JP6661954B2 - Method for evaluating structure including catalyst and electrolyte, and method for manufacturing fuel cell using the evaluation method - Google Patents

Description

  The present invention relates to a method for evaluating a catalyst metal exposure rate using a catalyst carrier, a catalyst comprising a catalyst metal supported on the catalyst carrier, and a structure including an electrolyte, and a method for manufacturing a fuel cell using the method.

  A polymer electrolyte fuel cell using a proton-conducting solid polymer membrane operates at a lower temperature than other types of fuel cells, such as a solid oxide fuel cell and a molten carbonate fuel cell. For this reason, polymer electrolyte fuel cells are expected as stationary power sources and power sources for mobile bodies such as automobiles, and their practical use has been started.

  Such a polymer electrolyte fuel cell generally uses an expensive metal catalyst typified by Pt (platinum) or a Pt alloy, which causes a high price of such a fuel cell. . Therefore, there is a demand for the development of a technology capable of reducing the amount of a noble metal catalyst used and reducing the cost of a fuel cell.

  In the structure including the electrode catalyst layer used for the fuel cell and the like as described above, an electrolyte is used as the ionic conductor. When a catalyst in which a catalyst metal is supported on a catalyst carrier is used, the catalyst metal, the catalyst carrier, and the electrolyte form a complicated microstructure. It is known that the fine structure affects the catalytic performance (power generation performance in a battery typified by a fuel cell). For example, in a fuel cell or an air cell, power generation performance is reduced when access to a reaction gas of a metal catalyst is hindered by an electrolyte. For this reason, a technique for evaluating the fine structure in detail is required.

  As a method for evaluating the fine structure of a structure including an electrode catalyst layer, for example, Non-Patent Document 1 describes a method for evaluating the ionomer (electrolyte) coverage of a catalyst metal.

J. Electroanal. Chem. , 693 (2013) 34-41.

  In order to accurately predict the actual catalyst performance (power generation performance), it is necessary to evaluate the structure in consideration of the access of the metal catalyst to the gas.

The method described in Non-Patent Document 1 utilizes the adsorption phenomenon of carbon monoxide gas to platinum, and determines the ionomer (electrolyte) coverage of the catalytic metal from the relative humidity (RH) dependence of the electric double layer capacity (C _dl ). I'm asking. However, this method does not consider the access of the metal catalyst to the gas because the ionomer (electrolyte) coverage is determined by an electrochemical method.

  Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for evaluating a structure in consideration of access to a gas of a metal catalyst.

  The present inventors have intensively studied to solve the above problems. As a result, the present inventors have found that the above problem can be solved by measuring the gas adsorption behavior on the catalyst metal using a catalyst carrier and a structure including an electrolyte and a catalyst composed of the catalyst metal supported on the catalyst carrier. The invention has been completed.

  ADVANTAGE OF THE INVENTION According to this invention, the ratio of the specific surface area (catalyst metal exposure rate) of the catalyst metal which gas can reach without passing through an electrolyte can be evaluated. Thus, it is possible to provide a method for evaluating a structure in which access to the gas of the metal catalyst is considered.

1 is a schematic cross-sectional view showing a basic configuration of a polymer electrolyte fuel cell obtained by a method for manufacturing a fuel cell according to one embodiment of the present invention. 1 is a schematic diagram showing a basic configuration of an air battery including an air battery electrode catalyst layer evaluated by the method of the present invention. The time change of the gas adsorption amount (A) and the gas adsorption amount (B) when measuring the gas adsorption amount is schematically shown.

In the method described in Non-Patent Document 1, the ionomer (electrolyte) coverage is determined by an electrochemical method. Therefore, unless the electrolyte and the catalyst metal or the electrolyte and the catalyst carrier are in direct contact, the electric double layer capacity (C _dl ) cannot be detected. For example, in the case where bubbles are formed in the electrolyte coating in the catalyst coated with the electrolyte, the catalyst metal disposed in the bubbles does not contact the electrolyte. In addition, as described later, in the case of a catalyst having pores capable of accommodating the catalyst metal, the catalyst metal carried (stored) inside the pores whose openings are covered with the electrolyte does not come into contact with the electrolyte. In such a case, gas access is hindered because the metal catalyst present in the bubbles and pores is coated with the electrolyte. Nevertheless, the specific surface area corresponding to the catalytic metal without contact with these electrolytes cannot be detected by electrochemical techniques.

  On the other hand, in the present invention, the ratio of the specific surface area of the catalytic metal to which the gas can reach without passing through the electrolyte with respect to the specific surface area of the entire catalytic metal (catalytic metal exposure rate) is evaluated by measuring the gas adsorption behavior. . Thereby, the fine structure can be evaluated in consideration of the access of the metal catalyst to the gas. For this reason, even in a structure including a fine structure in which the electrolyte and the catalyst metal are not in direct contact with each other, such as a case where the catalyst metal is present in bubbles or pores, the catalyst metal in which the fine structure is coated with the electrolyte is used. By detecting the area as an area, the catalyst performance (for example, power generation performance) can be predicted with high accuracy.

  In addition, in this specification, "the catalyst metal which gas can reach without passing through an electrolyte" is also called "exposed catalyst metal." In this specification, “/ g carrier” means “per 1 g of carrier”. Similarly, “/ g catalyst metal” means “per 1 g of catalyst metal”.

  Hereinafter, the present invention will be described in more detail, but 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 have been described with reference to the drawings, the same elements will be denoted by the same reference symbols in the description of the drawings, and redundant description will be omitted.

  In the present specification, “X to Y” indicating a range means “X or more and Y or less”. 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%.

[Structure]
One embodiment of the present invention measures the gas adsorption behavior on the catalyst metal using a catalyst support and a catalyst-containing catalyst metal supported on the catalyst support and a structure including an electrolyte, and determines the catalyst metal exposure rate. How to evaluate.

  In the present invention, a structure comprising a catalyst carrier, a catalyst comprising a catalyst metal supported on the catalyst carrier, and an electrolyte is used. Examples of the structure include electrode catalyst layers such as an electrode catalyst layer for a fuel cell and a cathode catalyst layer for an air cell, and a membrane catalyst layer assembly (CCM) and a membrane electrode assembly (MEA) containing these. it can. Of these, in the method of the present invention, the structure is preferably selected from the group consisting of a fuel cell electrode catalyst layer, a fuel cell membrane catalyst layer assembly, and a fuel cell membrane electrode assembly, and more preferably a fuel cell membrane catalyst layer assembly. A battery cathode catalyst layer is used. According to this embodiment, the fuel cell electrode catalyst layer exhibiting high power generation performance can be more easily selected.

