JP6846210B2 - Electrode catalyst and membrane electrode assembly and fuel cell using the electrode catalyst - Google Patents

Description

The present invention relates to an electrode catalyst, a membrane electrode assembly using the electrode catalyst, and a fuel cell.

In recent years, in response to social demands and trends against the background of energy and environmental problems, fuel cells that operate even at room temperature and can obtain high output density have been attracting attention as power sources for electric vehicles and stationary power sources. A fuel cell is a clean power generation system in which the product of the electrode reaction is water in principle and has almost no adverse effect on the global environment. In particular, polymer electrolyte fuel cells (PEFCs) are expected as power sources for electric vehicles because they operate at relatively low temperatures.

The structure of a polymer electrolyte fuel cell generally has a structure in which an electrolyte membrane-electrode assembly (MEA) is sandwiched between separators. The electrolyte membrane-electrode assembly is formed by sandwiching a polymer electrolyte membrane between a pair of electrode catalyst layers and a gas diffusible electrode (gas diffusion layer; GDL).

In a polymer electrolyte fuel cell having an electrolyte membrane-electrode assembly as described above, both electrodes (cathode and anode) sandwiching the solid polymer electrolyte membrane are represented by the reaction formulas described below according to their polarities. The electrode reaction is advanced to obtain electrical energy. First, hydrogen contained in the fuel gas supplied to the anode (negative electrode) side is oxidized by the catalyst component to become protons and electrons (2H ₂ → 4H ⁺ + 4e ⁻ : reaction 1). Next, the generated protons pass through the solid polymer electrolyte contained in the electrode catalyst layer and the solid polymer electrolyte membrane in contact with the electrode catalyst layer, and reach the cathode (positive electrode) side electrode catalyst layer. Further, the electrons generated in the electrode catalyst layer on the anode side are the conductive carrier constituting the electrode catalyst layer, the gas diffusion layer in contact with the side different from the solid polymer electrolyte film of the electrode catalyst layer, the separator, and the outside. It reaches the cathode side electrode catalyst layer through the circuit. Then, the protons and electrons that reach 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 a fuel cell, electricity can be taken out to the outside through the above-mentioned electrochemical reaction.

Here, in order to improve the power generation performance, improving the activity of the electrode catalyst in the electrode catalyst layer is an important key. Conventionally, platinum has been widely used as a catalyst metal for electrode catalysts from the viewpoint of activity. 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 in which the platinum content in the catalyst particles is reduced while maintaining the activity.

As such a platinum alloy-based catalyst, Patent Document 1 describes a catalyst in which the mode radius of the pore distribution of mesopores having a radius of 1 to 10 nm is 2.5 to 10 nm, and alloy fine particles are supported in the mesopores. Is disclosed.

International Publication No. 2014/060646

In the platinum alloy-based catalyst of Patent Document 1, there was room for further improvement in activity. Therefore, an object of the present invention is to provide a means capable of further improving the catalytic activity in an electrode catalyst in which alloy fine particles are supported on a catalyst carrier.

The present inventors have conducted diligent research in order to solve the above problems. As a result, they have found that the above problems can be solved by devising the configuration of the electrode catalyst in which the catalyst component containing the alloy fine particles is supported on the catalyst carrier, and have completed the present invention.

That is, the electrode catalyst according to the present invention has a configuration in which a catalyst component containing alloy fine particles composed of platinum and a metal component other than platinum is supported on a catalyst carrier. The catalyst carrier has mesopores having a radius of 1 nm or more, and the mode radius of the pore distribution of the mesopores is 1 nm or more and less than 2.5 nm. Further, at least a part of the alloy fine particles is supported in the mesopores. Then, the measured value Q [Å] of the lattice constant of the alloy fine particles is smaller than the theoretical value P [Å] of the lattice constant according to Vegard's law calculated by the following mathematical formula 1 (that is, Q <P). Characterized by points:

According to the present invention, as a result of shortening the distance between Pt atoms in the alloy fine particles contained in the catalyst metal, the d-orbital overlap between adjacent metal atoms increases and the d-band center decreases, resulting in an electrode. It is possible to further improve the activity of the catalyst.

It is a schematic cross-sectional explanatory view which shows the shape and structure of the electrode catalyst which concerns on one Embodiment of this invention. It is a schematic sectional drawing which shows the basic structure of the polymer electrolyte fuel cell which concerns on one Embodiment of this invention.

Hereinafter, an embodiment of the electrode catalyst of the present invention, a membrane electrode assembly (MEA) and a fuel cell using the same will be described in detail with reference to the drawings as appropriate. However, the present invention is not limited to the following embodiments. It should be noted that each drawing is exaggerated for convenience of explanation, and the dimensional ratio of each component in each drawing may differ from the actual one. Further, when the embodiment of the present invention is described with reference to the drawings, the same elements are designated by the same reference numerals in the description of the drawings, and duplicate description will be omitted.

Further, in the present specification, "X to Y" indicating a range means "X or more and Y or less". Unless otherwise specified, the operation and physical properties are measured under the conditions of room temperature (20 to 25 ° C.) / relative humidity of 40 to 50%.

[Electrode catalyst (catalyst)]
One embodiment of the present invention relates to an electrode catalyst in which a catalyst component containing alloy fine particles composed of platinum and a metal component other than platinum is supported on a catalyst carrier. Here, the catalyst carrier has mesopores having a radius of 1 nm or more, and the mode radius of the pore distribution of the mesopores is 1 nm or more and less than 2.5 nm. Further, at least a part of the alloy fine particles is supported in the mesopores. The measured value Q [Å] of the lattice constant of the alloy fine particles is smaller than the theoretical value P [Å] of the lattice constant according to Vegard's law calculated by the following mathematical formula 1.

In addition, in this specification, a metal component other than platinum is also simply referred to as "non-platinum metal". Further, the mode radius of the pore distribution of the mesopore is also simply referred to as "mode diameter of the mesopore".

FIG. 1 is a schematic cross-sectional explanatory view showing the shape and structure of the catalyst according to this embodiment. As shown in FIG. 1, the electrode catalyst 20 according to this embodiment is composed of a catalyst metal (alloy fine particles) 22 and a catalyst carrier 23. Further, the electrode catalyst 20 has a mesopore 24 having a radius of 1 nm or more. At this time, the mode diameter of the mesopore is 1 nm or more and less than 2.5 nm. Further, in the form shown in FIG. 1, the catalyst metal (alloy fine particles) 22 is substantially composed of platinum and a metal component other than platinum, and at least a part thereof is supported in the mesopores. Here, "substantially" means platinum in the catalyst metal in an amount of 80% by weight or more, more preferably 90% by weight or more, still more preferably 95% by weight or more, and particularly preferably 98% by weight or more (upper limit 100% by weight). And it is composed of alloy fine particles composed of metal components other than platinum. At least a part of the catalyst metal (alloy fine particles) 22 may be supported inside the mesopores 24, and a part of the catalyst metal (alloy fine particles) 22 may be supported on the surface of the carrier 23.

It can be confirmed by the following procedure that "alloy fine particles are supported in the mesopores". That is, a scanning electron microscope (SEM) and a transmission electron microscope (TEM) are used to identify the catalyst metal particles exposed on the surface of the catalyst particles and the catalyst metal particles in the mesopores. EDX (Energy Dispersive X-ray Spectroscopy) is used for each particle to measure the molar content ratio of the metal component, and confirm that the particles are alloy fine particles composed of platinum and non-platinum metal.

Further, the molar ratio of platinum to the metal component other than platinum in the alloy fine particles supported in the mesopores (hereinafter, "the molar ratio of platinum to the metal component other than platinum in the alloy fine particles supported in the mesopores" is given. (Simply also referred to as “platinum content molar ratio”) is preferably 1.0 to 10.0. By setting the molar ratio of platinum to such a range, the catalytic activity is remarkably improved. From the viewpoint of catalytic activity, the molar ratio of platinum is preferably 1.0 to 9.0, and more preferably 1.5 to 4.0. The value of "the molar ratio of platinum to metal components other than platinum in the alloy fine particles supported in the mesopores" specifies 10 to 50 catalytic metal particles in the mesopores, and EDX (energy) is used for each particle. Dispersive X-ray spectroscopy) is used to measure the molar ratio of metal components to the second decimal place, and then the value obtained by calculating the average molar ratio is adopted. At this time, the average molar ratio is obtained up to the second decimal place, and the second decimal place is rounded off.

Here, the molar ratio of platinum is the amount of the non-platinum metal precursor charged when supporting the non-platinum metal, the particle size of the platinum particles supported in the mesopores before the non-platinum metal is supported, and the non-platinum metal supported. It can be controlled by the degree of hydrophilicity of the previous carrier, the size of the mesopores of the carrier before supporting the non-platinum metal, or the defoaming treatment. The larger the amount of the non-platinum metal precursor charged, the smaller the molar ratio of platinum. The larger the particle size of the platinum particles supported in the mesopores, the more the alloying of the platinum particles and the non-platinum metal is promoted, and the smaller the molar ratio of platinum is. The higher the degree of hydrophilicity of the carrier before supporting the non-platinum metal, the easier it is to promote the introduction of the non-platinum metal precursor solution into the mesopores, the more the alloying of the platinum particles and the non-platinum metal is promoted, and the molar ratio of platinum is increased. It becomes smaller. The larger the mesopore size of the carrier before supporting the non-platinum metal, the easier it is to promote the introduction of the non-platinum metal precursor solution into the mesopores, the alloying of the platinum particles and the non-platinum metal is promoted, and the platinum-containing molars. The ratio becomes smaller. Further, if defoaming treatment is performed as necessary, the introduction of the non-platinum metal precursor liquid into the mesopores is easily promoted, the alloying of the platinum particles and the non-platinum metal is promoted, and the molar ratio of platinum is reduced. Further, the particle size of the platinum particles supported in the mesopores is controlled by performing heat treatment after supporting the platinum particles to grow the platinum particles; the preparation of the platinum metal precursor when supporting the platinum metal. It can be controlled by the amount or the like.

