These descriptions are omitted in FIG.

  The separators (5a, 5c) are obtained, for example, by forming a concavo-convex shape as shown in FIG. 1 by subjecting a thin plate having a thickness of 0.5 mm or less to a press treatment. The convex part seen from the MEA side of the separator (5a, 5c) is in contact with the MEA 10. Thereby, the electrical connection with MEA10 is ensured. Further, a recess (space between the separator and the MEA generated due to the concavo-convex shape of the separator) viewed from the MEA side of the separator (5a, 5c) is a gas for circulating gas during operation of the PEFC 1 Functions as a flow path. Specifically, a fuel gas (for example, hydrogen) is circulated through the gas flow path 6a of the anode separator 5a, and an oxidant gas (for example, air) is circulated through the gas flow path 6c of the cathode separator 5c.

  On the other hand, the recess viewed from the side opposite to the MEA side of the separator (5a, 5c) serves as a refrigerant flow path 7 for circulating a refrigerant (for example, water) for cooling the PEFC during operation of the PEFC 1. . Further, the separator is usually provided with a manifold (not shown). This manifold functions as a connection means for connecting cells when a stack is formed. With such a configuration, the mechanical strength of the fuel cell stack can be ensured.

  In addition, in embodiment shown in FIG. 1, the separator (5a, 5c) is shape | molded by the uneven | corrugated shape. However, the separator is not limited to such a concavo-convex shape, and may be any form such as a flat plate shape and a partially concavo-convex shape as long as the functions of the gas flow path and the refrigerant flow path can be exhibited. Also good.

  The fuel cell having the MEA of the present invention as described above exhibits excellent power generation performance. Here, the type of the fuel cell is not particularly limited. In the above description, the solid polymer fuel cell has been described as an example. However, in addition to the above, an alkaline fuel cell and a direct methanol fuel cell are used. And a micro fuel cell. Among them, a polymer electrolyte fuel cell (PEFC) is preferable because it is small and can achieve high density and high output. The fuel cell is useful as a stationary power source in addition to a power source for a moving body such as a vehicle in which a mounting space is limited. Among them, it is particularly preferable to use as a power source for a mobile body such as an automobile that requires a high output voltage after a relatively long time of operation stop.

  The fuel used when operating the fuel cell is not particularly limited. For example, hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, diethylene glycol and the like can be used. Of these, hydrogen and methanol are preferably used in that high output is possible.

  Further, the application application of the fuel cell is not particularly limited, but it is preferably applied to a vehicle. The electrolyte membrane-electrode assembly of the present invention is excellent in power generation performance and durability, and can be downsized. For this reason, the fuel cell of this invention is especially advantageous when this fuel cell is applied to a vehicle from the point of in-vehicle property.

[Electrolyte membrane-electrode assembly (MEA)]
The electrode catalyst described above can be suitably used for an electrolyte membrane-electrode assembly (MEA). That is, the second embodiment of the present invention is an electrolyte membrane-electrode assembly (MEA) including an electrode catalyst manufactured by the manufacturing method of the first embodiment, particularly an electrolyte membrane-electrode assembly (MEA) for fuel cells. is there. The electrolyte membrane-electrode assembly (MEA) of the second embodiment can exhibit high power generation performance and durability.

  The electrolyte membrane-electrode assembly (MEA) of the second embodiment has the same configuration except that the electrode catalyst (catalyst) obtained by the production method of the first embodiment is used instead of the conventional electrode catalyst. it can. Although the preferable form of MEA of this invention is demonstrated below, this invention is not limited to the following form.

  The MEA is composed of an electrolyte membrane, an anode catalyst layer and an anode gas diffusion layer, a cathode catalyst layer and a cathode gas diffusion layer which are sequentially formed on both surfaces of the electrolyte membrane. In this electrolyte membrane-electrode assembly, the electrode catalyst obtained by the production method of the first embodiment is used for at least one of the cathode catalyst layer and the anode catalyst layer.

(Electrolyte membrane)
The electrolyte membrane is composed of, for example, a solid polymer electrolyte membrane. For example, the solid polymer electrolyte membrane has a function of selectively allowing protons generated in the anode catalyst layer during operation of a fuel cell (such as PEFC) to permeate the cathode catalyst layer along the film thickness direction. The solid polymer electrolyte membrane also has a function as a partition for preventing the fuel gas supplied to the anode side and the oxidant gas supplied to the cathode side from being mixed.

