JP6675705B2 - Anode electrode catalyst, electrode catalyst layer using the catalyst, membrane electrode assembly, and fuel cell - Google Patents

Description

  The present invention relates to an anode catalyst, particularly an anode catalyst used for a fuel cell (PEFC), and an electrode catalyst layer, a membrane electrode assembly, and a fuel cell using the catalyst.

  A polymer electrolyte fuel cell (hereinafter abbreviated as PEFC) using a proton-conducting solid polymer membrane is different from other types of fuel cells such as a solid oxide fuel cell and a molten carbonate fuel cell. Operates at lower temperatures in comparison. For this reason, PEFC is expected as a stationary power supply and a power source for mobile bodies such as automobiles, and its practical use has also begun.

  In general, a catalyst in which noble metal particles typified by Pt (platinum) or a Pt alloy, which is a catalyst metal having excellent catalytic properties, is supported on a catalyst carrier is used for an electrode of such a fuel cell. However, such a catalyst using noble metal particles is expensive, which causes a high price of the fuel cell. Therefore, by maximizing the catalytic activity (HOR activity, ORR activity, etc.) of the catalyst using the noble metal particles, the performance of the fuel cell is improved and the amount of the noble metal used as the catalyst metal for the catalyst is reduced. Therefore, there is a demand for the development of a technology capable of reducing the cost of a fuel cell.

Further, as the required performance of the anode electrode catalyst of the fuel cell, (1) From the viewpoint of power generation performance, a high HOR (hydrogen oxidation reaction) activity is required in all operating conditions. (2) From the viewpoint of durability, low ORR (oxygen reduction reaction) activity is required in order to maintain the corrosion resistance of the carbon support of the cathode electrode at the time of startup. As shown in the following electrode reaction on the anode and cathode sides of the fuel cell, this is because at the time of startup, air (particularly O ₂ gas) is mixed with fuel gas (eg, H ₂ gas) supplied to the anode electrode side. Therefore, a battery reaction occurs in the anode electrode. As a result, on the cathode electrode side, the protons supposed to be supplied from the anode electrode side run short, and the protons are supplied by oxidizing the carbon that is the catalyst carrier from the cathode electrode, which is the catalyst carrier for the cathode electrode. Carbon deteriorates. Therefore, if the ORR activity of the anode electrode catalyst at the time of startup is low, the corrosion resistance of carbon, which is the catalyst carrier of the cathode electrode, is improved. Therefore, the required performance of the above (2) is that the anode electrode catalyst has a low ORR (oxygen reduction reaction). Activity is required.

(Here, HOR indicates a hydrogen oxidation reaction, HER indicates a hydrogen generation reaction, ORR indicates an oxygen reduction reaction, and OER indicates an oxygen generation reaction. During power generation, each reaction proceeds toward the right side of the arrow, and HOR, ORR Progresses.)
With respect to the required performance, Patent Document 1 discloses that a carbon powder carrier having a hydrophilic group of 0.7 to 3 mmol / g has an average particle size of 3.5 to 8 nm and a platinum specific surface area by CO adsorption. A catalyst for PEFC supporting platinum particles having a particle size of 40 to 100 m ² / g has been proposed. According to this, a catalyst for PEFC having excellent initial activity (initial power generation characteristics) and excellent durability can be provided.

JP 2010-12401 A

However, in Patent Document 1, although platinum particles having an average particle size of 3.5 to 8 nm are supported on the carrier, the specific surface area is as small as 40 to 100 m ² / g because the platinum particles are aggregated on the carrier. However, there is a problem that the catalytic activity is not sufficient.

  Therefore, the present invention has been made in view of the above circumstances, and has an anode having a large specific surface area and excellent catalytic activity (particularly high HOR activity and low ORR activity) without aggregation of catalytic metal particles on a catalyst carrier. An object is to provide an electrode catalyst.

  Another object of the present invention is to provide an anode electrode catalyst layer, a membrane electrode assembly, and a fuel cell which are excellent in power generation performance, using the above-mentioned anode electrode catalyst.

  The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found the following findings. That is, an anode in which a catalyst metal is disposed on a catalyst carrier and the specific surface area of the catalyst metal or the coordination number of the catalyst metal by XAFS (X-ray absorption fine structure) or the particle size of the catalyst metal has a predetermined value The inventors have found that an electrocatalyst solves the above problems, and have completed the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the catalyst metal arrange | positioned on a catalyst support | carrier can express the high specific surface area, without causing aggregation, and the anode electrode catalyst excellent in the catalytic activity (high HOR activity and low ORR activity) is obtained. Can be provided.

  Further, according to the present invention, the catalyst metal disposed on the catalyst carrier is constituted by a small coordination number that does not cause aggregation, so that a high specific surface area can be exhibited, and the catalytic activity (high HOR activity and low ORR activity) can be exhibited. ) Can be provided.

  Further, according to the present invention, the catalyst metal disposed on the catalyst carrier has a small particle size that does not cause aggregation, and thus can exhibit a high specific surface area, and has excellent catalytic activity (high HOR activity and low ORR activity). An anode electrode catalyst can be provided.

FIG. 1 is a schematic sectional view showing a basic configuration of a polymer electrolyte fuel cell according to one embodiment of the present invention. 4 is a drawing showing the relationship between ORR activity per unit platinum surface area and platinum's electrochemical specific surface area when platinum particles are used as catalytic metal particles. 3 is a drawing showing the relationship between ORR activity per unit platinum mass and electrochemical specific surface area of platinum when platinum particles are used as catalytic metal particles. 18.6 mg of a commercially available platinum-supported carbon catalyst (manufactured by Tanaka Kikinzoku Kogyo TEC10E50E) and 10.4 mg of the catalyst of the catalyst example obtained using platinum particles as the catalyst metal particles were weighed, and 19 mL of water and 6 mL of isopropanol were weighed. The mixture was dispersed in a mixed solution, and 100 μL of Nafion solution (DE521CS, 5 wt%, manufactured by Aldrich) was added thereto to prepare a catalyst ink. Thereafter, ultrasonic dispersion was performed for 1 hour or more. 10 μL of the prepared catalyst ink was applied to a polished glassy carbon electrode (φ5.0 mm, manufactured by Hokuto Denko) and dried in a dryer at 60 ° C. for 10 minutes. The surface coating state of the obtained electrode was confirmed by microscopic observation, and an electrode having no coating remaining on the catalyst layer and no protrusion was used for evaluation.

  Electrochemical measurements were performed in a normal three-chamber cell (Mick Lab). The electrolyte solution used was 0.1 M perchloric acid (Ultrapur, manufactured by Kanto Chemical). The counter electrode was a Pt line, and the reference electrode was a reversible hydrogen electrode (RHE). The potential control was performed using HZ-5000 (manufactured by Hokuto Denko). HR-301 (manufactured by Hokuto Denko) was used as a rotating electrode (RDE) device. The cell temperature was controlled at 25 ° C. (± 1 ° C.) using an external circulation type thermostat (CHL300, manufactured by YAMATO). For the measurement of CO stripping, an Ar balance gas (manufactured by Taiyo Nissin) of 1% CO was used. All measurements were performed in a draft.

After performing 20 cycles of scanning in the range of 0 to 1.2 V (RHE) at 100 mV / s as electrode pretreatment, measurements such as cyclic voltammetry (results are shown in FIG. 3) and convective voltammetry were performed. In the measurement of CO stripping, the electrode was kept at 0.05 V (RHE) for 30 minutes while rotating the electrode at 400 rpm in an electrolyte solution saturated with 1% CO gas. Under these conditions, it was confirmed that the CO adsorption amount reached saturation. After completely replacing the CO gas in the solution with nitrogen, CV measurement was performed from 0.05 V (RHE) to 1.2 V (RHE) at 20 mV / s for three cycles. The CVs of the second and third cycles were clearly overlapped. The amount of electricity at the CO stripping peak is calculated from the difference between the response currents after the first cycle and the second and subsequent cycles. Assuming that the maximum coverage of Pt by CO is 0.68, the conversion coefficient is 285.6 μC · cmPt ^−2. Was applied to calculate the electrochemically active surface area. The electrochemical area (ECA) was calculated by assigning this to the amount of platinum (FIG. 3 (a)).
From the value calculated based on the result of the CO stripping in FIG. 3A, it was found that the specific surface area of the platinum particles was 290 m ² / g. This value means that the average particle diameter is 1 nm or less, assuming that the platinum particles are spherical (FIG. 3B). 2 shows the relationship between the average coordination number of catalytic metal (Pt) atoms calculated by XAFS (X-ray absorption fine structure analysis) and the average particle size of catalytic metal (Pt) particles, and the results of XAFS measurement of the catalysts of the examples. It is a drawing. The average coordination number of the example obtained from the result was 3.3. Graph showing CV (cyclic voltammetry) at the third cycle in electrochemical measurement by a method of measuring an electrochemical specific surface area measured from hydrogen adsorption and desorption of platinum particles supported on a carbon support as a catalyst. FIG. TEM for Pt cluster / kB, which is a sample of the metal-supported carbon material of Example 1 obtained by supporting a platinum complex on a Ketjen black carrier and subjecting the complex to reduction by vacuum heating at 300 ° C. for 1 hour. A photograph is shown. 4 shows a TEM photograph of Pt particles / kB, which is a sample of a metal-supported carbon material of Comparative Example 2 obtained by reducing a dinitrodiammine platinum complex with sodium borohydride. The XRD pattern which measured the sample of Example 1 (Pt cluster / kB), the blank (only Ketjen black), and the sample of Comparative Example 1 (TEC10E50E) obtained by heat-treating the sample of Production Example 1 in an air atmosphere is shown. It is a drawing. 1 is a drawing showing a current-voltage curve obtained according to a method for measuring ORR activity in Example 1 and Comparative Examples 1 and 2. 3 is a drawing showing CV curves obtained by hydrogen adsorption and desorption for Example 1 and Comparative Examples 1 and 2. 1 is a diagram showing a current-voltage curve obtained in Example 1 and Comparative Example 1 according to a method for measuring a hydrogen oxidation reaction (HOR) activity.

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

  In this specification, “X to Y” indicating a range means “X or more and Y or less”, “weight” and “mass”, “weight%” and “mass%”, and “weight part” and “weight part”. Parts by mass "are treated as synonyms. Unless otherwise specified, the operation and measurement of physical properties are performed under the conditions of room temperature (20 to 25 ° C.) / Relative humidity of 40 to 50%.

[Fuel cell]
The fuel cell includes a membrane electrode assembly (MEA), and a pair of separators including an anode-side separator having a fuel gas flow path through which a fuel gas flows and a cathode-side separator having an oxidizing gas flow path through which an oxidizing gas flows. Have. The fuel cell of the present embodiment is excellent in durability and can exhibit high power generation performance.

  FIG. 1 is a schematic sectional view showing a basic configuration of a polymer electrolyte fuel cell (PEFC) according to one embodiment of the present invention. The PEFC 1 has a solid polymer electrolyte membrane 2 and a pair of catalyst layers (anode catalyst layer 3a and cathode catalyst layer 3c) sandwiching the 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). In this manner, the solid polymer electrolyte membrane 2, the pair of catalyst layers (3a, 3c) and the pair of gas diffusion layers (4a, 4c) constitute a membrane electrode assembly (MEA) 10 in a stacked state.

  In the PEFC 1, the MEA 10 is further sandwiched by a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 1, the separators (5a, 5c) are illustrated as being located at both ends of the MEA 10 illustrated. However, in a fuel cell stack in which a plurality of MEAs are stacked, the separator is generally used also as a separator for an adjacent PEFC (not shown). In other words, in the fuel cell stack, the MEAs are sequentially stacked with the separator interposed therebetween, thereby forming a stack. In an actual fuel cell stack, a gas seal portion is arranged between the separator (5a, 5c) and the solid polymer electrolyte membrane 2 or between the PEFC 1 and another PEFC adjacent thereto. In FIG. 1, these descriptions are omitted.

  The separators (5a, 5c) are obtained, for example, by pressing a thin plate having a thickness of 0.5 mm or less to form an uneven shape as shown in FIG. The protrusions of the separators (5a, 5c) viewed from the MEA side are in contact with the MEA 10. Thereby, an electrical connection with the MEA 10 is ensured. In addition, the recesses (spaces between the separator and the MEA generated due to the uneven shape of the separator) viewed from the MEA side of the separators (5a, 5c) are provided with gas for flowing gas during operation of the PEFC1. Functions as a flow path. Specifically, a fuel gas (for example, hydrogen) flows through the gas flow path 6a of the anode separator 5a, and an oxidizing gas (for example, air) flows through the gas flow path 6c of the cathode separator 5c.

  On the other hand, the concave portion viewed from the side opposite to the MEA side of the separators (5a, 5c) serves as a refrigerant flow path 7 for flowing a refrigerant (for example, water) for cooling the PEFC during operation of the PEFC1. . Further, the separator is usually provided with a manifold (not shown). This manifold functions as connecting means for connecting the cells when a stack is formed. With such a configuration, the mechanical strength of the fuel cell stack can be ensured.

  Note that, in the embodiment shown in FIG. 1, the separators (5a, 5c) are formed in an uneven shape. However, the separator is not limited to only such a concavo-convex form, as long as the function of the gas flow path and the refrigerant flow path can be exhibited, a flat form, an arbitrary form such as a partially concavo-convex shape. Is also good.

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

  The fuel gas used when operating the fuel cell is not particularly limited. For example, hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, diethylene glycol and the like can be used. Among them, hydrogen and methanol are preferably used because high output can be achieved.

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

  Hereinafter, 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 only the following embodiments.

[Catalyst (electrocatalyst)]
The catalyst of the present embodiment (also referred to as “electrocatalyst” in the present specification) includes a catalyst carrier and catalyst metal particles supported on the catalyst carrier. The catalyst used on the anode electrode side is called an anode electrode catalyst, and the catalyst used on the cathode electrode side is called a cathode electrode catalyst. Unless otherwise specified, the term “catalyst” or “electrocatalyst” means both the anode electrode catalyst and the cathode electrode catalyst. Here, the anode electrode catalyst according to the present embodiment includes a catalyst carrier and catalyst metal particles supported on the catalyst carrier, and the catalyst metal particles are measured by (a) CO stripping. (B) the average coordination number of the catalyst metal measured by XAFS (X-ray absorption fine structure) is 4 or less, and (c) the average particle size is 280 m ² / g or more. At least one of the requirements of 1 nm or less is satisfied.

The present inventors support platinum particles having an average particle size of 3.5 to 8 nm on the carrier in the catalyst of Patent Document 1, but have a specific surface area of 40 to 40 because the platinum particles are aggregated on the carrier. It was found that the catalytic activity (high HOR activation and low ORR activity) was not sufficient, being as small as 100 m ² / g. On the other hand, the present inventors have realized that the catalyst metal particles satisfy one or more of the above-mentioned requirements (a) to (c), and thus the platinum particles have a high specific surface area without causing aggregation on the support. It has been found that by being able to express, catalytic activity (high HOR activity and low ORR activity) can be improved.