[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 diagram showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 which is a specific example of a fuel cell. 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 (CCM) 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). ing. 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 shown as being located at both ends of the MEA 10 shown. 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 disposed between the separator (5a, 5c) and the solid polymer electrolyte membrane 2, or between the PEFC 1 and another PEFC adjacent thereto. 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. As a result, an electrical connection with the MEA 10 is ensured. In addition, the concave portion (the space between the separator and the MEA generated due to the uneven shape of the separator) as viewed from the MEA side of the separator (5a, 5c) is used to allow gas to flow during operation of the PEFC 1. Functions as a gas 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 recesses viewed from the side opposite to the MEA side of the separators (5a, 5c) serve as a coolant flow path 7 for flowing a coolant (for example, water) for cooling the PEFC 1 during operation of the PEFC 1. You. 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 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, a micro fuel Batteries and the like. 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 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 above-mentioned electrolyte membrane-electrode assembly is excellent in power generation performance and durability, and can be miniaturized.

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

<Electrode catalyst layer (catalyst layer)>
In one embodiment of the present invention, the structure is a fuel cell electrode catalyst layer (hereinafter, referred to as an “electrode catalyst layer” or a catalyst) comprising a catalyst carrier and a catalyst made of a catalyst metal supported on the catalyst carrier, and an electrolyte. "Catalyst layer").

  The form of coating of the catalyst with the electrolyte (the form of exposure of the catalytic metal) is not particularly limited. Specifically, the portion where the catalyst is coated with the electrolyte may be in one place or may be divided into a plurality of places, and may be in any form. Alternatively, the catalyst aggregate may be coated with an electrolyte. For example, when the catalyst metal exposure rate measured by the following method is 50%, even if a single island-shaped electrolyte covers 50% of the specific surface area of the catalyst metal, a plurality of divided island-shaped electrolytes may be used. May be in a form in which the total of the specific surface areas of the catalyst metals to be coated is 50%, or in any form.

  Further, the relationship between the electrolyte and the catalyst metal is not particularly limited. For this reason, the catalyst metal may or may not be present in the portion of the catalyst coated with the electrolyte.

Further, as described in detail below, the catalyst may have a primary hole (for example, a primary hole having a diameter of 10 nm or less) that can accommodate the catalyst metal (hereinafter, “the catalyst metal is accommodated in the present specification”). "Possible primary holes" are also simply referred to as "primary holes.") In this case, the electrolyte may coat the catalyst so as to cover the primary pore opening (inlet) or may expose the primary pore opening (inlet) (the pore opening is filled with electrolyte). (Not coated). Here, when the catalyst has primary holes, it is preferable that at least a part of the catalyst metal is carried (stored) inside the holes of the primary holes. When the pore opening of the catalyst is not covered with the electrolyte, the reaction gas is directly supplied to the catalyst metal supported inside the pore without passing through the electrolyte. Therefore, the transport resistance of the reaction gas to the catalyst metal inside the pores is further reduced, and the reaction gas (particularly, O ₂ ) is more quickly and more efficiently transported to the catalyst, and the catalytic reaction is more effectively performed. Can promote. For this reason, it is preferable that the primary pore opening (inlet) of the catalyst is not covered with the electrolyte.

In the conventional electrode catalyst layer, the electrolyte and the catalyst particles are brought into direct contact on the conductive carrier in order to sufficiently secure a three-phase interface where the reaction gas, the catalyst metal and the electrolyte (electrolyte polymer) are simultaneously present. However, the present inventors have found that in this configuration, most of the reaction gas (particularly O ₂ ) is transported to the catalyst metal via the electrolyte, so that the gas transport resistance is high and sufficient reaction gas reaches the catalyst metal. It was found that the catalyst could not exhibit sufficient activity. The present inventors have found that a catalyst can be effectively used by forming a three-phase interface (reaction site) with a reaction gas, a catalyst metal and water. It is not necessary to directly contact the catalyst metal and the electrolyte. To measure the coverage of the catalyst metal in a structure having a microstructure in which a three-phase interface (reaction site) is formed by the reaction gas, the catalyst metal, and water as described above. Electrochemical techniques such as electric double layer capacitance are not optimal. According to the method of the present invention, even in a structure having the above-described fine structure, the fine structure can be evaluated in consideration of access to the gas of the metal catalyst. Therefore, according to the method of the present invention, it is possible to easily and accurately evaluate and sort a structure including a large number of fine structures that form a three-phase interface (reaction site) by a reaction gas, a catalyst metal, and water.

The electrode catalyst layer for a fuel cell used in the method according to the present invention may be either a cathode catalyst layer or an anode catalyst layer, but the method according to the present invention is preferably applied to evaluation using a cathode catalyst layer. . This is because the diffusivity of the reaction gas (O ₂ ) at the cathode is lower than the diffusivity of hydrogen, which is a typical fuel.

  The material of the catalyst carrier constituting the catalyst is not particularly limited, and a known carrier material can be used. It is preferable that the catalyst carrier has a specific surface area and electron conductivity sufficient for supporting the catalyst metal. Specifically, the main component is carbon. More specifically, carbon particles composed of carbon black (Ketjen black, oil furnace black, channel black, lamp black, thermal black, acetylene black, etc.), activated carbon, and the like are included. "The main component is carbon" means that a carbon atom is included as a main component, and is a concept that includes both of only a carbon atom and substantially consisting of a carbon atom. May be included. The expression "consisting substantially of carbon atoms" means that impurities of about 2 to 3% by weight or less can be mixed.

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

The BET specific surface area of the support is substantially equal to the BET specific surface area of the catalyst. The BET specific surface area of the support is not particularly limited, but is preferably 50 to 1500 m ² / g in consideration of the availability in the market.

In the present specification, the “BET specific surface area (m ² / g carrier)” of the catalyst and the catalyst carrier is measured by a nitrogen adsorption method. Specifically, about 0.04 to 0.07 g of a sample (catalyst powder or catalyst carrier) 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 the 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.

The BET specific surface area (of the catalyst after supporting the catalyst metal) [the BET specific surface area of the catalyst per 1 g of support (m ² / g support)] is not particularly limited, but is, for example, 50 to 1500 m ² / g support. In the present specification, "the catalytic metal is supported inside the primary pores" can be confirmed using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

  It is not always necessary to use the granular catalyst carrier as described above as the catalyst carrier. That is, examples of the carrier include a non-porous conductive carrier, a nonwoven fabric made of carbon fibers constituting a gas diffusion layer, carbon paper, and carbon cloth. At this time, the catalyst can be supported on these non-porous conductive carriers, or can be directly attached to a non-woven fabric made of carbon fibers, carbon paper, carbon cloth, etc. that constitute the gas diffusion layer of the membrane / electrode assembly. It is.

  Further, the catalyst metal constituting the catalyst has a function of catalyzing an electrochemical reaction. The catalyst metal used for the anode catalyst layer is not particularly limited as long as it has a catalytic action on the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. The catalyst metal used for the cathode catalyst layer is not particularly limited as long as it has a catalytic action on the oxygen reduction reaction, and a known catalyst can be used in the same manner. Specifically, metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, copper, silver, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and alloys thereof Can be selected from

  Among them, the catalyst metal contained in the structure used in the method according to the present invention is preferably selected from the group consisting of a noble metal and an alloy containing a noble metal whose adsorption to a gas such as carbon monoxide is known. More specific examples of the noble metal include platinum, ruthenium, iridium, rhodium, palladium, osmium, and silver. When using an alloy containing a noble metal and a metal element other than a noble metal as the catalyst metal, for example, the content of the noble metal is set to 30 to 90 atomic%, and the content of the metal to be alloyed with the noble metal is set to 10 to 70 atomic%. Good to do. The noble metal contained in the alloy may be one kind or two or more kinds. Further, the metal element other than the noble metal may be one kind or two or more kinds.

