JP2018085260A - Method for producing electrode catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an electrode catalyst capable of obtaining a highly active electrode catalyst at low cost.SOLUTION: The method for producing an electrode catalyst includes steps of: preparing an electrode catalyst precursor in which a platinum-containing catalytic metal is supported on a carbon support; heating the precursor in an oxygen-containing environment at temperature higher than or equal to temperature lower than the combustion temperature of the carbon support by 150°C and temperature lower than or equal to temperature lower than the combustion temperature of the carbon support by 60°C; and decreasing the weight of the electrode catalyst precursor at a rate greater than 0% and less than 10%.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 a polymer electrolyte fuel cell having an electrolyte membrane-electrode assembly (MEA) as described above, the following reaction formulas are used depending on the polarity of both electrodes (cathode and anode) sandwiching the polymer electrolyte membrane. Electric energy is obtained by advancing the electrode reaction indicated by. 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 side of the electrode catalyst layer 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 electrode catalyst in the electrode catalyst layer is an important key. For example, Patent Document 1 discloses a carbon support obtained by heat-treating carbon particles on which catalyst particles A (for example, cobalt oxide particles) that promote carbon oxidation are supported. Patent Document 1 also carries catalyst particles B (for example, platinum particles) that catalyze the above-described electrochemical reaction using carbon particles having concave depressions formed on the surface by the catalyst particles A as a carrier. A fuel cell electrode catalyst is disclosed.

JP 2006-187744 A

  Patent Document 1 describes that the carbon support is useful as an electrode catalyst for a fuel cell that is desired to stably exhibit high catalytic activity over a long period of time. Moreover, in the electrode catalyst for fuel cells described in Patent Document 1, catalyst particles that catalyze the above-described electrochemical reaction are formed in a concave recess formed on the surface of carbon particles by catalyst particles A (for example, cobalt oxide particles). B (for example, platinum particles) is supported. Thus, it is described that the catalyst particles B can be highly dispersed and supported.

  As described above, by using the carbon support described in Patent Document 1, it is possible to obtain an electrode catalyst for a fuel cell that exhibits high catalytic activity over a long period of time. However, in the example of Patent Document 1, carbon particles on which cobalt oxide (catalyst particles A) are supported are prepared as a first step in order to obtain a carbon carrier having concave depressions formed on the surface. . Thereafter, cobalt oxide (catalyst particles A) is removed from the carbon support (carbon particles), and platinum (catalyst particles B) is supported again on the carbon support. In such a technique, there is a room for improvement from the viewpoint of process cost because the process of supporting the metal particles on the carbon support (carbon particles) is included a plurality of times.

  Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing an electrode catalyst, which can obtain a highly active electrode catalyst at a low cost.

  The present inventors have intensively studied to solve the above problems. As a result, the inventors have found that the above problems can be solved by a production method including heating an electrode catalyst precursor in which a platinum-containing catalyst metal is supported on a carbon support under predetermined conditions, and have reached the solution of the present invention.

  According to the present invention, a highly active electrode catalyst can be obtained at low cost. In the present invention, since the electrode catalyst precursor on which a catalyst metal that promotes the oxidation reaction of oxygen or the reduction reaction of oxygen is supported in advance is subjected to heat treatment, it is not necessary to support the metal particles a plurality of times, thereby reducing the process cost. It is done. Further, it is considered that a highly active electrode catalyst in which the catalyst metal is appropriately buried in the carbon support is obtained by heating such an electrode catalyst precursor under predetermined conditions.

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. 2 is an electron microscope image of the electrode catalyst obtained in Example 1. FIG. 2 is an electron microscopic image of an electrode catalyst obtained in Comparative Example 1.

[Electrocatalyst production method]
In one embodiment of the present invention, an electrode catalyst precursor in which a platinum-containing catalyst metal is supported on a carbon support is prepared, and the electrode catalyst precursor is heated in an oxygen-containing atmosphere. The present invention relates to a method for producing an electrocatalyst comprising reducing the weight by more than 0% and less than 10%.

  Another embodiment of the present invention provides an electrode catalyst precursor in which a platinum-containing catalyst metal is supported on a carbon support, and the electrode catalyst precursor has a temperature that satisfies the following relational expression 3 under an oxygen-containing atmosphere: It is related with the manufacturing method of an electrode catalyst including heating by.

However, in the above relational expression 3, T _heat (° C.) represents the temperature in the heating; T _carbon (° C.) represents the combustion temperature of the carbon support.

  According to the above method, since the electrode catalyst precursor on which the catalyst metal that promotes the hydrogen oxidation reaction or the oxygen reduction reaction is supported in advance is subjected to the heat treatment, it is not necessary to support the metal particles a plurality of times. For this reason, an electrode catalyst can be manufactured at low cost.