The average particle size (diameter) of the alloy fine particles in the mesopores is preferably 2.0 nm or more, more preferably 2.0 nm or more and 30.0 nm or less, and further preferably 3.0 nm or more and 10.0 nm or less. By setting the average particle size of the alloy fine particles in the mesopores to 2.0 nm or more, the catalytic activity is further improved. It is considered that this is because the ratio of the non-platinum metal in the alloy fine particles supported in the mesopores is improved, and a catalyst having a desired non-platinum metal content ratio can be easily obtained. Further, when the average particle size of the alloy fine particles in the mesopores is 2.0 nm or more, the alloy fine particles are supported relatively firmly in the mesopores, and contact with the electrolyte in the catalyst layer is more effectively suppressed. Be prevented. In addition, elution due to a change in potential can be prevented, and deterioration in performance over time can be suppressed. Therefore, the catalytic activity can be further improved, that is, the catalytic reaction can be promoted more efficiently. Further, when the average particle size of the alloy fine particles in the mesopores is 30.0 nm or less, the alloy fine particles can be supported inside the mesopores of the carrier by a simple method, and the electrolyte coverage of the alloy fine particles can be reduced. Can be done.

The "average particle size of the alloy fine particles in the mesopores" in the present invention adopts a value calculated as follows: That is, a scanning electron microscope (SEM) and a transmission electron microscope. (Transmission electron microscope; TEM) is used to identify the catalytic metal exposed on the surface of the catalytic particles and the catalytic metal in the mesopores. 10 to 50 catalyst metals in the mesopores are specified, the particle size (diameter) of each particle is obtained to the second decimal place, and the average value is calculated. At this time, the average value is obtained up to the second decimal place, and the second decimal place is rounded off to obtain the first decimal place.

In the electrode catalyst according to the present embodiment, the catalyst carrier has mesopores having a radius of 1 nm or more, and the mode radius (most frequent diameter) of the pore distribution of the mesopores is 1 nm or more and less than 2.5 nm, and is 1 nm. It is preferably 2 nm or more and 2 nm or less. In the present specification, since the pores having a radius of 1 nm or more are defined as mesopores, the mode diameter of the mesopores is naturally 1 nm or more. Further, when the mode radius of the pore distribution of the mesopores of the catalyst carrier is less than 2.5 nm, the electrolyte (electrolyte polymer) is less likely to penetrate into the mesopores, so that the catalytic activity is remarkably improved.

Further, the mode radius of the pore distribution of the mesopores of the catalyst carrier is preferably 0.6 or less, preferably 0.1 to 0.6, with respect to the average particle size of the alloy fine particles in the mesopores. More preferred. By satisfying such a relationship, the distance between the alloy fine particles and the inner wall surface of the pores of the catalyst carrier is shortened, and the space in which water can exist is further reduced (that is, the amount of water adsorbed on the surface of the alloy fine particles is reduced. Can be done). In addition, water is interacted with the inner wall surface of the hole, and the water is easily retained on the inner wall surface of the hole. Therefore, the formation reaction of the metal oxide becomes slower, and the formation of the metal oxide becomes more difficult. As a result, the deactivation of the surface of the alloy fine particles is further suppressed, and high catalytic activity can be exhibited (that is, the catalytic reaction can be further promoted). Further, the catalyst metal is supported relatively firmly in the pores (mesopores), and contact with the electrolyte in the catalyst layer is more effectively suppressed / prevented. In addition, elution due to a change in potential can be prevented, and deterioration in performance over time can be suppressed. Therefore, the catalytic activity can be further improved (that is, the catalytic reaction can be promoted more efficiently).

The pore volume of the pores (mesopores) having a radius of 1 nm or more and less than 2.5 nm in the catalyst carrier is not particularly limited, but is preferably 0.4 cc / g or more. When the pore volume is within the above range, more catalyst metal can be stored (supported) in the mesopores, and the electrolyte and the catalyst metal can be physically separated in the catalyst layer (catalyst metal and electrolyte). Contact can be suppressed / prevented more effectively). Therefore, the activity of the catalytic metal can be utilized more effectively. Also, the presence of many mesopores can promote the catalytic reaction more effectively. In addition, in this specification, the pore volume of a hole having a radius of 1 nm or more and less than 2.5 nm is also simply referred to as “the pore volume of a mesopore”. The pore volume of the mesopores is more preferably 0.4 to 3 cc / g carrier, and particularly preferably 0.4 to 1.5 cc / g carrier.

"Radius of pores of mesopores (nm)" means the radius of pores measured by the nitrogen adsorption method (DH method). The "mode radius (nm) of the pore distribution of mesopores" means the radius of the pores at the point where the peak value (maximum frequency) is taken in the differential pore distribution curve obtained by the nitrogen adsorption method (DH method). .. The radius (nm) of the mesopores of the catalyst carrier can be measured by applying the DH method.

The “pore volume of the mesopores” means the total volume of the mesopores having a radius of 1 nm or more and less than 2.5 nm existing in the catalyst carrier, and is represented by the volume per 1 g of the carrier (cc / g carrier). The "pore volume of mesopores (cc / g carrier)" is calculated as the lower area (integral value) of the differential pore distribution curve obtained by the nitrogen adsorption method (DH method). The pore volume of the catalyst carrier can be measured by applying the DH method.

The "differential pore distribution" is a distribution curve in which the pore diameter is plotted on the horizontal axis and the pore volume corresponding to the pore diameter in the catalyst carrier is plotted on the vertical axis. That is, when the pore volume of the catalyst carrier obtained by the nitrogen adsorption method (DH method) is V and the pore diameter is D, the difference pore volume dV is divided by the logarithmic difference d (logD) of the pore diameter. The value (dV / d (logD)) is obtained. Then, the differential pore distribution curve is obtained by plotting this dV / d (logD) with respect to the average pore diameter of each division. The differential pore volume dV refers to an increase in the pore volume between measurement points. In the present specification, the method for measuring the radius of the mesopore and the volume of the pores by the nitrogen adsorption method (DH method) is not particularly limited, and for example, "Science of adsorption" (2nd edition Seiichi Kondo, Tatsuo Ishihara, Abe). Co-authored by Ikuo, Maruzen Co., Ltd.) and "Analysis Method of Fuel Cell" (Yoshio Takasu, Masaru Yoshitake, Tatsumi Ishihara, Kagaku-Dojin), D.I. Dollion, G.M. R. Health: J.M. Apple. Chem. , 14, 109 (1964) and the like described in known literature can be adopted.

In the present specification, the radius and the pore volume of the mesopores by the nitrogen adsorption method (DH method) are referred to as D.I. Dollion, G.M. R. Health: J.M. Apple. Chem. , 14, 109 (1964).

The BET specific surface area (m ² / g carrier) of the ^{catalyst carrier is not particularly limited, but is preferably 600 m 2} / g carrier or more, more preferably ^{600 to 3000 m 2} / g carrier, and 1100 to 1800 m ² It is more preferably a / g carrier. With the specific surface area as described above, more alloy particles can be stored (supported) in the mesopores. Further, the electrolyte and the alloy fine particles in the catalyst layer can be physically separated from each other, and the contact between the alloy fine particles and the electrolyte can be more effectively suppressed / prevented. Therefore, the catalytic activity of the alloy fine particles can be used more effectively.

In the present specification, the "BET specific surface area (m ² / g carrier)" of the catalyst carrier is measured by the nitrogen adsorption method. More specifically, about 0.04 to 0.07 g of catalyst carrier powder is precisely weighed and sealed in a sample tube. This sample tube is pre-dried in a vacuum dryer at 90 ° C. for several hours to prepare a sample for measurement. An electronic balance (AW220) manufactured by Shimadzu Corporation is used for weighing. In the case of a coating sheet, the net weight of the coating layer, which is obtained by subtracting the weight of Teflon (registered trademark) (base material) of the same area from the total weight of the coating sheet, is used as the sample weight of about 0.03 to 0.04 g. .. Next, the BET specific surface area is measured under the following measurement conditions. By creating a BET plot from the range of relative pressure (P / P0) of about 0.00 to 0.45 on the adsorption side of the adsorption / desorption isotherm, the BET specific surface area is calculated from the slope and intercept.

(Catalyst metal (alloy fine particles))
The catalyst metal is a metal component having a function of catalyzing an electrochemical reaction, and in the electrode catalyst according to the present invention, the catalyst metal is used as a catalyst carrier in a form containing alloy fine particles of platinum and a metal component other than platinum. It is supported.

The non-platinum metal is not particularly limited, but is limited to ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, copper, silver, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, zinc and zirconium. And so on. Non-platinum metal is not particularly limited, catalytic activity, from the viewpoint of forming easiness of intermetallic compounds and L1 ₂ structure to be described later, is preferably a transition metal. Here, the transition metal refers to a group 3 element to a group 12 element, and the type of the transition metal is also not particularly limited. Catalytic activity, in view of the intermetallic compound or L1 ₂ structure formation easiness of the transition metal, vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), copper It is preferably selected from the group consisting of (Cu), zinc (Zn) and zirconium (Zr). Of these, cobalt (Co) is preferable. As described above, the activity is increased by containing the metal atom forming the intermetallic compound with platinum (Pt) among the transition metals. Since the transition metal easily forms an intermetallic compound with platinum (Pt), it is possible to achieve higher area specific activity (activity per unit area) while reducing the amount of platinum used. The transition metal may be alloyed with platinum alone, or two or more of them may be alloyed with platinum.

