JP6720611B2 - Method for manufacturing electrode catalyst - Google Patents

Description

The present invention relates to a method for producing an electrode catalyst. In particular, the present invention relates to a method for producing an electrode catalyst that can exhibit high activity.

In recent years, fuel cells, which can operate at room temperature and obtain high output density, have been attracting attention as electric power sources for electric vehicles and stationary power sources in response to social demands and trends due to energy and environmental problems. The fuel cell is a clean power generation system in which the product of the electrode reaction is water in principle and has little 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 constitution of the polymer electrolyte fuel cell is generally a structure in which an electrolyte membrane-electrode assembly (MEA) is sandwiched between separators. The electrolyte membrane-electrode assembly has a polymer electrolyte membrane sandwiched between a pair of electrode catalyst layers and a gas diffusion layer (gas diffusion layer; GDL).

In the polymer electrolyte fuel cell having the electrolyte membrane-electrode assembly as described above, in both electrodes (cathode and anode) sandwiching the polymer electrolyte membrane, it is represented by the following reaction formula according to its polarity. The electrode reaction proceeds and electric energy is obtained. First, hydrogen contained in the fuel gas supplied to the anode (negative electrode) side is oxidized by a catalyst component and becomes a proton and an electron (2H ₂ →4H ⁺ +4e ⁻ : reaction 1). Next, the produced protons reach the cathode (positive electrode) side electrode catalyst layer through the solid polymer electrolyte contained in the electrode catalyst layer and the solid polymer electrolyte membrane in contact with the electrode catalyst layer. Further, the electrons generated in the anode-side electrode catalyst layer are generated by the conductive carrier forming the electrode catalyst layer, the gas diffusion layer in contact with the side of the electrode catalyst layer different from the solid polymer electrolyte membrane, the separator and the outside. It reaches the cathode side electrode catalyst layer through the circuit. Then, 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, it becomes possible to take out electricity through the above-mentioned electrochemical reaction.

Here, in order to improve the power generation performance, improvement of the activity and durability (activity after durability test) of the electrode catalyst (catalyst particles) of the electrode catalyst layer is an important key. Conventionally, from the viewpoint of improving activity and durability, it has been necessary to use platinum as a catalyst component of an electrode catalyst. However, since platinum is a very expensive metal and is a rare metal in terms of resources, it is required to develop a platinum alloy-based catalyst that reduces the platinum content in the catalyst particles while maintaining the activity and durability. ing.

For example, Patent Document 1 has an L1 ₂ structure as the internal structure in a particular order parameter, the catalyst alloy particles having a relationship with a specific area average particle diameter to the number average particle size is reported. Patent Document 1 suppresses elution of metals other than platinum, exposes many highly active crystal planes, and has an appropriate d _N /d _A ratio, so that the activity can be improved, Further, it is described that it is possible to provide catalyst particles having high activity after the durability test.

International Publication No. 2015/020079

The catalyst particles described in Patent Document 1 are certainly excellent in catalytic activity and durability. Therefore, the fuel cell using the catalyst particles described in Patent Document 1 as an electrode catalyst can exhibit high power generation efficiency. On the other hand, there is no upper limit to the target of power generation efficiency, and further improvement in power generation efficiency (power generation performance) is required especially when using fuel cells that require higher performance such as power sources for homes and mobiles. ing.

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 that can further improve the activity.

The present inventors have conducted earnest research to solve the above problems. As a result, they have found that the above problems can be solved by appropriately controlling the heat treatment conditions of the carrier supporting the catalyst component, and have found that the above problems can be solved.

According to the method of the present invention, the specific surface area of the electrode catalyst can be increased. Therefore, the electrode catalyst produced by the method of the present invention can have improved activity (particularly mass specific activity).

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. Based on the temperature dependence curve of the order of the alloy particles, the transformation temperature at which the alloy particles are ordered/disordered and the temperature at which platinum atoms and non-platinum metal atoms can interdiffuse in the alloy particles (interdiffusion temperature) It is a figure for demonstrating the method of calculating|requiring.

The method for producing an electrode catalyst of the present invention comprises the following steps:
(A) An alloy particle composed of a platinum atom and a non-platinum metal atom is supported on a conductive carrier to produce a catalyst precursor particle (step (a)); and (b) the catalyst obtained in the step (a). After heating the precursor particles to the initial setting temperature, maintaining the initial setting temperature for less than 10 minutes, and then lowering the temperature at a rate of less than 5° C./minute (step (b)),
To have that. With this configuration, it is possible to suppress a decrease in the specific surface area of the electrode catalyst (specific surface area per 1 g of platinum). Therefore, the electrode catalyst produced by the method of the present invention can have improved activity (particularly mass specific activity). In the present specification, “specific surface area per 1 g of platinum” is also simply referred to as “specific surface area”.

In the above-mentioned Patent Document 1, the inventors of the present invention have disclosed that a specific highly active crystal plane is exposed and a catalyst particle having a specific area average particle diameter and number average particle diameter has a high activity. I found that I can demonstrate it. The inventors of the present invention have made further studies for the purpose of further improving the activity of the catalyst particles. As a result, the activity of the electrode catalyst (catalyst particles) can be reduced by shortening the heat treatment time for producing the catalyst particles and appropriately controlling the temperature lowering condition thereafter, as defined in the step (b). We have found that it can be further improved. The detailed mechanism that achieves the above effects is considered as follows. The following mechanism is speculative and does not limit the technical scope of the present invention. That is, Patent Document 1 describes that control of the temperature and time of heat treatment is important for adjusting the degree of order. Certainly, at the time of Patent Document 1, it was presumed that the degree of order could be increased by performing the heat treatment for some time. However, this time, while seeking a means for solving the above problems, if the heat treatment is carried out at a relatively high temperature for a long time, the area specific activity can be improved, but the specific surface area per 1 g of platinum is decreased, and as a result, the mass specific activity is reduced. It has been found that the improvement of is limited. For this reason, further studies were conducted on a method capable of increasing the specific surface area while maintaining the regularity. As a result, as described above, it was estimated that it is effective to shorten the heat treatment time, which is considered to be one of the main factors for the reduction of the specific surface area, and to appropriately control the temperature lowering condition thereafter. Specifically, by shortening the time of holding at a high temperature, it is possible to suppress the growth of the particle size (and hence the decrease of the specific surface area) due to the sintering or aggregation of the catalyst particles. On the other hand, it becomes difficult to sufficiently improve the regularity by reducing the holding time at high temperature. Therefore, by slowly lowering the temperature (cooling), platinum atoms and non-platinum metal atoms are interdiffused in the alloy (catalyst) particles, thereby suppressing the sintering and agglomeration of the catalyst particles (regularization). I thought it could be done).

Therefore, the electrocatalyst produced by the method of the present invention has an increased specific surface area and therefore can improve the mass specific activity even with a small platinum content. Further, the catalyst particles produced by the method of the present invention have excellent durability. In addition, in the electrocatalyst produced by the method of the present invention, the alloy particles are monodispersed on the carrier without aggregating at a predetermined ratio or more. Therefore, the electrode catalyst according to the present invention can be suitably applied to a fuel cell application in which higher performance is required, such as a power source for household use or driving of a moving body. That is, the membrane electrode assembly and the fuel cell having the electrode catalyst manufactured by the method of the present invention in the catalyst layer have excellent power generation performance.

Hereinafter, one embodiment of the method for producing an electrode catalyst of the present invention will be described in detail. However, the present invention is not limited to the following embodiments. Further, in the present specification, “X to Y” indicating a range includes X and Y and means “X or more and Y or less”. Unless otherwise specified, operations and measurements of physical properties are carried out under the conditions of room temperature (20 to 25°C)/relative humidity of 40 to 50%.

[Method for producing electrode catalyst]
The method for producing an electrode catalyst of the present invention comprises the following steps:
(A) An alloy particle composed of a platinum atom and a non-platinum metal atom is supported on a conductive carrier to produce a catalyst precursor particle (step (a)); and (b) the catalyst obtained in the step (a). After heating the precursor particles to the initial setting temperature, maintaining the initial setting temperature for less than 10 minutes, and then lowering the temperature at a rate of less than 5° C./minute (step (b)),
To have that.

(Process (a))
In this step, alloy particles composed of platinum atoms and non-platinum metal atoms are supported on a conductive carrier to produce catalyst precursor particles.

Here, the method for supporting the alloy particles composed of platinum atoms and non-platinum metal atoms on the conductive carrier is not particularly limited. For example, platinum ions derived from the platinum precursor and non-platinum metal ions derived from the non-platinum metal precursor may be sequentially loaded on the conductive carrier (step (a-1)). Alternatively, a mixed solution containing a platinum precursor and a non-platinum metal precursor is prepared, a reducing agent is added to this mixed solution, and platinum ions derived from the platinum precursor and non-platinum metal ions derived from the non-platinum metal precursor are simultaneously prepared. You may reduce and carry|support on a conductive support (process (a-2)). Among these, the above step (a-2) is necessary and necessary in [Step (1)] and (Step (2)) of [Production method of catalyst particles/catalyst (electrode catalyst)] of WO 2015/020079. If so, the same method as described in (Step (3)) can be adopted.

Hereinafter, the step (a-1) will be described.