  Moreover, according to the said method, a highly active electrode catalyst can be obtained. Although it does not restrict | limit the technical scope of this invention, it is estimated that this is based on the following mechanisms.

  By heating the electrocatalyst precursor in which the platinum-containing catalyst metal is supported on the carbon support under the above conditions, the oxidative decomposition of the carbon support proceeds at the portion in contact with the platinum-containing catalyst metal, and the catalyst metal becomes the carbon support. An electrode catalyst having a structure buried moderately can be obtained. Thereby, sintering of the catalyst metal is prevented, that is, an electrode catalyst in which the catalyst metal is supported in a highly dispersed state is obtained. In particular, the electrode catalyst having such a structure is advantageous from the following viewpoints when a catalytic metal is used in a polymer electrolyte fuel cell.

  Conventionally, in order for an electrochemical reaction in a polymer electrolyte fuel cell to proceed, it is necessary that a polymer electrolyte (ionomer) as a proton path and a catalytic metal as a reaction catalyst are in contact with each other. Has been. However, the present inventors form a three-phase interface with water even when the electrode catalyst does not contact the polymer electrolyte in the fuel cell electrode catalyst layer containing the electrode catalyst and the polymer electrolyte (ionomer). It was found that the electrode catalyst can be used effectively. Here, since the polymer electrolyte has the property of being easily adsorbed on the surface of the catalyst metal, the access of the reaction gas to the catalyst metal can be inhibited by the polymer electrolyte. Therefore, by using an electrode catalyst having a structure in which a catalyst metal is appropriately buried in a carbon support for a fuel cell electrode catalyst layer of a solid polymer fuel cell, it is possible to prevent the polymer electrolyte from coming into contact with the catalyst metal. . Thus, it is considered that the electrode catalyst can be effectively used by preventing the reaction active area on the surface of the catalytic metal from decreasing and further forming a three-phase interface with water.

  On the other hand, if the heat treatment is performed excessively beyond the scope of the present invention, the catalytic activity is decreased. This is presumed to be due to the fact that the platinum-containing catalyst metal has a higher carbon carrier decomposition activity than cobalt oxide and the like described in Patent Document 1. That is, when the heat treatment is excessively performed beyond the scope of the present invention, the oxidative decomposition in the heat treatment of the carbon support in the portion in contact with the platinum-containing catalyst metal proceeds excessively, and the contact between the catalyst metal and the carbon support. It is thought that the electron transfer path is narrowed by the decrease in area. In addition, in such an electrode catalyst in which the oxidative decomposition of the carbon support has proceeded excessively, the catalytic metal is completely buried in the carbon support, thereby making the reaction gas accessible to the catalytic metal and the three-phase interface due to water. The formation of is considered to be insufficient.

  Embodiments of the present invention will be described below. In addition, this invention is not limited only to the following embodiment. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

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

  The electrode catalyst precursor in which the platinum-containing catalyst metal used in the present invention is supported on a carbon support (hereinafter referred to as “electrode catalyst precursor in which a platinum-containing catalyst metal is supported on a carbon support” is simply referred to as “electrode catalyst precursor”. Is not particularly limited. The electrode catalyst precursor may be prepared by, for example, supporting a platinum-containing catalyst metal on a carbon support by the method described later, or a commercially available product may be used. Examples of such commercially available products include, but are not limited to, TEC10V30E, TEC10V40E, TEC10V50E (manufactured by TANAKA Holdings Co., Ltd.) and the like.

  The platinum-containing catalytic metal that can be used in the present invention has a function of catalyzing an electrochemical reaction. For example, the catalyst metal used in the anode catalyst layer of the fuel cell is not particularly limited as long as it has a catalytic action in the oxidation reaction of hydrogen, and a known platinum-containing catalyst metal can be used in the same manner. The catalyst metal used in the cathode catalyst layer of the fuel cell is not particularly limited as long as it has a catalytic action for the oxygen reduction reaction, and a known platinum-containing catalyst metal can be used in the same manner.

  In the present invention, a catalyst metal containing platinum is used. The platinum-containing catalytic metal has the advantages of excellent catalytic activity, poisoning resistance to carbon monoxide and the like, and heat resistance. A platinum-containing catalyst metal (hereinafter, “platinum-containing catalyst metal” is also simply referred to as “catalyst metal”) is a platinum-containing alloy composed of platinum atoms and non-platinum metal atoms, even if it is substantially composed of platinum atoms. There may be. The above “substantially consisting of platinum atoms” refers to the atoms constituting the catalyst metal having a platinum atom content exceeding 90 atomic%, preferably a platinum atom content of 99 atoms. % Or more (upper limit: 100 atomic%). Although the composition of the alloy depends on the type of metal to be alloyed, the content of platinum is preferably 30 to 90 atomic%, and the content of the metal to be alloyed with platinum is preferably 10 to 70 atomic%. In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added and having metallic properties. The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be used in the present application. More specifically, examples of the non-platinum metal atom include ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, copper, silver, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. One or more selected from can be exemplified.