FIG. 2 shows a drawing in which the relationship between the ORR activity and the electrochemical specific surface area of platinum was measured. FIG. 2A is a graph showing the relationship between ORR activity per unit platinum surface area and electrochemical specific surface area of platinum when platinum particles are used as catalyst metal particles. FIG. 2 (b) is a drawing showing the relationship between ORR activity per unit platinum mass and electrochemical specific surface area of platinum when platinum particles are used as catalyst metal particles. 2 (a) and 2 (b), when the specific surface area of platinum is 90 m ² / g or less (particle diameter of 3.1 nm or more), ORR activity per unit platinum surface area is accompanied by a decrease in specific surface area (increase in particle diameter). On the other hand, the ORR activity per unit mass of platinum decreases because the specific surface area of platinum decreases. On the other hand, when the specific surface area of platinum is 90 m ² / g or more (particle diameter 3.1 nm or less) and 120 m ² / g or less (particle diameter 2.3 nm or more), the specific surface area of platinum increases (particle diameter decreases). Since the ORR activity per unit platinum surface area decreases more than the effect, the ORR activity per unit platinum mass is almost the same as the ORR activity per unit platinum mass whose specific surface area of platinum is 60 m ² / g or more and 90 m ² / g or less. It can be seen that it is. However, these relations are merely empirical rules, and the physical basis is unknown, so that the unit platinum when the specific surface area of platinum exceeds 120 m ² / g and further increases (particle diameter further decreases from 2.3 nm) The ORR activity per mass is completely unpredictable. Further, the relationship between the HOR activity per unit mass of platinum and the specific surface area of platinum has not been investigated so far. However, the present inventors increased the specific surface area to a predetermined value far exceeding 120 m ² / g (the particle diameter was reduced to a predetermined value much smaller than 2.3 nm), and thereby the cathode electrode at the time of startup was increased. It has been found that a low ORR activity capable of maintaining the corrosion resistance of the carbon support can be realized. As a result, it can greatly contribute to the improvement of the durability of the fuel cell. Further, by increasing the specific surface area to a predetermined value far exceeding 120 m ² / g (the particle diameter is reduced to a predetermined value far smaller than 2.3 nm), a high HOR activity can be realized over the entire operating conditions. Was found. As a result, it can greatly contribute to improving the power generation performance of the fuel cell. Focusing on the relationship between the particle diameter and the average coordination number when platinum particles are used as the catalyst metal particles, and by satisfying the above requirement (b), the durability and power generation performance of the fuel cell are improved. It is found that it can do. FIG. 2 is based on the literature (HA Gasteiger et al., Applied Catalysis B: Environmental 56 (2005) 9-35). However, the “activity” on the vertical axis of the two graphs in FIGS. 2 (a) and 2 (b) indicates the oxygen reduction reaction (ORR) activity. Is almost the same as the measurement method described in this specification. The difference from this specification is that the potential scanning speed is 20 mV / s instead of 10 mV / s. The potential scanning range is about 0 → 1.0V (RHE). Hereinafter, the electrode catalyst will be described for each component.

(Catalyst carrier)
The catalyst carrier functions as a conductive carrier for supporting catalyst metal particles as a catalyst component, and as an electron conduction path involved in transfer of electrons between the catalyst metal particles as a catalyst component and other members. I do.

  The catalyst carrier may have a specific surface area for supporting catalyst metal particles as a catalyst component in a desired dispersed state and may have sufficient electron conductivity, and the main component is carbon. Is preferred. Specifically, as a catalyst carrier whose main component is carbon, carbon black such as Ketjen black (highly conductive carbon black), (oil) furnace black, channel black, acetylene black, thermal black, lamp black, activated carbon, Examples include carbon particles (carbon carrier) made of coke, natural graphite, artificial graphite, and the like. Here, “the main component is carbon” means that a carbon atom is contained as a main component, and is a concept that includes both of a carbon atom only and a substantially carbon atom. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, "consisting substantially of carbon atoms" means that mixing of impurities of about 2 to 3% by mass or less is permissible.

The BET specific surface area of the catalyst carrier may be a specific surface area sufficient to highly disperse and support catalytic metal particles as a catalyst component, but is preferably 20 to 1600 m ² / g, more preferably 80 to 1200 m ² / g. It is. When the specific surface area of the catalyst carrier is within such a range, 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.

  Although the size of the catalyst carrier is not particularly limited, the average particle diameter is about 5 to 200 nm, preferably 10 to 20 nm, from the viewpoint of simplicity of loading, catalyst utilization, and controlling the thickness of the catalyst layer in an appropriate range. The thickness is preferably about 100 nm.

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

(Catalyst metal particles for cathode electrode catalyst)
The catalytic metal that can be used in the present embodiment has a function of catalyzing an electrochemical reaction. Among them, the catalyst metal particles, which are the catalyst components that can be used in the cathode electrode catalyst, are not particularly limited as long as they have a catalytic action on the oxygen reduction reaction, and known catalyst metals can be used. Specifically, it can be selected from metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and alloys thereof. .

  Among them, those containing at least platinum are preferably used in order to improve catalytic activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like. That is, the catalyst metal is preferably platinum or contains platinum and a metal component other than platinum, and more preferably platinum or a platinum-containing alloy. Such a catalytic metal can exhibit high activity. Although the composition of the alloy depends on the type of the metal to be alloyed, the content of platinum is preferably 30 to 90 atomic%, and the content of the metal to be alloyed with platinum is preferably 10 to 70 atomic%. Note that an alloy is generally a metal element obtained by adding one or more metal elements or non-metal elements, and is a general term for an alloy having metallic properties. The alloy structure includes eutectic alloys, which are so-called mixtures in which the component elements are separate crystals, those in which the component elements are completely dissolved and in solid solution, and those in which the component elements are intermetallic compounds or compounds of metals and nonmetals. Some of them are formed, and any of them may be used in the present application. At this time, the catalyst metal particles of the catalyst component used for the cathode electrode catalyst can be appropriately selected from the above. In this specification, unless otherwise specified, the description of the catalyst metal for the anode catalyst layer and the catalyst metal for the cathode catalyst layer has the same definition for both. In the present embodiment, the catalyst component for the anode electrode catalyst and the catalyst component for the cathode electrode catalyst need not be the same, and may be appropriately selected so as to exhibit the above-described effects of the present embodiment.

  The shape and size of the catalytic metal particles as the catalyst component for the cathode electrode catalyst are not particularly limited, and the same shape and size as those of known catalyst components can be adopted. As the shape of the catalyst metal particles as the catalyst component for the cathode electrode catalyst, for example, particles, flakes, layers and the like can be used, but the particles are particularly preferable. At this time, the average particle diameter of the catalyst metal particles for the cathode electrode catalyst is preferably 1 to 30 nm, more preferably 3 to 30 nm, and particularly preferably 3 to 10 nm. When the average particle size of the catalytic metal particles for the cathode electrode catalyst is within such a range, the balance between the catalyst utilization rate related to the effective electrode area where the electrochemical reaction proceeds and the simplicity of loading is appropriately controlled. Can be done. When using a carrier having the above-described specific pore distribution, if the average particle size of the catalyst metal is 3 nm or more, the catalyst metal is relatively firmly supported in the micropores and the mesopores, and in the catalyst layer. Contact with the electrolyte is more effectively suppressed and prevented. In addition, the micropores remain without being blocked by the catalyst metal, and the gas transport path is better secured, so that the gas transport resistance can be further reduced. In addition, elution due to a potential change can be prevented, and a decrease in performance over time can be suppressed. Therefore, the catalytic activity can be further improved, that is, the catalytic reaction can be more efficiently promoted. On the other hand, when the average particle diameter of the catalyst metal particles is 30 nm or less, the catalyst metal can be supported inside the mesopores of the carrier by a simple method, and the electrolyte coverage of the catalyst metal can be reduced. The “average particle size of the catalytic metal particles for the cathode electrode catalyst” in the present embodiment is determined from the crystallite diameter determined from the half width of the diffraction peak of the catalyst component in the X-ray diffraction and the transmission electron microscope image. It can be measured as the average value of the particle diameter of the catalyst metal particles as the catalyst component.

  In the cathode electrode catalyst, the amount of the catalyst metal particles supported on the catalyst carrier is preferably 10 to 80% by mass, more preferably 30 to 70% by mass, based on the total amount of the cathode electrode catalyst. When the supported amount of the catalyst metal particles for the cathode electrode catalyst is within such a range, the balance between the degree of dispersion of the catalyst component on the catalyst carrier and the catalyst performance can be appropriately controlled. The amount of the catalytic metal particles, which is a catalytic component, in the cathode electrode catalyst can be measured by inductively coupled plasma emission spectroscopy (ICP).

(Catalyst component for anode electrode catalyst)
The catalytic metal that can be used in the present embodiment has a function of catalyzing an electrochemical reaction. Among these, the catalytic metal particles that are the catalyst components that can be used in the anode electrode catalyst have a catalytic action on the oxidation reaction of hydrogen and satisfy one or more of the following requirements (a) to (c): Things can be used. That is, the catalytic metal particles used for the anode electrode catalyst have (a) an electrochemical specific surface area of at least 280 m ² / g measured by CO stripping, and (b) an average of the catalytic metal measured by XAFS. It satisfies at least one of the requirements that the coordination number is 4 or less and (c) the average particle size is 1 nm or less. Hereinafter, each requirement will be described.

  First, the catalyst component that can be used in the anode electrode catalyst of the present embodiment is not particularly limited as long as it has a catalytic action on the hydrogen oxidation reaction, and a known catalyst metal can be used. Specifically, it can be selected from metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, and alloys thereof.

  Among them, those containing at least platinum are preferably used in order to improve catalytic activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like. That is, the catalyst metal is preferably platinum or contains platinum and a metal component other than platinum, and more preferably platinum or a platinum-containing alloy. Such a catalytic metal can exhibit high activity. Although the composition of the alloy depends on the type of the metal to be alloyed, the content of platinum is preferably 30 to 90 atomic%, and the content of the metal to be alloyed with platinum is preferably 10 to 70 atomic%. Note that an alloy is generally a metal element obtained by adding one or more metal elements or non-metal elements, and is a general term for an alloy having metallic properties. The alloy structure includes eutectic alloys, which are so-called mixtures in which the component elements are separate crystals, those in which the component elements are completely dissolved and in solid solution, and those in which the component elements are intermetallic compounds or compounds of metals and nonmetals. Some of them are formed, and any of them may be used in the present application. At this time, the catalyst metal particles of the catalyst component used for the anode electrode catalyst can be appropriately selected from the above. In this specification, unless otherwise specified, the description of the catalyst metal for the anode catalyst layer and the catalyst metal for the cathode catalyst layer has the same definition for both. In the present embodiment, the catalyst component for the anode electrode catalyst and the catalyst component for the cathode electrode catalyst need not be the same, and may be appropriately selected so as to exhibit the above-described effects of the present embodiment.

  The shape of the catalytic metal particles that are the catalyst component for the anode electrode catalyst is not particularly limited, and the same shape as a known catalyst component can be adopted. As the shape of the catalyst metal particles which are the catalyst components for the anode electrode catalyst, for example, particles, flakes, layers and the like can be used, but the particles are particularly preferable. The average particle size of the catalytic metal particles for the anode electrode catalyst must satisfy the requirement (c), which will be described in detail below.

  In the anode electrode catalyst, the amount of the catalyst metal particles supported on the catalyst carrier is preferably 10 to 80% by mass, more preferably 30 to 70% by mass, based on the total amount of the anode electrode catalyst. When the amount of the catalytic metal particles for the anode electrode catalyst is within such a range, the balance between the degree of dispersion of the catalyst component on the catalyst carrier and the catalytic performance can be appropriately controlled. The amount of the catalytic metal particles, which is a catalytic component, in the anode electrode catalyst can be measured by inductively coupled plasma emission spectroscopy (ICP).

  The catalyst metal particles are preferably loaded in a concentration range of 0.01 to 50% by weight, more preferably 0.01 to 15% by weight, based on the carrier material on which the catalyst metal particles are loaded. Here, the carrier material for supporting the catalyst metal particles is a carbon material as described above, or, when a functional group or a ligand is introduced into the carbon material, these functional groups or ligands are included. It can be an introduced carbon material. When the amount of the supported catalyst metal particles is 0.01 wt% or more, the function of the catalyst metal particles can be sufficiently obtained. On the other hand, when the amount of the supported catalyst metal particles is 50% by weight or less, the pore function of the carbon material is maintained, and a high BET surface area can be obtained.

<< About the requirement of the above (a) >>
The catalytic metal particles satisfying the requirement (a) have an electrochemical specific surface area measured by CO stripping of 280 m ² / g or more. As a result, the catalytic metal particles disposed on the catalyst carrier have a large specific surface area without causing agglomeration, so that excellent catalytic activity, in particular, HOR activity per unit platinum mass of the catalytic metal is improved. is there. Furthermore, since the ORR activity per unit platinum area of the catalyst metal is reduced more than the effect of increasing the specific surface area, it is possible to provide an excellent anode electrode catalyst which also has the effect of reducing the ORR activity per unit platinum mass.

  The electrochemical specific surface area measured by CO stripping can be measured by the following method. However, the method is not limited to the following method as long as the “electrochemical specific surface area measured from the adsorption and desorption of hydrogen” can be measured.

  First, a dispersion is prepared by dispersing a predetermined amount of the catalyst (10.4 mg when the amount of the catalytic metal particles supported on the carrier is 3.9 wt% with respect to the total amount of the catalyst) in 19 mL of water and 6 mL of isopropanol. A catalyst ink is prepared by adding 100 μL of a Nafion solution (DE521CS, 5 wt%, manufactured by Aldrich) to this dispersion. Thereafter, ultrasonic dispersion is performed for 1 hour or more. 10 μL of the prepared catalyst ink is applied to a polished glassy carbon electrode (diameter (φ) 5.0 mm, manufactured by Hokuto Denko) and dried in a dryer at 60 ° C. for 10 minutes. The surface coating state of the electrode is confirmed by microscopic observation, and an electrode having no remaining catalyst layer and no protrusion is used for evaluation.

  Electrochemical measurements were performed in a normal three-chamber cell (Mick Lab). As the electrolyte solution, 0.1 M perchloric acid (Ultrapur, manufactured by Kanto Chemical Co., Ltd.) is used. The counter electrode is a Pt line, and the reference electrode is a RHE (reversible hydrogen electrode). The potential control is performed using HZ-5000 (manufactured by Hokuto Denko). HR-301 (manufactured by Hokuto Denko) was used as a rotating electrode (RDE) device. The cell temperature is controlled at 25 ° C. (± 1 ° C.) using an external circulation type thermostat (CHL300, manufactured by YAMATO). For measurement using CO, an Ar balance gas (manufactured by Taiyo Nissin) of 1% by volume CO is used. All measurements will be performed in the draft.

As a pretreatment of the electrode, a range from 0 V (RHE) to 1.2 V (RHE) is scanned at 100 mVs ⁻¹ for 20 cycles, and then measurement such as cyclic voltammetry and convection voltammetry is performed. The electrode is kept at 0.05 V (RHE) for 30 minutes while rotating the electrode at 400 rpm in an electrolyte solution saturated with 1% by volume CO gas. Under these conditions, it is confirmed that the CO adsorption amount reaches saturation. After completely replacing the CO gas in the solution with nitrogen, three cycles of CV (cyclic voltammogram) measurement are performed from 0.05 V (RHE) to 1.2 V (RHE) at 20 mVs- ¹ . The CVs after the second cycle are clearly overlapped and observed. The amount of electricity at the CO stripping peak is calculated from the difference between the CVs after the first cycle and the second and subsequent cycles, and the electrochemically active surface area is calculated by applying a conversion coefficient of 285.6 μCcmPt- ² . The ECA (electrochemically effective surface area) can be calculated by assigning the calculated surface area to the supported amount of the catalyst metal particles.