Here, there is no particular limitation on the method of sequentially loading the platinum ions derived from the platinum precursor and the non-platinum metal ions derived from the non-platinum metal precursor on the conductive carrier. For example, here's how:
A platinum precursor is added to a solvent to prepare a platinum precursor-containing liquid. A conductive carrier and a reducing agent are added to this platinum precursor-containing liquid, and platinum ions derived from the platinum precursor are reduced and supported on the conductive carrier to obtain a liquid containing platinum-supported precursor particles. A non-platinum metal precursor and a reducing agent are added to a liquid containing the platinum-supported precursor particles, and non-platinum metal ions derived from the non-platinum metal precursor are reduced and supported on a conductive carrier to obtain platinum/non-platinum. A liquid containing metal-supported precursor particles is obtained. The platinum/non-platinum metal-supported precursor particles are heated and alloyed to produce catalyst precursor particles.

The above method will be described below.

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 a platinum salt and a platinum complex 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 of ammine salts such as hexaammineplatinum, carbonates, bicarbonates, halides such as platinum chloride, inorganic salts such as nitrite and oxalic acid, carboxylates such as formates, hydroxides and alkoxides. You can In addition, the said platinum precursor may be used individually by 1 type, or may be used as a mixture of 2 or more types.

The solvent used for preparing the platinum precursor-containing liquid is not particularly limited and is appropriately selected depending on the type of platinum precursor used. The form of the platinum precursor-containing liquid is not particularly limited and includes solutions, dispersions and suspensions. From the viewpoint of being able to uniformly mix, the platinum precursor-containing liquid is preferably in the form of a solution. Specific examples thereof include water, organic solvents such as methanol, ethanol, 1-propanol, and 2-propanol, acids, and alkalis. Of these, water is preferable, and pure water or ultrapure water is particularly preferable, from the viewpoint of sufficiently dissolving the platinum precursor (effectively ionizing platinum). The above solvents may be used alone or in the form of a mixture of two or more kinds.

The concentration of the platinum precursor in the platinum precursor-containing liquid is not particularly limited, but it is preferably 0.1 to 50% by weight, and more preferably 0.5 to 45% by weight in terms of metal.

Next, a conductive carrier and a reducing agent are added to the above platinum precursor-containing liquid, and platinum ions derived from the platinum precursor are reduced and supported on the conductive carrier to produce platinum-supported precursor particles. Here, the order of adding the conductive 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 conductive carrier, the conductive carrier is first treated with platinum. It is preferable to add the reducing agent after the addition to the precursor-containing liquid.

The conductive carrier functions as a carrier for supporting the alloy particles (catalyst particles) and an electron conduction path involved in the transfer of electrons between the catalyst particles and other members. The conductive carrier may be any one having a specific surface area for supporting the catalyst particles in a desired dispersed state and having sufficient electron conductivity as a current collector, and the main component is carbon. Is preferred. In addition, "a main component is carbon" means that a carbon atom is included as a main component, and it is a concept including both consisting of only carbon atoms and substantially consisting of carbon atoms. In some cases, an element other than carbon atoms may be included in order to improve the characteristics of the fuel cell. The phrase "substantially composed of carbon atoms" means that impurities of about 2 to 3% by weight or less can be mixed.

Specific examples of the conductive carrier include carbon black such as acetylene black, channel black, oil furnace black, gas furnace black (for example, Vulcan), lamp black, thermal black, and Ketjenblack (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 nanofibers Carbon nanohorn; carbon fibril; activated carbon; coke; natural graphite; artificial graphite and the like. Further, as the conductive carrier, zeolite template carbon (ZTC) having a structure in which nano-sized band-shaped graphene is regularly connected in a three-dimensional manner can also be mentioned.

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

Further, the size of the conductive carrier is not particularly limited, from the viewpoint of easy loading, catalyst utilization rate, controlling the thickness of the electrode catalyst layer in an appropriate range, and the like, the average particle diameter is 5 to 200 nm, The thickness is preferably about 10 to 100 nm. The "average particle diameter of the carrier" is the average crystallite diameter obtained from the half-value width of the diffraction peak of the carrier particles in X-ray diffraction (XRD) or the average particle diameter 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 carrier” means the average particle size of carrier particles examined from a transmission electron microscope image for a statistically significant number of samples (eg, at least 200, preferably at least 300). It is a value. Here, the “particle diameter” means the maximum distance among the distances between any two points on the contour line of the particle.

The amount of the conductive carrier added to the platinum precursor-containing liquid is not particularly limited, but it is preferably adjusted so as to be 2 to 70% by weight with respect to the total amount of the carrier. By setting the supported concentration in such a range, aggregation of the catalyst particles can be suppressed, and an increase in the thickness of the electrode catalyst layer can be suppressed, which is preferable. It is more preferably 5 to 60% by weight, and even more preferably more than 5% by weight and 50% by weight or less. From the viewpoint of further improving the mass specific activity, the supported concentration (supported amount, metal conversion) of the alloy particles (catalyst particles) is preferably 10 to 45% by weight. The supported concentration (supported amount) of the alloy particles (catalyst particles) is the total supported concentration (total supported amount) (metal conversion) of platinum atoms and non-platinum metal atoms on the conductive carrier. When the amount of the alloy particles (catalyst particles) supported is within such a range, the balance between the degree of dispersion of the catalyst components on the catalyst carrier and the catalyst performance can be controlled appropriately. The supported amount of the catalyst component can be examined by a conventionally known method such as ICP atomic emission spectroscopy (ICP), inductively coupled plasma mass spectrometry (ICP mass spectrometry), and fluorescent X-ray analysis (XRF). it can.

After adding the conductive carrier, stirring may be performed. As a result, the platinum precursor and the conductive carrier are uniformly mixed, so that the platinum particles can be uniformly dispersed on the conductive carrier. Here, the stirring conditions are not particularly limited as long as they can be mixed particularly uniformly. For example, it is possible to uniformly disperse and mix by using an appropriate stirrer such as a stirrer or a homogenizer, or by applying ultrasonic waves such as an ultrasonic dispersion device. The stirring temperature is preferably 0 to 50°C, more preferably 5 to 40°C. The stirring time may be appropriately set so that the dispersion is sufficiently performed, and is usually 1 to 60 minutes, preferably 5 to 40 minutes.

Further, the reducing agent is not particularly limited, and the same reducing agent as the conventional one can be used. For example, ethanol, methanol, propanol, formic acid, formate salts such as sodium formate and potassium formate, formaldehyde, sodium thiosulfate, citric acid, sodium citrate, citrate salts such as trisodium citrate, sodium borohydride (NaBH ₄ ) And hydrazine (N ₂ H ₄ ) can be used. Of the above reducing agents, trisodium citrate dihydrate can also act as an anti-aggregation agent. These may be in the form of hydrates. Further, two or more kinds may be mixed and used.

The form of addition 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. The solution form is preferable because it can be easily and uniformly mixed. Here, the solvent is not particularly limited as long as it can dissolve the reducing agent, and is appropriately selected depending on the type of the reducing agent. Specifically, the same solvent as the solvent used for preparing the platinum precursor-containing liquid can be used. However, the solvent used for the reducing agent solution and the solvent used for preparing the mixed solution do not have to be the same, but it is preferable that they are the same in consideration of uniform mixing property.

The amount of the reducing agent added is not particularly limited as long as it is an amount sufficient to reduce platinum ions. Specifically, the reducing agent is preferably added in an amount of 5 to 90 mol with respect to 1 mol of platinum ion (metal conversion). With such an amount, platinum ions can be sufficiently reduced. When two or more reducing agents are used, the total addition amount of these is preferably within the above range.

After adding the reducing agent, stirring may be performed. As a result, the platinum precursor and the reducing agent are uniformly mixed, so that a uniform reduction reaction is possible. Here, the stirring conditions are not particularly limited as long as they can be mixed particularly uniformly. For example, it is possible to uniformly disperse and mix by using an appropriate stirrer such as a stirrer or a homogenizer, or by applying ultrasonic waves such as an ultrasonic dispersion device. The stirring temperature is preferably 0 to 50°C, more preferably 5 to 40°C. The stirring time may be appropriately set so that the dispersion is sufficiently performed, and is usually 1 to 60 minutes, preferably 5 to 40 minutes.

After adding a conductive carrier and a reducing agent to the platinum precursor-containing liquid, platinum ions derived from the platinum precursor are reduced and supported on the conductive carrier to obtain a liquid containing platinum-supported precursor particles.

The conditions for the reduction reaction of the platinum precursor are not particularly limited as long as the platinum ions derived from the platinum precursor can be sufficiently reduced and supported on the conductive carrier. For example, the reduction reaction temperature is preferably near the boiling point of the solvent (solvent boiling point ±10°C, more preferably solvent boiling point ±5°C). Alternatively, the reduction reaction temperature is preferably 40 to 150°C, more preferably 60 to 100°C. The reduction reaction time is not particularly limited as long as the platinum precursor and the reducing agent can be uniformly mixed, but is preferably 0.5 to 24 hours, more preferably 1 to 8 hours. Under such conditions, platinum can be highly dispersed and carried by the conductive carrier. As the conductive carrier, only the conductive carrier may be added, or it may be added in the form of a suspension.