  The carbon support functions as a support for supporting the catalyst metal and an electron conduction path involved in the exchange of electrons between the catalyst metal and other members. In the present specification, the “carbon carrier” refers to a material containing a carbon atom as a main component, and is a concept including both a carbon atom only and a substantially carbon atom. 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.

  Specific examples of the carbon support include carbon blacks such as acetylene black, channel black, oil furnace black, gas furnace black (for example, Vulcan (registered trademark)), lamp black, thermal black, ketjen black (registered trademark), and the like. Graphitized acetylene black; graphitized channel black; graphitized oil furnace black; graphitized gas furnace black; graphitized lamp black; graphitized thermal black; graphitized ketjen black (registered trademark); Examples thereof include graphitized black pearl (registered trademark); carbon nanotube; carbon nanofiber; carbon nanohorn; carbon fibril; activated carbon; coke; natural graphite; Further, examples of the carbon support include zeolite-templated carbon (ZTC) having a structure in which nano-sized band-shaped graphene is regularly connected in a three-dimensional manner.

BET specific surface area of the carbon support is preferably less than ^{10 m} 2 / g carrier least 800 m ² / g carrier, and more preferably from 20~700m ² / g carrier, and more preferably 50 to 600 m ² / g carrier . With such a BET specific surface area, it is possible to prevent the catalyst metal from being buried excessively in the carbon support by heat treatment while supporting (highly dispersed) the catalyst metal on the carbon support. The “BET specific surface area (m ² / g carrier)” of the carrier is measured by a nitrogen adsorption method.

  In addition, the size of the carbon support is not particularly limited, but from the standpoint of controlling the ease of loading, catalyst utilization, and the thickness of the electrode catalyst layer within an appropriate range, the primary average particle size is 5 to 200 nm, The thickness 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 size of the carrier” means the average particle size of the carrier particles examined from a transmission electron microscope image of a statistically significant number (for example, at least 200, preferably at least 300) of samples. Value. Here, the “particle diameter” means the maximum distance among the distances between any two points on the particle outline.

  The catalyst metal can be supported on the carbon support by a known method and is not particularly limited. For example, known methods such as impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method) can be used. In the case of supporting a platinum-containing alloy, platinum ions and non-platinum metal ions may be sequentially supported on the carbon support. Alternatively, a mixed solution containing a platinum precursor and a non-platinum metal precursor is prepared, a reducing agent is added to the mixed solution, and platinum ions derived from the platinum precursor and non-platinum metal ions derived from the non-platinum metal precursor are simultaneously added. You may carry | support on a carbon support | carrier. As an example of a method for loading a catalyst metal on a carbon support, loading by a liquid phase reduction loading method will be described in detail below, but the loading method is not limited to the following.

First, a platinum precursor is added to a solvent to prepare a platinum precursor-containing liquid. Here, the platinum precursor 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.

  The solvent used for the preparation of the platinum precursor-containing liquid is not particularly limited, and is appropriately selected depending on the type of platinum precursor to be used. In addition, the form in particular of the said platinum precursor containing liquid is not restrict | limited, A solution, a dispersion liquid, and a suspension liquid are included. From the viewpoint of being able to mix uniformly, the platinum precursor-containing liquid 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 precursor (platinum is efficiently ionized), and it is particularly preferable to use pure water or ultrapure water. The above solvents may be used alone or in the form of a mixture of two or more.

  Although the density | concentration of the platinum precursor in a platinum precursor containing liquid is not restrict | limited in particular, it is preferable that it is 0.1-50 mass% in conversion of a metal, More preferably, it is 0.5-45 mass%.

  Next, a carbon support and a reducing agent are added to the platinum precursor-containing liquid, and platinum ions derived from the platinum precursor are reduced and supported on the carbon support to produce platinum-supported precursor particles. Here, the order of adding the carbon carrier and the reducing agent to the platinum precursor-containing liquid is not particularly limited, but considering the ease of dispersion of the platinum particles on the carbon carrier, the carbon carrier first contains the platinum precursor. It is preferable to add a reducing agent after adding to the liquid.