  FIG. 3A shows a specific example of the CV curve obtained by the above measurement method (Examples and Comparative Examples using Pt particles as catalyst metal particles). FIG. 3B shows the relationship between the specific surface area obtained by the above-described measurement method and the diameter (= average particle diameter) (m) of the Pt particles used in the examples and comparative examples calculated from the following equation (1). Shown in

The catalytic metal (Pt) particles satisfying the requirement (a) have an electrochemical specific surface area measured by CO stripping of 280 m ² / g or more, preferably 280 m ² / g or more and 930 m ² / g or less. . More preferably, it is 280 m ² / g or more and 560 m ² / g or less. The specific surface area of the catalyst metal (Pt) particles was set to 280 m ² / g or more, as shown in FIG. 3B, from the graphs obtained from Examples and Comparative Examples using platinum particles as catalyst metal particles. This is because the specific surface area of the region having an average particle diameter of 1 nm or less becomes 280 m ² / g or more. From the graphs obtained from the example and the comparative example in FIG. 3B, it can be said that the specific surface area of the comparative example (conventional example) having an average particle diameter of 2 nm or less should be 125 m ² / g or more. 930 m ² / g, which is the upper limit of the specific surface area, is because the diameter of one platinum atom is about 0.3 nm, so that the specific surface area is at most 930 m ² / g. The upper limit of 560 m ² / g of the preferred range is such that the diameter of platinum particles (average coordination number 3 or 4) composed of 4 or 6 platinum atoms is about 0.5 nm. For this reason, the specific surface area is defined as 560 m ² / g. However, it goes without saying that even when the specific surface area exceeds 560 m ² / g, the effects of the present invention can be sufficiently exhibited. Here, for example, when the catalyst metal is Pt, the number of Pt atoms contained in the particles having an average particle diameter of 3 nm is about 612, and the number of Pt atoms contained in the particles having an average particle diameter of 1 nm is about 10. is there.

<< About the requirement of (b) above >>
In the catalytic metal particles satisfying the requirement (b), the average coordination number of catalytic metal (Pt) atoms measured by XAFS (X-ray absorption fine structure analysis) is 4 or less. With such a configuration, the catalyst metal particles arranged on the catalyst carrier are configured with a small coordination number that does not cause aggregation, and thus can exhibit a high specific surface area. Further, it is also possible to realize atomization with an average particle diameter of 1 nm or less (about 0.5 nm) (see FIG. 4). Thereby, it is possible to provide an excellent anode electrode catalyst capable of improving the catalytic activity, especially the high HOR activity and the low ORR activity.

  The average coordination number of the catalytic metal atom measured by XAFS (X-ray absorption fine structure analysis) is preferably in the range of 3 to 4 (see FIG. 4).

  FIG. 4 shows the average coordination number of catalytic metal (Pt) atoms and the catalytic metal (Pt) atoms measured by XAFS (X-ray absorption fine structure analysis) for Examples and Comparative Examples in which platinum particles were used as catalytic metal particles. It is a figure which shows the relationship of the average particle diameter of Pt) particle | grains. In the figures, the coordination structure (molecular structure model) of the catalyst metal (Pt) particles of each example is shown.

  As shown in FIG. 4, in the catalytic metal (Pt) particles used in the examples, the average coordination number of the catalytic metal (Pt) atoms measured by XAFS is 4 or less, specifically 3.3, At this time, the average particle diameter of the catalyst metal (Pt) particles is approximately 0.45 to 0.55 nm.

  The measurement of the average number of ligands of the catalytic metal atom and the average particle size of the catalytic metal particles by XAFS (X-ray absorption fine structure analysis) can be determined by the method described in Examples described later.

<< About the requirement of the above (c) >>
The catalyst metal particles satisfying the requirement (c) have an average particle size of 1 nm or less. With this configuration, the catalyst metal particles disposed on the catalyst carrier have a small particle size that does not cause agglomeration, and thus can exhibit a high specific surface area. Thereby, it is possible to provide an excellent anode electrode catalyst capable of improving the catalytic activity, especially the high HOR activity and the low ORR activity. The average particle diameter of the catalytic metal atoms is preferably in the range of 0.3 nm to 1 nm, more preferably in the range of 0.5 nm to 1 nm. Here, the method of measuring the average particle diameter of the catalytic metal particles is as follows: the catalytic metal particles are assumed to be spherical and converted into diameters using the specific surface area obtained by CO stripping, which is the requirement of the above (a). , Calculated by the following equation (2). The diameter of the obtained catalyst metal is adopted as the value of the average particle diameter of the catalyst metal particles.

  However, the method for measuring that the average particle diameter of the catalytic metal particles satisfying the requirement (c) is 1 nm or less is as described above, but the average particle diameter of the catalytic metal particles is 1 nm or less. As grounds, the following four measurement data can also be grounds. The fourth is the measurement method described above.

  1. From the TEM observation result: No particles of about 1 to 2 m observed in the comparative example are observed (see FIGS. 6A and 6B). The TEM can be measured by the method described in Examples.

  2. From the XRD observation results: The peak of platinum is so small that the particle size cannot be calculated, and is broad (see FIG. 7). XRD can be measured by the method described in Examples.

  3. From the XAFS observation result: The particle diameter predicted from the coordination number measured by XAFS is 1 nm or less (see FIG. 4). XAFS can be measured by the method described in Examples.

  4. From the measurement of the electrochemical surface area by CO stripping: Assuming a sphere from the surface area, the calculated diameter should be less than 1 nm. The method for measuring the electrochemical surface area by CO stripping is as described above, and for details, see the explanation under the requirement (a).

要件 (d) requirements≫
In the present embodiment, in addition to satisfying one or more, preferably two or more of the above requirements (a) to (c), it is desirable to satisfy the following requirement (d). When two or more of the above requirements (a) to (c) are satisfied, it is excellent in that the effects of each requirement can be synergistically or compositely improved. As a requirement of (d), the catalytic metal particles have an oxygen reduction reaction activity per unit mass of platinum, and an electrochemical specific surface area of 60 to 90 m ² / g measured from hydrogen adsorption and desorption. 0.75 or less of the range of catalytic metal particles. By satisfying such a configuration, the limiting current density of oxygen measured by the rotating electrode method is reduced to about 2/3 of the conventional value. From such a viewpoint, the catalyst metal particles have a catalytic activity in which the relative oxygen reduction reaction activity per unit mass of platinum is 60 to 90 m ² / g in terms of electrochemical specific surface area measured from the adsorption and desorption of hydrogen. Preferably it is in the range of 0.65 or less of the particles. This is because the reaction mechanism of the oxygen reduction reaction was changed because the particle diameter of the catalyst metal (Pt) was reduced to 1 nm or less by a method for producing a catalyst (particularly, a catalyst metal) described later. That is, the catalyst metal (Pt) having a large particle diameter undergoes a four-electron reduction reaction, but when the particle diameter becomes 1 nm or less, the ratio of the two-electron reduction reaction sharply increases. To a degree. As a result, the oxygen reduction reaction (ORR) activity per unit surface area of the catalytic metal (Pt) is rapidly reduced more than the specific surface area is increased. Therefore, the oxygen reduction reaction activity per unit platinum mass has a particle diameter of 1 nm or less. At which point it begins to drop sharply (see FIGS. 8 and 9). By satisfying the above requirement (d), an excellent catalytic activity, particularly an effect of rapidly decreasing the ORR activity per unit area and per unit mass can be obtained. Further, it is possible to provide an excellent anode electrode catalyst having an effect of improving the HOR activity per unit mass of the catalyst metal because the specific surface area is increased.

  In the above requirement (d), the “electrochemical specific surface area measured from the adsorption and desorption of hydrogen”, that is, from the adsorption and desorption of hydrogen on the catalyst (Pt) particles supported on the catalyst carrier as an electrode catalyst The electrochemical specific surface area to be measured can be measured by the following method. However, the method is not limited to the following method as long as the “electrochemical specific surface area measured from the adsorption and desorption of hydrogen” can be measured.

  First, a dispersion is prepared by dispersing a predetermined amount of the catalyst (10.4 mg when the amount of the catalytic metal particles supported on the carrier is 3.9 wt% with respect to the total amount of the catalyst) in 19 mL of water and 6 mL of isopropanol. A catalyst ink is prepared by adding 100 μL of a Nafion solution (DE521CS, 5 wt%, manufactured by Aldrich) to this dispersion. Thereafter, ultrasonic dispersion is performed for 1 hour or more. 10 μL of the prepared catalyst ink is applied to a polished glassy carbon electrode (φ5.0 mm, manufactured by Hokuto Denko) and dried in a dryer at 60 ° C. for 10 minutes. The surface coating state of the electrode is confirmed by microscopic observation, and an electrode having no remaining catalyst layer and no protrusion is used for evaluation.

  The electrochemical measurement is performed in a usual three-chamber cell (manufactured by Mick Lab). As the electrolyte solution, 0.1 M perchloric acid (Ultrapur, manufactured by Kanto Chemical Co., Ltd.) is used. The counter electrode was a Pt line, and the reference electrode was RHE. The potential control is performed using HZ-5000 (manufactured by Hokuto Denko). The rotating electrode (RDE) device uses HR-301 (manufactured by Hokuto Denko). The cell temperature is controlled at 25 ° C. (± 1 ° C.) using an external circulation type thermostat (CHL300, manufactured by YAMATO).

Nitrogen gas is supplied to the electrolytic solution to keep it in a nitrogen atmosphere. A range of ⁰ to 1.2 V (RHE) is scanned 20 times at a scanning speed of 100 mVs ^-1 . Thereafter, scanning is performed three times in a range of ⁰ to 1.2 V (RHE) at a scanning speed of 50 mVs ^-1 . Obtaining electricity quantity Q _H from the hydrogen adsorption wave of the measured CV. Here, the third cycle CV is applied. Therefore, FIG. 5 is a graph showing CV (cyclic voltammetry) at the third cycle (relationship between voltage (potential) and current at the third cycle) in electrochemical measurement. In addition, a hatched portion surrounded by a hydrogen adsorption wave, an electric double layer, and a potential up to a maximum appearing immediately before a hydrogen generation current is integrated over time.

- in accordance with the following equation to calculate the electrochemically active surface area a of the platinum particles from the quantity of electricity Q _H from the hydrogen adsorption wave of the measured CV.

The conversion coefficient 2.1 Cm _Pt ^-2 is a value for a platinum polycrystalline electrode, but is generally applicable to nanoparticles.

  According to the following formula, a is normalized by the mass w of platinum supported on the GC disk electrode, and ECA is obtained.

  Next, in the above requirement (d), the “relative oxygen reduction reaction activity per unit platinum mass” of the catalytic metal particles of the present embodiment can be measured by the following method. However, the method is not limited to the following method as long as the “oxygen reduction activity per unit platinum mass of the catalytic metal particles” can be measured.

  First, a dispersion is prepared by dispersing a predetermined amount of the catalyst (10.4 mg when the amount of the catalytic metal particles supported on the carrier is 3.9 wt% with respect to the total amount of the catalyst) in 19 mL of water and 6 mL of isopropanol. A catalyst ink is prepared by adding 100 μL of a Nafion solution (DE521CS, 5 wt%, manufactured by Aldrich) to this dispersion. Thereafter, ultrasonic dispersion is performed for 1 hour or more. 10 μL of the prepared catalyst ink is applied to a polished glassy carbon electrode (φ5.0 mm, manufactured by Hokuto Denko) and dried in a dryer at 60 ° C. for 10 minutes. The surface coating state of the electrode is confirmed by microscopic observation, and an electrode having no remaining catalyst layer and no protrusion is used for evaluation.

  The electrochemical measurement is performed in a usual three-chamber cell (manufactured by Mick Lab). As the electrolyte solution, 0.1 M perchloric acid (Ultrapur, manufactured by Kanto Chemical Co., Ltd.) is used. The counter electrode is a Pt line, and the reference electrode is RHE. The potential control is performed using HZ-5000 (manufactured by Hokuto Denko). The rotating electrode (RDE) device uses HR-301 (manufactured by Hokuto Denko). The cell temperature is controlled at 25 ° C. (± 1 ° C.) using an external circulation type thermostat (CHL300, manufactured by YAMATO).

Oxygen gas is supplied to the electrolytic solution to keep it in an oxygen atmosphere. A range of ⁰ to 1.2 V (RHE) is scanned five times at a scanning speed of 100 mVs ^-1 . Thereafter, while rotating the electrode at 1600 rpm, scanning is performed from a start potential of 0.2 V (RHE) to an end potential of 1.2 V (RHE) at a scanning speed of 10 mVs ^-1 . The same is performed in a nitrogen atmosphere. In advance, an AC impedance measurement is performed for 30 seconds at a holding potential of 0.5 V (RHE), a frequency of 1000 Hz, and an AC amplitude of 15 mV to grasp the solution resistance.

  The response current obtained in the nitrogen atmosphere is subtracted from the response current obtained in the oxygen atmosphere, and the potential is corrected by the solution resistance. A simple Koutecky-Levich equation shown below:

(Where, i is the actual response current, i _k is activated dominant current, i _L denotes the limiting current.) To correct the effects of mass transfer, the activation dominant current i _k is a catalyst intrinsic activity calculate.

In the above requirement (d), the catalyst metal (Pt) particles having an electrochemical specific surface area of 60 m ² / g or more and 90 m ² / g or less measured based on the adsorption and desorption of hydrogen are used as a reference. According to the technology, the catalytic oxygen (Pt) particles having an electrochemical specific surface area in a range of 60 m ² / g or more and 90 m ² / g or less have the highest oxygen reduction activity per unit catalytic metal (Pt) mass, and are almost the same. I know it is a value. Therefore, it can be said that there is little difference in the oxygen reduction activity in the range ^{60 m} 2 / g or more ^90m 2 / g, in any of ^{60 m} 2 / g or more ^90m 2 / g or less in the range, the oxygen reduction reaction activity It is specified that it is 0.75 or less. The electrochemical specific surface area of 60 m ² / g or more and 90 m ² / g or less is based on the oxygen reduction activity per unit mass of catalytic metal (Pt) from the prior art as described above. This is for showing the maximum value in the range of.

(Method for producing anode electrode catalyst)
The anode electrode catalyst according to the present embodiment is manufactured by a method having the following steps. (A) This is a step of preparing a carbon material having pores to be used as a catalyst carrier. (B) introducing a metal complex into the carbon material. (C) heat-treating the carbon material into which the metal complex has been introduced, or reducing the metal complex by bringing the carbon material into contact with hydrogen to obtain a metal-supported carbon material which is an anode electrode catalyst supporting catalyst metal particles. .

Generally, as a method for introducing nano-sized metal particles into a carbon material used for a catalyst carrier, a metal complex such as Pt (NO ₂ ) ₂ (NH ₃ ) ₂ or H ₂ PtCl ₆ is reduced with sodium borohydride or the like. A reduction method using an agent has been used. However, in such a method, it is not easy to control and produce the catalyst metal particles having an average particle diameter of 3 nm or less.

  On the other hand, according to the method of the present embodiment, the catalyst metal is first introduced as a complex into the carbon material used for the catalyst carrier, so that the catalyst metal is supported on the surface of the carbon material at the atomic level. Thereafter, the catalyst metal atom is eliminated from the ligand by heat treatment or contact with hydrogen. The desorbed catalytic metal atoms may form a nanocluster of several atoms to several tens of atoms by a plurality of atoms gathering (sintering). Therefore, the catalyst metal can be introduced into the carbon material used in the catalyst carrier in a highly dispersed state, and the catalyst metal atoms are excessively increased as compared with the case where the catalyst metal is reduced using a reducing agent such as sodium borohydride. Aggregation can be suppressed. In addition, there is an advantage that a complicated operation in a manufacturing stage can be avoided.