  Among them, a catalyst metal containing at least platinum is preferably used from the viewpoint of catalytic activity as a catalyst metal of an electrode catalyst for a fuel cell. 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 used for the anode catalyst layer and the catalyst metal used for the cathode catalyst layer 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. However, the catalyst metal of the anode catalyst layer and the catalyst metal of the cathode catalyst layer do not need to be the same, and can be appropriately selected so as to exert the above-described desired action.

  The shape and size of the catalyst metal (catalyst component) are not particularly limited, and the same shape and size as those of known catalyst components can be adopted. As the shape, for example, a granular shape, a scale-like shape, a layered shape and the like can be used, but a granular shape is preferable.

  The average particle size of the catalyst metal (catalyst metal particles) is not particularly limited, but is, for example, 2 nm or more, preferably 2.5 nm or more. The upper limit of the average particle size of the catalyst metal (catalyst metal particles) is not particularly limited, but is, for example, 30 nm or less, and preferably 10 nm or less. If the average particle size of the catalyst metal is 2 nm or more, when using a carrier having primary vacancies, the catalyst metal is relatively firmly supported in the primary vacancies, and the catalyst metal contacts the electrolyte in the catalyst layer. More effectively suppressed and prevented. On the other hand, when the average particle size of the catalyst metal particles is 30 nm or less, the catalyst metal can be supported inside the primary pores of the carrier by a simple method.

  The “average particle diameter of catalyst metal particles” (diameter) and the “average particle radius of catalyst metal particles” are the crystallite radius determined from the half-width of the diffraction peak of the catalyst metal component in X-ray diffraction, and the transmission electron It is determined from the average value of the particle radii of the catalytic metal particles examined by a microscope (TEM). In the present specification, the “average particle diameter of the catalytic metal particles” and the “average particle radius of the catalytic metal” are the crystallite diameter and the crystallite radius obtained from the half width of the diffraction peak of the catalytic metal component in X-ray diffraction, respectively. is there.

The catalyst metal (catalyst component) preferably has a specific surface area of 60 m ² / g carrier or less measured electrochemically. The specific surface area of the catalytic metal measured electrochemically is more preferably 5 to 60 m ² / g support, and still more preferably 5 to 30 m ² / g support. Since the surface of the catalytic metal is hydrophilic and water generated by the catalytic reaction is easily adsorbed, water is easily retained in the primary pores in which the catalytic metal is stored. When water is retained in the primary pores, the gas transport path becomes narrow, and the diffusion rate of the reaction gas in the water is low, so that the gas transportability decreases. On the other hand, by making the specific surface area of the catalyst metal relatively small as in the above range, the amount of water adsorbed on the surface of the catalyst metal can be reduced. As a result, water is less likely to be retained in the primary pores, and the water content in the catalyst and further in the catalyst layer can be reduced. The “specific surface area of the catalytic metal measured electrochemically” in the present specification can be measured by, for example, a method described in Journal of Electroanalytical Chemistry 693 (2013) 34-41. Specifically, in the present specification, the “specific surface area of the catalytic metal measured electrochemically” adopts a value measured by the following method.

(Electrochemical measurement method of specific surface area of catalytic metal)
For the cathode catalyst layer, an electrochemically effective surface area (ECA) is determined by cyclic voltammetry. Here, a hydrogen gas humidified so as to be saturated at the measurement temperature is passed through the opposed anode, and this is used as a reference electrode and a counter electrode. Similarly, a humidified nitrogen gas is allowed to flow through the cathode. Immediately before the measurement is started, valves at the cathode inlet and outlet are closed and nitrogen gas is sealed. In this state, measurement is performed under the following conditions using an electrochemical measurement device (manufactured by Hokuto Denko Co., Ltd., model number: HZ-5000).

In the present embodiment, the content of the catalyst metal per unit catalyst application area (basis weight, mg / cm ² ) is not particularly limited as long as a sufficient degree of dispersion of the catalyst on the carrier and power generation performance can be obtained. It is 1 mg / cm ² or less. However, when the catalyst 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 (Pt) and platinum alloys has become a factor of 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 can be obtained.

In the present specification, inductively coupled plasma emission spectroscopy (ICP) is used to measure (confirm) the “content of catalyst metal (platinum) 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 metal (platinum) per unit catalyst application area (mg / cm ² )” by a person skilled in the art. Can be adjusted to control the amount.

  Further, the amount of the catalyst metal carried on the carrier (sometimes referred to as a carrying ratio) is not particularly limited. The loading ratio is preferably 10 to 80% by weight, more preferably 20 to 70% by weight, based on the total amount of the catalyst (that is, the carrier and the catalyst metal). It is preferable that the loading amount is in the above-mentioned range since sufficient dispersion of the catalyst component on the carrier, improvement of power generation performance, economical advantage, and catalytic activity per unit weight can be achieved. The “catalyst loading ratio” in the present invention is a value obtained by measuring the weight of the carrier before supporting the catalyst metal and the weight of the catalyst after supporting the catalyst metal.

  The fuel cell electrode catalyst layer used in the method of the present invention contains an electrolyte in addition to the above catalyst. Here, the electrolyte is not particularly limited, but is preferably an ion-conductive polymer electrolyte. The polymer electrolyte plays a role of transmitting protons generated around the catalyst active material on the fuel electrode side, and is therefore also called a proton conductive polymer.

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

  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 contains a polymer electrolyte having an EW of 1500 g / mol or less, more preferably contains a polymer electrolyte of 1200 g / mol or less, and particularly preferably has a high EW of 1100 g / mol or less. Contains molecular electrolyte.

  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 at least 600 g / mol. In addition, EW (Equivalent Weight) represents the equivalent weight of an exchange group having proton conductivity. The equivalent weight is a dry weight of the ion exchange membrane per equivalent of the ion exchange group, and is expressed in units of “g / mol”.

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

(Method for producing catalyst layer)
The method for producing the fuel cell electrode catalyst layer is not particularly limited, and for example, a known method such as the method described in Japanese Patent Application Laid-Open No. 2010-21060 is applied in a similar manner or appropriately modified.

  Hereinafter, the above method 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.

  The catalyst metal is supported on the catalyst carrier to form a catalyst powder. The loading of the catalyst metal on the catalyst carrier can be performed by a known method. For example, known methods such as an impregnation method, a liquid phase reduction supporting method using an acid such as citric acid, an evaporation to dryness method, a colloid adsorption method, a spray pyrolysis method, and a reverse micelle (microemulsion method) can be used. The catalyst carrier supporting the catalyst metal is optionally dried to obtain a catalyst (catalyst powder).