By the reduction reaction, platinum ions derived from the platinum precursor are reduced and supported on the conductive carrier, and a liquid containing platinum-supported precursor particles (platinum-supported precursor particle-containing liquid) is obtained. Here, if necessary, the platinum-supported precursor particles may be isolated from the platinum-supported precursor particle-containing liquid. Here, the isolation method is not particularly limited, and the platinum-supported precursor particles may be filtered and dried. If necessary, the platinum-supported precursor particles may be filtered and then washed (for example, washed with water). Further, the filtration and the washing step if necessary may be repeated. Further, the platinum-supported precursor particles may be dried after filtration or washing. Here, the platinum-supported precursor particles may be dried in air or under reduced pressure. The drying temperature is not particularly limited, but it can be performed, for example, in the range of 10 to 100°C, preferably room temperature (25°C) to 80°C. The drying time is also not particularly limited, but may be, for example, 1 to 60 hours, preferably 5 to 50 hours.

Next, a non-platinum metal precursor and a reducing agent are added to the liquid containing the platinum-supported precursor particles to prepare a non-platinum metal precursor-containing liquid. Here, the liquid containing the platinum-supporting precursor particles may be any liquid containing the platinum-supporting precursor particles, and may be the liquid after the reduction reaction (platinum-supporting precursor particle-containing liquid). Alternatively, as described above, after the platinum-supported precursor particles are isolated from the platinum-supported precursor particle-containing liquid, the platinum-supported precursor particles prepared by separately dispersing the platinum-supported precursor particles in a solvent are used. Good. The solvent that can be used in the latter case is not particularly limited, but a solvent that can dissolve the non-platinum metal precursor used is preferable. Therefore, a preferable solvent can be appropriately selected depending on the kind of the non-platinum metal precursor used. Specifically, the same solvents as those exemplified for the platinum precursor-containing liquid can be used. Of these, water is preferable, and pure water or ultrapure water is particularly preferable, from the viewpoint of sufficiently dissolving the non-platinum metal precursor (effectively ionizing the non-platinum metal). The above solvents may be used alone or in the form of a mixture of two or more kinds. The platinum-containing precursor particle-containing liquid and the solvent used for preparing the platinum precursor-containing liquid may be the same or different.

The order of addition of the non-platinum metal precursor and the reducing agent to the liquid containing the platinum-supported precursor particles is not particularly limited, but it is easy to disperse the non-platinum metal particles on the conductive carrier and alloy with platinum. In consideration of ease and the like, it is preferable to first add the non-platinum metal precursor to the platinum-supported precursor particle-containing liquid and then add the reducing agent.

The non-platinum metal precursor is not particularly limited, but non-platinum metal salts and non-platinum metal complexes can be used. More specifically, non-platinum metal nitrates, sulfates, ammonium salts, amines, carbonates, bicarbonates, halides such as bromides and chlorides, nitrites, inorganic salts such as oxalic acid, formates, etc. The carboxylic acid salts, hydroxides, alkoxides, oxides and the like of can be used. That is, a compound in which a non-platinum metal can be a metal ion in a solvent such as pure water is preferable. Of these, the non-platinum metal salt is more preferably a halide (especially chloride), a sulfate or a nitrate. The above non-platinum metal precursors may be used alone or as a mixture of two or more. The non-platinum metal precursor may also be in the form of a hydrate.

Here, the non-platinum metal (non-platinum metal atoms) is not particularly limited, catalytic activity, in view of the ease of regularization (L1 ₂ structure formed ease of), to be a transition metal atom preferable. Here, the transition metal atom refers to a Group 3 element to a Group 12 element, and the type of transition metal atom is not particularly limited. Catalytic activity, (ease of formation of the L1 ₂ structure) ease of ordering from the viewpoint of the transition metal atom, vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt It is preferably selected from the group consisting of (Co), copper (Cu), zinc (Zn) and zirconium (Zr). Of these, cobalt (Co) is preferable. As described above, the activity is increased by including the metal atom forming the intermetallic compound with platinum (Pt) among the transition metals. Since the above transition metal atom easily forms an intermetallic compound with platinum (Pt), the mass specific activity (activity per unit mass) can be further improved while reducing the amount of platinum used. Further, the alloy of the above transition metal atom and platinum can achieve higher area specific activity (activity per unit area) and durability (activity after durability test). The above transition metal atoms may be alloyed with platinum alone, or two or more may be alloyed with platinum.

The concentration of the non-platinum metal precursor in the non-platinum metal precursor-containing liquid is not particularly limited, but is preferably 0.01 to 10% by weight, and more preferably 0.01 to 5% by weight in terms of metal. .. Alternatively, the concentration of the non-platinum metal precursor is such that the mixing ratio of the platinum precursor and the non-platinum metal precursor (mixing ratio of platinum precursor:non-platinum metal precursor (molar ratio)) is alloy particles shown below. It is preferable that the concentration be such that With such an amount, the ratio of platinum atom to non-platinum metal atom of the catalyst particles is appropriately controlled (or platinum atom is controlled to 1.5 to 15 mol to 1 mol of non-platinum metal atom). , well ordered can (an L1 ₂ structure can satisfactorily form). The supported concentration of the alloy (catalyst) particles supported on the finally prepared carrier is adjusted by the amounts of the platinum precursor and the non-platinum metal precursor. However, even if the same preparation is performed before the heat treatment, the supported concentration may be slightly different when the heat treatment conditions are different.

Further, the reducing agent is not particularly limited, and the same reducing agent as exemplified in the reduction reaction of the platinum precursor can be used in the same form as described above.

The amount of the reducing agent added is not particularly limited as long as it is an amount sufficient to reduce non-platinum metal ions. Specifically, the amount of the reducing agent added is preferably 10 to 90 mol, based on 1 mol of the non-platinum metal ion (metal conversion). With such an amount, non-platinum metal ions can be sufficiently reduced. When two or more reducing agents are used, the total addition amount of these is preferably within the above range.

After adding the reducing agent, stirring may be performed. As a result, the non-platinum metal precursor and the reducing agent are uniformly mixed, which enables a uniform reduction reaction. Here, the stirring conditions are not particularly limited as long as they can be mixed particularly uniformly. For example, it is possible to uniformly disperse and mix by using an appropriate stirrer such as a stirrer or a homogenizer, or by applying ultrasonic waves such as an ultrasonic dispersion device. The stirring temperature is preferably 0 to 50°C, more preferably 5 to 40°C. The stirring time may be appropriately set so that the dispersion is sufficiently performed, and is usually 1 to 60 minutes, preferably 5 to 40 minutes.

After adding a non-platinum metal precursor and a reducing agent to a liquid containing platinum-supported precursor particles, non-platinum metal ions derived from the non-platinum metal precursor are reduced and supported on a conductive carrier to support platinum/non-platinum metal A liquid containing precursor particles is obtained.

The conditions for the reduction reaction of the non-platinum metal precursor are not particularly limited as long as the non-platinum metal ions derived from the non-platinum metal precursor can be sufficiently reduced and supported on the conductive carrier. For example, the reduction reaction temperature is preferably 10 to 60°C, more preferably 15 to 40°C. The reduction reaction time is not particularly limited as long as it can uniformly mix the non-platinum metal precursor and the reducing agent, but is preferably 0.1 to 12 hours, more preferably 0.5 to 4 hours. Under such conditions, the non-platinum metal can be highly dispersed and carried by the conductive carrier. Further, since the unreduced platinum precursor and non-platinum metal precursor can be further reduced with a reducing agent, platinum and non-platinum metal can be efficiently dispersed and supported on the conductive carrier.

By the above reduction reaction, non-platinum metal ions derived from non-platinum metal precursor are reduced and supported on a conductive carrier, and a liquid containing platinum/non-platinum metal-supported precursor particles (platinum/non-platinum metal-supported precursor particle-containing liquid ) Is obtained. Here, if necessary, the platinum/non-platinum metal-supported precursor particles may be isolated from the platinum/non-platinum metal-supported precursor particle-containing liquid. Here, the isolation method is not particularly limited, and the platinum/non-platinum metal-supported precursor particles may be filtered and dried. If necessary, the platinum-supported precursor particles may be filtered and then washed (for example, washed with water). Further, the filtration and the washing step if necessary may be repeated. Further, the platinum-supported precursor particles may be dried after filtration or washing. Here, the platinum-supported precursor particles may be dried in air or under reduced pressure. The drying temperature is not particularly limited, but it can be performed, for example, in the range of 10 to 100°C, preferably room temperature (25°C) to 80°C. The drying time is also not particularly limited, but may be, for example, 1 to 60 hours, preferably 5 to 50 hours.

The platinum/non-platinum metal-supported precursor particles obtained as described above are heated and alloyed. Thereby, catalyst precursor particles are obtained.

Here, the heating (alloying) conditions are not particularly limited as long as platinum and non-platinum metal can be sufficiently alloyed, and may be appropriately selected depending on the amount of platinum or non-platinum metal supported, the type of non-platinum metal, and the like. Good. Specifically, the heating (alloying) temperature is preferably 200 to 1500°C, more preferably 500 to 1200°C. The heating (alloying) time is preferably 0.5 to 10 hours, more preferably 1 to 4 hours.

The heating (alloying) may be performed in any atmosphere, but it is preferably performed in a non-oxidizing atmosphere in order to further reduce platinum or a non-platinum metal. 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 above inert gas may be used alone or in the form of a mixed gas of two or more kinds. The reducing gas atmosphere is not particularly limited as long as it contains the reducing gas, 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. 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. Is. With such a concentration, the oxidation of the alloy (platinum and non-platinum metal) can be sufficiently suppressed/prevented. Of the above, the heat treatment is preferably performed in a reducing gas atmosphere. Under such conditions, the catalyst precursor particles can improve the mass specific activity without aggregating on the carrier.