(Step (a) of preparing a carbon material having pores used in a catalyst carrier)
There is no particular limitation on the route of obtaining the carbon material used in the catalyst carrier. Commercially available products may be used, or they may be prepared by themselves. For example, carbon materials such as commercially available Ketjen black (highly conductive carbon black), (oil) furnace black, channel black, acetylene black, thermal black, lamp black, etc., activated carbon, coke, natural graphite, artificial graphite, etc. May be used. In the present embodiment, it can be said that it is desirable to use Ketjen Black, which is a highly conductive carbon black, from the viewpoint of power generation characteristics and the like.

(Step (b) of Introducing Metal Complex into Carbon Material Used in Catalyst Support)
The method of introducing the metal complex into the carbon material prepared in (a) (for example, a carbon material such as carbon black such as Ketjen black (highly conductive carbon black)) is not particularly limited. For example, (i) reacting a carbon material with a phosphorus compound to obtain a carbon material having a phosphorus ligand, and reacting the carbon material having a phosphorus ligand with a metal compound to form a metal on the phosphorus ligand. And (ii) a method of reacting a carbon material with a metal complex.

  Hereinafter, the methods (i) and (ii) will be described.

(I) reacting the carbon material prepared in (a) with a phosphorus compound to obtain a carbon material having a phosphorus ligand (b1), and reacting the carbon material having a phosphorus ligand with a metal compound And (b2) coordinating a metal to the phosphorus ligand. In this method, a phosphorus ligand is first introduced into the carbon material, and then a metal serving as a catalyst is added to the phosphorus ligand. The resulting metal complex is introduced and reacted. This reaction can proceed by a ligand exchange reaction in which a ligand of the metal complex is replaced with a phosphorus ligand having a strong coordination force. As a result, it can be supported as a complex in which a phosphorus ligand is coordinated to a metal atom.

  At this time, the phosphorus compound for introducing the phosphorus ligand to be used is not particularly limited, but a phosphorus compound represented by the following chemical formula is preferably used.

In the formula, Ph ¹ and Ph ² may be the same or different and are a substituted or unsubstituted phenyl group, and X is a halogen atom. As the halogen atom, Cl and Br are preferable, and Cl is more preferable. The substituent of Ph ¹ or Ph ² is not particularly limited, and is, for example, an alkyl group having 1 to 8 carbon atoms, an alkoxy group, or a halogenated alkyl group.

Examples of the phosphorus compound include chlorodiphenylphosphine, chlorobis (3,5-dimethylphenyl) phosphine, chlorobis (4-methoxyphenyl) phosphine, chlorobis [4- (trifluoromethyl) phenyl] phosphine, chlorodi (p-tolyl) ) Phosphine, bis (3,5-di-tert-butyl-4-methoxyphenyl) chlorophosphine, chlorobis [3,5-bis (trifluoromethyl) phenyl] phosphine and the like. When a phosphorus compound as described above is used, a complex having PPh ¹ Ph ² as a ligand can be introduced.

  The conditions under which the carbon material is reacted with the phosphorus compound are not particularly limited. Preferably, the carbon material, which has been cooled in advance by heating under vacuum and left to cool, is reacted with the phosphorus compound while replacing with nitrogen, preferably in the presence of an amine. The reaction temperature and reaction time are not particularly limited. Preferably, first, the carbon material is impregnated with an amine dissolved in a solvent, and a phosphorus compound is added little by little at -100 to 10C, preferably -100 to 5C, and mixed. Thereafter, the temperature of the reaction solution is raised to, for example, 0 to 100 ° C, preferably 10 to 30 ° C, and the reaction is performed with stirring. The reaction time after raising the reaction temperature is preferably 0.5 to 72 hours, more preferably 2 to 24 hours, and further preferably 12 to 24 hours.

  At this time, the solvent is not particularly limited, but an aprotic polar solvent can be preferably used. Examples of the aprotic polar solvent include tetrahydrofuran (THF), dimethylsulfoxide (DMSO), hexamethylphosphoric triamide (HMPT), dimethylformamide (DMF), acetone, and acetonitrile. Among them, THF is preferable.

  It is preferable to use a tertiary amine as the amine. Although it does not specifically limit as a tertiary amine, For example, trimethylamine, triethylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, diethylmethylamine (N, N-diethylmethylamine), dimethylethylamine ( N, N-dimethylethylamine) and the like. Among them, triethylamine is preferable.

  The amount of the phosphorus compound to be used is not particularly limited, but is preferably 0.1 to 50 mmol, more preferably 1 to 20 mmol, per 1 g of the carbon material. Within the above range, the reaction can proceed efficiently.

  After a carbon material having a phosphorus ligand is obtained, it is preferably washed, dried under vacuum and then reacted with a metal complex. The metal complex used is not particularly limited. Preferred platinum complexes include, for example, (1,5-cyclooctadiene) dimethylplatinum (II), (2,2′-bipyridine) dichloroplatinum (II), (ethylenediamine) iodoplatinum dimer, dichloro (1,10- Phenanthroline) platinum (II), dichloro (ethylenediamine) platinum (II), dichlorobis (dimethylsulfide) platinum (II), dichlorobis (ethylenediamine) platinum (II), trichloro (ethylene) platinum (II) (for example, trichloro (ethylene) ) Potassium platinum (II)), hexahydroxyplatinate (IV) (eg, sodium hexahydroxyplatinate (IV)), cis-bis (acetonitrile) dichloroplatinum (II), cis-diamminetetrachloroplatinum (IV) , Cis-dichlorobis (pyridine) Gold (II), cis-diammineplatinum (II) dichloride, cis-dichlorobis (diethylsulfide) platinum (II), cis-dichlorobis (triethylphosphine) platinum (II), cis-dichlorobis (triphenylphosphine) platinum (II) Cis-bis (benzonitrile) dichloroplatinum (II), trans-dichlorobis (triphenylphosphine) platinum (II), trans-dichlorobis (triethylphosphine) platinum (II), ethylenebis (triphenylphosphine) platinum (0) , Diaminedinitritoplatinum (II), platinum (0) -1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex, platinum (0) -2,4,6,8-tetramethyl- 2,4,6,8-tetravinylcyclotetrasiloxane complex, white (II) acetylacetonate, tetraammineplatinum (II) nitrate, dichloro (1,2-diaminocyclohexane) platinum (II), dichloro (1,5-cyclooctadiene) platinum (II), dichloro (dicyclopentadienyl) Platinum (II), tetraammineplatinum (II) chloride, tetrakis (triphenylphosphine) platinum (0), trimethyl (methylcyclopentadienyl) platinum (IV), bis (tri-tert-butylphosphine) platinum (0) And hexachloroplatinate (IV) (eg, potassium hexachloroplatinate (IV), tetrabutylammonium hexachloroplatinate (IV)), platinum iodide, platinum chloride, and the like.

  Preferred palladium complexes include, for example, palladium chloride, chloro (1,5-cyclooctadiene) methylpalladium (II), dichloro (1,5-cyclooctadiene) palladium (II), bicyclo ([2.2.1 Hepta-2,5-diene) dichloropalladium (II), (ethylenediamine) palladium (II) chloride and the like.

  The conditions under which the carbon material having the phosphorus ligand is reacted with the metal complex are not particularly limited. Preferably, the carbon material having the phosphorus ligand is reacted with the metal complex while stirring or refluxing in a nitrogen atmosphere. The reaction temperature is, for example, 0 to 150 ° C, preferably 20 to 100 ° C. The reaction time is, for example, 0.5 to 72 hours, preferably 1 to 12 hours.

The amount of the metal complex used is not particularly limited, but is preferably 0.001 to 10 mol, more preferably 0.01 to 5 mol, per 1 mol of the phosphorus ligand. Within the above range, the reaction can proceed efficiently. After the reaction, the mixture is filtered, washed, and dried by heating under vacuum to obtain a metal-supported carbon material that is an anode electrode catalyst. The introduction ratio of the metal complex to the introduced phosphorus ligand can be estimated from inductively coupled plasma (ICP) emission spectroscopy and ³¹ P-NMR measurement.

(Ii) Method of reacting a carbon material with a metal complex In this method, the metal complex is directly introduced into the carbon material and reacted. Depending on the coordination force of the ligand of the metal complex to be introduced, one or more of the ligands of the metal complex to be introduced can be eliminated or replaced with a solvent molecule.

  The conditions under which the carbon material reacts with the metal complex are not particularly limited. Preferably, the carbon material which has been dried by heating under vacuum in advance and allowed to cool is reacted with the metal complex while stirring or refluxing in a solvent. The reaction temperature and reaction time are not particularly limited. The reaction temperature is, for example, 0 to 100 ° C, preferably 10 to 30 ° C. The reaction time is, for example, 0.5 to 72 hours, preferably 2 to 24 hours.

  The solvent is not particularly limited as long as it dissolves the metal complex, and the same solvent as in the method (i) can be used.

  Although the metal complex to be used is not particularly limited, for example, a metal complex represented by the following chemical formula 2 can be preferably used.

Wherein M is selected from a group 8-10 metal;
In the formula, R ₁ and R ₂ are each independently a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 18 carbon atoms,
L ₁ and L ₂ are monodentate ligands, each independently being acetonitrile, benzonitrile, THF, diethyl sulfide, dimethyl sulfide, and pyridine, triphenylphosphine, tri-tert-butylphosphine, ethylene, cyclopentadiene Selected from the group consisting of enyl anion, methylcyclopentadienyl anion, pentamethylcyclopentadienyl anion, cyanide ion (CN ⁻ ); or
L ₁ and L ₂ are linked to form a bidentate ligand, wherein the bidentate ligand is dicyclopentadiene, 1,5-cyclooctadiene, norbonadiene, 2,2′-bipyridine, 1,10 -Phenanthroline, ethylenediamine, N, N, N'N'-tetramethylethylenediamine, and trans, trans-dibenzylideneacetone, bis (diphenylphosphino) methane, ethylenebis (diphenylphosphine), 1,3-bis (diphenylphosphine) Fino) propane, 1,4-bis (diphenylphosphino) butane, 1,2-bis (diphenylphosphino) benzene, 1,2-bis (dimethylphosphino) ethane, 1,1′-bis (diphenylphosphino) ) Is selected from the group consisting of ferrocene.

  Here, the alkyl group may be linear or branched. The substituent of the alkyl group is not particularly limited, and examples thereof include a hydroxyl group, a carboxyl group, an amino group, a cyano group, and a halogen atom. Specific examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, hexyl, and heptyl. Octyl group, nonyl group, decyl group and the like. Specific examples of the aryl group include a phenyl group, a biphenylyl group, and a naphthyl group, and the substituent of the aryl group is not particularly limited. For example, a halogen atom, an alkyl group having 1 to 8 carbon atoms, an alkoxy group, And a halogenated alkyl group.

Among them, a metal complex in which R ₁ and R ₂ are an alkyl group is preferable because the alkyl group is eliminated in a concerted manner so that the metal complex is easily reduced. In particular, (1,5-cyclooctadiene) dimethylplatinum (II), (1,5-cyclooctadiene) dimethylpalladium (II) and the like can be preferably used.

  The amount of the metal complex to be used is not particularly limited, but is preferably, for example, 0.01 to 100 wt%, more preferably 0.01 to 30 wt%, based on the carbon material. Within the above range, the reaction can proceed efficiently.

  After the reaction, the mixture is filtered, washed, and dried by heating under vacuum to obtain a metal-supported carbon material that is an anode electrode catalyst. The introduction rate of the metal complex can be estimated from inductively coupled plasma (ICP) emission spectroscopy.

(Step (c) of heat-treating the carbon material into which the metal complex is introduced or bringing the carbon material into contact with hydrogen to obtain a metal-supported carbon material that is an anode electrode catalyst on which catalytic metal particles are supported)
By heat-treating or bringing the carbon material into which the metal complex prepared in the above step (b) has been introduced into contact with hydrogen, the metal complex is reduced to a zero-valent metal. Then, the zero-valent metal aggregates to form catalyst metal particles (catalyst metal clusters) having an average particle size of 1 nm or less. In the catalytic metal particles (catalytic metal clusters), particles of 1 nm or less account for 50% or more of the total number of particles. According to the method of the present embodiment, the catalyst metal is first introduced as a complex, so that the catalyst metal particles can be supported with high dispersion. In addition, since the reaction can proceed gently as compared with a method of obtaining catalytic metal particles using a reducing agent, a metal which is an anode electrode catalyst having a predetermined particle diameter and having uniform particle diameters is used. A supported carbon material can be obtained.

  The mechanism by which heat treatment or treatment with hydrogen causes the average particle size to be 1 nm or less, and furthermore, the formation of catalytic metal particles in which 1 nm or less particles are 50% or more of the total number of particles is not clear. In the case of the metal complex represented by 2, by heating, metal particles (metal clusters) having an average particle size of 1 nm or less and 50% or more of the total number of particles are 1 nm or less by a mechanism such as the following formula. It is considered possible.

  The heat treatment method is not particularly limited. For example, after the carbon material into which the metal complex has been introduced is dried by heating under vacuum, it is preferably heated under an inert gas atmosphere. The temperature of the heat treatment is, for example, 100 to 400 ° C, preferably 150 to 400 ° C, more preferably 200 to 350 ° C, and further preferably 200 to 300 ° C. When the temperature of the heat treatment is 100 ° C. or higher, the metal complex is efficiently decomposed, and catalytic metal particles having an average particle size of 1 nm or less can be generated. Further, when the temperature of the heat treatment is 400 ° C. or lower, it is possible to suppress the catalyst metal particles from becoming excessively large. Therefore, catalytic metal particles (metal clusters) having an average particle size of 1 nm or less can be efficiently obtained. At this time, as for the catalyst metal particles (catalyst metal clusters), particles having a size of 1 nm or less can be efficiently obtained as 50% or more of the total number of particles. The time of the heat treatment is, for example, 0.1 to 10 hours, and more preferably 0.5 to 2 hours. Within the above range, the catalyst metal particles (catalyst metal clusters) of the present embodiment can be stably obtained. Note that the heat treatment may be performed plural times.

  Further, in the case of the metal complex represented by the above chemical formula 2, the catalyst having an average particle diameter of 1 nm or less and 50% or more of the total number of particles is 1 nm or less by a mechanism such as the following equation by hydrogen treatment. It is believed that metal particles (catalytic metal clusters) can occur.

  The conditions for the hydrogen treatment are not particularly limited. For example, a carbon material into which a metal complex has been introduced is dried by heating under vacuum, and then an inert gas such as nitrogen is introduced. Thereafter, a hydrogen gas is passed at, for example, 10 to 1000 cc / min, preferably 20 to 200 cc / min, and at a temperature of, for example, 0 to 150 ° C., preferably 20 to 100 ° C., for example, 0.1 to 10 hours. More preferably, it is contacted with hydrogen for 0.5 to 5 hours. If the temperature at the time of contacting with hydrogen is 0 ° C. or more, or the time of contacting with hydrogen is 0.1 hour or more, the metal complex can be efficiently decomposed and catalytic metal particles can be generated. In addition, when the temperature at the time of contacting with hydrogen is 150 ° C. or less, or the time at which the catalyst is contacted with hydrogen is 10 hours or less, it is possible to suppress the catalyst metal particles from becoming excessively large. Therefore, under the above conditions, catalyst metal particles (catalyst metal clusters) having an appropriate particle size and having a small variation in particle size can be efficiently obtained. Note that the hydrogen treatment may be performed a plurality of times at the same temperature or different temperatures. For example, the hydrogen treatment may be performed a plurality of times while increasing the temperature stepwise. When the hydrogen treatment is performed a plurality of times, the total time of contact with hydrogen is preferably within the above range. Further, in at least one hydrogen treatment, the temperature when contacting with hydrogen is preferably within the above range. As described later, the carbon material into which the metal complex has been introduced may come into contact with hydrogen during the cycle of hydrogen absorption / desorption measurement to gradually generate the metal complex. In such a case, instead of the above-described hydrogen treatment, a cycle of hydrogen adsorption / desorption measurement may be performed as a step of contacting with hydrogen. As an example, for example, 1,5-cyclooctadiene dimethylplatinum complex is reduced to metal (Pt) by contacting with hydrogen at 25 ° C. for 30 minutes. It can be said that the temperature condition at this time may be 25 ° C. to 100 ° C., and the hydrogen treatment time (time for contact with hydrogen) may be 6 minutes to 10 hours.