  The amount of carbon support added to the platinum precursor-containing liquid is not particularly limited, but is preferably adjusted to 0.1 to 70% by weight with respect to the total amount of the support. It is preferable to set the support concentration in such a range because aggregation of the catalyst metals can be suppressed and an increase in the thickness of the electrode catalyst layer can be suppressed. More preferably, it is 0.5-60 weight%, More preferably, it is 2-50 weight%.

  After adding the carbon support to the platinum precursor-containing liquid, stirring may be performed. Accordingly, since the platinum precursor and the carbon support are mixed uniformly, the catalyst metal particles can be uniformly dispersed 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. Moreover, what is necessary is just to set suitably as stirring time so that dispersion | distribution may fully be performed, and it is 1 to 60 minutes normally.

Moreover, it does not restrict | limit especially as a reducing agent, The same reducing agent as the past can be used. For example, ethanol, methanol, propanol, formic acid, formate such as sodium formate and potassium formate, formaldehyde, sodium thiosulfate, citrate such as citric acid, sodium citrate, trisodium citrate, sodium borohydride (NaBH ₄ ) And hydrazine (N ₂ H ₄ ). Of the above reducing agents, trisodium citrate dihydrate can also act as an aggregation inhibitor. These may be in the form of hydrates. Two or more types may be mixed and used. The addition form of the reducing agent is not particularly limited, and may be added to the platinum precursor-containing liquid as it is, or may be added to the platinum precursor-containing liquid in the form of a reducing agent solution previously dissolved in a solvent. A solution form is preferable because it can be easily and uniformly mixed.

  The addition amount of the reducing agent is not particularly limited as long as it is an amount sufficient to reduce platinum ions. Specifically, the addition amount of the reducing agent is preferably 5 to 90 mol with respect to 1 mol of platinum ions (in metal conversion). With such an amount, platinum ions can be sufficiently reduced. In addition, when using 2 or more types of reducing agents, it is preferable that these total addition amount is the said range.

  The reduction reaction conditions for the platinum precursor are not particularly limited as long as catalytic metal ions such as platinum ions can be sufficiently reduced and supported on the carbon support. For example, the reduction reaction temperature is preferably around the boiling point of the solvent (solvent boiling point ± 10 ° C., more preferably solvent boiling point ± 5 ° C.). Or reduction reaction temperature becomes like this. Preferably it is 40-150 degreeC, More preferably, it is 60-100 degreeC. Further, the reduction reaction time is not particularly limited as long as the platinum precursor and the reducing agent can be mixed uniformly, but it is preferably 0.5 to 30 hours, more preferably 1 to 8 hours. Under such conditions, the catalyst metal can be highly dispersed and supported by the carbon support.

  Through the reduction reaction, catalytic metal ions are reduced and supported on the carbon support, and an electrode catalyst precursor particle-containing liquid is obtained. Here, if necessary, the electrode catalyst precursor particles may be isolated from the reaction solution. Here, the isolation method is not particularly limited, and the electrode catalyst precursor particles may be filtered and dried. If necessary, the electrode catalyst precursor 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, after the filtration or washing, the electrode catalyst precursor particles may be dried. Here, the electrode catalyst precursor particles may be dried in the air or 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.

In order to make the average particle diameter of the catalyst metal within a desired range, the electrode catalyst precursor may be annealed in a reducing atmosphere after the catalyst metal is supported on the carrier. At this time, the annealing temperature is preferably in the range of 300 to 1200 ° C., more preferably in the range of 500 to 1150 ° C., and particularly preferably in the range of 700 to 1000 ° C. The reducing atmosphere is not particularly limited as long as it contributes to the grain growth of the catalyst metal, but it is preferably performed in a mixed atmosphere of a reducing gas and an inert gas. The reducing gas is not particularly limited, but hydrogen (H ₂ ) gas is preferable. The inert gas is not particularly limited, and helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), nitrogen (N ₂ ), and the like can be used. The inert gas may be used alone or in the form of two or more mixed gases. Further, the heat treatment time is preferably 0.1 to 2 hours, and more preferably 0.5 to 1.5 hours.

  The average particle diameter (diameter) of the platinum-containing catalyst metal in the electrode catalyst precursor is not particularly limited, but is, for example, 1 to 30 nm, preferably 2 nm or more and less than 10 nm, more preferably more than 3 nm and less than 10 nm. . By setting the average particle diameter (diameter) of the platinum-containing catalyst metal in the above range, the platinum-containing catalyst metal can be appropriately buried in the carbon support without requiring a complicated process while ensuring the specific surface area of the catalyst metal. . In addition, the average particle diameter (diameter) of a platinum containing catalyst metal is a value measured as follows. First, n particles are observed with a transmission electron microscope (TEM), and the particle diameter (equivalent circular diameter) when the area is a perfect circle is calculated backward from the projected area of each particle. The diameter (d (nm)) is measured. Using the particle diameter (d (nm)) of the particles thus obtained, the average particle diameter (nm) of the particles is calculated by the following formula (A). The number (n) of particles to be measured is not particularly limited, but is preferably a number having no statistically significant difference, for example, at least 300.