  It does not specifically limit as electrolyte material which comprises a solid polymer electrolyte membrane, A conventionally well-known knowledge can be referred suitably. For example, the fluorine-based polymer electrolyte and the hydrocarbon-based polymer electrolyte described as the polymer electrolyte in the following catalyst layer can be used in the same manner. At this time, it is not always necessary to use the same polymer electrolyte used for the catalyst layer.

  The thickness of the electrolyte membrane may be appropriately determined in consideration of the characteristics of the obtained fuel cell, and is not particularly limited. The thickness of the electrolyte membrane is usually about 5 to 300 μm. When the thickness of the electrolyte membrane is within such a range, the balance of strength during film formation, durability during use, and output characteristics during use can be appropriately controlled.

(Catalyst layer)
The catalyst layer is a layer where the battery reaction actually proceeds. Specifically, the oxidation reaction of hydrogen proceeds in the anode catalyst layer, and the reduction reaction of oxygen proceeds in the cathode catalyst layer. Here, the electrode catalyst obtained by the production method of the first embodiment may be present in either the cathode catalyst layer or the anode catalyst layer. Considering the necessity for improving the oxygen reduction activity, it is preferable to use the electrode catalyst obtained by the production method of the first embodiment at least for the cathode catalyst layer. However, the catalyst layer according to the above embodiment may be used as an anode catalyst layer, or may be used as both a cathode catalyst layer and an anode catalyst layer, and is not particularly limited.

  The catalyst layer includes an electrode catalyst and an electrolyte. The electrolyte is not particularly limited, but is preferably an ion conductive polymer electrolyte. Since the polymer electrolyte plays a role of transmitting protons generated around the catalyst active material on the fuel electrode side, it is also called a proton conductive polymer.

  The polymer electrolyte is not particularly limited, and conventionally known knowledge can be appropriately referred to. Polymer electrolytes are roughly classified into fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes depending on the type of ion exchange resin that is a constituent material.

  Examples of ion exchange resins constituting the fluorine-based polymer electrolyte include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride-per Examples thereof include fluorocarbon sulfonic acid polymers. From the viewpoint of excellent heat resistance, chemical stability, durability, and mechanical strength, these fluorine-based polymer electrolytes are preferably used, and particularly preferably fluorine-based polymer electrolytes composed of perfluorocarbon sulfonic acid polymers. Is used.

  Specific examples of the hydrocarbon electrolyte include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, and sulfonated poly. Examples include ether ether ketone (S-PEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon polymer electrolytes are preferably used from the viewpoint of production such that the raw material is inexpensive, the production process is simple, and the selectivity of the material is high.

  In addition, as for the ion exchange resin mentioned above, only 1 type may be used independently and 2 or more types may be used together. Moreover, it is not restricted only to the material mentioned above, Other materials may be used.

  Proton conductivity is important in polymer electrolytes responsible for proton transmission. Here, when the EW of the polymer electrolyte is too large, the ionic conductivity in the entire catalyst layer is lowered. Therefore, it is preferable that the catalyst layer of this embodiment contains a polymer electrolyte having a small EW. Specifically, the catalyst layer of this embodiment preferably has an EW of 1500 g / eq. The following polymer electrolyte is contained, More preferably, it is 1200 g / eq. The following polymer electrolyte is included, and particularly preferably 1000 g / eq. The following polymer electrolytes are included. On the other hand, if the EW is too small, the hydrophilicity is too high, making it difficult to smoothly move water. From such a viewpoint, the EW of the polymer electrolyte is preferably 600 or more. Note that EW (Equivalent Weight) represents the equivalent weight of the exchange group having proton conductivity. The equivalent weight is the dry weight of the ion exchange membrane per equivalent of ion exchange group, and is expressed in units of “g / eq”.