Further, in the above, the catalyst precursor particles are supported on the conductive carrier by the liquid phase reduction supporting, but the method is not limited to the above. In addition to the above methods, known methods such as an impregnation method, an evaporation-drying method, a colloid adsorption method, a spray pyrolysis method, and a reverse micelle (microemulsion method) can be used.

In this way, catalyst precursor particles are obtained. Here, the composition of the catalyst precursor particles is also not particularly limited, but the composition of the catalyst precursor particles and the alloy particles (catalyst particles) obtained after the subsequent step (b) are substantially the same. In view of the alloy particles catalyst activity (catalyst particles) (in particular the mass specific activity), (ease of formation of the L1 ₂ structure) height of order parameter, the composition of the catalyst precursor particles, the non-platinum metal atom 1 mol On the other hand, the platinum atom content is preferably 1.0 to 15 mol, more preferably 1.2 to 10 mol, and particularly preferably 1.5 to 5 mol. With such a composition, the alloy particles (catalyst particles) obtained after the next step (b) can further improve the mass specific activity and order. The composition of the catalyst precursor particles and the alloy particles (catalyst particles) (the content of each metal atom in the catalyst particles) is determined by inductively coupled plasma emission spectrometry (ICP mass spectrometry) or inductively coupled plasma mass spectrometry (ICP mass spectrometry). , Fluorescent X-ray analysis (XRF), etc.

Moreover, the size of the catalyst precursor particles is not particularly limited. For example, the average particle size of the catalyst precursor particles is preferably 1 to 15 nm, more preferably 2 to 10 nm or less. The average particle diameter (nm) of the catalyst precursor particles and the alloy particles (catalyst particles) described below 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, and the particle of each particle is calculated. 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 according to the following formula (A). The number of particles to be measured (n) is not particularly limited, but is preferably a number with no statistically significant difference, and is at least 300.

(Process (b))
The catalyst precursor particles obtained in the step (a) are heated to an initial set temperature, maintained at the initial set temperature for less than 10 minutes, and then cooled at a rate of less than 5° C./minute.

In this step, the initial set temperature is not particularly limited, but the alloy particles (catalyst precursor particles) are ordered/disordered, which is obtained from the temperature dependence curve of the degree of order of the alloy particles (catalyst precursor particles). It is preferably at or above the transformation temperature. In the present specification, "the transformation temperature at which the alloy particles (catalyst precursor particles) are ordered/disordered, which is obtained from the temperature dependence curve of the degree of order of the alloy particles (catalyst precursor particles)" is simply referred to as "transformation temperature". Also called. In this way, by setting the initial setting temperature to the transformation temperature or higher, the catalyst precursor particles (alloy particles) become a solid solution (structure in which platinum and non-platinum metal are randomly arranged). For this reason, the ordering proceeds more effectively (the L1 ₂ structure is more easily formed) when the temperature is lowered after the catalyst precursor particles are maintained at the initial set temperature, and the activity and durability of the obtained electrode catalyst are further improved. It can be effectively improved. Here, the transformation temperature depends on the composition of the alloy, the particle diameter of the alloy particles, and the like. Since the catalyst metal precursor particles and the catalyst particles supported on the conductive carrier in the electrode catalyst of the present invention can be regarded as having substantially the same composition and particle diameter, the transformation temperature of the catalyst metal precursor particles is the transformation temperature of the catalyst particles. Is substantially the same as.

In the present specification, the "transformation temperature" is the temperature at the boundary between the ordered and disordered alloy particles in the temperature dependence curve of the order of the alloy particles (catalyst metal precursor particles/catalyst particles). (That is, the temperature at which the regularity is 0 in the temperature dependence curve). The temperature dependence curve of the order of the alloy particles is prepared according to the following method.

<Method of creating temperature dependence curve of order of alloy particles>
It is necessary to measure the order in a state where thermodynamic equilibrium is reached at a certain temperature, and specifically, it can be performed by the following method. First, the prepared alloy particles are heated, and the maximum heating temperature of the alloy particles at that time is set to a temperature (° C.) or higher at which a solid solution is formed in the thermal equilibrium diagram of the alloy of the bulk body.

Next, at the maximum heating temperature obtained above and at a temperature reduced by 50° C. from the temperature, the ordering degree of the alloy particles is sequentially obtained, and the temperature is plotted on the horizontal axis and the ordering degree is plotted on the vertical axis. Create a temperature dependence curve. Here, "degree of ordering (%)" or "L1 ₂ structure rule of (%)" is, J. Mater. Chem. , 2004, 14, 1454-1460, and in the present specification, the peak area (Ia) of the maximum intensity of the X-ray diffraction (XRD) pattern and , Is defined as the ratio with the peak area (Ib) peculiar to the intermetallic compound. Specifically, the ordering degree is measured by performing X-ray diffraction (XRD) on the alloy particles (catalyst particles) at each temperature according to the following method to obtain an XRD pattern.

<Measurement method of degree of order of the L1 ₂ structure>
The alloy particles (catalyst particles) are subjected to X-ray diffraction (XRD) under the following conditions at each of the above temperatures to obtain an XRD pattern. In the obtained XRD pattern, the peak area (Ia) observed in the range of 2θ of 39 to 41° and the peak area (Ib) observed in the range of 31 to 34° are measured. Here, the peak observed in the 2θ value range of 39 to 41° is a peak peculiar to the lattice plane of platinum. The peak observed in the range of 39 to 41° is a peak representing the entire alloy particle structure. Also, peak 2θ value is observed in the range of 31 to 34 ° is the inherent peak L1 ₂ structure of the alloy particles.

Using the peak areas Ia and Ib, the following equation (1), and calculates degree of order of the L1 ₂ structure (%).

In the above formula (1), X is a value peculiar to the non-platinum metal atoms constituting the alloy particles. Specifically, X is a value shown in the table below.

Based on the degree of order at each temperature obtained above, the temperature is plotted on the horizontal axis and the degree of order is plotted on the vertical axis to create a temperature dependence curve. Based on this temperature dependence curve, the temperature at which the degree of order becomes 0 is determined, and this is taken as the transformation temperature. Taking the temperature dependence curve as shown in FIG. 2 as an example, in the temperature dependence curve of FIG. 2, the temperature at which the degree of order is 0% is “calculated from the temperature dependence curve of the degree of order of alloy particles. The transformation temperature at which the alloy particles are ordered/disordered”.

In this step, the heating temperature of the catalyst precursor particles is preferably equal to or higher than the transformation temperature thus obtained. Specifically, the heating temperature of the catalyst precursor particles is preferably 0°C or higher and lower than 150°C, more preferably 0 to 100°C, and particularly preferably 0 to 50°C higher than the transformation temperature. When heated to such a temperature, the catalyst precursor particles (alloy particles) become a solid solution (random arrangement of platinum and non-platinum metal) more efficiently. Therefore, the catalyst precursor particles can be more effectively ordered when the temperature is lowered after the catalyst precursor particles are heated and maintained at the initial set temperature (the order can be further improved).

Further, the heating atmosphere of the catalyst precursor particles is not particularly limited, but like the above heating (alloying), it is preferable to carry out in a non-oxidizing atmosphere in order to further promote the ordering. Here, the non-oxidizing atmosphere is the same as the above description of heating (alloying), and therefore the description is omitted here.

The rate of heating the catalyst precursor particles (temperature rising rate) is not particularly limited, but considering the effect of suppressing/preventing the aggregation and sintering of the catalyst precursor particles, the progress of ordering, etc., preferably 1 to 60° C./min. , And more preferably 5 to 30° C./min.

As described above, after heating the catalyst precursor particles to the initial set temperature (preferably above the transformation temperature), the catalyst precursor particles are maintained at this initial set temperature for less than 10 minutes. Here, if the maintaining time at the initial setting temperature is 10 minutes or more, the ordering degree of the obtained alloy (catalyst) particles is increased, but the specific surface area is greatly reduced. Therefore, the electrode catalyst having alloy particles obtained by maintaining the catalyst precursor particles at this initial set temperature for 10 minutes or more is inferior in mass specific activity (see Comparative Example below). The maintenance time of the catalyst precursor particles at the initial set temperature may be less than 10 minutes, preferably 5 minutes or less, more preferably 1 minute or less. Further, the lower limit of the maintenance time of the catalyst precursor particles at the initial set temperature is not particularly limited and may be 0 minutes or more, but is preferably 0.1 minutes or more. With such a maintenance time, the growth of the particle size (and hence the reduction of the specific surface area) due to the sintering and aggregation of the catalyst precursor particles (and thus the alloy particles) can be more effectively suppressed, and the alloy particles (electrode catalyst) The mass specific activity of can be further improved. The method of heating the catalyst precursor particles to the initial set temperature and further maintaining the temperature at that temperature is not particularly limited, and known means such as using an oven can be applied. Further, "maintaining the catalyst precursor particles at the initial setting temperature" means that the temperature of the catalyst precursor particles is changed to some extent with respect to the desired initial setting temperature in addition to the case of maintaining the catalyst precursor particles at the desired initial setting temperature. It also includes the case where the temperature is maintained within a range (for example, a desired initial set temperature ±5°C).