  From the viewpoint of further improving the catalyst activity, the weight ratio of the catalyst metal to the total weight of the catalyst metal and the carbon support (catalyst metal loading, metal conversion) in the electrode catalyst precursor is preferably 5 to 45 weights. %. More preferably, in the electrode catalyst precursor, the catalyst metal loading (in metal equivalent) is 10 to 35% by weight. When the supported amount of the catalyst metal is within such a range, the balance between the degree of dispersion of the catalyst component on the carbon support and the catalyst performance can be appropriately controlled. The amount of the catalytic metal supported can be examined by a conventionally known method such as inductively coupled plasma emission spectrometry (ICP atomic emission spectrometry), inductively coupled plasma mass spectrometry (ICP mass spectrometry), or fluorescent X-ray analysis (XRF). it can.

  In the method according to the present invention, the electrode catalyst precursor prepared as described above is heated (heat treatment) in an oxygen-containing atmosphere. This reduces the weight of the electrocatalyst precursor. In one embodiment of the present invention, the heating is performed so that the weight of the electrocatalyst precursor is reduced at a rate of more than 0% and less than 10%. In another embodiment of the present invention, heating is performed at a temperature satisfying the relational expression 3. By heating the electrocatalyst precursor under the above conditions, the oxidative decomposition of the carbon support proceeds at the portion in contact with the platinum-containing catalyst metal, and the electrode catalyst has a structure in which the catalyst metal is appropriately buried in the carbon support. Can be obtained. Thereby, a highly active electrode catalyst can be obtained.

  In the method according to the present invention, the heat treatment of the electrode catalyst precursor is performed in an oxygen (molecular oxygen) -containing atmosphere. By performing the heat treatment in an atmosphere containing oxygen (molecular oxygen), oxidative decomposition proceeds on the surface of the carbon support in contact with the platinum-containing catalyst metal. The heat treatment may be performed in an atmosphere containing a gas other than oxygen such as helium, argon, or nitrogen in addition to oxygen. The oxygen content of the atmosphere in the heat treatment is, for example, 1 to 80% by volume from the viewpoint of promoting the oxidative decomposition reaction, preferably more than 5% by volume and 50% by volume or less, more preferably more than 10% by volume. And 40% by volume or less. In a preferred embodiment, the heating is performed in an air atmosphere.

  The heat treatment may be performed using a conventionally known device, and is not particularly limited. For example, the heat treatment may be performed using an oven, a furnace, a low temperature dryer, or the like.

  In one embodiment, the rate of weight loss of the electrocatalyst precursor by heat treatment is greater than 0% and less than 10%. Preferably, the weight of the electrocatalyst precursor is reduced at a rate of 6% or more and less than 10% during heating. More preferably, the weight of the electrocatalyst precursor is reduced by more than 6% and less than 10% in heating. A highly active electrode catalyst can be obtained by performing the heat treatment at a weight reduction rate as described above. In the present specification, the weight reduction rate (weight reduction rate) of the electrode catalyst precursor is a value calculated by the method described in the examples.

In one embodiment, the heat treatment of the electrocatalyst precursor is performed below the combustion temperature (T _carbon ) of the carbon support. Thereby, it can prevent that a carbon support | carrier lose | disappears by combustion. That is, in one embodiment of the present invention, the temperature during heating is less than the combustion temperature of the carbon support. In addition, the combustion temperature of a carbon support | carrier can be calculated | required as an exothermic peak temperature of a differential thermal analysis (DTA) by performing the thermogravimetric analysis of a carbon support | carrier in the atmosphere which heat-processes as described in an Example. . In terms of the activity of the electrode catalyst, in a preferred embodiment, the heating is performed at a temperature that satisfies the following relational expression 2:

However, in the above relational expression 2, T _heat (° C.) represents the temperature in the heating; T _carbon (° C.) represents the combustion temperature of the carbon support.

In one embodiment, from the viewpoint of the activity of the obtained electrocatalyst, the heat treatment of the electrocatalyst precursor is performed at a temperature equal to or higher than the lower limit temperature, with a temperature obtained by subtracting 150 ° C. from the combustion temperature of the carbon support (T _carbon ). Do. That is, in the embodiment, the heating is performed at a temperature that satisfies the following relational expression 1:

However, in the above relational expression 1, T _heat (° C.) represents the temperature in the heating; T _carbon (° C.) represents the combustion temperature of the carbon support.