Here, an alloy is generally a general term for a metal element to which one or more kinds of metal elements or non-metal elements are added and which has metallic properties. The structure of the alloy includes a eutectic alloy, which is a mixture in which the component elements are separate crystals, a solid solution in which the component elements are completely fused, and a compound in which the component elements are intermetallic compounds or compounds of metals and non-metals. There are things that are forming.

Since the activity as a catalyst metal can be further enhanced, it is preferable that the alloy fine particles in the electrode catalyst have an intermetallic compound structure in which platinum atoms and metal atoms other than platinum are regularly arranged as an internal structure. Having an intermetallic compound structure can be detected by the presence of peaks peculiar to intermetallic compounds in the X-ray diffraction (XRD) pattern. The crystal structure of the alloy fine particles in the electrode catalyst is not particularly limited, but a face-centered cubic lattice structure is preferable from the viewpoint of excellent catalytic activity.

Further comprising alloy particles in the electrocatalyst is an L1 ₂ structure, it is preferable degree of order of the L1 ₂ structure (Extent of ordering) is 30 to 100%. The alloy fine particles having the above structure can exhibit high activity even with a small platinum content. Rules of the L1 ₂ structure is preferably 40 to 100%, more preferably 45 to 100%, even more preferably it is 47-95%. Thereby, the activity of the electrode catalyst (particularly the area ratio activity) can be further improved.

"Rules of the L1 ₂ structure (Extent of ordering) (%)" 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. , Defined as the ratio to the peak area (Ib) peculiar to intermetallic compounds. Specifically, "rules of the L1 ₂ structure (Extent of ordering) (%)" is a value measured by the following methods.

<Measurement method of degree of order of the L1 ₂ structure (Extent of ordering)>
The catalyst particles are subjected to X-ray diffraction (XRD) under the following conditions to obtain an XRD pattern. In the obtained XRD pattern, the peak area (Ia) in which the 2θ value is observed in the range 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 range of 2θ value in the range of 39 to 41 ° is the peak derived from (111) of the platinum portion or the alloy portion. 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 to calculate the degree of order of the L1 ₂ structure.

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

Here, Vegard's law is known as an empirical rule for expressing the relationship between the composition of an alloy and its lattice constant. This means that the lattice constant of the alloy can be obtained as a weighted average value using the mole fraction of each of the constituent metals of the alloy and the lattice constant of a single substance. For example, according to the Vegard law, the lattice constant a of the alloy consisting of a metal atom A and the metal atom B is the molar fraction of the metal atoms A in the alloy and the mole fraction of metal atoms B and N _A and N _B , When the lattice constant of the metal atom A alone and the lattice constant of the metal atom B alone are a _A and a _B , respectively, it is calculated by a = N _A a _A + N _B a _B.

The measured value of the lattice constant in the alloy is generally a value in accordance with the above-mentioned Vegard's law, or in some cases, a value larger than this. On the other hand, the alloy fine particles of the catalyst metal constituting the electrode catalyst according to the present invention are characterized in that they have a lattice constant smaller than the lattice constant according to Vegard's law. That is, in the electrode catalyst according to the present embodiment, the measured value Q [Å] of the lattice constant of the alloy fine particles contained in the catalyst metal is the theoretical value [Å] of the lattice constant P according to Vegard's law calculated by the following mathematical formula 1. It is characterized by being smaller than.

According to the electrode catalyst according to the present embodiment, the present inventors have found that it is possible to further improve the catalytic activity by having a lattice constant smaller than the theoretical value P according to Vegard's law. Was done. As the measured value Q of the lattice constant, the value measured by the method described in the column of Examples described later shall be adopted. Further, the relationship between P and Q is not particularly limited as long as Q <P is satisfied as described above, but the following formula indicates how much the measured value Q of the lattice constant is compressed with respect to the theoretical value P. The calculated compression ratio value is preferably −0.1% or less (that is, Q ≦ 0.999P), more preferably −0.2% or less (that is, Q ≦ 0.998P). More preferably, it is −0.3% or less (that is, Q ≦ 0.997P), and particularly preferably −0.4% or less (that is, Q ≦ 0.996P). When the value of the compressibility is within such a range, an electrode catalyst having particularly excellent catalytic activity can be provided. On the other hand, the lower limit of the value of the compressibility is not particularly limited, but from the viewpoint of ease of manufacture, it may usually be −2.0% or more (that is, Q ≧ 0.98P).

Here, the mechanism by which the catalytic activity is improved by having the above-mentioned configuration has not been completely clarified. However, since the smaller lattice constant means that the distance between Pt atoms is shortened, the d-band center may decrease due to the increase in the overlap of d-orbitals between adjacent metal atoms. It is considered that it contributes to the improvement of catalytic activity. That is, the decrease in the d-band center causes the antibonding orbital of the covalent bond between the 2p orbital of the oxygen atom, which is a reactant at the cathode, and the d-orbital of the catalytic metal atom to shift downward, thereby increasing its occupancy. As a result, it is presumed that the binding force between the oxygen atom and the catalytic metal atom is reduced, which optimizes the interaction between the oxygen atom and the catalytic metal atom, thereby improving the catalytic activity. To. It should be noted that this mechanism is based on speculation to the last, and the technical scope of the present invention is not affected by the mechanism.

In the electrode catalyst according to this embodiment, alloy fine particles made of platinum and non-platinum metal are supported in the mesopores. However, alloy fine particles may be present in a portion other than the mesopores. The composition of the catalyst metal present in the entire electrode catalyst is not particularly limited. From the viewpoint of catalytic activity and the like, the composition of the catalyst metal present in the entire electrode catalyst is preferably 1.0 to 10.0 mol of platinum with respect to 1 mol of non-platinum metal, and 1.0 to 9. It is more preferably 0 mol, and particularly preferably 1.5 to 4.0 mol. With such a composition, it is possible to exhibit high catalytic activity while reducing the platinum content, and it is possible to reduce the cost of the fuel cell. The composition of the catalyst metal present in the entire electrode catalyst can be measured by ICP-MS (inductively coupled plasma mass spectrometer).

The electrode catalyst includes the above alloy fine particles and other alloy particles such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, copper, silver, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. It may further contain a single catalyst component or an alloy.

The shape and size of the alloy fine particles are not particularly limited, and the same shape and size as those of known catalyst components can be adopted. As the shape, for example, granular, scaly, layered, etc. can be used, but granular is preferable.

In the electrode catalyst, the supported concentration of the catalyst metal (also referred to as the supported amount or the supported ratio) is not particularly limited, but is preferably 2 to 70% by weight with respect to 100% by weight of the total amount of the catalyst carrier. preferable. It is preferable to set the loading concentration in such a range because the aggregation of the catalyst particles can be suppressed and the increase in the thickness of the electrode catalyst layer can be suppressed. The supported concentration of the catalyst metal is more preferably 5 to 60% by weight, still more preferably 10 to 60% by weight. The amount of the catalyst metal carried can be examined by conventionally known methods such as inductively coupled plasma emission spectrometry (ICP atomic emission spectrometry), inductively coupled plasma mass spectrometry (ICP mass spectrum spectrum), and fluorescent X-ray analysis (XRF). it can.

(Catalyst carrier)
The material of the catalyst carrier has mesopores, and pores having a mode diameter of 1 nm or more and less than 2.5 nm can be formed inside the carrier, and the catalyst component is supported inside the mesopores in a dispersed state. It is not particularly limited as long as it has a sufficient specific surface area and sufficient electron conductivity. Preferably, the main component is carbon. Preferably, it is described in Japanese Patent Application Laid-Open No. 2010-2088887 (US Patent Application Publication No. 2011/318254) and International Publication No. 2009/075264 (US Patent Application Publication No. 2011/058308). It is preferable to use a carrier produced by the above method as a starting material, and a catalyst on which platinum and a non-platinum metal are supported is used as an electrode catalyst. In addition, carbon blacks such as acetylene black, channel black, oil furnace black, gas furnace black (for example, Balkan), lamp black, thermal black, and Ketjen black (registered trademark) are specifically considered to be carbon as the main component. Black Pearl®; Graphite acetylene black; Graphite channel black; Graphite oil furnace black; Graphite gas furnace black; Graphite lamp black; Graphite thermal black; Graphite Ketjen black; Graphite black pearl ; Carbon nanotubes; carbon nanofibers; carbon nanohorns; carbon fibrils; activated carbon; coke; natural graphite; artificial graphite and the like can be mentioned as examples of starting materials. "The main component is carbon" means that a carbon atom is contained as a main component, and is a concept including both a carbon atom and a substantially carbon atom, and an element other than the carbon atom is included. It may be included. "Substantially composed of carbon atoms" means that contamination of about 2 to 3% by weight or less of impurities can be tolerated.

In addition to the above carbon materials, porous metals such as Sn (tin) and Ti (titanium), and conductive metal oxides can also be used as carriers.

The average particle size (diameter) of the carrier is preferably 20 to 100 nm. Within such a range, the mechanical strength can be maintained even when the carrier is provided with the pore structure, and the catalyst layer can be controlled within an appropriate range. Unless otherwise specified, the value of the "average particle size of the carrier" is observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). A value calculated as the average value of the particle diameters of the particles shall be adopted. Further, the "particle size" means the maximum distance among the distances between arbitrary two points on the contour line of the particles.