  The catalytic metal particles (metal-carrying carbon material), which is the anode electrode catalyst obtained by the above-described production method, can support the catalytic metal on the carrier (carbon material) in a highly active state. Further, the amount of the catalyst metal can be reduced by forming the catalyst metal particles into a catalyst metal cluster of several atoms to several tens of atoms. Therefore, a catalyst material having improved activity per mass of the catalyst metal can be obtained. Therefore, the catalytic metal particles (metal-supported carbon material) obtained by the above production method can be suitably used for an anode electrode catalyst for a fuel cell.

  The above is the description of the characteristic portions of the present embodiment. Hereinafter, other components of the present embodiment will be described.

(Catalyst metal content per unit catalyst application area)
In the present embodiment, the catalyst metal content (mg / cm ² ) per unit catalyst application area is not particularly limited as long as a sufficient degree of catalyst dispersion and power generation performance can be obtained. １1 mg / cm ² . However, when the catalyst metal contains platinum or a platinum-containing alloy, the platinum content per unit catalyst application area is preferably 0.5 mg / cm ² or less. The use of expensive noble metal catalysts typified by platinum and platinum alloys has been a factor in the high cost of fuel cells. Therefore, it is preferable to reduce the amount of expensive platinum used (platinum content) to the above range to reduce costs. The lower limit is not particularly limited as long as power generation performance is obtained, and is, for example, 0.01 mg / cm ² or more. More preferably, the platinum content is between 0.02 and 0.4 mg / cm ² . In the present embodiment. Since the catalytic metal has a high specific surface area, the catalytic activity can be improved while reducing the amount of the expensive catalytic metal carried. Further, when a carrier having the above-described specific pore distribution is used, the activity per catalyst weight can be improved by controlling the pore structure of the carrier, thereby further reducing the amount of catalyst metal used. It is possible to do.

In the present specification, inductively coupled plasma emission spectroscopy (ICP) is used to measure (confirm) the “catalyst (platinum) content per unit catalyst application area (mg / cm ² )”. A person skilled in the art can easily carry out a method of obtaining a desired “content of catalyst (platinum) per unit catalyst application area (mg / cm ² )” by controlling the composition of the slurry (catalyst concentration) and the application amount. By doing so, the amount can be adjusted.

  The amount of the catalyst metal carried on the carrier (sometimes referred to as the carrying ratio) is preferably 10 to 80% by mass, more preferably 20 to 70% by mass, based on the total amount of the electrode catalyst (that is, the carrier and the catalyst metal). It is good to be mass%. It is preferable that the loading amount is in the above range, since the degree of dispersion of the metal catalyst particles, which is a sufficient catalyst component, on the catalyst carrier, the improvement in power generation performance, the economic advantage, and the catalyst activity per unit weight can be achieved.

[Catalyst layer]
As described above, the electrode catalyst of the present embodiment, in particular, the anode electrode catalyst can exhibit high catalytic activity, that is, can promote the catalytic reaction. Therefore, the electrode catalyst of the present embodiment can be suitably used for an electrode catalyst layer for a fuel cell, particularly, an anode electrode catalyst layer. That is, the present embodiment also provides the electrode catalyst of the present embodiment and an electrode catalyst layer for a fuel cell including the electrode catalyst.

  In the catalyst layer of the present embodiment, the electrode catalyst is coated with an electrolyte, but the electrolyte does not enter the mesopores or the micropores of the catalyst carrier. Therefore, the catalyst metal on the surface of the carrier comes into contact with the electrolyte, but the catalyst metal supported inside the pores (mesopores and micropores) is not in contact with the electrolyte. The catalytic metal in the mesopores and micropores forms a three-phase interface between oxygen gas and water in a non-contact state with the electrolyte, thereby increasing the reaction active area of the catalytic metal.

  The electrode catalyst of the present embodiment may be present in either the cathode catalyst layer or the anode catalyst layer, but is preferably used in the anode catalyst layer. Thereby, by combining high HOR activity and low ORR activity as catalyst activities, an anode catalyst layer having high power generation performance can be provided. Further, the electrode catalyst having mesopores and micropores as described above is preferably used particularly in the cathode catalyst layer. The electrode catalyst having mesopores and micropores as described above can effectively utilize the electrode catalyst without forming contact with the electrolyte by forming a three-phase interface with water. It is because it forms.

  The electrolyte is not particularly limited, but is preferably an ion-conductive polymer electrolyte. The polymer electrolyte is also called a proton conductive polymer because it plays a role in transmitting protons generated around the catalyst metal particles on the fuel electrode side.

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

  Examples of the ion exchange resin constituting the fluoropolymer electrolyte include, for example, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) and the like. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride-par Fluorocarbon sulfonic acid 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 perfluorocarbonsulfonic acid-based polymer. Is used.

  Specific examples of the hydrocarbon-based electrolyte include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, and sulfonated poly. Examples include ether ether ketone (S-PEEK) and sulfonated polyphenylene (S-PPP). From the viewpoint of production that the raw materials are inexpensive, the production process is simple, and the selectivity of the material is high, these hydrocarbon-based polymer electrolytes are preferably used. In addition, only one kind of the above-mentioned ion exchange resin may be used alone, or two or more kinds may be used in combination. Further, the present invention is not limited to only the above-described materials, and other materials may be used.

  In a polymer electrolyte responsible for proton transmission, proton conductivity is important. 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 low EW. Specifically, the catalyst layer of the present embodiment preferably has an EW of 1500 g / eq. It contains the following polymer electrolyte, more preferably 1200 g / eq. The following polymer electrolyte is contained, and particularly preferably 1000 g / eq. Including the following polymer electrolytes.

  On the other hand, if the EW is too small, the hydrophilicity is too high, and it is difficult to smoothly move water. 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 an exchange group having proton conductivity. The equivalent weight is the dry weight of the ion exchange membrane per equivalent of the ion exchange group, and is expressed in units of “g / eq”.

  Further, the catalyst layer includes two or more types of polymer electrolytes having different EWs in the power generation surface. At this time, the polymer electrolyte having the lowest EW among the polymer electrolytes has a relative humidity of the gas in the flow passage of 90% or less. It is preferable to use this region. By adopting such a material arrangement, the resistance value is reduced irrespective of the current density region, and the battery performance can be improved. The polymer electrolyte used in the region where the relative humidity of the gas in the flow path is 90% or less, that is, the EW of the polymer electrolyte having the lowest EW is 900 g / eq. It is desirable that: As a result, the above-described effects are more certain and significant.

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

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

  The catalyst layer of the present embodiment may include a liquid proton conductive material between the electrode catalyst (particularly, the catalyst metal particles) and the polymer electrolyte, which can connect the electrode catalyst and the polymer electrolyte in a state capable of conducting protons. By introducing the liquid proton conductive material, a proton transport path through the liquid proton conductive material is secured between the electrode catalyst and the polymer electrolyte, so that protons required for power generation can be efficiently transferred to the electrode catalyst (particularly, the catalyst). Metal particles) can be transported to the surface. As a result, the utilization efficiency of the electrode catalyst is improved, so that the amount of the electrode catalyst used can be reduced while maintaining the power generation performance. The liquid proton conductive material only needs to be interposed between the electrode catalyst and the polymer electrolyte, and the pores (secondary pores) between the porous carriers in the catalyst layer and the pores (micropores) in the porous carrier are formed. Holes or mesopores: primary holes).

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

  If water is used as the liquid proton conducting material, introduce water as the liquid proton conducting material into the catalyst layer by wetting the catalyst layer with a small amount of liquid water or humidified gas before starting power generation. Can be. Further, water generated by an electrochemical reaction during the operation of the fuel cell can be used as a liquid proton conductive material. Therefore, it is not always necessary to hold the liquid proton conductive material when the fuel cell starts operating. For example, it is desirable that the surface distance between the electrode catalyst (particularly, catalytic metal particles) and the electrolyte be 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 filled between the electrode catalyst and the polymer electrolyte (liquid conductive material holding portion) while maintaining the non-contact state between the electrode catalyst and the polymer electrolyte. It is possible to intervene, and a proton transport route by water between them can be secured.

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

  In the electrode catalyst of the present embodiment, the total area of the electrode catalyst in contact with the polymer electrolyte is smaller than the total area of the electrode catalyst exposed to the liquid conductive material holding portion.

  The comparison of these areas is based on, for example, the capacity of the electric double layer formed at the electrode catalyst-polymer electrolyte interface and the electrode catalyst-liquid proton conductive material interface when the liquid conductive material holding portion is filled with the liquid proton conductive material. By determining the magnitude relationship of That is, since the electric double layer capacity is proportional to the area of the electrochemically effective interface, the electric double layer capacity formed at the electrode catalyst-electrolyte interface is changed at the catalyst-liquid proton conductive material interface. If it is smaller than the capacity, the contact area of the electrode catalyst with the electrolyte is smaller than the area exposed to the liquid conductive material holding portion.

  Here, a method for measuring the electric double layer capacity formed at the electrode catalyst-electrolyte interface and the electrode catalyst-liquid proton conductive material interface, in other words, the contact area between the electrode catalyst and the electrolyte and between the electrode catalyst and the liquid proton conductive material. The magnitude relation will be described. That is, a method of determining the magnitude relationship between the contact area of the electrode catalyst with the electrolyte and the exposed area of the liquid conductive material holding section will be described.

That is, in the catalyst layer of the present embodiment,
(1) Electrode catalyst-polymer electrolyte (CS)
(2) Electrode catalyst-liquid proton conductive material (CL)
(3) Porous carrier-polymer electrolyte (Cr-S)
(4) Porous carrier-liquid proton conductive material (Cr-L)
Can contribute as electric double layer capacitance (Cdl).

Electric double layer capacitor, as described above, since that is directly proportional to the area of the electrochemically active surface, Cdl C-S _(electrode catalyst - electric double layer capacity of the polymer electrolyte interface) and Cdl _{C-L (electrode} The electric double layer capacity at the catalyst-liquid proton conductive material interface may be determined. The contribution of the above four types of interfaces to the electric double layer capacitance (Cdl) can be separated as follows.

  First, the electric double layer capacity is measured under high humidification conditions such as 100% RH and low humidification conditions such as 10% RH or less. In addition, as a measuring method of the electric double layer capacitance, cyclic voltammetry, electrochemical impedance spectroscopy, and the like can be given. From these comparisons, the contribution of the liquid proton conducting material (in this case, “water”), that is, the above (2) and (4) can be separated.

  Further, deactivation of an electrode catalyst (particularly, a catalyst metal), for example, when Pt is used as catalyst metal particles, by supplying a CO gas to an electrode to be measured to adsorb CO on the surface of the Pt particles. Due to the deactivation of the electrode catalyst (particularly the catalyst metal), its contribution to the electric double layer capacity can be separated. In such a state, the electric double layer capacity under the high humidification and low humidification conditions was measured by the same method as described above, and from these comparisons, the contribution of the electrode catalyst (particularly, the catalyst metal), that is, the above (1) and (2) can be separated.

  As described above, all the contributions (1) to (4) can be separated, and the electric double layer capacity formed at the interface between the electrode catalyst, the polymer electrolyte, and the liquid proton conductive material can be obtained.

  That is, the measured value (A) in the high humidification state is the electric double layer capacity formed at all the interfaces (1) to (4), and the measurement value (B) in the low humidification state is (1) and (3). Becomes the electric double layer capacitance formed at the interface of. In addition, the measured value (C) in the deactivated / highly humidified state of the electrode catalyst (particularly the catalyst metal) is the electric double layer capacity formed at the interface of (3) and (4), and the electrode catalyst (particularly the catalyst metal) is deactivated. The measured value (D) in the low humidification state is the electric double layer capacitance formed at the interface of (3).

  Therefore, the difference between A and C is the electric double layer capacitance formed at the interface of (1) and (2), and the difference between B and D is the electric double layer capacitance formed at the interface of (1). Then, by calculating the difference between these values, (AC)-(BD), the electric double layer capacitance formed at the interface of (2) can be obtained. The contact area of the electrode catalyst with the polymer electrolyte and the exposed area of the conductive material holding portion can be determined by, for example, TEM (transmission electron microscope) tomography in addition to the above.

  If necessary, a water repellent such as polytetrafluoroethylene, polyhexafluoropropylene, a tetrafluoroethylene-hexafluoropropylene copolymer, a dispersant such as a surfactant, glycerin, ethylene glycol (EG) ), Polyvinyl alcohol (PVA), propylene glycol (PG), and other thickening agents, and additives such as pore-forming agents.

  The dry 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. Note that the above applies to both the cathode catalyst layer and the anode catalyst layer. However, the dry thickness of the cathode catalyst layer and the anode catalyst layer may be the same or different.

(Method for producing catalyst layer)
Hereinafter, preferred embodiments for producing a catalyst layer will be described, but the technical scope of the present invention is not limited to only the following embodiments. In addition, since various conditions such as the material of each component of the catalyst layer are as described above, the description is omitted here.

  First, a carrier (also referred to herein as a “porous carrier” or a “conductive porous carrier”) is prepared. Specifically, the carrier may be produced as described in the method for producing the carrier. Thereby, the specific pore distribution (having micropores and mesopores and the pore volume of the micropores is not less than 0.3 cc / g carrier and / or the mode radius of the pore distribution of the micropores is not more than 0. Voids having a diameter of 3 nm or more and less than 1 nm can be formed in the carrier. In addition, carbon materials such as commercially available Ketjen Black (highly conductive carbon black), (oil) furnace black, channel black, acetylene black, thermal black, lamp black, etc., activated carbon, coke, natural graphite, artificial graphite, etc. May be used. Further, as described in the method for producing the anode electrode catalyst, a microporous carbon material having the above-described structural characteristics may be produced as the carbon material having pores used in the catalyst carrier.

  Next, the catalyst metal particles are supported on the porous carrier to obtain an electrode catalyst powder. In this case, the anode electrode catalyst in which the metal catalyst particles have a specific specific surface area, an average coordination number, or an average particle diameter can be manufactured by the above-described method for manufacturing an anode electrode catalyst. As for the cathode electrode catalyst, the above-described method for producing an anode electrode catalyst can be applied, and the supporting of the catalytic metal particles on the porous carrier can be performed by a known method. For example, known methods such as an impregnation method, a liquid phase reduction supporting method, an evaporation to dryness method, a colloid adsorption method, a spray pyrolysis method, and a reverse micelle (microemulsion method) can be used.

  Subsequently, a catalyst ink containing an electrode catalyst powder, a polymer electrolyte, and a solvent is prepared. The solvent is not particularly limited, and a common solvent used for forming a catalyst layer can be used in the same manner. Specifically, tap water, pure water, ion-exchanged water, water such as distilled water, cyclohexanol, methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol, tert-butanol, etc. And lower alcohols having 1 to 4 carbon atoms, propylene glycol, benzene, toluene, xylene and the like. Besides these, butyl acetate, dimethyl ether, ethylene glycol, and the like may be used as the solvent. These solvents may be used alone or in a mixture of two or more.