More preferably, with the temperature obtained by subtracting 130 ° C. from the combustion temperature (T _carbon ) of the carbon support as the lower limit, the electrode catalyst precursor is heated at a temperature equal to or higher than the lower limit temperature. That is, in the embodiment, the heating is performed at a temperature that satisfies the following relational expression 1a:

However, in the relational expression 1a, T _heat (° C.) and T _carbon (° C.) are the same as those in the relational expression 1.

  In one embodiment, heating is performed at a temperature that satisfies the relational expression 3. From the viewpoint of obtaining a particularly highly active electrode catalyst, in a more preferred embodiment, the electrode catalyst precursor is heated at a temperature satisfying the following relational expression 3a.

However, in the relational expression 3a, T _heat (° C.) and T _carbon (° C.) are the same as in the relational expression 3.

  In a more preferred embodiment, the electrode catalyst precursor is heated at a temperature that satisfies the following relational expression 3b.

However, in the relational expression 3b, T _heat (° C.) and T _carbon (° C.) are the same as in the relational expression 3.

  For example, when Vulcan® is used as the carbon support, the electrocatalyst precursor may be heated at a temperature in the range of 200-320 ° C., and in a preferred embodiment in the range of 280-320 ° C. At a temperature of within.

  Although the pressure may be reduced or increased during the heat treatment, the atmospheric pressure during the heat treatment may be within a range of 0.05 to 0.5 MPa, for example, and is preferably atmospheric pressure.

  Although the heating time required at the heating temperature is not particularly limited, for example, it may be determined by determining the time required for the electrode catalyst precursor weight to reach a steady state by thermogravimetric analysis. More specifically, the heat treatment time is, for example, more than 0.5 hours and within 24 hours, preferably 1 to 7 hours, more preferably more than 1 hour and less than 5 hours. By setting the heat treatment time within the above range, it is possible to suppress an increase in production cost due to a prolonged heating time while reducing the weight of the electrode catalyst precursor at a desired reduction rate.

  The rate of temperature increase during the heat treatment is also not particularly limited, but is preferably 5 to 30 ° C./min. By setting the rate of temperature rise to 5 ° C./min or more, temperature control is facilitated, and side reactions due to overshoot (a phenomenon that temporarily becomes higher than the target value) can be prevented. By setting the rate of temperature rise to 30 ° C./min or less, there is an advantage that side reactions can be prevented and the heat treatment process can be prevented from becoming too long. From the above viewpoint, the heating rate during the heat treatment is more preferably 10 to 20 ° C./min.

  In the electrode catalyst produced by the method of the present invention, the catalyst metal is highly dispersed on the carbon support. Moreover, when it uses for a polymer electrolyte fuel cell (PEFC), it can suppress that a polymer electrolyte contacts a catalyst metal, and can ensure the electrochemically effective surface area of a catalyst metal. For this reason, the electrode catalyst obtained by the manufacturing method according to the present invention can be suitably applied to fuel cell applications that require higher performance than household and mobile power sources. That is, the membrane electrode assembly and fuel cell having the electrode catalyst produced by the method of the present invention in the catalyst layer are excellent in power generation performance.

  That is, in one Embodiment of this invention, a membrane electrode assembly (MEA) provided with the catalyst layer containing the electrode catalyst manufactured by the method of this invention and a fuel cell are provided. Below, a membrane electrode assembly (MEA) provided with the catalyst layer containing the electrode catalyst which concerns on one Embodiment of this invention, a fuel cell, and these manufacturing methods are demonstrated.

[Electrolyte membrane-electrode assembly (MEA)]
The electrode catalyst produced by the method of the present invention can be suitably used for an electrolyte membrane-electrode assembly (MEA). That is, the present invention also provides an electrolyte membrane-electrode assembly (MEA) including the electrode catalyst according to the present invention, particularly an electrolyte membrane-electrode assembly (MEA) for fuel cells. The electrolyte membrane-electrode assembly (MEA) according to the present invention can exhibit high power generation performance (particularly area specific activity).

  The electrolyte membrane-electrode assembly (MEA) of the present invention can be applied in the same configuration except that the electrode catalyst (catalyst) obtained by the production method according to the present invention is used instead of the conventional electrode catalyst. 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 of the present invention 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 of the present invention 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 of the present invention at least in 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 the electrode catalyst and the electrolyte according to the present invention. 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”.