As described above, after maintaining the catalyst precursor particles at the initial set temperature for a short time, the temperature is lowered at a rate of less than 5° C./minute. Here, if the temperature lowering rate is 5° C./min or more, the catalyst precursor particles are rapidly cooled, the ordering does not proceed sufficiently, and the resulting alloy particles have a low ordering degree. Therefore, the electrode catalyst having alloy particles obtained by rapidly cooling the catalyst precursor particles at a rate of 5° C./minute or more after maintaining the initial set temperature has poor mass specific activity. The temperature lowering rate may be less than 5° C./min, preferably 4° C./min or less, more preferably 2° C./min or less, and particularly preferably 1° C./min or less. The lower limit of the temperature lowering rate is not particularly limited, but is preferably 0.01° C./min or more, more preferably 0.1° C./min or more, particularly preferably 0.2° C./min or more. In a preferred embodiment, the rate of temperature decrease after the initial set temperature is maintained is preferably 0.01 to 4°C/minute, more preferably 0.1 to 2°C/minute, and particularly preferably 0.2 to 1°C/minute. .. By cooling the catalyst precursor particles at such a temperature-decreasing rate, the resulting alloy (catalyst) particles have a higher degree of regularity (and therefore can exhibit higher activity). The temperature lowering means is not particularly limited, and known means can be applied.

Here, the lower limit of the temperature at which the temperature of the catalyst precursor particles is lowered (cooled) at the above-mentioned rate is determined from the temperature dependence curve of the degree of order of the alloy particles (catalyst precursor particles) in the alloy particles (catalyst precursor particles). It is preferable that the temperature is not higher than the temperature at which platinum atoms and non-platinum metal atoms can mutually diffuse. That is, the catalyst precursor particles are obtained at a rate of less than 5° C./minute up to a temperature below the temperature at which platinum atoms and non-platinum metal atoms can interdiffuse in the alloy particles, which is obtained from the temperature dependence curve of the order of the alloy particles. It is preferable to lower the temperature (cool). In the present specification, "the lower limit temperature at which platinum atoms and non-platinum metal atoms can interdiffuse in the alloy particles (catalyst precursor particles), which is obtained from the temperature dependence curve of the order of the alloy particles (catalyst precursor particles)" Is also simply referred to as "mutual diffusion lower limit temperature". By such a temperature to slowly cooling (cooling) because the platinum atom and a non-platinum metal atoms can interdiffusion, more easily formed to more effectively can proceed (L1 ₂ structure ordered alloy particles during cooling it can). Here, the lower limit temperature of mutual diffusion depends on the composition of the alloy, the particle diameter of the alloy particles, and the like. Since the catalyst metal precursor particles and the catalyst particles supported on the conductive carrier in the electrode catalyst of the present invention can be regarded as having substantially the same composition and particle diameter, the lower limit temperature of mutual diffusion of the catalyst metal precursor particles is It is substantially the same as the mutual diffusion lower limit temperature.

In the present specification, the “lower limit temperature of mutual diffusion” is the temperature at which the temperature dependence curve of the order of the alloy particles (catalyst particles) begins to reach a steady state. Specifically, the temperature dependence curve of the order of the alloy particles is created in the same manner as the above <method of creating the temperature dependence curve of the order of the alloy particles>. For example, in the same manner as above, taking the temperature dependence curve of FIG. 2 as an example, in the temperature dependence curve of FIG. 2, the difference (absolute value) in the degree of order between adjacent temperatures is 1% or less (lower limit=0% ) And a stable temperature is achieved. For example, in FIG. 2, the mutual diffusion temperature is 400° C. Here, the “difference in the degree of order between adjacent temperatures” means the degree of order (s _T ) at a certain temperature (T° C.) and the degree of order 50° C. lower than the above temperature ((T−50)° C.). the difference between the degree _{(s T-50) (=} | (s T) - (s T-50) | ( absolute value)), and order parameter at 50 ° C. lower than the temperature ((T-50) ℃) the difference between _{(s T-50)} and 100 ° C. lower than the temperature ((T-100) ℃) in the order parameter _{(s T-100) (=} | (s T-50) - (s T-100) | (Absolute value)).

It is preferable that the falling temperature (cooling temperature) of the catalyst precursor particles is equal to or lower than the lower limit temperature of mutual diffusion thus obtained. Specifically, the lowering temperature (cooling temperature) of the catalyst precursor particles is preferably 0° C. or higher and lower than 100° C., more preferably 0 to 50° C., particularly preferably 0 to 20° C. lower than the mutual diffusion lower limit temperature. .. When the temperature is lowered (cooled) to such a temperature, the platinum atoms and the non-platinum metal atoms do not interdiffuse in the alloy particles within a realistic time, so that the ordering degree of the obtained alloy particles can be maintained high. The "lower temperature limit of the catalyst precursor particles" means the temperature of the catalyst precursor particles, and is specifically the same as the atmospheric temperature in the heating container.

The catalyst precursor particles are cooled (cooled) to a temperature below the mutual diffusion lower limit temperature at a rate of less than 5° C./minute, and then cooled (cooled) to room temperature (25° C.) at the same rate to obtain an electrode catalyst according to the present invention. Good. However, it is preferable that the catalyst precursor particles are cooled (cooled) to a temperature below the mutual diffusion lower limit temperature at a rate of less than 5° C./minute and then further cooled (cooled) at a rate of 5° C./minute or more. After lowering (cooling) the catalyst precursor particles to a temperature below the mutual diffusion lower limit temperature at a rate of less than 5° C./minute, at a rate of 5° C./minute or more, a temperature at which particle growth due to sintering or aggregation of catalyst particles does not occur ( The temperature is preferably lowered (cooled) to preferably less than 200°C, more preferably 100°C or less, for example, room temperature (25°C). The temperature lowering (cooling) rate after lowering (cooling) the catalyst precursor particles to a mutual diffusion temperature or lower at a rate of less than 5° C./minute is more preferably 10° C./minute or more, particularly preferably 40° C./minute or more. is there. Further, the upper limit of the temperature lowering (cooling) rate after lowering (cooling) the catalyst precursor particles to the mutual diffusion temperature or lower at a rate of less than 5° C./minute is not particularly limited, but is preferably 400° C./minute or less. It is preferably 200° C./minute or less. By cooling (cooling) relatively slowly in this way and then cooling at a relatively higher rate, the growth of the particle size (and hence the reduction of the specific surface area) due to sintering and aggregation of the catalyst precursor particles (alloy particles) is further improved. It can be effectively suppressed. Therefore, the obtained electrode catalyst has a larger specific surface area while maintaining a high degree of regularity, so that it is possible to further improve the mass specific activity.

That is, according to a preferred embodiment of the present invention, the catalyst precursor particles, determined from the temperature dependence curve of the order of the alloy particles, up to a temperature at which platinum atoms and non-platinum metal atoms in the alloy particles can be interdiffused, After lowering the temperature at a rate of less than 5° C./minute, the temperature is further reduced at a rate of 5° C./minute or more. According to a further preferred embodiment of the present invention, the catalyst precursor particles are heated to a temperature below the temperature at which platinum atoms and non-platinum metal atoms can interdiffuse within the alloy particles, which is determined from the temperature dependence curve of the order of the alloy particles. After lowering the temperature at a rate of less than °C/min, at a rate of 5°C/min or more, a temperature at which particle growth due to sintering or aggregation of catalyst particles does not occur (preferably less than 200°C, more preferably 100°C or less, for example, The temperature is lowered to room temperature (25°C).

According to the above method, it is possible to sufficiently heat-treat the catalyst precursor particles and suppress the growth of the particle size (and hence the increase of the specific surface area) due to the sintering or aggregation of the catalyst particles. Therefore, the obtained alloy particles can increase the specific surface area while maintaining a high degree of ordering. Therefore, the electrode catalyst produced by the above method can exhibit high activity (particularly mass specific activity).

The electrode catalyst produced by the above method comprises alloy particles of platinum and a non-platinum metal (catalyst particles) supported on a conductive carrier. Here, the alloy particles (catalyst particles) are alloy particles composed of platinum atoms and non-platinum metal atoms. The term "alloy" is generally a generic term of metallic elements to which one or more metallic elements or non-metallic elements are added and which has metallic properties. The alloy particles (catalyst particles) according to the present invention, in the structure of the alloy, a eutectic alloy which is, so to speak, a mixture in which the constituent elements become separate crystals, those in which the constituent elements are completely melted into a solid solution, and the constituent elements Include an intermetallic compound or a compound of a metal and a nonmetal. In the present invention, the catalyst particles may be in any form, but include those in which at least platinum atoms and non-platinum atoms form an intermetallic compound.

Here, the composition of the alloy particles (catalyst particles) of platinum and non-platinum metal supported on the conductive carrier is not particularly limited, but is substantially the same as the composition of the catalyst precursor particles. Catalytic activity (especially mass specific activity), from the viewpoint of regulations of the height (L1 ₂ structure formed ease of), the composition of the alloy particles (catalyst particles), to non-platinum metal atom 1 mol, platinum The number of atoms is preferably 1.0 to 15 moles, more preferably 1.2 to 10 moles, and particularly preferably 1.5 to 5 moles. With such a composition, the alloy particles (catalyst particles) obtained after the next step (b) can further improve the mass specific activity and order.