  If necessary, the catalyst layer may be a water repellent such as polytetrafluoroethylene, polyhexafluoropropylene or tetrafluoroethylene-hexafluoropropylene copolymer, a dispersant such as a surfactant, glycerin, ethylene glycol (EG). ), A thickener such as polyvinyl alcohol (PVA) and propylene glycol (PG), and an additive such as a pore-forming agent may be contained.

  The film thickness (dry film thickness) of the catalyst layer is preferably 0.05 to 30 μm, more preferably 1 to 20 μm, and still more preferably 2 to 15 μm. The above applies to both the cathode catalyst layer and the anode catalyst layer. However, the cathode catalyst layer and the anode catalyst layer may be the same or different.

(Gas diffusion layer)
The gas diffusion layers (anode gas diffusion layer 4a, cathode gas diffusion layer 4c) are catalyst layers (3a, 3c) of gas (fuel gas or oxidant gas) supplied via the gas flow paths (6a, 6c) of the separator. ) And a function as an electron conduction path.

  The material which comprises the base material of a gas diffusion layer (4a, 4c) is not specifically limited, A conventionally well-known knowledge can be referred suitably. For example, a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper body, a felt, and a non-woven fabric can be used. The thickness of the substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. If the thickness of the substrate is within such a range, the balance between mechanical strength and diffusibility such as gas and water can be appropriately controlled.

  The gas diffusion layer preferably contains a water repellent for the purpose of further improving water repellency and preventing a flooding phenomenon or the like. Although it does not specifically limit as a water repellent, Fluorine type high things, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), are included. Examples thereof include molecular materials, polypropylene, and polyethylene.

  In order to further improve the water repellency, the gas diffusion layer has a carbon particle layer (microporous layer; MPL, not shown) made of an aggregate of carbon particles containing a water repellent agent on the catalyst layer side of the substrate. You may have.

  The carbon particles contained in the carbon particle layer are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately employed. Among them, carbon black such as oil furnace black, channel black, lamp black, thermal black, acetylene black and the like can be preferably used because of excellent electron conductivity and a large specific surface area. The average particle size of the carbon particles is preferably about 10 to 100 nm. Thereby, while being able to obtain the high drainage property by capillary force, it becomes possible to improve contact property with a catalyst layer.

  Examples of the water repellent used in the carbon particle layer include the same water repellent as described above. Among these, fluorine-based polymer materials can be preferably used because of excellent water repellency, corrosion resistance during electrode reaction, and the like.

  The mixing ratio of the carbon particles and the water repellent in the carbon particle layer is about 90:10 to 40:60 (carbon particles: water repellent) in weight ratio in consideration of the balance between water repellency and electron conductivity. It is good. In addition, there is no restriction | limiting in particular also about the thickness of a carbon particle layer, What is necessary is just to determine suitably in consideration of the water repellency of the gas diffusion layer obtained.

(Method for producing electrolyte membrane-electrode assembly)
The method for producing the electrolyte membrane-electrode assembly is not particularly limited, and a conventionally known method can be used. For example, a method of joining a gas diffusion layer to a catalyst layer transferred or applied to an electrolyte membrane by hot pressing and drying it, or a microporous layer side of the gas diffusion layer (when a microporous layer is not included) First, two gas diffusion electrodes (GDE) are prepared by applying a catalyst layer on one side of a base material layer in advance and drying, and then bonding the gas diffusion electrodes to both sides of a solid polymer electrolyte membrane by hot pressing. The application and joining conditions such as hot pressing can be adjusted appropriately according to the type of polymer electrolyte in the solid polymer electrolyte membrane or catalyst layer (perfluorosulfonic acid type or hydrocarbon type). Good.

[Fuel cell]
The above-mentioned electrolyte membrane-electrode assembly (MEA) can be suitably used for a fuel cell. That is, the third embodiment of the present invention is a fuel cell using the electrolyte membrane-electrode assembly (MEA) of the second embodiment. The fuel cell of the present invention can exhibit high power generation performance and durability. Here, the fuel cell of the third embodiment has a pair of an anode separator and a cathode separator that sandwich the electrolyte membrane-electrode assembly of the second embodiment.