[Manufacturing method of electrode catalyst]
The method for producing the electrode catalyst is not particularly limited, but after platinum particles are supported on a catalyst carrier to obtain a platinum particle-supporting carrier, a non-platinum metal is supported and alloyed with respect to the platinum particle-supporting carrier. Is preferable.

Further, in order to efficiently alloy the non-platinum metal with the platinum particles in the mesopores and shorten the lattice constant, heat treatment and hydrophilization treatment are performed on the catalyst carrier before contacting the non-platinum metal. Is preferable.

Hereinafter, a method for producing a suitable electrode catalyst will be described. The following description is an example of the manufacturing method, and the manufacturing method of the electrode catalyst according to the present invention is not limited to the method described below.

In one embodiment of the present invention, the method for producing an electrode catalyst includes a step (1) of adding a reducing agent to a solution containing a carrier and a platinum precursor to prepare a platinum particle-supporting carrier, and a platinum particle-supporting carrier and a non-platinum metal. It further includes a step (2) of mixing the precursors and further performing an alloying treatment, and further includes a step (A) of heat-treating and hydrophilizing the platinum particle-supported carrier. Here, the step (A) is preferably performed after the step (1) and before the step (2) from the viewpoint of promoting the alloying of the non-platinum metal in the mesopores. That is, suitable forms of the method for producing an electrode catalyst include a step (1) of adding a reducing agent to a mixed solution containing a carrier and a platinum precursor to prepare a platinum particle-supporting carrier, and a heat treatment on the platinum particle-supporting carrier. In this order, the step (A) of performing the hydrophilization treatment and the step (2) of mixing the non-platinum metal precursor with the heat-treated and hydrophilized platinum particle-supported carrier and further performing the alloying treatment are included. This is a method for producing an electrode catalyst.

Hereinafter, each step will be described.

Process (1)
The step (1) is a step of preparing a platinum particle-supporting carrier by adding a reducing agent to the mixed solution containing the carrier and the platinum precursor.

First, the carrier is prepared. In the production of an electrode catalyst having a specific pore distribution as described above, it is usually important to make the mesopore distribution of the carrier the pore distribution as described above. Therefore, as the carrier used, it is preferable to use a carrier having mesopores having a radius of 1 nm or more and a mode diameter of the mesopores of 1 nm or more and less than 2.5 nm. Carriers with mesopores are also referred to herein as "porous carriers". Specific examples of such carriers include Japanese Patent Application Laid-Open No. 2010-2088887 (US Patent Application Publication No. 2011/318254) and International Publication No. 2009/075264 (US Patent Application Publication No. 2011/058308). It can be manufactured in consideration of the method described in the publication such as the book). Thereby, pores having a specific pore distribution (having mesopores having a radius of 1 nm or more and the mode diameter of the mesopores being 1 nm or more and less than 2.5 nm) can be formed on the carrier.

The BET specific surface area of the carrier used is preferably 600 to 3000 m ² / g, more preferably 1000 to 1800 m ² / g. With the specific surface area as described above, sufficient mesopores can be secured, so that more alloy particles can be stored (supported) in the mesopores. Further, the electrolyte and the alloy particles in the catalyst layer can be physically separated from each other, and the contact between the alloy particles and the electrolyte can be more effectively suppressed / prevented. Therefore, the activity of the alloy particles can be utilized more effectively. In addition, the balance between the dispersibility of the catalyst component on the catalyst carrier and the effective utilization rate of the catalyst component can be appropriately controlled.

The mode radius (most frequent diameter) of the pore distribution of the mesopores of the carrier used is 1 nm or more and less than 2.5 nm, and preferably 1 nm or more and 2 nm or less. The pore volume of the pores (mesopores) having a radius of 1 nm or more and less than 2.5 nm of the carrier used is not particularly limited, but is preferably 0.6 cc / g or more, and more preferably 0.6 to 3 cc. It is a / g carrier, particularly preferably 0.6 to 1.5 cc / g carrier.

Further, a carrier having the above-mentioned specific pores that has been further heat-treated may be used as the carrier. By performing such a heat treatment, the amorphous portion of the carrier before the heat treatment is removed, so that the mode diameter of the mesopores of the carrier becomes large, and the introduction of the non-platinum metal precursor liquid into the mesopores is promoted. It is preferable because it is easy and the alloying of platinum particles and non-platinum metal is promoted.

Specifically, the heat treatment temperature of the carrier in the above heat treatment is preferably more than 1300 ° C. and 1880 ° C. or lower, more preferably 1380 to 1880 ° C., and even more preferably 1400 to 1860 ° C. The rate of temperature rise in the heat treatment is preferably 100 to 1000 ° C./hour, and particularly preferably 300 to 800 ° C./hour. The heat treatment time (holding time at a predetermined heat treatment temperature) is preferably 1 to 10 minutes, and particularly preferably 2 to 8 minutes. The heat treatment can be performed in an atmosphere of an inert gas such as argon gas or nitrogen gas.

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 ammine salts such as hexaammine platinum, carbonates, bicarbonates, halides such as platinum chloride, inorganic salts such as nitrites and oxalic acid, carboxylates such as formates, hydroxides, and alcoholides. Can be done. The platinum precursor may be used alone or as a mixture of two or more.

The solvent used when preparing the mixed solution containing the carrier and the platinum precursor is not particularly limited, and is appropriately selected depending on the type of the platinum precursor used. The form of the mixed solution is not particularly limited, and includes a solution, a dispersion, and a suspension. Specific examples thereof include organic solvents such as water, 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 ionic compound of platinum. The solvent may be used alone or in the form of a mixture of two or more.

The weight ratio of the carrier and the platinum precursor in the mixed solution is appropriately set in consideration of the amount of platinum supported, but it is preferably carrier: platinum = 1: 0.02 to 2.3.

The method for preparing the mixed solution containing the carrier and the platinum precursor is not particularly limited. For example, the platinum precursor is dissolved in a solvent and then a carrier is added to it; the carrier is added to the solvent and then the platinum precursor is added; the carrier and the platinum precursor are added to the solvent; the platinum precursor and the carrier Are added to the solvent separately and then mixed; any method may be used. Since the platinum precursor can uniformly coat the carrier, it is preferable to dissolve the platinum precursor in a solvent and then add the carrier to the solvent. The platinum concentration when the platinum precursor is dissolved in the solvent is not particularly limited, but the platinum concentration is preferably 0.1 to 50% by weight, preferably 0.5 to 50% by weight, based on the dissolved solution. More preferably, it is 20% by weight.

Moreover, it is preferable to stir the above-mentioned mixed solution in order to mix them uniformly. Here, the stirring conditions are not particularly limited as long as they can be mixed uniformly. For example, uniform dispersion and mixing can be performed by using an appropriate stirrer such as a stirrer or a homogenizer, or by applying ultrasonic waves such as an ultrasonic disperser. The stirring temperature is preferably 0 to 50 ° C, more preferably 5 to 40 ° C. Further, the stirring time may be appropriately set so that the dispersion is sufficiently performed.

Examples of the reducing agent include ethanol, methanol, propanol, formic acid, formic acid such as sodium formate and potassium formate, citrate such as formaldehyde, sodium thiosulfate, citrate, sodium citrate and trisodium citrate, and borohydride. Sodium borohydride (NaBH ₄ ), hydrazine (N ₂ H ₄ ) and the like can be used. These may be in the form of hydrates. Further, two or more types may be mixed and used. Further, the reducing agent may be added in the form of a reducing agent solution.

The amount of the reducing agent added is not particularly limited as long as it is sufficient to reduce the platinum ions. Specifically, the amount of the reducing agent added is preferably 1 to 200 mol, more preferably 1.5 to 100 mol, with respect to 1 mol of platinum ions. With such an amount, platinum ions can be sufficiently reduced. When two or more kinds of reducing agents are used, the total addition amount of these agents is preferably in the above range.

It is preferable to stir after adding the reducing agent. 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 uniformly. For example, uniform dispersion and mixing can be performed by using an appropriate stirrer such as a stirrer or a homogenizer, or by applying ultrasonic waves such as an ultrasonic disperser. The stirring temperature is preferably 0 ° C. to the boiling point of the solution. The stirring time is not particularly limited as long as the platinum precursor and the reducing agent can be uniformly mixed.

A platinum particle-supporting carrier is obtained by the above reduction reaction.

If necessary, the obtained platinum particle-supporting carrier may be isolated from the solution. Here, the isolation method is not particularly limited, and the platinum particle-supporting carrier may be filtered and dried. If necessary, the platinum particle-supporting carrier may be filtered and then washed (for example, washed with water). Moreover, the above-mentioned filtration and washing step may be repeated if necessary. Further, the platinum particle-supporting carrier may be dried after filtration or washing. Here, the platinum particle-supporting carrier may be dried in air or under reduced pressure. The drying temperature is not particularly limited, but can be, 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 can be, for example, in the range of 1 to 60 hours, preferably about 5 to 50 hours.

Further, in the step (1), the amount of platinum carried on the carrier can be controlled by appropriately setting the platinum concentration in the mixed solution, the immersion time of the carrier, the reduction conditions, and the like.

Process (A)
The step (A) is a step of heat-treating and hydrophilizing the platinum particle-supporting carrier obtained in the step (1). By such a heat treatment, the lattice constant of the obtained alloy fine particles can be shortened from the theoretical value. Further, the hydrophilization treatment promotes the introduction of the non-platinum metal precursor into the mesopores, and the catalyst particles in the mesopores can form alloy particles uniformly alloyed, thereby improving the catalytic activity. it can.