The size of the alloy particles (catalyst particles) is not particularly limited. For example, the average particle diameter of the alloy particles (catalyst particles) is preferably 1 to 15 nm, more preferably 2 to 10 nm.

Further, the alloy particles in the present embodiment has an L1 ₂ structure as an internal structure. “Having an L1 ₂ structure” means that the order of the L1 ₂ structure is more than 0%. The catalyst particles having the above structure can exhibit high activity and durability even with a low platinum content. Here, regulations of the L1 ₂ structure of the alloy particles is not particularly limited, considering the effect of improving the activity, 30% or more (upper limit: 100%) is preferably from. The catalyst particles having the above structure can exhibit high activity and durability even with a low platinum content. Here, regulations of the L1 ₂ structure, and more preferably 45% or more, particularly preferably 50% or more (upper limit: 100%) is. With this, since the particles have a structure in which atoms are regularly arranged in a certain proportion or more, the activity can be further improved, and the activity and durability of the catalyst particles can be further improved. The “degree of order of the L1 ₂ structure (extent of ordering) (%)” or “degree of order (%)” of the alloy particles is measured at room temperature (in the method for measuring the order of the L1 ₂ structure) ( It is measured in the same manner as above except that the measurement is performed at 25°C.

Further, the electrode catalyst produced by the above method has a large specific surface area (m ² /g Pt). Specifically, the specific surface area of the electrode catalyst according to the present invention is preferably 35 (m ² /g Pt) or more, more preferably 40 (m ² /g Pt) or more, and particularly preferably 50 (m ² /g Pt). Pt) or more. Here, the upper limit of the specific surface area is preferably as large as possible and is not particularly limited, but is usually 120 (m ² /g Pt) or less, and 90 (m ² /g Pt) or less. Here, the specific surface area means the specific surface area per 1 g of platinum, and the value measured in the following examples is adopted.

The electrocatalyst produced by the method of the present invention has an increased specific surface area, and therefore can improve the mass specific activity even with a small platinum content. Further, the electrode catalyst produced by the method of the present invention has excellent durability. In addition, in the electrocatalyst produced by the method of the present invention, the alloy particles are monodispersed on the carrier without aggregating at a predetermined ratio or more. Therefore, the electrode catalyst according to the present invention can be suitably applied to a fuel cell application in which higher performance is required, such as a power source for household use or driving of a moving body. That is, the membrane electrode assembly and the fuel cell having the electrode catalyst manufactured by the method of the present invention in the catalyst layer have excellent power generation performance.

That is, the present invention also provides a membrane electrode assembly (MEA) provided with a catalyst layer containing an electrode catalyst produced by the method of the present invention, and a fuel cell. Hereinafter, one embodiment of a membrane electrode assembly (MEA) including a catalyst layer containing an electrode catalyst according to the present invention and a fuel cell will be described.

[Electrolyte Membrane-Electrode Assembly (MEA)]
The electrode catalyst according to 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) containing the electrode catalyst of the present invention, particularly an electrolyte membrane-electrode assembly (MEA) for a fuel cell. The electrolyte membrane-electrode assembly (MEA) of the present invention can exhibit high power generation performance (particularly mass specific activity) and durability.

The electrolyte membrane-electrode assembly (MEA) of the present invention can have the same configuration except that the electrode catalyst (catalyst) according to the present invention is used instead of the conventional electrode catalyst. Hereinafter, preferred embodiments of the MEA of the present invention will be described, but the present invention is not limited to the following embodiments.

The MEA is composed of an electrolyte membrane, an anode catalyst layer and an anode gas diffusion layer, and a cathode catalyst layer and a cathode gas diffusion layer, which are sequentially formed on both surfaces of the electrolyte membrane. Then, 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. This solid polymer electrolyte membrane has a function of selectively permeating protons generated in the anode catalyst layer to the cathode catalyst layer along the thickness direction during operation of a fuel cell (PEFC or the like), for example. The solid polymer electrolyte membrane also has a function as a partition wall for preventing the fuel gas supplied to the anode side and the oxidant gas supplied to the cathode side from being mixed.

The electrolyte material that constitutes the solid polymer electrolyte membrane is not particularly limited, and conventionally known knowledge can be appropriately referred to. For example, the fluorine-based polymer electrolyte or the hydrocarbon-based polymer electrolyte described as the polymer electrolyte in the catalyst layer below can be used in the same manner. At this time, it is not always necessary to use the same polymer electrolyte as that 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 between strength during membrane formation, durability during use, and output characteristics during use can be controlled appropriately.

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

The catalyst layer contains the electrode catalyst according to the present invention and the electrolyte. The electrolyte is not particularly limited, but is preferably an ion conductive polymer electrolyte. The polymer electrolyte plays a role of transmitting protons generated around the catalyst active material on the fuel electrode side, and is therefore 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 the ion exchange resin constituting the fluorine-based polymer electrolyte include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like. Perfluorocarbon sulfonic acid type polymer, perfluorocarbon phosphonic acid type polymer, trifluorostyrene sulfonic acid type polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid type polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride-per Examples thereof include fluorocarbon sulfonic acid type polymers. From the viewpoint of excellent heat resistance, chemical stability, durability, and mechanical strength, these fluoropolymer electrolytes are preferably used, and particularly preferably fluoropolymer electrolytes composed of perfluorocarbon sulfonic acid polymers. Is used.

Specific examples of the hydrocarbon-based electrolyte include sulfonated polyether sulfone (S-PES), sulfonated polyaryl ether ketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, sulfonated poly Examples thereof include ether ether ketone (S-PEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon-based polymer electrolytes are preferably used from the viewpoint of production such that the raw materials are inexpensive, the production process is simple, and the material selectivity is high. The above-mentioned ion exchange resins may be used alone or in combination of two or more. Further, the material is not limited to the above-mentioned materials, and other materials may be used.

The conductivity of protons is important in the polymer electrolyte responsible for proton transfer. Here, if the EW of the polymer electrolyte is too large, the ion conductivity of the entire catalyst layer is lowered. Therefore, the catalyst layer of this embodiment preferably contains a polymer electrolyte having a small EW. Specifically, the catalyst layer of the present embodiment preferably has an EW of 1500 g/eq. The following polymer electrolyte is contained, and more preferably 1200 g/eq. The following polymer electrolyte is contained, and particularly preferably 1000 g/eq. The following polyelectrolytes are included. On the other hand, when the EW is too small, the hydrophilicity is too high, which makes it difficult to smoothly move water. From such a viewpoint, the EW of the polymer electrolyte is preferably 600 or more. 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 the ion exchange group, and is expressed in the unit of “g/eq”.

In addition, the catalyst layer contains two or more kinds of polymer electrolytes having different EWs in the power generation surface, and the polymer electrolyte having the lowest EW among the polymer electrolytes has a relative humidity of gas in the channel of 90% or less. It is preferable to use it in the area. By adopting such a material arrangement, the resistance value can be reduced regardless of the current density region, and the battery performance can be improved. As the EW of the polymer electrolyte used in the region where the relative humidity of the gas in the channel is 90% or less, that is, the EW of the polymer electrolyte having the lowest EW, 900 g/eq. The following is desirable. As a result, the above-mentioned effect becomes more reliable and remarkable.

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

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

In the catalyst layer, if necessary, a water repellent such as polytetrafluoroethylene, polyhexafluoropropylene, or a tetrafluoroethylene-hexafluoropropylene copolymer, a dispersant such as a surfactant, glycerin, ethylene glycol (EG ), polyvinyl alcohol (PVA), propylene glycol (PG) and other thickening agents, and pore-forming agents and other additives may be included.

The film thickness (dry film thickness) of the catalyst layer is preferably 0.05 to 30 μm, more preferably 1 to 20 μm, and further 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) has a function of promoting diffusion of the gas (fuel gas or oxidant gas) supplied through the gas passage of the separator into the catalyst layer, and electronic conduction. It has a function as a pass.

The material constituting the base material of the gas diffusion layer is not particularly limited, and conventionally known knowledge can be appropriately referred to. For example, a sheet-like material having conductivity and porosity such as carbon woven fabric, paper-like papermaking body, felt, and non-woven fabric can be mentioned. The thickness of the base material may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. When the thickness of the substrate is a value within such a range, the balance between the mechanical strength and the diffusibility of gas and water can be controlled appropriately.

The gas diffusion layer preferably contains a water repellent agent for the purpose of further enhancing water repellency and preventing a flooding phenomenon and the like. The water-repellent agent is not particularly limited, but is a fluorine-based high-performance agent such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, or tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Examples include molecular materials, polypropylene, polyethylene and the like.

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 adopted. Among them, carbon black such as oil furnace black, channel black, lamp black, thermal black, and acetylene black can be preferably used because they have excellent electron conductivity and a large specific surface area. The average particle size of the carbon particles is preferably about 10 to 100 nm. This makes it possible to obtain a high drainage property by the capillary force and also improve the contact property with the catalyst layer.

As the water repellent used for the carbon particle layer, the same water repellents as mentioned above can be mentioned. Among them, a fluorine-based polymer material can be preferably used because it is excellent in water repellency and corrosion resistance during electrode reaction.

The mixing ratio of the carbon particles and the water repellent agent in the carbon particle layer is about 90:10 to 40:60 (carbon particles:water repellent agent) in weight ratio in consideration of the balance between water repellency and electron conductivity. It's good. The thickness of the carbon particle layer is not particularly limited, and may be appropriately determined in consideration of the water repellency of the obtained gas diffusion layer.