  Further, the catalyst layer includes two or more types of polymer electrolytes having different EWs in the power generation surface. At this time, the polymer electrolyte having the lowest EW among the polymer electrolytes has a relative humidity of 90% or less of the gas in the flow path. It is preferable to use in the region. By adopting such a material arrangement, the resistance value becomes small regardless of the current density region, and the battery performance can be improved. The EW of the polymer electrolyte used in the region where the relative humidity of the gas in the flow channel is 90% or less, that is, the polymer electrolyte having the lowest EW is 900 g / eq. The following is desirable. Thereby, the above-mentioned effect becomes more reliable and remarkable.

  Further, it is desirable to use a polymer electrolyte having the lowest EW in a region higher than the average temperature of the cooling water inlet and outlet. As a result, the resistance value is reduced regardless of the current density region, and the battery performance can be further improved.

  Furthermore, from the viewpoint of reducing the resistance value of the fuel cell system, the polymer electrolyte having the lowest EW is within 3/5 from the gas supply port of at least one of the fuel gas and the oxidant gas with respect to the channel length. It is desirable to use it in the range area.

  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 layer (anode gas diffusion layer, cathode gas diffusion layer) promotes diffusion of gas (fuel gas or oxidant gas) supplied through the gas flow path of the separator to the catalyst layer, and electronic conduction. It has a function as a path.

  The material which comprises the base material of a gas diffusion layer 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 catalyst layer is transferred or applied to an electrolyte membrane by hot pressing, and this is dried, and the gas diffusion layer is bonded to the microporous layer side of the gas diffusion layer (if the microporous layer is not included) A gas diffusion electrode (GDE) is prepared by applying a catalyst layer in advance on one side of the base material layer and drying, and bonding the gas diffusion electrode to both sides of the solid polymer electrolyte membrane by hot pressing Can be used. Application and joining conditions such as hot pressing may be appropriately adjusted according to the type of polymer electrolyte in the solid polymer electrolyte membrane or catalyst layer (perfluorosulfonic acid type or hydrocarbon type).

[Fuel cell]
The above-mentioned electrolyte membrane-electrode assembly (MEA) can be suitably used for a fuel cell. That is, the present invention also provides a fuel cell using the electrolyte membrane-electrode assembly (MEA) of the present invention. The fuel cell of the present invention can exhibit high power generation performance (particularly mass specific activity) and durability.

  Here, the fuel cell includes a membrane electrode assembly (electrolyte membrane-electrode assembly, MEA), an anode-side separator having a fuel gas channel through which fuel gas flows, and a cathode having an oxidant gas channel through which oxidant gas flows. A pair of separators including a side separator. The fuel cell of the present invention is excellent in durability and can exhibit high power generation performance.

  Hereinafter, an embodiment of a membrane electrode assembly (MEA) having a catalyst layer using an electrode catalyst according to the present invention and a fuel cell 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 embodiments of the present invention are described with reference to the drawings, the same reference numerals are given to the same elements in the description of the drawings, and duplicate descriptions are 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.

(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 fuel cell 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.

  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.

(Preparation of electrode catalyst precursor)
Using Vulcan (registered trademark) XC72 (manufactured by Cabot Corporation, BET specific surface area: 220 (m ² / g carrier), primary average particle size: 37 nm) as a carbon support, platinum having an average particle size (diameter) of 3.4 nm was obtained. The electrode catalyst precursor was obtained by supporting the catalyst so that the support ratio was 10% by weight. That is, 46 g of carbon support was immersed in 1000 g (platinum content: 46 g) of a dinitrodiammine platinum nitric acid aqueous solution (platinum precursor content liquid) having a platinum concentration of 4.6% by mass and stirred, and then 100 ml of 100% ethanol was added as a reducing agent. did. This solution was stirred and mixed at the boiling point for 7 hours, and platinum was supported on the carbon support. And it filtered and dried and obtained the powder with a supporting rate of 10 weight%. Then, annealing treatment was performed by maintaining the temperature at 900 ° C. for 1 hour in a hydrogen atmosphere to obtain an electrode catalyst precursor.

The combustion temperature of the carbon support (exothermic peak temperature in DTA, T _carbon ) was determined by thermogravimetric analysis and found to be 387 ° C. The thermogravimetric analysis was performed under the following conditions.
Method TG-DTA
Temperature rising rate 5 ° C./min gas atmosphere An air measurement sample was placed in a platinum pan and measured.

Example 1
Using the above electrode catalyst precursor, heat treatment was performed in an electric furnace at 300 ° C. for 2 hours in an air atmosphere (atmospheric pressure), and air-cooled to obtain an electrode catalyst 1 (temperature increase rate: 10 ° C. / Min). An electron microscope image of the electrode catalyst 1 is shown in FIG. 2A. The weight reduction rate before and after heating was 8%. The weight reduction rate before and after heating was determined by the following formula.