The heat treatment conditions are not particularly limited, but for example, the heat treatment temperature is preferably 500 to 1200 ° C, more preferably 700 to 1100 ° C. The heat treatment time is preferably 0.1 to 3 hours, more preferably 0.1 to 1.5 hours. The heat treatment step may be performed in an air atmosphere or an inert gas atmosphere, but is preferably performed in a hydrogen atmosphere.

Examples of the hydrophilic treatment of the carrier include a method of introducing a hydrophilic group into the carrier as described in Japanese Patent Application Laid-Open No. 2012-124001. The hydrophilic group is preferably at least one selected from the group consisting of a hydroxyl group, a lactone group, and a carboxyl group.

The amount of the hydrophilic group introduced is appropriately set so that the alloy composition in the mesopores is in an appropriate range, but is preferably 0.01 to 5.0 mmol / g, preferably 0.1 to 3.0 mmol / g. It is more preferably g. The quantification of hydrophilic groups is carried out by a titration method, specifically by the method described in paragraph "0025" of JP2012-124001A, and the details are as follows.

The amount of hydrophilic groups is measured by the following titration method. That is, first, 2.5 g of the sample is washed and dried with 1 L of warm pure water. After drying, the sample is weighed so that the amount of carbon contained in the sample is 0.25 g, and after stirring with 55 ml of water for 10 minutes, ultrasonic dispersion is performed for 2 minutes. Next, the dispersion is moved to a glove box purged with nitrogen gas and the nitrogen gas is bubbled for 10 minutes. Then, a 0.1 M base aqueous solution is excessively added to the dispersion, and the basic solution is neutralized and titrated with 0.1 M hydrochloric acid to quantify the amount of functional groups from the neutralization point. Here, aqueous _{base, NaOH,} using three types of Na 2 CO 3, NaHCO _3, and subjected to neutralization titration tasks for each. This is because the type of functional group neutralized differs depending on the base used. In the case of NaOH, the carboxyl group, lactone group, and hydroxyl group, and in _{the case of Na 2} CO ₃ , the carboxyl group, lactone group, and NaHCO _This is because the case of 3 undergoes a neutralization reaction with the carboxyl group. Then, the amount of hydrophilic groups is calculated from the results of the three types and amounts of the three types of bases added by these titrations and the amount of hydrochloric acid consumed. Note that the confirmation of the neutralization point, using a pH meter, in the case of NaOH pH 7.0, in the case of _Na 2 CO ₃ pH 8.5, in the case of NaHCO ₃ and the neutral point of pH 4.5. As a result, the total amount of the carboxyl group, the lactone group, and the hydroxyl group is determined.

The introduction of the hydrophilic group can be carried out by contacting the carrier with an oxidizing solution. Examples of the oxidizing solution include solutions of sulfuric acid, nitric acid, phosphite, potassium permanganate, hydrogen peroxide, hydrochloric acid, chloric acid, hypochlorous acid, chromic acid and the like. Above all, it is preferable to use at least one of sulfuric acid and nitric acid because it is easy to introduce a hydrophilic group. This oxidizing solution treatment is not limited to the case where the carrier is brought into contact with the oxidizing solution once, but may be repeated a plurality of times. Further, when the acid treatment is performed a plurality of times, the type of the solution may be changed for each treatment.

The concentration of the oxidizing solution is preferably 0.1 to 10.0 mol / L, and the carrier is preferably mixed (immersed) in the solution. The mixed carrier dispersion is preferably agitated in order to mix uniformly. Here, the stirring conditions are not particularly limited as long as they can be mixed uniformly. For example, uniform dispersion and mixing can be performed by using an appropriate stirrer such as a stirrer or a homogenizer, or by applying ultrasonic waves such as an ultrasonic disperser. The stirring temperature is preferably 0 to 50 ° C, more preferably 5 to 40 ° C. Further, the stirring time may be appropriately set so that the dispersion is sufficiently performed.

Next, it is preferable to heat the dispersion liquid, and the heating promotes the introduction of hydrophilic groups. Here, the heating conditions are not particularly limited as long as they can impart hydrophilic groups to the carrier. For example, the heating temperature is preferably 50 to 100 ° C, more preferably 60 to 95 ° C. The heating time is preferably 0.5 to 3 hours.

Here, if necessary, the platinum-supported carrier after the hydrophilization treatment may be isolated from the dispersion. Here, the isolation method is not particularly limited, and the platinum-supported carrier may be filtered and dried. If necessary, the platinum-supported carrier may be filtered and then washed (for example, washed with water). Moreover, the above-mentioned filtration and washing step may be repeated if necessary. Alternatively, the platinum-supported carrier may be dried after filtration or washing. Here, the platinum-supported carrier may be dried in air or under reduced pressure. The drying temperature is not particularly limited, but can be, 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 can be, for example, in the range of 1 to 60 hours, preferably about 5 to 50 hours.

Further, the dispersion liquid of the platinum-supported carrier after the hydrophilic treatment may be used as it is in the step (2). In this case, it is preferable to add an alkali such as sodium hydroxide to the dispersion to adjust the pH (preferably, adjust the pH to 1 to 5).

Process (2)
The step (2) is a step of mixing a non-platinum metal precursor with a platinum particle-supported carrier that has been heat-treated and hydrophilized, and further alloying the platinum particles.

As the non-platinum metal precursor, a non-platinum metal salt and a non-platinum metal complex can be used. More specifically, non-platinum metals such as nitrates, sulfates, ammonium salts, amines, carbonates, bicarbonates, halides such as bromides and chlorides, inorganic salts such as nitrites and oxalates, formates, etc. Nitrite and hydroxides, alcoholides, oxides and the like can be used. That is, a compound in which a non-platinum metal can become a metal ion in a solvent such as pure water is preferably mentioned. Of these, as the salt of the non-platinum metal, a halide (particularly chloride), a sulfate, and a nitrate are more preferable. Specific examples of the non-platinum metal precursor include ruthenium chloride, ruthenium nitrate, sodium ruthenium, potassium ruthenium, iridium chloride, iridium nitrate, hexaammine iridium hydroxide, iridium chloride, ammonium iridium chloride, and iridium chloride. Examples thereof include potassium acid acid, ruthenium chloride, ruthenium nitrate, palladium chloride, palladium nitrate, dinitrodiammine palladium, iron chloride, cobalt sulfate, cobalt chloride and cobalt hydroxide. The non-platinum metal precursor 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.

The non-platinum metal precursor may be mixed with a platinum particle-supporting carrier as a non-platinum metal precursor liquid. The solvent used for the non-platinum metal precursor liquid is the same as the solvent listed in the column of the above step (1). The non-platinum metal concentration of the non-platinum metal precursor liquid is preferably 0.1 to 50% by weight, more preferably 0.5 to 20% by weight.

By mixing (immersing) the platinum particle-supporting carrier with the non-platinum metal precursor, a carrier carrying platinum and a non-platinum metal can be prepared.

Here, the method of mixing the hydrophilized platinum particle-supporting carrier and the non-platinum metal precursor is not particularly limited. For example, a platinum particle-supporting carrier is mixed (immersed) in a non-platinum metal precursor solution; a solvent dispersion of the hydrophilized platinum particle-supporting carrier and a non-platinum metal precursor (or non-platinum metal precursor solution) are mixed. Any method may be used.

The mixed weight ratio of the hydrophilized platinum particle-supporting carrier and the non-platinum metal precursor solution is appropriately set in consideration of the amount of the non-platinum metal supported, but the platinum particle-supporting carrier: non-platinum metal = 1: 0.05. It is preferably set to ~ 2.

Further, it is preferable that the platinum particle-supporting carrier and the non-platinum metal precursor solution that have been heat-treated and hydrophilized are mixed, and then uniformly mixed and stirred in order to uniformly support the non-platinum metal. Here, the stirring conditions are not particularly limited as long as they can be mixed uniformly. For example, uniform dispersion and mixing can be performed by using an appropriate stirrer such as a stirrer or a homogenizer, or by applying ultrasonic waves such as an ultrasonic disperser. The stirring temperature is preferably 0 to 50 ° C, more preferably 5 to 40 ° C. Further, the stirring time may be appropriately set so that the dispersion is sufficiently performed.

Further, in order to ensure that the non-platinum metal precursor adheres to the platinum particle-supporting carrier, the mixture of the platinum particle-supporting carrier and the non-platinum metal precursor that has been heat-treated and hydrophilized, or the non-platinum precursor liquid A reducing agent may be added. Examples of the reducing agent include ethanol, methanol, propanol, formic acid, formic acid such as sodium formate and potassium formate, citrate such as formaldehyde, sodium thiosulfate, citrate, sodium citrate and trisodium citrate, and borohydride. Sodium borohydride (NaBH ₄ ), hydrazine (N ₂ H ₄ ) and the like can be used. These may be in the form of hydrates. Further, two or more types may be mixed and used. Further, the reducing agent may be added in the form of a reducing agent solution.

The amount of the reducing agent added is not particularly limited as long as it is sufficient to reduce the non-platinum metal precursor. Specifically, the amount of the reducing agent added is preferably 1 to 20 mol, more preferably 1.5 to 10 mol, with respect to 1 mol of the non-platinum metal precursor. With such an amount, the non-platinum metal precursor can be sufficiently reduced. When two or more kinds of reducing agents are used, the total addition amount of these agents is preferably in the above range.