  The amount of the solvent constituting the catalyst ink is not particularly limited as long as the solvent can completely dissolve the electrolyte. Specifically, the concentration of the solid content including the catalyst powder and the polymer electrolyte is preferably 1 to 50% by mass, more preferably 5 to 30% by mass in the electrode catalyst ink.

  When additives such as a water repellent, a dispersant, a thickener, and a pore former are used, these additives may be added to the catalyst ink. At this time, the amount of the additive to be added is not particularly limited as long as the amount does not hinder the effect of the present embodiment. For example, the additive amount of each additive is preferably 5 to 20% by mass based on the total mass of the catalyst ink.

  Next, a catalyst ink is applied to the surface of the substrate. The method of coating the substrate is not particularly limited, and a known method can be used. Specifically, it can be performed using a known method such as a spray (spray coating) method, a gulliver printing method, a die coater method, a screen printing method, a doctor blade method, and the like.

  At this time, a solid polymer electrolyte membrane (electrolyte layer) or a gas diffusion substrate (gas diffusion layer) can be used as a substrate on which the catalyst ink is applied. In such a case, after forming a catalyst layer on the surface of a solid polymer electrolyte membrane (electrolyte layer) or a gas diffusion substrate (gas diffusion layer), the obtained laminate is directly used for production of a membrane electrode assembly. Can be used. Alternatively, a peelable substrate such as a polytetrafluoroethylene (PTFE) [Teflon (registered trademark)] sheet is used as a substrate, and after forming a catalyst layer on the substrate, the catalyst layer portion is peeled from the substrate. Thereby, a catalyst layer may be obtained.

  Finally, the coating layer (film) of the catalyst ink is dried at room temperature to 150 ° C. for 1 to 60 minutes under an air atmosphere or an inert gas atmosphere. Thereby, a catalyst layer is formed.

(Membrane electrode assembly)
According to the present embodiment, there is provided a fuel cell membrane electrode assembly including the fuel cell electrode catalyst layer. That is, the solid polymer electrolyte membrane 2, the cathode catalyst layer arranged on one side of the electrolyte membrane, the anode catalyst layer arranged on the other side of the electrolyte membrane, the electrolyte membrane 2 and the anode catalyst layer There is provided a fuel cell membrane electrode assembly having a pair of gas diffusion layers (4a, 4c) sandwiching the cathode catalyst layer 3c. And in this membrane electrode assembly, the anode catalyst layer is the catalyst layer of the embodiment described above. Therefore, also in the membrane electrode assembly of the present embodiment, excellent battery performance can be effectively exhibited by the excellent operation and effect of the anode catalyst layer of the present embodiment described above.

Considering the necessity of improving the proton conductivity and the transport characteristics (gas diffusivity) of the reaction gas (particularly, O ₂ ), the above-described carrier having the specific pore distribution is used for the cathode catalyst layer. Is preferred. However, the carrier having the above-described specific pore distribution may be used for the anode catalyst layer, or may be used for both the cathode catalyst layer and the anode catalyst layer, and is not particularly limited.

  According to the present embodiment, there is provided a fuel cell having the membrane electrode assembly of the above embodiment. That is, the present embodiment is a fuel cell having a pair of an anode separator and a cathode separator sandwiching the membrane electrode assembly of the above-described embodiment. Therefore, the fuel cell of the present embodiment is also excellent in that excellent cell performance can be effectively exhibited by the above-described excellent operation and effect of the anode catalyst layer of the present embodiment.

  Hereinafter, the components of the PEFC 1 using the catalyst layer of the above embodiment will be described with reference to FIG. However, this embodiment is characterized by the anode electrode catalyst and the anode catalyst layer using the same. Therefore, specific configurations of members other than the anode catalyst layer constituting the fuel cell can be appropriately modified with reference to conventionally known knowledge.

(Electrolyte membrane)
The electrolyte membrane is composed of, for example, a solid polymer electrolyte membrane 2 as shown in FIG. The solid polymer electrolyte membrane 2 has a function of selectively transmitting protons generated in the anode catalyst layer 3a to the cathode catalyst layer 3c along the thickness direction during the operation of the PEFC 1. Further, the solid polymer electrolyte membrane 2 also has a function as a partition wall for preventing the fuel gas supplied to the anode side and the oxidizing gas supplied to the cathode side from being mixed.

  The electrolyte material constituting the solid polymer electrolyte membrane 2 is not particularly limited, and conventionally known knowledge can be appropriately referred to. For example, the fluorine-based polymer electrolyte or the hydrocarbon-based polymer electrolyte described above as the polymer electrolyte can be used. 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 layer may be appropriately determined in consideration of the characteristics of the obtained fuel cell, and is not particularly limited. The thickness of the electrolyte layer is usually about 5 to 300 μm. When the thickness of the electrolyte layer is within such a range, the balance between the strength at the time of film formation, the durability at the time of use, and the output characteristics at the time of use can be appropriately controlled.

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

  The material constituting the base material of the gas diffusion layers (4a, 4c) is not particularly limited, and conventionally known knowledge can be appropriately referred to. For example, a conductive and porous sheet material such as a carbon woven fabric, a paper-like paper body, a felt, and a nonwoven fabric may be used. The thickness of the substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, and may be about 30 to 500 μm. When the thickness of the base material is within such a range, the balance between mechanical strength and diffusibility of gas, water, and the like can be appropriately controlled.

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

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

  The carbon particles contained in the carbon particle layer are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately used. Among them, carbon blacks such as oil furnace black, channel black, lamp black, thermal black, and acetylene black are 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, a high drainage property can be obtained by the capillary force, and the contact with the catalyst layer can be improved.

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

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

(Method of manufacturing membrane electrode assembly)
The method for producing the membrane / electrode assembly is not particularly limited, and a conventionally known method can be used. For example, a method can be used in which a catalyst layer is transferred or applied to a solid polymer electrolyte membrane by hot pressing and then dried, and then a gas diffusion layer is joined thereto. Alternatively, two gas diffusion electrodes (GDE) are prepared by coating the catalyst layer on one side of the base material layer in advance and drying it if the microporous layer side of the gas diffusion layer is not included. Then, the gas diffusion electrode can be joined to both surfaces of the solid polymer electrolyte membrane by hot press, and the application and joining conditions of the hot press and the like depend on the type of polymer electrolyte in the solid polymer electrolyte membrane and the catalyst layer. (Perfluorosulfonic acid type or hydrocarbon type).

(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. Further, the separator also has a function as a partition for separating the fuel gas, the oxidizing gas, and the coolant from each other. In order to secure these flow paths, as described above, it is preferable that each of the separators is provided with a gas flow path and a cooling flow path. As a material for forming the separator, conventionally known materials such as dense carbon graphite, carbon such as a carbon plate, and metal such as stainless steel can be appropriately used without any limitation. The thickness and size of the separator, the shape and size of each flow path provided, and the like are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics of the obtained fuel cell.

  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 membrane electrode assemblies are stacked via a separator and connected in series may be formed so that the fuel cell can exhibit a desired voltage. The shape and the like of the fuel cell are not particularly limited, and may be appropriately determined so as to obtain desired cell characteristics such as a desired voltage.

  The PEFC and the membrane electrode assembly described above use an anode electrode catalyst having excellent catalytic activity and durability and an anode catalyst layer using the same. Therefore, the PEFC and the membrane electrode assembly are excellent in power generation performance and durability.

  The PEFC of this embodiment and the fuel cell stack using the same can be mounted, for example, as a drive power source in a vehicle.

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

Example 1
(A) Production stage of anode electrode catalyst: preparation of catalyst carrier As a catalyst carrier of the anode electrode catalyst, Ketjen Black (also referred to as kB) (manufactured by Lion Corporation, trade name Ketjen Black EC600JD, average particle size of 34.0 nm, BET specific surface area 1270 m ² / g, volume occupied by all pores: 1.80 cm ³ / g, volume occupied by micropores: 0.50 cm ³ / g, volume occupied by mesopores: 1.30 cm ³ / g) Was prepared.

(B) Production step of anode electrode catalyst: catalyst carrier into which metal complex is introduced)
The kB prepared above was reacted with (1,5-cyclooctadiene) dimethylplatinum (II) in acetonitrile to obtain a carbon material into which a Pt complex represented by the following formula was introduced.

  Specifically, a magnetic stir bar and 0.5 g of kB prepared above were put into a 100 ml two-necked flask, a silicon rubber septum and a three-way cock were attached, and the mixture was heated to 150 ° C. to heat kB under vacuum for 6 hours. Dried. After drying, the flask was allowed to cool to room temperature, and then the flask was kept at 25 ° C. using a thermostat. Subsequently, 25.5 ml (Pt: 0.765 mmol) of a previously prepared (1,5-cyclooctadiene) dimethylplatinum (II) / acetonitrile solution was injected from the septum using a syringe, and the mixture was stirred for 10 minutes. Next, a condenser was attached to the flask, and the flask was heated in an oil bath set at 110 ° C. and refluxed for 6 hours. The (1,5-cyclooctadiene) dimethylplatinum (II) / acetonitrile solution used was prepared as follows. A magnetic stirrer bar was put into a 100 ml two-necked eggplant type flask, and 300.2 mg of (1,5-cyclooctadiene) dimethylplatinum (II) was added. Next, 30 ml of dehydrated acetonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the mixture was stirred for several minutes to dissolve (1,5-cyclooctadiene) dimethylplatinum (II) and (1,5-cyclooctadiene). A dimethylplatinum (II) / acetonitrile solution was prepared.

  After refluxing for 6 hours, the reaction solution was filtered using a 0.1 μm membrane filter (H010A047A manufactured by ADVANTEC, φ = 47 mm), and then washed using 50 ml of acetonitrile (manufactured by Wako Pure Chemical Industries, Ltd.). . The washed sample was put into a 200 ml two-necked flask together with a magnetic stirrer bar, attached with a three-way cock and a glass stopper, and dried by heating under vacuum at 100 ° C. for 6 hours.

(C) Step of heat-treating to obtain metal-supported carbon material as an anode electrode catalyst: Preparation of Pt cluster / kB)
The kB to which the 1,5-cyclooctadiene dimethylplatinum complex obtained above was adsorbed is put into a glass tube, and the inside of the glass tube is kept under reduced pressure (1.0 × 10 ⁻⁴ Pa) using a turbo molecular pump. The temperature of the glass tube C was increased from room temperature to 300 ° C. at a rate of 5 ° C./min, and then maintained at 300 ° C. for 1 hour. Thereafter, the glass tube was naturally cooled to room temperature, and a sample was taken out of the glass tube. The obtained sample is defined as Pt cluster / kB.

The ICP analysis value of the obtained Pt cluster / kB sample was Pt: 3.9 wt%. Further, the BET specific surface area was 1190 m ² / g.

Example 2
(A) Production stage of anode electrode catalyst: preparation of catalyst carrier)
The same Ketjen black (kB) as in Example 1 was prepared as a catalyst carrier for the anode electrode catalyst.

(B) Another embodiment of the production stage of the anode electrode catalyst: a catalyst carrier into which a metal complex has been introduced)
With respect to the kB prepared above, a diphenylphosphine ligand is introduced, and then the kB into which the diphenylphosphine ligand is introduced is reacted with (1,5-cyclooctadiene) dimethylplatinum (II) in acetonitrile to obtain the following formula: Thus, a carbon material into which a Pt complex was introduced was obtained.

  Specifically, a magnetic stir bar and 300 mg of kB prepared above were placed in a 50 ml two-necked eggplant type flask, and a silicone rubber septum and a three-way cock were attached to the mouths of the flask, respectively. The mixture was heated to 150 ° C. while stirring using a stirrer bar, and the kB was dried by heating under vacuum for 6 hours. After drying, the flask was allowed to cool to room temperature. Next, with the flask containing the dried kB under reduced pressure, 20 ml of a THF / triethylamine solution prepared in advance was injected from a septum using a syringe, followed by stirring at room temperature for 10 minutes. Here, the THF / triethylamine solution was added to 25 ml of dehydrated THF (manufactured by Wako Pure Chemical Industries, Ltd.) and 0.536 g of triethylamine (manufactured by Wako Pure Chemical Industries, Ltd.) in a 50 ml two-necked eggplant-shaped flask purged with nitrogen. Was used for several minutes with stirring. Subsequently, the flask was cooled to 0 ° C. using a thermostat and stirred for 30 minutes. After purging the flask with nitrogen to 1 atm, 0.788 g of chlorodiphenylphosphine (manufactured by Wako Pure Chemical Industries, Ltd.) was added. The mixture was added into the flask using a syringe and stirred for 10 minutes. Thereafter, the temperature of the thermostat was set to 25 ° C., and after the temperature reached 25 ° C., the mixture was further stirred for 15 hours to react. Thereafter, the mixture was filtered through a membrane filter (0.1 μm, T010A047A manufactured by ADVANTEC), and further washed well with 150 ml of THF. Next, the sample was stirred well in 2000 ml of ion-exchanged water for 30 minutes, washed well, filtered through a membrane filter (0.1 μm, H010A047A manufactured by ADVANTEC), and then dried under reduced pressure at 150 ° C. for 6 hours. This sample is designated as P / Kb.

  120 mg of P / kB prepared above and a magnetic stir bar were put into a Schlenk tube, and a silicon rubber septum was attached to the mouth of the Schlenk tube. The kB-P was dried by heating under vacuum at 150 ° C. for 6 hours while stirring using a stir bar, and then allowed to cool to room temperature. Subsequently, 4.8 ml of a previously prepared (1,5-cyclooctadiene) dimethylplatinum (II) / acetonitrile solution (Pt: 1.5 mmol / (1 g) was prepared under reduced pressure in the Schlenk tube containing the dried kB-P. -ZTC-P)) was injected from the septum using a syringe and stirred for 10 minutes. The (1,5-cyclooctadiene) dimethylplatinum (II) / acetonitrile solution was prepared by adding 60 mg of (1,5-cyclooctadiene) dimethylplatinum (II) (manufactured by Aldrich) to a 20 ml one-necked eggplant type flask. The inside of the flask was replaced with nitrogen, 4.8 ml of dehydrated acetonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the mixture was prepared by stirring at room temperature for several minutes.

  Next, a reflux condenser was attached to the Schlenk tube, and the flask was heated in an oil bath heated to 100 ° C. and refluxed for 12 hours. After 12 hours, the reflux was stopped and the Schlenk tube was allowed to cool. Then, the reaction solution was filtered using a 0.1 μm membrane filter (H010A047A manufactured by ADVANTEC, diameter φ = 47 mm), and then 50 ml of acetonitrile (sum Subsequently, the substrate was washed with 50 ml of diethyl ether. The washed sample was dried under vacuum at 100 ° C. for 6 hours.

(C) Step of heat-treating to obtain metal-supported carbon material as anode electrode catalyst: preparation of P-Pt cluster / kB)
The sample obtained above was placed in a glass tube, and the inside of the glass tube was kept under reduced pressure (1.0 × 10 ⁻⁴ Pa) using a turbo molecular pump, and the glass tube C was cooled from room temperature to 300 ° C. at 5 ° C. / The temperature was raised in minutes, and then maintained at 300 ° C. for 1 hour. Thereafter, the glass tube was naturally cooled to room temperature, and a sample was taken out of the glass tube. The resulting sample is designated as P-Pt cluster / kB.

  Also for the obtained P-Pt cluster / kB sample, the amounts of phosphorus and Pt contained in the sample can be determined from the ICP analysis. Further, the BET specific surface area can be determined from the analysis of the P-Pt cluster / kB sample.