(Separator)
The separator has a function of electrically connecting each cell in series when a plurality of single cells of a fuel cell such as a polymer electrolyte fuel cell are connected in series to form a fuel cell stack. The separator also functions as a partition that separates the fuel gas, the oxidant gas, and the coolant from each other. In order to secure these flow paths, as described above, each of the separators is preferably provided with a gas flow path and a cooling flow path. As a material constituting the separator, conventionally known materials such as dense carbon graphite, carbon such as a carbon plate, and metal such as stainless steel can be appropriately employed without limitation. The thickness and size of the separator and the shape and size of each flow path provided are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics of the obtained fuel cell.

  The manufacturing method of the fuel cell is not particularly limited, and conventionally known knowledge can be appropriately referred to in the field of the fuel cell.

  Furthermore, a fuel cell stack having a structure in which a plurality of electrolyte membrane-electrode assemblies are stacked and connected in series via a separator may be formed so that the fuel cell can exhibit a desired voltage. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

  The PEFC and the electrolyte membrane-electrode assembly described above use a catalyst layer that is excellent in power generation performance and durability. Therefore, the PEFC and the electrolyte membrane-electrode assembly are excellent in power generation performance and durability.

  The PEFC of the present embodiment and the fuel cell stack using the PEFC can be mounted on a vehicle as a driving power source, for example.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

<Example 1>
(Preparation of acid-treated carbon support)
² g of carbon support (Ketjen Black (registered trademark) KetjenBlackEC300J, average particle size: 40 nm, BET specific surface area: 800 m ² / g, manufactured by Lion Corporation) is added to 500 mL of 0.5 M HNO ₃ solution in a beaker. The mixture was stirred and mixed with a stirrer at 300 rpm for 30 minutes at room temperature (25 ° C.). Subsequently, a carbon support was obtained by performing a heat treatment at 80 ° C. for 2 hours under stirring at 300 rpm. Then, after filtering the carbon support, it was washed with ultrapure water. The above filtration and washing operations were repeated a total of 3 times. The carbon support was dried at 60 ° C. for 24 hours, and then an acid-treated carbon support A was obtained. The amount of at least one functional group selected from the group consisting of a lactone group, a hydroxyl group, an ether group, and a carbonyl group formed on the surface of the obtained acid-treated carbon carrier A is 1.25 μmol / m ² . The BET specific surface area was 850 m ² / g, and the average particle size was 40 nm.

  1 g of acid-treated carbon carrier A was added to 100 ml of ultrapure water placed in a beaker and subjected to ultrasonic treatment for 15 minutes to obtain carrier suspension A. The support suspension A was stirred at 10,000 rpm for 15 minutes at room temperature (25 ° C.) using a homogenizer, and then stirred until it was added to the catalyst particles.

(Process (1))
In 1000 ml of ultrapure water placed in a beaker, 5.625 g of trisodium citrate dihydrate as an aggregation inhibitor was dissolved and cooled to 4 ° C. Then, 112 g (677 mg in terms of Co amount) of 2.44 wt% cobalt chloride (CoCl ₂ .6H ₂ O) aqueous solution in trisodium citrate dihydrate solution, 40.6 wt% chloroplatinic acid (H ₂ [ 3 g (459 mg in terms of platinum) of an aqueous solution of PtCl ₆ ] · 6H ₂ O was added (platinum and cobalt concentrations in the mixed solution: cobalt 237 mg / 100 mL, platinum 122 mg / 100 mL). This was stirred and mixed with a stirrer at 4 ° C. for 5 minutes to prepare a precursor mixture.

(Process (2))
1.375 g of trisodium citrate dihydrate as an aggregation inhibitor was dissolved in 100 ml of ultrapure water and cooled to 4 ° C. (pH 8.1). After adjusting the pH to 9 using 1M NaOH, 2 g of sodium borohydride was added at room temperature (25 ° C.), and the mixture was stirred and mixed with a stirrer for 1 minute to prepare a reducing agent mixture.

(Process (3))
100 ml of the reducing agent solution (liquid temperature 4 ° C.) prepared above is added to the precursor mixed liquid (liquid temperature 4 ° C.) obtained above, and stirred and mixed at 300 rpm for 15 minutes at 4 ° C. Thus, a catalyst particle-containing liquid containing catalyst particles (Pt—Co mixed particles) was obtained.