In the step (2), the amount of the non-platinum metal supported on the carrier can be controlled by appropriately setting the non-platinum metal concentration of the non-platinum metal precursor liquid, the immersion time of the non-platinum metal precursor, and the like.

By the above treatment, a carrier on which platinum and a non-platinum metal are supported can be obtained.

Here, if necessary, platinum and non-platinum metal-supported carriers may be isolated from the dispersion. Here, the isolation method is not particularly limited, and platinum and non-platinum metal-supporting carriers may be filtered and dried. If necessary, the platinum and non-platinum metal-supporting carriers may be filtered and then washed (for example, washed with water). Moreover, the above-mentioned filtration and washing step may be repeated if necessary. In addition, the platinum and non-platinum metal-supported carriers may be dried after filtration or washing. Here, the platinum and non-platinum metal-supported carriers may be dried in air or under reduced pressure. The drying temperature is not particularly limited, but can be, 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 can be, for example, in the range of 1 to 60 hours, preferably about 5 to 50 hours.

Next, an alloying treatment is performed.

The specific method of the alloying treatment is not particularly limited, and a known method can be appropriately adopted. For example, a method of performing heat treatment and the like can be mentioned. The heat treatment conditions are not particularly limited as long as the alloying proceeds, but for example, the heat treatment temperature is preferably 600 to 1200 ° C., more preferably 800 to 1200 ° C. The heat treatment time is preferably 0.5 to 10 hours, more preferably 1 to 4 hours. The heat treatment atmosphere is not particularly limited, but the heat treatment is preferably performed in a non-oxidizing atmosphere in order to suppress and prevent oxidation of the alloy (platinum and 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 inert gas may be used alone or in the form of a mixed gas of two or more. The reducing gas atmosphere is not particularly limited as long as it contains a reducing gas, but a mixed gas atmosphere of a reducing gas and an 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.

After the alloying treatment, further heat treatment may be performed. By the heat treatment, may the rules of the L1 ₂ structure of the alloy particles in the catalyst is increased to 30 to 100%. Note that by selecting the heat treatment conditions, it is possible to control the degree of order of the L1 ₂ structure.

The heat treatment conditions are not particularly limited as long as the regularity can be increased to 30 to 100%, but control of the heat treatment temperature and time is important.

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

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

When the heat treatment temperature is 350 to 450 ° C., the heat treatment atmosphere is not particularly limited, but the heat treatment is preferably performed in a non-oxidizing atmosphere in order to suppress and prevent oxidation of the alloy (platinum and non-platinum metal). .. Here, since the non-oxidizing atmosphere has the same definition as the description in the above-mentioned alloying treatment column, the description thereof is omitted here. The reducing gas atmosphere is not particularly limited as long as it contains a reducing gas, but a mixed gas atmosphere of a reducing gas and an inert gas is more preferable. The concentration of the reducing gas contained in the inert gas is also 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, oxidation of alloys (platinum and non-platinum metals) can be sufficiently suppressed / prevented. Of the above, the heat treatment is preferably performed in a reducing gas atmosphere. Under such conditions, the regularity of the obtained catalyst particles (alloy particles) can be effectively controlled by 30 to 100% while suppressing the increase in the catalyst particle size.

When the heat treatment temperature is more than 450 ° C. and 750 ° C. or lower, it is preferable to perform the heat treatment for 10 minutes or more, more preferably 20 minutes or more. The upper limit of the heat treatment time at the heat treatment temperature is not particularly limited as long as it can maintain the state in which the catalyst particles are supported on the carrier, and is appropriately selected depending on the particle size and type of the catalyst particles. For example, the heat treatment time is usually 36 hours or less, preferably 24 hours or less, more preferably 10 hours or less, and even more preferably 5 hours or less.

When the heat treatment temperature is more than 450 ° C. and 750 ° C. or lower, the heat treatment atmosphere is not particularly limited, but the heat treatment is performed in a non-oxidizing atmosphere in order to suppress and prevent oxidation of the alloy (platinum and non-platinum metal). It is preferable to do so. Here, since the non-oxidizing atmosphere has the same definition as the description in the above-mentioned alloying treatment column, the description thereof is omitted here. Of the above, the heat treatment is preferably carried out in an inert gas atmosphere or a reducing gas atmosphere. Under the above conditions, the regularity of the obtained catalyst particles (alloy particles) can be effectively controlled by 30 to 100% while suppressing the increase in the catalyst particle size.

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

The upper limit of the heat treatment temperature is not particularly limited as long as it can maintain the state in which the catalyst particles are supported on the carrier, and is appropriately selected depending on the particle size and type of the catalyst particles. Further, although the regularity increases in proportion to the temperature and time during the heat treatment, there is a tendency for the particle size to increase due to sintering. Considering the above points, for example, the heat treatment temperature can be 1000 ° C. or lower. Under such conditions, it is possible to suppress an increase in the catalyst particle size and further suppress the aggregation of the obtained catalyst particles (alloy particles) on the carrier. In the above, the "inert gas atmosphere" and the "reducing gas atmosphere" have the same definitions as those described in the section of alloying treatment, and thus the description thereof will be omitted here. Under the above conditions, the regularity of the obtained catalyst particles (alloy particles) can be effectively controlled by 30 to 100% while suppressing the increase in the catalyst particle size.

From the above, according to the preferred embodiment of the present invention, the heat treatment after the alloying treatment is carried out in (a) a reducing gas atmosphere or an inert gas atmosphere at a temperature of 350 to 450 ° C. for a time exceeding 120 minutes. (B) Performed for 10 minutes or more in a reducing gas atmosphere or an inert gas atmosphere at a temperature of more than 450 ° C. and 750 ° C. or less; (c) In an inert gas atmosphere, at a temperature of more than 750 ° C. It is carried out for 10 to 120 minutes; or (d) under a reducing gas atmosphere at a temperature above 750 ° C. for 10 to 45 minutes.

[Fuel cell]
Another embodiment of the present invention is a membrane electrode assembly and a fuel cell containing the electrode catalyst of the first embodiment. The electrode catalyst of the electrode catalyst of the first embodiment can exhibit high activity (area specific activity (activity per unit area), mass ratio activity (activity per unit area)) even with a small platinum content. Therefore, the membrane electrode assembly and the fuel cell using the electrode catalyst of the first embodiment as the catalyst layer are excellent in power generation performance.

A fuel cell comprises a membrane electrode assembly (MEA) and a pair of separators including an anode-side separator having a fuel gas flow path through which fuel gas flows and a cathode-side separator having an oxidant gas flow path through which oxidant gas flows. Have. The fuel cell of this embodiment has excellent durability and can exhibit high power generation performance.

FIG. 2 is a schematic view showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 according to an embodiment of the present invention. The PEFC 1 first has a solid polymer electrolyte membrane 2 and a pair of catalyst layers (anode catalyst layer 3a and cathode catalyst layer 3c) sandwiching the solid polymer electrolyte membrane 2. The laminate 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) form the membrane electrode assembly (MEA) 10 in a laminated state.

In PEFC 1, the MEA 10 is further sandwiched by a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 2, the separators (5a, 5c) are shown so as to be 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 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. , FIG. 2 omits these descriptions.

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

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

In the embodiment shown in FIG. 2, the separators (5a and 5c) are formed into an uneven shape. However, the separator is not limited to such an uneven shape, and may be any shape such as a flat plate shape or a partially uneven shape as long as the functions of the gas flow path and the refrigerant flow path can be exhibited. May be good.

The fuel cell having the MEA of the present embodiment as described above exhibits excellent power generation performance and durability. Here, the type of the fuel cell is not particularly limited, and in the above description, the polymer electrolyte type fuel cell has been described as an example, but in addition to this, an alkaline type fuel cell and a direct methanol type fuel cell have been described. , Micro fuel cells and the like. Among them, a polymer electrolyte fuel cell (PEFC) is preferable because it is compact, has high density, and can have high output. Further, the fuel cell is useful as a power source for a mobile body such as a vehicle whose mounting space is limited, as well as a power source for stationary use. Above all, it is particularly preferable to use it as a power source for a mobile body such as an automobile, which requires a high output voltage after a relatively long operation stop.

The fuel used when operating the fuel cell is not particularly limited. For example, hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, diethylene glycol and the like can be used. Of these, hydrogen and methanol are preferably used because they can increase the 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 is excellent in power generation performance and durability, and can be miniaturized. Therefore, the fuel cell of the present invention is particularly advantageous when the fuel cell is applied to a vehicle from the viewpoint of in-vehicle performance. Therefore, the present invention provides a vehicle having the fuel cell of the present invention.

Hereinafter, the members constituting the fuel cell of the present embodiment will be briefly described, but the technical scope of the present invention is not limited to the following embodiments.

[Electrolyte Membrane-Electrode Assembly (MEA)]
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 first embodiment is used for at least one of the cathode catalyst layer and the anode catalyst layer.

(Catalyst layer)
The catalyst layer contains an electrode catalyst and an electrolyte.

In the catalyst layer, the catalyst is coated with an electrolyte, but the electrolyte does not penetrate into the mesopores of the catalyst (carrier). Therefore, the alloy fine particles on the surface of the carrier come into contact with the electrolyte, but the alloy fine particles supported inside the mesopores are in a non-contact state with the electrolyte. The reaction active area of the alloy fine particles can be secured by forming the three-phase interface between oxygen gas and water in the mesopores in a non-contact state with the electrolyte.

The electrode catalyst of the first embodiment may be present in either the cathode catalyst layer or the anode catalyst layer, but is preferably used in the cathode catalyst layer. As described above, the catalyst of the first embodiment can effectively utilize the catalyst by forming a three-phase interface with water without contacting with the electrolyte, but water is formed in the cathode catalyst layer. Is.