Comparative Example 1
(Preparation of Pt-supported carbon material)
A commercially available Pt-supported carbon material (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., trade name: TEC10E50E), which is an anode electrode catalyst in which Pt particles are supported on a carbon carrier, was prepared. This sample is designated as TEC10E50E. In TEC10E50E, (a) the electrochemical specific surface area of platinum measured by adsorption and desorption of hydrogen was 83 m ² / g, and the average particle size was 2.3 nm. Furthermore, the Pt particles supported on TEC10E50E have (d) an ORR activity per unit mass of platinum having an electrochemical specific surface area of 60 to 90 m ² / g measured from hydrogen adsorption and desorption. It was one of the Pt particles.

Comparative Example 2
(Preparation of Pt particles / kB)
For comparison with the complex-supported kB, Pt nanoparticles were supported on the kB using a general method. A magnetic stirrer bar and 0.5 g of kB were put in a 200 ml two-necked flask, a septum made of silicon rubber and a three-way cock were attached, and the mixture was heated to 150 ° C. and dried by vacuum heating kB for 6 hours. After drying, the flask was cooled to 0 ° C. using a thermostat. 35 ml of a 0.089 wt% aqueous solution of diammine dinitroplatinum [Pt (NO ₂ ) ₂ (NH ₃ ) ₂ ] and 350 ml of a 0.0105 wt% aqueous solution of sodium borohydride, which is an aqueous solution of a reducing agent, were prepared. And cooled. Subsequently, the kB cooled to 0 ° C. was impregnated with 30 ml of a 0 ° C. aqueous solution of diamine dinitroplatinum in vacuo, cooled to 0 ° C., and stirred for 30 minutes in a reduced pressure atmosphere. Next, the reaction solution was filtered using a 0.1 μm membrane filter (H010A047A manufactured by ADVANTEC, diameter φ = 47 mm), and the sample was thoroughly washed with ion-exchanged water. This sample was added to a 500 ml flask, the flask was cooled to 0 ° C. in a thermostat, 350 ml of a 0.0105 wt% sodium borohydride solution cooled to 0 ° C. was added, and the mixture was stirred at 0 ° C. for 20 minutes to obtain diammine dinitroplatinum. [Pt (NO ₂ ) ₂ (NH ₃ ) ₂ ] was reduced to produce platinum nanoparticles. The reaction solution was filtered using a 0.1 μm membrane filter (H010A047A manufactured by ADVANTEC, diameter φ = 47 mm). The sample was thoroughly washed with ion-exchanged water, and then dried under reduced pressure at 150 ° C. for 6 hours. This sample is designated as Pt particles / kB. Pt was 4.7 wt% in the Pt particles / kB (Pt-supported carbon material) sample. The BET specific surface area was 1000 m ² / g.

Table 1 below shows the BET specific surface area and the pore structure calculated from the results of nitrogen adsorption and desorption measurement of the commercially available carrier (kB) prepared above and the samples prepared in Example 1 and Comparative Example 2. Here, V _Total , V _micro , and V _meso represent the volume occupied by all pores, the volume occupied by micropores, and the volume occupied by mesopores, respectively.

  The BET specific surface area of the commercially available carrier (kB) prepared above and the carbon materials prepared in Example 1 and Comparative Example 2 was measured using BELSORP mini manufactured by Nippon Bell, and at a temperature of -196 ° C. Performed by the multipoint method.

  The contents of phosphorus and platinum were measured by inductively coupled plasma (ICP) emission spectroscopy. Here, as the content of phosphorus and platinum, a value measured using an inductively coupled plasma (ICP) emission spectrophotometer manufactured by SII Nanotechnology Co., Ltd. after decomposing a sample by alkali melting to form a solution was used. Table 1 shows the platinum content.

In the table, the specific surface area (m ² / g) represents the BET specific surface area (m ² / g) (plotted at P / P ₀ = 0.01 to 0.05). V _total (cm ³ / g) represents the total pore volume (cm ³ / g) (calculated from the nitrogen adsorption amount of P / P ₀ = 0.96). V _micro (cm ³ / g) represents the micropore volume (cm ³ / g) (calculated by the DR method). V _meso (cm ³ / g) represents the mesopore volume (cm ³ / g) (V _meso = V _total −V _micro ).

  TEM observation was performed on the carbon material into which the metal complex prepared in each of Examples 1 and 2 was introduced. Further, TEM observation was also performed on the catalyst carrier and the Pt particles / kB prepared in Comparative Example 2.

  Transmission electron microscope (TEM) observation was performed at an acceleration voltage of 200 kV using a transmission electron microscope JEM-2010 manufactured by JEOL Ltd. At the time of TEM observation, a small amount of ethanol was added to the sample, and the sample was suspended by ultrasonic treatment. The suspension was added dropwise to a microgrid (manufactured by Oken Shoji Co., Ltd .: popular product type B). It dried under reduced pressure for 30 minutes, and was set as the observation sample for TEM.

  The following can be confirmed from the carbon material into which the metal complex prepared in Example 1 was introduced, the catalyst support, and the TEM photograph of Pt particles / kB prepared in Comparative Example 2. In the TEM photograph of the sample of Comparative Example 2, platinum particles having an average particle size of 1 to 3 nm can be confirmed from any of the different regions of the sample. However, in the sample of Example 1, Pt (metal complex) was observed on the kB particles even though the amount of Pt carried was almost the same as 3.9 wt% as compared with 4.7 wt% of Comparative Example 2. Was not done. From this, it is considered that in the sample of Example 1, Pt (metal complex) is uniformly and highly dispersed in the kB carrier (inside or inside the pore) without aggregation.

(Measurement of electrochemical specific surface area measured by CO stripping)
With respect to Example 1 and Comparative Examples 1 and 2, the electrochemical specific surface area measured by CO stripping was measured.

FIG. 3A shows the electrochemical measurements of the Pt cluster / kB sample of Example 1 (denoted as Example in the figure) and the sample of Comparative Example 1 (denoted as TEC10E50E in the figure) by CO stripping. 4 is a drawing showing a relationship between current and potential obtained according to a typical method for measuring specific surface area. For the measurement of CO stripping, an Ar balance gas (manufactured by Taiyo Nissin) of 1% CO was used. All measurements were performed in a draft. After performing 20 cycles of scanning in the range of 0 to 1.2 V (RHE) at 100 mV / s as electrode pretreatment, measurements such as cyclic voltammetry (results are shown in FIG. 3) and convective voltammetry were performed. In the measurement of CO stripping, the electrode was kept at 0.05 V (RHE) for 30 minutes while rotating the electrode at 400 rpm in an electrolyte solution saturated with 1% CO gas. Under these conditions, it was confirmed that the CO adsorption amount reached saturation. After completely replacing the CO gas in the solution with nitrogen, CV measurement was performed from 0.05 V (RHE) to 1.2 V (RHE) at 20 mV / s for three cycles. The CVs of the second and third cycles were clearly overlapped. The amount of electricity at the CO stripping peak is calculated from the difference between the response currents after the first cycle and the second and subsequent cycles. Assuming that the maximum coverage of Pt by CO is 0.68, the conversion coefficient is 285.6 μC · cmPt ^−2. Was applied to calculate the electrochemically active surface area. The electrochemical area (ECA) was calculated by assigning this to the amount of platinum. FIG. 3B shows the electrochemical specific surface area measured by CO stripping using the samples of Example 1 and Comparative Example 1 (the notation in the figure is the same as that of FIG. 3A). It is a drawing showing the relationship between the specific surface area (m ² / g) of the obtained platinum particles and the average particle size (nm) of the platinum particles. That is, FIG. 3A is a graph showing the relationship between the current value (i, unit: mA μg ⁻¹ ) and the potential (E, unit: VvsRHE) of Example 1 and Comparative Example 1 measured by CO stripping. The relationship between the electrochemical specific surface area (S, unit; m ² g ⁻¹ ) of platinum calculated from the current value i and the average Pt particle size (D, unit: nm) is shown in the graph on the right. I have. Here, the electrochemical specific surface area of platinum S (m ² / g) = 6 / ((density of platinum ρ (g / m ³ ) × (diameter (average particle size) of platinum atoms D (m))) The average particle size (D, unit; nm) of the platinum particles is calculated from the electrochemical specific surface area (S, unit: m ² g ⁻¹ ) of the platinum from the formula (FIG. 3B). The numbers next to the circles plotting the respective measurement points of the Example (sample of Example 1) and TEC10E50E (sample of Comparative Example 1) indicate the electrochemical specific surface area of platinum at each measurement point.

From FIG. 3 (b), a graph showing the relationship between the specific surface area (S) of platinum and the Pt average particle size (D) obtained from Example 1 and Comparative Example 1 shows that in the region where the Pt average particle size is 1 nm or less. It can be seen that the specific surface area of platinum is 280 m ² / g or more. Also, from the graph showing the relationship between the specific surface area of platinum and the average particle diameter of Pt in FIG. 3B, the average particle diameter of Pt is smaller than that of Comparative Example 1 having a specific surface area of 121 m ² / g (about 2.3 nm). It is also understood that if the specific surface area is 125 m ² / g or more in a region having a Pt average particle diameter of 2 nm or less, the effect of the present invention may be sufficiently exerted (suggested).

  Here, the electrochemical specific surface area measured by CO stripping was measured according to the following measurement (calculation) method (condition).

  First, for the samples of Example 1 and Comparative Example 1, a fixed amount of the catalyst (10.4 mg when the amount of Pt particles supported on the carrier is 3.9 wt% based on the total amount of the catalyst) is dispersed in 19 mL of water and 6 mL of isopropanol. Thus, a dispersion was prepared. 100 μL of a Nafion solution (DE521CS, 5 wt%, manufactured by Aldrich) was added to the dispersion to prepare a catalyst ink. Thereafter, ultrasonic dispersion was performed for 1 hour or more. 10 μL of the prepared catalyst ink was applied to a polished glassy carbon electrode (φ5.0 mm, manufactured by Hokuto Denko) and dried in a dryer at 60 ° C. for 10 minutes. The surface coating state of the electrode was confirmed by microscopic observation, and an electrode having no coating on the catalyst layer and no protrusion was used for evaluation.

  The electrochemical measurement was performed using a normal three-chamber cell (Mick Lab Co., Ltd.). As the electrolyte solution, 0.1 M perchloric acid (Ultrapur, manufactured by Kanto Chemical Co., Ltd.) was used. The counter electrode was a Pt line, and the reference electrode was RHE. The potential control was performed using HZ-5000 (manufactured by Hokuto Denko KK). HR-301 (manufactured by Hokuto Denko KK) was used as a rotating electrode (RDE) device. The cell temperature was controlled at 25 ° C. (± 1 ° C.) using an external circulation type thermostat (CHL300, manufactured by YAMATO). For measurement using CO, an Ar balance gas (manufactured by Taiyo Nissin Co., Ltd.) of 1% by volume CO was used. All measurements were performed in a draft.

As a pretreatment of the electrode, a range of 0 V (RHE) to 1.2 V (RHE) was scanned at 100 mVs ^-1 for 20 cycles, and then measurements such as cyclic voltammetry and convection voltammetry were performed. The electrode was maintained at 0.05 V (RHE) for 30 minutes while rotating the electrode at 400 rpm in an electrolyte solution saturated with 1% by volume CO gas. Under these conditions, it was confirmed that the CO adsorption amount reached saturation. After completely replacing the CO gas in the solution with nitrogen, three cycles of CV measurement were performed at 0.05 mV (RHE) to 1.2 V (RHE) at 20 mVs- ¹ . CVs from the second cycle onward were clearly overlapped and observed. The amount of electricity at the CO stripping peak was calculated from the difference between the CVs at the first cycle and the second and subsequent cycles, and the electrochemically active surface area was calculated by applying a conversion coefficient of 285.6 μCcmPt- ² . ECA was calculated by assigning this to the amount of catalyst carried.

(Average coordination number of catalyst metal and average particle diameter of catalyst metal particles measured by XAFS)
Next, the sample of Example 1 was subjected to XAFS (X-ray absorption fine structure analysis) measurement.

  In the XAFS measurement, a transmission-type conventional XAFS was used. The sample was subjected to vacuum heating and drying at 100 ° C. for 6 hours in advance to remove the adsorbed water, and pellets were prepared from about 100 mg of the sample dried in an argon atmosphere glove box. The prepared pellet was set in a measurement sample cell for XAFS, then the cell was confined, and set in a measurement device. The measurement was performed at room temperature in a helium atmosphere.

  From the XAFS measurement results of the sample prepared in Example 1, the respective absorption edge fine structure (XANES) and wide area X-ray absorption fine structure (EXAFS) (Fourier transformed radial distribution function) were observed.

  With respect to the sample of Example 1, the measured wide area X-ray absorption fine structure (EXAFS) was analyzed, and the coordinating element species and the average coordination number of platinum were determined. The average coordination number of platinum was calculated by extracting a Pt-Pt bond from a radial distribution function obtained by Fourier-transforming EXAFS data, performing inverse Fourier transform, and performing curve fitting. Pt foil (coordination number 12) was used as a standard sample.

  Further, from the average coordination number of platinum atoms contained in the platinum particles (platinum cluster), the average particle size of the platinum particles was calculated as follows.

  Pt lattice constant: 0.39231 nm, Pt metal bond radius: 0.14 nm, one side of unit lattice (fcc): 0.67 nm, unit lattice 1 (63 atoms), unit lattice 2 (14 atoms) shown below ), The octahedral cluster (6 atoms), and the lattice volume of the tetrahedral cluster (4 atoms) were calculated to determine the equivalent spherical diameter, which was taken as the particle diameter of the platinum particles. In addition, the average coordination number of platinum atoms constituting the unit cells 1, 2, octahedral cluster, and tetrahedral cluster was calculated. FIG. 4 plots the relationship between the average coordination number of platinum atoms and the average particle size of platinum particles. Here, the particle diameter of one platinum atom (average coordination number 0) was set to atomic radius × 2 = 0.28 nm. By utilizing the relationship between the average coordination number of platinum atoms and the average particle size of platinum particles thus obtained, the average coordination of platinum atoms obtained from the samples of Examples 1 and 2 and Comparative Examples 1 and 2 was used. The average particle size of the metal particles corresponding to the order can be estimated (calculated).

  In the sample of Example 1, the average coordination number of platinum atoms (Pt-Pt) is 4.0 or less, specifically, about 3.3. Referring to FIG. It corresponds to the following metal (platinum) particles. It is difficult to observe metal (Pt) particles having such a size by TEM (see FIG. 6A).

(TEM Observation Results; Reinforcement Data for Pt Particles of Sample of Metal-Supported Carbon Material of Example Having Average Particle Diameter of 1 nm or Less)
TEM observation was performed on the samples of Example 1 and Comparative Example 2. FIG. 6A shows the metal-supported carbon material obtained by subjecting the sample prepared in the step (b) of Example 1 to a vacuum heat treatment (heat treatment) at 300 ° C. for 1 hour in the step (c). 10 shows a TEM photograph of Pt cluster / kB, which is a sample of FIG. FIG. 6B shows a TEM photograph of Pt particles / kB, which is a sample prepared in Comparative Example 2. From the results of the TEM observation of the samples of Example 1 and Comparative Example 2, the sample prepared in the step (b) of the example 1 was heat-treated at 300 ° C. in the step (c). As a result of observing different regions of the sample in the kB TEM photograph, the following was confirmed. In the Pt cluster / kB sample, Pt particles having a size of less than 1 nm are highly dispersed inside the kB particles. Therefore, Pt particles larger than 1 nm could not be observed from any of the different regions of the sample. Even with a high-precision TEM device, Pt particles of 1 nm or less (approximately 0.45 to 0.55 nm in average diameter) highly dispersed inside the kB particles can be obtained from any of the different regions of the sample. It could not be observed. On the other hand, in the Pt particles / kB, which is the sample of Comparative Example 2, it was observed from many different regions of the sample that platinum particles having a size of about 1 to 3 nm were dispersed inside the kB particles. That is, the phenomenon that Pt particles were not observed at all from different regions of the sample as in the example was not observed.