  Subsequently, a catalyst (catalyst powder), a polymer electrolyte, and an optional dispersion medium are mixed to prepare a coating liquid (catalyst ink). The dispersion medium used for preparing the coating liquid (catalyst ink) is not particularly limited, but includes, for example, water, hydrocarbons (eg, toluene, xylene, cyclohexane, etc.), alcohols (eg, methanol, ethanol, 1-propanol, isopropanol). , Butanol, etc.) and ketones (eg, acetone, methyl ethyl ketone, etc.). As the dispersion medium, these solvents can be used alone or in combination of two or more. Preferably, a water-alcohol mixture, more preferably a water-alcohol mixture having a mixing weight ratio of water and alcohol of 50/50 to 100/10, is used as the dispersion medium. By increasing the proportion of water in the water-alcohol mixture, it is possible to prevent the electrolyte from coating the catalyst excessively and to increase the catalyst metal exposure rate. On the other hand, by reducing the proportion of water in the mixture weight ratio of water and alcohol, the solubility of the polymer electrolyte is improved, and the catalytic metal exposure rate can be reduced. Therefore, the catalyst metal exposure rate can be controlled by adjusting the weight ratio of water to alcohol in the water-alcohol mixture. In consideration of further improvement in gas transportability and catalytic activity, the mixing weight ratio of water and alcohol is preferably 60/40 or more and less than 91/9, more preferably 65/35 to 90/10, and even more preferably 70/90. / 30 to 90/10.

  Water is not particularly limited, and tap water, pure water, ion-exchanged water, distilled water, and the like can be used. In addition, alcohol is not particularly limited. Specific examples include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol, and cyclohexanol. Of these, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol and 2-methyl-2-propanol are preferred. The alcohols may be used alone or in a mixture of two or more. That is, the alcohol is at least one selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol and 2-methyl-2-propanol. It is preferred that By using a lower alcohol having such a high affinity, extreme uneven distribution of the electrolyte can be prevented. Further, among the above alcohols, it is more preferable to use an alcohol having a boiling point of less than 100 ° C. By using an alcohol having a boiling point of less than 100 ° C., there is an advantage that the drying step can be simplified. Examples of alcohols having a boiling point of less than 100 ° C. include methanol (boiling point: 65 ° C.), ethanol (boiling point: 78 ° C.), 1-propanol (boiling point: 97 ° C.), 2-propanol (boiling point: 82 ° C.), and 2-methyl Examples thereof include those selected from the group consisting of -2-propanol (boiling point: 83 ° C). The above alcohols can be used alone or in combination of two or more.

  As described above, polymer electrolytes are roughly classified into fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes according to the type of ion exchange resin that is a constituent material. Of these, a fluoropolymer electrolyte is preferred. That is, the electrolyte is preferably a fluoropolymer electrolyte. By using such a hydrophobic fluorine-based polymer electrolyte, the electrolyte is more easily aggregated by increasing the water ratio in the solvent.

  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 about 1 to 50% by weight, more preferably about 5 to 30% by weight 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 above effect is not hindered. For example, the amount of each additive is preferably 5 to 20% by weight based on the total weight of the electrode 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 180 ° C. for 1 to 60 minutes under an air atmosphere or an inert gas atmosphere. Thereby, a catalyst layer is formed.

In one embodiment of the present invention, there is provided a method for producing a fuel cell, comprising a step of measuring a gas adsorption behavior to a catalyst metal by using a catalyst layer for a fuel cell by the following method to evaluate a catalyst metal exposure rate. You. In still another embodiment, a structure (a fuel cell catalyst layer, a fuel cell membrane catalyst layer assembly, or a fuel cell membrane electrode assembly) having a catalyst metal exposure rate of 50% or more evaluated by the method is referred to as ( A method for producing a fuel cell is provided. A structure (specifically, a catalyst layer for a fuel cell, a fuel cell membrane catalyst layer assembly or By using the fuel cell membrane electrode assembly), the gas transport resistance can be reduced, and the reaction gas (particularly, O ₂ ) can be directly supplied to the catalyst metal without passing through the electrolyte. In addition, when the reaction gas is supplied to the catalyst metal without passing through the electrolyte, the transport time of the reaction gas (particularly, O ₂ ) to the catalyst metal is shortened. Therefore, the catalytic metal can use the reaction gas more quickly. Therefore, the catalyst layer as described above can use the catalyst more effectively and improve the catalytic activity, that is, can promote the catalytic reaction. In this specification, the ratio of the specific surface area of the catalyst metal to which the gas can reach without passing through the electrolyte with respect to the total specific surface area of the catalyst metal is also simply referred to as “catalyst metal exposure rate”.

The catalyst metal exposure rate of the structure (the fuel cell catalyst layer, the fuel cell membrane catalyst layer assembly or the fuel cell membrane electrode assembly) used in the fuel cell manufacturing method according to the present invention is 55% or more and 60% or more. It is preferable that the values are larger in the order of 65% or more. With the above catalyst metal exposure rate, the coating of the catalyst metal with the electrolyte is reduced, and the reaction gas (particularly, O ₂ ) is supplied directly and more efficiently to the catalyst metal without the intermediary of the electrolyte. Can be further improved. Note that the upper limit of the ratio of the specific surface area of the catalyst metal (catalyst metal exposure rate) to which gas can reach without passing through the electrolyte is not particularly limited because it is preferably as high as possible, and is 100%.

(Membrane electrode assembly)
According to a further embodiment of the present invention, there is provided a fuel cell catalyst layer, a fuel cell membrane catalyst layer assembly, and a fuel cell membrane electrode assembly, wherein the catalyst metal exposure rate evaluated by the following method is 50% or more. Is done. 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. In this membrane electrode assembly, at least one of the cathode catalyst layer and the anode catalyst layer is the catalyst layer of the embodiment described above.

However, considering the necessity of improving the proton conductivity and the transport characteristics (gas diffusivity) of the reaction gas (particularly O ₂ ), at least the cathode catalyst layer may be the catalyst layer of the embodiment described above. preferable. However, the catalyst layer according to the above embodiment is not particularly limited, and may be used as an anode catalyst layer or as both a cathode catalyst layer and an anode catalyst layer.

  According to a further embodiment of the present invention, there is provided a fuel cell having the above-described membrane electrode assembly. That is, one embodiment of the present invention 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.

  Hereinafter, the components of the PEFC 1 using the catalyst layer of the above embodiment will be described with reference to FIG. However, the present invention is characterized by the catalyst layer. Therefore, specific configurations of members other than the 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 materials 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 formed of a carbon particle layer (microporous layer or microporous layer; MPL, not shown) made of an aggregate of carbon particles containing a water repellent. May be provided on the catalyst layer side.