(Process (4))
Next, the carrier suspension A containing 1 g of the acid-treated carbon carrier A is added to the catalyst particle-containing liquid obtained in the step (3), and the mixture is stirred and mixed at 300 rpm for 6 hours at room temperature (25 ° C.). The catalyst particles were supported on a carrier. Thereafter, the catalyst particle-supported carrier was filtered and washed with 2 L of ultrapure water. The filtration and washing operations were repeated a total of 3 times, followed by filtration to obtain a catalyst particle-supporting carrier.

  The catalyst particle-supported carrier was dried at 60 ° C. for 12 hours to obtain an electrode catalyst 1.

  The supported concentration (supported amount) of the catalyst particles of this electrode catalyst 1 was 31.3% by weight (Pt: 27.1% by weight, Co: 4.2% by weight) with respect to the support. The supported concentration was measured by ICP analysis. The same applies hereinafter.

<Example 2>
In the step (2), an electrode catalyst 2 was obtained in the same manner as in Example 1 except that the pH was not adjusted to 9 using 1M NaOH.

  The supported concentration (supported amount) of catalyst particles of this electrode catalyst 2 was 31.1% by weight (Pt: 27.2% by weight, Co: 3.9% by weight) with respect to the support.

<Comparative Example 1>
(Process (1))
1000 ml of ultrapure water placed in a beaker was cooled to 10 ° C., and 112 g of a 2.44 wt% cobalt chloride (CoCl ₂ .6H ₂ O) aqueous solution (677 mg in terms of Co amount) and 40.6 wt% chloroplatinic acid ( 3 g of H ₂ [PtCl ₆ ] · 6H ₂ O) aqueous solution (459 mg in terms of platinum) was added. This was stirred and mixed with a stirrer at 10 ° C. for 10 minutes to prepare a precursor mixture.

(Process (2))
A reducing agent mixed solution was prepared by dissolving 7 g of trisodium citrate dihydrate and 2 g of sodium borohydride as aggregation preventing agents in 100 mL of ultrapure water.

(Process (3))
100 ml of the reducing agent liquid mixture (liquid temperature 10 ° C.) prepared above is added to the precursor liquid mixture (liquid temperature 10 ° C.) obtained above, and the mixture is stirred and mixed at 300 rpm for 15 minutes at 10 ° C. A catalyst particle-containing liquid containing catalyst particles (Pt—Co mixed particles) was obtained by precipitation.

(Process (4))
Next, the carrier suspension A containing 1 g of the acid-treated carbon carrier A is added to the catalyst particle-containing liquid obtained in the step (3), and the mixture is stirred and mixed at 300 rpm for 6 hours at room temperature (25 ° C.). The catalyst particles were supported on a carrier. Thereafter, the catalyst particle-supported carrier was filtered and washed with 2 L of ultrapure water. The filtration and washing operations were repeated a total of 3 times, followed by filtration to obtain a catalyst particle-supporting carrier.

  The catalyst particle-supported carrier was dried at 60 ° C. for 12 hours to obtain an electrode catalyst 3.

  The supported concentration (supported amount) of the catalyst particles of this electrode catalyst 3 was 32.0% by weight (Pt: 27.6% by weight, Co: 4.4% by weight) with respect to the support.

(Catalyst performance evaluation)
<Measurement of area specific activity>
The electrode catalyst (comparative electrode catalyst) of each Example and each Comparative Example was 34 μg · cm ⁻² on a rotating disk electrode (geometric area: 0.19 cm ² ) composed of a glassy carbon disk having a diameter of 5 mm. In this manner, the electrode for performance evaluation was prepared by uniformly dispersing and supporting it together with Nafion (registered trademark).

The potential range of 0.05 to 1.2 V with respect to the reversible hydrogen electrode (RHE) in 0.1 M perchloric acid at 25 ° C. saturated with N ₂ gas with respect to the electrode of each example and each comparative example. Then, cyclic voltammetry was performed at a scanning speed of 50 mVs- ¹ . From the area of the hydrogen adsorption peak appearing at 0.05 to 0.4 V in the obtained voltammogram, the electrochemical surface area (cm ² ) of each electrode catalyst (comparative electrode catalyst) was calculated.