(XRD result; reinforcing data that the Pt particles of the sample of the metal-supported carbon material of the example have an average particle diameter of 1 nm or less)
<X-ray diffraction (XRD) measurement>
X-ray diffraction measurements were performed on the sample of Example 1 (Pt cluster / kB), blank (Ketjen black only), and the commercially available platinum-supported carbon catalyst of Comparative Example 1 (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Kogyo) obtained above. Was. X-ray diffraction measurement was performed using XRD-6100 manufactured by Shimadzu Corporation, and the radiation source was Cu-Kα, voltage 30 kV, and current 20 mA. FIG. 7 shows the results.

  7, in the XRD pattern of the sample of Comparative Example 1 (denoted as TEC10E50E in the figure), a peak derived from platinum was observed at around 40 °. However, in the XRD pattern of the sample of Example 1 (simply referred to as an example in the figure), no peak was observed at around 40 °, and a pattern similar to that of the blank was shown. This result suggested that the platinum particles supported in Example 1 were extremely fine as compared with the platinum particles of the sample of Comparative Example 1 (TEC10E50E).

(Evaluation of oxygen reduction reaction (ORR) activity of electrode catalyst)
For Example 1 and Comparative Examples 1 and 2, the oxygen reduction reaction (ORR) activity was measured. The oxygen reduction reaction (ORR) activity was also measured for other examples and comparative examples.

FIG. 8 is a drawing showing a current-voltage curve obtained in accordance with the method for measuring the oxygen reduction reaction activity in Example 1 (indicated as an example in the figure) and Comparative Examples 1 and 2. That is, a graph showing the relationship between each current value (i, unit: mAcm ² ) and voltage (E, unit; VvsRHE) for Example 1 and Conventional Examples 1 and 2 measured by oxygen reduction reaction (ORR) activity. It is.

Further, according to the method for measuring the oxygen reduction reaction (ORR) activity, the Pt amount, i _k , and ECA of the samples of Example 1 (described as Example in the figure) and Comparative Examples 1 and 2 were measured. ECA shown here is a value obtained from the adsorption / desorption wave of hydrogen (FIG. 9). In Examples and Comparative Example 2, the amount of platinum with respect to the weight of the catalyst was as small as 5 wt% or less, so that ECA could not be obtained by this method. Table 2 shows the results. The amount of Pt on the sample of the glassy carbon electrodes of the other examples and comparative examples were also measured i _k.

From Table 2, it can be seen that the activation dominant current per unit platinum mass at 0.85 V (RHE) in the example is significantly smaller than in Comparative Examples 1 and 2. Since the activation dominant current per unit platinum mass is the product of ECA and the activation dominant current per unit platinum surface area, the fact that the activation dominant current per unit platinum mass is small means that the activation per ECA or unit platinum surface area is small. It means that the dominant current is small. Here, it is already clear from the XRD data, the TEM image, and the CO stripping result that the ECA of the example is significantly larger than that of the comparative example 1. Therefore, the activation dominant current per unit platinum surface area is extremely small. Recognize. One of the factors that caused the activation dominant current per unit platinum surface area to decrease significantly is considered to be a decrease in the number of reactive electrons. From FIG. 8, the diffusion limit current of the example is clearly smaller than those of Comparative Examples 1 and 2. The diffusion limit current (i _L ) is represented by the following Levich equation.

  Here, n is the number of reaction electrons, F is the Faraday constant, A is the geometric area of the electrode, c is the bulk concentration of the reactant, D is the diffusion coefficient of the reactant, ν is the kinematic viscosity of the solution, and ω is the angular velocity.

Since the experiment was carried out under the same measurement conditions, c, D, ν, and ω were the same value, and the same value was used for the electrodes. Since F is a constant, it can be assumed that the cause of the decrease in the diffusion limit current is a decrease in the number of reactive electrons. Since the diffusion limit current is reduced by about 30% from about −6 mA / cm ² to −4 mA / cm ^2, it can be estimated that the average number of reactive electrons is reduced from 4 to 3 or less (0.75 or less). When the number of reactive electrons decreases, the current value that can be taken out also decreases proportionally, so that the current that can be taken out should be 0.75 or less.

The amount of Pt (μg) in Table 2 was obtained by measuring the catalyst metal (Pt) loading rate in the samples (electrode catalysts) of Example 1 and Comparative Examples 1 and 2 by ICP in advance, ) Weight multiplied by catalyst metal (Pt) loading. In i _k ^(Ag -1 at0.85Vvs.RHE), those obtained when calculating the ORR activity shown below. Here, _ik is the activation dominant current corrected for the effect of mass transport. In Comparative Example 2, since the average particle size of the Pt particles was smaller than that of Comparative Example 1, the mass specific activity (oxygen reduction activity per unit mass) of the oxygen reduction activity was higher than that of Comparative Example 1 even though the specific surface area was widened. Although it has dropped to about 76%, this indicates that the reduction in activity is already within the known range. From this, at least the catalytic metal particles of Example 1 have a relative oxygen reduction reaction activity per unit mass of an electrochemical specific surface area of 60 to 90 m ² / g measured from hydrogen adsorption and desorption. It was confirmed that the particle size of the catalyst metal particles was 0.75 or less.

  The following can be seen from FIG. 8 and Table 2. In Example 1, the ORR activity per unit mass of platinum was significantly reduced as compared with Comparative Examples 1 and 2, and the diffusion limit current density was reduced due to the increase in the rate of the two-electron reaction. From this, it can be seen that reducing the catalyst metal (Pt) particle diameter to 1 nm or less can rapidly reduce the ORR activity per unit platinum mass. Also, from the measurement results of the other Examples and Comparative Examples, the same results as those of Example 1 and Comparative Examples 1 and 2 were confirmed.

  Here, the oxygen reduction reaction activity was measured according to the following measurement method.

  First, in Example 1 and Comparative Examples 1 and 2, a fixed amount of the catalyst (10.4 mg when the amount of Pt particles supported on the carrier is 3.9 wt% based on the total amount of the catalyst) is dispersed in 19 mL of water and 6 mL of isopropanol. Thus, a dispersion was prepared. 100 μL of a Nafion solution (DE521CS, 5 wt%, manufactured by Aldrich) was added to the dispersion to prepare a catalyst ink. Thereafter, ultrasonic dispersion was performed for 1 hour or more. 10 μL of the prepared catalyst ink was applied to a polished glassy carbon electrode (φ5.0 mm, manufactured by Hokuto Denko) and dried in a dryer at 60 ° C. for 10 minutes. The surface coating state of the electrode was confirmed by microscopic observation, and an electrode having no coating on the catalyst layer and no protrusion was used for evaluation.

  Electrochemical measurements were performed in a normal three-chamber cell (Mick Lab). As the electrolyte solution, 0.1 M perchloric acid (Ultrapur, manufactured by Kanto Chemical Co., Ltd.) was used. The counter electrode was a Pt line, and the reference electrode was RHE. The potential control was performed using HZ-5000 (manufactured by Hokuto Denko). HR-301 (manufactured by Hokuto Denko) was used as a rotating disk electrode (RDE) device. The cell temperature was controlled at 25 ° C. (± 1 ° C.) using an external circulation type thermostat (CHL300, manufactured by YAMATO).

Oxygen gas is supplied to the electrolytic solution to keep it in an oxygen atmosphere. Scanning is performed five times in a range of 0 V (RHE) to 1.2 V (RHE) at a scanning speed of 100 mVs ^-1 . Thereafter, while rotating the electrode at 1600 rpm, scanning is performed from a start potential of 0.2 V (RHE) to an end potential of 1.2 V (RHE) at a scanning speed of 10 mVs ^-1 . The same is performed in a nitrogen atmosphere. In advance, an AC impedance measurement is performed for 30 seconds at a holding potential of 0.5 V (RHE), a frequency of 1000 Hz, and an AC amplitude of 15 mV to grasp the solution resistance.

  The response current obtained in the nitrogen atmosphere is subtracted from the response current obtained in the oxygen atmosphere, and the potential is corrected by the solution resistance. A simple Koutecky-Levich equation shown below:

(Here, i actual response current, i _k is activated dominant current, i _L is the diffusion limiting current showing a.) In correcting the effects of mass transfer, activation dominant current i _k is a catalyst intrinsic activity Is calculated.

(Evaluation of hydrogen oxidation reaction (HOR) activity of electrode catalyst)
For Example 1 and Comparative Example 1, the hydrogen oxidation reaction (HOR) activity was measured. The oxygen reduction reaction (ORR) activity was also measured for other examples and comparative examples.

FIG. 10 is a drawing showing a current-voltage curve obtained according to the method for measuring the hydrogen oxidation reaction (HOR) activity in Example 1 (shown as Example in the figure) and Comparative Example 1. That is, it is a graph showing the relationship between each current value (i, unit: mAcm ² ) and voltage (E, unit; VvsRHE) for Example 1 and Conventional Example 1 measured by hydrogen oxidation reaction (HOR) activity. .

Further, according to the measurement method of the hydrogen oxidation reaction (HOR) activity, Pt amount of the sample of Example 1 and Comparative Example 1 were measured i _k. Table 3 shows the results. The Pt content of samples of other examples and comparative examples were also measured i _k.

The amount of Pt (μg) in Table 3 is obtained by measuring the catalyst metal (Pt) loading rate in the sample (electrode catalyst) of Example 1 and Comparative Example 1 by ICP in advance, and adding the catalyst to the weight of the electrode catalyst (Pt). It is obtained by multiplying the metal (Pt) carrying rate. ^{_{i k (0.02Vvs.RHE / mAμg Pt -1}} ) are those obtained when calculating the HOR activity below is the effect corrected activation dominated current mass transport.

  The following can be seen from FIG. 10 and Table 3. The hydrogen oxidation reaction (HOR) activity of Example 1 (Pt cluster / kB) in which the amount of Pt was reduced to about 1/20 (0.16 / 3.44) as compared with Comparative Example 1 (TEC10E50E) was per electrode area. Are about the same. Therefore, it is understood that the HOR activity per unit mass is high. From the above, the present embodiment is characterized in that a catalyst metal (platinum) having a small particle diameter is used for the anode electrode catalyst. Since the average particle size of the catalyst metal (platinum) in Example 1 is smaller than that in Comparative Example 1 (see FIG. 3B and FIG. 4), the results shown in FIG. In this embodiment, it was confirmed that the hydrogen oxidation reaction (HOR) activity can be improved (can be increased). Also, from the measurement results of the other Examples and Comparative Examples, the same results as those of Example 1 and Comparative Examples 1 and 2 were confirmed.

  The method for measuring the hydrogen oxidation reaction (HOR) activity is basically the same as the method for measuring the oxygen reduction reaction (ORR) activity described above. The difference is that (1) the electrolytic solution is not an oxygen atmosphere but a hydrogen atmosphere; (2) the potential scanning range is -0.05 V → 0.2 V vs. (3) The potential scanning speed is 50 mV / s. Therefore, a specific method for measuring the hydrogen oxidation reaction (HOR) activity is omitted.

1: Solid polymer 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,
5. Separator,
5a: anode separator,
5c: cathode separator,
6a: anode gas flow path,
6c: cathode gas flow path,
7 ... refrigerant channel,
10 ... membrane electrode assembly (MEA).

Claims (11)

A carrier, an anode electrode catalyst comprising catalyst metal particles supported on the carrier,
The catalytic metal particles are granular platinum catalyst particles composed of platinum alone, XAFS average coordination number of the catalytic metal particles as measured by (X-ray absorption fine structure) of 4 or less, and an average particle diameter of 0 An anode electrode catalyst comprising a thickness of .55 nm or less. The BET specific surface area of the electrode catalyst, an anode electrode catalyst according to claim 1, characterized in that 1000 m 2 / ^g carrier or more. A carrier, an anode electrode catalyst comprising catalyst metal particles supported on the carrier,
The anode electrode catalyst, wherein the catalyst metal particles are granular platinum catalyst particles made of only platinum and satisfy the following requirements (a) to (b):
(A) the electrochemical specific surface area measured by CO stripping is 280 m ² / g or more;
(B) the average coordination number of the catalytic metal particles measured by XAFS (X-ray absorption fine structure) of 4 or less, and one in which the average particle size is composed of the following 0.55 nm.   The said catalyst metal particle is carried in the density | concentration range of 0.01-15 wt% with respect to the support material which supports the said catalyst metal particle, The Claims any one of Claims 1-3 characterized by the above-mentioned. Anode catalyst. Catalytic metal content of the catalyst per application area, the anode electrode catalyst according to any one of claims 1 to 4, characterized in that a 0.01 to 1 mg / cm ^2. The catalytic metal particles have a relative oxygen reduction reaction activity per unit mass of 0.75 of the catalytic metal particles having an electrochemical specific surface area of 60 to 90 m ² / g measured from hydrogen adsorption and desorption. The anode electrode catalyst according to any one of claims 1 to 5, wherein:   The anode support according to any one of claims 1 to 6, wherein the support is a carbon support.   An anode electrode catalyst layer for a fuel cell, comprising the anode electrode catalyst according to any one of claims 1 to 7 and an electrolyte.   A membrane electrode assembly for a fuel cell, comprising the anode electrode catalyst layer for a fuel cell according to claim 8.   A fuel cell comprising the fuel cell membrane electrode assembly according to claim 9. The method for producing an anode electrode catalyst according to claim 1, wherein (a) preparing a carbon material having pores to be used as a catalyst carrier; and (b) disposing the carbon material in an aprotic solvent. Obtaining a carbon material having a phosphorus ligand by reacting a phosphorus compound at, reacting the carbon material having a phosphorus ligand with a platinum compound, and coordinating platinum to the phosphorus ligand, or The carbon material is prepared in an aprotic solvent by the following chemical formula 2
( Where M is platinum ,
In the formula, R ₁ and R ₂ are each independently a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 18 carbon atoms,
L ₁ and L ₂ are monodentate ligands, each independently being acetonitrile, benzonitrile, THF, diethyl sulfide, dimethyl sulfide, and pyridine, triphenylphosphine, tri-tert-butylphosphine, ethylene, cyclopentadiene Selected from the group consisting of enyl anion, methylcyclopentadienyl anion, pentamethylcyclopentadienyl anion, cyanide ion (CN ⁻ ); or
L ₁ and L ₂ are linked to form a bidentate ligand, wherein the bidentate ligand is dicyclopentadiene, 1,5-cyclooctadiene, norbornadiene, 2,2′-bipyridine, 1,10 -Phenanthroline, ethylenediamine, N, N, N'N'-tetramethylethylenediamine, and trans, trans-dibenzylideneacetone, bis (diphenylphosphino) methane, ethylenebis (diphenylphosphine), 1,3-bis (diphenylphosphine) Fino) propane, 1,4-bis (diphenylphosphino) butane, 1,2-bis (diphenylphosphino) benzene, 1,2-bis (dimethylphosphino) ethane, 1,1′-bis (diphenylphosphino) ) Is selected from the group consisting of ferrocene. )
Reacting with a platinum complex represented by the following formula: and (c) heat-treating the carbon material into which the platinum complex has been introduced, or reducing the platinum complex by bringing the carbon material into contact with hydrogen to form platinum catalyst particles that are catalytic metal particles. Obtaining a platinum- carrying carbon material that is an anode electrocatalyst supported by a catalyst.