  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 can be preferably used because of their excellent electron conductivity and large specific surface area. The average particle size of the carbon particles is preferably about 10 to 100 nm. As a result, 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 catalyst layer is transferred or coated on a solid polymer electrolyte membrane by a hot press and dried (CCM), and then a gas diffusion layer is joined to the solid polymer electrolyte membrane, or the microporous layer side of the gas diffusion layer (microporous layer side). If no gas diffusion electrode is contained, two gas diffusion electrodes (GDE) are prepared by applying a catalyst layer on one side of the base material layer in advance and drying, and the gas diffusion electrodes are formed on both sides of the solid polymer electrolyte membrane. A method of joining by hot pressing can be used. The application and bonding conditions such as hot pressing may be appropriately adjusted depending on the type (perfluorosulfonic acid type or hydrocarbon type) of the polymer electrolyte in the solid polymer electrolyte membrane or the catalyst layer.

(Separator)
The separator has a function of electrically connecting each cell in series when a plurality of single cells of a fuel cell such as a polymer electrolyte fuel cell are connected in series to form a fuel cell stack. 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 above-mentioned PEFC and the membrane electrode assembly use a catalyst layer excellent in power generation performance and durability. 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.

[Air battery]
In the method according to the present invention, a cathode catalyst layer for an air battery or an air electrode including the cathode catalyst layer for an air battery may be used as a structure.

A general air battery has a concave positive electrode case having an air vent hole in which a current collector, a positive electrode catalyst layer, and a separator are sequentially laminated, and a negative electrode filled with a negative electrode active material and one size smaller than the positive electrode case. The case and the case are in close contact with each other. The air battery has a structure in which a space between the positive electrode case and the negative electrode case is sealed with a gasket. The general principle of the air battery is that oxygen (O ₂ ) supplied from an air vent hole is reduced to hydroxide ions (OH ⁻ ) or the like by a positive electrode catalyst and the metal (M ⁺ ) Is oxidized by hydroxide ions or the like, whereby an electrochemical reaction proceeds.

  The air battery may be either a liquid electrolyte type in which a non-aqueous electrolyte is impregnated in a separator, or a polymer gel electrolyte type battery also called a polymer battery or a solid polymer electrolyte (all solid electrolyte) type battery. . As for the polymer gel electrolyte and the solid polymer electrolyte, these can be used alone, or the polymer gel electrolyte and the solid polymer electrolyte can be used by impregnating the separator with the polymer gel electrolyte and the solid polymer electrolyte.

  FIG. 2 illustrates one embodiment of a preferable configuration of the air battery 101. The air battery 101 includes an air electrode having a positive electrode catalyst layer 104 formed on the surface of a positive electrode current collector 102, a negative electrode having a negative electrode active material layer 105 formed on a surface of a negative electrode current collector 103, the air electrode, and the air electrode. It has a separator 106 sandwiched between the negative electrode. FIG. 2 is a diagram schematically illustrating the configuration of the air battery, and thus does not illustrate a positive electrode case, a negative electrode case, a gasket, and an air vent hole.

  The cathode catalyst layer for an air battery used in the present invention includes a catalyst carrier, a catalyst comprising a catalyst metal supported on the catalyst carrier, and an electrolyte. The catalyst carrier, the catalyst metal, and the electrolyte are the same as those described above for the fuel cell. The cathode catalyst layer for an air battery is prepared by suspending a catalyst metal, a conductive carrier, and an electrolyte in an appropriate amount of a solvent together with an optional binder to prepare a slurry, drying the slurry, and pulverizing the slurry as necessary. obtain. The solvent used is not particularly limited. For example, water, hydrocarbons (eg, toluene, xylene, cyclohexane, etc.), alcohols (eg, methanol, ethanol, isopropanol, butanol, etc.), ketones (eg, , Acetone, methyl ethyl ketone, etc.). The obtained dried product is formed by press molding or the like and used as a catalyst layer.

  The negative electrode active material layer in the air battery may include the negative electrode active material. As a material used for the negative electrode active material, at least one element selected from the group consisting of lithium, sodium, potassium, magnesium, calcium, magnesium, aluminum, zinc, and iron, or an alloy thereof is preferable. The negative electrode active material layer may contain the negative electrode active material alone or may have a particulate negative electrode active material supported on a conductive carrier, and may further contain a binder if necessary.

  The current collector in the air battery collects electricity in the positive electrode catalyst layer or the negative electrode active material layer. Examples of the material of the current collector include stainless steel, nickel, aluminum, iron, titanium, and carbon. The shape of the current collector may be, for example, a plate shape such as a film shape or a plate shape, a mesh shape, or a grid shape in which holes are formed in a grid shape. The shape of the current collector is preferably a mesh from the viewpoint of current collection efficiency. In this case, a mesh-shaped cathode current collector is usually arranged inside the cathode layer.

  As the separator in the air battery, for example, a sheet material made of carbon paper, nonwoven fabric, carbon woven fabric, paper-like paper body, felt, or the like, or a porous film of polyethylene, polypropylene, or the like can be preferably used.

[Measurement of gas adsorption behavior]
In the present invention, the gas adsorption behavior to the catalytic metal is measured using the above-described structure to evaluate the catalytic metal exposure rate.

As the gas used for the measurement, a gas containing a gas to which the catalyst metal is adsorbed is employed. It is known that metals, particularly noble metals conventionally used as catalytic metals, adsorb certain gases. Examples of the gas adsorbed on the noble metal include carbon monoxide (CO); volatile sulfur-containing compounds (eg, sulfur oxides (SO _x ) such as sulfur dioxide (SO ₂ ), mercaptans such as methanethiol, and hydrogen sulfide ( H ₂ S)); nitrogen oxides (NO _x ) such as nitric oxide (NO); One of these gases may be used alone, or a mixed gas mixed at an arbitrary partial pressure may be used. Further, a mixed gas in which these adsorptive gases are mixed with helium or an inert gas (for example, nitrogen gas or argon gas) at an arbitrary ratio may be used. When the gas used for the measurement is, for example, platinum or a catalytic metal containing platinum and a metal component other than platinum, the gas preferably contains carbon monoxide (CO). The adsorptive gas, such as carbon monoxide, volatile sulfur-containing compounds, and nitrogen oxides, is contained, for example, at a rate of 1 to 100% (v / v) with respect to the entire measurement gas. In one embodiment, the measurement comprises 1 to 100% (v / v) of at least one selected from the above adsorptive gases and the balance at least one selected from the group consisting of helium, nitrogen and argon. Use gas. In the case of a mixed gas, from the viewpoint of the signal intensity of the adsorbed gas, the adsorbent gas may be contained more preferably at a ratio of 2 to 40% (v / v) based on the whole mixed gas. That is, a measurement gas consisting of at least one selected from the above adsorbent gases of 2 to 40% (v / v) and at least one selected from the group consisting of helium, nitrogen and argon as the balance is used. You may.

  In the present invention, the ratio of the specific surface area of the catalyst metal to which the gas can reach without passing through the electrolyte (catalyst metal exposure rate) is measured by utilizing the gas adsorption property of the catalyst metal and measuring the gas adsorption behavior to the catalyst metal. ) To evaluate. Examples of the measured gas adsorption behavior include the amount of gas adsorbed by the catalytic metal, the gas adsorption speed, and the change over time of the amount of adsorption.