Next, using an electrochemical measurement device, a potential scan was performed from 0.2 V to 1.2 V at a rate of 10 mV / s in 0.1 M perchloric acid saturated at 25 ° C. with oxygen. Furthermore, the current value at 0.9 V was extracted from the current obtained by the potential scanning after correcting the influence of mass transfer (oxygen diffusion) using the Koutecky-Levic equation. And the value which remove | divided the obtained electric current value by the above-mentioned electrochemical surface area was made into area specific activity ((micro | micron | mu) Acm ^<-2 >). A method using the Koutecky-Levic equation is described in, for example, Electrochemistry Vol. 79, no. 2, p. 116-121 (2011) (convection voltammogram (1) oxygen reduction (RRDE)) described in “Analysis of Oxygen Reduction Reaction on 4 Pt / C Catalyst”. The area specific activity is calculated by dividing the extracted current value of 0.9 V by the electrochemical surface area.

  The results are shown in Table 1.

<Measurement of catalyst effective surface area (ECA)>
The electrochemical surface area (cm ² ) was calculated as described in the column for measuring the area specific activity, and the catalyst effective surface area (ECA) was calculated by dividing by the electrode catalyst weight.

  The results are shown in Table 1.

  From the above results, in Examples 1 and 2 in which the aggregation inhibitor was added to both the precursor solution and the reducing agent solution, the ECA was higher than that of Comparative Example 1, and the area specific activity was also increased. Moreover, in Example 1 which adjusted pH by NaOH, ECA became higher.

1 ... Polymer electrolyte fuel cell (PEFC),
2 ... Solid polymer electrolyte membrane,
3 ... Catalyst layer,
3a ... anode catalyst layer,
3c ... cathode catalyst layer,
4a ... anode gas diffusion layer,
4c ... cathode gas diffusion layer,
5a ... anode separator,
5c ... cathode separator,
6a ... anode gas flow path,
6c ... cathode gas flow path,
7: Refrigerant flow path,
10: Electrolyte membrane-electrode assembly (MEA).

Claims (11)

(1) preparing a precursor mixture containing a platinum precursor, a non-platinum metal precursor and an anti-aggregation agent;
(2) preparing a reducing agent mixed solution containing a reducing agent and an aggregation inhibitor;
(3) The reducing agent mixed solution is added to the precursor mixed solution, and the platinum precursor and the non-platinum metal precursor are simultaneously reduced to obtain a catalyst particle-containing solution;
(4) adding a carbon carrier to the catalyst particle-containing liquid to obtain a catalyst particle-carrying carrier;
A method for producing an electrode catalyst, comprising:   The production method according to claim 1, wherein the content of the aggregation inhibitor in the precursor mixed solution is larger than the content of the aggregation inhibitor in the reducing agent mixed solution.   The production according to claim 1 or 2, wherein a solution temperature of at least one of the precursor mixed solution and the reducing agent mixed solution when the reducing agent mixed solution is added to the precursor mixed solution is 20 ° C or lower. Method.   The manufacturing method of any one of Claims 1-3 whose said aggregation inhibitor is a citrate or its hydrate.   The said reducing agent is a borohydride compound, It includes adding a borohydride compound to the aggregation inhibitor solution which adjusted pH to 8.5-10. Production method.   6. The total weight of the aggregation inhibitor in the precursor mixture and the aggregation inhibitor in the reducing agent mixture is 5 to 7 times the weight of the platinum precursor. The manufacturing method as described in. The carbon support has a total amount of at least one functional group selected from the group consisting of a lactone group, a hydroxyl group, an ether group, and a carbonyl group on the surface of 0.5 μmol / m ² or more. The manufacturing method of any one of these.   The manufacturing method according to claim 7, wherein the carbon support is obtained by performing a heat treatment after contacting a carbon material with an acidic solution.   The ratio of the non-platinum metal contained in the non-platinum metal precursor to the platinum contained in the platinum precursor (non-platinum metal / platinum molar ratio) is 0.4-20. The production method according to claim 1.   The electrolyte membrane-electrode assembly containing the electrode catalyst manufactured by the manufacturing method of any one of Claims 1-9.   A fuel cell comprising the electrolyte membrane-electrode assembly according to claim 10.