(Example 2)
The electrode catalyst precursor was heat-treated in the same manner as in Example 1 except that the heating temperature in Example 1 was changed to 250 ° C. (temperature increase rate: 10 ° C./min) to obtain an electrode catalyst 2. The weight reduction rate before and after heating was 6%.

(Comparative Example 1)
What was stored at 25 degreeC without heat-processing said electrode catalyst precursor was used as the comparative electrode catalyst 1. FIG. An electron microscope image of the comparative electrode catalyst 1 is shown in FIG. 2B. As compared with FIG. 2A, it can be seen that in FIG. 2B, white spot-like catalyst metal particles are exposed on the carbon support.

(Comparative Example 2)
A comparative electrode catalyst 2 was obtained by heating the electrode catalyst precursor in the same manner as in Example 1 except that the heating temperature in Example 1 was changed to 330 ° C. (temperature increase rate: 10 ° C./min). The weight reduction rate before and after heating was 10%.

About the electrode catalyst 1-2 obtained above and the comparison electrode catalyst 1-2, the specific surface area (m < ² > / g Pt) and area specific activity ((micro | micron | mu) A / cm < ² > Pt) were measured according to the following method. The results are shown in the table below.

[Measurement of electrochemical surface area (cm ² Pt) of platinum]
The amount of platinum supported per unit area of the rotating disk electrode on the rotating disk electrode (RDE, geometric area: 0.19 cm ² ) on each of the electrocatalysts of the example and the comparative example was formed by a glassy carbon disk having a diameter of 5 mm. There so that the 34 [mu] g / cm ^2, with Nafion® (Nafion (registered trademark) coating amount = 10 [mu] g / cm ^2), was uniformly applied to prepare a RDE electrode performance evaluation.

For the RDE electrodes for performance evaluation of each Example and Comparative Example, using an electrochemical measurement device, in a 0.1 M perchloric acid saturated with N ₂ gas at 25 ° C. against a reversible hydrogen electrode (RHE) Cyclic voltammetry was performed at a scanning speed of 50 mVs ^{−1 in} a potential range of 0.05 to 1.2 V. 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 Pt) of platinum in each electrode catalyst was calculated.

[Measurement of area specific activity]
For the RDE electrodes for performance evaluation of Examples and Comparative Examples, using an electrochemical measurement device, the rate was 10 mV / s from 0.2 V to 1.2 V in 0.1 M perchloric acid saturated with oxygen at 25 ° C. A potential scan was performed. 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. The value obtained by dividing the obtained current value by the electrochemical surface area (cm ² Pt) of platinum was defined as the area specific activity (μA / cm ² Pt). 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”.

  As shown in the above table, it can be seen that the electrode catalyst obtained by the production method according to the present invention has high catalytic activity (area specific activity). In addition, the measured value of the electrochemical surface area of the comparative electrode catalyst 2 was not stable, and the catalytic activity could not be measured. This is probably because the catalyst metal was excessively buried in the carbon support in the comparative electrode catalyst 2.

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 (6)

Preparing an electrocatalyst precursor in which a platinum-containing catalyst metal is supported on a carbon support; and heating the electrocatalyst precursor in an oxygen-containing atmosphere so that the weight of the electrocatalyst precursor exceeds 0%. A method for producing an electrocatalyst comprising reducing at a rate of less than 10%.   The method for producing an electrode catalyst according to claim 1, wherein a temperature in the heating is lower than a combustion temperature of the carbon support. The method for producing an electrode catalyst according to claim 1 or 2, wherein the heating is performed at a temperature satisfying the following relational expression 1.
However, in the above relational expression 1, T _heat (° C.) represents the temperature in the heating; T _carbon (° C.) represents the combustion temperature of the carbon support. The method for producing an electrode catalyst according to any one of claims 1 to 3, wherein the heating is performed at a temperature satisfying the following relational expression 2.
However, in the above relational expression 2, T _heat (° C.) represents the temperature in the heating; T _carbon (° C.) represents the combustion temperature of the carbon support.   The method for producing an electrocatalyst according to any one of claims 1 to 4, wherein, in the heating, the weight of the electrocatalyst precursor is reduced at a rate of more than 6% and less than 10%. An electrode catalyst comprising: preparing an electrode catalyst precursor in which a platinum-containing catalyst metal is supported on a carbon support; and heating the electrode catalyst precursor at a temperature satisfying the following relational expression 3 in an oxygen-containing atmosphere: Manufacturing method:
However, in the above relational expression 3, T _heat (° C.) represents the temperature in the heating; T _carbon (° C.) represents the combustion temperature of the carbon support.