  In one embodiment of the present invention, the gas adsorption behavior on the catalyst metal is a gas adsorption amount by the entire catalyst metal (A) and a gas adsorption amount by the catalyst metal exposed on the catalyst carrier (B). The “gas adsorption amount (A) by the entire catalytic metal” is also simply referred to as “gas adsorption amount (A)”. The “gas adsorption amount (B) by the catalyst metal exposed on the catalyst carrier” is also simply referred to as “gas adsorption amount (B)”. Since the amount of gas adsorbed by the catalytic metal is proportional to the specific surface area of the catalytic metal, the catalytic metal exposure rate can be calculated using the amount of gas adsorbed by the catalytic metal as the specific surface area of the catalytic metal. The ratio of the gas adsorption amount (B) to the gas adsorption amount (A) can be calculated as the specific surface area (B) of the catalyst metal exposed on the catalyst carrier to the specific surface area (A) of the entire catalyst metal. That is, in one embodiment of the present invention, the above structure is used to measure the gas adsorption amount (A) by the entire catalyst metal and the gas adsorption amount (B) by the catalyst metal exposed on the catalyst carrier. Then, a method for evaluating the catalytic metal exposure rate by the following equation (1) is provided. The method measures the gas adsorption amount (A) by the whole catalyst metal and the gas adsorption amount (B) by the catalyst metal exposed on the catalyst carrier by using the above structure, and calculates the following formula (1) It is also a method for inspecting a structure, including evaluating the catalytic metal exposure rate by using

In the above formula (1), “the gas adsorption amount (A) by the entire catalyst metal” (“gas adsorption amount (A)”) is the gas adsorption amount by the entire catalyst metal supported on the catalyst carrier. That is, the gas adsorption amount (A) (cm ³ / g catalyst metal) is determined by the gas adsorption amount of the catalyst metal exposed on the catalyst carrier (not coated with the electrolyte) and the gas adsorption amount of the catalyst metal coated with the electrolyte. This is the total amount with the amount of adsorption. In the above formula (1), the “gas adsorption amount (B) by the catalyst metal exposed on the catalyst carrier” (“gas adsorption amount (B)”) is the value of the amount of gas exposed on the catalyst carrier (coated with the electrolyte). (Not performed) is the amount of gas adsorbed by the catalytic metal (cm ³ / g catalytic metal). The measurement gas used for measuring the gas adsorption amount (A) and the measurement gas used for measuring the gas adsorption amount (B) usually have the same composition.

  In the above equation (1), the gas adsorption amount (A) is measured under conditions in which the molecular motion of the electrolyte is so active that the gas can pass through the electrolyte. The molecular motion of the electrolyte becomes active by increasing the temperature of the electrolyte, and is suppressed by lowering the temperature. The temperature at which the gas adsorption amount (A) is measured (the temperature of the structure used (for example, the electrode catalyst layer for a fuel cell)) differs depending on the contained electrolyte and cannot be unconditionally defined. It is 120 ° C. or less. The measurement of the gas adsorption amount (A) is performed, for example, under atmospheric pressure.

  In the above equation (1), the gas adsorption amount (B) is measured under the condition that the molecular motion of the electrolyte is suppressed to such an extent that the electrolyte does not pass through the gas. The temperature at which the gas adsorption amount (B) is measured (the temperature of the structure used (for example, the fuel cell electrode catalyst layer)) differs depending on the contained electrolyte and cannot be unconditionally defined. A) is a temperature lower than the measured temperature. More specifically, the temperature at which the gas adsorption amount (B) is measured is, for example, −150 to 0 ° C. The measurement of the gas adsorption amount (B) is performed, for example, under atmospheric pressure.

In one embodiment, the temperature T _(A) (° C.) at which the gas adsorption amount (A) is measured and the temperature T _(B) (° C.) at which the gas adsorption amount (B) is measured are 80 ≦ (T _(A) (° C.) − T _(B) (° C.)) ≦ 270.

  In one embodiment of the present invention, there is provided a method for evaluating a catalytic metal exposure rate, wherein a gas used for measuring a gas adsorption amount (A) and a gas adsorption amount (B) includes carbon monoxide. When using platinum or a catalytic metal containing platinum and a metal component other than platinum as the measurement gas, it is preferable to use a gas containing carbon monoxide. The content of carbon monoxide in the measurement gas is, for example, 1 to 100% (v / v), preferably 2 to 40% (v / v) based on the whole measurement gas.

  Hereinafter, the measurement method will be described in more detail by taking a method using a gas containing carbon monoxide as the measurement gas (CO adsorption method) as an example, but the measurement gas used in the present invention is limited to a gas containing carbon monoxide. Not something. The method described below can also be carried out by appropriately modifying the adsorptive gas other than carbon monoxide, which is known to adsorb to a catalytic metal (particularly, a noble metal) such as a volatile sulfur-containing compound and nitric oxide. In the following example, 50 ° C. is used as the measurement temperature of the gas adsorption amount (A), and −74 ° C. is used as the measurement temperature of the gas adsorption amount (B). Can be modified.

  The ratio of the specific surface area of the catalytic metal to which the gas can reach without passing through the electrolyte (catalytic metal exposure rate) can also be measured by the following CO adsorption method. The following method utilizes the selective adsorption of carbon monoxide (CO) to a catalytic metal (eg, platinum), and utilizes the following mechanism. That is, at 50 ° C., carbon monoxide (CO) passes through the electrolyte. Thus, at 50 ° C., CO chemisorbs to both the exposed (not electrolyte coated) and the electrolyte coated catalyst metal on the catalyst support. Therefore, the value of the gas adsorption amount (A) can be obtained by measuring the gas adsorption amount of the catalytic metal at a high temperature (for example, 50 ° C.).

  On the other hand, at low temperatures (eg, -74 ° C), carbon monoxide (CO) does not pass through the electrolyte. Thus, at low temperatures (e.g., -74 [deg.] C.), CO chemisorbs to the exposed (not electrolyte-coated) catalyst metal on the catalyst support, but the catalyst metal or openings coated with the electrolyte become It does not chemically adsorb to the catalyst metal carried (stored) inside the pores covered with the electrolyte. Therefore, the value of the gas adsorption amount (B) can be obtained by measuring the gas adsorption amount of the catalytic metal at a low temperature (eg, −74 ° C.).

  In the "CO adsorption method", among the evaluation methods according to the present invention, carbon monoxide is used as the adsorbed gas, the measurement temperature of the gas adsorption amount (A) is 50C, and the gas adsorption amount (B) is -74C. Method.