In the present embodiment, the catalyst content (mg / cm ² ) per unit catalyst coating area is not particularly limited as long as sufficient dispersity of the catalyst on the carrier and power generation performance can be obtained, and is, for example, 0.01 to 1 mg. / Cm ² . The platinum content per unit catalyst coating area ^{is preferably 0.5 mg / cm 2} or less. The use of expensive precious metal catalysts such as platinum, which constitutes alloy particles, is a factor in the high price of fuel cells. Therefore, it is preferable to reduce the amount of expensive platinum used (platinum content) to the above range to reduce the cost. The lower limit of the platinum content is not particularly limited as long as the power generation performance can be obtained, but is, for example, 0.01 mg / cm ² or more. More preferably, the platinum content is 0.02 to 0.4 mg / cm ² . In this embodiment, by controlling the pore structure of the carrier, alloy particles having high activity can be used and the activity per catalyst weight can be improved, so that the amount of expensive catalyst used can be reduced. Is possible.

In addition, in this specification, inductively coupled plasma emission spectroscopy (ICP) is used for measurement (confirmation) of "catalyst (platinum) content per unit catalyst coating area (mg / cm ^2)". Those skilled in the art can easily perform a method of reducing the desired "catalyst (platinum) content per unit catalyst coating area (mg / cm ² )", and control the composition (catalyst concentration) and coating amount of the slurry. The content can be adjusted by doing so.

The electrolyte is not particularly limited, but is preferably an ionic conductive polymer electrolyte. The polymer electrolyte is also called a proton conductive polymer because it plays a role of transmitting protons generated around the catalytically active material on the fuel electrode side.

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

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

Specific examples of the hydrocarbon-based electrolyte include sulfonated polyether sulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole, phospholated polybenzimidazole, sulfonated polystyrene, and sulfonated polyetherether. Examples thereof include ketone (SPEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon-based polymer electrolytes are preferably used from the viewpoint of manufacturing, such as low raw materials, simple manufacturing process, and high material selectivity.

As for the above-mentioned ion exchange resin, only one type may be used alone, or two or more types may be used in combination. Further, the material is not limited to the above-mentioned materials, and other materials may be used.

Proton conductivity is important in polymer electrolytes that are responsible for proton transfer. Here, if the EW of the polymer electrolyte is too large, the ionic conductivity of the entire catalyst layer decreases. Therefore, the catalyst layer of the present embodiment preferably contains a polymer electrolyte having a small EW. Specifically, the catalyst layer of this embodiment preferably has an EW of 1500 g / eq. It contains the following polymeric electrolytes, more preferably 1200 g / eq. It contains the following polymeric electrolytes, particularly preferably 1000 g / eq. It contains the following polymer electrolytes.

On the other hand, if the EW is too small, the hydrophilicity is too high and it becomes difficult for water to move smoothly. From such a viewpoint, the EW of the polymer electrolyte is preferably 600 or more. In addition, EW (Equivalent Weight) represents the equivalent weight of the exchange group having proton conductivity. The equivalent weight is the dry weight of the polymer electrolyte per equivalent of the ion exchange group, and is expressed in units of "g / eq".

The catalyst layer of the present embodiment may contain a liquid proton conductive material capable of connecting the catalyst and the polymer electrolyte in a proton conductive state between the catalyst and the polymer electrolyte. By introducing the liquid proton conductive material, a proton transport path is secured between the catalyst and the polymer electrolyte via the liquid proton conductive material, and the protons required for power generation can be efficiently transported to the catalyst surface. Is possible. As a result, the utilization efficiency of the catalyst is improved, so that the amount of the catalyst used can be reduced while maintaining the power generation performance. This liquid proton conductive material may be interposed between the catalyst and the polymer electrolyte, and has pores (secondary pores) between the porous carriers in the catalyst layer and pores (mesopores) in the porous carrier. Etc .: Can be placed in the primary vacancies).

The liquid proton conductive material is not particularly limited as long as it has ionic conductivity and can exhibit a function of forming a proton transport path between the catalyst and the polymer electrolyte. Specific examples thereof include water, a protonic ionic liquid, a perchloric acid aqueous solution, a nitric acid aqueous solution, a formic acid aqueous solution, and an acetic acid aqueous solution.

When water is used as the liquid proton conductive material, the water as the liquid proton conductive material should be introduced into the catalyst layer by moistening the catalyst layer with a small amount of liquid water or a humidifying gas before starting power generation. Can be done. Further, the water produced by the electrochemical reaction during the operation of the fuel cell can also be used as the liquid proton conductive material. Therefore, the liquid proton conductive material does not necessarily have to be held in the state of starting the operation of the fuel cell. For example, it is desirable that the surface distance between the catalyst and the electrolyte is 0.28 nm or more, which is the diameter of oxygen ions constituting water molecules. By maintaining such a distance, water (liquid proton conductive material) is intervened between the catalyst and the polymer electrolyte (liquid conductive material holding portion) while maintaining a non-contact state between the catalyst and the polymer electrolyte. This will ensure a water-based proton transport route between the two.

When a material other than water, such as an ionic liquid, is used as the liquid proton conductive material, it is desirable to disperse the ionic liquid, the polymer electrolyte, and the catalyst in the solution when preparing the catalyst ink. An ionic liquid may be added when the layer substrate is coated.

The catalyst layer may contain, if necessary, a water repellent such as polytetrafluoroethylene, polyhexafluoropropylene, or tetrafluoroethylene-hexafluoropropylene copolymer, a dispersant such as a surfactant, glycerin, or ethylene glycol (EG). ), Polyvinyl alcohol (PVA), propylene glycol (PG) and other thickeners, 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.

(Electrolyte membrane)
The electrolyte membrane is composed of, for example, a solid polymer electrolyte membrane. This solid polymer electrolyte membrane has, for example, a function of selectively permeating protons generated in the anode catalyst layer during operation of a fuel cell (PEFC or the like) into the cathode catalyst layer along the film thickness direction. Further, 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 constituting the solid polymer electrolyte membrane is not particularly limited, and conventionally known findings can be appropriately referred to. For example, the fluorine-based polymer electrolyte and the hydrocarbon-based polymer electrolyte described as the polymer electrolyte in the catalyst layer 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 a value within such a range, the balance between the strength during film formation, the durability during use, and the output characteristics during use can be appropriately controlled.

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

The material constituting the base material of the gas diffusion layer (4a, 4c) is not particularly limited, and conventionally known findings can be appropriately referred to. Examples thereof include conductive and porous sheet-like materials such as carbon woven fabrics, paper-like paper machines, felts, and non-woven fabrics. 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. If the thickness of the base material is within such a range, the balance between the mechanical strength and the diffusivity of gas, water, etc. can be appropriately controlled.

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

Further, 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 base material. It 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 blacks such as oil furnace black, channel black, lamp black, thermal black, and acetylene black can be preferably used because of their excellent electron conductivity and large specific surface area. The average particle size of the carbon particles is preferably about 10 to 100 nm. As a result, high drainage can be obtained due to the capillary force, and the contact with the catalyst layer can be improved.

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

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

(Manufacturing method of electrolyte membrane-electrode assembly)
The method for producing the electrolyte membrane-electrode assembly is not particularly limited, and a conventionally known method can be used. For example, a method of transferring or applying a catalyst layer to an electrolyte membrane by hot pressing and then joining a gas diffusion layer to the dried material, or a method of joining a gas diffusion layer to the microporous layer side of the gas diffusion layer (when the microporous layer is not included). , One side of the base material layer) is coated in advance and dried to prepare two gas diffusion electrodes (GDE), and the gas diffusion electrodes are bonded to both sides of the solid polymer electrolyte membrane by hot pressing. Can be used. The coating and bonding conditions of hot press and the like may be appropriately adjusted depending on the type of polymer electrolyte (perfluorosulfonic acid type or hydrocarbon type) in the solid polymer electrolyte membrane or the catalyst layer.

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

The method for manufacturing 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 and connected in series may be formed so that the fuel cell can exert a desired voltage. The shape of the fuel cell and the like are not particularly limited, and may be appropriately determined so as to obtain battery characteristics such as a desired voltage.

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 on a vehicle as a driving power source, for example.

The effects of the present invention will be described with reference to the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples. Unless otherwise specified, each operation is performed at room temperature (25 ° C.) / relative humidity of 40 to 50%.

(Synthesis Example 1)
Carrier A was prepared by the method described in WO 2009/075264. The BET specific surface area of the obtained carrier A was 1570 m ² / g, the mode radius of the pore distribution of the mesopores was 1.2 nm, and the pore volume of the mesopores was 0.73 cc / g.

(Synthesis Example 2)
The carrier A prepared in Synthesis Example 1 above was heated to 1800 ° C. under an argon atmosphere and then held at this temperature for 8 minutes to prepare a carrier B. The BET specific surface area of the obtained carrier B was 1200 m ² / g, the mode radius of the pore distribution of the mesopores was 1.65 nm, and the pore volume of the mesopores was 0.63 cc / g.

(Example 1)
1. 1. Preparation of Platinum Particle-Supported Carrier 19 g of Carrier A was immersed in 1000 g (platinum content: 8 g) of a dinitrodiammine platinum nitric acid solution having a platinum concentration of 4.6 wt%, and after stirring, 100 mL of 100% ethanol was added as a reducing agent. This solution was stirred and mixed at boiling point (about 95 ° C.) for 7 hours to support platinum on carrier A. Then, it was filtered and dried to obtain a platinum particle-supporting carrier. The supported concentration (supported amount) of platinum in this platinum particle-supported carrier was 29% by weight with respect to 100% by weight of the carrier. The supported concentration (supported amount) of platinum was measured by ICP analysis.