(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 in which a catalyst layer is transferred or applied to an electrolyte membrane by hot pressing and then dried, and a gas diffusion layer is joined to the electrolyte layer, or a microporous layer side of the gas diffusion layer (when the microporous layer is not included) In this case, two gas diffusion electrodes (GDE) are prepared by applying a catalyst layer on one side of the base material layer in advance and drying, and the gas diffusion electrodes are bonded to both sides of the solid polymer electrolyte membrane by hot pressing. If the coating conditions such as hot pressing and bonding conditions are appropriately adjusted depending on 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 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 passage through which a fuel gas flows, and a cathode having an oxidant gas passage through which an oxidant gas flows. It has a pair of separators consisting of side separators. The fuel cell of the present invention has excellent 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 to the following embodiments. In addition, each drawing is exaggerated for convenience of description, 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 have been described with reference to the drawings, the same reference numerals are given to the same elements in the description of the drawings, and overlapping description will be 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 has a solid polymer electrolyte membrane 2 and a pair of catalyst layers (anode catalyst layer 3a and cathode catalyst layer 3c) sandwiching the membrane. The laminated body of the solid polymer electrolyte membrane 2 and the catalyst layers (3a, 3c) is further sandwiched by a pair of gas diffusion layers (GDL) (anode gas diffusion layer 4a and cathode gas diffusion layer 4c). As described above, the solid 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 the PEFC 1, the MEA 10 is further sandwiched by a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 1, the separators (5a, 5c) are illustrated as being located 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 also as a separator for adjacent PEFCs (not shown). In other words, in the fuel cell stack, the MEAs are sequentially stacked via the separator to form the stack. In the actual fuel cell stack, the gas seal portion is arranged between the separator (5a, 5c) and the solid polymer electrolyte membrane 2 or between the PEFC 1 and another PEFC adjacent thereto. In FIG. 1, these descriptions are omitted.

The separators (5a, 5c) can be obtained, for example, by subjecting a thin plate having a thickness of 0.5 mm or less to a pressing process to form an uneven shape as shown in FIG. The convex portion of the separator (5a, 5c) viewed from the MEA side is in contact with the MEA 10. This ensures electrical connection with the MEA 10. In addition, the concave portion (the space between the separator and the MEA caused by the uneven shape of the separator) viewed from the MEA side of the separator (5a, 5c) is a gas for flowing the gas during the operation of the PEFC 1. Functions as a flow path. Specifically, a fuel gas (for example, hydrogen) is circulated through the gas passage 6a of the anode separator 5a, and an oxidant gas (for example, air) is circulated through the gas passage 6c of the cathode separator 5c.

On the other hand, the recess viewed from the side opposite to the MEA side of the separators (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 typically provided with a manifold (not shown). The manifold functions as a connecting means for connecting the cells when forming the stack. With such a structure, the mechanical strength of the fuel cell stack can be secured.

In addition, in the embodiment shown in FIG. 1, the separators (5a, 5c) are formed in an uneven shape. However, the separator is not limited to such an uneven shape, and may have any shape such as a flat plate shape or a partially uneven shape as long as it can exhibit the function of the gas flow path and the refrigerant flow path. 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 has a function as a partition wall that separates the fuel gas, the oxidant gas, and the coolant from each other. In order to secure these channels, it is preferable that each of the separators is provided with a gas channel and a cooling channel as described above. As a material for forming the separator, conventionally known materials such as dense carbon graphite, carbon such as carbon plate, metal such as stainless steel, and the like can be appropriately used without limitation. The thickness and size of the separator and the shape and size of each of the flow paths provided are not particularly limited, and can be appropriately determined in consideration of desired output characteristics of the obtained fuel cell.

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

Further, a fuel cell stack having a structure in which a plurality of electrolyte membrane-electrode assemblies are laminated via a separator and connected in series may be formed so that the fuel cell can exert a desired voltage. The shape and the like of the fuel cell are not particularly limited, and may be appropriately determined so that desired cell characteristics such as voltage can be obtained.

The PEFC and the electrolyte membrane-electrode assembly described above use a catalyst layer having excellent 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 in 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, and the polymer electrolyte fuel cell has been described as an example in the above description, but in addition to this, an alkaline fuel cell, a direct methanol fuel cell , A micro fuel cell, and the like. Among them, a polymer electrolyte fuel cell (PEFC) is preferable because it is small in size and can achieve high density and high output. Further, the fuel cell is useful as a stationary power source as well as a power source for a moving body such as a vehicle having a limited mounting space. Above all, it is particularly preferable that the power source is used as a power source for a mobile body such as an automobile, which requires a high output voltage after the operation is stopped for a relatively long time.

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. Among them, hydrogen and methanol are preferably used because they can achieve high output.

The 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 has excellent power generation performance and durability, and can be miniaturized. Therefore, the fuel cell of the present invention is particularly advantageous from the viewpoint of vehicle mountability when the fuel cell is applied to a vehicle.

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 to the following examples. In the following examples, unless otherwise specified, the operation was performed at room temperature (25°C). Further, unless otherwise specified, “%” and “part” mean “wt %” and “part by weight”, respectively.

Preparation Example A: Production of Catalyst Precursor Particle A 19 g of a carbon carrier was immersed in 1000 g of a dinitrodiamine platinum nitric acid aqueous solution (platinum content: 8 g) having a platinum concentration of 0.8% by weight, and after stirring, 100% methanol as a reducing agent 100 ml was added. As the carbon carrier, Ketjen Black (registered trademark) KetjenBlack EC300J (average particle diameter: 40 nm, BET specific surface area: 800 m ² /g carrier, manufactured by Lion Corporation) was used. This solution was stirred and mixed at the boiling point (about 95° C.) for 7 hours to support platinum on the carbon carrier. Then, the platinum particle-supporting carrier was obtained by filtering and drying.

20 g of the platinum particle-supporting carrier obtained above was dispersed in 2 L of water, and a cobalt precursor (cobalt sulfate, cobalt content 0.6 g (corresponding to 0.33 mol per mol of platinum)) was added. A reducing agent solution (10 g of sodium borohydride dissolved in 1 L of pure water) prepared separately was added to the whole, and the mixture was stirred and mixed with a stirrer at room temperature (25° C.) for 1 hour to cause reduction precipitation. Then, the precipitate was filtered and dried, and then alloying treatment was performed at 900° C. for 1 hour in a 100% by volume hydrogen gas atmosphere, whereby catalyst precursor particles A were manufactured.

The supported concentration (supported amount) of the catalyst metal precursor particles (Pt—Co alloy particles) in the catalyst precursor particles A thus obtained was 31.9% by weight (Pt: 29.0% by weight) based on the carrier. , Co: 2.9% by weight). The supported concentration was measured by ICP analysis. The same applies below. The average particle size of the catalytic metal precursor particles (Pt-Co alloy particles) was about 4 nm.

The transformation temperature and the mutual diffusion lower limit temperature of the catalytic metal precursor particles obtained in this example were 750° C. and 400° C., respectively.

Preparation Example B: Production of Catalyst Precursor Particles B In the same manner as in Preparation Example A above, a platinum particle-supporting carrier was obtained.

Next, 20 g of this platinum particle-supporting carrier was dispersed in 2 L of water, and a cobalt precursor (cobalt sulfate, cobalt content 1.0 g (corresponding to 0.6 mol per 1 mol of platinum)) was added. A reducing agent solution (10 g of sodium borohydride dissolved in 1 L of pure water) prepared separately was added to the whole, and the mixture was stirred and mixed with a stirrer at room temperature (25° C.) for 1 hour to cause reduction precipitation. Then, the precipitate was filtered and dried, and then alloying treatment was performed at 900° C. for 1 hour in a 100% by volume hydrogen gas atmosphere to produce catalyst precursor particles B.

The supported concentration (supported amount) of the catalyst metal precursor particles (Pt—Co alloy particles) in the catalyst precursor particles B thus obtained was 31.6% by weight (Pt: 26.9% by weight) based on the carrier. , Co: 4.7% by weight). The average particle size of the catalytic metal precursor particles (Pt-Co alloy particles) was about 4 nm.

The transformation temperature and the mutual diffusion lower limit temperature of the catalytic metal precursor particles obtained in this example were 750° C. and 400° C., respectively.

Example 1 Production of Electrode Catalyst A Catalyst precursor particles A were produced in the same manner as in Preparation Example A above.

With respect to the catalyst precursor particles A, the temperature was raised from room temperature (25° C.) to 750° C. at a rate of 10° C./min in a 100 volume% hydrogen gas atmosphere, and the temperature was maintained at 750° C. for 1 minute, and then 1° C./ It was cooled to 400° C. at a cooling rate of minutes. After the temperature reached 400° C., the electrode catalyst A was manufactured by rapidly cooling to 25° C. at a temperature decrease rate of 40° C./min. The order of this electrode catalyst A was measured and found to be 54%.

The supported concentration (supported amount) of the alloy particles (catalytic metal particles) in the electrode catalyst A thus obtained was 31.9% by weight (Pt: 29.0% by weight, Co: 2. 9% by weight).

Example 2: Production of Electrode Catalyst B Catalyst precursor particles B were produced in the same manner as in Preparation Example B above.