That is, the specific surface area (COMSA _{50 ° C.} ) (m ² / g catalyst metal) of the catalyst metal of the catalyst layer measured at 50 ° C. by the CO adsorption method corresponds to the total specific surface area of the catalyst metal. The specific surface area (COMSA- _{74 ° C.} ) (m ² / g catalyst metal) of the catalyst metal of the catalyst layer measured by the CO adsorption method at −74 ° C. is the ratio of the catalyst metal to which the gas can reach without passing through the electrolyte. It corresponds to the surface area. Therefore, COMSA _{50 ° C.} (m ² / g catalyst metal) and COMSA _{−74 ° C.} (m ² / g catalyst metal) were measured by the following CO adsorption method, and the obtained value was used to calculate the catalyst metal exposure rate (%) according to the following equation. Ask for. The smaller the catalyst metal exposure rate (%), the larger the ratio of the catalyst metal coated with the electrolyte (the ratio of the specific surface area of the catalyst metal that reaches the gas through the electrolyte). In the following formula (2), in the above formula (1), carbon monoxide is used as the gas, the gas adsorption amount (A) is measured at 50 ° C., and the gas adsorption amount (B) is measured at −74 ° C. Show the case.

(Evaluation method of catalytic metal exposure rate by CO adsorption amount)
A sample (a structure, for example, an electrode catalyst layer for a fuel cell) is dried in a vacuum oven at 100 ° C. for 5 hours or more. After drying for a predetermined time, the sample is cooled to room temperature (25 ° C.). Thereafter, about 100 mg is weighed and placed in an I-shaped tube, and then purged with hydrogen gas at room temperature (25 ° C.) for 10 minutes. The sample is heated to 100 ° C. in 20 minutes under flowing hydrogen gas. Then, it is kept at 100 ° C. for 15 minutes in a hydrogen atmosphere. Next, the flowing gas is switched to helium gas, and the sample is kept at a temperature of 100 ° C. for 15 minutes. Further, the temperature of the sample was lowered to 50 ° C. or −74 ° C., and maintained at this temperature for 15 minutes. According to the instructions, the amount of adsorbed CO (cm ³ / g catalytic metal) is measured. Note that a mixed gas of He: CO = 90: 10 (v / v) is used for the measurement. Based on the measured amount of CO adsorbed, the catalyst metal exposed as the specific surface area (B) of the catalyst metal exposed on the catalyst support with respect to the specific surface area (A) of the entire catalyst metal according to the formula (1) or the formula (2). Find the rate (%).

Taking the measurement at 50 ° C. and −74 ° C. as an example, a schematic time change of the gas adsorption amount (A) and the gas adsorption amount (B) when measuring the gas adsorption amount is shown in FIG. The gas adsorption amount gradually increases in the temperature maintaining process (50 ° C. or −74 ° C. in the above case) in which the above-described measurement gas is circulated, and becomes a constant value when the saturated adsorption amount is reached. In the CO adsorption method, such a saturated adsorption amount is adopted as the gas adsorption amount. In addition, the gas adsorption amount is plotted with respect to time from the time when the sample temperature is lowered to the measurement temperature (50 ° C. or −74 ° C. in the above case) and the flow of the measurement gas is started, and the integrated gas as shown in FIG. Obtain an adsorption plot. Based on the plot, the gas adsorption amount at any given time before reaching the saturated adsorption amount may be adopted as the gas adsorption amount (A) and the gas adsorption amount (B).

  The sample used for measuring the catalytic metal exposure rate based on the gas adsorption behavior may be a membrane catalyst layer assembly (CCM) or a membrane electrode assembly (MEA) in addition to the fuel cell electrode catalyst layer as described above. The fuel cell electrode catalyst layer may be the one applied to the substrate as it is, or may be used after being scraped off.

  In a membrane catalyst layer assembly (CCM) or a membrane electrode assembly (MEA) used as a measurement sample, a catalyst layer different from the measurement object is provided at a counter electrode of a catalyst layer (for example, a cathode catalyst layer) whose gas adsorption behavior is to be measured. (Eg, an anode catalyst layer) may be present. In this case, the measurement may be performed while preventing adsorption of the measurement gas to a catalyst layer (anode catalyst layer in the above example) different from the measurement target. The method of preventing adsorption of the measurement gas to the catalyst layer different from the measurement target is not particularly limited. For example, the entire catalyst layer different from the measurement target is covered with the polymer electrolyte membrane as described above, and the membrane is transferred by hot pressing or the like. By doing so, it is sufficient to prevent the measurement gas from entering the catalyst layer. When the measurement gas is prevented from being adsorbed by the polymer electrolyte membrane using the membrane electrode assembly (MEA), the GDL may be mechanically peeled off from the catalyst layer and then coated with the polymer electrolyte membrane. Thereby, adsorption of the measurement gas by the catalyst layer different from the measurement target can be suppressed.

  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. In the following examples, operations were performed at room temperature (25 ° C.) unless otherwise specified. Unless otherwise specified, “%” and “parts” mean “% by weight” and “parts by weight”, respectively.

<Experiment 1: Evaluation of oxygen reduction (ORR) activity>
Both surfaces of the membrane catalyst layer assembly (CCM) produced in the example were sandwiched between gas diffusion layers (24BC, manufactured by SGL Carbon) to obtain a membrane electrode assembly (MEA). With respect to the obtained membrane / electrode assembly, a power generation current (μA / cm ² (Pt)) per platinum surface area at 0.9 V was measured under the following evaluation conditions, and oxygen reduction activity was evaluated.

<Experiment 2: Evaluation of gas transport resistance>
About the above-mentioned membrane electrode assembly, Mashio et al. ECS Trans. , 11, 529, (2007), gas transport resistance was evaluated.

That is, the limiting current density (A / cm ² ) was measured using diluted oxygen. At this time, the gas transport resistance (s / m) was calculated from the slope of the limiting current density (A / cm ² ) with respect to the oxygen partial pressure (kPa). The gas transport resistance was proportional to the total pressure of the gas, and was separated into a component dependent on the total pressure of the gas (gas transport resistance due to molecular diffusion) and an independent component. Among them, the former is a transport resistance component in relatively large holes having a diameter of 100 nm or more existing in, for example, a gas diffusion layer, and the latter is a transport resistance component in relatively small holes less than 100 nm is present in a catalyst layer or the like. . Thus, the gas transport resistance in the catalyst layer was obtained by measuring the total pressure dependency of the gas transport resistance and extracting components independent of the total pressure.

(Example 1)
5 parts by weight of Ketjen Black (BET specific surface area: 718 m ² / g carrier) was sufficiently dispersed in 2500 parts by weight of a chloroplatinic acid aqueous solution (containing 0.2% by weight of platinum) using a homogenizer. In the Ketjen Black used, primary holes having a diameter of 10 nm or less were observed with an electron microscope.

  Next, 50 parts by weight of sodium citrate was added and mixed well to prepare a reaction solution. Further, using a reflux reactor, the reaction solution was refluxed at 85 ° C. for 4 hours while stirring to carry platinum on the surface of Ketjen black by reduction.

  After the completion of the reaction, the sample solution was allowed to cool to room temperature, and the Ketjen black powder carrying platinum was filtered off with a suction filtration device and sufficiently washed with water.

  Thereafter, the filtered powder was dried under reduced pressure at 80 ° C. for 6 hours to obtain a catalyst powder A having a loading of 50% by weight and an average particle diameter of the catalyst metal of 2.5 nm.