2. Heat treatment process 1. The platinum particle-supporting carrier obtained in 1 above was heat-treated in a hydrogen atmosphere at a temperature of 900 ° C. for 1 hour.

3. 3. Hydrophilization treatment step 2. To 20 L of a 3.0 mol / L nitric acid aqueous solution. 20 g of the platinum particle-supporting carrier heat-treated in 1 was added, and after stirring, the mixture was heated at 80 ° C. for 2 hours while maintaining the stirring. Then, it cooled to room temperature to obtain a platinum particle-supporting carrier which had been heat-treated and hydrophilized (hydrophilic group bond amount 1.2 mmol / g).

4. Cobalt alloying step To 60 g of cobalt chloride aqueous solution (cobalt concentration 0.66% by weight, cobalt content 0.4 g, pH 2), the above 3. 10 g of the platinum particle-supporting carrier obtained in the above-mentioned hydrophilization treatment was immersed, and the mixture was stirred and mixed with a stirrer at room temperature for 1 hour. Then, the solution was dried at 60 ° C. to obtain a platinum particle-supported carrier on which a cobalt metal precursor was further supported. Finally, the electrode catalyst (1) of this example was produced by subjecting it to an alloying treatment at 1000 ° C. for 2 hours in 100% by volume hydrogen gas. The supported concentration (supported amount) of the catalyst metal (alloy fine particles) in the electrode catalyst (1) was 32.3% by weight (Pt: 29.7% by weight, Co: 2.6% by weight) with respect to 100% by weight of the carrier. %, Pt: Co = 77.5: 22.5 (atomic%)). In the catalyst of this example, it was confirmed that at least a part of the alloy fine particles was supported in the mesopores.

(Example 2)
The electrode catalyst (2) of this example was produced by the same method as in Example 1 described above except that the carrier B was used instead of the carrier A and the supported amounts of platinum and cobalt were changed. The supported concentration (supported amount) of the catalyst metal (alloy fine particles) in the electrode catalyst (2) was 30.8% by weight (Pt: 26.4% by weight, Co: 4.) with respect to 100% by weight of the carrier. 4% by weight, Pt: Co = 64.4: 35.6 (atomic%)). In the catalyst of this example, it was confirmed that at least a part of the alloy fine particles was supported in the mesopores.

(Example 3)
The electrode catalyst obtained by the same method as in Example 2 described above was further alloyed in 100% by volume hydrogen gas at 1100 ° C. for 2 hours except that the supported amounts of platinum and cobalt were changed. By carrying out the above, the electrode catalyst (3) of this example was produced. The supported concentration (supported amount) of the catalyst metal (alloy fine particles) in the electrode catalyst (3) was 56.3% by weight (Pt: 49.5% by weight, Co: 6.) with respect to 100% by weight of the carrier. 8% by weight, Pt: Co = 68.7: 31.3 (atomic%)). In the catalyst of this example, it was confirmed that at least a part of the alloy fine particles was supported in the mesopores.

(Comparative Example 1)
The comparative electrode catalyst (1) of this Comparative Example was produced by the same method as in Example 1 described above except that Ketjen Black (manufactured by Lion Specialty Chemicals Co., Ltd.) was used as the catalyst carrier. The supported concentration (supported amount) of the catalyst metal (alloy fine particles) in the comparative electrode catalyst (1) was 50.9% by weight (Pt: 45.8% by weight, Co: 5) with respect to 100% by weight of the carrier. .1% by weight, Pt: Co = 73.1: 26.9 (atomic%)).

(Comparative Example 2)
The comparative electrode catalyst (2) of this Comparative Example was produced by the same method as in Example 1 described above except that acetylene black was used as the catalyst carrier. The supported concentration (supported amount) of the catalyst metal (alloy fine particles) in the comparative electrode catalyst (2) was 52.5% by weight (Pt: 47.9% by weight, Co: 4) with respect to 100% by weight of the carrier. It was .6% by weight, Pt: Co = 75.9: 24.1 (atomic%)).

(Comparative Example 3)
The comparative electrode catalyst (3) of this Comparative Example was produced by the same method as in Example 1 described above except that Black Pearl (manufactured by Cabot Corporation) was used as the catalyst carrier. The supported concentration (supported amount) of the catalyst metal (alloy fine particles) in the comparative electrode catalyst (3) was 51.2% by weight (Pt: 47.0% by weight, Co: 4) with respect to 100% by weight of the carrier. .2% by weight, Pt: Co = 77.2: 22.8 (atomic%)).

(Comparative Example 4)
The comparative electrode catalyst (4) of this comparative example was produced by the same method as in Example 1 described above except that graphitized Ketjen black was used as the catalyst carrier. The supported concentration (supported amount) of the catalyst metal (alloy fine particles) in the comparative electrode catalyst (4) was 32.5% by weight (Pt: 29.2% by weight, Co: 3) with respect to 100% by weight of the carrier. It was .3% by weight, Pt: Co = 72.8: 27.2 (atomic%)).

(Measurement of lattice constant of alloy fine particles constituting the electrode catalyst)
The lattice constants of the alloy fine particles constituting the electrode catalysts obtained in each of the above Examples and Comparative Examples were measured by a powder X-ray diffraction measurement method. Specifically, from the peak position (°) of the peak corresponding to the (220) plane observed in the region of 2θ = 68 to 72 °, the plane spacing is calculated from Bragg's equation shown below and converted to a lattice constant. It was calculated by doing.

Bragg's equation: 2dsinθ = nλ
(D: lattice spacing, θ: X-ray incident angle, λ: X-ray incident wavelength, n: integer)
It should be noted that all of the alloy fine particles constituting the electrode catalysts (1) to (3) have a face-centered cubic lattice structure at the time of measuring the lattice constant by this powder X-ray diffraction measurement method. confirmed.

The measured values of the obtained lattice constants are shown in Table 2 below together with the lattice constants (theoretical values) according to Vegard's law. In addition, the value obtained by subtracting the theoretical value from the measured value (if this value is negative, the catalyst is within the range of the present invention) and the value of the compression ratio calculated according to the following formula are also shown in Table 2 below.

(Evaluation of oxygen reduction activity when an electrode catalyst is used as a cathode)
<Manufacturing of rotating electrode (RDE) for performance evaluation>
^{The electrode catalysts obtained in each of the above Examples and Comparative Examples are supported on a rotating disk electrode (geometric area: 0.19 cm 2} ) composed of a glassy carbon disk having a diameter of 5 mm, respectively, per unit area of platinum. An electrode for performance evaluation was prepared by uniformly dispersing and supporting with Nafion so that the amount was 34 μg / cm ^2.

<Measurement of area specific activity (RDE)>
For each Example and Evaluation rotating electrode prepared above for Comparative Examples (RDE), in a 0.1M perchlorate of 25 ° C. saturated with N ₂ gas, to a reversible hydrogen electrode (RHE) Cyclic voltammetry was performed at a scanning speed of ^{50 mVs -1 in} the potential range of 0.05 to 1.2 V. ^{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 of the obtained voltammogram.

Next, using an electrochemical measuring device, potential scanning was performed from 0.2 V to 1.2 V at a speed of 10 mV / s in 0.1 M perchloric acid at 25 ° C. saturated with oxygen. Further, from the current obtained by the potential scanning, the influence of mass transfer (oxygen diffusion) was corrected 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 above-mentioned electrochemical surface area was defined as the area specific activity (μAcm- ² ). The method using the Koutecky-Levich equation is described in, for example, Electrochemistry Vol. 79, No. 2, p. It is described in "4 Analysis of oxygen reduction reaction on Pt / C catalyst" of 116-121 (2011) (convection voltammogram (1) oxygen reduction (RRDE)).

The production conditions, physical characteristics and evaluation results of each catalyst are shown in Table 2 below.

From the above results, the MEA using the electrode catalysts of Examples 1 to 3 showed significantly higher area specific activity than the MEA using the catalysts of Comparative Examples 1 to 4.

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),
20 ... Electrode catalyst,
22 ... Catalyst metal (alloy fine particles),
23 ... Catalyst carrier,
24 ... Meso hole.

Claims (7)

An electrode catalyst in which a catalyst component containing alloy fine particles composed of platinum and a metal component other than platinum is supported on a catalyst carrier.
The catalyst carrier has mesopores having a radius of 1 nm or more, and the mode radius of the pore distribution of the mesopores is 1 nm or more and less than 2.5 nm.
At least a part of the alloy fine particles is supported in the mesopores,
The alloy fine particles have a face-centered cubic lattice structure and
The electrode catalyst: The measured value Q [Å] of the lattice constant of the alloy fine particles is smaller than the theoretical value P [Å] of the lattice constant according to Vegard's law calculated by the following mathematical formula 1.

The electrode catalyst according to claim 1, wherein the value of the compression ratio calculated by the following formula is −0.2% or less.

The electrode catalyst according to claim 2 , wherein the value of the compressibility is −2.0% or more. The electrode catalyst according to any one of claims 1 to 3, wherein the molar ratio of platinum to a metal component other than platinum in the alloy fine particles supported in the mesopores is 1.5 to 4.0. The electrode catalyst according to any one of claims 1 to 4 , wherein the metal component other than platinum is cobalt (Co). A membrane electrode assembly comprising the electrode catalyst and electrolyte according to any one of claims 1 to 5. A fuel cell comprising the membrane electrode assembly according to claim 6.

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