With respect to the catalyst precursor particles B, the temperature was raised from room temperature (25° C.) to 750° C. at a rate of 10° C./min in a 100 vol% hydrogen gas atmosphere, and the temperature was maintained at 750° C. for 1 minute, and then 1° C./ It was cooled to 400° C. at a cooling rate of minutes. After the temperature reached 400° C., the electrode catalyst B was manufactured by rapidly cooling to 25° C. at a temperature decrease rate of 40° C./min. When the order of this electrode catalyst B was measured, it was 66%.

The supported concentration (supported amount) of the alloy particles (catalytic metal particles) in the electrode catalyst B thus obtained was 31.6% by weight (Pt: 26.9% by weight, Co: 4. 7% by weight).

Example 3: Production of Electrode Catalyst C In the same manner as in Preparation Example B above, catalyst precursor particles B were produced.

With respect to the catalyst precursor particles B, the temperature was raised from room temperature (25° C.) to 750° C. at a rate of 10° C./min in a 100 vol% argon gas atmosphere, and the temperature was maintained at 750° C. for 1 minute, and then 1° C./ It was cooled to 400° C. at a cooling rate of minutes. After the temperature reached 400° C., the electrode catalyst C was manufactured by rapidly cooling to 25° C. at a temperature decrease rate of 40° C./min. The order of this electrode catalyst C was measured and found to be 49%.

The supported concentration (supported amount) of the alloy particles (catalytic metal particles) in the electrode catalyst C thus obtained was 31.6 wt% (Pt: 26.9 wt %, Co: 4. 7% by weight).

Example 4: Production of Electrode Catalyst D Catalyst precursor particles B were produced in the same manner as in Preparation Example B above.

With respect to the catalyst precursor particles B, the temperature was raised from room temperature (25° C.) to 750° C. at a rate of 10° C./min in a 100 vol% argon gas atmosphere, and the temperature was maintained at 750° C. for 1 minute, then 0.5 It was cooled to 400° C. at a temperature decreasing rate of° C./min. After the temperature reached 400° C., the electrode catalyst D was manufactured by rapidly cooling to 25° C. at a temperature decrease rate of 40° C./min. The order of this electrode catalyst D was measured and found to be 58%.

The supported concentration (supported amount) of the alloy particles (catalytic metal particles) in the electrode catalyst D thus obtained was 31.6% by weight (Pt: 26.9% by weight, Co: 4. 7% by weight).

Comparative Example 1: Production of Comparative Electrode Catalyst E Catalyst precursor particles A were produced in the same manner as in Preparation Example A above.

With respect to the catalyst precursor particles A, the temperature was raised from room temperature (25° C.) to 650° C. at a rate of 10° C./min in a 100 vol% hydrogen gas atmosphere, and the temperature was maintained at 650° C. for 2 hours, then 40° C./ Comparative Electrode Catalyst E was prepared by quenching to 25° C. at a cooling rate of minutes. The order of this comparative electrode catalyst E was measured and found to be 31%.

The supported concentration (supported amount) of the alloy particles (catalyst metal particles) in the comparative electrode catalyst E thus obtained was 31.9% by weight (Pt: 29.0% by weight, Co: 2) based on the carrier. 1.9% by weight).

Comparative Example 2: Production of Comparative Electrode Catalyst F In the same manner as in Preparation Example A above, catalyst precursor particles A were produced.

With respect to the catalyst precursor particles A, the temperature was raised from room temperature (25° C.) to 700° C. at a rate of 10° C./min in a 100 volume% hydrogen gas atmosphere, and the temperature was maintained at 700° C. for 2 hours, and then 40° C./ Comparative Electrode Catalyst F was produced by quenching to 25° C. at a temperature decrease rate of minutes. The order of the comparative electrode catalyst F was measured and found to be 41%.

The supported concentration (supported amount) of the alloy particles (catalyst metal particles) in the comparative electrode catalyst F thus obtained was 31.9% by weight (Pt: 29.0% by weight, Co: 2) based on the carrier. 1.9% by weight).

Comparative Example 3: Production of Comparative Electrode Catalyst G Catalyst precursor particles A were produced in the same manner as in Preparation Example A above.

With respect to the catalyst precursor particles A, the temperature was raised from room temperature (25° C.) to 700° C. at a rate of 10° C./min in a 100 vol% hydrogen gas atmosphere, and the temperature was maintained at 700° C. for 4 hours, and then 40° C./ Comparative Electrode Catalyst G was produced by quenching to 25° C. at a temperature decrease rate of minutes. The order of the comparative electrode catalyst G was measured and found to be 48%.

The supported concentration (supported amount) of the alloy particles (catalyst metal particles) in the comparative electrode catalyst G thus obtained was 31.9% by weight (Pt: 29.0% by weight, Co: 2) based on the carrier. 1.9% by weight).

Comparative Example 4: Production of Comparative Electrode Catalyst H In the same manner as in Preparation Example B above, catalyst precursor particles B were produced.

With respect to the catalyst precursor particles B, the temperature was raised from room temperature (25° C.) to 900° C. at a rate of 10° C./min in a 100 volume% hydrogen gas atmosphere, and the temperature was maintained at 900° C. for 2 hours, and then 10° C./ Comparative Electrode Catalyst H was manufactured by quenching to 25° C. at a temperature decrease rate of minutes. The regularity of this comparative electrode catalyst H was measured and found to be 72%.

The supported concentration (supported amount) of the alloy particles (catalyst metal particles) in the comparative electrocatalyst H thus obtained was 31.6% by weight (Pt: 26.9% by weight, Co: 4) based on the carrier. It was 0.7% by weight).

Regarding the electrode catalysts A to D and the comparative electrode catalysts E to H obtained above, the specific surface area (m ² /g Pt) and the mass specific activity (μA/g Pt) were measured according to the following methods. The results are shown in Table 2 below.

<Measurement of specific surface area>
The electrode catalysts of Examples and Comparative Examples were each loaded with 34 μg/cm ² of platinum per unit area on a rotating disk electrode (RDE, geometric area: 0.19 cm ² ) composed of a glassy carbon disk having a diameter of 5 mm. ^A Nafion (registered trademark) (coating amount of Nafion=10 μg/cm ² ) was uniformly dispersed and carried so as to have a value of 2, and a RDE electrode for performance evaluation was produced.

For the RDE electrode for performance evaluation of each example and comparative example, using an electrochemical measuring device, in 0.1 M perchloric acid at 25° C. saturated with N ₂ gas, a reversible hydrogen electrode (RHE) was used. Cyclic voltammetry was performed at a scanning rate of 50 mVs ^{−1 in} the potential range of 0.05 to 1.2V. The electrochemical surface area (cm ² ) of each electrode catalyst was calculated from the area of the hydrogen adsorption peak appearing at 0.05 to 0.4 V in the obtained voltammogram. The value obtained by dividing this by the amount of platinum supported on the RDE electrode was taken as the specific surface area (m ² /g Pt).

<Mass specific activity measurement>
For the RDE electrodes for performance evaluation of the examples and comparative examples, using an electrochemical measuring device, in 0.1 M perchloric acid saturated with oxygen at 25° C., a speed of 10 mV/s from 0.2 V to 1.2 V. The potential scanning was performed at. Furthermore, the effect of mass transfer (oxygen diffusion) was corrected from the current obtained by the potential scanning using the Koutecky-Levich equation, and then the current value at 0.9 V was extracted. Then, the value obtained by dividing the obtained current value by the total amount of platinum carried (6.7 μg) calculated from the amount of platinum carried per unit area was taken as the mass specific activity (A/g Pt). The method using the Koutecky-Levich formula is described in, for example, Electrochemistry Vol. 79, No. 2, p. 116-121 (2011) (Convection voltammogram (1) Oxygen reduction (RRDE)) in "Analysis of oxygen reduction reaction on 4 Pt/C catalyst".

From the results of Table 2 above, the electrocatalysts A to D of Examples 1 to 4 have a mass specific activity that is higher than that of the comparative electrocatalysts E to H produced by the method deviating from the temperature lowering condition specified in the present invention. It can be seen that it can be significantly improved. This result is because the electrocatalysts A to D of Examples 1 to 4 can significantly increase the specific surface area as compared with the comparative electrocatalysts E to H produced by the method deviating from the heat treatment conditions of the present invention. Be considered.

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 (4)

An alloy particle composed of a platinum atom and a non-platinum metal atom is supported on a conductive carrier to produce a catalyst precursor particle;
Wherein the catalyst precursor particles, after heating to the initial set temperature was maintained for less than 10 minutes by the initial set temperature, possess that cooling at a rate of less than 5 ° C. / min,
The initial set temperature is equal to or higher than the transformation temperature at which the alloy particles are ordered/disordered, which is obtained from the temperature dependence curve of the order of the alloy particles.
The method for producing an electrode catalyst, wherein the non-platinum metal atom is a transition metal atom . A rate of less than 5° C./min for the catalyst precursor particles up to a temperature at which platinum atoms and non-platinum metal atoms can interdiffuse in the alloy particles, which is determined from the temperature dependence curve of the order of the alloy particles. The method according to claim 1, wherein the temperature is further lowered at a rate of 5° C./minute or more after the temperature is lowered at 5. The transition metal atom is selected from the group consisting of vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn) and zirconium (Zr). The method according to claim 1 , wherein the method is performed. The method of claim 3 , wherein the transition metal atom is cobalt (Co).