  Next, 10 parts by weight of catalyst powder A, 100 parts by weight of ion-exchanged water, 10 parts by weight of n-propyl alcohol (mixing weight ratio of water and n-propyl alcohol is 100/10), and 4.5 parts by weight Parts of the polymer electrolyte were mixed. As the polymer electrolyte, a NAFION (registered trademark) solution (manufactured by Aldrich, containing 20% by weight of NAFION (registered trademark), EW = 1000) was used. Further, the above mixture was sufficiently dispersed with an ultrasonic homogenizer and defoamed under reduced pressure to obtain a catalyst ink A. Catalyst ink A was used for forming a cathode catalyst layer and an anode catalyst layer.

Next, the catalyst ink A was applied to a size of 5 cm × 5 cm by a screen printing method on a transfer substrate made of polytetrafluoroethylene (PTFE) so that the basis weight of platinum was 0.12 mg / cm ² .

  Thereafter, the mixture was treated at 130 ° C. for 30 minutes to obtain a cathode catalyst layer A and an anode catalyst layer A having a film thickness (dry film thickness) of 6.5 μm.

For the cathode catalyst layer A obtained above, the catalytic metal exposure rate was measured by a CO adsorption method, and as a result, it was 38%. In addition, the specific surface area of the catalyst metal of the cathode catalyst layer A thus obtained was measured to be 29.6 m ² / g carrier.

  Gaskets (Teonex, Teionx, thickness: 25 μm (adhesive layer: 10 μm)) were arranged around both sides of a polymer electrolyte membrane (NAFION (registered trademark) NR211, thickness: 25 μm, manufactured by Dupont). Next, the cathode catalyst layer A and the anode catalyst layer A (size: 5 cm × 5 cm) prepared above were combined with each exposed portion of the polymer electrolyte membrane, and hot-pressed at 150 ° C. and 0.8 MPa for 10 minutes. As a result, a membrane catalyst layer assembly (1) (CCM (1)) was obtained.

The membrane electrode assembly (MEA (1)) produced using the membrane catalyst layer assembly (1) obtained above was evaluated for catalytic activity (Experiment 1) and gas transport resistance (Experiment 2). As a result, the generated current per platinum surface area of the membrane / electrode assembly (1) was 352 (μA / cm ² (Pt)), and the gas transport resistance was 25.1 (s / m).

(Example 2)
During the production of the catalyst ink A in Example 1, the weight ratio between ion-exchanged water and n-propyl alcohol was changed to 50 parts by weight and 50 parts by weight (the mixing weight ratio of water and n-propyl alcohol was 50/50). A modified catalyst ink B was prepared. A cathode catalyst layer B and an anode catalyst layer B were obtained in the same manner as in Example 1, except that the catalyst ink B was used instead of the catalyst ink A.

For the cathode catalyst layer B obtained by this method, the catalytic metal exposure rate was measured by a CO adsorption method, and as a result, it was 45%. Further, the specific surface area of the catalyst metal of the cathode catalyst layer B thus obtained was electrochemically measured and found to be 27.4 m ² / g carrier.

  A membrane catalyst layer assembly (2) (CCM (2)) was produced in the same manner as in Example 1 except that the cathode catalyst layer A and the anode catalyst layer A were changed to the cathode catalyst layer B and the anode catalyst layer B, respectively. Obtained.

For the membrane electrode assembly (MEA (2)) produced using the membrane catalyst layer assembly (2) obtained above, the catalytic activity (Experiment 1) and the gas transport resistance (Experiment 2) were evaluated. As a result, the generated current per platinum surface area of the membrane electrode assembly (2) was 689 (μA / cm ² (Pt)), and the gas transport resistance was 19.9 (s / m).

(Example 3)
During the production of the catalyst ink A in Example 1, the weight ratio of ion-exchanged water to n-propyl alcohol was changed to 80 parts by weight and 20 parts by weight (the mixing weight ratio of water and n-propyl alcohol was 80/20). A modified catalyst ink C was prepared. A cathode catalyst layer C and an anode catalyst layer C were obtained in the same manner as in Example 1 except that the catalyst ink C was used instead of the catalyst ink A.

As a result of measuring the catalytic metal exposure rate by the CO adsorption method for the cathode catalyst layer C obtained by the above method, the result was 65%. Further, the specific surface area of the catalyst metal of the cathode catalyst layer C thus obtained was 30.7 m ² / g as measured by electrochemical measurement.

  The membrane catalyst layer assembly (3) (CCM (3)) was prepared in the same manner as in Example 1 except that the cathode catalyst layer A and the anode catalyst layer A were changed to the cathode catalyst layer C and the anode catalyst layer C, respectively. Obtained.

For the membrane electrode assembly (MEA (3)) produced using the membrane catalyst layer assembly (3) obtained above, the catalytic activity (Experiment 1) and the gas transport resistance (Experiment 2) were evaluated. As a result, the generated current per platinum surface area of the membrane / electrode assembly (3) was 802 (μA / cm ² (Pt)), and the gas transport resistance was 13.2 (s / m).

  As described above, the catalytic metal specific surface area obtained by the electrochemical method, which is a conventional technique, is not suitable for predicting structural performance such as catalytic activity and gas transport resistance because access to the gas of the metal catalyst is not considered. On the other hand, according to the present invention, it is possible to evaluate a structure in which the access of the metal catalyst to the gas is taken into consideration, and it is also possible to use the structure to predict the performance of the structure such as catalytic activity and gas transport resistance.

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),
101 ... air battery,
102 ... Positive electrode current collector,
103 ... negative electrode current collector,
104: positive electrode catalyst layer,
105 ... Negative electrode active material layer,
106 ... separator.

Claims (5)

Using a structure comprising a catalyst and an electrolyte comprising a catalyst metal supported on the catalyst carrier and the catalyst metal,
A method of measuring the adsorption behavior of a gas containing carbon monoxide to the catalyst metal, and evaluating the catalyst metal exposure rate ,
The catalyst metal is platinum or contains a metal component other than platinum and platinum,
The catalyst metal exposure rate is calculated by the following formula, and the method for evaluating the catalyst metal exposure rate is as follows:
Here, COMSA _{T (A)} is a specific surface area of the catalyst metal of the catalyst layer measured at a temperature T (A) using a gas containing carbon monoxide, and COMSA _{T (B)} contains carbon monoxide. The specific surface area of the catalyst metal of the catalyst layer measured at a temperature T (B) using a gas. T (A) is -150 to 0 ° C, and T (B) is more than 0 ° C and not more than 120 ° C. It is. 2. The method of claim 1, wherein said T (A) is -74 <0> C and said T (B) is 50 <0> C. The structure, a fuel cell electrode catalyst layer, a fuel cell membrane catalyst layer assembly and is selected from the group consisting of a fuel cell membrane electrode assembly, the method according to claim 1 or 2. A method for manufacturing a fuel cell, comprising a step of evaluating a catalytic metal exposure rate by the method according to claim 3 . The manufacturing method according to claim 4 , wherein a structure having a catalytic metal exposure rate of 50% or more is used.